A method for identifying process window signature patterns in a device area of a mask is disclosed. The signature patterns collectively provide a unique response to changes in a set of process condition parameters to the lithography process. The signature patterns enable monitoring of associated process condition parameters for signs of process drift, analyzing of the process condition parameters to determine which are limiting and affecting the chip yields, analyzing the changes in the process condition parameters to determine the corrections that should be fed back into the lithography process or forwarded to an etch process, identifying specific masks that do not transfer the intended pattern to wafers as intended, and identifying groups of masks that share common characteristics and behave in a similar manner with respect to changes in process condition parameters when transferring the pattern to the wafer.

In the semiconductor industry, microlithography (or simply lithography) is the process of printing the circuit patterns on a semiconductor wafer (for example, a silicon or gallium arsenide wafer). Currently, optical lithography is the predominant technology used in volume semiconductor manufacturing. Optical lithography employs light in the visible to deep ultraviolet spectrum range to expose the resist on a wafer. In the future, extreme ultraviolet (EUV) and soft x-rays may be employed. Following exposure, the resist is developed to yield a relief image.
In optical lithography, a photomask (often called a mask or a reticle) is first written using electron-beam or laser-beam direct-write tools. A typical mask for optical lithography consists of a glass (or quartz) plate of six to eight inches on a side, with one surface coated with a thin metal layer (for example, chrome) of a thickness of about 100 nm. The chip pattern is etched into the metal layer, hence allowing light to transmit through. The area where the metal layer is not etched away blocks light transmission. In this way, a pattern may be projected onto a semiconductor wafer.
The mask contains certain patterns and features that are used to create desired circuit patterns on a wafer. The tool used in projecting the mask image onto a wafer is called a stepper or scanner (hereinafter collectively called "exposure tool"). FIG. 1 is a block diagram of an optical projection lithographic system 10 of a conventional stepper including an illumination source 12, an illumination pupil filter 14, a lens subsystem 16a-c, a mask 18, a projection pupil filter 20, and a wafer 22 on which the aerial image of mask 18 is projected.
Illumination source 12 may be laser source operated, for example, at UV (ultra-violet) or DUV (deep ultra-violet) wavelengths. The light beam is expanded and scrambled before it is incident on illumination pupil 14. Illumination pupil 14 may be a simple round aperture, or have specifically designed shapes for off-axis illumination. Off-axis illumination may include, for example, annular illumination (i.e., the pupil is a ring with a designed inner and outer radius), quadruple illumination (i.e., the pupil has four openings in the four quadrant of the pupil plane), and other shapes like dipole illumination.
After illumination pupil 14, the light passes through the illumination optics (for example, lens subsystem 16a) and is incident on mask 18. Mask 18 contains the circuit pattern to be imaged on wafer 22 by the projection optics. As the desired pattern size on wafer 22 becomes smaller and smaller, and those patterns becomes closer and closer to each other, the lithography process becomes more challenging. In an effort to improve imaging quality, current processing techniques employ resolution enhancement technologies ("RET"), such as, for example, optical proximity correction ("OPC"), phase shift masks ("PSM"), off-axis illumination ("OAI"), condenser and exit pupil filters, and so on.
Many of the RET technologies are applied on or directly to mask 18. For example, OPC and PSM, which modify the light wave to (1) compensate for the imperfection of the imaging property of the projection optics, for example, the OPC technology is used to compensate the optical proximity effect due to light interference, and/or (2) take advantage of designed light interferences to enhance the imaging quality, for example, the phase shift mask technology is used to create phase shifting between neighboring patterns to enhance resolution.
Notably, mask 18 may not be "perfect" due to its own manufacturing process. For example, corners on mask 18 may not be sharp but may be rounded and/or the linewidth may have a bias from design value where the bias may also depend on the designed linewidth value and neighboring patterns. These imperfections on mask 18 may affect the final imaging quality.
The projection optics (for example, lens subsystems 16b and 16c, and projection pupil filter 20) images mask 18 onto wafer 22. In this regard, the projection optics includes a projection pupil filter 20. Projection pupil filter 20 limits the maximum spatial frequency of the mask pattern that can be passed through the projection optics. A number called "numerical aperture" or NA often characterizes projection pupil filter 20. There are also proposed RET techniques that modify projection pupil filter 20, which is generally called pupil filtering. Pupil filtering may include modulation for both the amplitude and the phase on the passing light beams.
Due to the wavelength of light being finite, and current techniques employing wavelengths that are larger than the minimum linewidth that is printed on wafer 22, there are typically significant light interference and diffractions during the imaging process. The imaging process is not a perfect replication of the pattern on mask 18. Current techniques employ physical theory to model this imaging process. Further, due to the high NA value of current exposure tools, different polarizations of the light provide different imaging properties. To more accurately model the lithography process, a vector-based model may be used.
The projection optics may be diffraction-limited. However, lens subsystem 16b and 16c in the projection optics are most often not completely "perfect." These imperfections may be modeled as aberrations, which are often abstracted as some undesired phase modulation at the plane of projection pupil filter 20, and are often represented by a set of Zernike coefficients. After the light finally reaches the surface of wafer 22, they will further interact with the coatings on wafer 22 (for example, the photo-resist). In this regard, different resist thickness, different optical properties of the resist (for example, its refractive index), and different material stack under the resist (for example, bottom-anti-reflection-coating or BARC), may further affect the imaging characteristics. Some of these effects may also be abstracted by a modulation at the pupil plane.
When the resist is exposed by the aerial image and thereafter baked and developed, the resist tends to undergo complex chemical and physical changes. First principle and empirical models have been developed to simulate these processes.
When wafers are printed using an exposure tool, ideally, wafer 22 should be placed exactly at the focal plane of the projection optics, or a designated location away from the focal plane. However, due to the imperfect mechanical control of exposure tools, there is always a small deviation between the designated plane and the actual wafer plane. That deviation is called defocus, or sometimes just called "focus," and represented by a distance unit, e.g., 50 nm. The defocus introduces additional imperfections in the imaging path, and can also be characterized by a phase modulation at the pupil plane.
Furthermore, all wafers, and dice on the wafers, are ideally exposed by a designated amount of exposure dose, e.g., 20 mJ/cm2. However, due to the imperfections in the illumination control and changes in the reflectivity and uniformity of the film stacks on the wafers being patterned, there is always a small deviation between the ideal exposure dose and the actual exposure dose deposited on a die. That deviation is called exposure dose variation, or sometimes just called "exposure," and is represented by a percentage deviation from the ideal exposure dose, e.g., 10%.
The combination of focus and exposure errors means that the dimensions of the wafer features that are patterned may not match exactly with the dimensions required by the design. Since every structure responds differently to focus and exposure errors in different ways depending on the width, shape, and local environment of the specific structure, it is not possible to describe the response of every individual structure in a circuit pattern with a limited set of figures of merit.
In practice, the most common metric used to characterize a lithography process is the width of the smallest features being patterned on a given process layer for a given technology. This minimum dimension is referred to as the "critical dimension" or CD. While critical dimensions are actually intended to represent the three dimensional resist profile, the term CD is usually associated with a one-dimensional slice through the resist line, also referred to as the linewidth. In a looser definition, the term CD is often used to refer to any linewidth measurement even if it is not the minimum dimension on the device.
Under a certain lithographic setting (e.g., exposure tool, wavelength, NA, and so on), the amount of defocus and exposure dose variations that a circuit design can tolerate, while still producing functional chips, is called the design's "process window." The process window is often characterized as an area or region in the two-dimensional F-E plot, where "F" is defocus, and "E" is exposure dose variation. Such a plot may also be referred to as an "ED tree", so-called because of the tree-shaped process window which results when exposure (E) is plotted on the x-axis and defocus (D) is plotted on the y-axis. Some RET techniques (e.g., PSM, scattering bars in OPC, OAI) can enhance the process window for a certain circuit design. The settings of the exposure tool (e.g., NA) also have a big impact on the process window.
FIG. 2 shows one example of a process window 30 in the F-E plane. When a wafer is exposed in a F-E condition within process window 30, the chips made from dice on that wafer will be functional. When the wafer is exposed in a F-E condition outside process window 30, the chips from the wafer will not be functional. The larger process window 30, the more robust the circuit design is, and will have higher yield in manufacturing.
A process window for a lithography process is further limited because different patterns within a circuit design have different process windows. These differences may include shifts in the best focal plane position, shifts in the best exposure, and changes in the allowed range of focus and exposure. Different patterns also have different criteria for successful printing. While CD variation of up to +/−15% may be tolerable for some non-critical features, the tolerance for the most critical structures may be only half as much. The failure modes of different patterns may also be very different. Some patterns may be considered unacceptable due to excessive CD variation, others due to excessive changes in their sidewall profiles, and others may suffer from excessive line end pullback or corner rounding. Catastrophic pattern failures are also possible due to the interaction of neighboring structures. A CD variation that may be acceptable if a given feature were being printed as an isolated structure might cause bridging, necking, or other unacceptable pattern variations in a different local environment.
The ultimate goal of the lithography process is to deliver a robust and well maintained "common process window," that is, a process window in which every feature prints within specifications. An example of the overlapping of multiple process windows for individual structures leading to a common process window is shown in FIG. 3. The more different types of structures one desires to print with acceptable pattern fidelity in a single exposure, the more individual process windows need to overlap successfully and the tighter the overlapping common process window usually becomes. This common process window may also be plotted as a series of overlapping ED trees, and has been referred to in the literature as an "ED forest."
OPC is one of a number of techniques available to lithography process designers to optimize the process window overlap between all critical features by adjusting the mask level pattern so that, in principle, all patterns are reproduced at the desired wafer dimensions and shapes under a common set of focus and exposure conditions. However, due to the complex non-linear nature of the pattern transfer process, OPC remains a difficult technique to implement, test, and insert into production with the assurance that all features of interest are correctly transferred from mask to wafer in a manufacturing fab. It is particularly difficult to determine which limited set of structures should be measured and tracked on a regular basis to guarantee that all of the structures in the circuit design are printed correctly.
The definition of common process window used to this point has been phrased in terms of CD performance as the sole metric of process capability. In fact, the common process window for a viable process must be such that the entire three-dimensional pattern is replicated faithfully, including the sidewall profile and height of the remaining resist pattern after development. A complete, common process window would insure that the CD, sidewall angle (SWA), and resist loss (RL) during development are all within specifications for all structures in the circuit layer being patterned. In practice, the process window is often defined only in terms of the CD. A typical process window may be defined as the region of the F-E plane over which the critical dimensions are patterned within specified tolerances, such as +1-10% of the nominal target dimension.
In addition to focus and exposure, many other parameters can have an adverse impact on the common process window, including, but not limited to, lens aberrations (Zernike aberrations, scattered light, and other mid- to long-range spatial frequency errors), imperfections in the exposure tool illumination system (uniformity, localized partial coherence, and localized variations in pupil filling), and less than optimal optical proximity corrections. (See Wong, "Resolution Enhancement Techniques in Optical Lithography," SPIE Press, Bellingham, Wash., Volume TT47, ISBN 0-8194-3995-9 (2001), and Mahajan, "Aberration Theory Made Simple," SPIE Press, Bellingham, Wash., Volume TT06, ISBN 0-8194-0536-1 (1991)).
A typical integrated circuit device contains between 100 million to several billion structures, and there are typically several hundred devices or chips on a typical silicon substrate with a diameter of 200 or 300 mm. It is clearly impossible to measure the dimensions of every structure on a single device, and even more so to measure every device on every production wafer. In practice, a limited set of structures is defined, either within the device areas or placed in the scribe lines between device areas, for in-process monitoring and control.
One of the most difficult challenges in implementing complex OPC into production, such as leading edge model-based OPC, is the difficulty in determining which limited set of structures should be measured and tracked on a regular basis to guarantee that all of the structures in the circuit design are printed correctly. Since all patterns respond differently to changes in focus, exposure, and other process variables, a test structure that is sensitive to one parameter that must be monitored and controlled may be insensitive to other critical parameters. Thus, even if the process monitors seems to indicate that the process is in control, other patterns which are critical to the proper operation of the device may drift without being detected by the metrology plan of record. Insuring that all of the critical parameters are adequately monitored and controlled is a growing challenge in integrated circuit manufacturing.
In today's wafer fabs, exposure tool related optical conditions such as focus, exposure, illumination and aberration may be monitored using test masks and test wafers using specially designed test patterns, or by an exposure tool's self-metrology while undergoing maintenance checks. The optical analysis in these approaches is not in-situ, i.e., the extracted optical conditions are not present when product wafers are printed. Therefore the use of these data is limited.
It is also possible to use test patterns in the product mask's scribe lines, i.e., the spaces between the device areas, to print test patterns, and analyze the test patterns in the scribe lines to extract the optical conditions when the wafer is printed. This approach will take up the valuable space in the scribe lines, where many other patterns are needed, for example alignment patterns. Furthermore, this approach cannot analyze the optical conditions inside the device design itself.
In practice, a limited set of test structures is defined, either within the device areas or placed in the scribe lines between the device areas, for in-process metrology and process control. The dimensions of these test structures are usually chosen to be at or near the minimum feature size that will be patterned within the device, and are referred to as "the CD" of the layer being patterned regardless of whether the width of the structures being measured is actually the minimum or most critical dimension in the device.
The CD is intended to be measured as near as possible to the base of the three-dimensional resist structure, that is, at the resist-substrate interface, to assure the optimum feature size for subsequent process steps such as etch, film deposition, polishing, and ion implantation. This is often difficult due to the top-down viewing angle of scanning electron microscopes used for CD metrology (CD-SEMs) and the high aspect ratio of the three-dimensional profiles, which typically approach 3:1 (3 units depth in the z-direction for every one unit of width in the x-y plane). Scatterometry (SCD) and tilt-SEMs are intended to help resolve this problem and may be used to determine metrics of resist profile and resist loss in addition to CD, but they suffer from other sources of error and uncertainty as well. While it is possible to obtain a reasonable approximation of the CD at the resist-substrate interface for the specified test structures when the process is very close to optimal, the uncertainty in the true CD increases as the process drifts away from the optimal settings.
CD data from multiple test structures with different geometries may be collected in an effort to more closely monitor the common process window of the entire pattern transfer process. While this comes closer to monitoring the full process than simply measuring a single type of test structure, it falls far short of the ultimate goal of representing the performance of all patterns and structures within the device, including the effects of the local environment on the dimensional stability of each pattern. In addition, a full characterization of the common process window would need to take into account the full three-dimensional shape of the metrology patterns, including sidewall angle, sidewall curvature, or other deviations from an idealized trapezoidal shape, and the height of the pattern indicating resist loss from the top of the three-dimensional structure.
The non-linear manner in which each different structure responds to its own local environment and to the global changes in optical and other process conditions throughout the pattern transfer process from mask to wafer creates a complex manufacturing environment where it is difficult to determine, from a limited number of measurements, whether or not all of the desired features within the device are printed within specification, and whether or not all of the variable process condition parameters are being maintained at or near their optimum operating points. This leads to several related problems:
(1) The limited amount of metrology data and test structures cannot adequately ensure that the CDs across the device are within specifications and that the entire device will operate as intended. Since typical manufacturing cycle times can take several months, it is extremely disruptive to the entire business when a large number of wafers turn out to have unacceptably low yield of devices that work properly, requiring new lots to be started and deliveries to be substantially more expensive and behind schedule.
(2) Even when a variation in CD performance is detected, the proper corrective action to take is often unclear due to the confounding influences of focus, exposure, and other process conditions. Historically the easiest adjustment to make has been the exposure dose (See Levinson, "Lithography Process Control," SPIE press, Bellingham, Wash., Vol. TT28, ISBN 0-8194-3052-8 (1999)). However, this blind correction, that is, using only a single adjustable parameter to force a desired output on a limited set of data regardless of which of many parameters actually caused the process to deviate in the first place, often means that the root cause of the CD variation remains undetected and incorrectly compensated.
(3) If the process variation of the test structures was caused by a drift or shift in other parameters besides exposure, a simple exposure compensation or other blind adjustment may be adequate to correct the CD of the test structures, but not of all structures within the device, which could result in the final devices having reduced functionality and yield.
(4) Although crude correction such as a blind exposure dose adjustment may bring the metrology target CDs back into specification, if the error was in fact caused by a focus drift or other optical error instead of an exposure drift, the resulting resist profiles will not have the correct sidewalls intended for the process. Thus, when the wafers are etched, the final profile of the resulting etched structure may be incorrect, leading to improper circuit operation and device failure.
(5) Even if the wafers in question are adequately corrected by a simple dose or other blind correction, other wafers that are to be patterned with other device layouts may be patterned incorrectly with the same relative correction. Thus, by changing the only one parameter to compensate for drifts in other parameters, the process control algorithms for the entire production line may become unstable.
(6) Even if the process can be adequately corrected with a global adjustment of the exposure dose or some other blind correction, if the underlying source of the process variation is not correctly identified and corrected, it may continue to drift further until no amount of compensation of a single parameter can recover the desired process outputs. At that point, the orderly flow of wafers through the entire process line may be disrupted as CDs begin to fall outside the specification limits and the root cause analysis of the true source of the variation must be initiated at great cost and disruption to the manufacturing environment.
Many different approaches have been developed to try to improve CD monitoring and control systems. In particular, a number of techniques have been disclosed to try to separate out the influences of focus and exposure to solve some of the problems listed above. While some of these methods are partially successful, they all suffer from drawbacks in terms of metrology calibration and/or requirements for extensive test structures that do not adequately represent the circuit features. In addition, they are limited to focus and exposure only and do not include other optical parameters of interest. Many of these techniques require extensive metrology and test structure calibration and cannot be easily adapted to changes in circuit design and/or process targets.
U.S. Pat. No. 6,414,326 to Nguyen discloses a simple method to deconvolve focus and exposure errors by measuring two different test structures, one with an isolated pitch and the other with a dense pitch. Since these pitches respond differently to focus and exposure, a given combination of CD errors for the respective patterns should correspond to a unique set of focus and exposure errors. Like many similar efforts, this approach still suffers from an ambiguity in the sign of the focus error: a given combination of isolated and dense CD errors could be due to a focus shift of a given magnitude but in either the positive or negative direction. Nguyen teaches a possible solution using astigmatism of the lens to differentiate between the two focus directions for vertically vs. horizontally oriented features, but this requires extensive characterization of lens astigmatism across the field which may also be convolved with other lens parameters.
U.S. Pat. No. 6,673,638 to Bendik et al. discloses a system for creating line end test structures that are modified to print in a deliberately defocused state even when the exposure tool is at best focus. A comparison between differently modified structures can uniquely determine dose and focus errors; the sign ambiguity of the focus can be solved by printing features of opposite polarity (lines and spaces). This approach is restricted to special targets in the scribe line, not actual device geometries, and depends on line end metrology, which is less precise and more susceptible to convolution with other optical aberrations than line width (CD) measurements.
U.S. Pat. No. 6,929,892 to Shishido et al. discloses the use of an SEM with tilt capability or scatterometry to determine the sidewall profile of a highly isolated feature, which is known to be more susceptible to focus-induced variations than dense structures. The ambiguity in the sign of the focus error is said to be resolved by measuring isolated structures of opposite polarity. Like U.S. Pat. No. 6,673,638, this approach is limited to scribe line test structures, not actual device geometries, and the focus sensitive isolated structures are also sensitive to other aberrations.
U.S. Pat. No. 6,803,995 to Ausschnitt discloses a focus control system using special scribe line patterns wherein line end shortening of the segments of a long pattern ("schnitzl") can be imaged as line width changes in an optical measuring system. The effects of focus and exposure can be deconvolved using targets of opposite polarity, but the sign ambiguity of the best focus position can only be resolved by exposing some fields on the wafer at deliberately defocused conditions, resulting in potential lost chips and complicated exposure and metrology schemes. U.S. Pat. No. 6,643,596 to Firth et al. also discloses a system of deliberately inducing focus perturbations on a lot-by-lot basis to update a focus model. This results in better focus metrology at the expense of negatively impacting the CD control of each lot processed at less than optimal focus.
Various applications of scatterometry have been described as alternative approaches to separating the effects of focus and exposure while also providing CD metrology data. U.S. Patent Application Publication No. 2004/0190008 to Mieher et al. discloses the use of CD, SWA, and RL values derived from SCD spectra to determine a unique combination of focus and exposure conditions. U.S. Pat. No. 6,429,930 to Littau et al. discloses the use of SCD spectra to uniquely determine focus and exposure by comparison to a library of stored spectra and U.S. Patent Application Publication No. 2004/0223137 to Littau et al. discloses extracting an SCD-derived cross section and comparing it to simulated or measured cross sections as a function of F-E conditions. All SCD approaches are limited to arrayed test structures placed in the scribe lines, not device geometries, and are typically limited to one-dimensional line space patterns or at best regular arrays of two-dimensional features such as contact holes. It should also be kept in mind that while SCD does provide highly repeatable measurements, the CD values extracted from SCD curves are all modeled results based on regression, simulation, or lookup tables and do not represent direct measurements of the actual CD or sidewall angle.
Several approaches have been described using signal analysis of the SEM profiles or images to determine the sidewall profile by comparison to stored reference signals. U.S. Patent Application Publication No. 2002/0051567 to Ganz et al. discloses collecting images of assorted structures and comparing them to a library of the same patterns printed at different focus and exposure settings. This technique does not describe how an adequate set of patterns is determined to insure predictability over a range of F-E conditions, or to separate F-E effects from other imaging errors, nor does it result in CD metrology data of sufficient quantitative precision to insure that the process is operating within specifications. U.S. Pat. No. 6,909,930 to Shishido et al. discloses collecting CD-SEM data and analyzing the shape of the SEM line scan profiles or images to determine whether the CD errors are due to focus or exposure. This approach requires extensive calibration, therefore it can only be applied to specific structures which are carefully characterized beforehand and stored in a library. This technique is also sensitive to slight changes in the SEM line scan profile which may be induced by changes in the SEM conditions rather than the exposure tool conditions. U.S. Pat. No. 6,913,861 to Shishido et al. discloses creating special scribe line test structures such as diamond or other highly tapered patterns where the exposure dose is effectively varied along the structure. SEM line scan analysis is performed on these special structures to deconvolve the effects of focus and exposure. U.S. Pat. No. 6,791,082 to Komuro et al. discloses a similar approach using scribe line patterns of opposite polarity to separate the impact of focus and exposure and to resolve the ambiguity in the sign of any focal plane error. Both of these approaches depend on special scribe line targets, not actual device geometries, and rely on extensive look up tables and the stability of the SEM line scan to extract the condition of the exposure tool.
All of the above approaches aim to separate the contributions of focus and exposure on pattern CDs under the tacit assumption that all other optical parameters can be effectively ignored. U.S. Pat. No. 6,795,163 to Finders et al. shows that these other parameters can be as important, if not more so, in determining the patterned CD errors of a given line width as a function of pitch. Finders et al. disclose that the partial coherence, sigma, of the exposure tool can be adjusted to tilt the CD vs. pitch curve to suffer less CD variation across a range of pitches. This illustrates that even in a system that can adequately separate focus and exposure contributions under ideal conditions, the addition of a small illumination error can drastically impact the measured CD performance and so lead to incorrect determination of the computed focus and exposure adjustments.
It is therefore highly desirable to have a system and technique to effectively monitor or observe the lithography process's F-E condition inside the device with actual circuit design patterns, on any selected wafers and at any selected dice on that wafer. This need can be realized by a system and technique that can extract the F-E conditions of the lithographic process directly from printed patterns on product wafers, on any selected wafers and at any selected dice on that wafer.
It is further desired that this system and technique be able to insure the correct patterning of all structures within the device, not just the structure being measured. This need can be realized by a system and technique that can optimize the selection of the optimum set of measured patterns from actual device design patterns that forms a complete characteristic set such that the correct patterning of this set of patterns serves as measurable proof that all patterns within the device are reproduced within specifications.
Beyond the traditional F-E process window, other optical conditions, e.g., NA, illumination conditions, and aberrations, will also drift over time and impact the patterning of the device structures. It is also highly desirable that these other drifts can be extracted directly from the observations of the printed circuit patterns on wafers.
It is further desirable that this system and technique should be capable of quickly and effectively identifying specific patterns within the device that, when measured, will provide precise and specific feedback to the lithography control system indicating not just the CD values, but also the specific corrections that need to be applied to the system to bring the CDs back within specifications and to maintain the exposure tool and the lithography process at their optimum operating conditions. These needs can be realized by the system and technique to locate a complete characteristic set of patterns within the circuit whose collective response to the multivariate optical and process variations provides a unique monitoring and control solution.

Process window signature patterns for lithography process control


Application of inter-class and intra-class filtering, based on aggregate point-to-point distances, to vector data for purposes of filtering the vector data for purposes of pattern recognition. In some embodiments: (i) the inter-class filtering is based on Euclidean distance, in all dimensions, between vector data points in vector space; and/or (ii) the intra-class filtering is based on a distance, in all dimensions, between vector data points in vector space.

The present invention relates generally to the field of pattern recognition, and more particularly to selecting sub-sets of data associated with classes in pattern recognition in situations with noisy and/or sparse data.
The Wikipedia entry for "pattern recognition" (http://en.wikipedia.org/wiki/Pattern_recognition, as of Apr. 16, 2015) states as follows: "Pattern recognition is a branch of machine learning that focuses on the recognition of patterns and regularities in data, although it is in some cases considered to be nearly synonymous with machine learning . . . . Pattern recognition systems are in many cases trained from labeled 'training' data (supervised learning), but when no labeled data are available other algorithms can be used to discover previously unknown patterns (unsupervised learning) . . . . Pattern recognition algorithms generally aim to provide a reasonable answer for all possible inputs and to perform 'most likely' matching of the inputs, taking into account their statistical variation. This is opposed to pattern matching algorithms, which look for exact matches in the input with pre-existing patterns."
In identifying patterns and/or creating indicia of patterns to be identified, pattern recognition may employ data collected from machine based sensor hardware for various "classes." One example of this is when sensors collect data relevant to brain activity, where the "classes" are the different brains from which the sensor data is collected.

Feature selection algorithm under conditions of noisy data and limited recording

International Business Machines Corporation


A semiconductor device includes a Si substrate, an insulating film formed on onepart of the Si substrate, a bulk Si region grown on other part of the Si substrate other than the insulating film, Si1-xGex (0<x≦1) thin film formed on the insulating film in direct contact with the insulating film, and substantially flush with top of the bulk Si region, a first field effect transistor fabricated in the bulk Si region, and a second field effect transistor fabricated in the Si1-xGex thin film.

1. Field of the Invention
The invention relates to a semiconductor device and a method for manufacturing the same, particularly to a semiconductor device having a metal insulator semiconductor field effect transistor (MIS FET) characterized by high current drive power and having a channel formed of strained Si, strained SiGe or Ge.
2. Description of the Related Art
In recent years, it is considered for the purpose of realizing high-performance and high-function of a CMOS circuit device to use channel materials of high mobility such as strained Si or strained SiGe (including Ge).
The strained Si has an tensile strain in in-plain direction of the substrate. The band structure of the strained Si varies due to this tensile strain, so that both electron and hole mobilities increase in comparison with an unstrained Si. Usually, the strained Si is formed on a lattice relaxed SiGe of a greater lattice constant by epitaxial growth. The strain in the strained Si layer increases as the Ge composition of a SiGe template increases, resulting in increasing the mobility. If CMOS is fabricated by MOSFET having the strained Si channel, it is expected to operate at a higher speed than Si-CMOS of the same size.
On the other hand, the strained SiGe has a compressive strain in in-plain direction of the substrate and varies in its band structure due to this compressive strain, resulting in that the hole mobility increases in comparison with an unstrained Si. However, increase of the electron mobility is smaller in comparison with the hole mobility when the Ge fraction is not sufficiently high. When the SiGe channels have compressive strain of around 1% and Ge composition larger than around 80%, both electron mobility and hole mobility increase more than 2 times in comparison with the unstrained Si. As a result, the maximum enhancement of the mobility is provided in a pure Ge channel. If CMOS is fabricated by MOSFET having a strained SiGe of high Ge composition, it is expected to operate at higher speed than the strained Si-CMOS as well as Si-CMOS of the same size.
Further, the strained SGOI (SiGe-on-Insulator)-MOSFET (for example, MOSFET described in a non-patent literature (T. Tezuka et al., IEDM Technical Digests, p. 946 (2001)) fabricated by combination of the strained SiGe-MOSFET with a SOI (Si-on-Insulator) structure has merits obtained by the SOI structure such as decrease of junction capacitance, decrease of device size with the impurity density being lowered, as well as merit obtained by the high carrier mobility of the strained SiGe channel. Accordingly, if a CMOS logic circuit is fabricated by a MOSFET of a strained SGOI channel, an operation of higher-speed and lower power is expected.
However, since the SiGe has a band gap smaller than a conventional Si, a junction leakage current increases inevitably, resulting in lowering a breakdown voltage. Accordingly, for the SOC (System-on-Chip) application that integrates in a single LSI chip a plurality of kinds of MOSFETs such as LOP (Low Operation Power)-MOSFET for a low power operation and low standby power operation, LSP (Low Stand-by Power)-MOSFET and high breakdown voltage MOSFET as well as HP (High performance)-MOSFET for high speed operation, it is preferable that a SGOI channel is used for the HP-MOSFET and a bulk Si or SOI or a strained SOI is used for the LOP- and LSP-MOSFET.
An example which integrates strained SOI-MOSFETs and SGOI-MOSFETs is provided by, for example, a patent literature 1 (Japanese Patent Laid-Open No. 2001-160594). In this literature, the n channel has a bi-layer structure of a lattice-relaxed SiGe and a strained Si. Accordingly, SiGe layers are used in both p, n channels. However, because SiGe has a band gap smaller than a conventional Si regardless of strain or non-strain, a junction leakage current increases necessarily, resulting in lowering a withstand voltage. Accordingly, for SOC (System-on-Chip) application, it is difficult due to SiGe layer to satisfy specifications of leakage and breakdown voltage in devices other than HP-MOSFET.
In this way the conventional art provides a configuration that integrates a SOI-MOSFET and a SGOI-MOSFET for the purposed of realizing high-performance and high-function of CMOS circuit device. However, since this configuration uses a SiGe layer for both p, n channels, it is difficult due to the SiGe layer to satisfy specifications of leakage and breakdown voltage in devices other than HP-MOSFET. In other words, it is difficult to realize both high-speed operation and low-power operation.
Further, in reducing the size of a MOSFET of SOI structure, it is necessary to decrease a thickness of a channel layer on a buried oxide film. In particular, it is necessary for realizing an operation of a fully depleted device to decrease a film thickness to about ¼ of a gate length. This request means that it is necessary for making a gate length, for example, 20 nm to make a channel film thickness (additional value of film thickness of a strained Si and that of a lattice-relaxed SiGe in nMOSFET of the patent literature 1) nm. It is very difficult to realize such decreasing of film thickness in a multi-layer structure while maintaining productivity.
The present invention is to provide a semiconductor device capable of realizing an integrated circuit device having both high-speed operation and low-power operation by combining bulk Si, a SOI thin film, a SGOI thin film, etc. and a method of manufacturing the same.

Semiconductor device and method for manufacturing the same


The present invention relates to a contactless integrated circuit reader operating by inductive coupling, comprising an antenna circuit for sending an alternating magnetic field, circuits for applying an alternating excitation signal to the antenna circuit and circuits for modulating the amplitude of an antenna signal present in the antenna circuit according to data to be sent. The reader includes circuits for simulating the operation of a contactless integrated circuit, arranged to inhibit the application of the excitation signal to the antenna circuit and to apply a load modulation signal to the antenna circuit when data is to be sent. The load modulation signal is capable of disturbing a magnetic field sent by another contactless integrated circuit reader and of being detected by the other contactless integrated circuit reader.

The present invention relates to contactless integrated circuit readers and data transmission by inductive coupling.
As represented schematically in FIG. 1, a contactless integrated circuit reader 10 operating by inductive coupling is an active system that sends an alternating magnetic field FLD by means of an antenna circuit 11 and that sends data by modulating the amplitude of the magnetic field sent. Conversely, a contactless integrated circuit 20 is a passive device that does not send a magnetic field and comprises an antenna circuit 21 comparable by analogy to the secondary winding of a transformer the primary winding of which would be constituted by the antenna circuit 11 of the reader. The magnetic field FLD sent by the reader causes an induced alternating voltage Vac to appear in the antenna circuit of the integrated circuit, said induced voltage copying the amplitude modulations of the magnetic field and enabling the integrated circuit 10 to receive the data sent by the reader, after filtering and demodulating the induced voltage Vac. Furthermore, a contactless integrated circuit 20 sends data to such a reader by load modulation, i.e. by short-circuiting its antenna circuit by means of a switch driven by a load modulation signal Sx. The antenna short-circuits cause a disturbance of the magnetic field FLD that is passed onto the antenna circuit of the reader 10. The latter can therefore extract the load modulation signal Sx by filtering the signal present in its antenna circuit 11 and deduce the data sent by the contactless integrated circuit from it.
With reference for example to the ISO standards 14443-2/A or 14443-2/B or ISO 1569, designated hereafter "ISO/A", "ISO/B" and "ISO15", the antenna circuit of a contactless reader is excited by an alternating signal of a frequency of 13.56 MHz, the data transmission to a contactless integrated circuit is carried out by modulating the amplitude of the magnetic field with a modulating trough of 100% (ISO/A), of 10% (ISO/B) or of 10% to 30% (ISO15). The data transmission to a reader is carried out by load modulation by means of a sub-carrier of 847 KHz that is Manchester coded (standard ISO/A) or biphase shit keying (BPSK) coded (standard ISO/B) or by means of a sub-carrier of 423 KHz that is Manchester or frequency shift keying (FSK) coded (IS015).
The applications of this data transmission technique by inductive coupling are currently increasing, particularly in the fields of electronic payment and access control (smart cards and electronic badges) and in product identification (electronic tags). The contactless integrated circuits are arranged on portable supports (plastic cards, tag supports) having an antenna coil integrated therein. The antenna coil is sometimes integrated directly into the silicon wafer of the integrated circuits ("coil on chip"), in so-called "proximity" applications in which the maximum distance of communication is short and on the order of a few millimetres.
In many applications, the contactless integrated circuit readers are in the form of fixed terminals. However, these contactless terminals are capable of recording different pieces of information relating to the operations carried out, which are sometimes necessary to collect to correctly manage the installations. Thus, an access control terminal is capable of recording each time the door opens, the date, the time and the identity of the badge with which the opening of the door was requested. Similarly, an automatic payment terminal is capable of recording the time of each transaction and the identity of the card with which payment was made. In the applications that involve several terminals, it is sometimes desirable for this information to be collected by a data centralization system. To collect the information recorded, it is therefore necessary to provide an infrastructure of electric cables enabling the centralization system to be connected to each of the terminals. In other applications, the reading of the data recorded by a terminal is done manually by means of a terminal reader comprising a connector that is inserted into an output port of the terminal.
These various operations of reading data in fixed terminals prove to be tedious when they are done manually or costly when they require an infrastructure of electric cables.
The present invention aims to overcome this disadvantage.


A safety hypodermic needle and a method of using the same are disclosed. The safety needle comprises a hypodermic needle and a protective sheath molded of a flexible polymeric material. The protective sheath comprises a needle sleeve with an open central passage which houses the sharp needle point. The needle sleeve is supported on a plurality of inwardly bowed ribs in an unflexed “at rest” condition in which the needle point is retained inside the needle sleeve to prevent inadvertent needle sticks. Levers attached to the ribs are used to move the ribs from their inwardly bowed unflexed “at rest” condition to an outwardly bowed flexed condition to permit the needle to pass through the open central passage of the needle sleeve and into a patient's body. After the needle is removed from the patient's body, the ribs automatically return to the unflexed “at rest” condition without the assistance of any additional biasing or restoring means.

1. Field of the Invention
The present invention relates generally to hypodermic syringes and phlebotomy apparatus and more particularly to a safety hypodermic needle for disposable hypodermic syringes and phlebotomy apparatus and a method of using the safety needle to prevent inadvertent needle sticks or punctures.
2. Description of the Prior Art
Infectious diseases can be transmitted to medical personnel and others by way of inadvertent needle sticks or punctures with an infected needle of a hypodermic syringe or phlebotomy apparatus. Cases have been reported in which human HIV (AIDS) infection and other infectious diseases have been transmitted by accidental or inadvertent needle sticks. A number of devices have been developed for the purpose of preventing such needle sticks.
One prior art device comprises a spring-biased tube located within the lumen of the needle. After the needle has been used, the tube is advanced by the spring beyond the needle bevel point thereby protecting medical and other personnel from an inadvertent needle stick. This device is relatively complex, costly and reduces the effective lumen size of the needle.
Another type of prior art device in more common use employs a protective sheath external to the needle which is retractable to permit insertion of the needle into the body of the patient and is then slidable back over the needle past the needle point as, or after, the needle is withdrawn from the body. In some of this type of prior art protective device, a spring or axially resilient sheath is used to extend the sheath over the needle point upon withdrawal of the needle. Several of these prior art devices use a collapsible sheath formed by a plurality of resilient arms surrounding the needle. The arms are bowable or bendable outwardly away from the needle axis to expose the needle and are movable inwardly toward the needle axis with or without a biasing means to again enclose the needle within the sheath. Some of these devices require a positive step or a specific manual act by the phlebotomist or user to deploy the protective sheath after it is withdrawn from the patient's body. Still other devices are made from a plurality of parts making them more complex to manufacture and thus more costly to the consumer.
One of the primary shortcomings of the prior art devices which use protective sheaths of the foregoing type is that during at least some of the period of time between the preparation of the hypodermic syringe for an injection, or the phlebotomy apparatus for entering a vein, and the discarding of the used needle, inadvertent needle sticks of persons other than the patient are still possible. In some prior art devices, the protective sheath does not cover the needle tip prior to administering the needle to the patient, and in others, the protective sheath does not positively prevent exposure of the needle tip after administering the needle to the patient.
It would be desirable, therefore, to provide a safety hypodermic needle for use with a disposable hypodermic syringe, as well as for use with catheter needles and other types of body-penetrating hypodermic needles, that overcomes the foregoing limitations and shortcomings of the prior art devices, has a minimum number of parts, is economical to manufacture and is easy and convenient to use. In particular, it would be highly desirable and advantageous to provide a safety needle that is operable in its "at rest" state to positively prevent inadvertent exposure of the needle point at all times, both before and after use, and to permit exposure of the needle point for use on a patient only in response to a specific manual action or manipulation of the safety needle components on the part of the user, which may include breaking, rupturing or otherwise disengaging a member that retains the safety needle in its "at rest" safe state.
My prior U.S. Pat. No. 5,256,152, the entire disclosure of which is incorporated herein by reference, efficiently and effectively solves many of the aforementioned problems and shortcomings of other prior art safety devices for hypodermic needles and the like. The present invention provides still further improvements in those other prior art safety devices for hypodermic needles as will be described in detail in the following specification.


Disclosed herein are “ketannabis” (or “ketonnabis”) compositions including a combination of: (1) tetrahydrocannabinol (THC); (2) a ketone body component such as beta-hydroxybutyrate (BHB) and/or acetoacetate; and (3) a dietetically or pharmaceutically acceptable carrier. Also disclosed herein are methods of using such ketannabis compositions for producing desired physiological effects. The ketannabis compositions beneficially enhance the euphoric effects of THC without aggravating common side effects or even acting to reduce common side effects such as anxiety, disruption of short-term memory, appetite increases, heart rate increases, and blood pressure changes.

Ketosis
In periods of fasting, extreme exercise, and/or low carbohydrate consumption, glucose and glycogen stores in the body are rapidly used and can become quickly depleted. Failure to replenish glucose stores as they become depleted causes the body to metabolically shift to the creation of ketone bodies for energy. This metabolic state is called "ketosis".
Ketone bodies can be used by cells of the body as a fuel in addition or instead of glucose to satisfy the body's energy needs, including the brain and heart. During prolonged fasting, for example, blood ketone levels can increase to 2-3 mmol/L or more. It is conventionally understood that when blood ketones rise above 0.5 mmol/L, the heart, brain and peripheral tissues are using ketone bodies (e.g., beta-hydroxybutyrate and acetoacetate) as the primary fuel source. This condition is referred to as ketosis. Between 1.0 mmol/L and 3.0 mmol/L the condition is called "nutritional ketosis."
Upon transitioning into ketosis, or in other words, during ketogenic metabolism in the liver, the body uses dietary and bodily fats as a primary energy source. Consequently, once in ketosis, one can induce loss of body fat by controlling dietary fat intake and maintaining low carbohydrate intake to maintain a ketogenic metabolic state.
While in ketosis, the body is essentially burning fat for its primary fuel. The body initially cleaves fats into fatty acids and glycerol. It then transforms fatty acids into acetyl coenzyme A ("acetyl-CoA") molecules, which are then eventually transformed through ketogenesis into the water-soluble ketone bodies beta-hydroxybutyrate ("β-hydroxybutyrate" or "BHB"), acetoacetate, and acetone in the liver. BHB and acetoacetate are the ketone bodies used by the body for energy while acetone is removed as a by-product of ketogenesis. Although BHB is technically not a ketone, it is still referred to as a "ketone body" in the context of ketosis.
The metabolism of ketone bodies is associated with several beneficial effects. However, despite the many health advantages of pursuing a ketogenic diet or lifestyle and maintaining a state of nutritional ketosis, there remain significant barriers to pursuing and maintaining a ketogenic state. One of these barriers is the difficulty of transitioning into a ketogenic state. The fastest endogenous way to entering ketosis through depleting glucose stores in the body is through fasting combined with exercise. This is physically and emotionally demanding and is extremely challenging even for the most motivated and disciplined.
Additionally, the transition into ketosis is often accompanied by hypoglycemia which can cause lethargy and light-headedness in many, resulting in an uncomfortable physiological and mental state commonly referred to as the "low-carb flu" or "keto flu." In addition, many people experience a down regulation in their metabolism as the body goes into an "energy-saving" mode. Some suggest that these transitory symptoms may last as long as two to three weeks. During this transition period, if any meal or snack consisting of carbohydrates over the restrictive amount is consumed, there is a rapid termination of ketogenesis, causing the body to exit from its state of ketosis as the body shifts back to glucose utilization as its primary fuel. At this point, the difficult transition into ketosis must begin anew. Thus, despite the potential of a ketogenic diet for weight loss and other health benefits, serious limitations continue to hinder the full realization of its potential.
Tetrahydrocannabinol
Tetrahydrocannabinol (THC) is one of the major cannabinoid constituents of the cannabis plant. The particular type found in cannabis is (−)-trans-Δ9-tetrahydrocannabinol, though the more generic term THC may also refer to isomers such as stereoisomers and double bond isomers. THC is the major cannabinoid component responsible for the psychoactive effects of cannabis. It is typically the most abundant constituent of the flower/bud portion of the cannabis plant.
THC is currently used as an active ingredient in medicines intended to increase appetite, reduce nausea, and alleviate neuropathic pain and spasticity. THC is most commonly administered orally or via inhalation. THC is believed to interact with a variety of biological targets, including cannabinoid receptors such as CB1 and CB2 as well as neurotransmitter receptors such as the μ- and δ-opioid receptors. The psychoactive effects of THC are believed to result from inhibition of adenylate cyclase, which leads to a decrease in the concentration of cyclic adenosine monophosphate (cAMP).
Though THC has several positive uses, with other uses likely to be discovered in the future, some limitations are currently known to exist. Though feelings of euphoria are often associated with use of THC, users may also experience adverse side effects, such as anxiety, panic attacks, increased heart rate, and changes in blood pressure. Thus, despite benefits associated with THC as a supplement or drug, several limitations to its use remain.

Compositions and methods for delivering tetrahydrocannabinol and ketone bodies


Reinforced, molding compositions having improved ductility and melt flow properties. The present compositions contain a cyclo aliphatic polyester resin preferably comprising the reaction product of a cycloaliphatic C.sub.6 -C.sub.12 diol or chemical equivalent and C.sub.6 -C.sub.12 cycloaliphatic diacid or chemical equivalent, preferably an impact modifying amorphous resin which increases the ductility of the polyester resin but reduces the melt flow properties thereof, a high molecular weight polyetherester polymer which increases the melt flow properties of the polyester polymer without reducing the ductility thereof, and a glass filler to reinforce and stiffen the composition and form a reinforced molding composition.

1. Field of the Invention
The present invention relates to improvements in UV-stable reinforced molding compositions containing impact-modifying elastomeric polymers and fibrous filler such as glass fibers, in order to increase the flow properties thereof while still having good ductility and stiffness. The present compositions are based upon cyclo aliphatic polyester polymer blends with polyether-polyester copolymers as binder materials for the reinforced molding compositions. The blend may optionally contain aromatic polycarbonate polymers.
Thermoplastic polymers have many desirable properties that make them useful in injection molding applications. Some of these desirable properties include strength, toughness, heat resistance, and resistance to chemicals. It is known to add impact modifiers to polyester resins to improve the ductility or the notched Izod impact strength thereof. However the effect of such impact modifiers on reinforcing polyester resin compositions, such as those containing 30% by weight of reinforcing glass fibers, is a relatively modest improvement in ductility and, unfortunately, an increase in the melt viscosity or reduction in the melt flow, modulus and heat distortion properties of the composition.
One problem with polyesters in injection molding applications is that it is sometimes difficult to fill large molds requiring long flow lengths or very thin parts because of the high melt viscosity of the polymer. A solution to this problem is to raise the temperature of the polymer melt, thus lowering its viscosity. This solution is often not satisfactory for polyester polymers since polyesters tend to degrade, or lose molecular weight, at elevated processing temperatures.
Also, there are well known additives which reduce the melt viscosity of polyesters. However, these additives usually make the resulting molded material less rigid, less heat resistant, and/or function only by breaking down the molecular weight of the polyester resulting in reduced impact.
2. Description of Prior Art
Reference is made to commonly-assigned U.S. Pat. No. 5,486,562, the disclosure of which is hereby incorporated herein, for its disclosure of UV-stable weatherable molding compositions based upon PCCD aliphatic polyester binder materials containing impact-modifying elastomeric polymers and filler such as glass fibers, which compositions have enhanced melt flow properties while retaining good impact strength properties.
However, the biggest disadvantage of such compositions, when used to mold elements such as automotive trim and door handles, is the sacrifice of ductility and stiffness, resulting in brittleness, in order to improve the melt flow properties of the glass filled, reinforced molding composition.
Reference is also made to commonly-assigned U.S. Pat. No. 5,122,551, the disclosure of which is also incorporated herein, for its disclosure of glass-filled copolyether-polyester compositions containing copolyetherester elastomers. Reinforced copolyether-polyester compositions generally have superior tensile strength and flexural strength when combined with glass fibers treated with epoxy cyanurate sizing agents, as disclosed in said Patent, but do not have good weatherability.
Finally, reference is made to U.S. Pat. No. 4,342,678 which discloses glass fiber-reinforced thermoplastic molding compositions based upon mixtures of certain cycloaliphatic polyester polymers and glass fibers.

Reinforced aliphatic polyester molding composition having improved ductility/flow properties


A tightening device for adjusting the degree of tautness of a strapping member. The device comprises: a base; a first member attached to and extending at a first angle from a first side of the base; a second member attached to and extending at a second angle from a second side of the base, the members being in an opposed spaced apart relationship and cooperating with the base to define an interior; a first slot formed in a distal end of the first member with respect to the base, the first slot configured to receive the strapping member therethrough; a second slot formed in a distal end of the second member with respect to the base, the second slot configured to receive the strapping member therethrough in coordination with the opposing slot; and a tightening element configured for coupling the strapping member to the device, the tightening element for collecting and retaining a selected length of the strapping member within the interior; wherein adjustment of the tightening element modifies the length of the strapping member extending between the slots and thereby collected in the interior.

Residential and commercial buildings contain walls and floors typically assembled as frame assemblies with a series of vertical and horizontal structural members, also known as framing elements. In order for the frame assemblies to withstand vertical and horizontal loading, either static or dynamic, shear braces and/or cladding are typically attached to the framing elements on at least one side of the frame assemblies.
In the case of light framed wall assemblies such as steel framed walls, a flat steel strap known as a flat strap brace is attached on a diagonal (or perpendicular) to the framing elements, thereby increasing the stiffness of the frame assembly to resist lateral and racking loads. These flat strap braces are generally manually attached to opposing corners of the frame assembly, which can lead to undesirable pockets of slack strap material located between the adjacent framing elements. One disadvantage with this installation procedure is that it is difficult to install the flat straps as stretched taut, in order to be effective in resisting any applied loads, and therefore special tools or jigs are commonly used in attaching and thereby pre-tensioning or otherwise making taut the straps on the frame assembly.
One solution for controlling the tautness of diagonal strapping members is given in U.S. Pat. No. 6,185,898 by Pratt. Pratt describes modifying a wall assembly to incorporate a pair of laterally opposed vertical supports, which are used to attach a corresponding strap thereto. Each of the supports have an aperture that is sized to receive the straps by means of a cooperating force distributing member and a strap alignment member. Both members are positioned in the aperture to align and distribute loading from the tensioned straps. However, one disadvantage with Pratt's strapping arrangement is that it requires modification of the adjacent wall framing members to provide appropriate aperture to accommodate the force distributing and strap alignment members.


An optical transmitter which modulates the phases and intensities of double pulses and then transmits them, includes a branching section which branches each of the input double pulses to first and second paths, a first optical modulator placed in the first path, second and third optical modulators placed in series in the second path, and a combining section which combines the double pulses having traveled through the first path with the double pulses having traveled through the second path to output double pulses. A control section controls such that each of the first and second optical modulators performs any one of relative intensity modulation and relative phase modulation on the double pulses passing through, and the third optical modulator performs relative phase modulation on the double pulses passing through.

1. Field of the Invention
This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2007-228510, filed on Sep. 4, 2007, the disclosure of which is incorporated herein in its entirety by reference.
The present invention relates to an optical communication system in which an optical pulse is phase- and intensity-modulated and then transmitted and, more particularly, to an optical transmitter and a method for controlling a composite modulator used in the optical transmitter.
2. Description of the Related Art
The Internet, which is growing rapidly, is convenient, but, in actual fact, there is great apprehension about its security. The necessity for high-degree cryptographic technologies is ever increasing to maintain secrecy in communication. The cryptographic methods that are currently used in general are broadly classified into secret key cryptography, such as Data Encryption Standard (DES) and Triple DES, and public key cryptography, such as Rivest Shamir Adleman (RAS) and elliptic curve cryptography (ECC). However, these are cryptographic communication methods that guarantee the security of communication based on computational complexity. Ciphers according to these methods are in constant jeopardy of being broken with the advent of vast computing power or a cryptanalysis algorithm. In such a background, quantum key distribution (QKD) is attracting attention as a cryptographic key distribution technique that makes eavesdropping absolutely impossible.
In QKD, a photon is generally used as a medium of communication, and information is transmitted by being superposed on the quantum state of a photon. If an eavesdropper existing on a transmission path eavesdrops on the information by, for example, tapping a photon being transmitted, it is impossible to perfectly return the quantum state of the once-observed photon to the state before observation, according to Heisenberg's uncertainty principle. This causes a change in the statistics of the reception data detected by an authorized receiver. The detected change allows the receiver to detect the presence of the eavesdropper on the transmission path.
In the case of a quantum key distribution method utilizing the phase of a photon, a sender and a receiver (hereinafter, referred to as "Alice" and "Bob," respectively) organize an optical interferometer. Alice and Bob individually modulate the phase of each photon at random. Based on the depth difference between the modulated phases, an output of "0," "1," or "indeterminate" can be obtained. Thereafter, the conditions used when output data were measured are partly compared between Alice and Bob, whereby a sequence of random numbers can be finally shared between Alice and Bob. The sequence of random numbers shared here includes errors caused by external disturbances such as photon-receiver noises, noises leaking from a classical-channel signal, and noises caused depending on the precision of the interferometer. In addition, it should be thought that the sequence of random numbers also includes errors caused by an act of eavesdropping committed by an eavesdropper (hereinafter, referred to as "Eve"). Therefore, to obtain a final cryptographic key, Alice and Bob carry out error correction for eliminating the errors in the shared sequence of random numbers and privacy amplification for sifting out the information that Eve may possess.
For the configuration most suitable for practical use, a plug and play system is frequently used, which is shown in Ribordy, G., Gautier, J.-D., Gisin, N., Guinnard, O., and Zbinden, H. ("Automated 'plug & play' quantum key distribution," Electronics Letters, Vol. 34, No. 22, pp. 2116-2117), and others. In a plug and play system, an optical interferometer of a round-trip type is constructed so that a single interferometer functions as an interferometer for temporally separating a photon pulse and an interferometer for combining the temporally separated photon pulse pair again. Accordingly, this system has the merit that high-precision interference can be achieved if the optical path difference made in the interferometer is kept constant for a period of time longer than the duration of a round trip of a photon pulse.
However, QKD methods of such a round-trip type are unsuitable to increase the key sharing rate because phase modulators for modulating the phase of a photon pulse need to be used in two ways. In addition, there is also a demerit that the signal-to-noise ratio of a photon signal is degraded because the occurrence of backscattering light in a transmission path is inevitable.
On the other hand, according to QKD methods of a one-way type, a sender and a receiver have different asymmetric interferometers respectively. That is, the interferometer for temporally separating a photon pulse and the interferometer for combining the temporally separated photon pulse pair again are placed at distant locations. Accordingly, some techniques are needed to keep the optical path differences made in the multiple interferometers precisely equal. For example, Yuan, Z. L. and Shields, A. J. ("Continuous operation of a one-way quantum key distribution system over installed telecom fibre," Optics Express, Vol. 13, pp. 660-665), discloses a system in which a fiber stretcher is provided to one of the paths of the asymmetric interferometer on Bob's side and the length difference between the optical paths of the asymmetric interferometer is adjusted by controlling the fiber stretcher while monitoring interference characteristics.
However, since optical fiber has a linear expansion coefficient ranging from 10−6 to 10−5/K, an optical fiber line with a length of 100 cm (corresponding to a delay of 5 ns) extends/contracts approximately 100 to 1000 nm, with a 0.1-degree change in temperature. Since an optical signal to be used in QKD and general optical communication has a wavelength of 1550 nm, if an asymmetric interferometer having a delay of several nanoseconds is used, stable interference characteristics cannot be obtained unless temperature control of the entire optical fiber for delay is performed with a granularity smaller than 0.01 degrees. According to Bonfrate, G., Harlow, M., Ford, C., Maxwell, G., and Townsend, P. D. ("Asymmetric Mach-Zehnder germano-silicate channel waveguide interferometers for quantum cryptography systems," Electronics Letters, Vol. 37, No. 13, pp. 846-847), optical paths are installed in a small area by using planar lightwave circuit (PLC) technology, whereby temperature control is facilitated.
As described above, techniques have been gradually established for stabilizing the relative delay amounts in multiple interferometers, which has been a challenge in implementing one-way QKD. In response to this trend, one-way QKD has begun to develop in various ways in recent years. For example, Nambu, Y., Yoshino, K., and Tomita, A. ("One-Way Quantum Key Distribution System Based on Planar Lightwave Circuits," Japanese Journal of Applied Physics, Vol. 45, pp. 5344-5348) proposes a first one-way QKD system using a general two-input, two-output Mach-Zehnder interferometer. A second one-way QKD system using no phase modulator is also proposed in Nambu, Y., Yoshino, K., and Tomita, A. ("Quantum key distribution systems without optical switching using planar lightwave circuit," The 8th International Conference on Quantum Communication, Measurement and Computing, pp. 2-31). Both of these schemes are embodiments of the BB84 protocol using four quantum states (see Bennett, C. H. and Brassard, G., "QUANTUM CRYPTOGRAPHY: PUBLIC KEY DISTRIBUTION AND COIN TOSSING" in Proceedings of the IEEE International Conference on Computers, Systems, and Signal Processing, Bangalore (1984), pp. 175-179). Next, the first and second one-way QKD systems will be described.
FIG. 1A is a block diagram schematically showing the first one-way QKD system. According to the scheme shown in FIG. 1A (hereinafter, referred to as "scheme A"), four phase states are used.
First, an optical pulse generated by a light source 11 on Alice's side is temporally separated into a temporally separated pulse pair (hereinafter, referred to as double pulses) by a PLC asymmetric Mach-Zehnder (AMZ) interferometer 12, and the phase difference between these double pulses is modulated into any one of four states (0, π/2, π, and 3π/2) by phase modulators 13 and 14. Hereinafter, a coding set of phase differences of 0 and π will be referred to as "X basis," and a coding set of phase differences of π/2 and 3π/2 will be referred to as "Y basis."
In Bob, the phase difference between the double pulses received from Alice is modulated again into 0 or −π/2 by a phase modulator 16. Thereafter, the result of interference of the double pulses, which are combined by a PLC AMZ interferometer 17, is detected by one of photon detectors APD1 and APD2.
In the scheme A, there are two methods to carry out four-state phase modulation on Alice's side: a method by which a single phase modulator is driven with four values, and a method by which two phase modulators are driven each with two values. The former method, by which a single phase modulator is driven with four values, has the merit of reducing the space and power consumption of the sender because only one phase modulator is required. However, this method also has a demerit as follows. In a high-speed transmission system in which the system repetition rate exceeds 1 GHz, it is difficult to set each of the levels of four-valued driving signals with high precision, and each of the phase states of 0, π/2, π, and 3π/2 is deteriorated in precision, resulting in the key generation efficiency being degraded. On the other hand, according to the latter method, by which two phase modulators are driven each with two values, the four phase states can be generated with high precision by individually controlling the amplitude of each of the two-valued signals.
FIG. 1B is a block diagram schematically showing the second one-way QKD system. In the scheme shown in FIG. 1B (hereinafter, referred to as "scheme B"), two phase states and two time states are used.
First, on Alice's side, using a four-input, two-output PLC AMZ interferometer 21, optical pulses from light sources LD1 to LD4 are input to four input ports respectively. In the case of an optical pulse input from the light source LD1, since the optical pulse travels along only a long path of the interferometer 21, only a single pulse temporally delayed is sent out to a transmission line. In the case of an optical pulse input from the light source LD4, since the optical pulse travels along only a short path of the interferometer 21, only a single pulse relatively advanced is sent out to the transmission line. In the case of optical pulses input from the light sources LD2 and LD3, the X or Y basis can be generated depending on the phase difference between the optical pulses traveling along the long and short paths of the PLC AMZ interferometer 21. On Bob's side, each basis is decoded by using a two-input, four-output PLC AMZ interferometer 23 and detected by using one of photon detectors APDZ1, APD1, APD2, and APDZ2.
Hereinafter, a coding set corresponding to the case where only one of the double pulses exists as in the case of using the light source LD1 or LD4 will be referred to as "Z-basis." Note that the optical intensity of each of the double pulses made when the X or Y basis is selected is half the optical intensity made when the Z basis is selected because the total sum of the optical intensities of the double pulses needs to be equal to the optical intensity made when the Z basis is selected.
That is, according to the scheme B, a selection is made from the four light sources LD1 to LD4 to generate an optical pulse on Alice's side, and a photon is detected by using one of the photon detectors APDZ1, APD1, APD2, and APDZ2 on Bob's side, whereby it is possible to determine a bit and basis at the same time.
With respect to the configuration of the receiver, the schemes A and B each has a merit and demerit. The scheme B has the merit that it is possible to increase the distance and speed by an amount equivalent to a loss caused by a phase modulator because no phase modulator is required on Bob's side, but has the demerit that the power consumption is large because four photon detectors are required. On the other hand, the scheme A has a merit in terms of power consumption because only two photon detectors are used, but has the demerit of being unsuitable to increase the distance and speed due to the loss attributable to the phase modulator on Bob's side. Accordingly, considering the merits and demerits of the schemes A and B, a desirable sender is a transmitter that is applicable to both schemes. However, such a transmitter that can be applied to both the schemes A and B has not hitherto been proposed.
Moreover, in the scheme B shown in FIG. 1B, four light sources LD1 to LD4 are required. However, as a practical problem, it is extremely difficult to make the spectra of light output from the four light sources perfectly match. If the deviation is large, Eve can correctly determine a quantum state being transmitted by measuring wavelength deviation and thus can duplicate the quantum state without leaving any trace of eavesdropping.
To make the sender configuration according to the scheme B shown in FIG. 1B applicable to the scheme A shown in FIG. 1A, if multiple modulators are simply placed at an output of the PLC AMZ interferometer 21 on Alice's side, four modulators are required. This will be described with reference to FIGS. 2A and 2B.
FIG. 2A is a conceptual diagram collectively showing the modulations that are required to prepare the X, Y and Z bases. FIG. 2B is a signal constellation diagram showing the signal points according to the modulations shown in FIG. 2A. Referring to FIG. 2A, output from the two-input, two-output PLC AMZ interferometer 12 according to the scheme A are double pulses of the same intensity. When Z-basis modulation is performed, one of these double pulses is completely extinguished by using an intensity modulator. When X- or Y-basis modulation is performed, the intensities of both pulses are reduced by half by using an intensity modulator, and at the same time, it is necessary to produce a phase difference between the double pulses by using phase modulators. That is, four-state phase modulation (in steps of π/2) is needed to correspond with the receiver according to the scheme A, and three-state (0, ½, 1) intensity modulation is needed to correspond also with the receiver according to the scheme B. In FIG. 2B, required signal points are plotted on an IQ plane.
Referring to FIG. 2B, the phase of a point A does not need to be zero because the phase state of a Z-basis optical pulse is not restricted. Therefore, the point A can be any point on the same-intensity circle with as long a radius as the distance from the original point of the IQ plane to the point A. To realize such modulation, it is possible to utilize a modulation method described in Hayase, S., Kikuchi, N., Sekine, K., and Sasaki, S. ("Proposal of 8-state per Symbol (Binary ASK and QPSK) 30-Gbit/s Optical Modulation/Demodulation Scheme," ECOC 2003, Th.2.6.4). Hayase et al. discloses a modulator configured by using three optical modulators in total (two phase modulators and one intensity modulator) to implement 8-state (four values in phase and two values in intensity) amplitude phase shift keying (APSK) modulation.
FIG. 3A is a block diagram depicting the configuration of an ASK-QPSK transmitter described in Hayase et al. and FIG. 3B is a signal constellation diagram showing the signal points according to this transmitter.
Three modulators in total (a phase modulator 32 for (0, π) modulation, a phase modulator 33 for (0, π/2) modulation, and an intensity modulator 34 for (½, 1) modulation) are connected in cascade on the output side of a light source 31 as shown in FIG. 3A, whereby the required signal constellation on the IQ plane as shown in FIG. 3B can be prepared. However, when comparing the signal constellation in FIG. 3B with the signal constellation in FIG. 2B, there is no signal point of an intensity of 0 in FIG. 3B. Therefore, to supply this signal point, it is necessary to add one more intensity modulator. Specifically, an intensity modulator for (0, 1) modulation needs to be connected in cascade on the output side of the light source 31 in addition to the phase modulator 32 for (0, π) modulation, phase modulator 33 for (0, π/2) modulation, and intensity modulator 34 for (½, 1) modulation.
As described above, if an attempt is made to obtain a signal constellation as shown in FIG. 2B by utilizing the configuration of the transmitter according to Hayase et al., four optical modulators are required in total. It is desirable that the number of modulators to be used be as smalls as possible from the viewpoint of power consumption and space saving.

Optical transmitter and control method thereof


Disclosed herein is a touch panel, including: a transparent substrate; an electrode formed in a mesh pattern on the transparent substrate; and a wiring formed in a wavy pattern on the transparent substrate and connected to the electrode, the wiring having curve shape of first peaks and second peaks alternately continuing along a longitudinal direction.

1. Technical Field
The present invention relates to a touch panel.
2. Description of the Related Art
With the development of computers using a digital technology, devices assisting computers have also been developed, and personal computers, portable transmitters and other personal information processors execute text and graphic processing using a variety of input devices such as a keyboard and a mouse.
While the rapid advancement of an information-oriented society has been widening the use of computers more and more, it is difficult to efficiently operate products using only a keyboard and mouse currently serving as an input device. Therefore, the need for a device that is simple, has minimum malfunction, and is capable of easily inputting information has increased.
In addition, current techniques for input devices have progressed toward techniques related to high reliability, durability, innovation, designing and processing beyond the level of satisfying general functions. To attain these objects, a touch panel has been developed as an input device capable of inputting information such as text, graphics, or the like.
The touch panel is mounted on the display surface of an image display device such as an electronic organizer, a flat panel display including a liquid crystal display device (LCD), a plasma display panel (PDP), an electroluminescence (El) element or the like, or a cathode ray tube (CRT), so that a user selects the desired information while viewing the image display device.
The touch panel is classified into a resistive type touch panel, a capacitive type touch panel, an electromagnetic type touch panel, a surface acoustic wave (SAW) type touch panel, and an infrared type touch panel. These various types of touch panels are adapted for electronic products in consideration of signal amplification problems, resolution difference, level of difficulty of designing and processing technologies, optical characteristics, electrical characteristics, mechanical characteristics, environment-resistant characteristics, input characteristics, durability, and economic efficiency. Currently, a capacitive type touch panel and a digital resistive type touch panel have been used in a wide range of fields.
An example of the capacitive type touch panel of the prior art is shown in Korean Laid-Open Publication No. 10-2011-0120157. In the touch panel disclosed in the above published patent, a plurality of electrodes are formed on a transparent substrate while having biaxial direction and crossing each other.
In addition, wirings are formed at one ends of the plurality of electrodes such that the wirings are electrically connected to the electrodes. A flexible printed circuit board (FPCB) is electrically connected to pad parts formed on terminals of the wirings.
In the touch panel having the above structure according to the prior art, the electrodes are disposed in an active area of a transparent substrate, which is exposed to the outside through the transparent substrate or a window glass, and the wirings are disposed in a non-active area of the transparent substrate, which is not exposed to the outside.
The reason that the wirings are disposed in the non-active area is that the wiring is generally linear, and thus, does not have pattern uniformity with the electrodes disposed in the active area of the transparent substrate.
In other words, in the case where the electrodes are formed in a mesh pattern, the linear wirings and electrodes have uniform patterns. Therefore, when the electrodes and wirings are formed together in the active area, visibility of the touch panel becomes defective.
Due to this, the touch panel of the prior art has wirings disposed in the non-active area of the transparent substrate, like the touch panel disclosed in the published patent above.
In the structure of the touch panel of the prior art, the wirings are disposed in the non-active area of the transparent substrate, and thus, the width of the non-active area of the touch panel is disadvantageously enlarged.
This disadvantage becomes an obstacle to miniaturize terminal devices employing the structure of the touch panel, or causes the active area of the transparent substrate, which is a touch area, to be reduced as compared with the same sized devices.


A check valve for preventing reverse flow of jettable material within a jettable material firing chamber during a firing event includes a free-floating plug. The check valve further includes at least one holding post, wherein the free-floating plug is arranged between at least one wall of the firing chamber and the holding posts, the at least one wall and the holding posts restricting the movement of the free-floating plug within the chamber.

Printers are used to form images on media by controlled ejection of ink from a printhead. The printhead includes a number of firing chambers with a nozzle defined in each firing chamber. Ink present within a firing chamber of the printhead may be ejected through the nozzle and onto the media to form the image. Ejection of ink is facilitated through a firing event wherein the excitation of a number of firing devices located within the firing chamber ejects the jettable material through the nozzle.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.

Jettable material firing chamber check valve

Hewlett-Packard Development Company, L.P.


A fire starter for use with a grill (G) for cooking foods includes a combustible bag (A) placed on the grill. The bag's contents include charcoal (B) which, when lit, has a relatively long burn time. Interspersed in the bag with the charcoal are wood shavings (S) which have a shorter burn time than the charcoal. In one embodiment, the contents of the bag are poured into the grill. In another embodiment, one end (E1) of the bag is opened and placed on a grate (P). The other, upper end (E2) of the bag is opened and the lower end of the bag ignited. Setting the bag vertically produces a chimney effect that facilitates burning of the bag and its contents. When the bag is ignited, the shavings are also ignited and burn for a period sufficiently long to ignite the charcoal before being consumed.

This invention relates to cooking foods on a charcoal grill or the like; and, more particularly, to an improved way of adding large thick, dry wood shavings or chips mixed in with lump charcoal or charcoal briquettes as a way to ignite the charcoal.
As is well-known in the culinary arts, grilling food such as hamburgers, hot dogs, brats of various types, steaks, vegetables, etc., begins with someone placing charcoal briquettes in the bottom of a grill or fire pit and then igniting them. Once the charcoal is ignited and allowed to burn to a certain point (which varies according to who is doing the grilling and what is being grilled), the food is placed on a grill and cooked using the heat directed upward from the burning charcoal. Most charcoal is ignited ("started") using a flammable chemical (petroleum based) solvent. This "starter fluid" is either sprayed or poured onto to the charcoal and lit by applying a match or flame from a torch to the saturated briquettes. Alternately, a manufacturer will sell bags of charcoal marketed as a self-lighting charcoal; as, for example, Kingsford® Match Light® charcoal. Now, instead of spraying or pouring a starter fluid on the briquettes, the user simply applies a match to the charcoal to ignite it. Finally, in some instances other forms of lighting charcoal or used. These include, for example, grills that have an electric ignition or charcoal chimneys in which the briquettes are placed so to concentrate the heat of combustion.
Use of starter fluids and the like present certain hazards both to the person doing the lighting and those around them. Sprayed or poured fuel can inadvertently get on one's body or clothing and be inadvertently ignited causing someone to be burned. In other instances the fluid can get on flammable materials (e.g., paper plates, cups, napkins) in areas close to the grill and inadvertently set on fire. Another potential cause of harm occurs when the starter fluid is sprayed on an existing fire because someone does not believe the charcoal has been sufficiently lit, or if self-lighting charcoal is added to replenish the charcoal in the grill that has burned down to a level insufficient to cook food. In this regard it will be noted that it is not recommended to add self-lighting charcoal to an existing fire because the fire can jump up and spread to the bag, igniting fumes in the bag (or solvent remaining in the bag or on the user's hands) and causing serious injury.
In addition to these potential hazards, solvents produce volatile organic compound (VOC) emissions and can also add a disagreeable flavor to foods if the VOCs have not totally burned off before cooking is started.
As regards solvents added to the charcoal during manufacture of self-lighting charcoal, these tend to evaporate over time and affect the self-lighting capability of the charcoal, either reducing this capability or eliminating it altogether. Also, solvent emissions from self-lighting charcoal may necessitate the use of special, high cost barrier bags in which the product is sold, so to reduce or prevent the evaporation of solvents.
This invention described herein has significant advantages over all of these current methods.

Easy lighting charcoal briquettes with wood shavings


A drive system for a machine, in particular a weaving machine, is designed in a manner such that controlled electric power is applied to a rotary electric drive motor (2) as a function of particular angular positions of the motor and such that electrical energy applied to the motor is reduced or interrupted during phases of increasing angular speed of the motor. Phases of increasing angular speed are detected by the drive system to determine phases of increasing angular speed. A method for controlling an electrical motor drive system using a switchable reluctance motor to reduce or interrupt electrical energy supplied to the motor based on motor speed increases as a function of motor angular position is also disclosed.

A. Field
The present invention relates to a method for driving a machine comprising at least one periodically moving part and including an electric drive motor which is electrically powered as a function of its specific angular position. The invention also relates to a drive system fitted with a control unit for an electric drive motor.
B. Related Art
A method and a drive system of the above-mentioned kind are known from WO 99/27 426. Because the drive motor continuously applies a preferably constant torque to the described machine the angular speed of the drive motor is a function of said machine's moments of inertia. When said moments of inertia result in speed reduction, the motor adopts the same behavior—just as when the moment of inertia leads to an increase of motor speed. As a result, the fluctuations of the motor's angular speed are exaggerated. In general, such phenomena do not degrade machine operation, for example, as regards the operation of a weaving machine. However there may be a danger that speeds and/or accelerations will be excessive and that damage would follow. There is also a further danger that the speed of the machine will fluctuate so much that synchronization will be lost, for instance with respect to filling insertion with shed formation in air jet looms.

Method for driving a machine and drive for said machine


A plasma processing system for and method of utilizing an improved etch chemistry for effectively etching high aspect ratio silicon features. The process chemistry employs precursor gases suitable for producing a fluorine/chlorine etch chemistry as well as precursor gases suitable for forming chemical bonds of sufficient strength to create stable feature side-walls. The improved process chemistries include SO2/SF4/SiCl4, SO2/SF4/Cl2, SO2/SiF4/SiCl4, SO2SIF4/Cl2, O2/F2/Cl2, N2 O/F2/Cl2, and NO2/F2/Cl2-based chemistries.

1. Field of Invention
The present invention relates to etch chemistries and more particularly to a method for utilizing improved etch chemistries to etch high aspect ratio features.
2. Discussion of the Background
In the semiconductor industry there is a demand for increasing the speed of integrated circuits in general, and memory devices in particular. These demands force semiconductor manufacturers to make devices smaller and smaller on a surface of a semiconductor wafer. Accordingly, the increasingly small top critical dimensions (CDs) used to manufacture semiconductor chips require deep trench capacitors, which are used to store charge for memory, that must go deeper into the silicon to retain the same internal surface area, and, hence, the same capacitance. These smaller top CDs make it more difficult for etchant species to enter such deeply etched holes during etching and for effluent species to be exhausted from the feature as it etches deeper into the silicon wafer. This interaction results in much slower etching and therefore longer etch times, which in turn results in problems providing a mask that will survive the increasingly long etch times. Current technology is approaching a limit of the current masks to be effective with the current chemistry for deep trench etching.
Current deep trench etch chemistries rely on the dissociation of HBr with fluorine-containing gases and O2. By-products of these reactions include SiO2, HF, and other Si—F—Br species. Bromine etches silicon surfaces in a reaction that has a strong physical component in addition to a chemical component. This physical component implies silicon is etched more readily where there exists a direct line-of-sight between the silicon etching surface and the plasma. Silicon dioxide (SiO2), produced by the chemical interaction of silicon from the etched surface and oxygen (O2) from the plasma, forms on the vertical surfaces of the aforementioned trenches where there exists a lesser physical component for etching. In general, process manipulation of SiO2 formation is utilized to control the profile and width of the final trenches.
However, several limitations have been cited for deep trench etch pertaining to the current etch chemistry. For example, mask erosion, particularly near the feature entrance, has posed a formidable issue with current processes. At present, the mask erosion is attributed to chemical attack by HF that is formed by interactions between HBr and NF3. Additionally, mask erosion is attributed to physical sputtering by high energy ions, and decreasing SiO2 surface protection resulting from low silicon availability from smaller (high aspect ratio) features.
In addition to mask erosion, current process chemistries suffer from low etch rates at depths greater than 5 microns for 0.13 to 0.10 micron features or, more generally, once the feature aspect ratio L/d exceeds 50. Beyond this feature aspect ratio, the silicon etch depends primarily on chemical etch rather than physical etch (see FIG. 1).
And lastly, current process chemistries are unable to control the upper profile and maintain an anisotropic etch with parallel side-walls.
In summary, bromine chemistries, particularly those introduced to the plasma as HBr, create HF as a by-product when used in conjunction with fluorine chemistry. The presence of HF in the processing plasma leads to an aggressive attack of the oxide mask. Therefore, an improved chemistry eliminating hydrogen from the plasma is needed to alleviate the aforementioned shortcomings of current practice.

Method of etching high aspect ratio features