For IGBT, MCT or like devices, the substrate is formed with P+, N+ and N- layers and PN diffusions to define body and source regions in the N-layer and a MOS-gated channel at the upper surface. The N-layer is sized and doped (.about.10.sup.14 /cm.sup.3) to block reverse bias voltage. The N+ layer is >20 .mu.m thick and doped below .about.10.sup.17 /cm.sup.3 but above the N- doping to enhance output impedance and reduce gain at high V.sub.ce conditions. Or the N+ layer is formed with a thin (.about.5 .mu.m) highly doped (>10.sup.17 /cm.sup.3) layer and a thick (>20 .mu.m) layer of .about.10.sup.16 /cm.sup.3 doping. A platinum dose of 10.sup.13 to 10.sup.16 /cm.sup.2 is ion implanted and diffused into the silicon to effect lifetime control. Gate and source contacts and body and source diffusions have an inter-digitated finger pattern with complementary tapers to minimize current crowding and wide gate buses to minimize signal delay. P+ doping beneath and marginally surrounding the gate pads and main gate bus negates breakdown conditions in widely spaced body regions and convex localities at the source finger end. Wide secondary gate buses parallel to the gate fingers have a P+ doped central stripe and transverse shorting bars spaced along their length. A non-polarizable PECVD passivation film of low phosphorus PSG and nitride or oxynitride or of oxynitride alone is made by controlling ionized gas residence time, silane partial pressure, and oxygen ratio during deposition, to minimize incorporation of Si--H into the film.

This invention relates to a method for producing power semiconductor devices, and more particularly to insulated gate power device fabrication process and structure. More specifically, this application is directed to improvements in a single-mask process based on that disclosed in applicant's U.S. Pat. No. 4,895,810 to make four-layer(PNPN) devices, such as insulated gate transistors (IGT or IGBT), MOS controlled thyristors (MCT), emitter controlled thyristors and other gate controlled minority carrier devices, as well as power MOSFET devices.
U.S. Pat. No. 4,895,810 discloses a MOSFET fabrication process and structure which, among other advantages, substantially eliminates the incidence of fatal defects in a power device as a consequence of defects in, and/or misalignment between, the layers used in the production of such devices. This process uses a single mask to form all of the active device areas of a MOSFET structure, with recessed source regions self-aligned to an MOS gate structure and sized by sidewall spacers and an enhanced-conductivity body region underlying and self-aligned to the source regions.
Based on teachings available in the prior art, it was believed that the previously-disclosed MOSFET fabrication process and structure could be readily adapted to the fabrication of insulated gate bipolar transistors and other gate-controlled four-layer devices. That proved to be much more difficult than was thought.
The development of insulated gate bipolar transistors and other gate-controlled four-layer (PNPN) devices can be traced through the following references:
Atalla U.S. Pat. No. 3,206,670
New U.S. Pat. No. 3,210,563
Gentry, U.S. Pat. No. 3,324,359
Plummer, U.S. Pat. No. 4,199774
Becke et al, U.S. Pat. No. 4,364,075
Temple, U.S. Pat. No. 4,417,385
Baliga U.S. Pat. No. 4,443,931
Ohmi, Power Static Induction Transistor Technology, IEDM pp. 84-87 (See FIG. 7), 1979
Baliga, Power Junction Gate Field Controlled Devices, IEDM pp. 76-78, 1979
Plummer et al, Insulated Gate Planar Thyristors:
I--Structure and Basic Operation PA1 II--Quantitative Modeling PA1 A New Power Switching Device, IEDM pp. 264-267, 1982
IEEE Trans. Electron Devices, ED-27 pp. 380-394, 1980
Leipold et al, A FET-Controlled Thyristor in SIPMOS Technology, IEDM pp.79-82, 1980
Tihanyi, Functional Integration of Power MOS and Bipolar Devices, IEEE pp.75-78, 1980
Baliga et al, The Insulated Gate Rectifier (IGR):
Russell et al., The Comfet-A New High Conductance MO Gated Device, IEEE Electron Device Lett., EDL-4, pp. 63, 1983
Wheatley et al, COMFET - The Ultimate Power Device; A General Study of Power Devices, Solid State Technology pp. 121-128, Nov. 1985
Kuo et al., Modeling The Turn-off Characteristics of the Bipolar-MOS Transistor, IEEE Electron Device Lett., EDL-6, pp. 211-214, 1985
Kuo and Hu, Optimization of Epitaxial Layers for Power Bipolar-MOS Transistor, IEEE Electron Device Lett., EDL-7, p. 510-512, 1986
Lorenz, Selection Criteria for Power Semiconductor for Motor Drives, Proceedings of 1990 International Symposium on Power Semiconductor Devices and ICs, Tokyo, pp. 263-269, 1990
Tsunoda et al., Improved 600- and 1200 V-IGBT with Low Turn-off Loss and High Ruggedness, Proceedings of the Power Electronics Specialists Conference, San Antonio, Tex., pp. 9-16, June 1990
Baliga, MODERN POWER DEVICES, Ch. 7 and 8, 1987
With knowledge of this art, applicant tried to make insulated gate bipolar transistors based on applicant's prior work and experience and could not fabricate commercially operative devices. Such devices exhibited latchup under virtually all operating conditions, even when using a buffered N+ layer as taught by Becke et al. and analyzed by A. Nakagawa et al of Toshiba in "Non-Latchup 1200 V 75A Bipolar-Mode MOSFET with Large ASO" IEDM, pp. 860-861, 1984, and "Experimental and Numerical Study of Non-Latch-up Bipolar Mode MOSFET Characteristics" IEDM, pp.150-153, 1985.
Not only was latchup obtained under different conditions in applicant's experimental devices, latchup occurred in different cells and regions of the devices. Problems were particularly acute when trying to switch an inductive load. Current turnoff time also proved to be very slow >1.mu.S. At the same time, it remains important to maintain both a low forward voltage drop or on-resistance, and to have sufficient reverse blocking capability. Also, such devices require an adequate ability to withstand high voltage(V.sub.ce) short circuit conditions.
The performance requirements for IBGTs today has advanced substantially from where they were in the mid 1980's. More parameters are being evaluated for device selection such as discussed by Lorenz. The early analyses by Kuo and Nakagawa were optimizing for forward voltage drop and switching speed without considerations for ruggedness such as short circuit withstand capability and safe operating area (SOA). Given the more stringent requirements of the 1990's, the recommendations of these early works are no longer completely valid. For example, the optimal epi design--suggested by Kuo and Hu of >5 .mu.m thick N+ layer at 10.sup.18 /cm.sup.3 doping level operating with N- layer completely depleted would be a terribly weak device on short circuit withstand capability even though the forward voltage may be good.
A. Nakagawa et al (IEDM 85) describe the need for PNP common base current gain .alpha.>0.27 to maintain sufficient conductivity modulation hence a low forward voltage drop using an N+buffer layer under an N- drift region. No consideration was given to designing for ruggedness by epitaxial material selection. Device ruggedness is directly impacted by the high voltage/high current gain. We have discovered that this characteristic is affected by the N+ thickness and doping concentration. A. Nakagawa et al do not describe these aspects of their device although they and others have used about 3.times.10.sup.16 -10.sup.18 /cm.sup.3 doping concentrations in their analyses and discussions and less than about 20 micrometers thickness for the N+ buffer layer. Tsunoda et al. reported experiments with adjusting the N- layer thickness and the N+ doping profile, but nothing in regard to N+ layer thickness. The paper did not give any values on layer thicknesses or doping concentrations for the devices measured and analyzed.
Siemens has, conversely, proposed elimination of the N+ layer altogether and, instead, making the N- layer very thick, e.g., 200-350 micrometers, without minority carrier lifetime control, as described by T. Laska in "A 2000 V-Non-Punch-Through-IGBT with Dynamical Properties like a 1000 V-IGBT" IEDM, pp. 807-810, 1990. The main drawback of this long-base approach is very high forward voltage or conduction loss (high on-resistance). Petterteig and Rogne compared switching losses of various vendor's samples of IGBT-type devices including applicant's initial experimental devices, in EPE FIRENZE, 1991, and showed that, in hard turnoff condition, the long-base Siemens device does not completely switch off after a few microseconds compared to less than about one microsecond for the other devices.
Other latching countermeasures are known to have been tried in the prior art but with varied success and questionable applicability to the particular process, using a single mask and recessed source contact areas, employed by applicant to fabricate devices. Goodman et al. U.S. Pat. No. 4,587,713 uses a deeply implanted laterally-extending supplemental P+ doped region in the P-type base to reduce bipolar transistor gain. Blanchard U.S. Pat. No. 4,345,265 employs a distributed diode with lower breakdown voltage than the DMOS transistor to non-destructively absorb transients and a shunt conductance for the channel region to reduce both voltage and voltage gradient in the base. Yilmaz U.S. Pat. No. 4,809,045 provides paths for reverse current flow spaced from the emitter-base junction and enlarges the ratios of the base region and the emitter region surface areas in contact with the emitter electrode within a contact window. Nakagawa et al disclose, in UK Pat. Application No. 2,161,649A, various methods for avoiding latchup by keeping the saturation current of the device smaller than the latch-up current, including proportioning of active device areas and providing a hole-current path from the drain to the source.
Prior workers have also tried different ways to control minority carrier lifetimes within the device. Baliga, MODERN POWER DEVICES, pp. 36-58, 380-387 and 410-413, describes how the switching speed of the IGT, P-i-N rectifiers and other devices can be increased by the introduction of recombination centers in the N-base region to reduce minority carrier lifetime. In general, two approaches have been used, either diffusion of transition elements impurities such as gold or platinum into the silicon or by high energy particle bombardment, e.g., by neutron, proton, electron or gamma irradiation, to create lattice damage in the silicon. Among these approaches, Baliga teaches that electron irradiation is preferred, offering among various advantages tighter distribution in device characteristics. Using lifetime control involves tradeoffs in device operation, as discussed in Temple et al., "Optimizing Carrier Lifetime Profile for Improved Tradeoff Between Turn-Off Time and Forward Drop," IEEE Transactions on Electron Devices, Vol. ED-30, No. 7, pp 782-790, July 1983.
Conventionally, diffusion of transition elements impurities is performed for lifetime control purposes by .sup.1 deposition of a 100.ANG. to 1000.ANG. thick layer of the selected element onto a surface of the silicon wafer and diffusing atoms of the element from the layer into the silicon at a temperature in the range of 800.degree.-900.degree. C. The diffusion temperature determines the solid solubility of the impurity atoms in silicon and can be used to control the impurity density. Metal implantation has also been used for other purposes. For example, high dose implants have been used to create ohmic contacts in integrated circuits. Low dose implantation (up to 2.times.10.sup.13 /cm.sup.2) has been used to adjust Schottky barrier height in discrete devices and integrated circuits. In these procedures, the dose is retained near the surface.
The particle bombardment approach uses either electron, proton, neutron or gamma irradiation. It is typically performed at room temperature, and then the devices are subjected to a low-temperature annealing procedure, although Baliga states that high temperature (300.degree. C.) electron radiation has been used.
Several drawbacks exist, however, in these approaches to lifetime control. Both approaches, as practiced in the prior art, can substantially increase leakage current. The particle bombardment approach also causes threshold instability. Low temperature annealing is typically required to restore the desired threshold voltage by partially annihilating trapped charge in the gate oxide and at the gate oxide-silicon interface. Once the devices have been irradiated and annealed, however, they cannot be subjected to higher temperatures in further fabrication procedures, such as during die attachment. The devices are also subject to long-term instability during use in high temperature applications. Radiation defects anneal out between 300.degree. C. and 400.degree. C. This is a temperature range necessary to achieve good wetting of silicon to package during die attachment.
Evaporation and diffusion of transition metal impurities into silicon is not subject to such instability effects but, as conventionally practiced, is difficult to control. It also creates the largest increase in leakage current compared to similarly processed devices without lifetime control. For example, conventional diffusion of platinum from a layer evaporatively deposited onto the silicon surface yields an increased leakage current that is one to two orders of magnitude higher than the leakage current produced by irradiation and particle bombardment, and three orders of magnitude higher than no lifetime control. Alternatively, a technique for spinning on a layer of platinum (e.g., Emulsitone platinum film) is commonly used (See Lisiak et al, J. Appl. Phys. Vol. 46, No. 12, pg. 5229, Dec. 1975). This procedure also provides poor dosage control. Thus, a better lifetime control method is needed.
It has been previously observed and is the subject of applicant's co-pending U.S. patent application Ser. No. 07/663,297, SEMICONDUCTOR DEVICE WITH DOPED ELECTRICAL BREAKDOWN CONTROL REGION (continuation of Ser. No. 06/842,464, filed Mar. 21, 1986), that there are regions on a device layout that are prone to lower breakdown voltage than otherwise achievable from the active cells which tend to be of similar repetitive dimensions. These breakdown-prone regions are typically created out of necessity, for example, to provide gate bonding pads and low signal-delay buses. In order to retain the performance capability inherent in the cells while permitting proper interfacing and signal propagation on a chip, application Ser. No. 07/663,297 disclosed doping under these structures with the same dopant type as the body diffusion with well-matched junction depth to smooth out the transition from the body to diffusion under the gate so as to form a single contiguous region of smooth curvature. The base resistance of the parasitic bipolar transistor is reduced much below that of the active cells due to the pad/routing bus doping into the body regions. The net effect is the total elimination of premature breakdown and failure during inductive switching at gate pads/gate routing buses below the designed capability of the active cells. The active MOS channels around the periphery of the odd gate structures are also rendered completely inactive by so doing. Thus, a better way is needed to suppress breakdown under gate bus areas in large current MOSFET and IGBT-type devices without substantially reducing useful channel.
After a semiconductor device is processed and metallized, a passivation or scratch protection layer is typically deposited on the top surface. Only the bonding pads are opened to make electrical connections outside the chip after this step. This passivation layer must be a moisture and mobile ion barrier against the harsh environment that is hazardous to MOS devices in the packaging and assembly area. This goal is met in low voltage devices by using a silicon nitride-based film or a PSG (phosposilicate glass) film (<4%). The most popular methods in use today for film deposition are PECVD (Plasma Enhanced Chemical Vapor Deposition) and LTO (Low Temperature Oxide)deposition. PECVD can be used to deposit both nitride and oxide while the latter method (LTO) is used only for oxide. Both methods work very well for passivating low voltage semiconductor devices. When these same quality films are conventionally deposited on top of high voltage devices, however, undesirable polarization effect develops which is not observable at low voltage.
Polarization effect per se is known to the integrated circuits industry where it is not a serious problem but it is not at all well understood for high voltage applications. In a prior art disclosure (U.S. Pat. No. 4,399,449, column 8, lines 19-2), the inventors clearly specify the removal of a polarizable film of heavily doped silox (phosphorus content must exceed 6%, typically 8% is used, to have substantial reflow of the deposited silicon oxide film) in the guard ring area of a high voltage device. No details are disclosed as to the limits of the film property or the mechanism of the problem. The literature has been fairly silent on similar effects on lower doping PSG and silicon nitride films even though the problem of polarization has been recognized on other types of films such as borosilicate glass (Murakami et al., "Polarization Induced Instability in a Glass Passivated p-n Junction" J. Electrochem. Soc., Vol. 133, No. 7, pp. 1467-1471, July 1986. Stress, composition, and wet etching characteristics have been reported previously such as by Claassen et. al. (Characterization of Silicon-Oxynitride Films Deposited by Plasma-Enhanced CVD, ibid, pp. 1458-1463) for oxynitride films deposited with varying gas phase compositions. Barrier effectiveness of oxynitride has also been the subject of studies such as by Hashimoto et al. (Properties of PEVD SiOxNy Films as Selective Diffusion Barrier, ibid, pp. 1464-1467) for Zn. However, no information on polarizability has been disclosed on these films. Thus, further development of passivation films is needed for high voltage power switching devices.
Accordingly, a need remains for an IGBT-type power device structure and fabrication process that can produce high voltage solid-state power switches capable of conducting and switching high currents and voltages at high speed but without undesirable parasitic effects.

IGBT device with platinum lifetime control having gradient or profile tailored platinum diffusion regions


A data storage medium includes a data structure, called a disk control block, used for administration and control information for the data storage medium. One medium may contain multiple different disk control blocks, each addressing a different function. Each disk control block includes a control block identifier that specifies the function of the disk control block. Each control block also includes a set of standard access control parameters. If a drive encounters an unrecognized disk control block, the drive can still decode the standard control parameters, so that the drive behavior is not inconsistent with the requirements of the unrecognized disk control block.

A data storage medium typically includes an area for storage of various administration and control information, such as an identification of the medium, perhaps information regarding how the medium is partitioned into various separate sections, a directory or table of file names and dates, and perhaps information regarding access control. Administration and control information may reside in a particular physical location on a medium separate from a general data storage area. For example, compact discs (CD) used for data storage have a single spiral track, with an area near the start of the track called a lead-in area, and an area near the end of the track called a lead-out area. The information in the lead-in area and the lead-out area contains administration and control information used only by drives and operating systems, and is separate from the area used for data storage.
Sometimes, a data storage medium has a format that is specific to a proprietary drive mechanism, or specific to one computer operating system. Alternatively, some formats are defined by standards, so that a medium can be exchanged among drives from multiple manufacturers and may be used by multiple computer operating systems. Standards are useful in eliminating unnecessary variation, but standards may also inhibit change, even when change is needed. For example, CD's were originally developed for read-only digital audio. As the CD technology was extended to general data, and write-once media, and rewriteable media, accommodation of new features with backwards compatibility was always an issue. There is a need for a standard way of recording administration and control information, for interchangeable rewriteable media, that can accommodate unforseen needs for changes in the future.

Data structure for control information on rewriteable data storage media

Hewlett-Packard Development Company, L.P.


A self-aligned structure and method of etching contact holes in the self-aligned structure are described. The dielectric materials, etching methods, and etchants are chosen to provide high selectivity etching. The structure comprises an electrode with a silicon oxy-nitride cap and silicon oxy-nitride spacers on the sidewalls of the electrode and the cap. An etch stop layer of silicon nitride is deposited over the substrate covering the spacers and cap. A layer of silicon oxide is deposited over the etch stop layer. Etching methods and etchants are used which provide a ratio of the etching rate of silicon oxide to the etching rate of silicon nitride or silicon oxy-nitride of at least eight and a ratio of the etching rate of silicon nitride to the etching rate of silicon oxy-nitride of at least two.

(1) Field of the Invention
This invention relates to a high selectivity etching method for use in forming contact holes in self-aligned contact structures. More particularly the invention relates to selecting dielectrics, etching methods, and etchants to achieve high selectivity etching.
(2) Description of the Related Art
U.S. Pat. No. 4,954,867 to Hosaka describes the use of a layer of silicon oxy-nitride to protect the gate electrode and wirings from oxidation during high temperature processing steps. The invention does not describe the use of highly selective etching methods.
U.S. Pat. No. 5,286,667 to Lin et al. describes the use of silicon nitride or silicon oxy-nitride barrier layers in the fabrication of metal oxide semiconductor field effect transistors. The barrier layer aids endpoint detection for a plasma etch. The invention does not describe the use of highly selective etching methods.
U.S. Pat. No. 5,364,804 to Ho et al. describes a method of forming a self-aligned contact. The method uses tow silicon nitride layers but does not the use of highly selective etching methods.
U.S. Pat. No. 4,455,737 to Godejahn, Jr. describes a method of forming self-aligned gates and contacts for FET devices wherein mask alignment tolerances are increased and rendered non-critical.

Self-aligned contact structures using high selectivity etching

Taiwan Semiconductor Manufacturing Company Ltd.


Systems and methods are provided that facilitate power management in a processing device. The system contains a power management component and a coupled to the processing device. The power management component determines and input rate and target voltages and/or frequency. The power management component can scale voltages and/or frequencies based on target voltages and/or frequencies. Accordingly, power consumption can be reduced and processing devices can be more efficient.

Management of power consumption is important in electronic devices (e.g., battery-powered devices) such as laptop and notebook computer systems, cell phones, tablet computers, personal digital assistants (PDAs), portable media players, remote control units, hand-held devices including video game players, memory device, and the like. Consumers are increasingly demanding that these electronic devices use power efficiently.
However, many electronic devices may be used for a variety of computationally intensive applications such as three-dimensional (3D) rendering and video encoding and decoding, and the like. As a result, such devices can usually be used for limited periods of time.
Power dissipation (P) of a device is dependent on capacitance (C), clock frequency (f) and supply voltage (V), with P=CfV2. The upper limit of the clock frequency is determined by supply voltage. Accordingly, a reduction in the supply voltage results in corresponding reduction in power dissipation. Additionally, reduced supply voltage of a device results in an increase in delay through the device.


Flash memory devices include a pair of elongated, closely spaced-apart main active regions in a substrate. A sub active region is also provided in the substrate, extending between the pair of elongated, closely spaced-apart main active regions. A bit line contact plug is provided on, and electrically contacting, the sub active region and being at least as wide as the sub active region. An elongated bit line is provided on, and electrically contacting, the bit line contact plug remote from the sub active region.

Integrated circuit memory devices used for storing data can be divided into volatile memory devices or non-volatile memory devices. When the electric power supplied to the volatile memory devices is interrupted, the volatile memory devices lose data stored in the devices. However, even though the electric power supplied to non-volatile memory devices is interrupted, the non-volatile memory devices keep data stored in the devices. Thus, the non-volatile memory devices, for example, flash memory devices, may be used for memory cards, mobile communication terminals and many other applications.
FIG. 1 is a plan view illustrating a portion of a cell array region of a conventional NAND-type flash memory device.
With reference to FIG. 1, an isolation layer to define a plurality of line shaped active regions 1 is formed at a predetermined region of the cell array region. A string selection line SSL′ and a ground selection line GSL′ are formed to cross over the active regions 1. The string selection line SSL′ and the ground selection line GSL′ are disposed in parallel with each other and closely spaced-apart from each other. A plurality of control gate electrodes WL1′, . . . , WLn′, that is, n word lines WL1′, . . . , WLn′, are provided to cross over the active regions 1 between the string selection line SSL′ and the ground selection line GSL′. A plurality of floating gates 5 are interposed between the control gate electrodes WL1′, . . . , WLn′ and the active regions 1. An insulating interlayer is provided on the substrate including the control gate electrodes WL1′, . . . , WLn′. Bit line contact holes 15 penetrating the insulating interlayer, and bit line contact plugs filling the bit line contact holes 15, are provided. Bit lines 20 covering the bit line contact plugs and overlapping the active regions 1 are provided.
When the integration density of the conventional NAND-type flash memory device of FIG. 1 increases, the pitch of the bit lines 20 and the active regions 1 generally decreases. Nevertheless, the bit lines 20 should have low electrical resistance to allow high speed operation of the NAND-type flash memory device.
To solve the problems due to the decrease in the pitch of the bit lines 20, NAND-type flash memory devices have been suggested, wherein four adjacent strings share one bit line. A NAND-type flash memory device having a shared bit line is disclosed in U.S. Pat. No. 6,151,249 to Shirota et al. As described in this patent, first and second active regions adjacent to each other are formed in a semiconductor substrate, and predetermined regions of the first and second active regions are contacted with one bit line contact plug. Unfortunately, it may be difficult to provide low contact resistance between the bit line contact plug and the active regions.

Methods of fabricating flash memory devices having shared sub active regions


An adaptive synchronous vibration suppression apparatus for suppressing vibrations in a dynamic system subject to synchronous disturbance detects the energy representative of the synchronous component of the vibration induced by the synchronous disturbance; generates the Fourier coefficients, amplitude and phase components command; and applies the command to operate an actuator to apply a force to the system to suppress the detected vibration.

Mass-unbalance in rotating machines acts as an undesirable synchronous disturbance at all operating frequencies. With the use of magnetic bearings as active control elements it is possible to adaptively compensate for mass-unbalance loading, thus eliminating vibration and fatigue in the support structure of the rotor.
There are two former methods of performing mass unbalance compensation. In conventional autobalancing a notch filter centered at the frequency of rotation is inserted in the control loop. Because of the notch filter, the control law has no gain at the frequency of rotation; hence, the bearings become "soft" at this frequency. No bearing force is generated, and the rotor pivots about its center of mass as if it were in free space. The second former method is a model-based balancing approach. Here an estimate of the mass-unbalance eccentricity is obtained by subtracting the output of a plant model or observer from the measured rotor position.
In conventional autobalancing the notch frequency may be within or near the bandwidth of the control system (if the control system has a very low bandwidth balancing would be unnecessary). The disadvantage is that the stability margins of the system are severely degraded due to the phase lag contributed by the notch filter. Disturbance rejection properties near the notch frequency are also degraded. Furthermore, when the rotor spins through its critical speeds (i.e., bending modes) the notch filter must be disabled to avoid instability. This form of autobalancing is inappropriate for moving platform applications (e.g., jet engines) because such applications require high-bandwidth controllers and guaranteed stability margins.
Model-based balancing requires the implementation of an observer and may be sensitive to modeling errors and time-varying plant parameters. The disadvantage is that the balancing achieved can be only as good as the accuracy of the model used. Also, model-based balancing tends to restrict system bandwidth.
Magnetic bearing suspension systems are but one environment in which unwanted dynamic vibrations occur. They can occur in any type of rotary system with any type of suspension apparatus. Moreover, dynamic vibrations, rotary or not, can occur in any kind of mechanical or acoustic environment. For example: environmental vibrations in a duct caused by a fan; unwanted vibrations in a vehicle seat caused by the vehicle engine.

Adaptive synchronous vibration suppression apparatus

The Charles Stark Draper Laboratories, Inc.


A process for continuously producing a propylene-based block copolymer having an excellent impact resistance of the present invention, comprises:. a first polymerization step comprising polymerizing .alpha.-olefin comprising propylene in the presence of hydrogen and a stereoregular polymerization catalyst comprising a solid catalyst component containing magnesium, titanium, halogen atom and an electron-donor compound, an organoaluminum compound and, if required, an electron-donar compound in a single polymerization reactor; and. a second polymerization step comprising transporting .alpha.-olefin polymer obtained in the first polymerization step to a copolymerization reactor and copolymerizing propylene with .alpha.-olefin other than propylene in a gas phase substantially in the presence of said stereoregular polymerization catalyst used in the first polymerization step.

The present invention relates to a process for continuously producing a propylene-based block copolymer having an excellent impact resistance.
As methods of improving an impact resistance of crystalline polypropylene, there are known (1) a method of copolymerizing propylene with .alpha.-olefin which co-exists therewith in a small amount upon the polymerization of propylene, (2) a method of mechanically blending a rubber component with polypropylene, (3) a method of polymerizing propylene as a primary component and then copolymerizing propylene with .alpha.-olefin other than propylene, that is, carrying out a so-called block copolymerization, or the like.
However, in the case of the above method (1), there arises a problem that although the impact resistance of the resulting copolymer is improved, the rigidity thereof is considerably lowered so that the balance between the rigidity and the impact resistance is deteriorated. Further, in the case of the above method (2), although the balance between the rigidity and the impact resistance is improved, this method is disadvantageous in production costs because the rubber component blended are usually expensive.
Under these circumstances, the above block copolymerization method (3) is used as the most effective method for improving an impact resistance of crystalline polypropylene. In this block copolymerization method, a rubber-like component which is constituted by blocks composed of a copolymer of propylene and ethylene or the like, is produced in the presence of a resinous component constituted by blocks composed primarily of propylene. Both the components are blended with each other by being continuously subjected to the polymerization. The block polymerization method, which is referred to as "chemical blend", is favorably used.
Meanwhile, in order to reduce the production costs, the block copolymerization is carried out more advantageously by a continuous process in which the respective blocks are produced in separate polymerization reactors (if required, each block can be produced in two or more different polymerization reactors), than a batch process.
However, in the case of the process using an excessively large number of polymerization reactors, there arise disadvantages such as increase in installation costs or running costs. Therefore, it is desirable to conduct each block in a single polymerization reactor. In the case of the production of the block copolymer composed of two different blocks A and B, it is most desirable to produce the block copolymer in a continuous process using two reactors. In such a case, as conventionally known, a first reactor is used to prepare the resinous component composed primarily of propylene and a second reactor is used to prepare the rubber-like component.
Incidentally, there is a tendency that propylene-based block copolymer obtained by a simple continuous process using two reactors is deteriorated in impact resistance as compared with the block copolymer obtained by a batch process. It is suggested that the difference in impact resistance therebetween is caused due to the following mechanism.
That is, in each reactor used in the continuous process, there is a difference in residence time between respective reaction materials, i.e., a distribution of residence time thereof exist. For this reason, in the simple continuous process using two reactors, considerably large amount of polymer particles and catalyst particles are transferred from the first reactor to the second reactor before these materials remain in the first reactor for a necessary residence time (such a phenomenon is called "short pass"). The particulate mixture of polymer and catalyst particles short-passed through the first reactor cannot contain a sufficient amount of resinous component due to a short residence time in the first reactor and in addition exhibits a higher polymerization activity than those remaining in the first reactor for the defined residence time. The short-passed polymer particles turn into polymer particles having a higher rubber content than required in the second reaction. A rubber-like component contained in such a high rubber content polymer particles causes deteriorated dispersion when subjected to melt-mixing, resulting in forming so-called fish eyes in shaped products. The fish eyes thus formed are apt to cause centers of breakage of the molded product because excessive stress is concentrated at boundary surface portions thereof. Accordingly, it is considered that the resultant block copolymer unsuitably suffers from deterioration in impact resistance, especially low-temperature impact resistance.
In view of the afore-mentioned mechanism, in order to prevent the deterioration in impact resistance, it is effective to suppress the occurrence of such "short pass" of the polymer and catalyst particles. In order to attain this object, for example, Japanese Patent Publication (Kokoku) No. 49-12589 (1974) has proposed a process of using, in the afore-mentioned first polymerization stage, a plurality of polymerization reactors which are connected in series with each other. However, such a process is a multiple reactors process and, therefore, become disadvantageous in costs as described above.
Further, since an alternative method of suppressing the "short pass" of the particles in the first reactor, there is known a process of using a classification system. For example, Japanese Patent Applications Laid-open (Kokai) Nos. 51-135987 (1976) and 55-116716 (1980) disclose a process of subjecting the polypropylene particles in the first reactor to concentration and classification processes, thereby removing therefrom the catalyst particles short-passed through the first reactor or polypropylene particles having a small particle size due to insufficient growth. Furthermore, Japanese Patent Application Laid-open (Kokai) No. 55-106533 (1980) discloses a process in which a polymer slurry is discharged while stirring from the first reactor, then subjected to counter-flow washing, thereby producing a slurry containing substantially few amount of polypropylene particles having a small particle size, and then supply such a slurry to the second copolymerization reactor. However, in such a simple classification system, the impact resistance of the final product cannot be sufficiently improved.
In addition, Japanese Patent Application Laid-open (Kokai) No. 7-286004 (1995) discloses a method of continuously producing an olefin polymer by a classification system using a cyclone. However, such a method has the following problem. First, in the method, particles having a small particle size, especially fine particles having a diameter of less than 75 .mu.m, cannot be separated sufficiently, resulting in insufficient effects of suppressing the "short pass" of the polymer and catalyst particles in the first reactor. Second, in the case of the classification system using a cyclone, when the recycling percentage of the particles is increased to enhance its classification efficiency, there arise a problem that the productivity is considerably deteriorated.
On the other hand, apart from the afore-mentioned viewpoint of suppressing the "short pass", there is also known a method for improving the impact resistance of propylene-based block copolymer by supplying some kinds of assistants to the reaction system in a rubber polymerization stage. For example, Japanese Patent Application Laid-open (Kokai) No. 55-115417 (1980) discloses a method of supplying tertiary amine, ketone, ether, ester, acid amide or phosphoric acid amide; Japanese Patent Application Laid-open (Kokai) No. 57-147508 (1982) discloses a method of supplying a halogen-containing aluminum compound; Japanese Patent Application Laid-open (Kokai) No. 61-69821 (1980) discloses a method of supplying alcohol; Japanese Patent Application Laid-open (Kokai) No. 62-116618 (1987) discloses a method of supplying glycol ether; and Japanese Patent Application Laid-open (Kokai) No. 1-152116 (1989) discloses a method of supplying hydrogen sulfide.
However, when a magnesium compound supported highly active catalyst is used, the addition of such assistants cannot improve the impact resistance to a satisfactory extent. Specifically, when it is intended to improve the impact resistance, it is necessary to considerably reduce a polymerization activity of the rubber-like component. For this reason, there is caused a large gap between the polymerization activity to the rubber-like component in the second reactor and the activity of the propylene polymer in the first reactor, resulting in deteriorated productivity.
Thus, the afore-mentioned conventional techniques still exhibit various problems with respect to costs and properties of the products.
As a result of various studies by the present inventors, it has been found that by using a magnesium compound supported highly active catalyst which has a sharp particle size distribution, the short pass of the catalyst in the first polymerization stage is effectively suppressed, a propylene-based block copolymer having a good impact resistance can be produced with low costs. The present invention has been attained on the basis of this finding.

Process for continuously producing propylene-based block copolymer


The present invention relates to an optical fiber grating as an optical component comprising an optical fiber having a core and a cladding, and a grating photowritten in the optical fiber. In particular, in the optical fiber grating in accordance with the present invention, the optical fiber into which the grating periodically changing the refractive index in the waveguide along the advancing direction of light is photowritten has a depressed cladding type refractive index profile. Accordingly, when the configuration of the optical fiber having a depressed cladding type refractive index, employed as the object in which the grating is photowritten, is changed, the stability in characteristics as the optical component or the like can easily be improved.

1. Field of the Invention
The present invention relates to an optical component which selectively reflects a specific wavelength of propogating light and, in particular, to an optical fiber grating in which a core region of an optical fiber has a refractive index that changes periodically along its optical axis.
2. Related Background Art
Recently, as optical fiber communications technology advances, networks are becoming complex and signal wavelengths are being multiplexed thereby requiring a higher grade of system configuration. In such an optical communication system, the importance of optical circuit devices (optical components) has been increasing.
A fiber type element, as an example of typical configurations in optical components, is advantageous, for example, in that it has a small size and low insertion loss and can easily connect with an optical fiber. Known as such a fiber type element is a fiber type filter.
Recently, it has been well-known the refractive index of the core of silica type optical fibers that is doped with germanium oxide changes upon being irradiated with ultraviolet radiation. Studied and developed as a fiber type filter utilizing such a photoinduced refractive index change is an optical fiber type diffraction grating (optical fiber grating).
In this specification, the term "optical fiber grating" refers to an optical component comprising an optical fiber and a grating photowritten in the core region of the optical fiber.
The optical fiber type diffraction grating reflects a light component of light advancing through the optical fiber having a specific wavelength. In general, in order to make such a diffraction grating, a part of a core region of an optical fiber is irradiated with ultraviolet rays so as to form an area (grating) having a refractive index that changes periodically along the longitudinal direction (corresponding to a traveling direction of signal lights) of the core region.
In this specification, the center wavelength of light to be reflected by a grating is referred to as the reflection wavelength of the grating.

Low transmission loss optical fiber having a grating


A multi-piece display device for the point-of-sale display of produce and other damageable items, manufactured out of a closed cell foam material and of solid construction, with each piece being a monolithic, flexible support block, whereby each of said support blocks has a top surface and is of a different size than each other support block, and with each said support block other than the smallest support block suitably adapted to support upon its top surface a smaller said support block, thereby allowing the device to be arranged into any number of configurations for the display of produce or other items. The foam construction of the device protects the items from damage while being light weight and easy to clean.

Retail display stands, and in particular produce end cap risers, are well known in the industry. Conventional display stands are typically constructed of multiple components involving labor-intensive manufacturing processes. They are of a rigid construction and configured in a fixed manner, whereby the interrelation of the various components is fixed with regard to each other, resulting in a single "look" for the stand. In addition, because of the multiple components, seams, joints, gaps, and other structures are of necessity utilized, providing access points to water, mold, and bacteria, which can damage the produce or other items displayed thereon. The rigidity of these display stands requires the use of additional padding in order to reduce the likelihood of damage to the items to be displayed.
The prior art fails to offer all of the functionality disclosed in the present invention, and thus none of the prior art anticipates the present invention.
It is an objective of the present invention to provide a useful, improved end cap riser suitable for supporting produce and other damageable items in an aesthetically pleasing manner while at the same time protecting the items so displayed.
It is a further objective of the present invention to provide a useful, improved end cap riser that is easily configurable in an unlimited number of arrangements.
It is a further objective of the present invention to provide a useful, improved end cap riser that is easy to manufacture.
It is a further objective of the present invention to provide a useful, improved end cap riser which is light weight, easy to clean, is impervious to water or other liquid penetration, and will not absorb odors.
It is a further objective of the present invention to provide a useful, improved end cap riser which is not easily damaged and which can satisfy its other objectives even if it becomes slightly damaged.
Other objectives of the present invention will be readily apparent from the description that follows.


The present invention relates to a system and method for scoring peptide matches. Embodiments of the present invention improves identification of peptides and proteins by introducing an appropriate signal detection based scoring system and what is believed to be the new concept of an extended match. To score a match between a first peptide and a second peptide, a stochastic model may be generated based on one or more match characteristics associated with the first peptide, the second peptide and their fragments. A first probability that the first peptide matches the second peptide, and second probability that the first peptide does not match the second peptide, may be calculated based on the stochastic model. And a match between the first peptide and the second peptide may be scored based at least in part on a ratio between the first probability and the second probability.

Mass Spectrometry (MS) combined with database searching has become the preferred method for identifying proteins in the context of proteomics projects (See, e.g., Fenyo Beavis, Proteomics, A Trends Guide, July 2000, 22-26 Elsevier). In a typical proteome project, the proteins of interest are separated by one or two dimensional gel electrophoresis, or they can also be provided as mixtures of a small number of proteins fractionated by column chromatography. By using an enzyme, e.g. trypsin, the proteins are then digested into peptides. The measurement of the masses of the thus obtained peptides provides a peptide mass fingerprint (PMF). Such a PMF can be used to search a database or can be compared to another experimental PMF (See, e.g, Zhang, W. and Chait, B. T. 2000: ProFound: an expert system for protein identification using mass spectrometric peptide mapping information, Anal. Chem., 72:2482-2489, and James, P. ed. 2000: Proteome Research: Mass Spectrometry, Springer, Berlin). In certain circumstances, PFMs are not specific enough to the original protein to permit its non-ambiguous identification. In such cases, a second procedure may be applied, such as fragmentation (also referred to as dissociation) of the peptides (See, e.g., Papayannopoulos, I. A. 1995: The interpretation of collision-induced dissociation mass spectra of peptides, Mass Spectrometry Review, 14:49-73), which breaks the peptides into smaller molecules whose masses are measured. This procedure is called tandem mass spectrometry, tandem-MS, MS2 or MS/MS. The masses of the fragments constitute a very specific data set that is used to identify the original peptide. By extension, the MS/MS data for several peptides of a protein constitute a very specific data set that is used to identify the original protein (See, e.g., Henzel, W. J. et al. 1993: Identifying protein from two-dimensional gels by molecular mass searching of peptide fragments in protein sequence databases, Proc. Natl. Acad. Sci. USA, 90:5011-5015, McCormack, A. L. et al. 1997: Direct analysis and identification of proteins in mixture by LC/MS/MS and database searching at the low-femtomole level, Anal. Chem., 69:767-776, James, P. ed. 2000: Proteome Research: Mass Spectrometry, Springer, Berlin).
Embodiments of the present invention improve the identification of the peptides based on MS/MS data, which comprise the measurement of the parent peptide mass and the measurement of the masses of its fragments.
A very common procedure when searching a database of biological sequences with mass spectrometry (See, e.g., Snyder, A. P. 2000: Interpreting Protein Mass Spectra, Oxford University Press, Washington D.C.) data is to compare the experimental spectra with theoretical spectra generated from the biological sequences stored in the database (See, e.g., James, P. ed. 2000: Proteome Research: Mass Spectrometry, Springer, Berlin). A scoring system is used to rate the matching between theoretical and experimental data. Typically, the database entry with the highest score is taken as the right representation of the experimental data. Ideally, the score is supplemented by a p-value estimating the probability to find a score equal or higher by random chance only. The p-value is used to give a measure of confidence to a match found in the database.
To date, the common practice for evaluating or scoring peptide matches has been manual analysis of spectra by trained technicians. While such methods are suitable for some mass spectrometry applications, manual analysis is a bottleneck in high throughput environments since data quality cannot be steadily maintained in high-throughput settings, causing automatic systems for scoring matches to suffer from low accuracy. High throughput systems for processing mass spectrometry data thus call for high quality scoring systems.
Scoring systems have several goals to meet. For example, one may be interested in searching large databases, such as an entire genome, as well as in detecting low-abundance proteins. Large databases require a very small rate of false positives since the erroneous peptide matches would be too numerous otherwise. This stresses the need for a very selective scoring system. In cases of low-abundance proteins, the MS data generally yielded is of lower quality compared to high abundance proteins. This in turn stresses the need for a very sensitive scoring system.
Currently available scoring systems lack selectivity because they can only take into consideration a small portion of the information available from mass spectra. For example, Bafna and Edwards, (See, e.g., Bafna, V. and Edwards, N. 2001: SCOPE: a probabilistic model for scoring tandem mass spectra against a peptide database, Bioinformatics, 17:S13-S21) consider only fragment masses, do not rely on parent peptide charge, and also do not calculate the likelihood ratio of observing a correct match versus observing a random match. Bafna and Edwards do not attempt to detect global patterns corresponding to structural constraints resulting from physical principles, like series of consecutive fragment matches. The same can also be said for the scoring system presented in Dancik et al. (See, e.g., Dancik, V., Addona, T. A., Clauser, K. R., Vath, J. E. and Pevzner, P. A. 1999: De novo peptide sequencing viatandem massspectrometry: a graph-theoretica approach, J. Comp. Biol., 6:327-342) and Havilio et al. (See, e.g., Havilio, M., Haddad, Y. and Smilansky, Z. 2003: Intensity-based statistical scorer for tandem mass spectrometry, Anal. Chem., 75:435-444), or other systems like that disclosed in European Patent Application No. EP 1 047 107 (assigned to Micromass Limited) and Zhang et al. (See, e.g., Zhang, N., Aebersold, R. and Schwikowski, B. 2002: ProbId: A probabilistic algorithm to identify peptides through sequence database searching using tandem mass spectral data, Proteomics, 2:1406-1412). In addition, Bafna and Edwards do not use optimal statistics in their scoring process.
Other available scoring systems include Mascot (See, e.g., Pappin, D. J. C., Hojrup, P. and Bleasby, A. J. 1993: Rapid identification of proteins by peptide-mass fingerprinting. Curr. Biol., 3:327-332), Sequest (See, e.g., Eng, J. K., McCormack, A. L. and Yates, J. R. III 1994: An approach to correlate tandem mass spectral data of peptides with amino acid sequences in a protein database, J. Am. Soc. Mass Spectrom., 5:976-989, and U.S. Pat. No. 6,017,693), and SONAR MS/MS (available from ProteoMetrics Canada). The latter systems rely on ad hoc empirical definition of correlation between experimental spectra and theoretical peptide sequence.
Many authors, such as Anderson et al. (See, e.g, Anderson, D. C., Li, W., Payan, D. G. and Noble, W. S. 2003: A new algorithm for the evaluation of shotgun peptide sequencing in proteomics: support vector machine classification of peptide MS/MS spectra and SEQUEST scores, J. Proteome Res., 2:137-146), Keller et al. (See, e.g., Keller, A., Nesvizhskii, A. I., Kolker, E. and Aebersold, R. 2002: Empirical statistical model to estimate the accuracy of peptide identification made by MSIMS and database search, Anal. Chem., 74:5385-5392), Moore et al. (See, e.g., Moore, R. E, Young, M. K. and Lee, T. D. 2002: Qscore: An algorithm for evaluating sequest database search results, J. Am. Soc. Mass Spectrom., 13:378-386), and Sadygov et al. (See, e.g., Sadygov, R. G., Eng, J., Durr, E., Saraf, A., McDonald, H., MacCoss, M. J. and Yates, J. 2002: Code development to improve the efficiency of automated MS/MS spectra interpretation, J. Proteome Res., 1:211-215), have recently developed systems to validate Sequest results automatically. Keller et al. (supra) also applies to Mascot. These systems constitute a hybrid category of model-based systems (mainly multivariate statistics) developed on top of heuristic systems. Their performance is generally superior to the original heuristic system but far from optimal. Compare Keller et al. (See, e.g., Keller, A., Nesvizhskii, A. I., Kolker, E. and Aebersold, R. 2002: Empirical statistical model to estimate the accuracy of peptide identification made by MS/MS and database search, Anal. Chem., 74:5385-5392) and FIG. 10.

System and method for scoring peptide matches


An asphalt blend used for paving is described. The blend contains polyethylene which has been modified by shearing action in the presence of an O-containing gas (such as oxygen or ozone). The blend has improved viscosity at high temperatures and reduced stiffness at low temperatures. A paving mix prepared using the asphalt blend has an improved Marshall Test Value (ASTM DI559), indicating that the paving mix should have a reduced tendency to become rutted under the load of traffic.

Asphalt is a widely used material of construction.
It is known to blend asphalts with polymeric materials so as to improve certain properties of the modified asphalt.
The use of polymer modifiers increases the cost of the final composition, so a cost-benefit analysis is required before commercial use becomes a reality.
For example, block styrene-butadiene elastomer (also known as "block SB rubber" and "block SBS rubber") is used to modify paving asphalts which are used in road construction. The so-modified paving asphalts typically exhibit excellent physical properties.
However, the cost of the block styrene-butadiene elastomer has restricted its use in paving applications. Thus, it is apparent that a need exists for a polymer modified asphalt that is conveniently prepared from a comparatively inexpensive polymer.


A method of recycling sodium-based salts used for digesting wood in a digester during the manufacture of pulp and paper. The method comprises collecting a black liquor from the digester, concentrating the black liquor, and adding a salt to the black liquor in an amount sufficient to reduce the viscosity thereof. Preferred salts are thiocyanate salts. The black liquor is then oxidized to produce a green liquor and a causticizer added to the green liquor to produce a white liquor containing the sodium-based salts to be recycled. The white liquor is then returned to the digester.

The most common process used for the production of pulp and paper is known as the Kraft process. J. Gierer, Wood Sci. Technol. 14, 241-266 (1980). In this operation, wood chips and various chemicals known as white liquor are cooked in a digester to produce pulp and a residual black liquor.
The black liquor contains wood components, including lignin, dissolved during digestion and also contains inorganic materials such as sodium sulfate and sodium carbonate. The black liquor leaving the digester has a concentration of about 15 percent total solids. In order to burn efficiently in a recovery boiler, the liquor must be concentrated, usually in multiple-effect evaporators, to about 65 percent total solids. The liquor is then burned in the recovery boiler where further concentration of the liquor and combustion of the liquor solids occur. The inorganic components are recovered from the liquor in the boiler, redissolved in water, and then causticized to regenerate the white liquor used to digest the wood chips in the first step of the process.
In order for this process to be cost effective, however, the cooking chemicals which react and become a part of the black liquor must be efficiently recovered. J. Smook, Handbook for Pulp and Paper Technologists, 2nd ed., 1992, Chapt. 7 and 10. As mentioned previously, in order to regenerate these chemicals, the black liquor is subjected to several treatments that include evaporation and burning. These two steps play a crucial role due to their large energy consumption. Because the costs of energy have greatly increased in recent years, the pulp and paper industry has begun processing black liquor with higher solids concentrations in the recovery boiler. L. Soderhjelm, Paperi ja Puu 9, 642-652 (1986). Higher solids enhance recovery boiler performance by providing increased boiler capacity, lower emissions, and higher thermal efficiency. M. Boone, 1991 Tappi Kraft Recovery Operations Short Course, 93-97 (1991). The ability to concentrate black liquor is limited, however, by its rheological (deformation and flow) properties. Black liquor shows an exponential increase in viscosity as its solids content rises P. Ramamurthy, A. Mujumdar, A. van Heiningen, G. Kubes, Tappi, 195-202 (April 1992)), thereby preventing its processability in terms of transport, storage, and handling. As a result, black liquor having a solids content greater than about 70 percent has too high a viscosity to pump or otherwise process.
Black liquor is a complex aqueous system made up of several components including, polysaccharides, lignin, salts, and fatty acids. Previous research has reported conflicting results as to which of these components may be responsible for the elevated viscosity. Both the lignin (J. Small, A. Fricke, Ind.Eng.Chem.Prod.Res.Dev. 24, 608-614 (1985)) and the polysaccharide (L. Soderhjelm, 1989 Int'l.Chem. Recovery Conf. Proc., 95-99 (1989)) fractions may be the cause. Nonetheless, strong (or concentrated) black liquor becomes a sticky, unpumpable liquid with increasing solids content. M. Boone, 1991; P. Ramamurthy et al., April 1992. Even with less concentrated, more pumpable liquor, pluggage and scaling in the recovery boiler are a critical issue. R. Ryham, S. Nikkanen, 1992 Kraft Recovery Operations Short Course, 222-238 (1992).
In order to prevent the problems described above, methods such as heat treatment (L. Soderhjelm, 1986; R. Ryham, 1992 Int'l. Chem. Recov. Conf., 581-588 (1992); L. Soderhjelm, Appita 41, No. 5, 299-392 (1988)) and oxidation (E. Milanova, G. Dorris, Jour. of Pulp and Paper Science 16, No. 3, J94-J101, (1990); W. Frederick, T. Adams, 1992 Kraft Recovery Operations Short Course, 97-112 (1992)) are being used to reduce the viscosity of black liquor and obtain a higher solids content. In the heat treatment process, the liquor is removed from the evaporators and heated at an elevated temperature for an extended period of time (i.e. about 140.degree. C. for 2 hours) (L. Soderhjelm, 1988). This procedure results in an irreversible decrease in viscosity due to a depolymerization of the large polymer chains present within black liquor. R. Ryham et al., 1992. In the oxidation process, the liquor is exposed to air in order to convert the sulfide in black liquor to thiosulfate. E. Milanova et al., 1990. This oxidation reaction provides a reduction in viscosity by lowering the residual alkali concentration. This reduction is, however, reversible, and addition of alkali following the oxidation will return the liquor to its original viscosity.
Both heat treatment and oxidation have significant disadvantages. They may cause an increase in viscosity if the black liquor has an initially low residual alkali. W. Frederick et al., 1992. Both processes are also cost intensive and may not be worth the advantage that they provide. For example, heat treatment requires energy to raise the temperature of the liquor. Similarly, oxidation rids the liquor of its fuel value which requires more energy input. J. Smook, 1992. A more advantageous procedure for reducing the viscosity of black liquor to obtain a processable, high solids liquid is needed.
In addition to heat treatment and oxidation, other methods exist for lowering the viscosity of alkaline waste liquor, including black liquor. U.S. Pat. No. 4,911,787 discloses a method and an apparatus for concentrating black liquor wherein CO.sub.2 gas is added to the black liquor to reduce its boiling point and its viscosity. The disadvantages of this method include the requirement of additional equipment needed to dissolve the CO.sub.2 in the liquor. Because the addition of CO.sub.2 to black liquor results in the generation of H.sub.2 S, an additional oxidation step such as adsorption, membrane separation, or low temperature processing may be required. Furthermore, the absorption of CO.sub.2 in quantities necessary for viscosity reduction is adversely limited by the temperature and pH of the liquor.
U.S. Pat. No. 4,734,103 discloses a high solids black liquor having the property of reduced turbulent flow/drag comprising a high solids black liquor which contains a few parts per million of a water soluble terpolymer such as acrylic acid-acyrylamide-sulfo lower alkyl acrylamide polymer. Additional equipment is needed to produce the polymers which are added to the black liquor.
The present invention results in a high solids content black liquor of much lower viscosity than enabled by the methods disclosed above.

Method of reducing the viscosity of a black liquor using thiocyanate salt


An antenna module includes an antenna substrate including a glass substrate having first and second surfaces opposing each other, an antenna pattern disposed on the first surface, and a wiring structure connected to the antenna pattern and extending to the second surface, and a semiconductor package including a semiconductor chip, having an inactive surface and an active surface, on which a connection pad is disposed, an encapsulant encapsulating the semiconductor chip, a connection member including a redistribution layer connected to the connection pad, and a through-via penetrating the encapsulant and connecting the redistribution layer and the wiring structure to each other.

With the recent trend for the thinning of electronic devices, various components mounted on a mobile device, such as a smartphone, need to be miniaturized. Accordingly, when an antenna module for millimeter wave (mmWave) and 5th generation (5G) communications is applied to a mobile device, there are many limitations on the size and thickness of the antenna module to secure the degree of freedom of a mounting position in a set and to significantly reduce a process.


A system and method for updating IR signal information remotely for control devices are disclosed.

A universal remote control device includes infra-red code corresponding to the consumer electronic devices that are controlled by the universal remote control device. A set of infra-red signal information is programmed and embedded into the firmware of the universal control device during the manufacture of the universal remote control device. As new consumer devices appear on the market, an existing universal remote control device needs to be updated with the infra-red code corresponding to the new consumer electronic devices. For example, the universal remote control device is updated via a hardware port connection. The logistics associated with such an update is time consuming and inconvenient. FIG. 1 illustrates the logistics associated with the existing technology for updating universal remote control devices. FIG. 1 shows an update cycle (100), a consumer (102) packing her universal remote control device for shipping (104) to arrive at a service center (106) where the universal remote control device is updated and then shipped back (108) to consumer (102). Such an update cycle (100) takes a period (110) of about 4 days. A more convenient method of updating the infra-red information associated with a universal remote control device is needed.


A vacuum assisted stick and lath placer has a magazine for holding a stack of elongate members for transverse placement onto an upper surface of a tiered lumber package of longitudinally aligned tiers of lumber. A selectively actuable shear positioned beneath the magazine is selectively horizontally actuable so as to push a bottom-most elongate member from beneath the stack of elongate members into a pickup position along a travel path of a selectively telescoping vacuum pickup. The selectively telescoping vacuum pickup is selectively extendable between a retracted position, a first extended position corresponding to the pickup position, and a second extended position corresponding to the upper surface of the tiered lumber package.

So called "sticks" or "spacing sticks" are used in a sawmill to hold apart successive tiers of lumber in a stack of lumber so that the stack can be dried. Lath on the other hand are much thinner than sticks and are used to bind lumber stacks together by insertion laterally across tiers of longitudinally aligned lumber, between successive tiers.
Previously most spacing stick and lath placing machines (placers) were separate machines and usually designed differently, for one purpose or the other (spacing sticks or lath). One example of a stick placer used for spacing lumber for drying purposes is U.S. Pat. No. 3,643,621 issued to Newnes. The device utilizes a plurality of single magazines with a placing device below each magazine. The device is well suited for the purpose it was intended, that of delivering spacing sticks of a certain width and thickness, but does not work effectively with thin lath used for finished lumber packages (to be transported or shipped) and could not easily be combined to accomplish both tasks.
An example of a lath placer is U.S. Pat. No. 5,244,341, issued to Dion, which utilizes a rotary vacuum actuator that picks the lath up off of a short curved stack and then rotates back and drops the lath a short distance onto the package. This device is useful for delivering thin packaging lath, but cannot effectively deliver spacing sticks used for spacing lumber for drying and could not be used in a combined system for delivering both lath and spacing sticks.
U.S. Pat. No. 3,968,886, issued to Leon, can only place either spacing sticks, or, possibly, lath at any one time, due to the width of each unit and, because of the constraint of the restricted area above the lumber stack, could not be combined to successfully place both spacing sticks or lath through the same apparatus.
Applicant is also aware of U.S. Pat. No. 3,169,646, which issued to Mason. The Mason device is designed for spacing sticks and, again, could only capably handle either spacing sticks, or possibly lath, at any one time. No means are provided for positive placement of spacing sticks or lath. As the surface of a lumber stack is rarely completely level, given that each piece of lumber is usually not exactly the same shape as the adjacent piece, spacing sticks are dropped from the Mason device, thereby increasing the likelihood of the stick being bounced and misplaced. It is also not provided that spacing sticks be placed positively at the ends of the lumber stacks, where sawmills require a flush end face of the stack to reduce checking as the lumber stack is dried.


A device for the fixation of bones is disclosed. The device includes a block, a bone plate integral to the block which has at least one plate hole for accommodating a fastener, a first guide channel on the block for accommodating a first longitudinal carrier, and a second guide channel on the block for accommodating a second longitudinal carrier. The first and second guide channels are parallel to each other and the axes of the guide channels are in a plane which is parallel to the bone-contact surface of the bone plate. A cylinder defined by the first guide channel does not intersect the cylinders defined by the bone plate holes and a cylinder defined by the second guide channel does intersect the cylinders defined by the bone plate holes.

For the anterior fusion of vertebra segments (fractures, tumors, infections, congenital and post traumatic kyphoses, deformities) a wide variety of plate- as well as rod-systems are available.
Some of the advantages of plate systems such as the one disclosed in PCT/US93/08433, are the relatively small dimensions and the generally easy handling. Important disadvantages of these known plate-system consist therein that the area of fusion cannot actively be set under compression, a great assortment of expensive plate implants, and in the case of deformities no possibilities of correction.
Rod systems, such as the ones disclosed in PCT/US93/10908 or PCT/EP94/01606, do not have the above mentioned disadvantages of the plate-systems, but they are naturally larger in their dimensions and more difficult to handle.
U.S. Pat. No. 4,289,123 discloses an orthopedic appliance which includes a pair of brackets anchored to bone and connected by a pair of rods. However, the disclosed device is bulky and cumbersome to use.


A film forming, photosensitive, heat-resistant resin composition including a varnish of a polyimide precursor having no photosensitivity in itself, a polymeriziable monomer or oligomer compatible with the varnish and capable of providing a high-heat-resistant polymer upon being polymerized, and a polymerization initiator for the monomer or oligomer. The resin composition is useful for the production of circuit substrates and semiconductor devices for high-density mounting, since it can effectively avoid a reduction of the layer thickness during film formation, and ensures a low cost production process. The pattern formation process using such a resin composition is also disclosed. The polymeric composite having a particles-in-matrix microstructure and the production process thereof are also disclosed.

1. Field of the Invention
The present invention relates to a film forming, photosensitive, heat-resistant resin composition and a process for the formation of a heat-resistant insulating resin pattern using such composition. The film formed from the photosensitive, heat-resistant resin composition (in the present specification, the term "film" is used in a broad sense to indicate various coatings, films, thin films, etc.) adheres excellently to base materials and has good heat resistance, moisture resistance, insulating properties, toughness, abrasion resistance, and weather resistance, and further, can be formed at a low cost. Further, the process for formation of a pattern according to the present invention is advantageous in that the use of a photoresist for masking is not necessary, and a pattern of heat-resistant insulating resin film formed by this process is useful as one of the components of a circuit board or a semiconductor device, and can be utilized, for example, as a protective film or an insulating film (layer insulating film) in printed circuits, printed boards, wiring boards, and electronic components for high-density mounting. The term "base material" or "base material to be treated" as used in the present specification refers to mean general-use substrates including semiconductor substrates, ceramic substrates, metallic substrates, and various layered films and wiring.
The present invention also relates to a polymeric composite and a production process thereof. More particularly, the present invention relates to a polymeric composite or "polymer blend" having a particles-in-matrix microstructure. A matrix component of the polymeric composite comprises a polyimide resin which has a good heat resistance, and therefore can be advantageously utilized in the fields of electronics, transporting equipments, aircraft and aerospace industries, and a particles component thereof comprises the conventional curable resin, particularly an acrylic resin or a phosphazenic resin. Since it can exhibit an excellent heat resistance, insulating properties and toughness which are characteristic of the polyimide resins including polyimide engineering plastics, and also can show a low stress, the polymeric composite of the present invention can be advantageously used as a heat-resistant insulating layer or film such as a protective film or an interlayer insulator in printed circuits, printed boards and wiring boards and the like for high-density mounting as well as in electronic components or devices.
2. Description of the Related Art
Solder jointing is utilized for mounting IC chips in printed circuits, printed boards, wiring boards and electronic components including multi-chip modules or the like (as exemplified in FIGS. 1 and 2) for high-density mounting, and accordingly, the insulating films used for the above-described circuit substrates should be able to withstand the heat applied during the soldering. Further, since a large amount of information must be rapidly processed, reductions in the size and increases in the capacity of information processors are required. Semiconductor devices constituting a major part of such processors have been integrated through a reduction in the size of unit elements, thus enabling LSIs and VLSIs to be put to practical use. The quantity of heat (heat value) emitted from a semiconductor device increases with an increase in the integration of unit elements, and in an LSI, the heat value amounts to about 10 W.
Integration is achieved by a multi-layerization of the circuit, and when forming a semiconductor integrated circuit element, insulators are needed for layer insulation and surface protection, and inorganic insulators, such as phosphosilicate glass (abbreviated to "PSG"), silicon dioxide (SiO.sub.2) and silicon nitride (Si.sub.3 N.sub.4), are used for this purpose.
Although the above-described inorganic insulators have excellent properties such as dielectric strength and heat resistance, it is difficult to form an insulating film having a large thickness therefrom because inorganic insulating films are formed by a chemical vapor deposition process (abbreviated to "CVD").
The surfaces of semiconductor substrates to be coated with an insulating film have a significant number of fine uneven portions having a large aspect ratio, and inorganic insulating films take on a form which is similar to the form of the surface of the substrate, and this raises the problems of impossibility of smoothing the substrate surface and insufficient coverage.
Accordingly, investigations have been made into the use of polyimide, which can be coated by spin coating and has excellent heat resistance, not only as a surface protective film of a semiconductor integrated circuit element but also as a layer insulating film. A polyimide film for use as a surface protective film or a layer insulating film can be formed by dissolving a polyimide precursor, such as bismaleimide, polyamide acid or diamine, in a solvent, such as N-methyl-2-pyrrolidone (abbreviated to "NMP"), coating the resulting solution on a semiconductor substrate by a method such as spin coating, and heating the coating to a temperature of 150 to 400.degree. C. to cause a cyclodehydration reaction to occur, and thus cause the coating to be cured. The cyclodehydration reaction is also referred to as a polyimidalization reaction. Since the polyimide used herein has no photosensitivity in itself, a fine polyimide pattern may be formed by coating a photoresist on a polyimide precursor film, forming a resist pattern by photolithography, transferring the resist pattern to the lower layer by wet etching or plasma etching to form a pattern comprising a polyimide precursor, and heat-treating the pattern to cause a cyclodehydration reaction to occur, to thereby form a polyimide pattern.
A polyimide having photosensitivity in itself, which enables a polyimide to be patterned to any form, has been developed and is commercially available from various manufacturers. In this photosensitive polyimide, a photosensitive functional group is incorporated in the molecule of a polyimide precursor, and photoreaction occurs only in an exposed portion for polymerization, thereby varying the solubility between the unexposed portion and the exposed portion, and development is then conducted by making use of a solvent to dissolve and remove the unexposed portion while leaving only the exposed portion.
In subsequent heat treatment, the photosensitive groups have a poor heat resistance and are thermally decomposed and removed with the advance of cyclodehydration, so that only the polyimide portions having good heat resistance remain. The photosensitive groups can be introduced into the polyimide precursor through a covalent bond, an ionic bond or the like, and various photosensitive polyimides are commercially available.
The use of the above-described photosensitive polyimides, however, have the problem of high cost of the photosensitive polyimide per se, in addition to a large reduction in the film thickness which occurs as a result of the decomposition of a photosensitive group. Further, both non-photosensitive polyimides and photosensitive polyimides have the problem of poor moisture resistance.
For reference, the following patents may be mentioned as examples of patents describing processes for the formation of a pattern.
Japanese Unexamined Patent Publication (Kokai) No. 56-22428 discloses a process for the formation of a polyimide pattern, characterized by comprising the steps of (1) forming a film of a photosensitive polyimide precursor on a substrate; (2) irradiating the film with light in a pattern form and conducting development of the pattern; (3) heating the developed polyimide precursor pattern to convert the pattern to a polyimide pattern; and (4) treating the resultant polyimide pattern with an etchant for polyimide. A polyimide precursor bonded to a photosensitive group through a chemical bond or mixed with a photosensitive compound (such as bichromate) is used as the photosensitive polyimide precursor. In this process, the development residue of unexposed portions can be easily removed, so that through-holes free from defects can be obtained.
Japanese Unexamined Patent Publication (Kokai) No. 59-107346 discloses a heat-resistant photosensitive material comprising a photosensitive polyimide precursor including structural units represented by the following formula: ##STR1## wherein R.sub.1 and R.sub.2 are each an aromatic ring group, R.sub.3 is a thietane ring, and COOR.sub.3 is bonded to the amide group at its ortho-position. An insulating, heat-resistant polyimide pattern having good adhesion to the semiconductor substrate can be prepared through the use of such photosensitive material in the formation of a pattern.
In addition to these Japanese Kokais, although it is not considered to be relevant to the present invention, Japanese Unexamined Patent Publication (Kokai) No. 54-109828 discloses a heat-resistant photoresist composition which comprises 100 parts by weight of at least one polymer selected from a variety of organic polar solvent-soluble, heat-resistant polymers including polyimide, and 0.1 to 100 parts by weight, preferably 1 to 50 parts by weight of a monomeric compound containing at least two ethylenically unsaturated double bonds in its molecule. The amount of the monomeric compound incorporated into the heat-resistant polymer should not exceed 100 parts by weight, because larger amounts cause a reduction of the heat resistance of the resulting photoresist. This is because the specified monomeric compounds do not exhibit excellent heat resistance after curing of the resist.
The use of photosensitive polyimides as layer-insulating films in the production of integrated circuits wherein a considerable amount of heat is generated during use is desired in the art. As described above, photosensitive polyimides, however, have the problem of lowering the precision of the pattern due to the reduction in the film thickness resulting from the decomposition of the photosensitive groups during heat-treating of the photosensitive polyimide precursor to convert it into a polyimide, and further, photosensitive polyimides have the problem of the high cost of the material per se.
With regard to the use of the polyimide or polyimide resins, it is also well-known from Japanese Unexamined Patent Publication (Kokai) Nos. 62-30122, 63-86746 and 63-175854, for example, that the polyimide is mixed with curable resins or other additives such as polymaleimides, or novolak resins to form a polyimide resin composition useful in the formation of films or other molded articles having an excellent heat resistance and molding properties. However, the prior art publications including these Japanese Publications do not teach novel polymeric composite and production process thereof according to the present invention which will be described in detail hereinafter.
Further, hereinbefore, the polyimide resins including polyimide engineering plastics have been used in the formation of heat-resistant insulating layers, for example, protective films or interlayer insulators in the high-density mounting printed circuits, printed boards, electronic components and other devices. Because of lower dielectric constant thereof than that of conventional inorganic insulating materials, it is widely recognized that the polyimide resins are effective to improve characteristics of the integrated circuit (IC) devices, and in practice, they are able to ensure potential advantages such as passivation and interlayer insulation in microelectronics devices. Note that the polyimide insulators are considered to be more preferable than the inorganic insulators, because they generally have a dielectric constant of about 3.5 and also exhibit many excellent thermal and mechanical properties.
However, the polyimide resins, if used as the protective film or interlayer insulator in electronics and microelectronics devices including semiconductor devices, suffer from problems such as warpage of wafers and crack of chips. These defects are caused due to a large difference in a thermal coefficient of expansion (TCE) between the polyimide resins and the underlying materials such as aluminum as the wiring material or silicon dioxide (SiO.sub.2) as the passivation material, and can be varied depending upon the film thickness of the polyimide resins and the layer structure of the devices.
The defects due to the above-mentioned large difference in TCE can be reduced by using the polyimide resins having a low TCE as is disclosed, for example, in Japanese Unexamined Patent Publication (Kokai) No. 4-224824; U.S. Pat. No. 4,690,999; and Y. Misawa et al., IEEE Transactions on Electron Devices, ED-34, No. 3, March 1987. However, even if the low TCE resins are used, the defects cannot be avoided, when the polyimide resins are used at an increased thickness of film or the polyimide resins are subjected to the radiation exposure process.
In addition to the above drawbacks, recently developed photosensitive polyimide resins have problems that upon postbaking of the resins for obtaining the corresponding polyimide, a loss in the thickness of the resulting polyimide film can be increased to about 50% or more and also a stress of the film can be increased in comparison with the case using photoinsensitive polyimide resins, since photosensitive groups having a large molecular weight are volatilized from the film, along with water as a byproduct.

Photosensitive, heat-resistant resin composition and process for using same to form patterns as well as polymeric composite and production process thereof


A dispenser for a refrigerator is provided that increases a usable space of a storage compartment of the refrigerator. The dispenser includes a chute which receives contents from an inside of the refrigerator and discharges the contents to an outside through an opening provided on an end of the chute. A cover selectively opens or shuts the opening. A first unit causes the cover to slide relative to the opening so as to open or shut the opening.

1. Field
This relates to a dispenser for a refrigerator, and, more particularly, to a dispenser that dispenses contents such as, for example, ice and/or water from a refrigerator.
2. Background
Dispensers are typically provided in a freezing chamber door of a refrigerator to allow ice or water to be easily dispensed without opening the door. However, the placement of dispensers and/or corresponding structure to make and dispense ice and/or water on the inside of the door detracts from the usable space within the storage chamber. Further, access to electrical and mechanical ice making components through a dispensing chute can present a hazard if foreign objects are introduced through a dispensing chute. Additionally, cold air can be lost through the dispensing chute, and warm air can be introduced into the refrigerator through the dispensing chute, thus degrading efficiency of the refrigerator.

Dispenser and refrigerator including the same


In an apparatus scanning an alignment mark formed on a silicon substrate by an electron beam to determine the center position of the alignment mark based on the reflected signal waveform, a proportional relationship holds between a beam size which is the thickness of the electron beam and the amount of offset between the detected mark position and the actual mark position. More specifically, when the beam size is small, the amount of offset of the detected position from the actual position is small. In the mark position determining apparatus according to the present invention, the alignment mark is detected a plurality of times by the electron beams having a plurality of sizes, and based on the mark detection positions obtained by the respective detections, the mark detection position when scanning is carried out by an electron beam having a beam size of 0 is calculated.

1. Field of the Invention
The present invention relates to an apparatus and a method for determining a mark position on a wafer, and more particularly, to an apparatus and a method for determining a mark position used in delineating a plurality of registered patterns using a beam such as an electron beam in lithography of semiconductor device fabrication.
2. Description of the Background Art
In lithography of semiconductor device fabrication, a pattern generation apparatus is conventionally known. This apparatus prestores a desired pattern in a storage device, and delineates the stored pattern by electron beam exposure on a silicon substrate, which is coated with resist and mounted on a stage. In lithography of semiconductor device fabrication, 10 to 30 patterns such as a pattern for forming an oxide film and a pattern for forming a gate electrode of a transistor must be registered. In order to register the patterns, the position of an alignment mark which is a groove formed on the silicon substrate must be determined. The position of a pattern formed in the previous step is determined by the position of the alignment mark. In the recent development of LSI whose patterns get smaller, the patterns must be registered with high accuracy of 0.1 .mu.m or less. Therefore, extremely high accuracy is required for detection of the alignment mark.
Information on an electron signal reflected from the silicon substrate irradiated with an electron beam is different between in a portion including the alignment mark and in a portion not including the alignment mark. In determination of the position of the alignment mark, this difference is used. More specifically, the vicinity of the alignment mark on the silicon substrate is scanned by the electron beam and the position of the mark is determined based on a reflected electron signal detected by scanning.
FIG. 13 shows a specific structure of a conventional apparatus for determination of an alignment mark position.
Referring to FIG. 13, a silicon substrate 126 having resist 125 is irradiated with an electron beam 103 emitted from an electron gun (not shown). Information on an electron signal reflected from silicon substrate 126 irradiated with electron beam 103 is detected by a reflected signal detector 106. Electron beam 103 is deflected by a beam deflector 104 constituted of opposing electrodes, and scans the vicinity of an alignment mark 111 of silicon substrate 126 depending on the degree of deflection. The intensity of the reflected electron signal indicates a curve shown in FIG. 14. In this figure, the distance for which the beam moves on a line including the alignment mark on the silicon substrate by scanning is plotted along the abscissa, and the intensity of the electron signal reflected from the silicon substrate is plotted along the ordinate. This curve is generally called a reflected signal waveform. When the line including the alignment mark is scanned as shown in FIG. 14, ideal reflected signal waveform 113 is in symmetry. The level of waveform 113 is high in a portion not including the alignment mark and low in a portion including the alignment mark. By finding the center position of the symmetrical reflected signal waveform, the center position of the alignment mark is determined. The position of the silicon substrate is determined by an output from a laser interferometer, and the position at which the silicon substrate is irradiated with the electron beam is determined by a voltage applied to beam deflector 104. Since the alignment mark is formed by a groove having a depth of approximately 0.1 to 1.0 .mu.m as shown in FIG. 13, resist 125 becomes thick in the portion of the groove, and the distance to the substrate from which the electron is reflected becomes long. Therefore, electrons lose energy in resist 125 in their path. This is the reason why the level of the reflected signal waveform in the portion including the alignment mark becomes low.
A "threshold method" and an "autocorrelation method" are employed as a method for calculating the center position of the alignment mark based on the reflected signal waveform shown in FIG. 14. These methods will be described.
FIG. 15 shows the reflected signal waveform converted into an electric signal by detector 106, and FIG. 16 is a diagram for describing the signal processing of the reflected signal waveform by the threshold method.
Referring to FIG. 15, the intensity of a signal 114 reflected from the portion including the alignment mark (groove) tends to be smaller than that of a signal 127 reflected from the region not including the alignment mark (hereinafter referred to as a "base line"). In the threshold method, a threshold level 115 is set at a height of 30 to 70%, when the minimum value of the signal reflected from the portion including the alignment mark is 0% and the base line is 100% as shown in FIG. 16. Then, crossing points 128a and 128b between threshold level 115 and reflected signal waveform 113 are calculated, and a center position 117 between two crossing points 128a and 128b is determined as the center position of the alignment mark.
On the other hand, in the autocorrelation method, the reflected signal waveform shown in FIG. 15 is digitally sampled and input to the apparatus. Here, assume that the digitally sampled waveform is D(X). The waveform D(X) is substituted in an autocorrelation function Z(X) shown by the following expression (1). The waveform indicated by Z(X) calculated according to the expression (1) is called an autocorrelation signal. ##EQU1##
Note that in the expression (1), a variable W is arbitrarily set as a width a little larger than that of the alignment mark (groove). By the processing of the reflected signal waveform shown in FIG. 15 with the autocorrelation method according to the expression (1), the autocorrelation signal shown in FIG. 17 is calculated. The autocorrelation signal indicates a so-called centroid of the reflected signal waveform, peak position 119 of which is to be determined as the center position of the alignment mark.
However, in the above described apparatus for determining the alignment mark position, the center position of the alignment mark cannot be always determined accurately because of the following reason. As shown in FIG. 19A, in the actual lithography, a thin film 120 of atoms of platinum, tungsten or the like is sometimes formed between silicon substrate 126 and resist 125. Since the atoms of platinum or tungsten of thin film 120 have a large atomic number and a large density, the reflection coefficient of an electron is extremely large. Therefore, when the thickness of thin film 120 is different in the alignment mark portion as shown in FIG. 19A, the reflected signal waveform is in asymmetry as shown in FIG. 19B. More specifically, the intensity of the signal reflected from the thick portion of thin film 120 is relatively large, while that of the signal reflected from the thin portion of thin film 120 is relatively small. Therefore, center position 121 of the alignment mark calculated from reflected signal waveform 113 by the threshold method tends to shift towards the side of thin film 120 having a small thickness as shown in FIG. 19B. Similarly, also when the peak position is calculated by the autocorrelation method, the peak position shifts towards the side of thin film 120 having a small thickness as shown in FIG. 19C.
If thin film 120 is formed uniformly in symmetry in the alignment mark portion, such shift in the mark center position does not occur. However, as shown in FIG. 18, the thin film is currently formed with a spattering method. In the spattering method, a voltage is applied between silicon substrate 126 and a target 205, and the material of target 205 is deposited on silicon substrate 126 as a thin film. Therefore, thin film 120 at alignment mark 111 having a three-dimensional shape varies in thickness depending on its positional relationship with target 205. In an example shown in FIG. 18, the left portion of alignment mark 111 in the figure has a large thickness since the film is directly exposed to target 205, while the right portion of alignment mark 111 has a small thickness since this portion is shadowed by silicon substrate 126.

Apparatus for determining mark position on wafer