In order to reinforce a working hull, such as the fuselage of an aircraft and in particular that of a helicopter, a frame (C) is embodied made of a composite material in the form of a monolithic monobloc structure. This structure is constituted by a profile whose internal flange (16) and the external half-flanges (18) principally comprise unidirectional fibers which extend over its entire length. As a variant, the lower section of the frame is embodied separately in the form of a panel bordered over its entire periphery by lateral half-flanges which also principally comprise unidirectional fibers. After assembling the two sections of the frame, the half-flanges are then opposite each other in the elongation.

In rotary wing aircraft, such as helicopters, and fixed wing aircraft, the fuselage, whose structure is essentially a hull, may be required to bear localized stresses requiring the presence of one or more frames to distribute these stresses inside the working structure. In the case of a helicopter, frames such as these, especially reinforcement frames, are usually used for fixing the engine or engines and the transmission units to the rotor on the top of the fuselage. In fixed wing or rotary wing aircraft, reinforcement frames may also be used to fix the resistant elements of the undercarriage.
As shown in detail in the document FR-A-2 539 701, the method is known for producing the fuselage of a helicopter and in particular the reinforcement frames of this fuselage made of a composite material constituted by carbon fibers embedded in a plastic mould.
In this document, each of the frames includes two vertical struts and two horizontal crosspieces whose extremities are fixed to the extremities of the vertical struts. The struts and the crosspieces comprise a casing made of a composite material encompassing a honeycomb-shaped material. More precisely, the casing of the vertical struts has a cross section in the form of a high-shaped cap closed to the outside by a composite strip, whereas the casing of the horizontal crosspieces is formed of two U-shaped sections disposed back-to-back and connected by two composite strips. The assembling between the lateral beams and the horizontal beams is effected by glueing by making the extremities of the vertical struts penetrate into the recessed sections of the extremities of the horizontal crosspieces.
A reinforcement frame embodied in this way presents a number of drawbacks. Thus, the conception described only makes it possible to embody frames whose shape is approximately rectangular and is not applicable to frames having a different shape, said shape being, for example, circular or polygonal. Furthermore, the segmenting into three elements of the upper portico-shaped section of the frame results in discontinuities in the transmission to the entire frame structure of localized stresses applied to the latter, for example at locations used for the fixing of the main transmission box or the resistant devices of the undercarriage. Moreover, the positioning of the braces bearing these localized stresses has not been proved to be satisfactory. Finally, the flanges of the vertical struts of the frame are suddenly interrupted when these struts are connected onto the lower beam, which increases the structural discontinuity of the frame.
In addition, the document U.S. Pat. No. 4,593,870 describes a structure designed to constitute the lower part of the fuselage of an aircraft, such as a helicopter. This structure includes two webs made of a composite material between which placed is an alveolar material. In the lower part of the structure, the webs present deformations constituting the starts of folding bucklings when the structure of the fuselage is compression-stressed in a vertical direction under the effect of an impact of this structure at high speed.

Frame made of a composite material, especially for the fuselage of an aircraft, and its method of production

Societe Nationale Industrielle et Aetospatiale


A novel multilayered sleeve-like printing blanket is mountable on gapless cylinders or tubular blanket carriers, thereby minimizing vibration when operated at high rotational speeds. An exemplary printing blanket comprises a seamless outer printing surface layer; at least one reinforced elastomer layer, the elastomer layer being reinforced by fibers substantially parallel with the inward and outward sides of the cylindrical tube defined by the reinforced elastomer layer; and a resiliently compressible layer. The oriented fibers reinforce the elastomer layer such that the modulus of elasticity in the circumferential direction of rotation is increased. Exemplary methods for forming one or more of the layers are also disclosed herein.

It is known in offset printing to use cylinders lined with a printing blanket to permit the printing of a paper web which is pinched and driven between cylinders. Previously, the blankets were fastened onto the cylinders with their ends entered and locked into a longitudinally extending gap in the cylinder. This caused a number of inconveniences. In effect, the confronting ends of the blanket necessarily left a certain space therebetween, so that the paper web exhibited unprinted areas. Moreover, this way of fastening blankets into "gapped" cylinders imparted to the cylinder-blanket assembly a dissymmetry which generated vibrations during the rotation of the cylinder. Therefore, the speed and the efficiency of the printing machines was necessarily limited.
Gapped cylinders created a problem known as "fall off at the gap" for printing blankets having a fabric layer located between a printing surface and compressible foam layer. The fabric compressed the foam near the gap because it could not elongate sufficiently, and consequently decreased printing sharpness. U.S. Pat. Nos. 4,303,721 and 4,812,357 disclosed the use of an elastomer between the printing and foam layers to avoid fall off at the gap.
It is known that "seamless" and resiliently compressible blankets can be mounted around gapless cylinders in the manner of a continuous tube or sleeve.
For example, U.S. Pat. Nos. 3,983,287 and 4,378,622 disclosed tubular outer layers disposed around an inner compressible layer. The Canadian Patent Application No. 2,026,954 of Gaffney et al. suggested that a compressible foam layer disposed directly beneath a printing surface layer was needed to avoid bulges on either side of nip during operation, although it was also suggested that fabric could be inserted between layers.
U.S. patent application Ser. No. 07/682,048 of Bresson, filed Apr. 8, 1991, on the other hand disclosed a seamless blanket in which at least one hard elastomer layer, e.g. a substantially non-compressible material such as cured rubber, was employed between a surface printing layer and a compressible layer to minimize vibration in the blanket at high rotational velocities. The elastomer could optionally be reinforced with fibers. The multi-layered blanket was seamless in that it could be mounted around a cylinder without any surface interruptions, in the manner of a sleeve, thus permitting axial symmetry and allowing printing machines using such cylinders to operate at high speeds with minimum vibration.
Because seamless blankets are not secured by gaps in the cylinder, new problems arise regarding blanket installation and mounting, the avoidance of creeping or slippage during rotation, and removal after use, to name but a few. Unitary, cylindrically-shaped blankets can be axially mounted or dismounted on cylinders using compressed air, which is passed in a substantially radial direction from holes located within the cylinder. For example, U.S. Pat. No. 4,903,597 of Hoage et al. teaches that compressed air or gas is used to expand the sleeve to a limited extent for facilitating mounting and dismounting operations.
Thus, seamless blankets must be sufficiently resilient to provide compressibility for generating nip pressure; and yet they must have sufficient dynamic stability such that the circumferential (e.g. angular) velocity of the surface printing layer is not altered in passing through the nip. The uniformity of the velocity at which the printing surface passes through the nip is important to achieving web control (i.e. the printed material is not slipping relative to the rotating blanket) as well as to achieving good image resolution during rotation (i.e. no smearing of the image or distortion in the blanket surface).
Such antagonistic demands require a novel seamless, multi-layered printing blanket and method for making the same.


Provided is a fixing device comprising: a fixing rotating body; a magnetizing coil; a pressing member forming a fixing nip through which a recording sheet passes; a demagnetizing coil unit set including a pile of demagnetizing coil units each including demagnetizing coils of different sizes, and canceling out part of magnetic flux generated by the magnetizing coil in a non-sheet-passing region; a sheet information acquisition unit acquiring sheet information including information relating to a width of the recording sheet; and an operation control unit controlling each demagnetizing coil according to the width, wherein in each demagnetizing coil unit, the demagnetizing coils are arranged such that a smaller demagnetizing coil is surrounded by a larger demagnetizing coil and the demagnetizing coils are in a same plane extending along a surface of the magnetizing coil, and a combination of sizes of the demagnetizing coils differs among the demagnetizing coil units.

(1) Field of the Invention
The present invention relates to a fixing device and an image forming device, and in particular to an electromagnetic induction heating-type fixing device and an image forming device using the same.
(2) Description of Related Art
With the growing demand for energy conservation in the field of image forming devices in recent years, an electromagnetic induction heating-type fixing device having high energy efficiency is attracting attention.
The electromagnetic induction heating-type fixing device includes a fixing rotating body such as a fixing roller and a fixing belt, a magnetizing coil, and a demagnetizing coil. The magnetizing coil is disposed along an axial direction of the fixing rotating body, and generates an alternating field by passage of alternating current to heat the fixing rotating body by induction. The fixing rotating body heated by induction thermally fixes a toner image formed on a passing recording sheet.
The demagnetizing coil is disposed in a non-sheet-passing region of the fixing rotating body through which the recording sheet does not pass, and includes winding wire whose ends are connected together to form a closed loop. With this configuration, the demagnetizing coil generates magnetic flux in such a direction that part of magnetic flux generated by the magnetizing coil and trying to pass the demagnetizing coil is canceled out, thereby suppressing an increase in temperature in the non-sheet-passing region of the fixing rotating body. As a result, thermal degradation of the fixing rotating body and other peripheral members is prevented.
The following patent literatures disclose technology to suppress an increase in temperature in the non-sheet-passing region, in a case where recording sheets of different sizes are used. In such a case, the demagnetizing coil as described above is provided in a plurality so that demagnetization is performed according to a size of the non-sheet-passing region determined when each of the recording sheets passes therethrough.
For example, Japanese Patent Application Publication No. 2009-145421 discloses a fixing device having a structure in which a plurality of demagnetizing coils of different sizes are piled on a magnetizing coil such that a smaller demagnetizing coil is placed on a larger demagnetizing coil (first prior art).
Japanese Patent Application Publication No. 2010-197947 discloses a fixing device having a structure in which a plurality of demagnetizing coils of different sizes are arranged such that a smaller demagnetizing coil is surrounded by a larger demagnetizing coil and that the demagnetizing coils are in a same plane extending along a surface of a magnetizing coil (second prior art). The second prior art differs from the first prior art in that the demagnetizing coils of different sizes are arranged along the surface of the magnetizing coil so as to extend laterally, rather than to be piled on the magnetizing coil.
In the conventional fixing device described above, however, when more demagnetizing coils corresponding to recording sheets of a wider variety of sizes are provided, the following problems arise.
In the fixing device pertaining to the first prior art, since a pile of the demagnetizing coils is placed on the magnetizing coil, the device becomes large in a radial direction of the fixing rotating body. In addition, as the number of piled demagnetizing coils increases, the distance between an upper demagnetizing coil and the magnetizing coil increases and thus demagnetization efficiency is reduced accordingly. Therefore, when a large number of recording sheets corresponding to the upper demagnetizing coil pass and toner images are thermally fixed thereon continuously, over-temperature in the non-sheet-passing region cannot be completely suppressed and thus thermal degradation of the fixing rotating body can occur.
In the fixing device pertaining to the second prior art, since the number of surrounding demagnetizing coils is increased, the width of an outermost demagnetizing coil increases in a circumferential direction of the fixing rotating body and thus the device becomes large accordingly.

Konica Minolta Business Technologies, Inc.


The present invention provides a semiconductor device and a method for manufacturing the same. The method for manufacturing the semiconductor device comprises: providing a silicon substrate having a gate stack structure formed thereon and having {100} crystal indices; forming an interlayer dielectric layer coving a top surface of the silicon substrate; forming a first trench in the interlayer dielectric layer and/or in the gate stack structure, the first trench having an extension direction being along <110> crystal direction and perpendicular to that of the gate stack structure; and filling the first trench with a first dielectric layer, wherein the first dielectric layer is a tensile stress dielectric layer. The present invention introduces a tensile stress in the transverse direction of a channel region by using a simple process, which improves the response speed and performance of semiconductor devices.

1. Field of the Invention
The present invention relates to semiconductor technology, and particularly, relates to a semiconductor device and a method for manufacturing the semiconductor device.
2. Description of Related Art
In the process of manufacturing Complementary Metal-Oxide Semiconductor (CMOS), with the scaling of the critical dimension of semiconductor devices, stress is typically introduced into the channel region for improving mobility of carriers and performance of semiconductor devices.
The following table is shown by Scott E. Thompson et al. in Uniaxial-Process-Induced Strained-Si: Extending the CMOS Roadma (IEEE Transactions on Electron Devices, Vol 53, No. 5, February 2006).
Unit: 10−12 cm2/dyn(001) silicon<100><110>polarityπ∥π⊥π∥π⊥π11π12(π11 + π12 +(π11 + π12 −π44)/2π44)/2n-MOSFET−42.6/−102−20.7/53.4−35.5/−31.6−14.5/−17.6p-MOSFET 9.1/6.6 −6.2/−1.171.7/71.8−33.8/−66.3
The table shows comparison of piezoresistance coefficients between a MOSFET on a silicon chip of crystal indices (001) and bulk silicon. The piezoresistance coefficients are well known in the semiconductor technology for predicting and measuring mobility of electrons and holes. In the table, π∥ is the piezoresistance coefficient in the longitudinal direction, and π⊥ is the piezoresistance coefficient in the transverse direction of the channel region. As for a silicon chip having a crystal indices (001), π∥ and π⊥ may be expressed as functions of three fundamental cubic piezoresistance coefficients π11, π12 and π44, respectively. The influence of piezoresistance coefficients on mobility of carriers may be expressed as: Δμ/μ≈|π∥σ∥+π⊥σ⊥, wherein Δμ/μ is the fractional change in mobility, σ∥ and σ⊥ are longitudinal and transverse stresses of the channel region, respectively. As shown in the above table, the tensile stress in transverse direction of the channel region enhances mobility of carriers for both PMOS transistors and NMOS transistors.
However, in related art, stress is typically introduced in the longitudinal direction of the channel region, for example, by Dual Stress Liner (DSL) technology and Stress Memorization Technology (SMT), and so on.
Taking the DSL technology as an example, an NMOS transistor is covered by a tensile stress liner, and a PMOS transistor is covered by a compressive stress liner, thereby improving mobility of carriers in the NMOS transistor and PMOS transistor, respectively. Therefore, in the manufacturing process, the DSL technology requires formation of respective stress liners for different types of transistors, which is complicated. The SMT requires forming stress liners on devices firstly and then performing an annealing process to the devices, which is also complicated.
Therefore, a new type of semiconductor device is needed to solve the above problems existing in the related art, in order that stress is more sufficiently applied to MOS transistors, and performance of the MOS transistors may be improved.

This patent is subject to a terminal disclaimer.

Semiconductor device and method for manufacturing the same

Institute of Microelectronics, Chinese Academy of Sciences


A method of determining, at a mobile device, side information including compression state information. The method includes receiving, from a server, a unique side information identifier identifying a unit of side information used by the server for compressing data, determining, based on the side information identifier, if the unit of side information is resident on said device, and if the unit of side information is resident on the mobile device, loading the side information for decompressing the data. Otherwise, if the unit of side information is not resident on the mobile device, the method includes requesting the unit of side information from one of the server and another device.

In the field of data communication, data is typically compressed so that the amount of information being transmitted is reduced. Such data compression enables less traffic and therefore faster transmission. Compression also reduces storage requirements, which is especially important in communication to portable or mobile communication devices with limited storage capacity. In conventional communication between a server and a mobile communication device, requested data, such as message data, a website, or a digital file, is encoded, or compressed, by the server, and then transmitted. A decoder at the mobile communication device decodes the compressed data, and processes it appropriately, for example, displaying it to the user.
Side information, or a priori information shared by both the encoder and decoder, can be used in the compression and decompression of transmitted data to improve compression performance. The choice of side information influences the compression ratio achieved by the compression. Significantly improved compression can be achieved in systems, known as interactive compression systems, that maintain shared caches of side information. A class of such systems is grammar-based compression of which Yang-Kieffer (YK) data compression is a member. Side information that is correlated with the data being compressed is utilized in YK compression to build a grammar and collect frequency counts. This is used to achieve better compression of the data being compressed.
It is important that both encoder and decoder use the same side information in compression and decompression, thereby using the same parameters (e.g. YK grammar and frequency counts) for compression and decompression, respectively. It is therefore desirable to provide a method of communicating side information for interactive compression.
It is an object of the present invention to obviate or mitigate at least one disadvantage of previous methods of interactive compression.

Method and apparatus for communicating compression state information for interactive compression


In a state where a driver sees a region near a vehicle, a finally-requested output-shaft torque is set so that a response is hastened in a deceleration and slowed in an acceleration. Thereby, a vehicle takes a forward descending position in which the front end of the vehicle is descending, which gives a driver a sense of deceleration or a sense of turning. Further, this position causes a front wheel load acting on the ground to increase and a rear wheel load acting on the ground to decrease, in comparison to a normal position. This thereby makes it easier for the vehicle to decelerate when practically decelerating or turning, and further enables turning to slightly over-steer. A resultant vehicular kinetic characteristic becomes comparable with a sense that is expected by the driver.

Vehicular kinetic characteristics such as running, turning, or stopping are changed depending on operating points of devices (e.g., engine, steering, suspension, brake, or other vehicular mechanisms), further, depending on slopes of roads. Therefore, a driver conducts predictive operations after understanding the vehicular kinetic characteristics, or conducts modifying operations after understanding vehicular actions. Namely, the driver needs to respond to variations of the vehicular characteristics.
Specific Examples are as Follows.
1) Characteristics variations due to devices
Switching transmission shift positions changes a driving characteristic to an accelerator operation. For instance, an acceleration/operating gain varies because of a gear ratio, or a response varies because of operating points of a torque converter or an engine.
Further, a response is changed by variations in engine operating points, e.g., engine revolution numbers or loads. For instance, in a gasoline-port injection engine, a response is changed by a response of an air system, switching due to a control, or a control of a valve for an inlet/outlet air.
Furthermore, in general, a vehicle is designed to slightly under-steer as a turning curvature increases (or a lateral acceleration increases). For instance, a vehicle is designed by considering a weight distribution, a suspension geometric structure, a suspension kinematics, or a tire characteristic. The vehicle that is thus designed tends to go short of additional steering when the vehicle enters a sharper curve during turning.
2) Characteristics variations due to road shapes
A road slope changes a vertical load balance in the front and rear wheels, which thereby further changes a steering characteristic. For instance, in an ascending slope, the load in the front wheel decreases, so the vehicle tends to under-steer. In contrast, in a descending slope, the load in the front wheel increases, so the vehicle tends to over-steer. Further, a vehicular kinetic characteristic is changed depending on a road-surface frictional coefficient μ. Therefore, the driver needs to understand a road surface condition.
Driver's recognition or sense of acceleration or turning during vehicle's traveling is differentiated even when the same acceleration or the same turning is conducted in individual cases as follows: when a curve or a slope is present ahead of a vehicle, when a preceding vehicle is present ahead of a vehicle, or when a road becomes narrower ahead of a vehicle. Further, conditions such as brightness or weather surrounding the relevant vehicle affect the driver's recognition. The recognition or the sense of the driver is changed depending on a distance of a driver's gaze.
In detail, as a vehicle position slants, a sense of acceleration or a sense of turning may become strong. For instance, when the front end of a vehicle goes up (nose up) because of driving, the sense of accelerating may increase. When the front end of a vehicle goes down (nose diving) because of braking, a sense of decelerating may increase. Further, when a vehicle rolls during turning, a sense of turning may increase.
Thus, a driver needs to properly conduct an operation since relationships between various parameters are changed by influences of the vehicular characteristics or road environments. The various parameters include actual accelerating, decelerating, or turning action; vehicular positions at the relevant actions; and driver's operations for individual parts of the vehicle that cause the foregoing


A data transfer apparatus has a casing with an entrance slot in which a magnetic tape cassette is to be inserted. Upon full insertion of the cassette to a preassigned standby position, a cassette shift mechanism is activated to transport the cassette from the standby position to a data transfer position opposite a substantially fixed magnetic head. A load/eject lever on the front panel of the casing is to be manually turned following the shifting of the cassette to the data transfer position, in order to cause a pair of drive spindles to move into driving engagement with the hubs of the cassette. Since the drive spindles remain retracted, instead of being automatically sprung into driving engagement with the cassette hubs, unless the load/eject lever is manipulated following the shifting of the cassette to the data transfer position, a cleaning cassette can be used with the apparatus for cleaning the magnetic head without the danger of ruining the drive spindles as a result of forced contact with the cleaning cassette.

Our invention relates to apparatus for the transfer (recording and/or reproduction) of data to and/or from magnetic tape packaged in cassette form. More specifically, our invention deals with improvements in data transfer apparatus of the type described and claimed in U.S. Pat. No. 4,701,817 issued Oct. 20, 1987, to Uemura under the same title herewith and assigned to the assignee of our instant application. The data transfer apparatus of our invention is particularly well suited for the storage and retrieval of digitized data, although we do not wish our invention to be limited to this particular application.
In magnetic tape cassette apparatus in general, it is essential that the tape cassette on being loaded therein be precisely positioned with respect to the transducer or magnetic head for proper data transfer therewith. The usual construction of the tape cassette apparatus has been such, however, that the tape cassette on being inserted in the entrance slot of the apparatus is first moved to a preassigned data transfer position. Then the transducer is moved into contact with the tape of the positioned tape cassette preparatory to the commencement of data transfer. Since the tape cassette and the transducer are both independently movable in such apparatus, difficulties have been encountered in some instances in exactly positioning them with respect to each other.
A solution to this problem is found in the above cross-referenced U.S. Pat. No. 4,701,817. This patent makes the movement of the transducer unnecessary; only the tape cassette, on being loaded fully in the apparatus, is moved linearly to the data transfer position opposite the transducer. Then the pair of motor-driven spindles, forming parts of a tape transport, are moved into driving engagement with the hubs of the tape cassette being held in the data transfer position. The movements of the tape cassette to the data transfer position, and of the drive spindles into driving engagement with the cassette hubs, are both automatic, successively taking place upon loading of the tape cassette in the apparatus.
We have found some shortcomings in this prior art apparatus. One is the need for the provision of a complex and bulky tape transport shift mechanism for automatically moving the drive spindles into and out of driving engagement with the cassette hubs. Another shortcoming manifests itself in the use of what is known as the "cleaning cassette" for cleaning the gapped surface of the magnetic head and other required parts of the apparatus.
Such a cleaning cassette is described and claimed in Miyao et al. U.S. Pat. No. 4,748,526. Shaped and sized exactly like the magnetic tape cassette, the cleaning cassette is inserted in the entrance slot of the apparatus like the magnetic tape cassette. Thereupon, also like a the tape cassette, the cleaning cassette is automatically transported to the data transfer position, enabling the user to clean the head surface manually by inserting a cleaning stick in a guide passageway defined in the cleaning cassette. The cleaning cassette differs from the tape cassette in having no apertures for admitting the drive spindles. As the drive spindles are thus prevented from moving into the loaded cleaning cassette, so are the usual pair of tape guide pins which are disposed on both sides of the head. The operator can thus manipulate the cleaning stick without interference with the guide pins.
As has been stated, however, the apparatus is so constructed as to automatically actuate the drive spindles into driving engagement with the cassette hubs upon loading of the cassette in the apparatus. Therefore, upon insertion of the cleaning cassette, the drive spindles move into abutment against the bottom wall of the cleaning cassette under spring pressure. Such forced abutment of the drive spindles against the cleaning cassette gives rise to the danger of ruining the spindles or other parts associated therewith.

Manually-operated loading and ejecting mechanism for a magnetic tape cassette apparatus


A liquid level control structure and a method for its production. The liquid level control structure is comprised of a wafer having substantially flat top and bottom surfaces and a channel for containing a marking fluid. The channel is defined by inwardly sloping walls that extend through the wafer and that join with the top surface of the wafer to define protrusions. The protrusions interact with the marking fluid's surface tension so as to control the location of an unbounded surface of the fluid within the channel.. An alternative embodiment liquid level control structure uses a thin film layer deposited over the wafer's top surface that extends over the protrusions to form lips. Those lips interact with the marking fluids surface tension to control the location of the unbounded surface.. The methods for producing the liquid level control structures use semiconductor fabrication techniques such as photolithography and anisotropic etching.

Because acoustic ink printers (ALP) avoid the clogging and manufacturing problems of the more conventional drop-on-demand, nozzle-based ink jet printers, they represent a promising direct marking technology. While significant effort has gone into developing acoustic ink printing, see, for example, U.S. Pat. Nos. 4,751,530; 4,751,534; 5,028,937; and 5,041,849, various problems remain to be solved before AIP becomes a viable marking technology.
An acoustic ink printer utilizes acoustic energy to eject droplets from an unbounded surface of a marking fluid onto a recording surface. Typically this involves focusing acoustic energy from an ultrasonic transducer, using either a spherical or a fresnel (reference U.S. Pat. No. 5,041,849) acoustic lens, into a focal area near the unbounded surface. If the acoustic energy is sufficient, an ink droplet having a diameter about the same as the acoustic wavelength is ejected. For a more detailed description of the ejection process reference is made to U.S. Pat. Nos. 4,308,547 and 5,028,937, and the citations therein.
As may be appreciated, acoustic ink printers are sensitive to the spacing between the acoustic energy's focal area and the unbounded surface. Since the acoustic focal plane is generally fixed, it is important that the unbounded surface be properly and accurately positioned. Indeed, since current practice dictates that the acoustic focal area be within about one wavelength of the unbounded surface, typically about 10 micrometers, the position must be very accurately controlled. While various liquid level control structures and techniques have been tried, see, for example, U.S. Pat. No. 5,028,937 (which discusses positioning the unbounded surface with a perforated membrane), and U.S. patent application Ser. No. 07/810,248, filed Dec. 19, 1991 (which discloses an anisotropically etched liquid level control structure having inwardly protruding knife-edged lips), all have their problems.
It would be beneficial to have a liquid level control structure that accurately controls the location of the unbounded surface of a liquid, that is producible at low cost, that allows droplets to be ejected onto a recording medium, and that readily attaches to the other sections of the print head.

Anisotropically etched liquid level control structure


A seatbelt buckle system is disclosed that allows rotation of the seatbelt buckle in a transverse direction with respect to the vehicle body. The system includes a buckle fixed to a buckle attachment plate. The buckle attachment plate has a through aperture that cooperates with a fastener for attaching the buckle attachment plate to a vehicle structure such as a vehicle seat. Additionally, a spring is disposed between the buckle attachment plate and the head of the fastener. Further, the through aperture in the buckle attachment plate is oversized such that the buckle attachment plate and attached buckle can rotate along a longitudinal axis of the fastener.

Conventional vehicles typically have both front and rear seatbelt assemblies for restraining vehicle occupants during a vehicle collision. While seatbelt systems are very effective at reducing a vehicle occupant's injuries resulting from a vehicle collision, they can cause some discomfort to the vehicle occupant as well.
Prior art systems have tried to minimize the occupant's discomfort caused by the seatbelt system by, for example, attaching the seatbelt buckle to the vehicle structure using a flexible member such as seatbelt webbing or a flexible metal strap or cable. While these prior art methods have achieved their intended purpose, many problems still exist. For example, manufacturing consistency and quality may be reduced using the webbing, cable or metal strap designs. In some cases, occupant comfort is also sacrificed.
Therefore, what is needed is a new and improved system and method for attaching the seatbelt buckle to the vehicle structure. This new and improved system and method should provide enhanced manufacturing consistency and quality as well as enhancing vehicle occupant comfort.


A method for preventing or reducing restenosis wherein a 27-hydroxycholesterol or a 25,26 and/or 27-aminocholesterol, or a sterol 27-hydroxylase stimulant is administered in a restenosis preventing and/or reducing amount.

Various surgical bypass and angiographic procedures are routinely employed for increasing blood flow to an organ, usually the heart. These operative and non-operative procedures injure to a greater or lesser extent the interior wall of the lumen of the blood vessel at the target site. This endothelial injury often leads through a cascade of events to restenosis. For example, balloon, laser or rotameter angioplasty, in which a catheter is inserted into the arterial system to place a balloon, laser or blade at the stenosis, is quite successful in widening a narrowed area of a blood vessel lumen. However, endothelial injury occurs at the site of the lesion, leading to restenosis in an estimated 20-40% of patients.
It has been shown in animals that endothelial injury initiates a process that leads to narrowing of the injured artery (stenosis), and this model is related and is used to study the events that occur following endothelial injury.
The major current theory for explaining restenosis is that once the endothelial cells are injured or removed by the invasive procedure, circulating platelets cover the denuded areas and release potent growth factors, such as platelet derived growth factor, which stimulate the growth and migration of underlying smooth muscle cells. Other growth factors such as fibroblast growth factors have also been implicated. For these reasons, anti-growth factors are being evaluated for the prevention of atherosclerosis.
Many factors are thought to potentially participate in restenosis. Further, hemodynamic forces responsible for the original lesion are not generally alleviated by angioplasty and may be aggravated at plaque disruption. The thrombo-resistant nature of the arterial lumen is reduced due to the generation of markedly thrombogenic surfaces of complex geometrical configuration, and changed permeability characteristics permitting possible direct interaction between blood-borne elements such as the aforementioned platelets and the arterial lumen. In summary, the surgical and angiographic procedures necessarily result in injury to vessel walls, which results in restenosis in 20-40% of patients.
27-hydroxycholesterol (cholest-5-ene-3.beta.,27-diol) is normally present in biological fluid after neonatal life. Recently, the IUB changed certain rules of nomenclature, and the compound now referred to as 27-hydroxycholesterol was previously called 26-hydroxycholesterol. Two methyl groups are attached to carbon number 25 of cholesterol, but only one can be enzymatically hydroxylated, which was previously named carbon number 26, but is now named as carbon number 27.
U.S. Pat. No. 4,427,688 by Javitt describes the administration of 26-hydroxycholesterol (sic., 27-hydroxycholesterol) and various derivatives and analogs thereof for reducing cholesterol synthesis and/or cholesterol accumulation in the body tissues; hence, teaching the use of 27-hydroxycholesterol compounds for the treatment of atherosclerosis. Thereafter, as disclosed in U.S. Pat. No. 4,939,134, Javitt, et al. discovered that 27-aminocholesterol and certain amino-substituted analogs and derivatives thereof, are more potent inhibitors of cholesterol synthesis and accumulation than 27-hydroxycholesterol.
Javitt filed Japanese application 107488/82 in 1982, published as 019206/91 on Nov. 14, 1991 ("JPA"), largely corresponding in disclosure to U.S. Pat. No. 4,427,688 with insertion of additional information for further supporting use of 27-hydroxycholesterol in treatment of atherosclerosis. The JPA notes that Kandutsch, et al., Science, 201, 498 (1978) mentioned that oxygenated cholesterol has an inhibitory effect on the proliferation of fibroblasts and lymphocytes in vitro, perhaps by inhibiting HMG CO-A reductase, the rate-limiting enzyme in cholesterol biosynthesis, which is consistent with the idea that cholesterol is essential to cell proliferation. Javitt tested this theory by seeding hamster aortic smooth muscle cells at low density in culture wells and coulter counting control and 27-hydroxycholesterol exposed cells six days later. The 27-hydroxycholesterol at the tested concentration inhibited the proliferation by about 50%. Although a potential lead, in vitro muscle cell proliferation inhibition, in itself, does not teach nor suggest the use of the same substance for preventing restenosis in vivo. Indeed, some have interpreted the inhibitory effect by oxysterols on vascular smooth muscle cells as a toxic effect. Zhou, et al., Proc. Soc. Exp. Biol. Med., 202:75-80; Nassem, et al., Biochem. Internat., 14:71-84. Also see Baranowski, et al., Atherosclerosis, 41:255-260. Further, it has been recently reported that high doses of Lovastatin, a potent cholesterol lowering drug, in a randomized, double blind placebo controlled trial, did not decrease restenosis six months following percutaneous transluminal coronary angioplasty, although the Lovastatin did markedly decrease LDL-cholesterol level, as expected. Thus, as of today, the cholesterol lowering biological activity of a drug, while perhaps indicating potential use in the treatment of atherosclerosis, is not predicative nor suggestive of use for combating restenosis. As discussed above, restenosis is a multi-faceted phenomena, distinct from atherosclerosis, and the mechanism of which is at best only partially understood.

Administration of a 27-hydroxycholesterol or related compound or sterol-27-hydroxylase stimulant to prevent restenosis following vascular endothelial injury


A phase shift mask having a phase shifter with an edge angle ranging from 70.degree. to 85.degree. or 95.degree. to 110.degree. is used as a reticle in forming a resist pattern so that the exposure pattern applied to the resist has a light intensity distribution with constant light intensity contrast. A fine resist pattern having a predetermined width no more than the wavelength of the light used to form the pattern is produced precisely and reproducibly under constant developing conditions. In addition, there is provided on the side wall of the phase shifter of the phase shift mask a light shielding film which, due to its width, cannot be resolved as an exposure pattern itself. A region in which the light intensity is reduced from the constant level corresponding to the width of the light shielding film in the exposure pattern is formed by the projection lens. Therefore, a fine resist pattern having a predetermined width no more than the wavelength of the light used to form the pattern is produced precisely and reproducibly using constant developing conditions. As a result, semiconductor devices with good performance can be manufactured with high yield.

As semiconductor devices are highly integrated, a photlithographic technique for forming a fine resist pattern with high precision has been vigorously studied. For example, a technique capable of forming a pattern 0.3 micron or less wide on a substrate is required for a semiconductor element which operates at several tens of GHz. However, since the resist materials used as masks for etching are limited, light having a wavelength of 248 microns or longer has to be used. In this respect, the precision of a pattern is generally the same as the wavelength of light.
FIG. 9 is a view showing a reducing projection exposure apparatus which is generally used for such pattern formation. In the exposure apparatus, a wafer 15, on which a resist having a predetermined thickness is disposed, is put on a wafer stage 14 and light from an extra-high pressure mercury lamp as a light source passes through a photomask on which a predetermined mask pattern is formed, that is, a reticle 12 and then it is projected onto to the resist on the wafer 15 through a reducing projection lens 13. In addition, .theta..sub.1 designates an angle formed by the optical axis of the projection lens 13 and a line formed by connecting an intersecting point of the optical axis and the wafer to the radius of the exit pupil of the projection lens.
In general, the limit of resolution (R) of the reducing projection exposure apparatus is represented by the numerical aperture (NA=sin.theta..sub.1) of the projection lens and the wavelength (.gamma.) of light as shown in the following equation (1), where k.sub.1 is a constant indicating resist performance which is 0.612 in a case of a spherical projection lens according to a theory by Rayleigh. EQU R=k.sub.1 .gamma./NA (1)
In addition, when the resist pattern is actually formed, the depth of focus (DOF) shown in the following equation (2) is necessary for a curve or a step difference of the substrate. The DOF is generally set to 1.5 microns or more. In the equation (2), k.sub.2 is a constant. EQU DOF=k.sub.2 .gamma./(NA).sup.2 ( 2)
Meanwhile, it is thought that .gamma. may be decreased or NA may be increased according to the equation (1) in order to form a fine exposure pattern by the reducing projection exposure apparatus. However, when .gamma. is decreased, it becomes very difficult to make a lens and when the NA is increased, the DOF is reduced. Thus, there is a limit in forming the fine resist pattern in the exposure apparatus in addition to the resist material and it is difficult to actually form a pattern of at least the same resolution as the wavelength.
As described above, recently, a method for forming a resist pattern using a phase shift mask has been proposed as a methods of forming a fine resist pattern not restricted by the resist material and the exposure apparatus.
FIGS. 7(a) and 7(b) are views showing the structure and a principle of a phase shift mask, in which FIG. 7(a) is a sectional schematic view showing the structure of a phase shift mask and FIG. 7(b) is a graph showing a light intensity distribution on a surface perpendicular to an optical axis of a lens in a case where coherent light is partially applied to the phase shift mask shown in FIG. 7(a) and the diffracted light is focused by the lens. Referring to these figures, reference numeral 10 designates a phase shift mask which comprises a quartz substrate 2 and a phase shifter 1. In addition, in FIG. 7(b), the part where the light intensity is nearly 0 corresponds to an edge of the shifter 1.
Next, a method for forming a resist pattern using the phase shift mask will be described hereinafter.
The phase shift mask 10 is used as a reticle. When light from a light source is applied to a wafer on which a resist is applied by the reducing projection exposure apparatus shown in FIG. 9, the light from the light source is diffracted by an edge of the phase shifter 1 which comprises a wide resist towards a lower part of the phase shifter 1. Thus, a region in which a light intensity is lowered is only formed just under the edge of the phase shifter 1. Then, the transmitted light having the light intensity distribution shown in FIG. 7(b) is applied to the wafer on which the resist is present. Then, the resist on the wafer is subjected to pattern exposure and normal developing processing. As a result, a fine resist pattern having a precision which is one-half of the wavelength of the light can be formed. In addition, when a negative type resist is used as the resist on the wafer, an opening pattern is formed Just under the edge of the phase shift mask. Alternatively, when a positive type resist is used, the resist just under the edge of the phase shift mask is left on the wafer and a resist pattern in the form of a line is formed on the wafer.
FIGS. 8(a) and 8(b) are sectional views showing steps in manufacturing the phase shift mask. In these figures, the same references as those in FIGS. 7(a) and 7(b) designate the same or corresponding parts and reference numeral 1a designates a resist responsive to a negative type electron beam (referred to as an EB hereinafter) such as chloromethyl styrene. More specifically, as shown in FIG. 8(a), the resist 1a for the negative type EB is applied to the quartz substrate 2 and an EB exposure and developing process are normally performed. Then, as shown in FIG. 8(b), the resist 1a at an exposed region is left on the substrate 2 and then the phase shift mask 10 shown in FIG. 7(a) can be produced.
According to the conventional method for forming a resist pattern, the phase shift mask is used as a reticle and a fine exposure pattern is projected onto a resist and then the resist is developed. As a result, a fine resist pattern of a precision equal to or less than the wavelength of exposing light can be formed.
However, in the conventional resist pattern forming method using the phase shift mask, while a fine resist pattern of the same precision as the wavelength of light or less can be formed, an edge angle .theta..sub.2 of the phase shifter 1 varies in manufacturing the phase shift mask as shown in FIG. 8. Therefore, the light intensity distribution of the exposure pattern obtained through the phase shift mask 10 shown in FIG. 7(b) also varies, so that the contrast of the light intensity in the light intensity distribution can not be constant. Thus, in order to obtain a fine resist pattern having a predetermined width, the amount of development of the resist has to be controlled by changing the developing conditions, such as developing time each time in developing the resist after the exposure pattern is applied. However, since this process is very troublesome and can not be performed with high precision, the dimensions of the resist pattern still vary, so that it is very difficult to form the resist pattern having a predetermined width easily with high yield and reproducibility. Especially, when the contrast of the light intensity in the exposure pattern is reduced, the reactivity of the resist in the developing process is reduced. Therefore, if the amount of development of the resist is increased by increasing the developing time, the difference in the development of an upper layer and a lower layer of the resist is increased. For example, when an opening pattern is formed on the negative type resist, the opening becomes overhanging shape and the dimensional precision of the pattern is reduced. When such a resist pattern is used in the processing of the wafer thereafter, the processing dimensions vary and characteristics of the product can be adversely affected.


A shower plate of a processing gas supply unit disposed in a processing chamber of a substrate processing apparatus to supply a processing gas into a processing space in the processing chamber. The shower plate is interposed between a processing gas introduction space formed in the processing gas supply unit for introduction of the processing gas and the processing space. The shower plate includes processing gas supply passageways which allow the processing gas introduction space to communicate with the processing space. The processing gas supply passageways include gas holes formed toward the processing gas introduction space and gas grooves formed toward the processing space, the gas holes and gas grooves communicating with each other. A total flow path cross sectional area of all the gas grooves is larger than a total flow path cross sectional area of all the gas holes.

Generally, a substrate processing apparatus includes a chamber for accommodating a wafer serving as a substrate. The substrate processing apparatus performs a plasma process on the wafer by using plasma generated from a processing gas in a processing space in the chamber. The processing gas is supplied into the processing space in the chamber through a shower head disposed at an upper portion of the chamber.
FIGS. 10A and 10B schematically show a configuration of a shower head in a conventional substrate processing apparatus. FIG. 10A illustrates a cross sectional view of a conventional shower head. FIG. 10B illustrates a bottom view of the conventional shower head. Further, FIG. 10A illustrates a cross sectional view taken along a line 10A-10A of FIG. 10B.
As shown in FIGS. 10A and 10B, a shower head 90 includes a circular plate-shaped shower plate 91, a circular plate-shaped cooling plate 92 disposed on the shower plate 91 and a plate supporting body 93 for supporting the shower plate 91. The plate supporting body 93 is formed of a cylindrical member having a portion bored from the bottom. The shower plate 91 and the cooling plate 92 are received in the bored portion. The cooling plate 92 and the plate supporting body 93 form a space 94 between the cooling plate 92 and the plate supporting body 93. A processing gas is introduced into the space 94 from a processing gas inlet pipe 95. Further, the shower plate 91 faces a processing space (not shown) in the chamber.
The shower plate 91 and the cooling plate 92 have a plurality of gas holes 96 and 97 formed therethrough in their thickness directions, respectively. The space 94 communicates with the processing space via the gas holes 96 and 97. The processing gas introduced into the space 94 is supplied into the processing space through the gas holes 96 and 97. Further, since the gas holes 96 are arranged dispersedly as shown in FIG. 10B, the processing gas is also supplied dispersedly.
However, as known conventionally, plasma in the processing space flows into the gas holes 96 and 97 to cause abnormal discharge in the gas holes 96 and 97. When abnormal discharge occurs, alumite is peeled off from the cooling plate 92 to generate particles.
Accordingly, the gas holes of the shower plate or the cooling plate are formed in a labyrinthine shape to prevent plasma from flowing into the gas holes, thereby preventing abnormal discharge in the gas holes (see, for example, Japanese Laid-open Publication No. 2007-5491 and U.S. Patent Application Publication No. 2006/0288934 A1).
However, even though the gas holes are formed in a labyrinthine shape, when the shower plate is used for a while, abnormal discharge occurs in the gas holes.
In the shower plate 91 having the gas holes 96 in which abnormal discharge occurs, part of the gas holes 96 near to the processing space are expanded in a balloon shape as shown in FIG. 11. Accordingly, local discharge is generated in the gas holes 96, and the gas holes 96 are gradually eroded by the local discharge. If an expanded level of the gas holes 96 exceeds a certain value, it is assumed that abnormal discharge can occur therein.

Shower plate and substrate processing apparatus


A TFT 123 formed on a glass substrate 101 has a crystalline silicon film 108 that serves as an active region. The crystalline silicon film 108 is formed by forming an a-Si film 103 containing hydrogen on the glass substrate 101, thereafter adding nickel 104 to the surface of the a-Si film 103 and subjecting the a-Si film 103 to which the nickel 104 has been added to heat treatment. The crystal grain size of each crystal of the crystalline silicon film 108 is smaller than the size of the channel region of a TFT 123. With this arrangement, a high-performance semiconductor device that has stable characteristics with little characteristic variation and a high integration density and is simply fabricated with high yield can be provided.

The present invention relates to a semiconductor device that has an active region of a crystalline silicon film obtained by crystallizing an amorphous silicon film and a method for fabricating the device. The present invention is effective, in particular, for a semiconductor device that employs a thin film transistor (TFT) provided on a substrate having an insulating surface and is able to be utilized for an active matrix type liquid crystal display device, a contact-type image sensor, a three-dimensional IC and the like.
In recent years, there have been attempts to form a high-performance semiconductor device on an insulating substrate of glass or an insulating film for the achievement of a large-size high-resolution liquid crystal display device, a high-speed high-resolution contact-type image sensor, a three-dimensional IC and the like. It is general to use thin-film-shaped silicon semiconductors as semiconductor elements for use in these devices. The silicon semiconductors can be roughly categorized into the two types of an amorphous silicon semiconductor (a-Si) and a silicon semiconductor having crystallinity.
The amorphous silicon semiconductor, which can be relatively easily fabricated by the vapor deposition method at a low fabricating temperature and suitable for mass production, is most generally used. However, the amorphous silicon semiconductor has inferior physical properties of electrical conductivity and so on with respect to the silicon semiconductor having crystallinity. Therefore, in order to obtain a higher-speed characteristic, it is strongly demanded to establish a method for fabricating a semiconductor device made of a silicon semiconductor having crystallinity. As a silicon semiconductor having crystallinity, there are known polysilicon, microcrystal silicon, amorphous silicon including a crystalline component and semi-amorphous silicon having a state intermediate between the crystalline property and the amorphous property.
As a method for obtaining a silicon semiconductor having crystallinity, there are known the following methods (1) through (3).
(1) A method for directly forming a film having crystallinity in a film-forming stage
(2) A method for forming an amorphous semiconductor film and crystallizing the film by the energy of laser light
(3) A method for forming an amorphous semiconductor film and crystallizing the film by applying thermal energy
However, according to the aforementioned method (1), crystallization progresses concurrently with the film forming process. Therefore, in order to obtain a silicon film having crystals of a large grain size, it is indispensable to increase the thickness of the silicon film. It is technically difficult to uniformly form a silicon film having satisfactory semiconductor properties thoroughly on the entire surface of the substrate.
According to the aforementioned method (2), which utilizes the crystallization phenomenon through a melting and solidifying process, the grain boundaries are satisfactorily processed although the grain size is small, allowing a high-quality crystalline silicon film to be obtained. However, taking the excimer laser, which is currently most generally used, as an example, it is difficult to uniformly process the entire surface of a large-area substrate since the laser stability is not sufficient.
According to the aforementioned method (3), which is advantageous in terms of uniformity and stability inside the substrate by comparison with the methods (1) and (2), is used for a microminiature high-definition LCD panel employing a quartz substrate. However, in this case, after growing crystals through heat treatment at a temperature of 600xc2x0 C. for a long time of about 30 hours, the crystals are further subjected to heat treatment at an high temperature of about 1000xc2x0 C. for several tens of minutes to several hours for the promotion of improvement in crystallinity, and this results in a prolonged processing time and a degraded throughput. If a TFT is fabricated with this crystallized silicon film, then only the device characteristic of a field effect mobility of about 100 cm2/Vs can be obtained.
In order to solve the aforementioned problems, a method of an improvement of the aforementioned method (3) is disclosed in Japanese Patent Laid-Open Publication No. HEI 7-335905. This Japanese Patent Laid-Open Publication No. HEI 7-335905 discloses a reduction in heating temperature, a reduction in processing time and an improvement in crystallinity by utilizing a catalytic element that promotes the crystallization of the amorphous silicon film.
Specifically, a trace quantity of a metallic element of nickel, palladium or the like is introduced into the surface of the amorphous silicon film, and thereafter heat treatment is performed. With regard to the mechanism of low-temperature crystallization, the generation of a crystalline nucleus occurs in the early stage with the metallic element serving as the nucleus. Subsequently, the metallic element serves as a catalyst to promote the crystal growth for the rapid promotion of the crystallization, according to the understanding. In this sense, the aforementioned metallic element is referred to as a xe2x80x9ccatalytic elementxe2x80x9d hereinafter. By comparison with the twin crystal structure in one particle of the crystalline silicon film crystallized by the normal solid phase epitaxy, the crystalline silicon film that has undergone crystal growth with the catalytic element forms an aggregate of a number of columnar crystals, each of which has an almost ideal monocrystalline internal state.
According to the method of the aforementioned Japanese Patent Laid-Open Publication No. HEI 7-335905, crystals grow sidewise (in a direction parallel to the substrate) from the region into which the catalytic element is introduced by crystallizing only the region into which the catalytic element is selectively introduced with the other portion remaining in a state of an amorphous silicon film through selective introduction of the catalytic element into part of the amorphous silicon film and heating of the same and further prolonging the heating time.
Furthermore, according to the method of the aforementioned Japanese Patent Laid-Open Publication No. HEI 7-335905, the sidewise crystal growth distance is increased by forming the amorphous silicon film that is the start film to be crystallized by the low pressure CVD method, and the active region of the thin film transistor is formed by using the sidewise crystal growth region.
In contrast to this, the Japanese Patent Laid-Open Publication No. HEI 7-307286 discloses another example of the use of the catalytic element, or the use of the catalytic element for dehydrogenation in the amorphous silicon film.
Specifically, the dehydrogenating reaction in the amorphous silicon film is promoted by introducing the catalytic element into the amorphous silicon film containing hydrogen and heating the film at a low temperature of not higher than 550xc2x0 C., and thereafter, the amorphous silicon film is crystallized by laser light application. The dehydrogenation in the amorphous silicon film is thus promoted and thereafter the amorphous silicon film is crystallized by laser light application. Therefore, the film exfoliation is hard to be caused by rapid dehydrogenation of the silicon film even if the laser light application is performed, and a crystalline silicon film having uniform crystallinity is obtained.
As disclosed in the aforementioned Japanese Patent Laid-Open Publication No. HEI 7-335905 and the Japanese Patent Laid-Open Publication No. HEI 7-307286, the crystalline silicon film obtained by introducing the catalytic element into the amorphous silicon film and crystallizing the film through heat treatment is excellent in terms of crystallinity. In particular, the crystal orientation is closer to the conventional monocrystal than the polycrystal. Through confirmation with a TEM (Transmission Electron Microscope), the present inventor has obtained a distinct diffraction pattern that exhibits a monocrystal state even in a wide range of selected area of a diameter of 25 xcexcm.
The above is because a crystalline silicon film fabricated with a catalytic element has undergone a definitely different peculiar crystal growth from that of a crystalline silicon film fabricated by the conventional solid phase epitaxy method that has a very low nucleus incident rate and causes only the temporary generation of a crystalline nucleus. Therefore, in the crystalline silicon film fabricated with the catalytic element, the crystal grain grown from each crystalline nucleus grows very large to have a grain size of up to 10 xcexcm to 30 xcexcm. The crystal particle is normally called the grain. However, there exist a number of more minute particles inside the crystal grain grown as a crystal from an identical nucleus, and therefore, the crystal grain is referred to as a domain hereinafter.
If a plurality of TFT""s are fabricated with such a crystalline silicon film, then the particle diameter of each domain is very large and randomly exist. Accordingly, there are included TFT""s fabricated inside the domain and TFT""s fabricated across the grain boundaries. Therefore, if a TFT is fabricated inside the domain, a high-performance TFT is obtained. However, if a TFT is fabricated across the grain boundary, the TFT has an inferior ability. This consequently causes a problem that the TFT characteristics (mobility, threshold voltage value, etc.) vary within the crystalline silicon film.
As proposed in Japanese Patent Laid-Open Publication No. HEI 7-335905, this problem seems to be simply solved by the method of selectively introducing the catalytic element into the amorphous silicon film and growing a crystal sidewise from the region into which the catalytic element has been introduced. However, according to this method, the characteristic variation becomes more significant. The above is because nuclei randomly occur in the region into which the catalytic element has been introduced before the sidewise crystal growth, and the domain grown from each nucleus merely progresses further sidewise. Therefore, domains elongated in the direction of growth exist along the direction of growth in the region to be used as a TFT active region, and therefore, it is sometimes the case where a TFT is fabricated across the grain boundary. This consequently varies the TFT characteristics.
It is to be noted that the domain mentioned in connection with the present invention emerges as a stepped portion by etching the Si surface with hydrofluoric acid or oxidizing the Si surface, and the domain can also be confirmed as a difference in contrast by an optical microscope.
Accordingly, the object of the present invention is to provide a stable high-performance semiconductor device having little characteristic variation and a high-performance semiconductor device having a high integration density. Another object is to provide a semiconductor device fabricating method capable of simply fabricating such a semiconductor device with high yield.
In order to achieve the above object, there is provided a semiconductor device comprising a plurality of thin film transistors formed with a silicon film having crystallinity serving as an active region on a substrate having an insulating surface,
the silicon film being a polysilicon including a catalytic element for promoting crystallization of the silicon film itself, and the silicon film having a constituent crystal grain size smaller than a size of a channel region of each of the thin film transistors.
The silicon film crystallized with the catalytic element has a crystalline structure of an aggregate of columnar crystals from a microscopic viewpoint as described above. The silicon film structure itself reduces the defects inside the crystal grain. If the silicon film is used for the active regions (source/drain region and channel region) of the thin film transistor, then a high current driving ability is provided. In order to reduce the characteristic variation between elements while keeping this high current driving ability, the grain boundary is required to be controlled. However, it is theoretically required to perform control at the microscopic level, which is impossible.
Therefore, according to the semiconductor device of the above constitution, it has been discovered that the above object can be achieved by constructing the active regions of a plurality of thin film transistors of the crystalline silicon film including the catalytic element for promoting the crystallization and setting the crystal grain size of each crystal in the crystalline silicon film smaller than the size of the channel region of each thin film transistor. That is, by setting the size of crystal grain constituting the crystalline silicon film smaller than the size of the channel region formed in the thin film transistor, the characteristic variation of the thin film transistor can be remarkably improved.
In particular, the active matrix substrate for liquid crystal display use or the like is required to have higher characteristic uniformity since the characteristic variations of the thin film transistors for driving the pixel electrodes appear as a display unevenness. Therefore, by applying the present invention to the active matrix substrate or the like, a device of sufficient display quality can be obtained, and a driver monolithic structure in which a driver circuit is concurrently formed in the peripheral portion can be provided.
In one embodiment of the present invention, the constituent crystal grain size of the silicon film is not greater than 5 xcexcm.
In this constitution, the crystal grain size of each polysilicon including the catalytic element should preferably be not greater than 5 xcexcm. It has been discovered that the characteristic variations of the normally formed thin film transistors can be more surely reduced if the crystal grain size is within this range.
If the crystal grain size of the silicon film is greater than 5 xcexcm, then the thin film transistors are sometimes fabricated across the grain boundaries, increasing the characteristic variations of the thin film transistors.
In one embodiment of the present invention, the catalytic element is the element of nickel and the concentration of the element of nickel in the silicon film is within a range of 1xc3x971016 to 1xc3x971018 atoms/cm3.
In this constitution, the catalytic element to be contained in the silicon film that constitutes the active regions of the thin film transistors should preferably be the element of nickel. That is, it has been discovered that the element of nickel can form a silicon film of the best crystallinity among catalytic elements.
It has also been discovered that a silicon film of satisfactory crystallinity can be formed by setting the catalytic element concentration in the silicon film to 1xc3x971016 to 1xc3x971018 atoms/cm3.
If the catalytic element concentration in the silicon film is lower than 1xc3x971016 atoms/cm3, then the effect of sufficient crystal growth cannot be obtained since the concentration is less than the solubility limit.
If the catalytic element concentration in the silicon film becomes higher than 1xc3x971010 atoms/cm3, then the device characteristics receive bad influence to cause an increase in leak current or the like.
Also, there is provided a semiconductor device fabricating method comprising:
a process for forming an amorphous silicon film containing hydrogen on a substrate having an insulating surface;
a process for adding to a surface of the amorphous silicon film a catalytic element for promoting crystallization of the amorphous silicon film; and
a process for crystallizing the amorphous silicon film by subjecting the amorphous silicon film to which the catalytic element has been added to heat treatment.
According to the semiconductor device fabricating method, the amorphous silicon film containing hydrogen is formed on the substrate having the insulating surface, and thereafter, the catalytic element for promoting the crystallization is added to the amorphous silicon film containing hydrogen. If the amorphous silicon film to which the catalytic element has been added is subjected to heat treatment, then the crystal growth starts from the upper surface side of the amorphous silicon to crystallize the amorphous silicon film. As a result, the crystallized silicon film has a satisfactory crystalline structure of a columnar crystal network structure, and the grain size of individual crystal becomes minute. That is, the intended crystalline silicon film of the present invention is obtained. By employing such a crystalline silicon film, the TFT characteristic variation inside the substrate is improved to allow a semiconductor device having excellent characteristic uniformity to be provided.
Also, there is provided a semiconductor device fabricating method comprising:
a process for adding a catalytic element for promoting crystallization of an amorphous silicon film to a substrate having an insulating surface;
a process for forming the amorphous silicon film containing hydrogen on the surface which belongs to the substrate and to which the catalytic element has been added; and
a process for crystallizing the amorphous silicon film by subjecting the amorphous silicon film to heat treatment.
According to the semiconductor device fabricating method, the catalytic element for promoting the crystallization of the amorphous silicon film is added to the substrate having an insulating surface, and thereafter, the amorphous silicon film containing hydrogen is formed on the surface of the substrate to which the catalytic element is added. The, upon subjecting the amorphous silicon film to heat treatment, crystal growth starts from the lower surface side of the amorphous silicon to crystallize the amorphous silicon film. As a result, the crystallized silicon film has a crystalline structure of a satisfactory columnar crystal network structure, and the grain size of individual crystal becomes minute. That is, the intended crystalline silicon film of the present invention is obtained. By employing such a crystalline silicon film, the TFT characteristic variation inside the substrate is improved to allow a semiconductor device having excellent characteristic uniformity to be provided.
In one embodiment of the present invention, the hydrogen concentration in the amorphous silicon film is within a range of 3 to 25 atomic percent.
The semiconductor device fabricating method of the embodiment is based on the following phenomenon discovered by the present inventor. According, to the examination carried out by the present inventor, it has been discovered that the hydrogen in the amorphous silicon film exerts a great influence on the crystal form. That is, the crystal grain size of the crystalline silicon film obtained through the heat treatment after the addition of the catalytic element drastically changes across a specified value depending on the concentration of hydrogen contained in the amorphous silicon film.
FIG. 9 is a graph showing a relation between the hydrogen concentration in the initial amorphous silicon film and the crystal grain size of the silicon film crystallized by the catalytic element. In this case, the element of nickel is used as the catalytic element. Despite that the concentration of the element of nickel is set identical (5xc3x971012 atoms/cm2 by the concentration in the surface after addition), as shown in FIG. 9, the crystal grain size abruptly increases when the hydrogen concentration is reduced to a value under a specified value. This threshold value is about 3 to 5 atomic %.
FIG. 10A is a view of an optical microscope photograph of the surface state of a crystalline silicon film obtained by crystallizing an amorphous silicon film having a hydrogen concentration of not higher than 3 atomic %. As shown in FIG. 10A, if the hydrogen concentration in the amorphous silicon film is not higher than 3 atomic %, then a very large crystal grain that exceeds a grain size of 30 xcexcm is observed. FIG. 10B is a view of an optical microscope photograph of the surface state of a crystalline silicon film obtained by crystallizing an amorphous silicon film having a hydrogen concentration of about 10 atomic %. FIG. 10A and FIG. 10B have an identical magnification ratio. If the hydrogen concentration in the amorphous silicon film is about 10 atomic %, then the crystal grain is very small, and as shown in FIG. 10B, it is very difficult to confirm the crystal grain size by an optical microscope. According to the observation by TEM, the crystal grain size was about 1 to 2 xcexcm.
As described above and apparent from the curve of the graph of FIG. 9, the crystal growth states shown in FIGS. 10A and 10B have quite different growth modes rather than on the extension of change in hydrogen concentration. Then, the threshold value across which the growth mode changes exists within the hydrogen concentration range of 3 to 5 atomic %. If the hydrogen concentration in the amorphous silicon film is lower than the threshold value of 3 atomic %, then the growth from each nucleus is great and a gigantic crystal grain is formed although the density of occurrence of crystalline nuclei is extremely reduced. If the hydrogen concentration in the amorphous silicon film exceeds the threshold value of 5 atomic %, then the growth from each nucleus is little and the crystal grain becomes minute although the density of occurrence of crystalline nuclei is extremely increased. In either case, the density of occurrence of crystalline nuclei is changed by the concentration of the added catalytic element. However, the changes are limited in the respective modes, and a decisive difference depending on the change in hydrogen concentration in the amorphous silicon film can be observed at whatever catalytic element concentration.
Of course, the addition of the catalytic element should preferably be little considering the influence on the semiconductor. However, if the addition of the catalytic element is little, then an uncrystallized region remains in the crystalline silicon film as shown in FIGS. 10A and 10B, degrading the semiconductor characteristics. How the uncrystallized region remains largely depends on the difference in hydrogen concentration in the amorphous silicon film. In the case of the low hydrogen concentration in FIG. 10A, the uncrystallized region remains in a large region in correspondence with the giganticness of the crystal grain. Strangely enough, the occurrence of a crystalline nucleus in this uncrystallized region is not observed at all. In the case of the high hydrogen concentration in FIG. 10B, where the crystalline nuclei are minute and the density of occurrence of the crystalline nuclei is high, if the uncrystallized region remains at the same areal rate as that in the case of FIG. 10A, then the individual uncrystallized regions are small and uniformly dispersed inside the film. Not only the nonuniformity simply attributed to the crystal grain but also how the uncrystallized region remains exert a great influence on the semiconductor characteristic variation. Particularly when it is desired to restrain the catalytic element, the low hydrogen concentration is not permitted in terms of uniformity. In contrast to this, when the hydrogen concentration is within the range of 3 to 25 atomic %, as proposed by the present invention, there is no problem in terms of device characteristic uniformity even if the uncrystallized region remains a little so long as the uncrystallized region is crystallized through the subsequent heat treatment.
The mechanism of the occurrence of the above phenomenon is not clearly discovered. Although conjectural, the following mechanism can be considered. The catalytic element has already been diffused in a metal state in the amorphous silicon film before the crystallization (during temperature increase) of the amorphous silicon film. The catalytic element in the metal state causes reaction in the amorphous silicon film to form a silicide. In the silicified location, the crystallization of the amorphous silicon film progresses. The crystallization will be described depending on cases in which the hydrogen concentration is low and is high.
If the hydrogen concentration in the amorphous silicon film is low, taking the state of occurrence of the crystalline nucleus in the amorphous silicon film into consideration, the added catalytic element moves in the amorphous silicon film to cause crystallization, and therefore, aggregates in excess of a specified amount are formed in spots here and there. Then, each of these aggregates becomes a nucleus to form a gigantic crystal grain. Therefore, almost no catalytic element exists between the adjoining nuclei, and no new nucleus occurs there.
If the hydrogen concentration in the amorphous silicon film is high, it is presumed that hydrogen is preventing the movement of the catalytic element. Consequently, the catalytic element contributes to the crystallization in the originally added state without movement. As a result, crystalline nuclei uniformly occur in the amorphous silicon film, and minute crystal particles are uniformly formed without growing large since the quantity of catalytic element in each crystalline nucleus is small.
Therefore, as described above, in order to achieve the objects of the present invention, the hydrogen concentration in the amorphous silicon film that contains hydrogen is required to be not lower than 3 atomic %. In contrast to this, the upper limit of the hydrogen concentration is based at least on the condition that the film exfoliation of the silicon film should not be caused by the release of a large amount of hydrogen from the silicon film through the heat treatment for the crystallization of the amorphous silicon film. From this point of view, the hydrogen concentration should preferably be not higher than 25 atomic %. Therefore, by setting the hydrogen concentration in the amorphous silicon film within a range of 3 to 25 atomic %, the occurrence of crystalline nuclei such that minute crystal particles are uniformly formed is caused to allow the characteristic variation of the thin film transistor to be more surely reduced. If the hydrogen concentration in the amorphous silicon film is lower than 3 atomic %, then it is sometimes the case where a gigantic crystal grain is formed and a thin film transistor is fabricated across the grain boundary, causing the characteristic variation of the thin film transistors. If the hydrogen concentration in the amorphous silicon film exceeds 25 atomic %, then the film exfoliation is caused by the release of a large amount of hydrogen from the silicon film, exerting a bad influence on the device characteristics of the thin film transistors.
In one embodiment of the present invention, the amorphous silicon film is formed by a plasma CVD method at a heating temperature of not higher than 400xc2x0 C.
According to the semiconductor device fabricating method of the embodiment, by forming an amorphous silicon film at a heating temperature of not higher than 400xc2x0 C. by the plasma CVD method, the hydrogen concentration in the amorphous silicon film can be formed roughly uniformly within the aforementioned specified range, and this allows the method to be applied also to a large-area substrate with good repeoducibility.
In one embodiment of the present invention, the element of nickel is used as the catalytic element.
According to the semiconductor device fabricating method of the embodiment, it has been discovered that a crystallization promoting effect can be produced with a trace quantity of one sort or a plurality of sorts of the elements of Ni, Co, Pd, Pt, Cu, Ag, Au, In, Sn, Al and Sb and, in particular, the most remarkable crystallization promoting effect can be obtained when nickel (Ni) is employed. The reason for the above can be given by the following model. The element of nickel does not singly effect but produces the crystal growth effect by being silicified through bonding with the amorphous silicon film. The crystalline structure in the above stage effects as a sort of mold when the amorphous silicon film is crystallized, promoting the crystallization of the amorphous silicon film. The element of nickel forms a silicide of NiSi2 reacting with two silicon (Si) elements. This NiSi2 has a fluorite type crystal structure, and the crystalline structure bears a close resemblance to the diamond structure of single crystal silicon. Furthermore, the aforementioned NiSi2 has a lattice constant of 5.406 xc3x85, which is very close to the lattice constant of 5.430 xc3x85 of the diamond structure of the crystal silicon. Therefore, the aforementioned NiSi2 is the ultimate one as a mold for crystallizing the amorphous silicon film and able to mostly promote the crystallization of the amorphous silicon film.
In one embodiment of the present invention, after the addition of the element of nickel to the surface of the amorphous silicon film or the surface of the substrate, the nickel concentration of the surface is within a range of 1xc3x971012 to 5xc3x971013 atoms/cm
According to the semiconductor device fabricating method of the embodiment, it has been discovered that setting the nickel concentration on the surface to 1xc3x971012 to 5xc3x971013 atoms/cm2 after the addition of nickel to the surface of the amorphous silicon film or the surface of the substrate is preferable in forming a silicon film of satisfactory crystallinity.
If the nickel-concentration is lower than 1xc3x971012 atoms/cm2, then the amorphous silicon film is not crystallized since the minimum concentration that causes the crystallization is not lower than 1xc3x971012 atoms/cm2.
If the nickel concentration exceeds 5xc3x971013 atoms/cm2, then the influence of nickel remaining in the grain boundaries increases to exert a bad influence on the semiconductor characteristics. Specifically, the leak current in the turning-off stage increases in the thin film transistor, and this causes the characteristic variations of the thin film transistors.
In one embodiment of the present invention, the process for adding the element of nickel to the surface of the amorphous silicon film or the surface of the substrate is performed by spin coating a nickel solution on the surface of the amorphous silicon film or the surface of the substrate.
According to the semiconductor device fabricating method of the embodiment, the method of spin coating a nickel solution on the surface of the amorphous silicon film or the surface of the substrate is effective as a method for adding the element of nickel to the surface of the amorphous silicon film or the surface of the substrate.
According to this method, by performing spin coating with a solution in which nickel is dissolved, the nickel concentration in the solution is controlled to enable the trace quantity control of nickel to be introduced into the surface of the amorphous silicon film or the surface of the substrate.
In the solution in which nickel is dissolved according to the above method, it is preferable to employ acetate or nitrate of nickel as a solute and employ an alcohol-based material of ethanol or isopropyl alcohol (IPA) as a solvent. By employing a solution constructed of the above solute and solvent, a stabilized crystal growth can be obtained on the entire surface of the amorphous silicon film. Particularly on a large-size substrate of a liquid crystal display device or the like, excellent film quality can be obtained with uniformity throughout the entire substrate surface.
In one embodiment of the present invention, the process for adding the element of nickel to the surface of the amorphous silicon film or the surface of the substrate is performed by DC sputtering the element of nickel at a low voltage.
According to the semiconductor device fabricating method of the embodiment, by adding nickel to the surface of the amorphous silicon film or the surface of the substrate by DC sputtering at a low voltage, very good uniformity is obtained and particles and the like scarcely cause the nonuniformity of crystal growth although the method is inferior to the spin coating method in terms of trace control at a low concentration.
The reason why the term of xe2x80x9cadditionxe2x80x9d is intentionally used instead of xe2x80x9cfilm formationxe2x80x9d is that the sputtering is performed by such a trace quantity that it is insufficient for film formation.
In one embodiment of the present invention, the heating process for crystallizing the amorphous silicon film has a first step for releasing excessive hydrogen existing in the amorphous silicon film and a second step intended for crystal growth of the amorphous silicon film.
According to the semiconductor device fabricating method of the embodiment, the heat treatment for crystallizing the amorphous silicon film containing hydrogen should preferably be performed in the two steps of the first-step heat treatment for releasing the excessive hydrogen existing in the amorphous silicon film and the second-step heat treatment intended for the crystal growth in the amorphous silicon film. This is because the above arrangement allows the elimination of film exfoliation that might occur when the heat treatment intended for the achievement of crystallization is abruptly performed, by performing the first-step heat treatment and thereafter performing the second-step heat treatment intended for crystallization.
In this case, the crystallization performed by extracting hydrogen from the amorphous silicon film seems to be contradictory to the purport of the present invention. However, the hydrogen concentration in the amorphous silicon film in the catalytic element adding stage is important according to the present invention, and the dehydrogenating process performed after the catalytic element addition does not matter. Although the reasons for the above have not been clearly discovered, there has been obtained the reality that the dehydrogenating process performed after the catalytic element addition does not matter also through experiments.
In one embodiment of the present invention, the heating process of the first step is performed within a temperature range of 450xc2x0 C. to 530xc2x0 C., and the heating process of the second step is performed within a temperature range of 530xc2x0 C. to 650xc2x0 C.
According to the semiconductor device fabricating method of the embodiment, the first-step heat treatment should preferably be performed within the temperature range of 450xc2x0 C. to 530xc2x0 C. in reducing the hydrogen concentration in the amorphous silicon film. The above is because the temperature range of 400 to 450xc2x0 C. is the boundary considered from the energy of bonding of hydrogen to silicon and also from the experimental evidence, and the effective dehydrogenating effect can be practically obtained only at a temperature of not lower than 450xc2x0 C. That is, if the first-step heat treatment is performed at a temperature lower than 450xc2x0 C., then no effective dehydrogenating effect can be obtained on the amorphous silicon film containing hydrogen. If the heat treatment temperature in the first step becomes higher than 530xc2x0 C., then the dehydrogenation rate is increased, as a consequence of which the film exfoliation of the silicon film tends to easily occur. Furthermore, if the heat treatment temperature in the first step becomes higher than 530xc2x0 C., then the crystallization of the amorphous silicon film is started by the effect of the catalytic element, and therefore, the temperature in the first step is required to be not higher than 530xc2x0 C. Therefore, the hydrogen in the amorphous silicon film is required to be released slowly and sufficiently through the first-step heat treatment.
The second-step heat treatment should preferably be performed within the temperature range of 530xc2x0 C. to 650xc2x0 C. in crystallizing the amorphous silicon film. The temperature that causes the crystallization of the amorphous silicon film is required to be not lower than 530xc2x0 C. That is, if the temperature in the second step is lower than 530xc2x0 C., then the amorphous silicon film cannot be crystallized. However, if the temperature is excessively high, then the crystallization rate is so fast that the crystal defects of dislocation and the like frequently occur. Therefore, the upper limit of the temperature in the second step becomes about 650xc2x0 C. That is, if the heating temperature in the second step exceeds 650xc2x0 C., then the crystal defects of dislocation and the like frequently occur.
In one embodiment of the present invention, the semiconductor device fabricating method further comprises a process, which is to be performed after the crystallization of the amorphous silicon film through heat treatment, for moving most of the catalytic element remaining in the crystallized silicon film toward a region outside a region in which a semiconductor element is to be formed.
The semiconductor device fabricating method of the present invention is considerably characterized in that the amorphous silicon film is crystallized by the catalytic element. However, even with a trace quantity of addition, the existence of such a metal element in the semiconductor film itself is unfavorable.
Therefore, the semiconductor device fabricating method of the embodiment prevent the catalytic element from exerting a bad influence on the semiconductor element with the provision of the process for moving most of the catalytic element remaining in the silicon film to a region other than the semiconductor element forming region after the catalytic element is utilized for the crystallization process of the amorphous silicon film.
In one embodiment of the present invention, the semiconductor device fabricating method further comprises a process, which is to be performed after the crystallization of the amorphous silicon film through heat treatment, for further promoting the crystallinity of the silicon film by applying laser light to the crystallized silicon film.
According to the semiconductor device fabricating method of the embodiment, the method of crystallizing the amorphous silicon film containing hydrogen through heat treatment and thereafter further promoting the crystallinity of the silicon film by the application of laser light to the crystallized silicon film is effective as a method for improving the semiconductor device performance or, in particular, the current drive ability by improving the crystallinity of the silicon film crystallized by the catalytic element. The reasons for the above will be described below.
When intense light of laser or the like is applied to the crystallized silicon film, the grain boundaries are intensively processed due to the difference in melting point between the crystalline silicon film and the amorphous silicon film. However, in the crystalline silicon film formed by the normal solid phase epitaxy method, the crystalline structure is in the twin crystal state, and therefore, the inside of the crystal grain remains as a twin crystal defect after the application of intense light. In contrast to the above, the crystalline silicon film crystallized by the catalytic element is formed of columnar crystals, and the inside of the crystalline silicon film is in a single crystal state. Therefore, if the grain boundaries are processed by the application of intense light, then a crystalline silicon film of a good quality close to the single crystal state throughout the entire surface is obtained. That is, the method of crystallizing the amorphous silicon film containing hydrogen through heat treatment and thereafter further promoting the crystallinity of the silicon film by the application of laser light to the crystallized silicon film is very effective in terms of crystallinity. Laser light is applied to the silicon film that originally has crystallinity, and therefore, variation in laser light application is largely alleviated in contrast to the method of performing crystallization by directly applying laser light to the amorphous silicon film, causing no problem about uniformity.
The laser light to be used in this stage has a very high absorption coefficient with respect to the silicon film so long as the wavelength is not longer than 400 nm, allowing only the silicon film to be instantaneously heated without giving any thermal damage to the substrate of glass or the like. In particular, the XeCl excimer laser having a wavelength of 308 nm has a great output. Therefore, the beam size at the time of application to the substrate can be increased, and this allows the laser to easily cope with a large-area substrate. The output is relatively stabilized, which is desirable for the application to a mass-production apparatus. By applying the above-mentioned laser light to the surface of the silicon film in a manner that the radiation energy density of the laser light becomes 200 to 450 mJ/cm2, the crystallinity of the silicon film crystallized by the catalytic element is promoted to allow a crystalline silicon film of a very high quality to be obtained. If the radiation energy density of the laser light is smaller than 200 mJ/cm2, then the silicon film is scarcely melted, as a consequence of which the promotion of crystallinity cannot sufficiently be achieved. If the radiation energy density is greater than 450 mJ/cm2, then the crystallinity obtained by the catalytic element is completely lost or reset, causing the problem of nonuniformity observed in the conventional laser crystallization.
In one embodiment of the present invention, the semiconductor device fabricating method further comprises a process, which is to be performed after the crystallization of the amorphous silicon film through heat treatment, for further promoting the crystallinity of the silicon film by subjecting the crystallized silicon film to heat treatment at an elevated temperature higher than the heat treatment temperature in an oxidizing atmosphere.
According to the semiconductor device fabricating method of the embodiment, the method of crystallizing the amorphous silicon film containing hydrogen through heat treatment and thereafter further promoting the crystallinity by performing heat treatment in an oxidizing atmosphere at a temperature higher than the heat treatment temperature is also effective as another method for improving the crystallinity of the silicon film crystallized by the catalytic element to further improve the performance, or, in particular, the current drive ability of the semiconductor device. If the silicon film crystallized by the catalytic element is subjected to heat treatment in an oxidizing atmosphere at a high-temperature (for example, 800xc2x0 C. to 1100xc2x0 C.), then oversaturated Si atoms caused by the oxidizing operation are supplied to the silicon film. As a result, the oversaturated Si atoms enter the crystal defects (in particular, dangling bond) in the silicon film, allowing the defects to be removed. Therefore, the density of defects in the silicon film crystallized by the catalytic element is remarkably reduced and the mobility is remarkably improved, allowing the semiconductor device performance to be remarkably improved.

Semiconductor device and method for fabricating the device