Crystallization method, crystallization apparatus, processed substrate, thin film transistor and display apparatus Number:7,410,848 from the United States Patent and Trademark Office (PTO) owispatent There are provided a crystallization method which can design laser beam having a light intensity and a distribution optimized on an incident surface of a substrate, form a desired crystallized structure while suppressing generation of any other undesirable structure area and satisfy a demand for low-temperature processing, a crystallization apparatus, a thin film transistor and a display apparatus. When crystallizing a non-single-crystal semiconductor thin film by irradiating laser beam thereto, irradiation light beam to the non-single-crystal semiconductor thin film have a light intensity with a light intensity distribution which cyclically repeats a monotonous increase and a monotonous decrease and a light intensity which melts the non-single-crystal semiconductor. Further, at least a silicon oxide film is provided on a laser beam incident surface of the non-single-crystal semiconductor film.<H crystallization, Crystallization, Crystallization, 7410848.html, Patent, pto, 7410848

Title: Crystallization method, crystallization apparatus, processed substrate, thin film transistor and display apparatus

Abstract: There are provided a crystallization method which can design laser beam having a light intensity and a distribution optimized on an incident surface of a substrate, form a desired crystallized structure while suppressing generation of any other undesirable structure area and satisfy a demand for low-temperature processing, a crystallization apparatus, a thin film transistor and a display apparatus. When crystallizing a non-single-crystal semiconductor thin film by irradiating laser beam thereto, irradiation light beam to the non-single-crystal semiconductor thin film have a light intensity with a light intensity distribution which cyclically repeats a monotonous increase and a monotonous decrease and a light intensity which melts the non-single-crystal semiconductor. Further, at least a silicon oxide film is provided on a laser beam incident surface of the non-single-crystal semiconductor film.

Patent Number: 7,410,848 Issued on 08/12/2008 to Jyumonji, et al.

Inventors: Jyumonji; Masayuki (Yokohama, JP), Ogawa; Hiroyuki (Yokohama, JP), Matsumura; Masakiyo (Yokohama, JP), Hiramatsu; Masato (Yokohama, JP), Kimura; Yoshinobu (Yokohama, JP), Taniguchi; Yukio (Yokohama, JP), Kato; Tomoya (Yokohama, JP)
Assignee: Advanced LCD Technologies Development Center Co., Ltd. (Yokohama, JP)

Appl. No.: 10/878,331

Filed: June 29, 2004

Foreign Application Priority Data


Jun 30, 2003 [JP]			2003-189093
Jul 08, 2003 [JP]			2003-193779
Sep 01, 2003 [JP]			2003-308935
Dec 01, 2003 [JP]			2003-402197
Mar 26, 2004 [JP]			2004-093200

Current U.S. Class: 438/166 ; 257/E21.561

Current International Class: H01L 21/84 (20060101)

Field of Search: 438/151-166 257/E21.561

References Cited [Referenced By]

U.S. Patent Documents


5424230	June 1995	Wakai
6393042	May 2002	Tanaka
6734635	May 2004	Kunii et al.
2002/0047580	April 2002	Kunii et al.

Foreign Patent Documents


1407601	Apr., 2003	CN
2003-178979	Jun., 2003	JP

Other References

Wenchang Yeh, et al., "Proposed Sample Structure for Marked Enlargement of Excimer-Laser-Induced Lateral Grain Growth in Si Thin Films", Jpn. J. Appl. Phys., vol. 41, Part 1, No. 4A, Apr. 2002, pp. 1909-1914. cited by other .
M. Matsumura, "Advanced Laser-Crystallization Technologies of Si for High-Performance TFTs", The Ninth International Display Workshops (IDW'02) Proceedings, pp. 263-266. cited by other .
Masato Hiramatsu, et al., "Effect of Stacked Capping Layer for Phase-Modulated Excimer Laser Crystallization Method", Japan Society of Applied Physics, the 63.sup.rd academic lecture in autumn 2002, preliminary manuscript correction 2, pp. 779, 26a-G-2. cited by other .
Minhong Lee, et al., "Relationship Between Fluence Gradient and Lateral Grain Growth in Spatially Controlled Excimer Laser Crystallization of Amorphous Silicon Films", Journal of Applied Physics, vol. 88, No. 9, Nov. 1, 2000, pp. 4994-4999. cited by other .
Chang-Ho Oh, et al., "Optimization of Phase-Modulated Excimer-Laser Annealing Method for Growing Highly-Packed Large-Grains in Si Thin-Films", Applied Surface Science 154-155, 2000, pp. 105-111. cited by other .
Satoshi Yoshimoto, et al., "A New Sample Structure for Position-Controlled Giant-Grain Growth of Silicon Using Phase-Modulated Excimer-Laser Annealing", Jpn. Appl. Phys., vol. 40, Part 1, No. 7, Jul. 2001, pp. 4466-4469. cited by other .
Y. Sano, et al., "Highly Packed and Ultra-Large Si Grains Grown By a Single-Shot Irradiation of Excimer-Laser Light Pulse", Electrochemical Society Proceedings, vol. 2000-31, pp. 261-268. cited by other .
Wen-Chang Yeh, et al., "Preparation of Giant-Grain Seed Layer for Poly-Silicon Thin-Film Solar Cells", Jpn. J. Appl. Phys., vol. 38, Part 2, No. 2A, Feb. 1, 1999, pp. L110-L112. cited by other .
Chang-Ho Oh, et al., "Preparation of Position-Controlled Crystal-Silicon Island Arrays by Means of Excimer-Laser Annealing", Jpn. J. Appl. Phys., vol. 37, Part 1, No. 10, Oct. 1998, pp. 5474-5479. cited by other .
Mitsuru Nakata, et al., "A New Nucleation-Site-Control Excimer-Laser-Crystallization Method", Jpn. J. Appl. Phys., vol. 40, Part 1, No. 5A, May 2001, pp. 3049-3054. cited by other .
Yoshinobu Kimura, et al., "Microscopic Beam Profile and its Relationship With the Morphology of Poly-Si Film Grown Laterally by a Phase-Modulated Excimer-Laser Crystallization Method", 22.sup.nd Meeting of the Electrochemical Society (Salt Lake City, U.S.A.) (7 pgs), 2001. cited by other .
M Jyumonji, et al., "High-Resolution Beam Profiler New Powerful Tool for Engineering Laterally-Grown Grain Morphology", IDW '02, pp. 1387-1388. cited by other .
"Separate-Volume Flat Panel Display 1999", Nikkei Microdevices, Nikkei Business Publications, Inc., 1998, pp. 132-139. cited by other .
Masakiyo Matsumura, "Silicon Thin Film Having Giant Crystal Grains and Formed by Light Irradiation Using Excimer Laser", Ouyobuapplied Surface Science 154-155 (2000), pp. 543-547. cited by other .
Kohki Inoue, et al., "Amplitude and Phase Modulated Excimer-Laser Melt-Regrowth Method of Silicon Thin-Films a New Growth Method of 2-D Position-Controlled Large-Grains", Ouyobuapplied Surface Science 154-155, C vol. J85-C, No. 8, 2002, pp. 624-629. cited by other.

Primary Examiner: Booth; Richard A.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier & Neustadt, P.C.

Claims

What is claimed is:

1. A projection type crystallization method for a non-single-crystal semiconductor film, comprising: homogenizing pulse laser light by making the pulse laser beam incident on a homogenizer, in which the pulse laser beam is transformed into a plurality of light fluxes incident at different angles, and emitting pulse laser beam homogenized in light intensity by these plurality of light fluxes; modulating the pulse laser beam by making the plurality of the light fluxes of the different angles incident on a phase modulation optical system including a plurality of phase modulation sections to form a repetitious pattern in which the light intensity of the pulse laser beam homogenized in the homogenizing repeats a monotonous increase and a monotonous decrease, in a light intensity distribution in which maximum peaks of the light intensity of the repetitious pattern are equal to each other and so are minimum peaks, and emitting the modulated pulse laser beam therefrom; melting the non-single-crystal semiconductor film of an image-forming region, the image-forming region being formed as the pulse laser beam modulated in the modulating, forms an image on the laser beam incident surface by an image formation optical system; and crystallizing the image formation region melted with the pulse laser beam in a lateral direction.

2. The crystallization method according to claim 1, further comprising: providing a cap film on the laser beam incident surface of the non-single-crystal semiconductor film, and wherein the crystallizing grows the image-forming region melted with the pulse laser beam into crystals in the lateral direction by a thermal storage effect of the cap film.

3. The crystallization method according to claim 2, further comprising: dehydrogenating the non-single-crystal semiconductor film after providing the cap film.

4. The crystallization method according to claim 1, wherein the crystallizing in the lateral direction starts from a location corresponding to the minimum value of the light intensity distribution of the repetitious pattern.

5. The crystallization method according to claim 2, wherein the cap film includes a silicon oxide film and a thickness of the silicon oxide film in a range of not less than 30 nm and not more than 500 nm.

6. The crystallization method according to claim 2, wherein the cap film includes a silicon oxide film and a thickness of the silicon oxide film in a range of not less than 100 nm and not more than 370 nm.

7. The crystallization method according to claim 1, wherein the repetitious pattern comprises an isosceles triangle.

8. The crystallization method according to claim 1, wherein the light intensity of the pulse laser light is, in a relative value, 0.9 or higher and no more than 1.0.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from prior Japanese Patent Applications No. 2003-189093, filed Jun. 30, 2003; No. 2003-193779, filed Jul. 8, 2003; No. 2003-308935, filed Sep. 1, 2003; No. 2003-402197, filed Dec. 1, 2003; and No. 2004-093200, filed Mar. 26, 2004, the entire contents of all of which are incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present application relates to a technique to manufacture a field effect transistor at a surface layer part of a non-single-crystal semiconductor thin film, and to single-crystal or polycrystal semiconductor thin film substrate used to manufacture a field effect transistor, and to crystallization method, a crystallization apparatus, a thin film transistor and a display apparatus suitable for manufacture of a display apparatus such as a liquid crystal or an organic EL or an electronic apparatus such as an information processing apparatus in which a field effect transistor are incorporated.

2. Description of the Related Art

A display apparatus such as a liquid crystal display unit is formed at an amorphous semiconductor film formed on a glass substrate. Specifically, as a display mode of a liquid crystal display, there is currently adopted an active matrix mode which switches individual pixels, and an amorphous silicon thin film transistor (a-SiTFT) is mainly used for a pixel switching element. Since information to be processed is digitalized and subjected to an improvement of speed due to expansion of an IT market, high performances is demanded in a display apparatus which displays such information. As means for satisfying this demand, a switching speed is increased by forming a switching transistor of respective pixels on a crystal area, thereby improving the picture quality.

In addition, miniaturization is enabled by having circuit treating data of each pixel built-in.

In the technical development of the liquid crystal display (LCD), the studies are keenly advanced with 1. realization of the high definition, 2. realization of a high numerical aperture, 3. a reduction in weight, 4. a reduction in cost and others being determined as objectives. In order to realize these performances, a technique using a polycrystal semiconductor thin film transistor (Poly-SiTFT) has come to the front. Since the Poly-SiTFT has the higher mobility than that of the a-SiTFT by two figures or more, an element size can be reduced, and a integrated circuit can be formed. Therefore, a drive circuit or an arithmetic operation circuit can be also mounted on the LCD.

A method for manufacturing a polycrystal semiconductor thin film transistor based on an excimer laser crystallization method according to the prior art will now be described with reference to FIGS. 12A to 12D. For example, as shown in FIG. 12A, an underlying protective film (e.g., an SiO.sub.2 film, an SiN film, an SiN/SiO.sub.2 laminated film or the like) 102 and an amorphous silicon thin film 103 are deposited on a glass substrate 101 as shown in FIG. 12A. Then, as shown in FIG. 12B, an excimer laser (XeCl, KrF or the like) 104 whose beam has been shaped into a square form or an elongated form by an optical system is used to irradiate a surface of the amorphous silicon thin film. Then, the amorphous silicon thin film 103 is converted from an amorphous structure into a polysilicon structure through a melt and solidification process in a very short time of 50 to 100 nano seconds by irradiation and heating of the excimer laser 104. When the entire surface of the amorphous silicon film 103 is scanned and heated by the excimer laser 104 in a direction indicated by an arrow 105, such a polycrystal silicon thin film 106 as shown in FIG. 12C is formed.

The above-described process is called an excimer laser annealing technique (which will be referred to as an ELA method hereinafter). The ELA method is used when manufacturing a high-quality polycrystal thin film on a substrate which is made of a material having a low melting point such as glass. In regard to these points, the detail is described in, e.g., Nikkei Microdevices, separate-volume Flat Panel Display 1999 (Nikkei Business Publications, Inc., 1998, pp. 132-139).

A thin film transistor shown in FIG. 12D is manufactured by using the polycrystal silicon thin film 106 described in FIG. 21C. A gate insulating film 107 such as an SiO.sub.2 film is provided on the polycrystal silicon thin film 106 of this TFT by film formation. Further, a source impurity implantation area 108 and a drain impurity implantation area 109 are provided. A gate electrode 110 is provided on the gate insulating film, a protective film 111 is formed, and a source electrode 113 and a drain electrode 114 are formed. The TFT which can control a current between the source and drain by a voltage of the gate electrode is brought to completion by the above-described steps.

However, a grain size of a crystal obtained by this ELA method is approximately 0.1 .mu.m. Therefore, in case of the thin film transistor (TFT) formed in this crystallized area, many crystal grain boundaries exist in a channel area of one thin film transistor. As a result, this transistor has the mobility of 40 to 60 cm.sup.2/Vs and an on/off current ratio of approximately 10.sup.7 and hence it is greatly inferior to an MOS transistor formed at single-crystal Si. Irregularities are generated in characteristics of each thin film transistor due to nonuniformity in the number of crystal grain boundaries and, in particular, there is a problem that this transistor is not suitable for a display apparatus which requires uniform display in one screen.

Furthermore, in order to improve the performances of the TFT, there has been reported a "phase modulation excimer laser crystallization method" which is a technique to single-crystallize polycrystal silicon as a method evolved from the ELA method. In the phase modulation excimer laser crystallization method, laterally grown Si crystal grain r2 whose positions are controlled can be formed by controlling a beam profile B shown in FIG. 2C. As a thesis concerning such a phase modulation excimer laser crystallization method, there is, e.g., The Ninth International Display Workshops (IDW' 2) Proceedings pp. 263-266. In the phase modulation excimer laser crystallization method, formation of a laterally grown Si crystal grain is facilitated by utilizing a controlled beam profile. In the conventional ELA method, although there is, e.g., Journal of Applied Physics Vol. 88, No. 9, 1 Nov. 2000, pp. 4994-4999 concerning a correlation of a beam profile and a crystallized cell, there is a great difference between these theses since the beam profile is not controlled in the latter.

The TFT characteristics are greatly improved without an adverse affect of the crystal grain boundaries by forming the TFT in a single crystal grain, thereby forming a function element such as processor, a memory, sensor and others. As such a crystallization method, there is, e.g., a crystallization method described in W. Yeh and M. Matsumura, Jpn. Appl. Phys. Vol. 41 (2002) 1909 or a crystallization method described in Japan Society of Applied Physics, the 63rd academic lecture in autumn 2002, preliminary manuscript correction 2, p. 779, 26a-G-2, Masato Hiramatsu and et. al.

The former reference by W. Yeh describes a cap film formed of an SiON/SiO.sub.2 film or a cap film formed of an SiO.sub.2 film. Phase-modulated laser beam with a fluence of 0.8 J/cm.sup.2 is irradiated to an amorphous silicon film through this cap. There is described a method for crystallizing the amorphous silicon film by laterally growing a crystal grain in a direction parallel to the cap film.

Furthermore, the latter reference by Hiramatsu describes irradiation of phase-modulated laser beam which is homogenized to an amorphous silicon film through a cap film formed of an SiO.sub.2 film with a substrate being heated. There is described a method by which a melted area of the amorphous silicon film can be subjected to crystal growth in the lateral direction.

However, when the silicon film is crystallized by using the conventional phase modulation excimer laser crystallization method, the following problem occurs. Laterally grown Si crystal grains r2 as well as polycrystal grains r3 on the outer thereof are generated as shown in FIG. 2D, a fine crystal grain r4 is produced at the center, and crystal grain breaking areas r5 may be further generated. That is because a light intensity distribution is not optimized.

Actually observing a structure crystallized by the phase modulation excimer laser crystallization method, single-crystallized areas r2 with a large grain size are generated, but other undesirable cells r4 and r5 are also produced.

Moreover, the method described in the reference by W. Yeh can obtain a crystal grain with a large grain size which is not less than a crystal grain size 10 .mu.m. However, a fine crystal grain with a small grain size may be generated in the vicinity of a crystal grain grown to have a large grain size in some cases, and there is a demand to relatively evenly (i.e., densely) form crystal grains with a large grain size all together as an entire film structure.

Additionally, in the methods described in the reference by W. Yeh and the reference by Hiramatsu, there is a demand for low-temperature or ordinary-temperature processing with respect to a temperature of a substrate in order to increase a grain size of crystal grains. For example, in a conventional crystallization apparatus 300 shown in FIG. 31, laser beam 250 is irradiated while heating a substrate 5 in a high-temperature area by using a heater 301 included in a mount base 206. The heater 301 receives a power from a power supply 302 which is controlled by a controller 303, and has a capability to heat the substrate 5 to a temperature area of 300 to 750.degree. C.

The substrate heating temperature may exceeds, e.g., 500.degree. C. in some cases. Then, general-purpose glass (e.g., soda glass) or plastic is apt to be transformed or deformed due to heating, and the low-temperature processing is a prerequisite in order to adopt such general-purpose glass for a substrate in a liquid crystal display (LCD). Further, in a large-screen LCD, there is a tendency to reduce a plate thickness of a substrate since there is a strong demand to reduce a weight thereof, and deformation is apt to occur due to heating. Therefore, the low-temperature processing is a prerequisite in order to assure the flatness of a thin substrate.

It is an object of the present invention to provide a crystallization method and apparatus, a thin film transistor and display apparatus which can design pulse laser beam ("laser beam" described below means pulse laser beam) having a light intensity and a distribution optimized on an incident surface of a substrate, form a desired crystallized structure while suppressing occurrence of other undesirable structure areas and satisfy a demand for low-temperature processing.

BRIEF SUMMARY OF THE INVENTION

To achieve this aim, the present invention has the following structure. A laser beam intensity JL with which lateral growth starts, a laser light intensity JB which can be inputted are checked in advance. A beam profile is measured on the same surface as a substrate surface. A beam profile is set to have a waveform which has a monotonous increase and a monotonous decrease such that a minimum laser intensity becomes not less than JL and a maximum laser beam intensity becomes less than JB, e.g., a triangular waveform. At this time, since a position at which JL is obtained becomes a crystallization start position, a crystal position can be defined.

A crystallization method according to the present invention irradiates to a non-single-crystal semiconductor thin film laser beam having a light intensity distribution which cyclically repeats a monotonous increase and a monotonous decrease at predetermined intervals in an irradiation area of the non-single-crystal semiconductor film. When irradiating the laser beam, as to the light intensity distribution, it is assumed that the light intensity which is equal to or above a light intensity which melts the non-single-crystal semiconductor film and allows it to grow in the lateral direction is a minimum value. Furthermore, it is presumed that the light intensity which is lower than the light intensity which causes breaking in the laterally grown crystal grain is a maximum value. These are the characteristics of the invention. By irradiating the laser beam having such a light intensity distribution, the crystal grain stably grows in the lateral direction without being broken. Then, it becomes a large crystal grain structure with an even size suitable for a thin film transistor (area 3 in FIG. 3).

Moreover, the minimum value of the light intensity distribution is characterized in that the non-single-crystal semiconductor thin film is melted. By irradiating laser beam having such a light intensity distribution, the structure of the non-single crystal semiconductor thin film is all crystallized and becomes a polycrystal structure (area 2 in FIG. 3).

Additionally, the maximum value of the light intensity distribution is characterized in that the minimum value of the light intensity distribution is lower than the light intensity which melts the non-single-crystal semiconductor film, and in a light intensity range lower than the light intensity which causes breaking in the laterally grown crystal grain. By irradiating laser beam having such a light intensity distribution, a ratio of the polycrystal structure and the amorphous structure can be arbitrarily changed (areas 1 and 2 in FIG. 3).

The maximum value and the minimum value of the light intensity are set in accordance with conditions of at least a film thickness and a temperature of a non-single-crystal semiconductor thin film. For example, under the condition of a substrate temperature of 500.degree. C., it is possible to set a beam profile BP shown in FIG. 9B. It is to be noted that the beam profile BP shown in FIG. 9B has a light intensity on a vertical axis being a standardized dimensionless index. This standardized light intensity index can be converted into a laser fluence having an actual unit (J/cm.sup.2). For example, the light intensity index can be converted into a laser fluence (J/cm.sup.2) at each position by multiplying the light intensity index by an average laser fluence (J/cm.sup.2).

According to the present invention, there is provided a crystallization apparatus which crystallizes a non-single-crystal semiconductor thin film by irradiating laser beam thereto, comprising: a laser beam source; a mount base on which a substrate having the non-single-crystal semiconductor thin film mounted thereon; a spatial intensity modulation optical element which is inserted between the laser beam source and the substrate and modulates a light intensity distribution on an incident surface of the substrate; means for measuring an intensity and a distribution of laser beam on the incident surface of the substrate by using the laser beam (beam profile measuring device); means for designing a light intensity distribution that a monotonous increase and a monotonous decrease are cyclically repeated at predetermined intervals in an irradiation area, a minimum value of the light intensity distribution is a value exceeding a light intensity with which the non-single-crystal semiconductor thin film is melted and a light intensity lower than a light intensity with which the laterally grown crystal grain is broken is a maximum value when designing the preset intensity and the distribution of the laser beam as targets; and means for leading the laser beam modulated by the spatial intensity modulation optical element to the incident surface of the substrate in such a manner that the measured light intensity and distribution match with the set targets.

It is desirable that the measuring means has a fluorescent screen on the incident surface to which a reference light beam enters and measurement is carried out with the fluorescent screen being arranged on substantially the same level as the incident surface of the substrate.

It is desirable that the spatial intensity modulation optical element uses a homogenization optical system including a phase shifter as will be described later. The homogenization optical system is constituted of a homogenizer including a pair of small lenses and optical components such as a plurality of sets of condenser lenses.

Here, the "laser fluence" means a scale of the light intensity representing the laser energy density, which is obtained by integrating an energy quantity per unit area into that per unit time.

Furthermore, the "beam profile" means a light intensity distribution of laser beam which enters a crystallization target film. It is to be noted that the reference light beam which enters a profiler (beam profile measurement portion) are the same as a light source used for laser annealing. However, it does not have to have the same laser fluence required for crystallization, it may have a light intensity required for measurement of beam profile.

Moreover, the "preset light intensity and distribution as targets" means the following based on a later-described empirical test. They are an intensity (laser fluence) and a distribution (beam profile) of the laser beam with which it is confirmed that the non-single-crystal semiconductor thin film is melted and subjected to lateral crystal growth and that the crystallized film is not broken.

FIG. 3 is a state diagram showing a qualitative relationship between a temperature, a light intensity and a structure of a semiconductor (e.g., silicon) by forming dimensionless vertical and horizontal axes. In the drawing, a characteristic line JC indicates a boundary (boundary of crystallization) on which a non-single-crystal semiconductor is crystallized (re-crystallized) or not. A characteristic line JL indicates a boundary (boundary of lateral growth) on which a crystal grain grows in the lateral direction or not. A characteristic line JB indicates a boundary on which the grown crystal grain is finally broken or not.

In an area 1 below the characteristic JC, a physical state of the non-single-crystal semiconductor does not vary.

In an area 2 between the characteristic lines JC and JL, the non-single-crystal semiconductor is crystallized (re-crystallized) but does not grow in the lateral direction.

In an area 3 between the characteristic liens JL and JB, the crystal grain stably grows in the lateral direction without being broken.

In an area 4 above the characteristic line JB, the film (crystal structure) is broken under various kinds of stresses in or after the growth of the crystal grain.

Here, the "film breaking" means that a regular structure (film structure) constituting the film is broken in the broad sense. It means that the laminated structure or the cap film is broken by a stress generated when the crystal grain grows in the lateral direction or that the crystallization target film is broken by a stress generated during the lateral growth in the narrow sense. Alternatively, it means that a defect such as a crack is generated in the crystal grain or the crystal grain boundary due to hydrogen contained in the cap film or the crystallization target film.

In regard to the means for solving the above-described problem, there has been described that the attention is paid to the beam profile and the light intensity, the monotonous decrease and the monotonous increase are observed, the light intensity range must be not less than JL which is required for the lateral growth and the crystal grain must fall within a range which is not more than JB. Further, the present inventors and others have keenly studied on densely forming crystal grains each of which is as large as at least one thin film transistor can be formed. Furthermore, they have found that irradiation of parallel laser beam (unhomogenized light beam) in the prior art cannot precisely increase a grain size of a crystal grain. Although a cause of this matter is not revealed in the strict sense, it is estimated that the following is the cause.

FIG. 32 is a characteristic curve diagram showing a substrate 5 having an optical system formed of a phase shifter 204 and a non-single-crystal semiconductor layer, and a light intensity distribution after parallel laser beam is transmitted through the phase shifter 204. In this light intensity distribution, a component from a first inverse peak wave 291 to a next peak wave 292 contributes to lateral growth. On the other hand, in regard to a higher-order oscillatory wave 293 outside this waveform, a crystal nucleus is generated due to the inverse peak wave and a fine crystal grain is produced. Therefore, an entire film cannot be evenly and densely crystallized with a large grain size. That is, with the parallel laser beam, since the light beam obtained by modulating a phase of the laser beam includes the higher-order oscillatory wave 293, it was found that crystal grains with a large grain size cannot be densely formed.

According to the crystallization method of the present invention, crystal grains with a relatively large grain size can be densely aligned and formed by causing the homogenized laser beam to enter a non-single-crystal semiconductor film through a phase modulation optical system and a silicon oxide film as an insulating film. The laser beam which does not include the higher-order oscillatory wave 293, has such a light intensity distribution BP as shown in FIG. 13B and has been transmitted through the phase modulation optical system is irradiated to the non-single crystal semiconductor film. The crystal grains with a large grain size can be densely (evenly) aligned and formed. The light intensity distribution BP shown in FIG. 13B is a light intensity distribution having V-shaped grooves as shown in FIG. 13C when three-dimensionally illustrated in a perspective view. This light intensity distribution BP has a plurality of peak patterns with inverted-triangular cross sections. Here, the present inventors and others refer to this shape as a peak pattern with an inverted-triangular cross section. When a step portion 204a is set at the center and seen as one shape in FIG. 13B with a pitch width PW in FIG. 13A, its cross section has an inverted-triangular shape, and hence it is referred to as the peak pattern with the inverted-triangular cross section. The shape shown in FIG. 9B is referred to as a triangular shape because gaps W1 and W2 of a step portion 31a are regarded as one shape and its light intensity distribution BP provided by cross section has a triangular shape. It is just a difference in position of an eye view when grasping one shape, and there is no substantial difference.

In the light intensity distribution having each peak pattern with an inverted-triangular cross section in FIG. 13C, amplitudes PH are equal and pitch intervals PW are also equal. The phase modulation optical system uses, e.g., a phase shifter.

Moreover, a solidification start temperature of a melted part of the non-single-crystal semiconductor film irradiated with the laser beam has physical properties inherent to the semiconductor film as a target. Thus, the present inventors and others have considered that a start fluence of lateral growth is a numeric value inherent to the semiconductor film and found that it is a substantially fixed value irrespective of the fluence of the pulse laser. In regard to termination of lateral growth, there are the following two cases. The lateral growth is terminated when a cooling speed is higher than a growth speed and a new nucleus is generated in a growth direction, and when there is a physical factor such that the cap film or the semiconductor film is peeled off due to instantaneous heating. In particular, as to occurrence of peeling, it has been found that existence of a flat part in the inverse peak pattern largely contributes to peeling since peeling of the semiconductor film occurs when an energy which is not less than a given value is irradiated into the semiconductor film.

Additionally, a substrate temperature dependency of a lateral growth distance has been evaluated by utilizing generation of light beam having peak patterns with optimum inverted-triangular cross sections obtained by the phase modulation optical system and a thermal storage effect of an appropriate cap film. As a result, as shown in FIG. 20, it has been discovered that Si crystal grains with a large grain size can be obtained even at a room temperature. As to the light beam having the peak patterns with the optimum inverted-triangular cross sections, a maximum value and a minimum value of the peak pattern with the inverted-triangular cross section are optimized, and a distance between the maximum values is sufficiently increased.

The present invention is based on the above-described knowledge, and has the following structure.

The crystallization method according to the present invention is a crystallization method which crystallizes a non-single-crystal semiconductor film by irradiating laser beam to it. Further, it is characterized in that at least a silicon oxide film is provided on a laser beam incident surface of the non-single-crystal semiconductor film and the laser beam is laser beam which has a light intensity distribution having a plurality of peak patterns with inverted-triangular cross sections.

The crystallization apparatus according to the present invention is a crystallization apparatus which crystallizes a non-single-crystal semiconductor film by irradiating laser beam thereto. The crystallization apparatus comprises: a laser beam source; a mount base on which a substrate having a non-single-crystal-semiconductor film is mounted; a homogenizer which is provided between the mount base and the laser beam source and homogenizes the laser beam in regard to a light intensity; and a phase modulation optical system which is provided between the homogenizer and the mount base and has a plurality of parts which modulate a phase of laser beam homogenized by the homogenizer.

A processed substrate according to the present invention comprises: a substrate formed of at least one material of an insulator, a semiconductor and a metal; a first insulating layer provided on the substrate; an amorphous semiconductor film or a non-single-crystal semiconductor film provided on the first insulating layer; and a second insulating layer which is provided on the amorphous semiconductor film or the non-single-crystal semiconductor film and has a thickness which is not less than 150 nm and not more than 350 nm. As the first insulating layer and the second insulating layers, silicon oxide films are optimum.

A thin film transistor according to the present invention is a pixel of a display apparatus and a thin film transistor which drives this pixel. The thin film transistor comprises: an insulative substrate; a channel area formed in a crystal grain with a large grain size formed by forming a silicon oxide film as a cap film on a non-single-crystal semiconductor film formed on the substrate, causing laser beam which has a light intensity distribution with a plurality of peak patterns with inverted-triangular cross sections to enter from the silicon oxide film, allowing the laser beam to reach the non-single-crystal semiconductor film through the silicon oxide film, melting the non-single-crystal semiconductor film, storing heat in the silicon oxide film provided on a laser beam incident surface of the non-single-crystal semiconductor film, delaying a solidification speed of the non-single-crystal-semiconductor film and crystallizing the non-single-crystal semiconductor film in a lateral direction; a source area and a drain area which are provided to sandwich the channel area and have predetermined impurities doped therein; a gate insulating film formed on the channel area; a gate electrode formed on the gate insulating film; an interlayer insulating film covering the gate electrode; a source electrode which electrically communicates with the source area from the interlayer insulating film side; and a drain electrode which electrically communicates with the drain area from the interlayer insulating film side.

A display apparatus according to the present invention is a display apparatus which has a pair of substrate bonded with each other through a predetermined gap therebetween and an electro-optic material held in the gap, forms an opposed electrode on one substrate and forms a pixel and a thin film transistor which drives the pixel on the other substrate, the thin film transistor comprising: an insulative substrate; a channel area formed in a crystal grain with a large grain size formed by forming a silicon oxide film as a cap film on a non-single-crystal semiconductor film formed on the substrate, causing laser beam which has a light intensity distribution with a plurality of peak patterns with inverted-triangular cross sections to enter from the silicon oxide film, allowing the laser beam to reach the non-single-crystal semiconductor film through the silicon oxide film, melting the non-single-crystal semiconductor film, storing heat in the silicon oxide film provided on a laser beam incident surface of the non-single-crystal semiconductor film, delaying a solidification speed of the non-single-crystal-semiconductor film and crystallizing the non-single-crystal semiconductor film in a lateral direction; a source area and a drain area which are provided to sandwich the channel area and have predetermined impurities doped therein; a gate insulating film formed on the channel area; a gate electrode formed on the gate insulating film; an interlayer insulating film covering the gate electrode; a source electrode which electrically communicates with the source area from the interlayer insulating film side; and a drain electrode which electrically communicates with the drain area from the interlayer insulating film side.

In this specification, the "phase sifter" is an example of a phase modulation optical system and means a spatial intensity modulation optical element which is used to modulate a phase of laser beam. It is discriminated from a phase shift mask which is used in an exposure step in a photolithography process. By introducing a progressive design concept to the phase shifter, a one-dimensional light intensity distribution BP which is schematically shown in FIG. 14B can be obtained. That is, it is possible to obtain a light intensity distribution BP which has different intensity tilt angles .theta., pitch widths PW and bias intensities PH (intensity in a root area). The phase shifter has a step formed to a quartz base substance as, e.g., a transparent material. The step of the phase shifter is formed into a size with which a phase of incoming light beam can be modulated to have a predetermined phase angle, e.g., 180.degree. by a process of etching or the like.

In the present invention, pulse laser beam whose light intensity distribution is optimized are irradiated. That is, pulse laser beam shown in FIGS. 13B, 26A and 29C from which the affect of the higher-order oscillatory wave 293 is eliminated is irradiated to a semiconductor film (an amorphous film or a polycrystal film) to be crystallized through a silicon oxide film. As shown in FIG. 17, the non-single-crystal semiconductor film as a crystallization target, e.g., the amorphous silicon film 252 is heated by irradiation of the pulse laser beam 250, and its temperature (T.sub.Si) is high at the end of the pulses. During the pulse irradiation, heat generated in the amorphous silicon film 252 as the crystallization target is transferred to, e.g., a low-temperature silicon oxide film (SiO.sub.2 film) provided as the cap film 253 on the earlier stage. After end of the pulse irradiation (after irradiation of the laser beam is interrupted), the amorphous silicon film 252 as a crystallization target starts to be cooled down, and heat stored in the cap film 253 is diffused toward the amorphous silicon film 252 as the crystallization target. In this manner, the cap film 253 dominantly serves as a heat capacitor, and a high-temperature liquid phase state of the amorphous silicon film 252 can remain longer than that when the cap film 253 is not used.

However, the cap film 253 partially returns heat transferred from the melted amorphous silicon film 252, but holds a large quantity of heat therein. Therefore, the melted amorphous silicon film 252 is supplied with heat from the cap film 253, and a solidification start time of the melted amorphous silicon film 252 can be delayed. As a result, a lateral growth distance of the crystal grains is increased, and the crystal grains with a large grain size are densely aligned and formed. The above-described supplied of heat from the cap film 253 greatly varies depending on a film thickness of the cap film 253. That is, according to the method of the present invention, a cooling speed of the semiconductor film is moderated by the silicon oxide film which is the cap film 253 with heat storage properties which is in contact with the amorphous silicon film as the semiconductor film. The single-crystal grains or crystal grains close to them with a large grain size can be obtained at a room temperature without heating the substrate.

It is desirable to set the film thickness of the cap film 253 to be not less than 30 nm and not more than 500 nm in terms of the heat storage characteristics, and it is most preferable to set it to be not less than 100 nm and not more than 370 nm (see FIGS. 23 and 33). When the film thickness is lower than 30 nm, a heat storage quantity of the SiO.sub.2 cap film becomes insufficient, and the large crystal grains with a desired size cannot be obtained. On the other hand, when the film thickness is larger than 500 nm, a heat transfer quantity (heat release; a thermal diffusion quantity) in a thickness direction from the crystallization target film (non-single-crystal semiconductor film) toward the SiO.sub.2 cap film 253 is increased, and hence the object of the heat storage cannot be successfully achieved.

Further, the laser beam is homogenized in relation to an incident angle by a first fly-eye lens as a homogenization optical system (homogenizer) and a first condenser optical system. Furthermore, they are homogenized in relation to a light intensity by a second fly-eye lens and a second condenser optical system. When the laser beam homogenized in relation to the incident angle and the light intensity are transmitted through the phase shifter 204 shown in FIG. 13A, the light intensity has a shape in which a monotonous increase and a monotonous decrease are repeated as shown in FIG. 13B. This becomes the above-described ideal light intensity distribution BP. The light intensity distribution BP shown in FIG. 13B has a shape with an inverted-triangular cross section, and a maximum peak value and a minimum peak value are projecting, and there is no flat portion. Moreover, this light intensity distribution has equal amplitudes PH and equal pitch intervals PW. That is, since the homogenized laser beam subjected to phase modulation does not include a higher-order oscillatory component, the large crystal grains with a size according to a width gap W between the steps 4a and 4a of the phase shifter can be theoretically grown in the lateral direction when such laser beam is irradiated to the film to be crystallized. At this time, since the heat energy is supplied to the film to be crystallized by the thermal storage effect of the insulating layer, a series of processes from melting, solidification and crystallization and crystal grain lateral growth can be facilitated, and a size of the crystal grains is increased. Since film breaking of the non-single-crystal semiconductor film is apt to occur when an angle .theta. of the peak portion becomes moderate in the light intensity distribution BP in FIG. 13B, it is desirable to set the light intensity distribution BP in such a manner that the angle .theta. of the peak portion becomes an angle which is as sharp as possible.

As described above, according to the present invention, the laser beam having a light intensity and a distribution optimized on the incident surface of the substrate can be designed, and a desired crystallized structure can be formed while suppressing occurrence of any other undesirable structure area such as film breaking. That is, the crystal grains stably grow in the lateral direction without being broken, and become a large crystal grain structure with even sizes which is suitable for a thin film transistor (area 3 in FIG. 3).

Additionally, according to the present invention, in light intensity distribution, it is determined that a light intensity which is equal to or above a light intensity with which a structure of the non-single-crystal semiconductor film is crystallized is a minimum value. Further, it is determined that a light intensity lower than a light intensity with which the crystallized crystal grains grow in the lateral direction is a maximum value. As a result, the structure of the non-single-crystal semiconductor film can be all crystallized to be a polycrystal structure (area 2 in FIG. 3).

Furthermore, according to the present invention, in the light intensity distribution, it is determined that a light intensity equal to or larger than a light intensity with which the structure of the non-single-crystal semiconductor film is crystallized is a maximum value in a light intensity range lower than a light intensity which produces breaking in the laterally grown crystal grains. Moreover, it is determined that a light intensity lower than a light intensity with which the structure of the non-single-crystal semiconductor thin film is crystallized is a minimum value. As a result, a ratio of the polycrystal structure an the non-polycrystal structure, e.g., amorphous structure, can be freely changed (areas 1 and 2 in FIG. 3).

Additionally, according to the present invention, Si crystal grains with a large grain size can be formed by room-temperature processing, and the demand for low-temperature processing can be satisfied. Therefore, it is possible to adopt a glass substrate or a plastic substrate which is thinner than that in the prior art as the substrate.

Further, according to the present invention, since the precise crystal grains with a large grain size can be aligned and formed on the entire film, it is possible to manufacture a TFT for a large-screen LCD with a higher operating speed and less irregularities in threshold voltage.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a structural block diagram showing a embodiment of crystallization apparatus according to the present invention;

FIG. 2A is a view showing a beam profile A;

FIG. 2B is a plan view schematically showing a crystallized structure formed by laser beam irradiation having the beam profile A;

FIG. 2C is a view showing a beam profile B;

FIG. 2D is a plan view schematically showing a crystallized structure formed by laser beam irradiation having the beam profile B;

FIG. 3 is a state diagram showing a qualitative relationship between a temperature, a light intensity and a structure;

FIGS. 4A and 4B are cross-sectional type drawings illustrating steps when manufacturing a semiconductor element according to the present invention;

FIG. 5A is a view showing a beam profile C;

FIG. 5B is a plan view schematically showing a crystallized structure formed by irradiation of laser beam having the beam profile C;

FIG. 6 is a state diagram showing a quantitative relationship between a substrate temperature, a laser fluence and a structure;

FIG. 7A is a beam profile characteristic diagram showing both a simulation result and an actual result concerning crystallization;

FIG. 7B shows an SEM image representing amorphous Si and crystal Si in a laser irradiation area;

FIG. 8A is a characteristic diagram showing a relationship between lateral growth, film breaking and a laser fluence;

FIG. 8B shows an SEM image of an Si thin film in a lateral growth process;

FIGS. 9A, 9B and 9C are a cross-sectional view schematically showing a part of a phase shifter, a beam profile characteristic diagram formed by using the phase shifter, and an SEM image representing a repeated pattern of a crystallized structure grown in the lateral direction by irradiation of laser beam having a profile;

FIGS. 10A to 10F are views respectively showing modifications of the beam profile;

FIG. 11 is a schematic perspective view of a display apparatus;

FIGS. 12A to 12D are cross-sectional type drawings illustrating steps when manufacturing a semiconductor element;

FIGS. 13A, 13B and 13C are a view showing a phase shifter and a substrate, a view showing a light intensity distribution of homogenized laser beam transmitted through the phase shifter, and a view three-dimensionally showing a light intensity distribution of the laser beam;

FIG. 14A is a view schematically showing a light intensity distribution on a substrate of laser beam whose phase is modulated;

FIG. 14B shows a scanning type electronic microscope (SEM) image representing a sample crystallized by single-shot irradiation of pulse laser beam;

FIG. 15 is a structural block diagram showing an outline of a crystallization apparatus according to the present invention;

FIG. 16 is an internal perspective block diagram showing an optical system of the apparatus according to the present invention;

FIG. 17 is a cross-sectional type drawing illustrating a laminated structure associating with present invention;

FIG. 18 shows an SEM image representing an effect of the present invention;

FIG. 19 is a characteristic view showing the effect of the present invention;

FIG. 20 is a characteristic view showing the effect of the present invention;

FIG. 21 is a characteristics view showing the effect of the present invention;

FIG. 22 is a structural block diagram illustrating another embodiment of FIG. 15;

FIG. 23 is a characteristic view showing the effect of the present invention;

FIG. 24 is a characteristic view showing the effect of the present invention;

FIG. 25 is a characteristic view showing the effect of the present invention;

FIG. 26A is a light intensity distribution diagram;

FIG. 26B shows an SEM image of a sample after Secco-etching;

FIG. 26C shows an SEM image of a sample after Secco-etching;

FIG. 27 is a type drawing illustrating an effect of the present invention;

FIG. 28 is a characteristic view showing the effect of the present invention;

FIG. 29A shows an SEM image of a sample in which large crystal grains are densely arranged;

FIG. 29B shows an SEM image showing a part of the sample in FIG. 29A in an enlarged manner;

FIG. 29C is a light intensity distribution diagram of laser beam irradiated to the sample described in FIG. 29B;

FIG. 30 is a cross-sectional type drawing showing a thin film transistor according to the embodiment of the present invention;

FIG. 31 is a structural block diagram showing an outline of a conventional apparatus;

FIG. 32A is a view showing a phase shifter and a substrate;

FIG. 32B is a view showing a light intensity distribution after parallel pulse laser beam is transmitted through the phase shifter;

FIG. 33 is a characteristic view showing a relationship between a film thickness (nm) of an amorphous silicon film and a lateral growth distance (.mu.m) of crystal grains; and;

FIG. 34 is a characteristic view showing a relationship between a film thickness (nm) of an amorphous silicon film and a film thickness (nm) of a cap film.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments according to the present invention will now be described hereinafter with reference to the accompanying drawings.

FIG. 1 is a schematic view showing a laser crystallization apparatus embodying the present invention. In a laser crystallization apparatus, an attenuator 2 and a beam profile modulation portion 3 are arranged at a starting end of an optical axis a of a laser beam source 1 containing the homogenization optical system, and a semiconductor substrate 5 is provided at a trailing end through a mirror 4. Further, a beam profile measurement portion 6 is provided to be aligned with the semiconductor substrate 5, and the semiconductor substrate 5 and the beam profile measurement portion 6 are fixed to a moving stage 7.

Furthermore, a control personal computer 8 as a controller is set, the beam profile measurement portion 6 is connected on an input side of the personal computer 8, and control systems of the attenuator 2, the beam profile modulation portion 3 and the moving stage 7 are respectively connected to an output side of the same.

The attenuator 2 optically modulates an intensity (power) of laser beam by adjusting an angle of a multilayer film coating filter of an inductor, and includes a sensor, a motor and a control system which are not illustrated.

The beam profile modulation portion 3 modulates a spatial intensity distribution of laser beam, and is constituted of a phase shifter 31 and a image formation optical system 243. The phase shifter 31 generates an inverse peak pattern in which a light intensity becomes minimum at a phase shift portion by alternately shifting a phase of light beam passing through a mask pattern by 0 and .pi., for example. This inverse peak pattern is used to control a position of an area (crystal nucleus) which is first solidified on the semiconductor substrate 5 and allow a crystal to grow in a lateral direction from this position toward the periphery (lateral growth). Thus, a crystal grain with a large grain size is provided at a specified position. At this time, a desired beam profile is set based on a shape of the phase shifter, a distance from the semiconductor substrate 5, an angular distribution of laser beam and others. The phase shifter 31 includes a sensor, an actuator and a control system which are not illustrated and used for replacement of a mask pattern or positioning in an optical axis direction.

The homogenization optical system is disclosed in detail in the specification or the like of Jpn. Pat. Appln No. 2003-110861 precedently filed by the present inventors and others, and constituted of a homogenizer including a pair of small lenses and optical components such as a plurality of sets of condenser lenses. The semiconductor substrate 5 is held at a focal position of this homogenization optical system, and laser beam 50 is irradiated. A shape and a width of an inverse peak pattern are controlled based on a pattern of a phase modulation phase shifter 31 and a defocusing quantity at this moment. In case of a proximity type crystallization apparatus (FIG. 15), a width of the inverse peak pattern is enlarged in proportion to a 1/2 power of a gap d between the phase shifter 31 and the semiconductor substrate 5.

The beam profile measurement portion 6 receives ultraviolet excimer laser beam on a fluorescent screen 61 to be converted into visible light beam, and receives on a CCD 63 the visible light beam reflected on a mirror 62 in order to simultaneously measures an intensity and a beam profile of the laser beam. The intensity of the laser beam may be separately measured by using a semiconductor power meter or the like. Moreover, the ultraviolet excimer laser beam may be directly received on the CCD 63.

The fluorescent screen 61 is set on a plane which is the same level with or on a plane parallel with the semiconductor substrate 5. When the fluorescent screen 61 is set on the parallel plane with a step, the fluorescent screen 61 is positioned at the same height as that of the semiconductor substrate 5 by moving up and down the moving stage 7 and measurement is carried out. As a result, a beam profile of the laser beam on the substrate surface can be measured under the same condition as that in case of actual beam irradiation.

An image received on the CCD 63 is inputted to the personal computer 8 and sliced on an arbitrary scanning line, and an intensity and a beam profile of the laser beam are measured based on an intensity distribution of an image signal.

Then, the measured intensity is compared with a preset target intensity, an operation quantity is calculated, and an angle of the attenuator 2 is adjusted while feeding back in such a manner the measured intensity becomes the target intensity by outputting an operation signal to the attenuator 2.

Additionally, the measured beam profile is compared with a preset target beam profile, and an operation quantity is calculated. Operation signals are outputted to the beam profile modulation portion 3 and the moving stage 7, a position of the phase shifter 31 and a height of the moving stage 7 are adjusted while feeding back in such a manner that the measured beam profile becomes the target beam profile.

The moving stage 7 can be moved in the three-dimensional direction, i.e., a front-and-back direction, a right-and-left direction and an up-and-down direction, and includes a sensor, an actuator and a control system which are used for positioning in an in-plane direction or an optical axis direction and not illustrated. The beam profile measurement portion 6 is moved and positioned at a laser beam irradiation position by this moving stage 7, and designed in such a manner that an intensity and a beam profile of the laser beam can be measured in advance before irradiating the laser beam onto the substrate.

The laser crystallization apparatus embodying the present invention has the above-described structure. In a laser crystallization step, the moving stage 7 is first moved in the in-plane direction in order to position an end of the optical axis a of the laser beam source 1 containing the homogenization optical system on the fluorescent screen 61 of the beam profile measurement portion 6, and the laser beam is irradiated to measure an intensity and a beam profile thereof.

Then, an angle of the attenuator 2, a position of the phase shifter 31 and a height of the moving stage 7 are respectively positioned in such a manner that the measured intensity and beam profile match with the preset targets. Subsequently, the moving stage 7 is moved in the in-plane direction, the end of the optical axis a is then positioned in a predetermined crystal area of the semiconductor substrate 5, a gap d is also set in case of the proximity type crystallization apparatus (FIG. 15), and the laser beam having the preset intensity and beam profile are irradiated.

The above-described measurement, positioning and beam irradiation are repeated, crystal areas which have various sizes are separately formed in the same substrate at the same time. In place of alternately performing measurement, positioning and beam irradiation in this manner, it is possible to first perform all measurements, calculate an operation quantity required for position, and then carry out positioning and beam irradiation at the same time in accordance with each crystal area.

First, as a preparation of the substrate, as shown in FIG. 4A, an insulator substrate is selected (e.g., Corning 1737 glass, melted quartz, sapphire, plastic, polyimide and others). On a surface thereof is formed a first thin film 102 (e.g., an SiO.sub.2 film with a film thickness of 300 nm formed by a plasma vapor deposition method using tetraethylorthosilicate (TEOS) and O.sub.2, or SiN/SiO.sub.2 laminated film alumina, mica and others). An amorphous semiconductor thin film 103 (e.g., amorphous Si, amorphous SiGe or the like with a film thickness of 200 nm obtained by the plasma chemical vapor deposition method) as a second thin film is formed on a surface of the first thin film 102. On a surface of the second thin film is further formed an SiO.sub.2 film 1070 with a film thickness of, e.g., 200 nm as a cap film by the plasma chemical vapor deposition method using tetraethylorthosilicate (TEOS) and O.sub.2. Then, dehyd