JP2006261183A - Thin film semiconductor device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a thin film semiconductor device in which a crack-free polycrystalline silicon film thicker than before is formed on a substrate of different kind such as a glass substrate. <P>SOLUTION: The thin film semiconductor device has a polycrystalline silicon film formed directly on a glass substrate wherein the average crystal grain area is 80 square μm or above. It is obtained by irradiating an amorphous silicon film with an area 13 of weak laser light intensity and then irradiating it with an area 14 of strong laser light intensity when the polycrystalline silicon film is scanned with a laser beam and rendered to the polycrystalline silicon. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a semiconductor element substrate such as a thin film solar cell, a TFT (Thin Film Transistor) substrate, and a semiconductor element (hereinafter collectively referred to as a thin film semiconductor device).

  In recent years, research on forming a crystalline silicon film on a non-conductive dissimilar substrate such as a glass substrate has been actively conducted. The crystalline silicon film formed on this heterogeneous substrate can be used widely for TFTs, thin film solar cells, and the like.

  A thin-film solar cell is formed by forming a crystalline silicon film having good crystallinity on a low-cost substrate by a low-temperature process, and using this for a photoelectric conversion device, thereby reducing cost and improving performance. By using this crystalline silicon film for a solar cell, long-wavelength light that is not observed in a solar cell made of amorphous silicon and that is not sensitive to solar cells made of amorphous silicon is not observed. Can also be converted into electrical energy. This technology is expected to be applicable not only to solar cells but also to photoelectric conversion elements such as optical sensors.

  In general, a solar cell made of a crystalline silicon film uses a technique of directly depositing a crystalline silicon film by a plasma CVD method. It is known that a crystalline silicon film can be formed on a substrate at a low temperature by this method, and is said to be effective for cost reduction.

In this plasma CVD method, the silane-based source gas is diluted about 15 times or more with hydrogen, the plasma reaction chamber pressure is 10 mTorr to 10 Torr, the substrate temperature is 150 ° C. to 550 ° C., preferably 400 ° C. or less. The film is formed by setting it within the range. Thereby, a crystalline silicon film is formed on the substrate. However, with this method, the crystal grain size is at most several μm, and it is difficult to increase the grain size beyond the film thickness. Moreover, in this method, columnar crystals grow from the substrate, but there are many defects inside the crystals, and the quality of the crystals is not so good. In addition, the quality of the i layer, which is the basis of the power generation function, is drastically lowered when doping is performed to optimize the device structure. For these reasons, it has been difficult for a photoelectric conversion element to achieve an efficiency significantly exceeding 10% with a single cell advantageous for cost reduction. Further, it has been difficult for polycrystalline silicon to have a mobility exceeding 10 cm ² / Vs.

  On the other hand, various attempts to form crystalline silicon by laser scanning have been studied, and a method using a continuous wave laser is disclosed in JP-A-2001-351863 (Patent Document 1). This method forms amorphous silicon on a heterogeneous substrate, and melts and crystallizes into polycrystalline silicon by scanning a strip-like continuous light source, making it possible to grow long crystal grains in the scanning direction. .

When crystallization is performed using this continuous wave laser, it has been attempted to use a solid-state laser such as Nd: YAG or Nd: YVO ₄ . By using these solid-state lasers, it has become possible to significantly reduce running costs and at the same time form high-quality polycrystalline silicon.

  A polycrystalline silicon film for a display TFT substrate is required to be flat because a MOSFET is formed on the surface, and it has been reported that it can be made very flat by using solid-state laser light (for example, Non-patent document 1).

  Further, a method of heating with a fundamental wave of a YAG laser using a light absorption layer has been proposed. By using this method, it is said that a polycrystalline silicon film having a large grain size can be obtained more efficiently than the method using the second harmonic (see, for example, Non-Patent Document 2).

Furthermore, Japanese Patent Application Laid-Open No. 2003-68644 (Patent Document 2) discloses a method for melting and crystallizing a silicon film using a plurality of pulse lasers. This method irradiates a second weak pulse laser beam to a portion once melted and crystallized by the first pulse laser to grow crystal grains in the lateral direction and shift this process in the lateral direction. However, it is possible to grow a crystal that is long in the lateral direction by repeatedly performing the process.
JP 2001-351863 A Japanese Patent Laid-Open No. 2003-68644 IEICE Transactions vol. j85-cNo. 8 (2002) p601 63rd Applied Physics Related Conference Lecture Proceedings (2002.9 Niigata University) Volume 2 26a-G-6 (p780)

  However, the conventional technique has a problem that cracks are likely to occur in the film.

More specifically, as described above, as a laser beam for directly heating and melting a precursor film such as an amorphous silicon film, a method using the second harmonic of the Nd: YAG or Nd: YVO ₄ laser, or a pulse Attempts have been made to crystallize using an excimer laser, which is a laser.

  However, when crystallizing a film thickness exceeding 1 μm, such as a solar cell, by melting and crystallizing the amorphous silicon film using the laser beam, if 1 μm is melted and crystallized by a single irradiation, Cracks occur in the film.

  This is considered as follows. When the precursor film is melted by laser light irradiation and is crystallized by being cooled, the temperature of the upper silicon film changes from a temperature range exceeding the melting point to room temperature. On the other hand, when a transparent dissimilar substrate is used, direct heating with a laser beam cannot be expected, so that the substrate is heated only by heat transfer from the heated silicon film. However, in general, when crystallization is performed with a laser beam, the irradiation time of the laser beam is several milliseconds or less, so that the upper silicon film is cooled from the melting point in a state of being hardly heated. A tensile stress is applied to the silicon film due to the difference in temperature change between the silicon film and the substrate. If this stress exceeds the critical tensile stress of the silicon film, the silicon film will crack. Since the critical tensile stress is inversely proportional to the square root of the thickness of the silicon film, cracks are more likely to occur as the silicon film becomes thicker.

  Since there is the above-mentioned problem and a film thickness of 100 nm is sufficient for manufacturing a general TFT, examination of increasing the thickness of an amorphous silicon film exceeding 500 nm and the crystal grain size at that time No consideration has been made.

  In general, when a thin-film solar cell using a crystalline silicon film is manufactured, a film thickness of about 2 μm or more is required in order to perform sufficient light absorption. When a silicon film having a crack is used for a solar cell element, the leakage current flowing through the end face of the crack is extremely increased. In a more severe case, it is short-circuited and does not function as a pn element. In order to produce a polycrystalline silicon film for a solar cell, it is an indispensable condition to produce a crack-free thick polycrystalline silicon film.

  It is even more important when producing a lateral device, for example, a polycrystalline silicon film for TFT. In the horizontal device, the carrier moves in the horizontal direction. In the case of a TFT, current is controlled by carriers flowing through a channel portion formed between a source and a drain. This channel is formed by being inverted by the gate voltage in the vicinity of the surface of the polycrystalline silicon film. Therefore, if there is a crack in the silicon film, the carrier cannot travel at all.

  The same applies to the case of manufacturing a bipolar transistor. When forming a bipolar transistor in an integrated circuit, it is common to produce a planar type bipolar transistor. However, in the collector of the bipolar transistor, carriers run in the lateral direction and are collected by the collector electrode. Therefore, if there are cracks in the polycrystalline silicon film, carrier movement is hindered, collector resistance increases, and it is difficult to satisfy the required performance.

  In applying these polycrystalline silicon films formed by laser annealing to various devices, it is necessary to perform crystallization with a large film thickness, but it is possible to produce a film that can be used for the generation of cracks due to the above problems. It was impossible.

  Accordingly, an object of the present invention is to provide a thin film semiconductor device in which a polycrystalline silicon film having a thicker film than that of the prior art in which cracks do not occur is produced on a different substrate such as a glass substrate by solving the above-described problems and laser annealing. It is in.

  In order to achieve the above object, the present invention is configured as follows.

  The thin film semiconductor device according to the invention of claim 1 is characterized in that, in the polycrystalline silicon film directly formed on the glass substrate, the average crystal grain area is 80 square μm or more.

  According to a second aspect of the present invention, in the thin film semiconductor device according to the first aspect, the polycrystalline silicon film is formed on a thermal buffer layer formed on a glass substrate.

  According to a third aspect of the present invention, in the thin film semiconductor device according to the second aspect, the thermal buffer layer is any one of a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a laminated structure thereof. To do.

  According to a fourth aspect of the present invention, in the thin film semiconductor device according to any one of the first to third aspects, the glass substrate contains 1% or more of impurities in its constituent materials.

  According to a fifth aspect of the present invention, in the thin film semiconductor device according to the fourth aspect, the glass substrate is made of aluminosilicate glass or borosilicate glass.

A sixth aspect of the present invention is the thin film semiconductor device according to any one of the first to fifth aspects, wherein the polycrystalline silicon film has a thickness of 500 nm or more and an average crystal grain area of 100 square μm or more. <Key points of the invention>
The present invention has the following configuration.

When a polycrystalline silicon film is used for a TFT or a solar battery, it is necessary to use an inexpensive glass substrate. In general, a glass substrate containing more than 1% of a constituent material other than silicon oxide is inexpensive. A thermal buffer layer and an impurity diffusion prevention layer are formed on such a glass substrate. As such a layer, a SiO ₂ film, a SiN film, a SiON film, or a laminated structure thereof can be used, but any layer can be used as long as it performs the functions of thermal buffering and preventing impurity diffusion. On top of this, an amorphous silicon film is deposited to a desired thickness. By irradiating this with laser, the amorphous silicon film is converted into a polycrystalline silicon film. This laser irradiation is performed by the following method.

For example, as shown in FIG. 1A, a sample in which an amorphous silicon film 03 is formed on a heterogeneous substrate 01 via a silicon oxide film (SiO ₂ film) 02 is irradiated with laser light 12 and melted by laser annealing. When crystallizing the polycrystalline silicon film 03a, the laser beam 12 is composed of two laser beam regions 13 and 14 as shown in FIG. A region with high light intensity (region with high laser light energy density) is used.

  As a method of forming the region 14 with high laser beam intensity (region with high laser beam energy density) and the region 13 with low laser beam intensity (region with low laser beam energy density), the laser beam irradiation region of one region 14 is There is a method in which the laser beam energy density is increased by reducing the laser beam energy density, and the laser beam energy density of the other region 13 is decreased by expanding the laser beam irradiation region. In this way, by providing a difference in the laser beam irradiation region, and increasing the laser beam power in the laser beam region having a high energy density (region 14 having a high laser beam intensity), the difference can be further increased. Is possible. There is no particular limitation on the shape of the laser light in each of the regions (the region 13 where the laser light intensity is weak and the region 14 where the laser light intensity is strong), and is perpendicular to the scanning direction or the scanning direction shown as the sample moving direction X in FIG. Although it is easy to process into a shape having a Gaussian distribution in the direction, laser light having a uniform shape in a direction perpendicular to the scanning direction may be used.

An Nd: YVO ₄ laser can be used as the laser light source 15 that is the light source of the laser light, but is not limited to the laser light source 15, and an amorphous silicon film or a crystalline silicon film can be melted. Any light having a wavelength may be used. Specifically, a semiconductor laser, Nd: YAG laser, He—Ne laser, excimer laser, or the like can be used. In this method, it is desirable to use continuously oscillating laser light.

  In performing laser beam irradiation using the laser beam 12 having the two laser beam regions 13 and 14 as described above, the amorphous silicon film 03 is first heated in the region 13 where the laser beam intensity is weak, and thereafter The scanning is performed in the heating direction in the region 14 where the laser light intensity is high. By irradiating the laser beam 12 in this order, a thicker film thickness can be crystallized without causing cracks.

  When heating the structure of a transparent heterogeneous substrate such as amorphous silicon / glass or quartz with a laser beam, when heating for a long time with a laser beam with a low energy density, or when heating with a laser beam with a high energy density for a short time If the same amount of energy is used, the temperature gradient of the dissimilar substrate such as glass becomes gentler when heating at a lower energy density for a longer time. This is because the effect of heat transfer becomes larger during heating for a longer time.

  This finding can be clarified by thermal analysis. FIG. 2 shows the analysis results of the temperature distribution at the end of heating when a certain amount of energy is irradiated for a short time (10 nm) and when irradiated for a long time (100 nm). The sample to be irradiated was assumed to be an amorphous silicon film (film thickness: 1 μm) and a heterogeneous substrate (thickness: 1 mm) made of quartz. It can be seen that the temperature gradient on the substrate surface side is steep when irradiated for a short time, and becomes gentle when irradiated for a long time.

  In general, the crystallization of silicon by laser light generally uses laser light irradiation of about several nsec to several μsec. With such a laser beam irradiation time, the amount of heat is not uniformly distributed over the entire substrate, and the substrate temperature has an internal gradient. When the film thickness of the amorphous silicon film is 1 μm or less within the laser beam irradiation time of several nsec to several μsec, the film is at room temperature at a position deeper than several tens of μm from the substrate surface. The heat is not transmitted.

  On the other hand, when the temperature rises to a temperature at which the amorphous silicon film melts, the amorphous silicon film reaches a temperature exceeding 1400 ° C. Therefore, there is a temperature difference of about 1400 ° C. between several tens of μm from the surface side of the substrate. The silicon film melted from this state is solidified by cooling and becomes room temperature. In this process, the silicon film undergoes thermal contraction. On the other hand, since the temperature rise of the substrate is 200 to 300 ° C., it hardly heat shrinks as compared with the silicon film. At this time, a crack is generated by the tensile stress applied to the silicon film. Since the tensile stress increases as the temperature difference increases, it is necessary to increase the temperature on the substrate side. For that purpose, it is necessary to heat for a long time so that a temperature gradient becomes small.

  However, it is not always good to heat as long as possible. When heated very slowly, the temperature of the substrate also rises because there is sufficient time for heat transfer. When it is slowly heated to a temperature at which the amorphous silicon film melts, the temperature of the substrate also rises to a similar temperature. In the case of using an inexpensive glass substrate, since it cannot be raised to about 600 ° C., desirably 450 ° C. or higher, there is a limit to the slow heating.

  Therefore, the substrate temperature is raised by irradiating with a laser beam (region 13 having a low laser beam intensity) that raises the temperature near the surface of the glass substrate to a temperature of 600 ° C. or lower. Thereafter, a laser beam that melts only the amorphous silicon film at once (region 14 having a high laser beam intensity) is irradiated. The laser beam that raises the temperature near the surface of the glass substrate is specifically a laser beam having a shape in which the amorphous silicon film is irradiated for a long time at a low energy density. The laser beam that melts only the amorphous silicon film at once is a laser beam that heats amorphous silicon for a short time at a high energy density.

  In this way, the laser beam irradiation (region 13 with low laser beam intensity) that raises the substrate temperature and the laser beam irradiation (region 14 with high laser beam intensity) that melts amorphous silicon can be divided into two times. It is possible to crystallize a thick film without causing cracks.

  Irradiation with a laser beam for raising the substrate temperature (region 13 where the laser beam intensity is weak) is not limited to being performed once, and may be performed in several steps. Further, the irradiation with the laser beam for melting the amorphous silicon (region 14 having a high laser beam intensity) is not limited to one irradiation.

  In addition to the laser beam irradiation method described above, further ingenuity is necessary in order not to cause cracks. When the above method is used, the vicinity of the surface of the substrate becomes a high temperature exceeding 600 ° C. If a low-cost glass substrate is used, impurities in the glass diffuse into the silicon. In particular, since the substrate temperature is raised to about 600 ° C. and then melted, the glass substrate and the silicon film are in contact with each other at a high temperature for a long time. Therefore, as shown in FIG. 1A, for example, it is necessary to form a silicon oxide film 02 as a thermal buffer layer having a function of preventing impurity diffusion between the heterogeneous substrate 01 and the amorphous silicon film 03. is there. Although it is desirable to use the silicon oxide film 02 for the thermal buffer layer, the present invention is not limited to this, and any silicon nitride film or silicon oxynitride film may be used as long as it can withstand high temperatures and prevent diffusion of impurities.

  By the above method, it becomes possible to form a thicker polycrystalline silicon film on a glass substrate than before, and to produce an electronic circuit having a solar cell or a bipolar transistor on the glass substrate. became. Specifically, a film having a thickness of 200 nm or more and a crystal grain size of 80 square μm or more can be obtained.

According to the present invention, in a polycrystalline silicon film directly formed on a glass substrate, a thin film semiconductor device having an average crystal grain area of 80 square μm or more, that is, a high-quality polycrystalline silicon film having high hole mobility. A thin film semiconductor device can be obtained. For example, in the case of a high-quality polycrystalline silicon film having a crystal grain size exceeding 200 square μm, the mobility is 160 cm ² / Vs or higher, and a high mobility comparable to that of single crystal silicon can be obtained.

  Hereinafter, embodiments of the present invention will be described. In addition, the following Examples show an example of this invention and this invention is not limited to these.

  An embodiment of the present invention will be described with reference to FIG.

As shown in FIG. 1A, a silicon oxide film 02 was formed on an aluminosilicate glass substrate as a heterogeneous substrate 01, and a 1 μm amorphous silicon film 03 was formed thereon. The silicon oxide film 02 was formed using a plasma CVD method. A mixed gas of SiH ₄ and N ₂ O was used as the source gas. The amorphous silicon film 03 was formed by a Cat-CVD (Catalytic-Chemical Vapor Deposition) method, and a mixed gas of SiH ₄ and H ₂ was used as a source gas.

  Crystallization was performed by irradiating the sample with laser light 12. At that time, a crystallization trial was made using two kinds of laser beams. The specifications of the used laser beam are as follows.

  (A) Laser light (long axis: 200 μm, short axis: 30 μm) shaped into an ellipse as shown in FIG. 5 using two cylindrical lenses.

  (B) As shown in FIG. 6, one laser beam region (region 04 where the laser beam intensity is weak) is elliptical (major axis 350 μm, minor axis 300 μm), and another laser beam. Laser light whose region (region 05 where the laser light intensity is strong) is an ellipse (major axis: 200 μm, minor axis: 30 μm) shaped using a cylindrical lens.

Diode-excited Nd: YVO ₄ laser light was used as the laser light source. When crystallization was performed using the above laser beam (A), when a sample having an amorphous silicon film exceeding 500 nm was crystallized, cracks occurred in the film (see the photograph in FIG. 3).

  Using the laser beam (B), the laser beam region with a long short axis (region 04 with low laser beam intensity) is irradiated first, and then the laser beam region with a short short axis (region 05 with high laser beam intensity) is irradiated. In this case, it was possible to make crack-free up to 1.1 μm (see the photograph in FIG. 4).

  When laser light (B) is used and the amorphous silicon film is irradiated only with a laser light region having a long short axis (region 04 with low laser light intensity), the condition for changing the amorphous silicon film to a crystalline silicon film When the laser beam (B) was irradiated at, cracks were generated from the same film thickness as that of the laser beam (A). At this time, the output of the laser beam region (the laser beam intensity region 04) having a long short axis and the laser beam region (the laser beam intensity region 05) having a short minor axis are also combined. Cracks occurred even after irradiation. When thermal analysis simulation was performed on the output of a laser beam region having a long short axis that does not cause cracking (region 04 where the laser beam intensity is weak), the laser beam was required not to exceed the melting point of silicon.

  In addition, when the laser beam region having a short minor axis does not exceed the melting point of silicon and the laser beam region having a short minor axis (region 05 having a strong laser beam intensity) is irradiated, It was found that cracks occurred when the output of the short laser beam region (region 05 where the laser beam intensity was strong) was large. A thermal analysis simulation was also conducted in this case, and it was found that when a crack was generated when laser light was irradiated, the temperature exceeded the strain point at any location on the glass substrate.

  Therefore, in order to prevent cracks from occurring, a laser beam region having a long short axis (region 04 having a low laser beam intensity) is heated so that the output does not exceed the melting point of silicon, and the short axis is a short laser. For the light region (region 05 where the laser light intensity is strong), it has been found that the output must not exceed the strain point of the glass substrate.

  Next, in order to crystallize a thicker silicon film, an attempt was made to make the laser beam into a more appropriate shape.

  FIG. 7 shows the shape of the laser beam in the second embodiment. A homogenizer was attached so that the laser beam intensity in the horizontal direction, that is, the direction perpendicular to the scanning direction was uniform, and the laser beam was irradiated. As in Example 1, two types of laser light (region 06 with low laser light intensity and region 07 with high laser light intensity) were used. The homogenizer was used for two types of laser beams.

  As in the first embodiment, the laser beam region (region 06 with low laser beam intensity) irradiated to the amorphous silicon film 03 first is the laser beam region (region 07 with high laser beam intensity) irradiated thereafter. When the output was weaker than that, cracks were reduced. As shown in FIG. 7, the size of the two laser beam regions is as follows. The first laser beam region irradiated with the laser beam region (region 06 where the laser beam intensity is weak) is 500 μm in the scanning direction, and the laser beam irradiated thereafter is laser beam. The region (region 07 where the laser beam intensity is strong) is 10 μm, and both are 300 μm in the direction perpendicular to the scanning direction.

  As a result of thermal analysis of the output for reducing the cracks, the laser beam region (region 06 where the laser beam intensity is low) to be irradiated first is an output that does not melt the amorphous silicon 03, and the laser beam region to be irradiated thereafter ( It was found that the region 07) where the laser light intensity is strong is a case where the output is set to be equal to or higher than the melting point of silicon. By this method, it was possible to make a polycrystal without cracks to a film thickness of 2.4 μm.

  It was also effective to irradiate the region 07 having a high laser beam intensity on the region 06 having a low laser beam intensity. In this case, the amorphous silicon film is first heated for a long time in the region 06 where the laser beam intensity is low, and then exceeds the melting point in the region 07 where the laser beam intensity is high. Thereafter, cooling is performed through a weak laser intensity region in the cooling process, but cracks can be reduced by such an irradiation method.

  An amorphous silicon film having a thickness of 2 μm was formed on a glass substrate made of borosilicate glass, and an amorphous silicon film was formed thereon. The amorphous silicon film was formed to a thickness of 100 nm to 1 μm, and the same crystallization treatment as in Examples 1 and 2 was performed. By this crystallization treatment, any film thickness of 100 nm to 2 μm of the amorphous silicon film can be crystallized and changed to a polycrystalline silicon film.

  The crystal grain size of the formed polycrystalline silicon film was identified by EBSP (Electron Backscattered Diffraction Pattern). As a result, the crystal grain size varied with the film thickness as shown in FIG. This change in crystal grain size is due to the difference in cooling rate depending on the film thickness, and it has been found that the crystal grain size can be increased by laser crystallization of a thicker amorphous silicon substrate. When the film thickness is 200 nm or more, the crystal grain size is 80 square μm or more, and when the film thickness is 1 μm or more, the crystal grain size is 100 square μm or more.

The hole mobility was measured for the sample thus prepared. The hole mobility was measured by laser annealing amorphous silicon ion-implanted with phosphorus at 1 × 10 ¹⁸ cm ⁻³ . When the hole mobility was measured, the mobility rapidly increased when the crystal grain size exceeded 80 square μm, and the mobility became 160 cm ² / Vs or more when the crystal grain size exceeded 200 square μm. This value is a high mobility comparable to that of single crystal silicon, and it was found that a high-quality polycrystalline silicon film can be formed by increasing the crystal grain size.

It is a figure which shows the middle of manufacture of the crystalline silicon type thin film semiconductor device which concerns on Example 1 of this invention. It is the figure which showed the difference in the temperature gradient on the substrate surface side when the fixed amount of energy is irradiated for a short time and when irradiated for a long time. 6 is a drawing-substituting photograph showing the surface of a crystalline silicon film crystallized using the laser beam of FIG. FIG. 7 is a drawing-substituting photograph showing the surface of a crystalline silicon film crystallized using the laser beam of FIG. 6. It is a schematic diagram which shows the shape of the laser beam (A) used as a comparison of this invention. It is a schematic diagram which shows the shape of the laser beam (B) used in Example 1 of this invention. It is a schematic diagram which shows the shape of the laser beam used in Example 2 of this invention. It is a graph which shows the relationship between the film thickness in Example 3 of this invention, and a crystal grain diameter.

Explanation of symbols

01 Dissimilar substrate 02 Silicon oxide film (SiO ₂ film)
03 Amorphous silicon film 03a Polycrystalline silicon film 04 Low laser light intensity area 05 High laser light intensity area 06 Low laser light intensity area 07 High laser light intensity area 12 Laser light 13 Low laser light intensity area 14 Region with strong laser light intensity 15 Laser light source

Claims (6)

  A thin film semiconductor device characterized in that an average crystal grain area of a polycrystalline silicon film directly formed on a glass substrate is 80 square μm or more. The thin film semiconductor device according to claim 1,
A thin film semiconductor device, wherein the polycrystalline silicon film is formed on a thermal buffer layer formed on a glass substrate. The thin film semiconductor device according to claim 2,
A thin film semiconductor device, wherein the thermal buffer layer is a silicon oxide film, a silicon nitride film, a silicon oxynitride film, or a laminated structure thereof. In the thin film semiconductor device according to any one of claims 1 to 3,
A thin film semiconductor device, wherein the glass substrate contains 1% or more of impurities in its constituent materials. The thin film semiconductor device according to claim 4,
A thin film semiconductor device, wherein the glass substrate is made of aluminosilicate glass or borosilicate glass. In the thin film semiconductor device according to any one of claims 1 to 5,
2. The thin film semiconductor device according to claim 1, wherein the polycrystalline silicon film has a film thickness of 500 nm or more and an average crystal grain area of 100 square μm or more.