JP2004311895A - Liquid crystal display device using thin film transistor, and its manufacturing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a manufacturing method of a liquid crystal display device which is excellent in display quality and to form a polycrystalline thin film transistor directly on a substrate of low heat resistance such as resin by reducing the defect level in grain boundary/crystal and stabilizing and improving the performance of the thin film transistor in a process for polycrystallizing amorphous silicon in a manufacturing process of a thin film transistor used for liquid crystal driving of the liquid crystal display device. <P>SOLUTION: In the method, the dehydrogenation treatment temperature of amorphous silicon before crystallization is set to 430 to 480°C and the dehydrogenation time is set to 20 to 50 minutes, or the dehydrogenation temperature is set to 480 to 500°C and the dehydrogenation time is set to 5 to 20 minutes, or dehydrogenation treatment from only amorphous silicon is carried out without raising dehydrogenation from a silicon oxide film or a silicon nitride film and glass by ultraviolet rays such as UV light and excimer laser. It is possible to reduce defect in a polycrystalline silicon film or in an interface with an oxide film therebelow, to improve characteristics or to manufacture a polycrystalline thin film transistor array on a resin substrate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a method of manufacturing an active matrix type liquid crystal display device (TFT-LCD) using a thin film transistor (TFT) as a switching element, and aims to make the performance of the TFT stable and high performance. Is to improve the productivity without impairing the display characteristics of the TFT-LCD.
[0002]
[Prior art]
An active matrix type liquid crystal display device, which combines an active matrix substrate in which thin film transistors are arranged in a matrix on a transparent insulator such as a glass substrate, a color filter substrate also serving as a counter electrode, and a liquid crystal, has a flat image display device. With the expectation of, the commercialization of flat displays has been promoted, opening up a large market not only for notebook computers but also for OA monitors.
[0003]
In particular, a liquid crystal display device driven by a thin film transistor using a polycrystalline silicon film for a semiconductor layer has an advantage that a peripheral driving circuit and the like can be formed over a glass substrate, and the number of mounting points can be reduced. Is showing.
[0004]
There have been some prior examples of a method for manufacturing a liquid crystal display device using a thin film transistor made of polycrystalline silicon, and examples thereof are described in Patent Documents 1 to 4. In addition, there are some prior examples of a method of forming a thin film transistor and the like on a resin substrate, and for example, Patent Literatures 5 to 7 disclose such methods.
[0005]
As an example, FIG. 6 shows a main cross-sectional view of a TFT array substrate. A silicon nitride film 2, a silicon oxide film 3, and a hydrogenated amorphous silicon film 4, which are insulating layers, are successively formed on a glass substrate 1 by using a plasma CVD method. At this time, in order to prevent hydrogen in the silicon film from bumping when the amorphous silicon film is polycrystallized by laser annealing, the substrate is heated to about 470 to 500 ° C. immediately after the formation of the hydrogenated amorphous silicon film. To dehydrogenate the amorphous silicon film in advance. Next, after removing the native oxide film on the amorphous silicon film using buffered hydrofluoric acid or the like, the amorphous silicon film is polycrystallized by irradiating a laser beam such as an excimer laser. .
[0006]
Next, in a first photolithography step, the semiconductor layer is patterned into an island shape so as to leave a portion where a channel is formed. Next, a silicon oxide film 5 is formed as a gate insulating film by a method such as a plasma CVD method. Next, after only the resist is patterned in the second photolithography step, phosphorus is doped into the polycrystalline silicon film 4 by an ion doping method in order to form a storage capacitor.
[0007]
Next, the gate electrode 6 is patterned in a third photolithography step. Next, boron is doped into the polycrystalline silicon film 4 from above the gate electrode 6 by an ion doping method in order to form a p-ch TFT.
[0008]
Next, a resist pattern is formed in a fourth photolithography step, and phosphorus is doped from above the resist by an ion doping method in order to form an n-ch TFT. After that, the gate electrode 6 is patterned by etching, the resist is stripped, and a small amount of phosphorus is doped to form an LDD structure of the n-ch TFT.
[0009]
Next, after the gate electrode 6 and the interlayer insulating film 7 between the source electrode 8 and the drain electrode 9 are formed by a plasma CVD method or the like, a crystallization process for activating ion-doped impurities is performed by heat treatment.
[0010]
Next, in a fifth photolithography step, contact holes for making contact between the transistor and the source electrode 8 and the drain electrode 9 are formed.
[0011]
Next, a metal of a source electrode and a drain electrode material is formed by a sputtering method, and a source electrode 8 and a drain electrode 9 are formed in a sixth photolithography step.
[0012]
Next, in order to reduce the order of defects in the semiconductor film, after performing a hydrogen plasma treatment, a passivation film 10 is formed by a method such as plasma CVD, and a contact hole is formed in the passivation film in a seventh photolithography process. I do.
[0013]
Next, a transparent conductive film to be a terminal electrode is formed by a sputtering method or the like, and the terminal electrode is patterned in an eighth photolithography step, thereby completing the formation of the thin film transistor array substrate.
[0014]
Before forming the terminal electrodes, an organic film or the like may be formed or a reflective film may be formed to form a thin film transistor array for a display device using reflected light.
[0015]
[Patent Document 1]
JP-A-11-10370 (pages 6 and 8)
[Patent Document 2]
JP 2001-166326 A (pages 2-3)
[Patent Document 3]
JP 2001-264813 A (page 3-4)
[Patent Document 4]
JP 2001-267581 A (pages 4 to 5)
[Patent Document 5]
JP 2000-97765 A (page 6)
[Patent Document 6]
JP-A-2002-208592 (pages 9 to 10)
[Patent Document 7]
JP 2001-358351 A (page 3-4)
[0016]
[Problems to be solved by the invention]
During dehydrogenation annealing before crystallization by laser annealing, dehydrogenation from the underlying insulating film occurs simultaneously with dehydrogenation from the hydrogenated amorphous silicon. A defect order is generated at the interface of the crystalline silicon film, and the crystal grain boundary and the defect level in the crystal at the time of crystallization increase, and the performance of the transistor decreases.
[0017]
An object of the present invention is to provide a manufacturing method capable of stably and improving the performance of a thin film transistor and obtaining a liquid crystal display device having excellent display quality.
[0018]
Further, in order to form a polycrystalline silicon thin film transistor directly on a resin substrate having low heat resistance such as plastic, the process temperature must be 200 ° C. or lower. An object of the present invention is to provide a manufacturing method capable of obtaining a liquid crystal display device in which a polycrystalline thin film transistor is formed directly on a resin substrate having low heat resistance.
[0019]
[Means for Solving the Problems]
A method for manufacturing a liquid crystal display device according to the present invention for solving the above problems is manufactured by the following method.
[0020]
FIG. 4 shows the relationship between the dehydrogenation annealing temperature and the threshold voltage ΔVth (Vth (n) −Vth (p)) when the dehydrogenation annealing time is 1200 sec. It becomes smaller and the transistor performance is improved. However, if the temperature is set too low, the amount of hydrogen in the film will increase, and the subsequent crystallization by laser annealing will cause the hydrogen in the film to boil, causing film peeling. is there.
[0021]
FIG. 5 shows the relationship between the dehydrogenation annealing time and the threshold voltage ΔVth when the dehydrogenation annealing temperature is 495 ° C., and the longer the dehydrogenation time, the larger the threshold voltage ΔVth. As before, if the amount of hydrogen in the film is large, bumping of hydrogen occurs during laser annealing, so it is necessary to set the optimal time.
[0022]
From the above, the temperature of the dehydrogenation annealing after the amorphous silicon was formed before the polycrystalline silicon was formed by the laser annealing method was set to the range of 430 to 480 ° C. Is set in the range of 20 to 50 minutes, or the temperature of the dehydrogenation annealing is set in the range of 480 to 500 ° C., and the annealing time is set in the range of 8 to 20 minutes, so that the insulating film below the amorphous silicon film is formed. And the defects at the interface with the insulating film in and below the polycrystalline silicon film can be reduced.
[0023]
According to Patent Literature 1, in Examples, it is described that dehydrogenation annealing before crystallization is performed at 400 ° C. for 2 hours. If the temperature is lowered and the time is prolonged, hydrogen in the film can be reduced and bumping can be prevented. However, there is a problem that the processing time is prolonged and the processing capacity of the apparatus is reduced.
[0024]
As described above, in order to improve and stabilize the transistor characteristics and maintain the productivity, it is necessary to optimize the temperature and time of the dehydrogenation annealing before the laser annealing crystallization. Thus, the characteristics of the transistor can be stably and improved, and a thin film transistor array substrate that does not impair the display quality of the liquid crystal display device can be manufactured.
[0025]
Also, instead of heating the dehydrogenation treatment together with the glass substrate to a high temperature, use is made of light in the ultraviolet region where glass or a material such as a silicon oxide film or a silicon nitride film absorbs little and only amorphous silicon absorbs. By performing the dehydrogenation process, the dehydrogenation process can be efficiently performed only on the amorphous silicon, and similarly, the transistor characteristics can be improved and stabilized. According to this method, a polycrystalline thin film transistor can be formed directly on a substrate having low heat resistance such as a resin.
[0026]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1
Hereinafter, the present invention will be described in detail with reference to FIGS.
[0027]
FIG. 1 is a cross-sectional view when a silicon nitride film 12, a silicon oxide film 13, and a hydrogenated amorphous silicon film 14, which are insulating layers, are successively formed on a substrate 11 by a plasma CVD method. In the present embodiment, the substrate 11 is a glass substrate.
[0028]
After preheating the glass substrate to about 300 to 450 ° C., a 50 nm-thick silicon nitride film is formed in a film formation chamber. Next, after a silicon oxide film is continuously formed to a thickness of 100 to 300 nm, an ia-Si film is further continuously formed to a thickness of 50 nm. Thereafter, the substrate is continuously heated at 460 ° C. for 20 to 50 minutes to dehydrogenate the hydrogen in the a-Si film. At this time, heating is not performed at 480 ° C. or more so as not to dehydrogenate from the silicon nitride film 12 and the silicon oxide film 13. The dehydrogenation is performed in a nitrogen atmosphere while controlling the pressure to, for example, 300 to 800 Pa.
[0029]
The films 12 to 14 may be formed continuously in the same film forming chamber, or the film forming chamber may be changed for each film type.
[0030]
Dehydrogenation heating may be performed after the substrate is once brought out from the film forming apparatus to the atmosphere after the film formation.
[0031]
Next, after removing the natural oxide film on the amorphous silicon film using buffered hydrofluoric acid or the like, a laser having an energy density of 400 to 500 mJ / cm ² is used using, for example, an excimer laser (wavelength: 308 nm). The amorphous silicon film is polycrystallized by irradiating it with light.
[0032]
The subsequent steps will be described with reference to FIGS. First, in a first photolithography step, a semiconductor layer is patterned into an island shape so as to leave a portion where a channel is formed. Next, a silicon oxide film 15 is formed as a gate insulating film by a method such as a plasma CVD method. Next, after patterning only the resist in the second photolithography step, phosphorus is doped into the polycrystalline silicon film 14 by an ion doping method in order to form a storage capacitor.
[0033]
Next, the gate electrode 16 is patterned in a third photolithography step.
[0034]
Next, boron is doped into the polycrystalline silicon film 14 from above the gate electrode 16 by an ion doping method to form a p-ch TFT.
[0035]
Next, a resist pattern is formed in a fourth photolithography step, and phosphorus is doped from above the resist by an ion doping method in order to form an n-ch TFT. After that, the gate electrode 16 is patterned by etching, the resist is stripped, and a small amount of phosphorus is doped to form an LDD structure of an n-ch TFT.
[0036]
Next, after the gate insulating film 16 and the interlayer insulating film 17 between the source electrode 18 and the drain electrode 19 are formed by a plasma CVD method or the like, a crystallization process for activating the ion-doped impurities is performed by a heat treatment.
[0037]
Next, in a fifth photolithography step, contact holes for making contact between the transistor and the source electrode 18 and the drain electrode 19 are formed.
[0038]
Next, a metal of a source electrode and a drain electrode material is formed by a sputtering method, and a source electrode 18 and a drain electrode 19 are formed in a sixth photolithography step.
[0039]
Next, in order to reduce defect levels in the semiconductor film, after performing a hydrogen plasma treatment, a passivation film 20 is formed by a method such as plasma CVD, and a contact hole is formed in the passivation film in a seventh photolithography step. Form.
[0040]
Next, a transparent conductive film to be the terminal electrode 21 is formed by a sputtering method or the like, and the terminal electrode is patterned in an eighth photolithography process, thereby completing the formation of the thin film transistor array substrate.
[0041]
Before forming the terminal electrodes, an organic film or the like may be formed or a reflective film may be formed to form a thin film transistor array for a display device using reflected light.
[0042]
Embodiment 2
Hereinafter, the present invention will be described in detail with reference to FIGS.
[0043]
FIG. 1 is a cross-sectional view when a silicon nitride film 12, a silicon oxide film 13, and a hydrogenated amorphous silicon film 14, which are insulating layers, are successively formed on a substrate 11 by a plasma CVD method. In the present embodiment, the substrate 11 is a glass substrate.
[0044]
For example, a glass substrate is introduced into the above apparatus, the substrate is preheated to about 300 to 450 ° C., and then a first silicon nitride film is formed to a thickness of 50 nm in a film forming chamber. Next, after a silicon oxide film is continuously formed to a thickness of 100 to 300 nm, an ia-Si film is further continuously formed to a thickness of 50 nm. After that, the substrate is continuously heated to 480 to 500 ° C. to remove hydrogen in the a-Si film. At this time, the heating time is set to 5 to 20 minutes so that the silicon nitride film 12 and the silicon oxide film 13 are not dehydrogenated. The dehydrogenation is performed in a nitrogen atmosphere while controlling the pressure to, for example, 300 to 800 Pa.
[0045]
The films 12 to 14 may be formed continuously in the same film forming chamber, or the film forming chamber may be changed for each film type.
[0046]
Dehydrogenation heating may be performed after the substrate is once brought out from the film forming apparatus to the atmosphere after the film formation.
[0047]
Hereinafter, a thin film transistor array is formed in a manner according to the first embodiment.
[0048]
Embodiment 3
Hereinafter, the present invention will be described in detail with reference to FIGS.
[0049]
FIG. 1 is a cross-sectional view when a silicon nitride film 12, a silicon oxide film 13, and a hydrogenated amorphous silicon film 14, which are insulating layers, are successively formed on a substrate 11 by a plasma CVD method. In the present embodiment, the substrate 11 is a glass substrate.
[0050]
For example, a glass substrate is introduced into the above apparatus, the substrate is preheated to about 300 to 450 ° C., and then a first silicon nitride film is formed to a thickness of 50 nm in a film forming chamber. Next, after a silicon oxide film is continuously formed to a thickness of 100 to 300 nm, an ia-Si film is further continuously formed to a thickness of 50 nm. Thereafter, UV light is applied for 1 hour at an illuminance of 20 mW / cm ² to dehydrogenate.
[0051]
The films 12 to 14 may be formed continuously in the same film forming chamber, or the film forming chamber may be changed for each film type.
[0052]
Hereinafter, a thin film transistor array is formed in a manner according to the first embodiment.
[0053]
Embodiment 4
Hereinafter, the present invention will be described in detail with reference to FIGS.
[0054]
FIG. 1 is a cross-sectional view when a silicon nitride film 12, a silicon oxide film 13, and a hydrogenated amorphous silicon film 14, which are insulating layers, are successively formed on a substrate 11 by a plasma CVD method. In the present embodiment, the substrate 11 is a glass substrate.
[0055]
For example, a glass substrate is introduced into the above apparatus, the substrate is preheated to about 300 to 450 ° C., and then a first silicon nitride film is formed to a thickness of 50 nm in a film forming chamber. Next, after a silicon oxide film is continuously formed to a thickness of 100 to 300 nm, an ia-Si film is further continuously formed to a thickness of 50 nm. After that, the ia-Si film is dehydrogenated by irradiating the ia-Si film with a pulse of excimer laser light having an energy density of 200 to 250 mJ / cm ² at a frequency of 300 Hz. At this time, for example, the irradiation area is set to 200 × 0.4 mm, and irradiation is performed while shifting by 5% in the short side direction for each pulse (that is, while overlapping by 95%). The laser irradiation energy density for dehydrogenation is about one half of the laser irradiation energy density used for polycrystallization of the amorphous silicon film described in Embodiment 1.
[0056]
The films 12 to 14 may be formed continuously in the same film forming chamber, or the film forming chamber may be changed for each film type.
[0057]
Hereinafter, a thin film transistor array is formed in a manner according to the first embodiment.
[0058]
Embodiment 5
Hereinafter, the present invention will be described in detail with reference to FIGS.
[0059]
FIG. 1 is a cross-sectional view when a silicon nitride film 12, a silicon oxide film 13, and a hydrogenated amorphous silicon film 14, which are insulating layers, are successively formed on a substrate 11 by a plasma CVD method. In the present embodiment, the substrate 11 is a transparent resin substrate.
[0060]
After preheating the resin substrate to about 180 to 200 ° C., a 50 nm-thick silicon nitride film is formed in a film forming chamber. Next, after a silicon oxide film is continuously formed to a thickness of 100 to 300 nm, an ia-Si film is further continuously formed to a thickness of 50 nm. After that, the ia-Si film is dehydrogenated by irradiating the ia-Si film with a pulse of excimer laser light having an energy density of 200 to 250 mJ / cm ² at a frequency of 300 Hz. At this time, for example, the irradiation area is set to 200 × 0.4 mm, and irradiation is performed while shifting by 5% in the short side direction for each pulse (that is, while overlapping by 95%). The laser irradiation energy density for dehydrogenation is about one half of the laser irradiation energy density used for polycrystallization of the amorphous silicon film described in Embodiment 1.
[0061]
The films 12 to 14 may be formed continuously in the same film forming chamber, or the film forming chamber may be changed for each film type. However, the film formation temperature is set to 200 ° C. or lower, which is the temperature that the resin can withstand.
[0062]
Next, after removing the native oxide film on the amorphous silicon film using buffered hydrofluoric acid or the like, the amorphous oxide film is irradiated with a laser beam such as an excimer laser as described in Embodiment 1 to form an amorphous silicon film. Polycrystalline silicon film. The subsequent steps will be described with reference to FIGS.
[0063]
First, in a first photolithography step, a semiconductor layer is patterned into an island shape so as to leave a portion where a channel is formed. Next, a silicon oxide film 15 is formed as a gate insulating film by a method such as a plasma CVD method. Next, after patterning only the resist in the second photolithography step, phosphorus is doped into the polycrystalline silicon film 14 by an ion doping method in order to form a storage capacitor.
[0064]
Next, the gate electrode 16 is patterned in a third photolithography step.
[0065]
Next, boron is doped into the polycrystalline silicon film 14 from above the gate electrode 16 by an ion doping method to form a p-ch TFT.
[0066]
Next, a resist pattern is formed in a fourth photolithography step, and phosphorus is doped from above the resist by an ion doping method in order to form an n-ch TFT. After that, the gate electrode 16 is patterned by etching, the resist is stripped, and a small amount of phosphorus is doped to form an LDD structure of an n-ch TFT.
[0067]
Next, after the gate electrode 16 and the interlayer insulating film 17 between the source electrode 18 and the drain electrode 19 are formed by a plasma CVD method or the like, a crystallization process for activating ion-doped impurities is performed by a laser annealing process.
[0068]
Next, in a fifth photolithography step, contact holes for making contact between the transistor and the source electrode 18 and the drain electrode 19 are formed.
[0069]
Next, a metal of a source electrode and a drain electrode material is formed by a sputtering method, and a source electrode 18 and a drain electrode 19 are formed in a sixth photolithography step.
[0070]
Next, in order to reduce defect levels in the semiconductor film, after performing a hydrogen plasma treatment, a passivation film 20 is formed by a method such as plasma CVD, and a contact hole is formed in the passivation film in a seventh photolithography step. Form.
[0071]
Next, a transparent conductive film to be the terminal electrode 21 is formed by a sputtering method or the like, and the terminal electrode is patterned in an eighth photolithography process, thereby completing the formation of the thin film transistor array substrate.
[0072]
Before forming the terminal electrodes, an organic film or the like may be formed or a reflective film may be formed to form a thin film transistor array for a display device using reflected light.
[0073]
In the third to fifth embodiments, the dehydrogenation treatment of the amorphous silicon film is not performed by heating the entire substrate to a high temperature, but the substrate or the material such as the silicon oxide film or the silicon nitride film is less absorbed. A method of performing dehydrogenation treatment using an excimer laser and a UV lamp as an irradiation light source of ultraviolet region light absorbed only by the above is exemplified. As a result, the dehydrogenation process can be efficiently performed only on the amorphous silicon, and similarly, the transistor characteristics can be improved and stabilized. According to this method, a polycrystalline thin film transistor can be directly formed on a substrate having low heat resistance such as a resin. The light source of light energy in the ultraviolet region is not limited to an excimer laser and a UV lamp as long as the above object is achieved.
[0074]
【The invention's effect】
Dehydrogenation from the silicon nitride film and the silicon oxide film under the amorphous silicon film is reduced, defects at the interface with the oxide film in and under the polycrystalline silicon film are reduced, and the mobility of the transistor is increased. Can be reduced, characteristics can be stably and improved, and a thin film transistor array substrate excellent in display quality of a liquid crystal display device can be manufactured. Further, a polycrystalline thin film transistor can be directly formed over a substrate having low heat resistance such as a resin.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view at the time of performing dehydrogenation annealing in an embodiment of the present invention.
FIG. 2 is a cross-sectional view of a transistor portion of the TFT array substrate according to the embodiment of the present invention.
FIG. 3 is a sectional view of a terminal portion of the TFT array substrate according to the embodiment of the present invention.
FIG. 4 is a diagram showing a relationship between a dehydrogenation annealing temperature and electric characteristics of a thin film transistor.
FIG. 5 is a diagram showing a relationship between a dehydrogenation annealing time and electric characteristics of a thin film transistor.
FIG. 6 is a main cross-sectional view of a TFT array substrate in the related art.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Silicon nitride film 3 Silicon oxide film 4 Amorphous silicon film or polycrystalline silicon film 5 Gate insulating film 6 Gate electrode 7 Interlayer insulating film 8 Source electrode 9 Drain electrode 10 Passivation film 11 Glass substrate or resin substrate 12 Silicon film 13 silicon oxide film 14 amorphous silicon film or polycrystalline silicon film 15 gate insulating film 16 gate electrode 17 interlayer insulating film 18 source electrode 19 drain electrode 20 passivation film 21 terminal electrode

Claims (9)

In a method for manufacturing a liquid crystal display device using a thin film transistor in which a semiconductor layer made of polycrystalline silicon, a gate insulating film, a gate electrode, an interlayer insulating film layer, a source electrode and a drain electrode are sequentially formed on a glass substrate for driving a liquid crystal, Manufacturing polycrystalline silicon from porous silicon by laser annealing, wherein the temperature of dehydrogenation annealing after forming amorphous silicon is in the range of 430 to 480 ° C. Method. 2. The method according to claim 1, wherein the time of the dehydrogenation annealing after the formation of the amorphous silicon is in the range of 20 to 50 minutes. In a method for manufacturing a liquid crystal display device using a thin film transistor in which a semiconductor layer made of polycrystalline silicon, a gate insulating film, a gate electrode, an interlayer insulating film layer, a source electrode and a drain electrode are sequentially formed on a glass substrate for driving a liquid crystal, When polycrystalline silicon is formed from porous silicon by a laser annealing method, the temperature of dehydrogenation annealing after forming amorphous silicon is in the range of 480 to 500 ° C., and the annealing time is in the range of 5 to 20 minutes. A method of manufacturing a liquid crystal display device. In a method for manufacturing a liquid crystal display device using a thin film transistor in which a semiconductor layer made of polycrystalline silicon, a gate insulating film, a gate electrode, an interlayer insulating film layer, a source electrode and a drain electrode are sequentially formed on a glass substrate for driving a liquid crystal, A liquid crystal display device characterized in that, when polycrystalline silicon is formed from porous silicon by a laser annealing method, an amorphous silicon film is formed and then dehydrogenation treatment is performed by irradiating light energy in an ultraviolet region. Production method. 5. The method according to claim 4, wherein the light energy in the ultraviolet region is selected from one of laser light and UV lamp light. Manufactures a liquid crystal display device using a thin film transistor for directly driving a liquid crystal on which a semiconductor layer made of polycrystalline silicon, a gate insulating film, a gate electrode, an interlayer insulating film layer, a source electrode and a drain electrode are directly formed on a resin substrate such as a plastic material. In the method, a semiconductor layer made of polycrystalline silicon is formed from an amorphous silicon layer by a laser annealing method. A method for manufacturing a liquid crystal display device that performs dehydrogenation treatment by irradiating energy. 7. The method according to claim 6, wherein the light energy in the ultraviolet region is selected from one of laser light and UV lamp light. A liquid crystal display device using a thin film transistor for directly driving a liquid crystal, in which a semiconductor layer made of polycrystalline silicon, a gate insulating film, a gate electrode, an interlayer insulating film layer, a source electrode and a drain electrode are directly formed on a resin substrate such as a plastic material. The polycrystalline silicon is obtained by polycrystallizing an amorphous silicon film by a laser annealing method, and the amorphous silicon film is irradiated with light energy in an ultraviolet region prior to the laser annealing method. A liquid crystal display device that has been dehydrogenated. 9. The liquid crystal display device according to claim 8, wherein the light energy in the ultraviolet region is selected from one of laser light and UV lamp light.

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