JP3741791B2 - Semiconductor film crystallization method and thin film transistor manufacturing method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a semiconductor film crystallization method for annealing a semiconductor film to crystallize the semiconductor film, and a method of manufacturing a thin film transistor using the crystallization method. More specifically, the present invention relates to a semiconductor film crystallization technique using a laser melt crystallization method.
[0002]
[Prior art]
In an active matrix substrate of a liquid crystal display device, it is desired to manufacture a thin film transistor (hereinafter referred to as TFT) by a low temperature process so that a glass substrate can be used as the substrate. Here, among the silicon films necessary for forming the channel region and the like of the TFT, the amorphous silicon film can be formed by a low temperature process, but has a drawback that the mobility of the TFT is low.
[0003]
Therefore, a laser melt crystallization method in which an amorphous silicon film on a substrate is melted and crystallized by irradiating a laser beam has been studied. Here, the energy density of the laser light is set to a level sufficient for the amorphous silicon to transfer to the polycrystalline silicon, and then irradiated with a constant energy density.
[0004]
[Problems to be solved by the invention]
However, the conventional laser melt crystallization method has various problems such as irradiation time, but there is a problem that both the crystallinity and surface roughness characteristics of the silicon film cannot be improved any more. . That is, in the laser melt crystallization method, as shown in FIG. 1, when the energy density E is increased, the silicon film is melted and solidified at a temperature equal to or higher than “▲” and Ec indicated by the alternate long and short dash line L1. To do. Here, as the energy density E is increased, the polycrystallization progresses. However, when the energy density E exceeds “□” and Ea indicated by the dotted line L2, the silicon film is microcrystallized, the mobility is lowered and the surface roughness is increased. This will happen. Although the detailed mechanism of such a phenomenon has not been elucidated, in the laser melt crystallization conditions that have been studied so far, the crystallinity of the silicon film and the surface due to the occurrence of the above-mentioned microcrystallization and surface roughness are described. There is a limit to further improving both characteristics of roughness.
[0005]
In view of the above problems, the object of the present invention is to further improve the crystallinity without roughening the surface of the semiconductor film by considering the conditions that have not been studied for laser melt crystallization. An object of the present invention is to provide a method for crystallizing a semiconductor film, and a method for manufacturing a TFT using the same.
[0006]
[Means for Solving the Problems]
In order to solve the above problems, in the method for crystallizing a semiconductor film according to the present invention, the semiconductor film on the substrate is irradiated with pulsed laser light to crystallize the semiconductor film. When the thickness is in the range of 30 nm to 80 nm and the pulsed laser beam is irradiated with a single shot in advance, a lower limit value of the energy density at which the semiconductor film is completely melted is set, and the pulsed laser is viewed from the semiconductor film. The pulse oscillation is applied to the semiconductor film under the condition that the energy density of light tends to shift from low density to high density, and the energy density of the pulsed laser light does not exceed the lower limit when irradiated with high density. It is characterized by irradiating with laser light.
[0007]
In this case, the conditions are set so as not to exceed the energy density at which the semiconductor film is completely melted when the pulsed laser beam is irradiated at a high energy density.
[0008]
In the present invention, the semiconductor film on the substrate is not suddenly irradiated with high-density pulsed laser light, but the energy density of the pulsed laser light tends to shift from low density to high density as seen from the semiconductor film. Irradiate with pulsed laser light under conditions. In addition, when the energy density of the pulsed laser beam is irradiated at a high density, the conditions are set so as not to exceed the melting energy density of the semiconductor film. When laser irradiation is performed in this way, microcrystallization occurs even when high-density laser light is irradiated, which causes microcrystallization in conventional laser melt crystallization, resulting in reduced mobility and surface roughness. Does not happen. Therefore, since the energy density of the pulsed laser beam that can be finally irradiated can be set high, the crystallinity can be improved.
[0009]
In the present invention, the semiconductor film is irradiated with the pulsed laser light under the condition that the energy density of the pulsed laser light tends to shift from low density to high density as viewed from the semiconductor film, and then viewed from the semiconductor film. It is preferable that the pulsed laser beam is irradiated to the semiconductor film under a condition that the energy density of the pulsed laser beam tends to shift from high density to low density.
[0010]
In the present invention, it is preferable to irradiate the semiconductor film with the pulsed laser light at least once in the high density state after irradiating the semiconductor film with a high energy density of the pulsed laser light. . By adopting such laser irradiation conditions, even if there is a variation in energy density during laser irradiation, the above variation is absorbed by repeated high-density laser irradiation, so a semiconductor film with no variation in crystallinity can be formed. Obtainable.
[0011]
In the present invention, when the irradiation region of the pulsed laser beam with respect to the semiconductor film is relatively moved, it is preferable that the irradiation regions for each pulse are moved so as to overlap each other. With this configuration, even when a semiconductor film formed over a large-area substrate is crystallized, discontinuity in crystallinity and surface roughness at the overlapping portion can be reduced.
[0012]
In the present invention, the thickness of the semiconductor film is preferably in the range of 30 nm to 80 nm. In particular, when manufacturing a TFT, it is preferable that the thickness of the semiconductor film constituting at least the channel region be in the range from 30 nm to 80 nm. This is because even when laser irradiation with the same energy density is performed, if the film thickness is too thin, such as less than 30 nm, the polycrystalline semiconductor film is changed to amorphous. Further, if the thickness of the semiconductor film exceeds 80 nm, the crystal grain size of the silicon film varies in the thickness direction.
[0013]
The present invention is characterized in that the pulsed laser beam is selectively irradiated to a region where the thin film transistor is to be formed in the semiconductor film.
Such a method for crystallizing a semiconductor film is effective in shortening the process.
The method for crystallizing a semiconductor film of the present invention can be used to form a TFT from the crystalline semiconductor film obtained by the method, and the manufactured TFT can be used on, for example, an active matrix substrate for a liquid crystal display device. To be manufactured.
[0014]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the drawings.
[0015]
[Embodiment 1]
In any embodiment of the present invention, the amorphous silicon film is polycrystallized by a laser melt crystallization method. In this laser melt crystallization method, as shown in FIG. 1, when the energy density E is increased, the silicon film is melted and solidified above Ec indicated by “▲” and one-dot chain line L1 to be polycrystallized. Here, as the energy density E is increased, the polycrystallization progresses. However, when the energy density E exceeds “□” and Ea indicated by the dotted line L2, the silicon film is microcrystallized, the mobility is lowered and the surface roughness is increased. This will happen. Further, when the silicon film is thin, even if the energy density E does not exceed Ea, if the energy density E exceeds “◯” and Eb indicated by a two-dot chain line L3, an amorphous silicon film is formed. . Note that if the energy density E exceeds Ed shown by “□” and the solid line L4, it evaporates.
[0016]
Therefore, in any form, when the amorphous silicon film is polycrystallized by the laser melt crystallization method, it is an essential condition that the energy density E is in the range from Ec to Ea and not more than Eb. is there. That is, within such an energy density range, the amorphous silicon film can be polycrystallized. Here, as the energy density E is increased, the crystallization proceeds, so that the silicon film is irradiated with the laser having the maximum energy density E within the above energy density range.
[0017]
In the method for crystallizing a semiconductor film according to this embodiment, for example, as shown in FIG. 2, a spot LS of a pulsed laser beam is first formed in the + x direction with respect to an amorphous silicon film Si formed on a substrate (not shown). Then, the spot LS is slightly shifted in the + y direction, and then the spot LS is applied to the entire surface of the amorphous silicon film Si while scanning the spot LS in the −x direction. With this as one cycle, in this embodiment, laser irradiation is repeated on the entire surface of the amorphous silicon film. Note that laser irradiation is performed in a vacuum atmosphere or an inert gas atmosphere.
[0018]
When the amorphous silicon film Si is crystallized by irradiating the silicon film Si on the substrate with the pulsed laser beam in this way, in this embodiment, a silicon oxide film of about 200 nm is formed on the substrate by ECR-CVD. After forming the (underlying protective film), an amorphous silicon film of about 50 nm is formed on the surface by LP-CVD. Thereafter, as shown in FIG. 3, the energy density of the pulsed laser beam is seen from the silicon film. Low density (for example, 160 mJ / cm ² ) To high density (eg, 310 mJ / cm ² The silicon film is irradiated with pulsed laser light under a condition that tends to shift to). That is, in this embodiment, the energy density E of the pulsed laser beam shifts from a low density to a high density as viewed from a certain point of the silicon film, rather than irradiating the silicon film with a high density pulsed laser beam. The pulsed laser beam is irradiated under conditions that tend to Also in this case, the value E2 having the highest energy density does not exceed the lower limit Ea.
[0019]
When laser irradiation is performed in this manner, the above-mentioned microscopic crystallization occurs in the conventional laser melt crystallization, and even if high-density laser light is irradiated that causes a decrease in mobility or surface roughness, the above-mentioned microscopic crystallization occurs. Crystallization does not occur.
[0020]
For example, when the maximum value E2 of the energy density is changed, the crystallinity of the silicon film when the energy density E reaches the maximum value E2 in multiple stages as in this embodiment is shown in FIG. ”And a solid line L11. Further, the crystallinity of the silicon film when suddenly irradiated with a high-density pulsed laser beam (energy density is E2) as in the prior art is indicated by “◯” and a solid line L13 in FIG. Here, since the vertical axis in FIG. 4 is the half width of the Raman peak, the smaller the value, the higher the crystallinity. As can be seen by comparing these results, according to the laser melt crystallization of this embodiment, the maximum value E2 of the energy density E can be set to a value that is considerably close to the lower limit value Ea, and the crystallinity can be increased. . On the other hand, according to the conventional laser melt crystallization, even if the maximum value E2 of the energy density E is brought close to the lower limit value Ea, the crystallinity does not increase. The reason why the half width of the Raman peak jumps up near the lower limit Ea is that microcrystallization occurs in the silicon film.
[0021]
Similarly, when the maximum value E2 of the energy density is changed, the roughness of the silicon film surface when the energy density E reaches the maximum value E2 in multiple steps as in this embodiment is shown in FIG. ”And a solid line L21. Further, the crystallinity of the silicon film when suddenly irradiated with a high-density pulsed laser beam (energy density is E2) as in the prior art is indicated by “◯” and a solid line L23 in FIG. Here, since the vertical axis of FIG. 5 is the difference between the maximum value and the minimum value on the average surface in the measurement region, the larger the value, the rougher the surface. As can be seen by comparing these results, according to the laser melt crystallization of this embodiment, even if the maximum value E2 of the energy density E is set to a value very close to the lower limit Ea and the crystallinity is increased, silicon The film surface is not rough. On the other hand, in the conventional laser melt crystallization, the surface of the silicon film is extremely rough as long as the degree of crystallinity does not increase even if the maximum value E2 of the energy density E approaches the lower limit Ea.
[0022]
Therefore, according to this embodiment, since the energy density of the pulsed laser beam that can be finally irradiated can be set high, the crystallinity can be improved without roughening the surface of the silicon film. In addition, the defect density in the silicon film can be reduced.
[0023]
In the present invention, when the irradiation region of the pulsed laser beam with respect to the silicon film is relatively moved, as shown in FIG. 2, the irradiation regions (spots LB) for each pulse may be moved so as to overlap each other. preferable. With this configuration, even when a silicon film formed on a large-area substrate is crystallized, discontinuity in crystallinity and surface roughness at the overlapping portion can be reduced.
[0024]
In this embodiment, the thickness of the silicon film is about 50 nm. However, when the thickness is in the range of 30 nm to 80 nm, a stable polycrystalline silicon film can be obtained with certainty. That is, as shown in FIG. 1, even when laser irradiation with the same energy density is performed, if the film thickness is too thin, such as less than 30 nm, the polycrystalline silicon film changes to amorphous. Because. Further, if the thickness of the semiconductor film exceeds 80 nm, the crystal grain size of the silicon film varies in the thickness direction.
[0025]
In the conditions shown in FIG. 3, the energy density E is set to reach the maximum value E2 in seven stages. However, the pulsed laser beam is used so that the energy density tends to shift from low density to high density. If irradiation is performed, the number of steps is not limited. For example, the maximum value E2 may be set in two stages in consideration of throughput.
[0026]
[Embodiment 2]
In this embodiment, as shown in FIG. 6, after irradiating the pulsed laser beam under the condition that the energy density of the pulsed laser beam tends to shift from low density to high density as seen from the silicon film, the pulse is seen from the silicon film. The pulsed laser beam is irradiated under the condition that the energy density of the oscillation laser beam tends to shift from high density to low density. When such laser irradiation conditions are employed, the crystallinity of the silicon film when the maximum energy density value E2 is changed so as to exceed the lower limit value Ea as shown by “□” and the solid line L12 in FIG. Even when a high-density laser beam is irradiated, the crystallinity of the silicon film is recovered by the low-density laser irradiation performed later, and the crystallinity is remarkably high.
[0027]
Further, when the laser irradiation condition of this embodiment is adopted, the roughness of the silicon film surface when the maximum energy density value E2 is changed is shown as “□” and a solid line L22 in FIG. The surface of the silicon film is less rough for a high price.
[0028]
In this embodiment as well, when the irradiation region of the pulsed laser beam is relatively moved, it is preferable that the irradiation regions (spots LB) for each pulse are overlapped as shown in FIG. . With this configuration, even when a silicon film formed on a large-area substrate is crystallized, discontinuity in crystallinity and surface roughness at the overlapping portion can be reduced. Moreover, it is preferable to obtain a stable polycrystalline silicon film by setting the film thickness of the silicon film to a range from 30 nm to 80 nm. Furthermore, if the pulsed laser beam is irradiated so that the energy density is shifted from low density to high density, and then the pulsed laser beam is irradiated so as to shift from high density to low density, then that step The number is not limited, and may be set to reach the maximum value E2 in two stages, for example.
[0029]
[Embodiment 3]
In either of the first and second embodiments, as shown in FIG. 7 or FIG. 8, after the energy density of the pulsed laser beam becomes high as viewed from the silicon film, the pulsed laser beam is used in this high density state. It is preferable to irradiate the silicon film at least once. The irradiation conditions shown in FIG. 7 correspond to the case where this embodiment is combined with Embodiment 1, and the irradiation conditions shown in FIG. 8 correspond to the case where this embodiment is combined with Embodiment 2.
[0030]
By adopting such laser irradiation conditions, even if there is a variation in energy density during laser irradiation, the above variation is absorbed by repeated high-density laser irradiation, so a silicon film with no variation in crystallinity can be formed. Obtainable.
[0031]
[Example]
Such a method for crystallizing a semiconductor film can be used to form a TFT from the crystalline semiconductor film thus obtained, and the TFT manufactured in this way can be used, for example, on an active matrix substrate for a liquid crystal display device. To be manufactured. Therefore, as an application example of the present invention, an example of manufacturing TFTs on an active matrix substrate of a liquid crystal display device will be described.
[0032]
(Configuration of active matrix substrate)
FIG. 9A is an explanatory diagram schematically showing the configuration of the active matrix substrate of the liquid crystal display device.
[0033]
In this figure, a liquid crystal display device 1 has a pixel region 5 partitioned and formed by a signal line 3 and a scanning line 4 on an active matrix substrate 2, in which an image signal is passed through a pixel TFT 10. A liquid crystal capacitor 6 of the liquid crystal cell is inputted. A data driver section 7 including a shift register 71, a level shifter 72, a video line 73, and an analog switch 74 is configured for the signal line 3, and a scan driver including a shift register 81 and a level shifter 82 for the scanning line 4. Part 8 is configured. In the pixel region 5, a storage capacitor 51 may be formed between the pixel line 5 and the preceding scanning line 4.
[0034]
In the data driver unit 7 and the scan driver unit 8, as illustrated in FIG. 9B, a CMOS circuit constituted by N-type TFTs n1 and n2 and P-type TFTs p1 and p2, as exemplified by a two-stage inverter, It is formed with high density. However, the TFT 10 of the active matrix portion 9 and the TFTs n1 and n2 of the data driver portion 7 and the P-type TFTs p1 and p2 have the same basic structure and are manufactured in the same process.
[0035]
As the active matrix substrate 2, only the active matrix unit 9 is configured on the substrate, the data driver unit 7 is configured on the same substrate as the active matrix unit 9, and scanning is performed on the same substrate as the active matrix unit 9. Some have a driver unit 8 and some have a data driver unit 7 and a scan driver unit 8 on the same substrate as the active matrix unit 9. Even in the case of the driver-embedded active matrix substrate 2, the shift register 71, level shifter 72, video line 73, analog switch 74, and the like included in the data driver unit 7 are all configured on the active matrix substrate 2. There are a driver built-in type and a partial driver built-in type in which some of them are formed on the active matrix substrate 2, and the present invention can be applied to both.
[0036]
10 is an enlarged plan view showing one of the pixel regions of the active matrix substrate, FIG. 11A is a cross-sectional view taken along the line II ′ of FIG. 10, and FIG. It is sectional drawing in the II-II 'line. Since the TFTs in the data driver unit 7 and the like basically have the same structure, the illustration thereof is omitted.
[0037]
In these drawings, in any pixel region 5, the TFT 10 is connected to the source region 11 and the pixel electrode 19 which are electrically connected to the data line 3 through the contact hole 17 of the interlayer insulating film 16 on the substrate 20. The drain region 12 electrically connected through the contact hole 18 of the interlayer insulating film 16, the channel region 13 for forming a channel between the drain region 12 and the source region 11, and gate insulation with respect to the channel region 13 The gate electrode 15 is opposed to the film 14. The gate electrode 15 is configured as a part of the scanning line 4. A base protective film 21 made of a silicon oxide film is formed on the surface side of the substrate 20.
[0038]
(TFT manufacturing method)
With reference to FIG. 12, the manufacturing method of TFT is demonstrated. 12 is a process sectional view of the TFT corresponding to the section taken along the line II ′ of FIG.
[0039]
In this example, the following processes are performed using a 235 mm square non-alkali glass plate as the substrate.
[0040]
(Base protective film formation process)
In FIG. 12A, first, a silicon oxide film having a thickness of 200 nm to be the base protective film 21 is formed on the surface of the substrate 20 under a temperature condition of 250 ° C. to 300 ° C. by an ECR-PECVD method. The silicon oxide film can also be formed by the APCVD method. In this case, the silicon oxide film is formed using monosilane and oxygen as source gases in a state where the temperature of the substrate 20 is set in a range from 250 ° C. to 450 ° C.
[0041]
(Semiconductor film deposition process)
Next, an intrinsic silicon film 30 (semiconductor film) is deposited on the surface of the base protective film 21 to a thickness of about 50 nm. In this example, the amorphous silicon film 30 is deposited at a deposition temperature of 425 ° C. using a high-vacuum LPCVD apparatus while disilane, which is a source gas, flows in 200 SCCM. In this high vacuum type LPCVD apparatus, a substrate is disposed inside a reaction chamber, and the temperature in the reaction chamber is first maintained at 250 ° C. In this state, the operation of the turbo molecular pump is started, and after steady rotation is reached, the temperature in the reaction chamber is raised from 250 ° C. to a deposition temperature of 425 ° C. over about 1 hour. During the first 10 minutes after the start of the temperature increase, no gas is introduced into the reaction chamber, the temperature is increased in vacuum, and then a nitrogen gas having a purity of 99.9999% or more continues to flow at 250 SCCM. After reaching the deposition temperature, 200 SCCM of disilane which is a raw material gas is supplied, and 1000 SCCM of helium for dilution having a purity of 99.9999% or more is supplied.
[0042]
In forming the silicon film 30, a PECVD method or a sputtering method may be used. According to these methods, the film formation temperature can be set in a range from room temperature to 350.degree.
[0043]
(Annealing process by laser melt crystallization method)
Next, as shown in FIG. 12B, the amorphous silicon film 30 is irradiated with laser light to modify the silicon film 30 into polycrystalline silicon. In this example, for example, xenon chloride (XeCl) excimer laser (wavelength: 308 nm) is irradiated. In this step, laser irradiation is performed in a vacuum atmosphere or an inert gas atmosphere with the substrate 20 at room temperature (25 ° C.).
[0044]
In performing this annealing step, any of the first to third embodiments described above can be applied. Here, the base protective film 21 and the silicon film 30 are formed on the entire surface of the substrate 20, and laser annealing may be performed on the entire surface. However, laser irradiation is selectively performed only on the region where the TFT is to be formed. The laser annealing time may be shortened.
[0045]
(Silicon film patterning process)
Next, as shown in FIG. 12C, the silicon film 30 that has been subjected to the annealing process is patterned using a photolithography technique to form an island-shaped silicon film 31.
[0046]
(Gate insulating film formation process)
Next, as shown in FIG. 12D, a gate oxide film 14 made of a silicon oxide film is formed on the silicon film 31 under a temperature condition of 250 ° C. to 300 ° C. by an ECR-PECVD method.
[0047]
(Gate electrode formation process)
Next, after forming a tantalum thin film having a thickness of 600 nm on the surface side of the gate oxide film 14 by sputtering, the tantalum thin film is patterned using a photolithography technique to form the gate electrode 15. In this example, when forming the tantalum thin film, the substrate temperature is set to 180 ° C., and an argon gas containing 6.7% nitrogen gas is used as a sputtering gas. The tantalum thin film thus formed has an α structure and a low specific resistance.
[0048]
(Impurity introduction process)
Next, impurity ions are implanted into the silicon film 31 using the bucket electrode 15 as a mask by using a bucket type mass non-separation type ion implantation apparatus (ion doping apparatus). As a result, the source region 11 and the drain region 12 are formed in a self-aligned manner with respect to the gate electrode 15. At this time, a portion of the silicon film 31 where the impurity ions are not implanted becomes the channel region 13.
[0049]
Note that in the case of forming a P-channel TFT, diborane diluted with hydrogen gas so as to have a concentration of 5% is used as a source gas. In the case of forming an N-channel TFT, phosphine diluted with hydrogen gas as a source gas so as to have a concentration of 5% is used.
[0050]
(Interlayer insulation film formation process)
Next, as shown in FIG. 12E, a silicon oxide film having a thickness of 50 nm is formed as the interlayer insulating film 16 under a temperature condition of 250 ° C. to 300 ° C. by PECVD. The source gas at this time is TEOS and oxygen. The substrate temperature is 250 ° C to 300 ° C.
[0051]
(Activation process)
Next, heat treatment is performed at 300 ° C. for 1 hour in an oxygen atmosphere to activate the implanted phosphorus ions and modify the interlayer insulating film 16.
[0052]
(Wiring process)
Next, contact holes 17 and 18 are formed in the interlayer insulating film 16. Thereafter, the source electrode (data line 3) is electrically connected to the source region 11 through the contact holes 17 and 18, the drain electrode (pixel electrode 19) is electrically connected to the drain region 12, and the TFT 10 is connected. Form.
[0053]
(Main effects of the embodiment)
As described above, in the manufacturing method of the active matrix substrate of this example, since the method of increasing the energy density at the time of laser irradiation in multiple steps is used in the annealing process, the crystallinity is good and the surface is rough. A polycrystalline silicon film having no defects can be obtained. Therefore, a TFT having a high operation speed can be manufactured. The laser annealing step may be performed after patterning the amorphous silicon film.
[0054]
【The invention's effect】
As described above, in the semiconductor film crystallization method according to the present invention, the semiconductor film on the substrate is not suddenly irradiated with a high-density pulsed laser beam, but the pulsed laser beam is viewed from the semiconductor film. It is characterized by irradiating pulsed laser light on the condition that the energy density tends to shift from low density to high density. Therefore, in the present invention, the above-mentioned microcrystallization is not caused even by irradiation with high-density laser light that causes microcrystallization to occur in conventional laser melt crystallization, resulting in lower mobility or surface roughness. I don't get up. Therefore, since the energy density of the pulsed laser beam that can be finally irradiated can be set high, the crystallinity can be improved.
[Brief description of the drawings]
FIG. 1 is an explanatory diagram showing a relationship between energy density and change in silicon in laser melt crystallization.
FIG. 2 is an explanatory view schematically showing laser spot scanning conditions in laser melt crystallization.
FIG. 3 is an explanatory diagram showing laser melt crystallization conditions according to Embodiment 1 of the present invention.
FIG. 4 is a graph showing the relationship between energy density and crystallinity in laser melt crystallization.
FIG. 5 is a graph showing the relationship between energy density and surface roughness in laser melt crystallization.
FIG. 6 is an explanatory diagram showing laser melt crystallization conditions according to Embodiment 2 of the present invention.
FIG. 7 is an explanatory diagram showing laser melt crystallization conditions according to Embodiment 3 of the present invention.
FIG. 8 is an explanatory diagram showing another laser melt crystallization condition according to Embodiment 3 of the present invention.
FIG. 9A is an explanatory view schematically showing an active matrix substrate of a liquid crystal display device according to an embodiment of the present invention, and FIG. 9B is an explanatory view of a CMOS circuit used in its drive circuit.
FIG. 10 is an enlarged plan view showing a pixel region on an active matrix substrate.
11A is a cross-sectional view taken along line II ′ of FIG. 10, and FIG. 11B is a cross-sectional view taken along line II-II ′ of FIG.
12 is a process sectional view of the TFT corresponding to the section taken along the line II ′ of FIG. 10 in the embodiment of the present invention.
[Explanation of symbols]
1. Liquid crystal display device
2 ... Active matrix substrate
3 ... Signal line
4 ... Scanning line
5 ... Pixel area
6. Liquid crystal capacity
9 ... Active matrix part
10 ... TFT
11 ... Source region
12 ... Drain region
13 ... Channel formation region
14 ... Gate insulating film
15 ... Gate electrode
30, Si ... silicon film (semiconductor film)
31 ... Island-like silicon film (semiconductor film)
LS ... Spot of laser beam

Claims (6)

In crystallizing the semiconductor film by irradiating the semiconductor film on the substrate with pulsed laser light,
The thickness of the semiconductor film ranges from 30 nm to 80 nm,
When the pulse oscillation laser beam is irradiated with a single shot in advance, a lower limit value of the energy density at which the semiconductor film is completely melted is set,
A condition in which the energy density of the pulsed laser beam tends to shift from a low density to a high density when viewed from the semiconductor film, and the lower limit value is not exceeded when the energy density of the pulsed laser beam is irradiated at a high density And irradiating the semiconductor film with the pulsed laser beam.   2. The semiconductor laser according to claim 1, wherein the semiconductor film is irradiated with the pulsed laser light under a condition that the energy density of the pulsed laser light tends to shift from a low density to a high density as viewed from the semiconductor film, Accordingly, the semiconductor film crystallization method is characterized in that the semiconductor film is irradiated with the pulsed laser light under a condition that the energy density of the pulsed laser light tends to shift from high density to low density.   3. The pulse oscillation laser light is applied to the semiconductor film at least once in the high density state after the energy density of the pulse oscillation laser light becomes high when viewed from the semiconductor film. Irradiation, a method for crystallizing a semiconductor film.   4. The method according to claim 1, wherein when the irradiation region of the pulsed laser beam with respect to the semiconductor film is relatively moved, the irradiation regions for each pulse are moved so as to overlap each other. A method for crystallizing a semiconductor film.   5. The method for crystallizing a semiconductor film according to claim 1, wherein the pulsed laser light is selectively irradiated to a region where the thin film transistor is to be formed in the semiconductor film.   6. A method for manufacturing a thin film transistor, comprising forming a thin film transistor from a crystalline semiconductor film obtained by the method for crystallizing a semiconductor film as defined in claim 1.

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