JPH08139331A - Method of manufacturing thin film transistor - Google Patents

Abstract

PURPOSE: To form a polycrystalline semiconductor thin film having a large crystal grain size for a short time by irradiating an excimer laser beam on an amorphous semiconductor thin film to produce crystal nuclei and by making the solid phase growth. CONSTITUTION: On a glass substrate 1 an amorphous Si thin film 2 is formed, on which an excimer laser beam 3 is irradiated at an adequate energy whereby the film 2 itself rises its temp. because of an efficiency absorption of this energy in Si, thus producing crystal nuclei. It is then annealed at 550-700 deg.C (low temp). for several hours to make the solid phase growth to form a polycrystalline Si thin film 4. By this growth, a polycrystalline Si thin film 4 having a large crystal grain size of 1μm or more.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a thin film transistor used in, for example, a liquid crystal display device.

[0002]

2. Description of the Related Art Thin film transistors have been actively studied in recent years because they can be applied to liquid crystal display devices and the like. In manufacturing a thin film transistor, an amorphous silicon thin film or a polycrystalline silicon thin film is generally used for the active layer of the transistor, but these thin films contain many crystal defects and strains. However, the increase in leak current and the decrease in on-current have become problems. Conventionally, in order to solve these problems, high temperature annealing, low temperature long time annealing, laser annealing and the like have been performed.

Solid phase growth and laser annealing are used for crystal growth from an amorphous silicon thin film to a polycrystalline silicon thin film, but these are generally used alone,
It is performed for the purpose of crystal growth.

[0004]

By the way, in the production of liquid crystal display elements and the like, it is becoming difficult to cope with lower temperatures, shorter steps, and improved performance. It has been found that the electrical characteristics of a silicon-based transistor are improved as the active layer is closer to single crystal silicon, that is, the size of silicon crystal is increased and crystal defects are decreased. However, in the case of solid-phase growth, for example, as the above-described crystal growth, the number of crystal nuclei and the size of crystal grains cannot be controlled because accidental generation of crystal nuclei is used. Further, if the fabrication is performed at a low temperature (700 ° C. or less), strains, crystal defects and the like due to crystal growth and process are left, which leads to deterioration of transistor characteristics.

In view of the above points, the present invention makes it possible to lower the temperature and shorten the process time during crystal growth, and
It is intended to provide a method of manufacturing a thin film transistor, which is capable of manufacturing a thin film transistor having good electric characteristics by enlarging crystal grains.

[0006]

In the method of manufacturing a thin film transistor according to the first aspect of the present invention, an amorphous semiconductor thin film 2 is irradiated with an excimer laser 3 to generate crystal nuclei, and then solid phase growth is performed to form grains. To obtain a polycrystalline semiconductor thin film 4 having a large diameter,
A thin film transistor is manufactured by using this polycrystalline semiconductor thin film 4 as an active layer.

In the method of manufacturing a thin film transistor according to the second aspect of the present invention, the amorphous semiconductor thin film 2 is irradiated with the first excimer laser 26 to control the number of crystal nuclei generated, and then the first excimer laser 26 is used. The polycrystalline semiconductor thin film 4 is obtained by irradiating the second excimer laser 27 having the same or higher irradiation energy and crystal growth, and the polycrystalline semiconductor thin film 4 is used as an active layer to manufacture a thin film transistor.

A method of manufacturing a thin film transistor according to a third aspect of the present invention is the method of manufacturing a thin film transistor according to the first or second aspect of the invention, in which after the polycrystalline semiconductor thin film 4 is obtained, an excimer laser 5 is irradiated to the polycrystalline semiconductor film. The strain and crystal defects remaining in the thin film 4 are removed.

[0009]

In the first aspect of the present invention, the amorphous semiconductor thin film 2 is used.
By irradiating the excimer laser 3 on the amorphous semiconductor thin film 2 itself, the temperature rises and crystal nuclei are generated. At this time,
The generation of crystal nuclei is controlled by changing the irradiation laser wavelength, the number of irradiations, the irradiation area, and the irradiation energy. Subsequently, for example, solid-phase growth at 550 ° C. to 700 ° C. increases the grain size, and the polycrystalline semiconductor thin film 4 having large crystal grains can be obtained at low temperature in a short time. By using this large grain size polycrystalline semiconductor thin film 4 for the active layer, a thin film transistor having excellent electric characteristics can be manufactured.

In the second aspect of the present invention, the number of generated crystal nuclei can be controlled by irradiating the amorphous semiconductor thin film 2 with the first excimer laser 26. That is, the number of generated crystal nuclei can be limited. Then, by irradiating the second excimer laser 27 having an irradiation energy equal to or higher than that of the first excimer laser 26, the crystal grows to have a large grain size, and the polycrystalline semiconductor thin film 4 having a large grain size at a low temperature in a short time 4 Is obtained. By using this large grain size polycrystalline semiconductor thin film 4 for the active layer, a thin film transistor having excellent electric characteristics can be manufactured.

In the third aspect of the present invention, in the manufacturing method of the first or second aspect of the invention, the polycrystalline semiconductor thin film 4 is obtained and then irradiated with an excimer laser 5 so that the polycrystalline semiconductor thin film 4 remains on the polycrystalline semiconductor thin film 4. Strains and crystal defects are removed. The polycrystalline semiconductor thin film 4 from which these strains and crystal defects are removed
Is used as the active layer, a thin film transistor having better electric characteristics can be manufactured.

[0012]

Embodiments of the method of manufacturing a thin film transistor according to the present invention will be described below with reference to the drawings. The example is applied to the production of a liquid crystal display element.

1 to 9 show an embodiment of the present invention. First, as shown in FIG. 1, a film thickness of 100 nm is formed on one insulating substrate for forming a liquid crystal display device, for example, a glass substrate 1.
Hereinafter, in this example, the amorphous silicon thin film 2 having a thickness of about 80 nm is formed by, for example, the plasma CVD method or the low pressure CVD method. Then, the excimer laser 3 is applied to the amorphous silicon thin film 2 at an appropriate energy, that is, 50 mJ / cm ² to 2.
Irradiation is performed with energy of 00 mJ / cm ² . In this example, the irradiation energy was 170 mJ / cm ² . Since the excimer laser 3 is efficiently absorbed by silicon, the amorphous silicon thin film 2 itself is heated by the irradiation of the excimer laser 3 to generate crystal nuclei. At this time, the number of generated crystal nuclei is controlled by changing the irradiation laser wavelength, the number of irradiations, the irradiation area, and the irradiation energy. As the irradiation energy,
When it is less than 50 mJ / cm ^{2, the} number of nucleation and the number of nucleation are small, and when it is more than 200 mJ / cm ² , it becomes difficult to control the number of nucleation.

Next, annealing is performed at a temperature of 550 ° C. to 700 ° C. for several hours (for example, furnace annealing by an electric furnace) to carry out solid phase growth to form a polycrystalline silicon thin film 4 as shown in FIG. . By this solid phase growth, a polycrystalline silicon thin film 4 having a large grain size of 1 μm or more (so-called huge) can be obtained.

Next, as shown in FIG. 3, the polycrystalline silicon thin film 4 is irradiated with an excimer laser 5 to remove strains and crystal defects remaining in the polycrystalline silicon thin film 4. The irradiation energy of the excimer laser 5 is energy that does not melt the polycrystalline silicon thin film 4, and is, for example, 10
It can be set to 0 mJ / cm ^{2 to} 250 mJ / cm ² .

Next, as shown in FIG. 4, the polycrystalline silicon thin film 4 thus obtained is selectively etched so as to leave the pattern of the thin film transistor formed thereafter. Subsequently, a gate insulating film 6 is deposited on the entire surface including the surface of the patterned polycrystalline silicon thin film 4. That is, for example, a silicon oxide film (SiO ₂ film) 7 having a film thickness of about 60 nm is formed by an atmospheric pressure CVD method, and a silicon nitride film (S) having a film thickness of about 50 nm is formed thereon by a low pressure CVD method.
i ₃ N ₄ film) 8 is formed, and a silicon oxide film (SiO ₂ film) 9 having a film thickness of about 10 nm is further formed thereon by the CVD method.
To form a gate insulating film 6 having a three-layer film structure.

Thereafter, in order to control the threshold voltage Vth of the thin film transistor, if necessary, for example, boron ions are implanted into the polycrystalline silicon thin film 4 with a dose amount of about 1 to 8 × 10 ¹² cm ² .

Next, a polycrystalline silicon film having a film thickness of, for example, about 300 nm to be a gate electrode is formed on the gate insulating film 6. Since this polycrystalline silicon film needs to have a low resistance, it is doped with, for example, phosphorus to reduce the resistance. afterwards,
As shown in FIG. 5, the polycrystalline silicon film is patterned by selective etching to form a gate electrode 11. Further, the silicon oxide film 9 and the silicon nitride film 8 of the gate insulating film 6 are patterned by selective etching.

Next, as shown in FIG. 6, in order to form the source region and the drain region of the thin film transistor, for example, arsenic ions (As.sup. ⁺ ) Are applied to the portion other than the gate electrode 11 through the resist mask 12 by 2.times.10. ¹⁴ ~ 1 x 10 ¹⁵
Ion implantation is performed with a dose amount of about cm ² and activated to form the source region 13 and the drain region 14.

Next, as shown in FIG. 7, an interlayer insulating film 16 made of, for example, SiO _{2 and having} a film thickness of about 500 nm is formed to protect and insulate the electrodes. If necessary for the SiO ₂ film of the interlayer insulating film 16, phosphorus, arsenic, lead, antimony,
Contains boron and the like. In the interlayer insulating film 16, one of the source region 13 and the drain region 14, in this example, the contact hole 17 facing the source region 13 is formed.

Next, as shown in FIG. 8, an Al film having a film thickness of, for example, about 300 nm including the contact hole 17 is formed, and the Al film is patterned by selective etching to form an Al film connected to the source region 13. Signal line 1
8 is formed. In order to insulate and isolate the signal line 18, for example, an SiO ₂ -based interlayer insulating film 19 is formed to have a film thickness of about 500 nm. If necessary, the SiO ₂ -based interlayer insulating film 19 may contain 0 to 8 wt% phosphorus, arsenic, lead, antimony, boron, or the like.

Next, as shown in FIG. 9, a plasma SiN film, a plasma SiO ₂ film, an Al film, a Ti film, a Ta film or the like is formed as an external diffusion preventing film for hydrogen components.
In this example, as shown in FIG. 9, a plasma silicon nitride film 20 having a film thickness of, for example, about 500 nm is formed on the interlayer insulating film 19. Here, N ₂ annealing treatment is performed at 250 ° C. to 500 ° C. to accelerate hydrogenation.

Next, a contact hole 22 is formed so as to face the drain region 14 or the source region 13, which is the drain region 14 in this example. Further, the plasma silicon nitride film 20 on the region where the pixel electrode 23 is formed is selectively removed by etching. This is to increase the light transmittance in the pixel portion. Next, an ITO (indium tin oxide) thin film that is a transparent electrode including the contact hole 22 is formed to have a film thickness of, for example, about 100 nm, and is patterned to form a pixel electrode 23 formed of the ITO thin film connected to the drain region 14. To do. Thus, the so-called TF in which the thin film transistor Tr and the pixel electrode 23 are formed
The T substrate 24 is obtained.

According to the method of manufacturing the thin film transistor Tr described above, the amorphous silicon thin film 2 is irradiated with the excimer laser 3 to generate crystal nuclei. The number of crystal nuclei can be controlled by controlling the number of times and the irradiation energy of the irradiation area. Then, by performing solid phase growth at 550 ° C. to 700 ° C., the polycrystalline silicon film 4 having a large crystal grain size can be formed. That is, the polycrystalline silicon film 4 having a large crystal grain size and thus a small number of crystal grains can be formed at a lower temperature and in a shorter time than in the conventional case.

By using this polycrystalline silicon film 4 as the active layer of the thin film transistor Tr, it is possible to improve the electrical characteristics of the thin film transistor, such as reducing the leak current and increasing the on-current.

Further, after the amorphous silicon film 2 is crystallized into the polycrystalline silicon film 4 by solid phase growth, the excimer laser 5 is irradiated to the strain and crystal remaining in the polycrystalline silicon thin film 4. Defects and the like are removed, the transistor characteristics can be further improved, and a high-performance thin film transistor can be obtained.

In addition, since the excimer laser is efficiently absorbed by silicon, the silicon thin film of the active layer can be annealed without heating the glass substrate 1, and the degree of freedom in selecting the substrate 1 is expanded, and the liquid crystal display device When applied to manufacturing, it is advantageous when manufacturing a drive circuit on a large substrate.

10 to 13 show another embodiment of the present invention. In this example, as shown in FIG. 10, an amorphous silicon thin film 2 having a film thickness of 100 nm or less, in this example, about 80 nm is formed on one insulating substrate for forming a liquid crystal display element, for example, a glass substrate 1 by plasma treatment. The film is formed by the CVD method or the low pressure CVD method. And this amorphous silicon thin film 2
Then, the excimer laser 26 is irradiated to generate crystal nuclei.
The excimer laser 26 has a weak irradiation energy, for example, irradiation energy of 50 mJ / cm ^{2 to} 200 mJ / cm.
Irradiate at ² to control the number of crystal nuclei generated. When the irradiation energy is less than 50 mJ / cm ² , it contributes only to the temperature rise of the silicon thin film 2, the nucleation and the number of nuclei generated are small, and the nucleation also occurs in the irradiation of the excimer laser 27 next time, and the whole crystallizes. Will end up. Also, the irradiation energy is 200
If it exceeds mJ / cm ^{2, the} number of crystal nuclei generated cannot be controlled and the entire silicon thin film 2 is completely crystallized only by laser irradiation.

Subsequently, as shown in FIG. 11, an excimer laser 27 having an irradiation energy equal to or higher than the irradiation energy of the excimer laser 26 is irradiated to grow a crystal,
A polycrystalline silicon thin film 4 having a large crystal grain size is formed. Since the number of crystal nuclei is limited, the number of crystal grains is limited,
A polycrystalline silicon thin film 4 having a large crystal grain size can be obtained.

Next, as shown in FIG. 12, the polycrystalline silicon thin film 4 is irradiated with an excimer laser 5 to remove strains and crystal defects remaining in the polycrystalline silicon thin film 4. The irradiation energy of the excimer laser 5 at this time is
Energy that does not exceed the irradiation energy of the excimer laser 27 for the second time and energy that does not melt the polycrystalline silicon thin film 4, and is 100 mJ as described above.
/ Cm ² can be a ~250mJ / cm ^2.

Thereafter, this polycrystalline silicon thin film 4 is used as an active layer of a thin film transistor, and through steps similar to those shown in FIGS. 4 to 9, which are not shown, finally, as shown in FIG. A TFT substrate 24 in which a thin film transistor Tr and a pixel electrode 23 are formed on 1 is obtained. Note that FIG.
In FIG. 9, parts corresponding to those in FIG.

According to the manufacturing method of a thin film transistor Tr in this embodiment, by irradiating the excimer laser 26 of the irradiation energy 50mJ / cm ² ~200mJ / cm ² with respect to the amorphous silicon thin film 2, control the crystal nuclei incidence Then, the polycrystalline silicon thin film 4 having a large crystal grain size can be formed by irradiating the excimer laser 27 having the irradiation energy equal to or higher than that of the excimer laser 26 to grow the crystal. By using this polycrystalline silicon thin film 4 for the active layer of the thin film transistor Tr, it is possible to improve the electrical characteristics of the thin film transistor, such as reducing the leak current and increasing the on-current.

Further, by irradiating the obtained polycrystalline silicon thin film 4 with the excimer laser 5, strains, crystal defects, etc. remaining in the polycrystalline silicon thin film 4 can be removed, and further electrical characteristics can be improved. An improvement is obtained.

Also in this embodiment, the excimer laser 2 is used.
Since the crystal nucleation and crystal growth are performed by irradiation of 6,27,
Since the processing time is short, for example, about 5 minutes per sheet, 2 hours for 25 sheets (about 20 hours in the conventional solid phase growth), and a polycrystalline silicon thin film with large crystal grains can be obtained at low temperature, The substrate 1 is not affected by heat and the degree of freedom in selecting the substrate is increased. For example, the substrate 1 is suitable for production of a liquid crystal display element.

The irradiation energy of the excimer lasers 3, 5, 26, and 27 in each of the above-mentioned embodiments is for the case where the film thickness of the silicon thin film is 100 nm or less, and about 50 nm is possible. Energy increases.

In the above example, the invention is applied to the thin film transistor used for the liquid crystal display element, but it is needless to say that the invention can be applied to the manufacture of other thin film transistors.

[0037]

According to the first aspect of the present invention, an amorphous semiconductor thin film is irradiated with an excimer laser to generate crystal nuclei, and then solid phase growth is performed. A polycrystalline semiconductor thin film having a large crystal grain size can be formed. By using this polycrystalline semiconductor thin film as an active layer of a thin film transistor, it is possible to manufacture a thin film transistor having excellent electrical characteristics such as reducing leak current and increasing on-current. When manufacturing a thin film transistor on a substrate by lowering the process temperature, the substrate is not affected by thermal effects (deformation, warpage, etc.), so the degree of freedom in selecting the substrate is widened, and it can be applied to, for example, the production of liquid crystal display elements. If it is suitable,

According to the second aspect of the present invention, the amorphous semiconductor thin film is irradiated with the first excimer laser to control the number of generated crystal nuclei, and then the irradiation energy is equal to or higher than that of the first excimer laser. By irradiating the second excimer laser for crystal growth, a polycrystalline semiconductor thin film having a large crystal grain size can be formed in a short time without heating the substrate. By using this polycrystalline semiconductor thin film as an active layer of a thin film transistor, it is possible to form a thin film transistor having excellent electric characteristics such as reduction of leak current and increase of on-current. Since the excimer laser is efficiently absorbed by the semiconductor, it is possible to form a polycrystalline semiconductor thin film without heating the substrate, and the degree of freedom in selecting the substrate is widened, and it is suitable for application in the production of liquid crystal display devices, for example. .

According to the third aspect of the present invention, in the manufacturing method of the first or second aspect of the invention, after the polycrystalline semiconductor thin film is obtained, the excimer laser is further irradiated to the inside of the crystal remaining in the polycrystalline semiconductor thin film. The crystal defects and strains of can be removed,
The electrical characteristics of the thin film transistor can be further improved.

[Brief description of drawings]

FIG. 1 is a manufacturing process diagram (1) showing an example of a method of manufacturing a thin film transistor according to the present invention.

FIG. 2 is a manufacturing process diagram (2) showing the example of the method of manufacturing the thin film transistor according to the present invention.

FIG. 3 is a manufacturing process diagram (3) showing the example of the method of manufacturing the thin film transistor according to the present invention.

FIG. 4 is a manufacturing process diagram (4) showing the example of the method of manufacturing the thin film transistor according to the present invention.

FIG. 5 is a manufacturing step diagram (5) showing the example of the method of manufacturing the thin film transistor according to the present invention.

FIG. 6 is a manufacturing process diagram (6) showing an example of a method of manufacturing a thin film transistor according to the present invention.

FIG. 7 is a manufacturing process diagram (7) showing the example of the method of manufacturing the thin film transistor according to the present invention.

FIG. 8 is a manufacturing process diagram (8) showing the example of the method of manufacturing the thin film transistor according to the present invention.

FIG. 9 is a manufacturing process diagram (9) showing the example of the method of manufacturing the thin film transistor according to the present invention.

FIG. 10 is a manufacturing process diagram (1) showing another example of the method of manufacturing a thin film transistor according to the present invention.

FIG. 11 is a manufacturing process diagram (2) showing another example of the method of manufacturing a thin film transistor according to the present invention.

FIG. 12 is a manufacturing process diagram (3) showing another example of the method of manufacturing a thin film transistor according to the present invention.

FIG. 13 is a manufacturing process diagram (4) showing another example of the method of manufacturing a thin film transistor according to the present invention.

[Explanation of symbols]

1 Insulating Substrate 2 Amorphous Silicon Thin Film 3 Excimer Laser 4 Polycrystalline Silicon Thin Film 5 Excimer Laser 6 Gate Insulating Film 7 SiO ₂ Film 8 Si ₃ N ₄ Film 9 SiO ₂ Film 11 Gate Electrode 12 Resist Mask 13 Source Region 14 Drain Region 18 Al signal line 23 Pixel electrode Tr Thin film transistor 26 Excimer laser

Claims (3)

[Claims] 1. An amorphous semiconductor thin film is irradiated with an excimer laser to generate crystal nuclei, and then solid phase growth is performed to obtain a polycrystalline semiconductor thin film having a large grain size. The polycrystalline semiconductor thin film is used as an active layer. A method of manufacturing a thin film transistor, which is used for. 2. An amorphous semiconductor thin film is irradiated with a first excimer laser to control the number of generated crystal nuclei, and then a second excimer laser having an irradiation energy equal to or higher than that of the first excimer laser. And a crystal growth to obtain a polycrystalline semiconductor thin film, and the polycrystalline semiconductor thin film is used as an active layer. 3. The method according to claim 1, wherein after the polycrystalline semiconductor thin film is obtained, excimer laser irradiation is performed to remove strains and crystal defects remaining in the polycrystalline semiconductor thin film.
3. The method for manufacturing a thin film transistor according to item 1.