JP2003273121A - Thin-film transistor and manufacturing method thereof - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a simple and highly efficient laser annealing process wherein diameters of crystal grains in a crystallized semiconductor film are made gigantic with excellent uniformity, in a thin-film transistor and a manufacturing method thereof. <P>SOLUTION: A reflective film 3 for reflecting a laser beam wavelength is formed on a substrate 1 via an underlying film 2 to face the end side of an island-like a-Si film 5. Then, the upper surface of the substrate is vertically irradiated with a laser beam (a). A region having the reflective film 3 is double- heated by the direct beam and the reflected beam of the laser beam (a), and the region having no reflective film 3 is heated by only the direct beam of the laser beam (a). Thus, both ends of the island-like a-Si film 5 are separated into higher and lower temperature parts to form a temperature gradient. The heat from the island-like a-Si film 5 is efficiently given to the substrate 1, but the cooling of the higher temperature part is delayed so that the crystal of a p-Si film as a crystallized semiconductor film is grown laterally from the higher to the lower temperature part. Thus, Si crystal grains of large grain diameters can be obtained with excellent uniformity. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin film transistor for irradiating a polycrystalline or amorphous semiconductor film with laser light to form a crystallized semiconductor film and a method for manufacturing the thin film transistor.

[0002]

A thin film transistor (T
thin Film Transistor (TFT)
Is mainly a liquid crystal display device (Liquid Crystal).
l Display (LCD) is used as a switching element for controlling the voltage applied to the pixel. LCD
In order to realize low cost, large area, and high performance in manufacturing, a method for manufacturing a high-performance TFT at low temperature (600 ° C. or lower) is being sought. Among them, the laser annealing method is becoming mainstream because it has very little thermal influence on the underlying substrate, can realize high throughput, and can utilize inexpensive glass substrates. This laser annealing method uses amorphous silicon (amorphous-silicon: a-Si) on an insulating film.
The film is irradiated with laser light to be melted and recrystallized to form a poly-silicon (p-Si) film. At this time, uneven irradiation intensity of the laser beam and a-Si
Due to the non-uniformity of heat conduction in the film, small grains with non-uniform grain size are produced.

In order to solve this problem, Japanese Patent Laid-Open No. 9-2
In 60676, the following laser annealing method is proposed. FIG. 11 shows a conceptual diagram of this laser annealing method. In the figure, a light shielding layer 22 such as a metal film is provided on a substrate 21.
Is formed, an interlayer film 23 having an ultraviolet light transmitting property is formed thereon, and an amorphous silicon layer 24 is further formed thereon. Then, the laser light a is slanted with respect to the upper surface of the substrate.
Irradiate. The laser beam a is incident on the upper surface of the amorphous silicon layer 24 directly, and is once incident on the interlayer film 23, is reflected by the light shielding layer 22, and is incident on the lower surface of the amorphous silicon layer 24. As a result, both surfaces of the amorphous silicon layer 24 are heated, so that the temperature gradient in the thickness direction is relaxed and the crystal grain size is made uniform.

However, in this method, the heat flow is uniform, so that the uniformity of the crystal grains is improved, but the crystal grain size is about the same as the conventional size. Therefore, variations in TFT characteristics are improved, but leakage current, mobility, on-current value, etc. are not sufficiently improved. Further, in the embodiment, the laser light is irradiated at an angle of 15 ° with respect to the horizontal direction of the substrate, but the laser light focal depth of a general laser annealing apparatus is 0.1 m.
If m and the incident beam width are 0.5 mm, the angle of the laser beam that can perform annealing with uniformity is in the range of 90 ° to 78 ° with respect to the horizontal direction of the substrate.
At the angle of the embodiment, there is also a problem that the intensity of the laser beam with which the amorphous silicon layer 24 is irradiated is not uniformed, that is, nonuniform crystal grains are formed.

To improve the TFT characteristics, p-Si is used.
It is necessary to increase the crystal grain size of 1 with good uniformity. Therefore, various laser annealing methods have been proposed. For example, in Electron Letters volume 30pp.1956-1957,
The double pulse method, which uses two excimer lasers to increase the average grain size to the micron level, and the Japanese Journal
In Applied Physics volume 37 pp. L492-495, it is said that 7-micron crystal grains can be formed by the excimer laser crystallization technique by the phase shift method. However, these methods have problems that the laser device or the optical system between the laser device and the substrate has a large-scale structure, the work efficiency is low, and the energy utilization efficiency of the laser light is low. If the optical system becomes large, a large installation space is required. If the work efficiency is poor, the productivity is reduced, and if the energy utilization efficiency is low, the life of the laser light source is shortened and the operating cost increases. Occurs.

In order to solve such a problem, the present invention, in a thin film transistor and a manufacturing method thereof, provides a simpler and more efficient laser annealing for enlarging the crystal grain size of a crystallized semiconductor film with good uniformity. It was designed to propose a law.

[0007]

In order to achieve the above object, the present invention has the following constitution.

That is, in the method of manufacturing a thin film transistor of the present invention, a step of forming a reflective film that reflects the wavelength of laser light on a substrate, and a transparent film that is transparent to the wavelength of laser light is used as the reflective film. A step of forming a film, a step of forming a polycrystalline or amorphous semiconductor film on the transparent film, and a step of separating the polycrystalline or amorphous semiconductor film into islands, This achieves the above object.

Further, preferably, the reflection film is inclined at 45 to 89 ° with respect to the vertical direction of the substrate.

Further, preferably, the reflection film is formed in a flat shape.

Further, preferably, the reflection film is formed in a concave shape.

Also, preferably, the reflection film is formed in an island shape.

Preferably, the distance between the edge of the reflective film and the edge of the polycrystalline or amorphous semiconductor film separated into islands is 0 to 2 μm.

Preferably, the film thickness of the transparent film is 0.1 to 10.0 μm.

Preferably, the reflective film also serves as the wiring material of the TFT.

In the thin film transistor of the present invention, a reflective film that reflects the wavelength of laser light, a transparent film that is transparent to the wavelength of laser light, and an island-shaped crystallized semiconductor film are laminated on a substrate. The crystallized semiconductor film is crystallized by irradiating an island-shaped polycrystal or amorphous semiconductor film with laser light from above and laser light from below reflected by the reflection film. Is characterized in that.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings.

1 to 5 are conceptual diagrams illustrating a method of manufacturing a thin film transistor according to the present invention. FIG. 1 is a plan view of an a-Si film as an amorphous semiconductor film to be a crystallized semiconductor film and a reflective film, and FIGS.
It is a B'cross section. Further, FIGS. 4 and 5 show a-S of FIG.
It is a schematic diagram which shows the temperature distribution and crystal growth direction when irradiating a laser beam to i film. In FIG. 1, a reflective film 3 that reflects the wavelength of laser light is formed on a substrate 1 through a base film 2, and a transparent film 4 that is transparent to the wavelength of laser light is formed on this reflective film 3. To do. Then, a-Si is formed on the transparent film 4.
A film 5 is formed, and a region to be a semiconductor layer of the TFT is separated into islands. The reflective film 3 is exposed to the side of the end of the island-shaped a-Si film 5.

After that, laser light a is irradiated perpendicularly to the upper surface of the substrate. A part of the laser light a is incident on the upper surface of the island-shaped a-Si film 5, and a part of the laser light a passes through the translucent film 4 and is incident on the reflective film 3. The laser light a incident on the reflective film 3 is reflected and incident on the lower surface of the island-shaped a-Si film 5. As a result, the region with the reflection film 3 is doubly heated by the direct light and the reflected light of the laser light a, and the region without the reflection film 3 is laser light a.
It is heated only by direct light. Therefore, island-shaped a-Si
Both ends of the film 5 are divided into a high temperature part and a low temperature part, and a temperature gradient is generated. FIG. 13B shows the temperature distribution immediately after laser light irradiation between CC ′ in FIG. 1. A region without the reflection film 3 (AA 'in FIG. 1) has a low temperature, and a region with the reflection film 3 (BB' in FIG. 1) has a high temperature. Island-shaped a-Si film 5
Heat is efficiently released to the substrate 1, and cooling of the high temperature part is delayed. FIG. 13C shows the temperature distribution immediately after the temperature at the end of the low temperature section AA ′ reaches the crystallization temperature Tc. Crystals of the p-Si film as the crystallized semiconductor film grow laterally from the low temperature portion to the high temperature portion. This makes it possible to obtain large-sized Si crystal grains with good uniformity.

The substrate in the present invention may be made of any material such as glass, Si and plastic. The light-transmitting film in the present invention has a property of transmitting laser light and has a thickness of 0.1 to 10.0 μm. The laser light in the present invention may be pulsed laser such as KrF or XeCl excimer laser, or CW (C
including continuous wave) laser. Further, the wavelength includes the entire range of VUV (vacuum ultraviolet light) to IR (infrared light).

The reflection film in the present invention shields and reflects laser light, and in addition to Al, W, WSi, etc.,
Any material such as silicide (a compound of metal and silicon) or metal that reflects ultraviolet rays may be used. Also,
Island-shaped a-at an angle of 45 to 89 ° with respect to the vertical direction of the substrate
Tilt toward the Si film. In this case, as shown in FIG. 12, when the laser beam a irradiated vertically is reflected by the reflection film 3 to irradiate the entire width of the lower surface of the a-Si film 5, the vertical direction of the substrate 1 and the reflection film 3 form. The angle θ can be defined as follows, where W is the width of the a-Si film 5 and T is the thickness of the translucent film 4. θ ≧ 90 ° −0.5 × tan−1 (W / T) (0 ≦ θ <9
0 °) For example, when W = 2 μm and T = 1 μm, θ ≧ 90 ° −0.5 × tan −1 (2/1) and tan −1 (2/1) = 63.4 °, so θ ≧ It becomes 58.3 °. Note that θ = 58.3 ° is the optimum angle, and an angle larger than that (however, less than 90 °) may be used.

The reflecting film may be formed in any shape such as a concave shape or an island shape as shown in FIGS. 6 and 7 in addition to the flat shape. In the case of the concave surface, the laser light can be condensed on the concave surface and the irradiation energy density of the reflected light can be concentrated in a narrow range. In the case of islands, island-shaped a-Si
It is possible to vertically reflect the reflected light in the lateral direction from the reflective film provided on the side of the film to increase the irradiation energy intensity of the reflected light. The distance between the edge of the reflective film and the edge of the island-shaped a-Si film is 0 to 2 μm. The thickness is preferably 1 μm, more preferably 0 μm.

The embodiments of the present invention will be described in more detail below. FIG. 8 shows a cross-sectional view of the manufacturing process of the thin film transistor according to the present invention. FIG. 8 shows a manufacturing process of a thin film transistor using a planar reflection film, and FIGS. 9 and 10 show manufacturing processes of a thin film transistor using a concave reflection film and an island reflection film. In FIG.
As shown in (1), TEOS (Tetra Ethy) is formed on a substrate 1 such as glass by plasma CVD.
An oxide film of an insulating material such as SiO 2 is formed to a thickness of 500 nm at a substrate temperature of 450 ° C. for a deposition time of 25 minutes to form a base film 2. next,
As shown in (2) to (4), the resist material 2a is formed on top of this.
Is applied and exposed to form a pattern. For example, CH
Dry etching with F3 + O2 to a depth of 200
The step 2b having a thickness of 2 nm is formed, and then the resist material 2a is removed. At this time, etching is controlled so that the taper angle is 1 to 45 °. Next, as shown in (5), an Al film of 100 n is formed thereon by, for example, sputtering.
Then, the reflective film 3 is formed. And (6) ~
As shown in (8), a resist material 3a is applied on this and exposed to form a pattern. For example, BCL3 +
Dry etching with CH4 is performed to taper the Al surface.
Only the film is left, and then the resist material 3a is removed. Next, as shown in FIG.
The SiO 2 film is formed to a thickness of 800 nm by D at a substrate temperature of 500 ° C. for a deposition time of 40 minutes to form a transparent film 4.

Next, as shown in (10), LP (Low Pressure) using, for example, Si 2 H 6 is used.
e) Flow rate of 150-scc of a-Si film 5 by CVD
m, a pressure of 8 Pa, a substrate temperature of 450 ° C. and a deposition time of 70 minutes to form a 100 nm film. After that, as shown in (11) to (13), a resist material 5a is applied on this and exposed to form a pattern, and dry etching is performed by, for example, BCL3 + CH4 to form the a-Si film 5 into an island shape. After processing, the resist material 5a is removed. And (1
As shown in 4), the laser light a of the KrF excimer laser a
At 350 mJ · cm −2 for laser annealing to crystallize the a-Si film 5. The laser light a is
At the same time as being absorbed by the upper surface of the a-Si film 5, the light is incident on the light-transmitting film 4 where there is no a-Si film 5. Translucent film 4
The laser light a incident on is reflected at the position where the reflection film 3 exists, and is absorbed by the lower surface of the a-Si film 5. As a result, the laser beam a is irradiated to the upper and lower surfaces of the a-Si film 5 where the reflection film 3 is present, and therefore the temperature becomes higher than that where the reflection film 3 is not provided. Therefore, a temperature difference in the lateral direction is generated in the a-Si film 5 and the growth of crystal grains is promoted, so that a crystallized semiconductor film having a large crystal grain size can be obtained.

Thereafter, as shown in (15), a SiO2 film is formed thereon by, for example, LPCVD at a substrate temperature of 500.
A film having a thickness of 100 nm is formed at a temperature of 60 ° C. for 60 minutes to form a gate oxide film 6. Next, as shown in (16), an Al film is formed thereon by, for example, sputtering at a substrate temperature of 10
The gate electrode 7 is formed by depositing a 100 nm film at 0 ° C. for a deposition time of 10 minutes. Then, as shown in (17) to (19), a resist material 7a is applied on this, an exposure is performed to form a pattern, and the Al film is processed into an island shape by performing dry etching with, for example, BCL3 + CH4, After that, the resist material 7a is removed. Next, (20) to (21)
As shown in FIG.
The laser beam a of KrF excimer laser is irradiated at an intensity of 150 mJ · cm −2 by injecting at 2.0V15 cm −2 at kV. As a result, the ion implantation region is electrically activated to form the source / drain portions.

Next, as shown in (22), a SiO2 film is formed thereon by, for example, plasma CVD at a substrate temperature of 50.
The passivation film 8 is formed by forming a film of 200 nm at a deposition time of 20 minutes at 0 ° C. And (23) to (25)
As shown in FIG. 5, a resist material 8a is applied thereon, exposed to form a pattern, and dry etching is performed, for example, with CHF3 + O2 to form an electrode lead-out contact hole 8b, and then the resist material 8a is removed. . Then, as shown in (26), an Al film is formed thereon by sputtering, for example, at a substrate temperature of 100 ° C. for a deposition time of 10 minutes to form a metal film 9 for electrodes. Then, as shown in (27) to (29), a resist material 9a is applied on this, exposed to form a pattern, and dry etching by, for example, BCL3 + CH4 is performed to separate the electrode metal 9 into each electrode. After that, the resist material 9a is removed.

In FIGS. 9 (6) to 9 (8), the reflection film 3 under the island-shaped a-Si film 5 is removed by etching, but it may be left as it is. This makes it possible to simplify the process and diffusely reflect the laser light incident on that portion, thereby further improving the laser irradiation efficiency of laser annealing.

The manufacturing process of the thin film transistor using the concave reflection film is basically the same as that of FIG. 8, and the etching process of FIG. 9C is replaced by wet etching. In this case, buffered HF or the like is used as the chemical solution.

[0029]

As described above, the method of manufacturing a thin film transistor according to the present invention comprises a laser light reflection film on a substrate,
A transparent film for laser light and an a-Si film are formed.
The Si film is separated into islands, and the upper surface of the substrate is irradiated with laser light perpendicularly. Therefore, according to the present invention, the vertically irradiated laser light is reflected by the reflection film and is incident on the lower surface of the island-shaped a-Si film, and that portion is double-heated. There is a temperature difference between the two, which promotes the increase in the size of Si crystal grains. Further, by adjusting the position of the reflective film, a crystallized semiconductor film in which the positions of crystal grain boundaries are controlled can be manufactured.

In addition to crystallization, this reflective film is effective for activating ion-implanted impurities. In the conventional method, since the reflected laser light from the lower surface is radiated by this method, it is possible to reduce the point that the laser light can be activated with a lower laser light intensity and the adverse effect of the laser light on areas other than the activated region.

In addition to crystallization and activation, it is also effective for improving the interface between the semiconductor film and the transparent film, for example, p-Si / SiO2 interface characteristics. Since heating by laser light is extremely high temperature and short time compared with the conventional method, p-Si / SiO 2 is used.
It is expected that the impurity level at the two interfaces will be reduced and the TFT characteristics will be improved (higher ON current value, lower leakage current, etc.).

Besides, the reflective film can also serve as the wiring material of the TFT and the auxiliary electrode material, in which case the number of manufacturing steps can be reduced. Further, the reflection film has an effect of blocking the light incident from the lower surface of the substrate and preventing the generation of photocurrent in the TFT. Further, since the heat conduction efficiency is high, it functions as a heat sink, and has an effect of preventing the temperature rise of the entire substrate.

[Brief description of drawings]

FIG. 1 is a plan view of an a-Si film and a reflective film which are semiconductor films of a TFT of the present invention.

FIG. 2 is a sectional view taken along the line AA ′ of FIG.

FIG. 3 is a sectional view taken along line BB ′ of FIG.

FIG. 4 is a schematic diagram showing a temperature distribution when a-Si film is irradiated with laser light.

FIG. 5 is a schematic diagram showing a crystal growth direction when a-Si film is irradiated with laser light.

FIG. 6 is a sectional view of a concave reflecting film.

FIG. 7 is a cross-sectional view of an island-shaped reflective film.

FIG. 8 is a cross-sectional view of a manufacturing process of a thin film transistor using a planar reflective film embodying the present invention.

FIG. 9 is a cross-sectional view of the manufacturing process of the thin film transistor using the concave reflection film according to the present invention.

FIG. 10 is a cross-sectional view of the manufacturing process of the thin film transistor using the island-shaped reflective film according to the present invention.

FIG. 11 is a conceptual diagram of a laser annealing method in which laser light is obliquely irradiated.

FIG. 12 is a schematic diagram illustrating an optimum angle of a reflective film.

FIG. 13 is a graph showing a temperature distribution between CC ′ of FIG. 1.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Substrate 2 Base film 2a Resist material 2b Step 3 Reflective film 3a Resist material 4 Translucent film 5 a-Si film 5a Resist material 6 Gate oxide film 7 Gate electrode 7a Resist material 8 Passivation film 8a Resist material 8b Contact hole 9 Electrode Metal 9a Resist material 21 Substrate 22 Light-shielding layer 23 Interlayer film 24 Amorphous silicon layer a Laser light b C-C 'temperature distribution c immediately after laser irradiation C when a part reaches the crystallization temperature Tc
-C 'temperature distribution

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Mikihiko Nishitani             292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa             Inside the LCD Advanced Technology Development Center (72) Inventor Yoshinobu Kimura             292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa             Inside the LCD Advanced Technology Development Center (72) Inventor Masato Hiramatsu             292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa             Inside the LCD Advanced Technology Development Center (72) Inventor Fumiki Nakano             292 Yoshida-cho, Totsuka-ku, Yokohama-shi, Kanagawa             Inside the LCD Advanced Technology Development Center F-term (reference) 2H092 JA24 JA28 JB21 KA04 KA07                       KB04 KB21 MA05 MA07 MA13                       MA19 MA30 MA37 NA21 PA01                       PA12                 5F052 AA02 BB02 BB07 CA04 DA02                       DB02 EA13 FA25 JA01                 5F110 AA06 AA07 CC02 DD01 DD02                       DD05 DD12 DD13 DD17 DD30                       EE03 EE44 FF02 FF32 GG02                       GG13 GG47 HJ01 HJ13 HJ23                       HL03 HL23 NN02 NN23 NN35                       NN43 NN45 NN46 NN47 NN54                       PP03 PP07

Claims (9)

[Claims] 1. A step of forming a reflective film for reflecting a wavelength of laser light on a substrate in a step before laser annealing for irradiating a polycrystalline or amorphous semiconductor film with laser light to produce a crystallized semiconductor film. A step of forming a transparent film that is transparent to the wavelength of the laser light on the reflective film, and a step of forming a polycrystalline or amorphous semiconductor film on the transparent film. And a step of isolating a crystalline or amorphous semiconductor film into islands. 2. The method of manufacturing a thin film transistor according to claim 1, wherein the reflective film is inclined at 45 to 89 ° with respect to the vertical direction of the substrate. 3. The method of manufacturing a thin film transistor according to claim 1, wherein the reflective film is formed in a planar shape. 4. The method of manufacturing a thin film transistor according to claim 1, wherein the reflective film is formed in a concave shape. 5. The method of manufacturing a thin film transistor according to claim 1, wherein the reflective film is formed in an island shape. 6. The distance between the edge of the reflective film and the edge of the polycrystalline or amorphous semiconductor film separated into islands is 0 to 2 μm.
The method of manufacturing a thin film transistor according to claim 1, wherein m is m. 7. The thickness of the transparent film is 0.1 to 10.0.
The method of manufacturing a thin film transistor according to claim 1, wherein the thickness is μm. 8. The method of manufacturing a thin film transistor according to claim 1, wherein the reflective film is also used as a wiring material of the thin film transistor. 9. A structure in which a reflective film that reflects the wavelength of laser light, a transparent film that is transparent to the wavelength of laser light, and an island-shaped crystallized semiconductor film are stacked on a substrate. The crystallized semiconductor film is crystallized by irradiating an island-shaped polycrystalline or amorphous semiconductor film with laser light from above and laser light from below reflected by the reflective film. And a thin film transistor.