JPH02181419A - Laser anneal method - Google Patents

Abstract

PURPOSE:To prevent film separation from an edge part and also to enable irradiation with higher energy so as to obtain a TFT excellent in property by a covering the edge part of a sample with a mask so as to shut out a laser beam when annealing a film-shaped semiconductor device which is formed on a substrate by laser beams. CONSTITUTION:A glass substrate 1 whose distortion temperature is about 640 deg.C is kept at 550 deg.C, and a pressure reducing CVD film 2 is accumulated under the condition of pressure/Torr with SiH4 gass, which is diluted to 20% with He gass, as material. Next, the substrate 1 is kept at 480 deg.C, and a surface protective film 3 is accumulated with SiH4, which is diluted to 4% with He gas, and O2 as materials, and then a mask 4 about 0.5mm thick, consisting of material which does not transmit a laser beam such as Si, W, Mo, etc., is formed at the edge of a sample 5. Thereafter, a substrate 5 is irradiated with an Ar laser from outside to inside, or it is irradiated with an excimer laser which emit pulsed lights having high repetition period, so as to anneal a region 5 not covered with the mask 4.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for manufacturing a semiconductor device, and particularly to a laser annealing method for manufacturing a thin film transistor.

[Conventional technology]

In recent years, thin film transistors, which are thin film semiconductor devices for active matrix
Polycrystalline silicon (TPT) is an excellent material for achieving high image quality.
ne 5ilicon.

Po1y-S i ) is used for short. This Po1y-5i is produced by low pressure CVD method or plasma CVD method.
(PCVD method). A quartz glass or ordinary glass plate is used as the substrate.

When using a normal glass plate, the maximum temperature of the process is approximately 6
Since there is a large restriction of 00° C., a method of recrystallizing by irradiating only the surface layer of Po1y-Siv& with laser without giving any thermal effect to the glass plate is being considered. This method improves crystallinity and improves TPT characteristics compared to low-temperature thermal annealing that does not affect the glass substrate.

Conventionally, this laser irradiation method was disclosed in Japanese Patent Application Laid-Open No. 57-2106.
As described in No. 24, by selectively forming a dielectric thin film such as an oxide film or a nitride film as an anti-reflection film, it is possible to irradiate only the necessary parts of a patterned element with a laser beam of appropriate power, As described in 1985-5 [1316], a method of manufacturing a conductor device by using an energy beam scanning method was studied.

[Problem to be solved by the invention]

In the above conventional technology, laser irradiation is applied to the entire surface of the substrate to form a dielectric film on the entire substrate or a portion of the dielectric film, and annealing is performed on only the desired portion of the semiconductor device on the substrate to obtain negative crystal grains, thereby improving electrical characteristics. was improving. In order to further improve the electrical characteristics, the crystal grains can be made larger by increasing the laser energy, but if the laser energy is increased to a level greater than -, the film will peel off from the substrate due to laser irradiation. This problem has not been studied in the prior art described above, and there is a limit to the size of crystal grains that can be obtained without film peeling, especially when the silicon film to be annealed is thinned.

An object of the present invention is to improve the TPT characteristics by increasing the laser energy without causing film peeling, thereby obtaining large crystal grains, in order to improve the characteristics of thin film semiconductor devices.

[Means to solve the problem]

The above purpose is to apply low pressure CV l') method or PC
When irradiating a silicon film deposited by the VD method with a laser beam, this is achieved by not irradiating the laser beam onto the edge of the substrate where film peeling first begins even if the entire surface of the substrate is irradiated with the laser beam with the same energy.

[Effect]

The thickness of a silicon film deposited on a substrate by low pressure CVD or PCVD varies depending on the equipment, substrate size, and film forming conditions, but for example, a silicon film is deposited on a 100 m square substrate by low pressure CVD. With this method, it is possible to deposit a film with variation in film thickness within ±5% within the substrate. However, the film thickness rapidly decreases at the edge of the substrate.

Therefore, in a method in which the entire substrate is irradiated with laser at the same energy, as the energy is increased, the film will first peel off from the edges of the substrate, even if no peeling occurs at the center of the substrate. This can be achieved by, for example, 100% by atmospheric pressure CVD method.
Similar film peeling occurs even when a protective film is deposited, and as the thickness of the silicon film becomes thinner, the film peels off at lower energy. By not irradiating the edge portion with the laser beam, the irradiation energy can be increased to the threshold energy that causes peeling in the center of the substrate, so that larger crystal grains can be obtained over the entire substrate.

〔Example〕

The present invention will be explained in detail below.

Figure 1 shows a glass substrate 1 with a strain temperature of approximately 640°C being heated to 550°C.
Using monosilane gas diluted to 20% with helium gas as a raw material, low-pressure CVD1 was carried out at a pressure of I Torr.
12 is deposited. At this time, for example, if the size of the glass substrate 1 is 100 + m + square and the film is deposited to a thickness of 1500, the thickness distribution of the LPGVD film 2 within the substrate can be reproduced within ±5%. Next, the substrate 1 is kept at 480° C., and a surface protective film 3 is formed by about 1% by normal pressure CVD using monosilane gas diluted 4% with helium gas and oxygen as raw materials. Deposit 00 people.

Next, a mask 4 of silicon, high-melting point metal such as tungsten or molybdenum, which does not transmit laser light and has a thickness of Q and a drawing density of 5 is set on the sample. At this time, the mask is set so as to cover about 5 m from the edge of the sample. Then the second
As shown in the figure, the sample 5 with the mask set thereon is irradiated with laser light while being scanned in the direction indicated by the arrow. When the laser beam is, for example, an argon laser that oscillates continuous light, scanning of the sample in the X-axis direction is performed outside the sample substrate 5, and the scanning speed changes, resulting in different irradiation conditions within the plane of the sample 5. Prevents changes in recrystallization state.

Furthermore, when using an excimer laser or the like that oscillates pulsed light with a high repetition rate, the pulse repetition rate and the scanning speed of the sample 5 are linked to irradiate the entire surface of the sample the same number of times. When the repetition period is slowed down, as shown in FIG. 3, the sample 5 is scanned in steps, and the irradiation area of the laser beam that can be irradiated at one time is scanned in accordance with the number of oscillations. At this time, the edge portion of the sample 5 is not irradiated with laser light. These methods prevent the edge of the sample from being irradiated with laser light, thereby preventing the film from peeling off from the edge of the sample. In FIG. 4, a sample was prepared in the same manner as described above, and the sample was made of, for example, XeCQ with a beam area of 10 nwn square.

This figure shows the state of film peeling when the entire surface of the sample is irradiated with laser light using an excimer laser (wavelength: 308 nm) with a gas source of When the sample is scanned in the direction of the arrow, one film peels off at the edge, and when the laser beam is applied to the area adjacent to the peeled part, the film also peels off, and when the entire surface of the sample is irradiated. Film peeling occurs in the shaded area. This film peels off from the edge part about 511cm.
This can be prevented by not irradiating the dark blue area with laser light. The energy that causes the silicon film to peel varies greatly depending on the silicon film thickness. 100 in the same manner as described above in Figure 5.
A silicon film thickness of 200 to 35 mm on an on-angle glass substrate
The protective film was deposited in the same manner as described above.
000 people deposited. X the sample as shown in Figure 4.
The entire surface of the sample was irradiated with one pulse at each energy by scanning the substrate with an excimer laser using eCQ as a gas source. The X-ray diffraction intensity was measured by cutting out a 20+a angle in the center of the sample substrate, and the relationship between the X-ray diffraction intensity corrected for the film thickness and the silicon film thickness is shown. shows the area where this occurs. When the film peels off at the center of the sample, the amount of silicon film decreases, so the X-ray diffraction intensity also decreases. Film peeling at the edges is 11 in the center! ! This occurs at a lower energy than peeling, and it is necessary to irradiate the laser beam with a lower energy than when creating an element on the entire sample substrate. However, by not irradiating the edge part of the sample with laser light, the irradiation energy intensity can be increased until the film peels off in the center part.

FIG. 6 shows the correlation between the laser energy and the mobility when a TPT was formed after irradiating laser light at the same energy after depositing 1500 low pressure CVD films in the same manner as described above. Increasing the laser beam intensity improves the TPT characteristics, prevents film peeling at the edge of the sample, and irradiates the laser beam with even higher energy to form TPT with better characteristics.

〔Effect of the invention〕

According to the present invention, it is possible to prevent the peeling off from the edge portion of the substrate due to laser irradiation, and the irradiation energy can be increased until the film peels off at the center of the substrate, thereby improving the crystallinity of the Po1y-Si film. The characteristics of TPT can also be improved.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view of the sample and mask during laser irradiation according to the present invention, Figs. 2 and 3 are views showing the state of the sample from the laser irradiation side and the scanning direction of the sample, and Fig. 4 is a view of the sample edge. Figure 5 shows the area where convergence occurs when the laser beam is irradiated on the part.
FIG. 6 is a diagram showing the relationship between the laser irradiation energy and the TPT characteristics. 1...Glass substrate, 2...LPGVD film, 3...
Si○2 protective film, 4... laser blocking mask, 5...
sample.

Claims (1)

[Claims] 1. In a method of annealing a thin film semiconductor device used on a substrate with laser light, the method is characterized in that film peeling due to laser irradiation is prevented by not irradiating the edge portion of the sample with the laser light. Laser annealing method. 2. If the sample is wider than the laser beam area, or if a continuous wave or high repetition frequency laser light source is used, it is recommended to install a mask at a predetermined location on the edge of the sample substrate that does not transmit the laser beam. A laser annealing method according to claim 1, characterized in that: 3. When using a pulsed laser light source, the laser annealing method according to claim 1 is characterized in that the repetition period and the movement of the sample substrate are linked to move the sample or the laser beam while avoiding the edge portions. .