JPH0360021A - Manufacture of semiconductor crystalline film - Google Patents

Abstract

PURPOSE:To enable uniform temperature rise and solidification starting from the central section by setting the beam shape according to the scanning speed. CONSTITUTION:A silicon film formed on a glass substrate is monocrystallized through irradiation of laser beams. The shape of this laser beam is defined to have a principal heating part 1 and two auxiliary heating parts 2 provided continuously at both sides behind this principal heating part 1. In this case, the length L1mum of the principal heating part and the length L2mum of the auxiliary heating part in the scanning direction of the laser beam are set to satisfy the following two formulas, when the scanning speed of the laser beam is vcm/ sec, L1>10<-4>Xv...(1), L2>2X10<-2>Xv...(2).

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a method for manufacturing a semiconductor crystal thin film, and in particular to a method for producing a single crystalline semiconductor thin film by irradiating a polycrystalline or amorphous silicon thin film formed on a glass substrate with a laser beam. The present invention relates to a method for manufacturing a semiconductor crystal thin film.

(Prior Art and its Problems) Conventionally, there is a laser beam crystallization method in which polycrystalline or amorphous silicon is irradiated with a laser beam to form a single crystal. Various attempts have been made to obtain high quality single crystal films from polycrystalline or amorphous silicon using this laser beam crystallization method.
For example, by making the beam shape of a continuous wave argon laser into a donut shape and making the intensity distribution of the laser beam a so-called bimodal type, the central part of the scanning line of the laser beam can be cooled quickly, and the central part of the scanning line of the laser beam can be cooled quickly. It has been proposed to form a high-quality thin film single crystal by slowly cooling the crystal and growing the single crystal from the center to both sides of the laser beam scanning line.

However, in this conventional method for manufacturing semiconductor crystal thin films,
There was a problem in that the temperature could not be raised uniformly in the direction of the silicon film thickness, making it impossible to obtain a high-quality semiconductor crystal thin film.

In other words, the argon laser light is 0.1~
Most of the light energy is absorbed at a thickness of 0.2 μm. Therefore, if the film thickness is 0.5 μm, the remaining 0.3
The portion with a diameter of a little more than μm is heated by supplying energy by thermal conduction. Therefore, if the irradiation time is 10 μsec or less, sufficient time necessary for heat conduction will not be available, and only the surface will be heated. In particular, in the conventional beam shape, the beam length in the scanning direction at the center is short, and the irradiation time becomes extremely short depending on the scanning speed. In such a situation,
When the back side of the silicon film is melted, the temperature rise on the front side becomes very large, exceeding the boiling point, and if there is a cap layer, a reaction between the cap layer and the silicon occurs, and the However, a good single crystal thin film cannot be obtained.

Also, if you set the surface temperature to the best temperature,
On the back surface side, the temperature does not rise to the melting point, and this portion becomes a large number of nuclei, resulting in the formation of a polycrystalline silicon film.

(Objective of the Invention) The present invention was devised in view of the problems of the conventional method, and by setting the beam shape corresponding to the scanning speed, uniform temperature rise and solidification from the center can be achieved. It is an object of the present invention to provide a method for forming a semiconductor thin film that can perform the following steps.

(Means for Solving the Problems) According to the present invention, a semiconductor crystal film is formed on a glass substrate, and the silicon film is irradiated with a laser beam and heated to melt and solidify the silicon film to form a single crystal. In the manufacturing method, the beam shape of the laser beam is such that it has a main heating part and auxiliary heating parts provided continuously to the main heating part at both rear parts of the main heating part in the scanning direction of the laser beam. It is characterized by having a shape, thereby achieving the above object.

(Example> Hereinafter, the present invention will be explained in detail based on the accompanying drawings.

According to the present invention, a silicon film formed on a glass substrate is irradiated with a laser beam to form a single crystal.

As the glass substrate, a #7059 substrate that contains almost no sodium ions is preferably used.

The surface of this glass substrate is coated with silicon oxide to prevent contamination of the silicon layer from the substrate when irradiated with a laser beam and to reduce thermal shock when irradiated with a laser beam. (Sin2) Thickness of film etc. is 0.5~2μ
A polycrystalline or amorphous silicon film is formed to a thickness of about 0.5 μm on the glass substrate as described above, and a silicon oxide (SiO2) film is further formed to a thickness of 0.05 μm as a cap layer. ~2
It is formed to a thickness of about μm and irradiated with a laser beam.

As the laser beam, a continuous wave argon laser with a power of 0.5 to 20 W is preferably used.

FIG. 1 is a diagram showing the beam shape of a laser beam used in the method for manufacturing a semiconductor crystal film according to the present invention.

The beam shape is such that it has a main heating section 1 and two auxiliary heating sections 2 that are successively provided on both sides of the rear of the main heating section 1 .

The main heating section 1 is formed in a generally rectangular shape with a wide area so that it can sufficiently heat the silicon layers in the center of the beam and both measuring sections to the back side. The auxiliary heating section 2 is formed to be long so that the silicon layer on both sides of the beam can be solidified more slowly than the silicon layer at the center.

In this case, the length of the main heating part in the scanning direction of the laser beam, 1 μm, and the length of the auxiliary heating part, 2 μm, satisfy the following two equations when the scanning speed of the laser beam is v (m/s eC). It is desirable that the length be such that

L+ >10-'xv・ ・ ・ ・ ・ ・ ・
(1) L2 >2X 10-2XV ・---■
The reason why a length that satisfies the above two equations is desirable is as follows.

That is, Figure 2 shows the temperature on the back side of the silicon layer when the temperature on the front side of the silicon layer reaches 1400°C, which is considered to be the melting point of silicon, when the laser beam irradiation time is varied. For the irradiation power density, the optimum value for each irradiation time is used.

The irradiation time for humans (10-
When the sample was annealed under conditions where the surface side reached 1400℃, the temperature on the surface side was 1
When the temperature was considerably higher than 600° C., and when analyzed in the depth direction using XPS, a reaction with the cap layer was observed at a depth of 0.1 μm from the surface. On the other hand, the irradiation time of B (10-'
This phenomenon was not observed in sec). As a result, when the scanning speed of the laser beam is vcm/sec, the length of the tip of the beam shape, which is 9 μm, is L+
It can be seen that the silicon layer cannot be heated uniformly unless >10-'x v · -- · -■. To measure the temperature on the silicon surface, a high-speed response germanium photodiode detects the infrared rays emitted from the heated silicon surface, the output is stored in a digitizer, and this signal is corrected based on the temperature characteristics of the elemental radiation. Go and find out.

Next, Fig. 3 shows the time change of cooling the back side of the silicon layer from 1400°C.
Since the temperature has risen to nearly 00°C, the time required to lower the temperature by 200°C until the central part of the scanning width begins to harden is at most 2
About msec is required. Therefore, in order to solidify from the center, it is necessary to irradiate the outer part with 2 m5ec even after the beam at the center is interrupted. This allows the scanning speed of the laser beam to be v cm / s
It can be seen that when e c, the length L2 μm of the side part of the beam shape cannot be kept warm between the sides of the beam in the silicon layer unless L2 > 2X 10-'XV .

Note that it is desirable to provide a taper M3 at the connecting portion between the main heating section 1 and the auxiliary heating section 2 in order to make the temperature gradient gentle when transferring from the main heating section 1 to the auxiliary heating section 2.

Further, the shape of the laser beam as described above is formed by modifying the beam shape using a jig or by combining several beams.

Incidentally, the scanning speed of the laser beam was set to 10 cm/5
e c, L+ = 200 μm, L2 = 300 μm,
When conducted at a power density of 4 kW/cm2, a good single crystal semiconductor film was obtained.

(Effects of the Invention) As described above, according to the method for manufacturing a semiconductor crystal film according to the present invention, the beam shape of the laser beam can be changed to the main heating section and both rear sides of the main heating section in the scanning direction of the laser beam. Since the shape has an auxiliary heating section that is continuous with the main heating section, it is possible to completely melt the silicon film to the back side, and also to crystallize the silicon film from the center of the beam scanning area. This makes it possible to obtain large single-crystal thin films of extremely high quality.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the shape of the laser beam used in the method of the present invention that irradiates the silicon film, FIG. 2 is a diagram showing the relationship between the scanning speed of the laser beam and the temperature on the back side of the silicon film, and FIG. FIG. 3 is a diagram showing the relationship between the scanning speed of the laser beam and the cooling temperature of the silicon film. 1. Main heating section 2. Auxiliary heating section 3. Tapered section

Claims (2)

[Claims] (1) Melt and heat the silicon film formed on the glass substrate by irradiating the silicon film with a laser beam and heating it.
In the method for manufacturing a semiconductor crystal film that is solidified to become a single crystal, the beam shape of the laser beam is provided in a main heating section and on both rear sides of the main heating section in the scanning direction of the laser beam so as to be continuous with the main heating section. 1. A method for manufacturing a semiconductor crystal thin film, characterized in that the semiconductor crystal thin film has a shape having an auxiliary heating section. (2) The length L_1 μm of the main heating part and the length L_2 μm of the auxiliary heating part in the scanning direction of the laser beam,
2. The method of manufacturing a semiconductor crystal thin film according to claim 1, wherein the length is set to satisfy the following two equations when the scanning speed is vcm/sec. L_1>10^-^4×v...(1) L_2>
2×10^-^2×v...(2)(3) Claim (1) or claim 1, characterized in that a tapered part is provided at a connecting part between the main heating part and the auxiliary heating part. The method for producing a semiconductor crystal thin film according to (2).