JPH03138925A - Semiconductor-film crystallizing method - Google Patents

Abstract

PURPOSE:To obtain a semiconductor-film crystallizing method by which the temperature distribution in the film thickness direction of a semiconductor film can be controlled accurately and simply by providing a second insulating film on a semiconductor film which is provided on a first insulating film, laminating a metal film on the second insulating film, and thereafter projecting an energy beam from the side of an insulating substrate. CONSTITUTION:An amorphous silicon semiconductor film 3 is formed on a first insulating film 2 by a plasma CVD method using silane gas or disilane gas and the like. A second insulating film 4 comprising silicon oxide is further formed on the semiconductor film 3 by the same war as for the first insulating film 2. A molybdenum film 5 is formed on the second insulating film 4 by a vacuum vapor deposition method, a sputtering method and the like. The temperature distribution in the film-thickness direction of the semiconductor film 3 immediately after the projection of an ion energy beam can be accurately controlled. Thus, the temperature gradient in the thickness direction of the semiconductor film can be made approximately constant. The semiconductor film comprising the large single crystal having excellent crystalline property is obtained.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention relates to a method for crystallizing a semiconductor film, and more specifically, the present invention relates to a method for crystallizing a semiconductor film, and more specifically, to a method for crystallizing a semiconductor film. The present invention relates to a method of making a semiconductor film into a single crystal by irradiating the single crystal semiconductor film with an energy beam such as a laser beam from the substrate side.

[Conventional technology]

S O
It is seen as promising in I (Silicon On In5ulator) technology, etc., and for example, it is possible to obtain large single crystal regions with few defects by promoting grain size growth and localizing grain boundaries in the crystallized layer of silicon films. techniques have been reported (e.g. JAPANESE JOURNA
L OF APPLIED P)IYsIcs, Vo
l, 28. No. 1゜JANUARY, 1989
．． (See pp-L128-L130).

The above technique will be explained based on FIG. FIG. 2 shows a partial cross-sectional view, in which silicon oxide (S) is placed on a silicon wafer 55.
iO2) IK 54 is formed, and a polycrystalline silicon film 53 is deposited thereon by the CVD method. Furthermore, a transparent polyethylene glycol (liquid, molecular weight of about 600 or less) layer 52 is provided on the silicone film 53 as a cooling medium. At this time, the thickness of the polyethylene glycol layer 52 (about 0.5 to about 2 mm) is kept constant by the transparent glass plate 51.

In this state, the silicon film 53 is irradiated with scanning laser light, which is an energy beam, to melt and solidify the silicon film 53 to form a single crystal.

In the absence of the glass plate 51 and the polyethylene glycol layer 52, the upper surface of the silicon film 53 comes into contact with the atmospheric gas, so that the silicon film 53 immediately after irradiation with laser light
The temperature distribution in the thickness direction is such that the lower W153b of the silicon film 53 in contact with the silicon oxide film 54 is cooled faster than the lower surface side 53a, the upper surface side 53a is at a higher temperature, and the lower surface side 53
b will have a steep temperature gradient at a low temperature.

On the other hand, according to the above-described method in which a cooling medium is brought into contact with the silicon film 53, the upper surface side 53a of the silicon film 53 is cooled by the polyethylene glycol layer 52 to the same extent as the lower surface side 53b and radiates heat. The temperature gradient in the thickness direction is approximately constant. This promotes the growth of crystal grain size and provides a large single crystal.

[Problems to be Solved by the Invention] However, in the above-mentioned conventional technology, two layers, the fairly thick liquid polyethylene glycol layer 52 covering the surface of the silicon film S3 formed on the substrate and the glass plate 51, are exposed to laser light. passes through and melts the silicon film 53, so the focus of the laser beam tends to shift due to the difference in the refractive index of the 14N, the change in the thickness of the polyethylene glycol 152 due to vibration, etc. Furthermore, since the polyethylene glycol layer 52, which is liquid at room temperature, is used, the polyethylene glycol N52 boils due to the heat from the silicon film 53 before the silicon film 53 melts, causing bubbles and the like to interfere with the optical path of the laser beam. It can easily become a hindrance.

Therefore, a method can be considered in which a silicon film formed on a transparent glass substrate is irradiated with laser light from below the glass substrate, but if the laser light is scanned and irradiated without forming anything on the silicon film, no formation will occur. In a single crystal, approximately 1
It has been found that an inconvenience occurs in that the crystal orientation rotates within a range of several degrees per 00 μm. For this reason, it is not possible to obtain a semiconductor film with good crystallinity, and the desired semiconductor properties cannot be expected.The reason for the rotation of the crystal orientation is, as already mentioned, the glass substrate side (bottom side) of the silicon film. This is because the lower surface side of the silicon film solidifies faster than the upper surface side due to the lower temperature. In order to solve this problem, it is sufficient to form films of the same material and approximately the same thickness on the upper and lower parts of the silicon film, for example, methods 1 to 2 shown below can be used.

■ A method of depositing a thick silicon film on a glass substrate and growing an oxide film through thermal oxidation.

■ A method of attaching a glass plate on top of the silicon film on the glass substrate.

■ A method of forming oxide films above and below a silicon film using a vapor phase growth method such as CVD.

However, in method (2), the growth rate of an oxide film such as silicon oxide is extremely slow, and it is necessary to form a silicon film, which is the source of the oxide film, to be considerably thick, which is practically difficult.

Furthermore, in method (2), it is difficult to adhere the glass plate to the silicon film with good consistency, and microscopic contact at the bonding surface is insufficient.

Furthermore, in method (2), if the oxide film exceeds about 1 μm, cracks tend to occur, which is a problem.

Therefore, the present invention solves the above-mentioned problems in a method for crystallizing a semiconductor film formed on a light-transmitting insulating substrate such as glass, and improves the thickness of the semiconductor film immediately after irradiation with an energy beam such as a laser beam. An object of the present invention is to provide a method for crystallizing a semiconductor film that can accurately and easily control the directional temperature distribution.

[Means to solve the problem]

The above-mentioned problem is solved by the means described below.

That is, a non-single crystal semiconductor film is provided on a light-transmitting insulating substrate or a first insulating film provided on the substrate, and a second insulating film is provided on the semiconductor film.
After providing an insulating film and laminating a metal film on the second insulating film,
By a semiconductor film crystallization method characterized by irradiating an energy beam from the insulating substrate side! i problem is solved.

[Effect]

Next, the operation of the present invention will be explained.

According to the semiconductor film crystallization method of the present invention, when a laser beam, for example, is used as the energy beam, the semiconductor film is irradiated with the laser beam mainly through only the light-transmitting insulating substrate. Therefore, there is no need for the laser light to pass through a fairly thick layer of liquid polyethylene glycol, unlike in the prior art, and the path of the laser light is not distorted by this extra layer.

Furthermore, by forming the insulating film formed on the semiconductor film and the metal film formed on the insulating film to a predetermined thickness, it is possible to accurately control the temperature distribution in the back thickness direction of the semiconductor film immediately after energy beam irradiation. The temperature gradient of the semiconductor film can be reduced, and a single crystal semiconductor film with good crystallinity can be obtained.

Note that the film thicknesses of the insulating film provided on the semiconductor film and the metal film provided on the insulating film can be set to various thicknesses by, for example, a vapor phase growth method such as a CvD method, a sputtering method, or a vacuum evaporation method. Can be done objectively and easily.

〔Example〕

An embodiment according to the present invention will be described in detail based on the drawings.

FIG. 1 is a partial sectional view showing this embodiment. 1 is a translucent insulating substrate with a thickness of about 0. 7mm glass substrate (
Here, we use #7059 borosilicate glass, which has extremely low alkali metal elements. Laughing gas (N 20
) and a first insulating film 2 of silicon oxide having a thickness of about 0.5 μm is formed by plasma CVD or the like using silane gas or disilane gas. Note that here, the first insulating film 2
may be silicon nitride, silicon carbide, or the like.

Further, if a transparent quartz glass or the like is used for the substrate 1, the first insulating film 2 may not be formed.

This is because the materials of the silica glass and the first insulating film 2 are similar, so there is no need to consider the diffusion of impurities from the substrate 1.

On the first insulating film 2, a non-single-crystal silicon semiconductor film 3 having a thickness of about 0.5 μm is formed by a plasma CVD method using silane gas or disilane gas. This semiconductor film 3 is annealed at a temperature of about 550 to about 600° C. after being formed to undergo dehydrogenation treatment.

The semiconductor film 3 is further coated with about 0.0% by the same method as the first insulating film 2. A second insulating film 4 of silicon oxide with a thickness of 5 μm is formed. Note that, like the first insulating film 2, the second insulating film 4 may also be made of silicon nitride, silicon carbide, or the like.

A molybdenum metal film 5 having a thickness of approximately 2 μm is formed on the second insulating film 4 by vacuum evaporation, sputtering, or the like. In addition to molybdenum, the metal film 5 may be made of a metal or alloy with a high melting point such as nickel, tantalum, or tungsten, which has a melting point higher than at least aluminum, as a material that can absorb the heat from the semiconductor film 3. The thermal conductivity of the substrate 1 is about 1 to 2 orders of magnitude higher than that of the substrate 1.

The thicknesses of the first and second insulating layers 2, 4 and the metal film 5 can be easily changed by appropriately setting conditions such as gas flow rate. For example, the thickness of the semiconductor film 3 is about 0.5 μm.
On the other hand, the first and second insulating films 2 and 4 have a thickness of about 0.01 to about 1
.mu.m, and the metal film 5 is formed to have a thickness in the range of about 0.5 to about 10 .mu.m. Here, the lower limit of the thickness of the first and second insulating films 2 and 4 is the minimum thickness as a barrier layer that prevents the diffusion of impurities from the metal film 5 and the substrate 1, and the upper limit is the maximum thickness that does not cause cracks. It is as thick as possible.

Further, the lower limit of the metal film 5 is the minimum thickness for heat dissipation when irradiated with an energy beam such as a laser beam, and the upper limit is the maximum thickness set from the viewpoint of ease of film formation. Here, if the beam is irradiated with, for example, helium gas or the like being blown onto the metal film 5 side, the heat dissipation effect will be promoted, so the lower limit of the thickness can be set to about 0.1 μm.

In the above configuration, laser light is scanned and irradiated from below the substrate 1 . The laser beam is a continuous wave argon laser beam with an output power of about 0.7 to about 1.5 watts, focused to a beam diameter of about 10 to about 300 μm, and a scanning speed of about 1 to about 20 c.
Scan at a speed of about m/sec. Note that, in addition to laser light, an electron beam or the like may be used as the energy beam.

According to the above conditions, a high quality single crystal semiconductor film with extremely few defects can be obtained. That is, in this embodiment, by setting the thickness of the second insulating film 4 formed on the semiconductor film 3 and the metal film 5 formed on the second insulating film 4, the thickness of the semiconductor film 3 melted by laser light can be reduced. It is possible to suppress the rotation of the crystal orientation of the formed single crystal as much as possible by avoiding dependence in the film thickness direction to the extent that A single crystal film with good crystallinity can be obtained.

It should be noted that the present invention is not limited to the embodiments described above and shown in the drawings, but can be implemented with appropriate modifications within the scope of the gist.

〔Effect of the invention〕

As explained above, according to the semiconductor film crystallization method of the present invention, the insulating film formed on the semiconductor film and the metal film formed on the insulating film cause the semiconductor film to be exposed in the film thickness direction immediately after energy beam irradiation. temperature distribution can be precisely controlled. As a result, the temperature gradient in the thickness direction of the semiconductor film can be made almost constant, and a large single-crystal semiconductor film with good crystallinity can be obtained.

In addition, when a semiconductor film formed on a transparent insulating substrate is irradiated with an energy beam such as a laser beam from the insulating substrate side, the temperature distribution is affected by the insulating film and metal film formed on the semiconductor film. This method eliminates the need for a device to fix a fairly thick layer of liquid polyethylene glycol as in the past, and bubbles are generated as the polyethylene glycol layer boils, creating a focal point for the energy beam. A semiconductor film with good -J'W crystallinity is obtained without any deviation.

Furthermore, in order to manufacture devices such as silicon TPT, for example, this method is used when forming an amorphous silicon film on a large area and using a low-temperature process on an inexpensive glass substrate and then crystallizing it. This can be said to be extremely suitable.

[Brief explanation of the drawing]

FIG. M1 is a partial sectional view showing one embodiment of the present invention, and FIG. 2 is a partial sectional view showing a conventional technique. 1... Substrate, 2... First insulating film, semiconductor film, second insulating film. Metal film, laser light.

Claims (1)

[Claims] A non-single crystal semiconductor film is provided on a light-transmitting insulating substrate or a first insulating film provided on the substrate, a second insulating film is provided on the semiconductor film, and a metal film is provided on the second insulating film. 1. A method for crystallizing a semiconductor film, which comprises stacking a semiconductor film and then irradiating an energy beam from the insulating substrate side.