JPS5939790A - Production of single crystal - Google Patents

Abstract

PURPOSE:To form a silicon single crystal film having high quality in the desired position on a substrate, by providing an oxidized film of silicon provided with a level difference and a polycrystalline silicon film on the substrate then subjecting the films to a recrystallization treatment by melting. CONSTITUTION:A level difference 23 is formed by a photoetching method or the like on an oxidized film 22 of silicon formed on a silicon substrate 21; thereafter, a polycrystalline silicon film 24 is formed thereon. Laser light is irradiated to a region A including the part 23 and the peripheral part thereof to melt the film 24, thereby forming molten silicon 25. The molten silicon is allowed to cool and the molten silicon is cooled and solidified with the central point O of the part 23 having the lower temp. owing to the higher rate of cooling as a base point, whereby the material for semiconductors having the film 24, the polycrystalline silicon 26 formed in the stage of recrystallization and the single crystal silicon 27 film formed by the recrystallization on the substrate 21 through the film 22 is obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION (Technical Field) The present invention relates to a method for manufacturing a single crystal, and particularly to a method for growing a semiconductor single crystal on an insulating film.

(Prior art and its problems) 5OS (silicon-on-silicon/fire) has been put into practical use as a method for growing a single crystal on an insulating film. SO8
In this method, a silicon single crystal is grown epitaxially on the surface of a sapphire crystal, which is an insulator, but since a sapphire crystal is used as a substrate, a silicon single crystal layer can only be formed on the surface of the substrate.

For this purpose, a method called graph-o-epitaxy has been proposed. In this method, a relief is applied to an amorphous insulating film, and the polycrystalline deposited on the film is turned into a single crystal according to the shape of the relief, in order to obtain the desired single crystal. . Figure 1(a).

(b) is a schematic diagram for explaining the principle of graphoepitaxy, where 1 is an insulating substrate, 12 is a material to be crystallized, which is usually a thin film of a semiconductor material deposited on it.

Reliefs 13a and 13b are formed on the surface of the substrate 11, and are etched into various shapes depending on the plane orientation of the single crystal to be obtained. In FIG. 1(a), a single crystal with a (100) plane orientation is expected to grow, whereas in FIG. 1(b), a single crystal with a 110> plane orientation is expected to grow. However, graphoepitaxy has not been put into practical use due to many technical difficulties.

Other methods for manufacturing single crystals include seeding epitaxy, which uses a substrate crystal as a seed crystal to grow the crystal laterally onto the insulating film, and forms an island-shaped polycrystalline layer on the insulating film. Island epitaxy, which controls the growth of a single grain (single crystal) when melting and resolidifying the polycrystalline layer, has been proposed, but each method is technically difficult or requires a high-quality single crystal. No crystals were obtained.

It is.

9 □ Ah, L/-f is good 5 □ □ Purpose) An object of the present invention is to provide a method for producing a single crystal in which recrystallization occurs from near the center of the molten portion during resolidification of the crystal material.

(Summary of the Invention) The present invention is characterized in that a temperature difference is created in the melted portion, and includes the step of forming an insulating film having a thermal conductivity different from that of the substrate on the surface of the substrate; a step of forming a stepped portion in an insulating film according to its thermal conductivity; a step of depositing a material to be made into a single crystal so as to cover the stepped portion; and a step of forming the material in the stepped portion and its surrounding area. The above object was achieved by including a step of melting and then resolidifying.

The present invention will be described in detail below based on examples.

(Embodiment of the Invention) (Fig. 2, Fig. 3, and Fig. 5 are cross-sectional views of a substrate according to the manufacturing process showing one embodiment of the present invention. A case will be described in which a silicon substrate is used and polycrystalline silicon is used as the material to be made into a single crystal.A silicon oxide film 22 is formed on the surface of a silicon substrate 21 by an appropriate method such as oxidation or vapor deposition.

Next, a step portion 23 is formed on the surface of the oxide film 22 using photolithography or the like. Then, a polycrystalline silicon film 24 is deposited to cover this stepped portion 23. (FIG. 2) Next, a region including the stepped portion 23 and its peripheral portion (region indicated by A in FIG. 2) is heated using a laser to melt the polycrystalline silicon film 24. 25 shown in FIG. 3 is molten polycrystalline silicon.

Now, here, an oxide film 22 is formed as an insulating film on the surface of the silicon substrate 21, but the two differ greatly in thermal conductivity. That is, silicon, oxide film 2
The thermal conductivity of silicon substrate 21 is 0.0030117 cm-5-de8, while that of silicon substrate 21 is 0.3 m/,
・S・deg. Therefore, as shown in FIG. 3, the temperature of the melted polycrystalline silicon 25 in contact with the stepped portion 23 is low because the oxide film 22 is thin and lies on other parts. Therefore, the temperature distribution of polycrystalline silicon 25 in the molten state in the lateral direction of FIG. 3 is as shown in FIG. 4. Note that the coordinates of the center position of the stepped portion 23 are indicated by 0 point, and the range of the stepped portion 23 is indicated by B.

When the molten polycrystalline silicon 25 with such temperature distribution cools and re-solidifies, crystallization starts from the peripheral point C where the temperature is low and the center point 07, and the crystallization begins at the step portion 23 where the temperature is high.
This is completed at the edge H point. The direction of progress of crystallization is shown by arrows in FIG.

Nucleation of recrystallization occurs at points C and C', and crystal growth begins from there.

Since the crystal grown from point C is in contact with unmolten polycrystalline silicon at that portion, most of the crystal becomes polycrystalline.

On the other hand, a crystal grown from point C' can grow from a single nucleus without any external interference, and single crystal growth progresses to point H.

FIG. 5 is a diagram showing a state in which resolidification is completed in this manner. 26 is recrystallized polycrystalline silicon, and 27 is recrystallized single crystal silicon.

The edge film 32, 33, and 34 are a source electrode, a drain electrode, and a dirt electrode, respectively. A device formed in this manner exhibits characteristics equivalent to or close to those of a device formed directly on a single crystal substrate.

In addition, in forming the step portion mentioned above, in this example, the insulating film in the part where the material to be single-crystalized was deposited was made thinner than in other parts, but this is due to the thermal conductivity of the substrate. This is because the ratio was higher than that of the insulating film.

If the thermal conductivity relationship is reversed, the insulating film is configured to be thicker in the portion where the material to be single-crystalized is deposited than in other portions. Further, when the insulating film has a two-layer structure, it is necessary to form an appropriate level difference in consideration of the thermal conductivity of each layer and that of the substrate.

In any case, in the area where the material to be single-crystalized is deposited, the temperature distribution during the re-solidification stage after melting will be lower in the center and surrounding areas, as shown in Figure 4. A stepped portion must be formed.

As a means for melting the material to be made into a single crystal, in addition to the silicon oxide film shown in this embodiment, a silitopadene nitride film or a composite thereof can also be used. In the case of a combination of a silicon substrate and a silicon oxide film, the thickness of the insulating film is 0.3 μm to 1.0 μm, and the thickness of the stepped portion is 0.05 μm.
m to 0.5 μm is suitable. Various surface shapes can be considered for the stepped portion, but generally it is a rectangular shape with a length of 5 μm.
~1000 μm. The range to be irradiated with the laser or electron beam is optimally the area including the stepped portion and its surrounding area of 2 μm or more.

(Effects of the Invention) As described above in detail based on Examples, 1. In this invention, it is possible to form a single crystal in a desired shape by utilizing the difference in thermal conductivity between the substrate and the insulating film. So,
A 3D LSI in which elements are integrated three-dimensionally because single crystals can be grown freely not only on the substrate surface but also in all parts.
It can be used in high-speed semiconductor devices with reduced junction capacitance.

[Brief explanation of the drawing]

Figures 1 (a) and (b) are schematic diagrams for explaining the principle of graphoepitaxy, Figures 2, 3, and 5.
It is a diagram in which an FET is formed in a direct single crystal. ! :,'! 21... Substrate, 22... Insulating film, 23
. . . Step portion, 24 . . . Material to be single crystallized. 2. First Patent Applicant: Makoto Ishiita, Director of the Agency of Industrial Science and Technology (b)

Claims (1)

[Claims] A step of forming an insulating film having a thermal conductivity different from that of the substrate on the surface of the substrate, a step of forming a stepped portion in the insulating film according to the thermal conductivity, and a step of covering the stepped portion. 1. A method for producing a single crystal, comprising the steps of depositing a material to be crystallized, and melting and resolidifying the material in the stepped portion and the surrounding area.