JPS6130023A - Formation of soi - Google Patents

Abstract

PURPOSE:To obtain SOI by covering a part of Si thin film surface with a film which is more easily evaporated than Si and single crystallizing it around the exposed region of Si through the heating within a short period of time. CONSTITUTION:A poly-Si or amorphous Si thin film 6, SiO2 thin film 7 (more difficult to evaporate than Si) are stacked on a quartz substrate 5. It is then irradiated with the laser beam, the Si 6 is melted and heating is suspended. Heat of film 6 does not escape to the substrate 5, convection is not generated at the surface of substrate due to the heating within a short period of time, Si is partly vaporated at the surface of an aperture 10 getting vaporization heat, it is cooled more effectively and quicker than the circumference. Thereby, Si single crystal region is obtained around the aperture 10. In the case of heating by laser beam, use of SiO2 film in the thickness of about 850Angstrom is effective. According to this structure, the SOI single crystal can be formed at the desired region regardless of the underlayer structure.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a method of heating and melting a semiconductor film on an insulating layer to form a single crystal.

(Prior art and learning points) Conventionally, a polycrystalline or amorphous semiconductor thin film on an insulating film is heated, melted, and stirred to produce a single crystal or a crystal with a large grain size close to a single crystal (SOI: 8emic).
A number of studies have been conducted on methods for obtaining onductor, on-engine, and 5ulator) f.

Generally, a part of the substrate is heated and melted using an electron beam, laser beam, flash lamp, strip heater, etc. in a short period of time, and the heat is conducted into the substrate or escapes by radiation due to thermoluminescence. There are various methods for cooling and solidifying the material.

One is a method (seeding epitaxial growth method) in which the semiconductor film is provided at a location (seed) in contact with a single crystal substrate, and a single crystal continuous with the substrate is grown by solidifying from this seed.

In addition, the shape of the heating beam was modified so that the rear part of the interface between the heated and molten part and the solid part (solid-liquid interface) was convex in the direction of the beam movement, so that the minute crystal grains generated at the beginning of the beam scan could be removed. A method to obtain a large single crystal by propagating the crystallinity of the crystal in a constantly expanding manner (shaped beam method)
There is.

Another method is to modify the shape of the lower part of the semiconductor thin film to control the path of heat escape to the substrate, thereby extending the properties of the crystal grains initially generated during solidification at a desired position (heat sink method). ).

However, the seeding epitaxial method requires an extra area called a seed, and when making LSI transistors, a certain distance between the gate part of the single crystal and the seed is required, making it necessary to make a large single crystal. In reality, it is difficult to make a high-quality single crystal for the gate part.

With the shaped beam method, there is no continuity between the single crystals between different beam paths, grain boundaries are always present, and the single crystal region can only be formed into stripes where the beam travels. This is inconvenient for application to large scale integrated circuits.

Although the heat sink method has the advantage of not wasting excess area and can create a single crystal in any location by providing a heat sink part on the base, it has the disadvantage that it depends on the base structure, and it is difficult to make devices in multiple layers. In such cases, there are limitations on where the single crystal can be made, or it is necessary to provide a buffer layer between the eyebrows, complicating the manufacturing process.

FIG. 1 is a cross-sectional view of a sample for SOI formation by a conventional heat sink method. An electrically insulating 8 iodine film 2 is attached on a silicon substrate 1 having high thermal conductivity, and a heat sink 4 is provided by making a part of the film thinner so that heat can easily escape.
A polycrystalline or amorphous silicon thin film 3e is grown thereon. When the heat sink 4 and the silicon thin film 3 around it are heated and melted by a light beam or the like, and then the heating source is removed, a lot of heat escapes from the heat sink 4 to the substrate 1, so that the silicon thin film 3 directly above the center of the heat sink 4 escapes. Since it begins to solidify and the surrounding area cools and solidifies, epitaxial growth occurs using the initially solidified crystal grains as nuclei, so that at least a single crystal larger than the heat sink 4 can grow.

As mentioned before, this method has the advantage of being able to form a single crystal in a predetermined location like the heat sink part 4, but the heat sink must have good heat dissipation. If a device is fabricated on the base, heat conduction will be poor, making it impossible to selectively form a heat sink, and a single crystal will not grow.

(Objective of the Invention) An object of the present invention is to provide a method that eliminates the above-mentioned drawbacks and can form a single crystal semiconductor film at any location regardless of the underlying structure.

(Structure of the Invention) The present invention provides an SOI forming method in which a semiconductor thin film on an insulating layer is heated and melted in a bath, solidified, and the semiconductor thin film is made into a single crystal. It is characterized in that it is covered with a film and then subjected to a short heat treatment to form a single crystal around the exposed portion of the semiconductor film.

(Example) The present invention will be described below based on an example and with reference to the drawings. In the explanation, silicon, which is commonly used as a semiconductor, will be used as an example.

FIG. 2 shows a cross-sectional structure of a sample according to the present invention.

Here, reference numeral 5 is a quartz substrate, but it has poor thermal conductivity, and it may be a semiconductor substrate with an insulating film formed on the surface, for example, as long as it has poor heat dissipation regardless of the underlying structure. 6 is a polycrystalline or amorphous silicon film to be made into a single crystal, and the film thickness Fi is about 0.5 μm.

7 is a film that is less likely to evaporate than silicon, which prevents the evaporation of the silicon film 6, and 8i0. Or Si, N.

Since it is only necessary to prevent evaporation of silicon, the film thickness is increased by heating for a short time using lamp annealing, melting the silicon film 6, and then stopping the heating. For an Ar laser, the annealing conditions are, for example, an output of 5 W and a beam diameter of 40 μm. The heat of the silicon film 6 escapes in one direction in the lateral direction through the silicon film 6 and in the other direction by radiation. However, the heat cannot escape from the quartz substrate 5 because the heat conduction of quartz is poor. Furthermore, since the outside of the sample is a gas such as air or a vacuum, the thermal conductivity is low, and since heating is very short, convection does not occur, and heat generally does not escape. However, since the silicon film 6d is melted, a portion of the silicon evaporates on the surface of the opening 10, absorbs the heat of vaporization, and is efficiently cooled. Therefore, it cools down faster than the surrounding area. As a result, a silicon single crystal region centered around the opening 10 can be obtained using the same principle as the heat sink method explained in FIG.

In this method, when heating with a laser beam, etc., 7 is replaced with an antireflection film, for example, S10 with a thickness of 850A. By using a film, the surrounding temperature can be increased by +, and cooling can be more efficiently performed through the opening 10.

In the above explanation, silicon is used as the semiconductor film 6, and Sin to 8isN4 is used as the evaporation prevention film 7, but any material may be used as long as it satisfies the relationship of ease of evaporation near the melting point of the semiconductor film 6. That is clear.

(Effects of the Invention) According to the method of the present invention, an SOI single crystal can be formed at any location regardless of the underlying structure.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a sample for SOI formation using the conventional heat sink method, where 1 is a silicon substrate, 2 is a SiO substrate, 3
td polycrystalline silicon, 4 is a heat sink. FIG. 2 is a cross-sectional view of a sample for forming 8UI by the method of the present invention, where 5 is a quartz substrate, 6Fi polycrystalline silicon, 7 is an evaporation prevention film 8iU, or 81. N, , 10 are openings. Figure 1 Figure 2 n

Claims (1)

[Claims] In an SOI formation method in which a semiconductor thin film on an insulating layer is heated, melted, and solidified to make the semiconductor thin film into a single crystal, a part of the semiconductor surface is covered with a film that is less likely to evaporate than the semiconductor, and then a short period of time is applied. A method for forming an SOI, comprising performing a heat treatment to form a single crystal around an exposed portion of the semiconductor film.