JPH0722315A - Method for manufacturing semiconductor film - Google Patents

Abstract

PURPOSE:To form a single crystalline semiconductor film in the controlled crystal orientation at an arbitrary position even on an amorphous insulator such as a glass substrate, etc. CONSTITUTION:An amorphous silicon film 2 is deposited on a glass substrate 1, on the other hand, protrusions 4 are formed on the parts of the surface of a single crystal silicon substrate 3. Next, the flat surfaces of the single crystal silicon substrate 3 are brought into contact with the amorphous silicon film 2 to be overlapped with one another and then the surface of the amorphous silicon film 2 and the flat surfaces of the protrusions 4 closely adhering to one another are heated at 550 deg.C for about ten hours in nitrogen atmosphere. Through this heat treatment, the crystallinity of the single crystal silicon substrate 3 can be transferred to the regions of the amorphous silicon film 2 closely adhering to the protrusions 4 of the single crystal substrate 3 thereby enabling a single crystal silicon film 5 leaving it intact in solid state to be formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a single crystal semiconductor film formed on an insulating base, that is, a so-called SOI (Silicon on Insulator) structure, for forming an electronic circuit. It is a thing. The single crystal silicon film produced by the method of the present invention is used in many fields such as solar cells, active matrix type liquid crystal display devices, optical sensors, high speed devices, highly integrated LSIs, high breakdown voltage devices, radiation resistant devices, and three-dimensional integrated circuits. can do.

[0002]

2. Description of the Related Art The SOI structure forming technique includes a recrystallization method,
There are a lateral solid phase growth method, an epitaxial growth method, an insulating layer embedding method, a laminating method and the like. A general description of the SOI structure forming technology is described in detail in "SOI Structure Forming Technology" (published by Sangyo Tosho Co., Ltd., 1987). In the lateral solid phase growth method, a part of the silicon substrate is covered with a silicon oxide film, and an amorphous silicon film is deposited on the silicon oxide film.
Perform low temperature annealing at about ℃. In the portion of the amorphous silicon film that is in direct contact with the silicon substrate, the silicon substrate serves as a seed, and epitaxial growth is first performed in the solid phase in the vertical direction, and then in the solid state in the horizontal direction on the silicon oxide film. To grow epitaxially. As a result, an SOI structure in which a single crystal silicon film exists on the silicon oxide film is obtained. The lateral solid phase growth method has an SOI structure of 600 ° C.
Since it can be achieved at a low temperature, the thermal effect on the semiconductor device formed in the lower layer is small.
If it is deposited by the VD method, the conventional manufacturing method can be applied as it is, it has mass productivity, and it has a multi-layered SOI.
The structure also has advantages such as being able to grow simultaneously from the same seed portion.

A solar cell that directly converts sunlight into electric energy was invented in 1976 by Mr. Carlson of the American RCA Corporation, and a solar cell using amorphous silicon was developed (see US Pat. No. 4,064,521). In a solar cell, the conversion efficiency of solar energy into electric power is higher in a single crystal system than in an amorphous system, and the reliability is also high. But,
Amorphous systems predominate because single-crystal substrates are expensive.

An amorphous silicon thin film transistor for a liquid crystal display comprises a semiconductor film, source / drain electrodes and a gate electrode. Amorphous silicon and polycrystalline silicon are practical semiconductor layers. Generally, amorphous silicon is similar to the process of making a solar cell.
It is formed by a plasma CVD method using SiH ₄ as a source gas.

[0005]

A major problem of amorphous silicon solar cells is reliability. The initial conversion efficiency of solar energy into electric power is about 1 in the first year depending on use.
It decreases by 0%, and thereafter decreases by 1-2% every year. The cause has not been identified yet, but O contained in the semiconductor film,
Impurities such as N and the presence of SiH ₂ existing in the semiconductor film are considered. Some ideas have been made in the method of manufacturing an amorphous silicon film based on the idea of this cause. According to one method, the reliability can be improved by reducing impurities in the semiconductor film, and an ultra-high vacuum film forming apparatus is used to form an amorphous silicon film or the like at an ultimate vacuum of about 1/10 ⁹ Pa. ing. Another idea is that energy generated when electrons and holes are recombined causes a dangling bond to deteriorate the characteristics, and a multilayer structure is adopted to prevent these recombination. ing. In any case, the problem of deterioration of conversion efficiency of amorphous silicon solar cells imposes restrictions on the environment in which they are used, and in order to improve their reliability, multilayering and high quality semiconductor films are required. However, the manufacturing process is complicated and the cost is increased.

Although there are solar cells using polycrystalline silicon, the problem of polycrystalline solar cells lies in how to approach the conversion efficiency of single crystalline solar cells. Polycrystals have many grain boundaries as an essential problem. Grain boundaries hinder the movement of electrons and holes. It also serves as a place where electrons and holes recombine. It is necessary not to create grain boundaries in the electron movement direction. To solve this problem, a method of increasing the size of crystal grains to reduce the grain boundary area is used.

An amorphous silicon thin film transistor for a liquid crystal display also has a great reliability problem, like an amorphous silicon solar cell. As a typical one, there is a threshold voltage shift by applying a gate bias. The threshold voltage is a gate voltage at which the drain current of a thin film transistor rises sharply. The difference in work function between the semiconductor and the gate metal, the Fermi level inside the semiconductor, the fixed charge at the interface between the semiconductor and the gate insulating film, and the gate insulation. It is determined by the fixed charge at the interface between the film and the gate electrode. The reliability for a short time including the initial stage is SiN which is the gate insulating film.
It depends on x, and the film quality of the amorphous silicon film may be involved in the long term. If solar cells and liquid crystal displays can be manufactured at low cost using single-crystal silicon films, there is nothing better than that.

Among the methods for producing a single crystal silicon film,
In the lateral solid phase growth method, the single crystallizable region is a small range of about 10 μm from the seed portion. This means that there is a limit to the distance at which solid phase growth can be performed in the horizontal direction after single crystal growth in the vertical direction from the seed portion, and the distance is about 10 μm. Therefore, a large area SOI structure cannot be formed. Further, when an active element is formed on the grown single crystal silicon film, there is a restriction on the distance between the active element and the exposed portion of the single crystal substrate used as the seed, and therefore the degree of freedom in design is low.

In the lateral solid phase epitaxy method, the substrate supporting the insulating film under the semiconductor film to be single crystallized serves as a seed. Therefore, in the lateral solid phase epitaxy method, the substrate is a single crystal substrate. Can only be applied in case of. For example, when the substrate is an amorphous substrate such as glass, the lateral solid phase growth method cannot be applied. It is an object of the present invention to provide a method for forming a single crystal semiconductor film whose crystal orientation is controlled on an amorphous insulator substrate such as a glass substrate at an arbitrary position and in an arbitrary size. .

[0010]

According to the present invention, a substrate surface having an amorphous or polycrystalline semiconductor film on the surface thereof is formed on a region of the semiconductor film, which is made of the same material as the semiconductor film and is intended to be a single crystal. A heat treatment is performed while closely adhering the convex portion of the single crystal substrate having a convex portion having a flat surface in the corresponding region as a seed material to solidify the region of the semiconductor film that is in close contact with the convex portion of the single crystal substrate. It is single-crystallized in a phase state, and then the seed material is separated from the single-crystallized semiconductor film.
The seed material is a single crystal piece prepared as a substance different from the substrate having the amorphous or polycrystalline semiconductor film.

[0011]

EXAMPLE One example is shown in FIG. (A) An amorphous silicon film 2 having a thickness of 5000 to 10000Å, for example, about 5 is formed on a glass substrate 1 by LPCVD.
Deposit to a thickness of 000Å. In the LPCVD method for depositing the amorphous silicon film 2, SiH ₄ is used as a source gas, for example. In order to improve the homogeneity of the film quality of the amorphous silicon film 2, Si _{2 is used} as the source gas instead of SiH _4.
It may be formed at a low temperature by using H ₆ . Separately from the glass substrate 1, a concave portion is determined by photolithography and etching on a part of the surface of the single crystal silicon substrate 3 to form a convex portion 4. The depth of the recess is several thousand Å to several μm, for example, about 1 μm.
m. The surface of the convex portion 4 is the surface of the original single crystal silicon substrate 3 and is a flat surface.

(B) The native oxide film on the surface of the amorphous silicon film 2 on the glass substrate 1 and the native oxide film formed on the surface of the convex portion 4 of the single crystal silicon substrate 3 are removed with a hydrofluoric acid solution. After that, the single crystal silicon substrate 3 is brought into contact with the single crystal silicon substrate 3 so that the flat surface of the convex portion 4 overlaps the amorphous silicon film 2 on the substrate 1. Then, a high voltage is applied from the power supply device 6 between the glass substrate 1 and the single crystal silicon substrate 3, and the surface of the amorphous silicon film 2 and the flat surface of the convex portion 4 of the single crystal silicon substrate 3 are formed by electrostatic pressure bonding. While closely contacting with each other, heating is performed in a nitrogen atmosphere at 500 to 600 ° C., for example, 550 ° C. for about 10 hours. The voltage applied from the power supply device 6 by the electrostatic pressure bonding method is, for example, 0.5 to 1.5 KV.

By this heat treatment, the crystallinity of the single crystal silicon substrate 3 is transferred to the region of the amorphous silicon film 2 that is in close contact with the convex portion 4 of the single crystal silicon substrate 3, and the single crystal silicon remains in the solid state. The film 5 is formed. After the heat treatment, the single crystal silicon substrate 3 is separated from the glass substrate 1. A portion of the silicon film on the glass substrate 1 which is not single-crystallized (a portion which remains amorphous) is removed by etching. As the etching liquid at this time, for example, a solution in which hydrofluoric acid and nitric acid are mixed at an appropriate ratio can be used. When treated with this solution, the single crystallized silicon film 5 remains without being etched, and the amorphous silicon film is removed.

As described above, only the portion of the amorphous silicon film 2 to which the convex portion 4 of the single crystal silicon substrate 3 adheres is single crystallized. Therefore, by forming a convex portion having a desired size at a desired position on the single crystal silicon substrate 3, the single crystal silicon film 5 corresponding to the position and the size can be obtained.

As a single crystal substrate used as a seed material, instead of the single crystal silicon substrate 3 of the embodiment, another single crystal body such as a sapphire substrate, an SOS (silicon on sapphire) substrate, an alkaline earth metal fluoride is used. (CaF ₂ , S
rF ₂ , BaF _2, etc.) can also be used. The substrate on which the amorphous or polycrystalline silicon film to be single-crystallized is not limited to the glass substrate of the embodiment, but a silicon substrate on which a silicon oxide film is formed, a glass substrate on which a silicon oxide film or a silicon oxide film is formed. An insulating film such as a multilayer film of a silicon oxide film and a silicon nitride film may be formed. In the embodiment, the electrostatic pressure bonding method is used as a method for bringing the convex portion 4 of the single crystal silicon substrate 3 into close contact with the amorphous silicon film 2, but as another method, for example, a method of applying a load to perform pressure bonding. Alternatively, a method of bringing the two substrates into close contact with each other in a vacuum can be used. Although an amorphous silicon film is used as the semiconductor film to be monocrystallized in the embodiment, a polycrystalline silicon film may be used. The present invention can be variously modified.

[0016]

According to the present invention, a crystal that serves as a seed for crystal growth is brought into close contact with the crystal from the outside, and thus a single crystal thin film having a controlled crystal orientation is formed even on an amorphous substrate such as a glass substrate. You can The position and pattern of the single crystal semiconductor film to be obtained can be arbitrarily formed depending on the position and the pattern of the convex part of the single crystal substrate to be the seed, which increases the degree of freedom in design.

Since the seed (seed crystal) is brought into contact with the outside, it is not necessary to form a seed region as in the conventional case, and therefore, the integrated circuit can be highly integrated. By partially forming a single crystal silicon film as in the example and removing the region that is not single crystallized by etching, an island pattern can be formed without going through the photography step, and the manufacturing process can be shortened. Can be converted. The method of the present invention has a simple method and does not require a complicated process, so that the yield is improved.

[Brief description of drawings]

FIG. 1 is a process sectional view showing an example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Glass substrate 2 Amorphous silicon film 3 Single crystal silicon substrate 4 Convex portion 5 Formed single crystal silicon film 6 Power supply device

Claims (2)

[Claims] 1. A substrate surface having an amorphous or polycrystalline semiconductor film on the surface, made of the same material as the semiconductor film, and having a flat surface in a region corresponding to a region of the semiconductor film to be single-crystallized. A heat treatment is performed while closely adhering the convex portion of the single crystal substrate having the convex portion as a seed material to single crystallize a region of the semiconductor film in close contact with the convex portion of the single crystal substrate in a solid state, Then, a method for manufacturing a semiconductor film, in which the seed material is separated from the single crystallized semiconductor film. 2. The method for producing a semiconductor film according to claim 1, wherein the seed material is a single crystal piece prepared as a substance different from the substrate having the amorphous or polycrystalline semiconductor film.