JP2857456B2 - Method for manufacturing semiconductor film - Google Patents

Description

The present invention relates to a so-called SOI (Silicon On Insu) having a single crystal silicon film on an insulating base to form an electronic circuit.
The present invention relates to a method for manufacturing a single crystal silicon film called a "lator" structure.

The single-crystal silicon film manufactured by the method of the present invention is an active matrix type liquid crystal display device, highly integrated.
It can be used in many fields such as LSIs, high voltage devices, radiation resistant devices, and 3D integrated circuits.

(Prior art) There are several methods for SOI structure formation technology, and a general description is given in detail in "SOI structure formation technology" (published by Sangyo Tosho Co., Ltd., 1987). Of 1
One is a silicon wafer direct bonding technology.

In silicon wafer direct bonding technology, single-crystal silicon substrates with oxide films formed on their surfaces are brought into close contact with each other so that the oxide films are in contact with each other, and heat-treated at about 700 ° C in an oxidizing atmosphere to directly connect the oxide films. Join. Thereafter, one of the silicon substrates is etched by an etch-back method until a predetermined thickness is obtained, thereby forming an SOI substrate.

(Problem to be Solved by the Invention) In the above-described silicon wafer direct bonding technology, it is necessary to etch back one silicon substrate to a thickness that can obtain desired device characteristics. At that time, the following problem occurs. .

(1) When etching back by dry etching, the etch rate of silicon is usually about 8000Å / min by magnetron RIE, and the thickness of the silicon substrate needs to be about 500 μm from the viewpoint of its strength. The time required for the etch back is several hours to several tens of hours, and the throughput is extremely deteriorated.

(2) When etching back by a dry etching method, a silicon substrate which will later be an element formation surface is damaged. Extra processing steps such as wet surface treatment and sacrificial oxidation are required later to remove the damage.

(3) In the case of etching back by wet etching, the uniformity of etching is poor and a serious problem occurs as the diameter increases.

(4) In the case of etching back by the wet etching method, it is necessary to mask the exposed surface and side surface of one silicon substrate to be a supporting substrate, which requires an extra step.

The present invention eliminates the etch-back process found in conventional methods, manufactures SOI substrates by a process suitable for mass production, has in-plane uniformity that can accommodate large diameters, and does not damage the element formation surface. It is intended to do so.

(Means for Solving the Problems) In the present invention, a first substrate obtained by epitaxially growing a single crystal silicon film on a sapphire substrate and a second substrate having at least a surface made of an insulator are formed by combining a first substrate with a first substrate. The two substrates are brought into close contact with each other so that the single crystal silicon film and the insulating surface of the second substrate are in contact with each other, heated to join the single crystal silicon film to the insulating surface of the second substrate, and then the sapphire substrate is separated.

The second substrate having at least an insulator is a single crystal silicon substrate having a thermal oxide film formed on its surface, a silicon nitride film formed thereon, and a glass substrate having a silicon oxide film or silicon For example, a nitride film is formed. In the case of the second substrate in which an insulating film is formed over a silicon substrate, the silicon substrate may have no semiconductor element formed thereon, or may have a semiconductor element already formed.

(Embodiment) An embodiment will be described with reference to FIG.

(A) A single-crystal silicon film 2 is epitaxially grown on a sapphire substrate 1 to a thickness of several thousand degrees by a well-known method such as thermal decomposition of SiH ₄ .

On the other hand, a silicon oxide film 4 is formed on a single crystal silicon substrate 3 by thermal oxidation to a thickness of about 10,000 to 15,000.

(B) Both substrates are bonded so that the single crystal silicon film 2 and the silicon oxide film 4 are in contact with each other. In this state, heat treatment is performed in a heating furnace at 900 to 1000 ° C. for 30 to 60 minutes.

(C) The sapphire substrate 1 is separated from the silicon substrate 3. At this time, the sapphire substrate 1 and the single crystal silicon film 2
Since the adhesion between the silicon oxide film 4 and the single-crystal silicon film 2 is stronger than the adhesion between the silicon oxide film 4 and the single crystal silicon film 2, only the sapphire substrate 1 is separated and the silicon oxide film 4 on the silicon substrate 3 The SOI structure has the single crystal silicon film 2 remaining.

 FIG. 2 shows another embodiment.

For example, a silicon oxide film 5 is formed as a mask material on the sapphire substrate 1, and the silicon oxide film 5 is patterned by photolithography and etching so that the sapphire substrate 1 which is to be an active region later on the SOI substrate is exposed.

A single crystal silicon film 2 is epitaxially grown on the exposed sapphire substrate. The single-crystal silicon film 2 has the same thickness as the silicon oxide film 5, or when formed to be thinner than the silicon oxide film 5 as described later with reference to FIG. 3, the silicon oxide film 5 is etched to project the single-crystal silicon film 2. Let it. The thickness of the single crystal silicon film 2 is determined to an appropriate value in consideration of a later sapphire substrate peeling step, a depth of the active region, and the like. The thickness of the single crystal silicon film 2 is, for example, about 3000 °.

On the other hand, a silicon oxide film 4 is formed on the silicon substrate 3 as in FIG.

The two substrates are bonded together so that the single crystal silicon film 2 and the silicon oxide film 4 are in contact with each other.
A heat treatment is performed at 0 to 1000 ° C. for 30 to 60 minutes.

When the sapphire substrate 1 is separated from the silicon substrate 3,
An SOI structure is obtained in which the single crystal silicon film 2 partially remains on the silicon oxide film 4 on the silicon substrate 3. In this SOI structure, the single crystal silicon film 2 is patterned, and an SOI substrate is formed in a state where the active region has been subjected to element isolation.
Therefore, the element isolation step can be omitted.

When the single crystal silicon film 2 is selectively grown on the sapphire substrate 2, as shown in FIG. 3A, the single crystal silicon film 2 is formed to be thinner than the silicon oxide film 5. (B), if the silicon oxide film 5 is etched so that the single crystal silicon film 2 protrudes, the single crystal silicon film 2 adheres closely to the silicon oxide film 4 and furthermore, the dimensional accuracy in the lateral direction is increased. Also gets better. Fig. 3 (B)
In the state described above, a cavity is formed between the silicon oxide film 5 and the surface of the second substrate, and the gas sealed therein may expand. In this case, the two substrates are brought into close contact in a vacuum. What should be done is.

As the heat treatment for bonding between the single crystal silicon film 2 and the silicon oxide film 4, instead of being put in a heating furnace, scanning is performed by irradiating a laser beam from the sapphire substrate 1 side, Other heating means may be used, such as scanning by irradiating heat rays from the silicon substrate 3 side.

(Effects of the Invention) In the present invention, a single crystal silicon film epitaxially grown on a sapphire substrate is brought into close contact with the insulating surface of the second substrate, heated and joined, and then the sapphire substrate is separated from the single crystal silicon film. To get SOI structure,
An SOI structure can be easily realized at a high throughput without an etch-back step.

The single-crystal silicon film on which the element is formed is formed by epitaxial growth, and has no etch-back process. Therefore, the in-plane uniformity of the film thickness is excellent, and it is easy to obtain a desired film thickness. Also, there is no damage on the element formation surface.

Sapphire substrates are more expensive than silicon substrates.
However, when a single crystal silicon film formed on a sapphire substrate is adhered to, for example, a silicon oxide film formed on a silicon substrate, and heated to join the single crystal silicon film and the silicon oxide film, the sapphire substrate Since the upper single crystal silicon film disappears, the single crystal silicon film can be regenerated and reused by cleaning the surface of the sapphire substrate and then performing epitaxial growth again.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view of a process showing one embodiment, FIG. 2 is a cross-sectional view of a halfway process showing another embodiment, and FIG. 3 shows one method for selectively forming a single crystal silicon film on a sapphire substrate. It is a process sectional view. 1 ... sapphire substrate, 2 ... single crystal silicon film, 3 ...
... Silicon substrate, 4 ... Silicon oxide film.

Claims (1)

(57) [Claims] A first substrate obtained by epitaxially growing a single crystal silicon film on a sapphire substrate, and a second substrate having at least a surface made of an insulator are combined with a single crystal silicon film of the first substrate and a second substrate. A method for manufacturing a semiconductor film, in which both substrates are brought into close contact with each other so that the insulating surfaces of the substrates are in contact with each other, heated to join the single crystal silicon film to the insulating surface of the second substrate, and then the sapphire substrate is separated.