JPH0637703B2 - Semiconductor thin film manufacturing method - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a semiconductor thin film, and more particularly to low temperature formation of a semiconductor thin film having excellent orientation.

BACKGROUND ART A crystalline or amorphous semiconductor thin film is used for a semiconductor device. Among crystalline semiconductor thin films, many thin films of polycrystalline or microcrystalline (for example, microcrystalline silicon) have been studied. These are usually formed on the substrate, but when the substrate is not a single crystal, the thin film formed is likely to be non-oriented.

However, if orientation can be freely imparted to these thin films, it becomes possible to give anisotropy to electrical properties or optical properties, which can lead to the development of new functions. This is very important.

Conventionally, there has been a demand for a technique for forming a semiconductor thin film having orientation on a non-single crystal substrate such as glass or a polymer film.

The present inventor has conducted photodecomposition of silane and fluorosilane
Method was basically completed to obtain a semiconductor thin film having orientation at a low temperature, and was previously proposed (Japanese Patent Application No. 60-2
No. 15173 (Japanese Patent Laid-Open No. 62-76612).

However, the photo-CVD method has a practical problem that as the film forming time becomes longer, the light-transmitting window becomes cloudy, though gradually, and the amount of light transmission gradually decreases.

As a result of further study to solve this problem, the inventors of the present invention have found that even if the substrate temperature is 300 ° C. or lower by using a raw material gas in which hydrogen is added to a mixed gas of fluorosilane and silane in an amount of 5 times or more, The present invention has been completed by finding that a semiconductor thin film having an orientation can be grown on a substrate with a good orientation by discharge decomposition, which has a large area and high-speed manufacturability as compared with photo-CVD, and is highly practical.

DISCLOSURE OF THE INVENTION The present invention relates to a single crystal or a non-heated product obtained by subjecting a mixed gas consisting of silane, fluorosilane, and hydrogen of 5 times or more, and more preferably 10 times or more of silane, fluorosilane, to discharge decomposition. A method of manufacturing a semiconductor thin film, characterized in that an oriented semiconductor thin film is formed on a single crystal substrate.

Hereinafter, the present invention will be described in detail.

In the present invention, as silane, Si _m H _{2m + 2} (m = 1 to 1
Monosilane, disilane, trisilane and the like represented by (an integer of 3) are effectively used. As the fluorosilane, fluoromonosilane represented by SiH _4-n F _n (n = 1 to 4) or Si ₂ F ₆ is effectively used.

Further, in the present invention, p-type or n-type impurity doping can be performed by making a group III compound or a group V compound coexist.

Examples of the Group III or V compound used herein include I
A hydride of a group II or group V element is preferable, and specific examples thereof include diborane (B ₂ H ₆ ), phosphine (PH ₃ ),
Examples include arsine (AsH ₃ ).

In the present invention, a single crystal or non-single crystal material can be used as the substrate on which the semiconductor thin film is formed.

Then, when a single crystal material, particularly a silicon substrate whose surface is cleaned, is used, the semiconductor thin film is epitaxially grown from the cleaned surface. On the other hand, when a non-single crystal material is used, a semiconductor thin film well oriented in the <110> direction can be obtained in the source gas composition of the present invention. In particular, I would like to point out that the latter case has an extremely important significance in industry. This is because, according to the prior art, a thin film formed by using a non-single-crystal material is usually non-oriented, but according to the present invention, it is possible to freely give orientation and a semiconductor having anisotropy. This is because it is expected to form a thin film.

Since the substrate temperature is as low as about 200 ° C. under the semiconductor thin film forming conditions of the present invention, there is also an advantage that a large number of various materials that can withstand these temperature conditions can be effectively used.

The present invention decomposes a mixed gas containing fluorosilane, silane and an excess amount of hydrogen, preferably a mixed gas containing 5 times or more, and more preferably 10 times or more the amount of hydrogen with respect to silane and fluorosilane, by discharging, It is a method of forming a semiconductor thin film on a heated crystalline substrate or amorphous substrate.

High-frequency glow discharge, DC glow discharge, microwave discharge, etc. can be effectively used for the discharge decomposition in the present invention.

In the present invention, as described above, it is preferable to carry out the discharge decomposition in the state of coexisting with hydrogen of 5 times or more the amount of fluorosilane and silane, and more preferably 10 times the amount of silane and fluorosilane. The above gas mixed with hydrogen is discharged and decomposed.

Concerning this mixed gas ratio, it is convenient to express it as a source gas supply flow rate (capacity) ratio to a thin film forming apparatus for forming a semiconductor thin film. The preferable range of the flow rate ratio is as follows. That is, fluorosilane / silane = 0.5 to 50, particularly preferably 1 to 20. Group III or V as required
Group compounds can be added, but the addition amount of these is group III or group V compound / (silane + fluorosilane)
A ratio value of 1 * 10 ^{-7 to} 0.1 is sufficient. Also, hydrogen /
(Fluorosilane + silane) is 5 or more. This is because a semiconductor thin film that is covered and has excellent orientation tends to be easily formed in a region where the amount of hydrogen added is large. However, if the amount of hydrogen added is too large, the growth rate of the semiconductor thin film is reduced, which is not preferable, and therefore hydrogen / preferable in the present invention is preferable.
The mixing ratio of (fluorosilane + silane) is 5 to 100, more preferably 10 to 50, and particularly preferably 12 to 30.

The method of forming the mixed gas is not a critical factor and is not particularly limited. For example, by introducing a premixed gas outside the forming apparatus, or by using a thin inside the forming apparatus,
It is useful to mix hydrogen or a compound of group III or group V so as to satisfy the above-mentioned degree of dilution. Of course, there is no problem to use fluorosilane or silane mixed with hydrogen and / or a compound of group III or group V.

In the present invention, the power source for generating electric power used for discharge decomposition is not a critical condition and is not particularly limited.
As a concrete example, a high frequency power supply, a direct current high voltage power supply, a microwave power supply, etc. are useful.

Further, in the present invention, there is no particular critical limitation on the pressure of the mixed gas and the electric power supplied during the decomposition of the discharge.
These conditions affect the growth rate of the semiconductor thin film, and the semiconductor thin film excellent in orientation can be effectively grown by appropriately changing the substrate temperature according to the growth rate.

Further, one of the excellent features of the present invention is that the temperature for forming a semiconductor thin film having excellent orientation is extremely low as compared with the conventional method.

[Preferred Embodiments for Carrying Out the Invention] Next, embodiments of the present invention will be described. Discharge means,
A single crystal or non-single crystal substrate whose surface has been cleaned by cleaning and / or etching is placed in a thin film forming apparatus having at least a substrate introducing unit, a substrate holding unit, a substrate heating unit, a gas introducing unit, and a vacuum exhaust unit, and a vacuum is provided. Heat the substrate under exhaust to 100-400 ℃. The raw material gas has a flow ratio of fluorosilane to silane of 1 to 10 and a flow ratio of hydrogen to (fluorosilane + silane) of 10 times or more.
When a group III or group V compound is added, if necessary, the ratio of the amount of the group III compound or group V compound added to (silane + fluorosilane) is set to 1 * 10 ^{−7 to} 0.1 and the compound is supplied to the apparatus. It The pressure in the apparatus is reduced to 5 Torr or less by the vacuum exhaust means, and the discharge is started at 1 to 100 W.
Since the thin film starts to be formed at the start of the discharge, the discharge is stopped at the time when the required film thickness is reached in consideration of the film forming rate. Further, the film formation time can be determined while the film thickness is being measured by the film thickness monitor.

[Effect of the Invention] The semiconductor thin film having excellent orientation obtained in the present invention can be formed even at a substrate temperature as low as 300 ° C or lower, and even at an extremely low temperature of 200 ° C or lower. The present invention provides an extremely useful technique in the field of semiconductor device manufacturing, where a low-temperature technique for forming a semiconductor thin film or a semiconductor device is highly desired for high integration.

Further, the present invention does not require harmful mercury as a sensitizer unlike the photo-CVD method, and is therefore an excellent technique from the viewpoint of pollution prevention. Furthermore, because it achieves higher speed film formation than the photo-CVD method, it must be said that it is a technology that is superior from a practical viewpoint.

Example 1 A thin film forming apparatus equipped with a high-frequency power introducing means, a discharge electrode, a substrate introducing / extracting means, a substrate holding means, a substrate heating means, a gas introducing means, a vacuum exhausting means, and a substrate introducing / extracting chamber was used in the present invention. Was carried out. N of the cleaning agent which is a substrate for film formation using the substrate loading / unloading means
The type silicon wafer <110> was introduced from the substrate introducing / extracting chamber by using the substrate introducing / extracting means, and set on the substrate holding means. The substrate was heated to 250 ° C. by the substrate heating means while being evacuated by the vacuum evacuation means. Monosilane / difluorosilane / hydrogen was introduced at a flow rate ratio of 1/5/100, and the pressure inside the thin film forming apparatus was adjusted to 1 Torr by the pressure adjusting mechanism installed in the vacuum exhaust means. When the temperature of the substrate and the pressure in the thin film forming apparatus became constant, 20 W of high frequency power was applied to the discharge electrode by the high frequency power introduction means to start glow discharge. Discharge is stopped when the film thickness reaches about 6000A.
The average film formation rate was 0.4 A / s. After cooling, the substrate was taken out and observed. As a result, the substrate surface was a mirror surface with no fog. The surface was observed by reflection electron beam diffraction (RHEED) to obtain the same streak-like Laue spots as the substrate, and it was confirmed that the single crystal thin film was epitaxially grown from the surface. The specific resistance was 100 Ω · cm or more.

[Embodiment 2] The present invention is performed by using a thin film forming apparatus equipped with a high-frequency power introducing means, a discharge electrode, a substrate introducing / extracting means, a substrate holding means, a substrate heating means, a gas introducing means, a vacuum exhausting means, and a substrate introducing / extracting chamber. Was carried out. A glass plate of a cleaning agent, which is a substrate for film formation, was introduced from the substrate introduction / extraction means by using the substrate introduction / extraction means and set on the substrate holding means. The substrate was heated to 200 ° C. by the substrate heating means while being evacuated by the vacuum evacuation means. 1/6/120 monosilane / difluorolane / hydrogen
The pressure inside the thin film forming apparatus was adjusted and maintained at 3 Torr by the pressure adjusting mechanism provided in the vacuum evacuation means. When the temperature of the substrate and the pressure in the thin film forming apparatus became constant, high frequency power of 30 W was applied to the discharge electrode by the high frequency power introducing means to start glow discharge. Film thickness is about 5000
When it reaches A, the discharge is stopped. Average deposition rate is 1A / s
Met. After cooling, the substrate was taken out and observed,
It was a mirror surface with no fogging on the substrate surface. X-ray diffraction (XRD
It was confirmed by (1) that the semiconductor thin film was well oriented in the <110> direction.

Claims (7)

[Claims] 1. Silane, fluorosilane, and (silane +
A method for producing a semiconductor thin film, characterized by discharge-decomposing a mixed gas consisting of hydrogen in an amount five times or more that of fluorosilane) and forming it on a substrate. 2. The method according to claim 1, wherein the composition ratio of the mixed gas to be decomposed by discharge is 10 times or more of hydrogen relative to silane and fluorosilane. 3. The method according to claim 1, wherein a group III compound or a group V compound is added to the mixed gas. 4. The process according to claim 1, wherein the fluorosilane is fluoromonosilane represented by SiH _4-n F _n (n = 1 to 4) or Si ₂ F ₆ . 5. The process according to claim 1, wherein the silane is Si _m H _{2m + 2} (m = 1 to 3 is an integer). 6. The method according to claim 1, wherein the substrate is a substrate made of a single crystal material or a non-single crystal material. 7. Silane, fluorosilane, and (silane +
The production method according to claim 1, wherein a mixed gas containing hydrogen in an amount 5 times or more that of fluorosilane) is decomposed by glow discharge and formed on a heated single crystal substrate or non-single crystal substrate.