JPH0733317B2 - Manufacturing method of n-type single crystal thin film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing a single crystal thin film, and more particularly to low temperature formation of an n-type silicon single crystal thin film.

[Background Art] A low-temperature formation method of a single crystal thin film has recently attracted attention as a very important technology for achieving high integration of semiconductor devices, and various approaches have been taken for this purpose. However, for example, thermal CVD of monosilane (Chemical V
apor Deposition: about 1000-1100 ℃ by chemical vapor deposition
A high temperature of about 600 to 700 ℃ was required in the photo-CVD method of fluorosilane or disilane according to the results of our study. As described above, the conventional technique still requires a considerably high temperature, and at present, a technique for forming a single crystal thin film at a sufficiently low temperature has not been completed.

The present inventor photoly decomposes silane and fluorosilane (photo-CVD
Method), a technique for forming a single crystal thin film at low temperature was basically completed, and was previously proposed (Japanese Patent Publication No. 05-047518).
No. 05-047519, No. 05-049637, No.
06-050730).

However, this photo-CVD method has a practical problem that as the film formation time becomes longer, the light-transmissive window becomes slightly cloudy and the amount of light transmission gradually decreases.

As a result of further study to solve this problem, by using a raw material gas obtained by adding an excessive amount of hydrogen to a mixed gas of fluorosilane and silane, the single crystal silicon thin film was It has been found that n-type doping is possible by growing by electric discharge decomposition, which has higher practicality than in CVD in terms of large area, high-speed manufacturability, and the like, and by allowing a Group V compound to coexist in the mixed gas, The present invention has been completed.

DISCLOSURE OF THE INVENTION The gist of the present invention is a method for producing a single crystal thin film, which is characterized in that a mixed gas consisting of silane, fluorosilane, a group V compound and an excessive amount of hydrogen is discharged and decomposed to be formed on a substrate. It is a thing.

Hereinafter, the present invention will be described in detail.

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

The group V compound used in the present invention is preferably a hydride of a group V element, and PH ₃ and AsH ₃ are particularly preferable. From the viewpoint of toxicity during exhaust gas treatment, PH ₃ is particularly preferable.

The present invention allows an excess amount of hydrogen to be present together with the fluorosilane, the silane and the group V compound, that is, a mixed gas of the fluorosilane, the silane, the group V compound and the excess amount of hydrogen, preferably silane, fluorosilane and the group V compound. On the other hand, it is a method of forming an n-type single crystal thin film on a heated crystalline substrate by forming a mixed gas containing hydrogen in an amount of 5 times or more, and discharging the mixed gas.

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

Further, in the present invention, a single crystal thin film is epitaxially grown on a substrate, and in a particularly preferred embodiment, on a substrate made of a single crystal, and a silicon wafer, sapphire or the like is used as the substrate.

In the present invention, as described above, it is preferable to carry out discharge decomposition in the state where an excessive amount of hydrogen coexists with fluorosilane, silane and V-type compound, but more preferable embodiments include silane, fluorosilane and V
It is a gas that is mixed with hydrogen in an amount 5 times or more that of the type compound and decomposed by discharge.

It is convenient to express this mixed gas ratio by the ratio of the source gas supply flow rates (capacity) to the thin film forming apparatus for forming a single crystal 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. The amount of V-type compound added is such that the ratio of V-type compound / (silane + fluorosilane) is 1 * 10 ^-7
About 0.001 is enough. Further, hydrogen / (fluorosilane + silane + V type compound) is 5 or more. This is because the n-type single crystal thin film tends to be formed in a region where the amount of hydrogen added is excessive. However, if the amount of hydrogen added is too large, the growth rate of the n-type single crystal thin film is reduced, which is not preferable. Therefore, the preferable mixing ratio in the present invention is hydrogen /
(Fluorosilane + silane + V type compound) 5 to 100, more preferably 10 to 50, and particularly preferably 12 to 30.

In the present invention, the method of forming the mixed gas is not a critical factor and is not particularly limited. For example, it is useful to introduce a premixed gas outside the forming apparatus or to mix hydrogen in the forming apparatus so as to satisfy the above dilution degree. Of course, there is no problem in using hydrogen-diluted fluorosilane or silane.

Further, in the present invention, the power source for generating the electric power used for the 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 n-type single crystal thin film, and the n-type single crystal thin film can be effectively epitaxially grown by appropriately changing the substrate temperature according to the growth rate.

One of the particularly excellent features of the present invention is that the temperature for forming the n-type single crystal thin film 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 substrate of a single crystal material whose surface is cleaned by cleaning and / or etching is placed in a thin film forming apparatus having at least a substrate introducing means, a substrate holding means, a substrate heating means, a gas introducing means, and a vacuum exhausting means, and a substrate under vacuum exhausting 100 ~ 400 ℃
Heat to. The raw material gas has a flow ratio of fluorosilane to silane of 1 to 10 and an addition ratio of V group compound to (silane + fluorosilane) of 1 * 10 ^{-7 to} 0.001 and flow rate of hydrogen to (fluorosilane + silane + V group compound). The ratio is supplied to the apparatus at a ratio of 5 times or more, more preferably 10 times or more. Evacuate the pressure in the device to 10 To
The discharge is started at 1 to 100 W as rr or less. 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.

[Advantages of the Invention] The substrate temperature of the n-type single crystal thin film obtained in the present invention is
It is formed at a low temperature of 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 a technique excellent in terms of preventing pollution. Furthermore, since it is possible to achieve higher-speed film formation than the photo-CVD method, it must be said that it is an excellent technique from a practical viewpoint.

[Embodiment] The present invention is implemented by using a thin film forming apparatus equipped with high-frequency power introducing means, discharge electrode, substrate introducing / extracting means, substrate holding means, substrate heating means, gas introducing means, vacuum exhausting means, and substrate introducing / extracting chamber. Example. Using the substrate loading / unloading means, the substrate that has been cleaned has already been cleaned.
An n ^- type silicon wafer (100) 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. Then phosphine (P
H ₃ ) (monosilane (SiH ₄ ) + difluorosilane (SiH
₂ F ₂ )) to 1 * 10 ^-5 and monosilane (SiH ₄ ) / difluorosilane (SiH ₂ F ₂ ) /
Hydrogen is introduced at a flow rate ratio of 1/5/100, and the pressure inside the thin film forming apparatus is adjusted to 1 Torr by the pressure adjusting mechanism installed in the vacuum exhaust means.
Adjusted and held at r. 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 0.2 A / s. After cooling, the substrate was taken out and observed. As a result, the substrate surface was a mirror surface with no fog. Observe the surface by reflection electron diffraction (RHEED),
The same streak-like Laue spots as the substrate were obtained, and it was confirmed that the n-type single crystal thin film was epitaxially grown from the substrate surface. The resistivity was 0.02 Ω · cm or more.

Claims (7)

[Claims] 1. A method for producing an n-type single crystal thin film, which comprises discharging and decomposing a mixed gas consisting of silane, fluorosilane, a V-group compound and an excess amount of hydrogen to form 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 such that hydrogen is at least 5 times as much as that of silane, fluorosilane and V group compound. 3. The method according to claim 1, wherein the group V compound is PH ₃ or AsH ₃ . 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 method 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 n-type single crystal thin film is epitaxially formed on the crystalline substrate. 7. The method according to claim 1, wherein a mixed gas consisting of silane, fluorosilane, a V-group compound and hydrogen is decomposed by glow discharge and epitaxially formed on a heated crystalline substrate.