JPS59227713A - Novel method for producing silicon fluoride thin film - Google Patents

Abstract

PURPOSE:To form a fluorinated silicon thin film on a substrate in high productivity, by the glow discharge decomposition of a gas composed of a higher fluorinated silane and a higher silane diluted with He and/or H2. CONSTITUTION:A substrate such as silicon single crystal wafer, glass, stainless steel, ceramic, etc. is placed in a reaction chamber having a glow-discharging means, and then, a gaseous mixture composed of a higher fluorinated silane of formula SinF2n+2 (n is integer of >= (especially hexafluorodisilane of formula Si2F6; n=2) and a higher silane of formula SimH2m+2 (m is integer of >=2) (especially disilane; n=2) diluted with 1-100 time volume of He and/or H2 is introduced into the reaction chamber. The gas is decomposed by glow discharge to deposit a fluorinated silicon thin film on the substrate in high productivity.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a fluorinated silicon thin film, and more particularly to a method for forming a fluorinated silicon thin film at high speed.

Silicon thin films are used for a variety of purposes, including solar cells, photoreceptor drums, image reading devices, and image display devices, but fluorinated silicon thin films have recently attracted particular attention because they do not deteriorate when exposed to light. is being built.

Fluorinated silicon thin films are similar to hydrogenated silicon thin films.
The thin film formed by glow discharge decomposition has particularly good properties as a semiconductor.

Conventionally, the raw material gas for glow discharge decomposition of fluorinated silicon thin films has been tetrafluorosilane (Si
Although tetrafluorosilane (F+) is used, it functions as an etching material for silicon thin films during glow discharge, and it has not been possible to form a thin film using this alone. Therefore, in order to form a thin film, hydrogen or monosilane must coexist with the fluorinated silane, hydrogen radicals, hydrogen ions, etc. must be generated during glow discharge, and glow discharge must be performed in the presence of hydrogen or monosilane.

However, even in such cases, the silicon thin film formation rate was very low, at most 1 to 2 people/sec, probably due to the etching phenomenon of tetrafluorosilane itself.

That is, in the conventionally known methods, it is completely difficult to form a fluorinated silicon thin film at high speed, and the productivity is far inferior to that of a hydrogenated silicon thin film.

As a result of intensive study on a method for forming fluorinated silicon thin films at high speed, the present invention and others have found that the above drawbacks can be solved by using a gas mainly composed of higher fluorinated silane instead of the conventional tetrafluorinated silane. This discovery was made and the present invention was completed.

That is, the present invention has the general formula S inF 2nr2 (where n is n≧
) is an integer equal to 2), and S
A mixed gas in which high-grade silane expressed as imH2m-+-2- (where m is an integer of m≧2) is diluted with at least one type of helium or hydrogen (hereinafter referred to as helium, etc.) is decomposed by glow discharge. The present invention provides a method for producing a fluorinated silicon thin film, characterized in that the fluorinated silicon thin film is formed on a substrate.

The present invention will be explained in detail below.

The higher fluorinated silane used in the present invention has the general formula S i
nF 2n-+4 (where n is an integer n≧2), such as hexafluorodisilane, hefluorinated trisilane, +fluorinated tetrasilane 961
86, among others, hexafluorodisilane (n=2 in the general formula) is particularly preferred. Because disilane hexafluoride is a compound with a boiling point of approximately -19°C, it exists as a gas under normal temperature and pressure conditions, and can be introduced into the glow discharge decomposition equipment as is without any heat treatment. This is because it has the above advantages.

Although the laboratory production method of higher fluorinated silanes such as hexafluorinated disilane used in the present invention is known in the literature, it has never been commercially available due to the difficulties in industrial production. Therefore, as a matter of course, no study has been conducted to conduct glow discharge decomposition experiments using a large amount of it. However, the inventors of the present invention have recently developed a technique for producing this in a high yield, and studies using this have finally been conducted. Of course, in the present invention, hexafluorodisilane and the like produced by a known method can be used as is, as described later.

The higher silane used in the present invention has the general formula SimH2m+
2 (where m is an integer of m≧2), examples of which include disilane, trisilane, and tetrasilane 9000, with disilane (m=2 in the general formula) being particularly preferred. These may be obtained by a physical method such as silently discharging monosilane, or may be obtained by a chemical method such as reducing polychlorosilane such as hexachlorodisilane.

For the glow discharge decomposition operation of the present invention, a glow discharge decomposition method known per se may be applied as is.

That is, a silicon single crystal wafer, glass, on which a fluorinated silicon thin film is to be formed in a reaction chamber capable of glow discharge;
A substrate made of stainless steel, ceramics, etc. is placed. Next, a mixed gas of higher fluorinated silane and higher silane diluted with helium or the like is supplied into the reaction chamber, and glow discharge energy is applied to the gas to form a fluorinated silicon thin film on the substrate under reduced pressure. It is.

In the present invention, a fluorinated silicon thin film is formed in a temperature range from room temperature (approximately 20° C.) to 400° C., and thin film formation is possible even at room temperature. In addition, in the examples described later, an example was shown in which the thin film formation temperature was 300°C.

The formation rate of a fluorinated silicon thin film mainly depends on factors such as the composition ratio of higher fluorinated silane and a mixed gas consisting of higher silane and helium, etc., the flow rate of the mixed gas, the pressure during glow discharge, and the applied glow discharge power. It depends and changes.

S inF: zn+2 / S 1m82m+2
It is preferable to vary the mixing composition ratio between 100/1 and 1/100 in order to maintain the high-speed formability of the thin film and the fluorine content within a desired range.

On the other hand, the dilution rate with helium etc. is S 1nF2r++
2 and S i mH2Jn+2, 1 to 100
Double the capacity. By diluting higher fluorinated silane or the like with helium or the like in this manner, it is possible to improve the semiconductor properties of the resulting silicon thin film.

In addition, three factors, the flow rate of the mixed gas, the pressure during glow discharge, and the applied glow discharge power, have no effect on the film formation rate. First, the film formation rate increases depending on both the gas flow rate and the electric power. However, in a range where the power is further increased and exceeds a certain value, only the gas flow rate changes depending on the ratio. (1) On the other hand, regarding pressure, there is a relationship such that when the electric power is constant, the film formation rate decreases as the pressure increases, and when the electric power increases, the film formation rate increases as the pressure increases.

The semiconductor properties of the thin film obtained in this way vary depending on the factors such as the above-mentioned gas flow rate, pressure, applied force, and film formation temperature, but in particular, the formation temperature is changed from room temperature to 250 to 450°C.
By raising the temperature to .degree. C., the photoelectric properties can be improved.

Note that the pressure for glow discharge decomposition is in the range of 10 mTorr to 10 TOrr, similar to the usual glow discharge decomposition, and the applied power may be a value in the range of power density 0.01 to 1 w/cnT.

In a preferred embodiment of the present invention, that is, in order to increase the formation rate of the fluorinated silicon thin film and to improve the semiconductor properties of the film, the formation temperature of the thin film is set at 250 to 450°C.
and further increasing the glow discharge power until the film formation rate changes only depending on the gas flow rate.
Under these glow discharge decomposition conditions, it is sufficient to perform glow discharge decomposition of higher fluorinated silane and a mixed gas of higher silane such as helium.

The higher fluorinated silane gas used in the present invention can be synthesized by any known method and used as it is. For example, silicon may be directly reacted with tetrafluorosilane at high temperature, or higher chlorosilane or higher bromide silane may be reacted with a metal fluoride such as zinc fluoride to perform an transesterification reaction. But that's fine.

FIG. 1 is an IR spectrum diagram of a fluorinated silicon thin film formed on a silicon single crystal wafer by the method of the present invention. As is clear from the figure, both Si--F bonds and Si--H bonds are present.

Focusing on the St-F bond here, the absorption peak near 1150 cm''-l caused by SiFn is
This is relatively small compared to the absorption peak around 830 cm'' caused by F 2 , suggesting that the film quality of the fluorinated silicon thin film of the present invention is improved.

Furthermore, although conventional glow discharge decomposition using tetrafluorosilane was not able to form a thin film by itself, why is it that the method using high-grade fluorinated silane of the present invention has a similar effect on fluorination? The detailed reason why a silicon thin film is formed is unknown, but it is speculated that higher fluorinated silane has a 5i-5i bond and is more reactive than tetrafluorinated silane. be done.

EXAMPLES The present invention will be explained in more detail with reference to Examples below.

Example-1 RF capacitively coupled high frequency plasma CVD (chemical
A silicon wafer made by FZ Oval and a 7059 glass substrate made by Corning were placed in the substrate installation part of the vapor deposition chamber, and the pressure was evacuated to 10-7 Torr or less using an oil diffusion pump. Next, 15 cc each of disilane hexafluoride (disilane hexafluoride used in this example has a boiling point of -19.1°C, and its IR chart is shown in Figure 2 for reference), disilane, and helium were added. / min % into the glow discharge chamber at a flow rate of 20 cc/min and 180 cc/min,
Inside the discharge chamber 1. 1 while maintaining the pressure at OT orr.
3.56MHz high frequency with power density of 0.48w/cI
1 was applied and discharged for 11 minutes. During this time, the thin film formation temperature was 300°C. The thickness of the silicon thin film formed on the 7059 glass substrate was measured with a stylus thickness meter and was 6200 people, and the thin film formation rate was 9.3 people/s.
It was found that ec is extremely fast.

The light absorption coefficient α determined from the visible light absorption of the obtained thin film is:
It has a large value of 2.0*10 noon cm-' at a wavelength of 500 nrn. The optically forbidden tea towel obtained from the muff ~ hν plot was a large value of 2.1 eV. In addition, in this thin film, the photosensitivity (σph/σd), which is expressed as the ratio of photoconductivity (σph) to dark conductivity (σd) under AMI irradiation, is greater than 1'l'lO3, and has excellent photoconductivity. It was found that it has certain characteristics. The IR spectrum of the thin film formed on the silicon wafer is shown in Fig. 1.
, St H-.

It can be seen that absorption peaks related to SiH4 etc. are observed in the figure.

Example-2 The disilane flow rate was 10 cc/min, and the pressure was 0.
A thin film was formed in the same manner as in Example-1 except that the temperature was 7 Torr. The thin film formation rate was 6.0 people/sec. Example-3 The disilane flow rate was 30 cc/min and the pressure was 5T.
orr and the power density is 0.48 w/cJ
When a thin film was formed in the same manner as in Example 1, the formation rate increased to 13.7 people/see.

[Brief explanation of the drawing]

FIG. 1 is an IR spectrum chart of a fluorinated silicon thin film obtained by the method of the present invention, and FIG.
FIG. 2 is an IR spectrum chart of hexafluorodisilane used in the present invention. In the figure, the vertical axis is the transmittance (%), and the horizontal axis is the wave number (cm-
' ) is shown. Patent applicant Mitsui Toatsu Chemical Co., Ltd.

Claims (4)

[Claims] (1) General formula 5inFxn+2 (where n is n
a higher fluorinated silane represented by (an integer ≧2);
SimH2mf2 (where m is an integer of m≧2) is diluted with at least one type of helium or hydrogen (hereinafter referred to as helium), and a mixed gas is decomposed by glow discharge and deposited on the substrate. 1. A method for producing a fluorinated silicon thin film, characterized by forming a fluorinated silicon thin film. (2) The method according to claim 1, wherein the higher fluorinated silane in the mixed gas is at least hexafluorodisilane (n=2 in the general formula). (3) The higher silane in the mixed gas is at least disilane (
The method according to claim 1, which is m-2) in the general formula. (4) Claim 1, wherein the higher fluorinated silane in the mixed gas is disilane hexafluoride (n=2 in the general formula), and the higher silane is disilane (m=2 in the general formula) the method of.