JPH06101448B2 - Method for manufacturing amorphous silicon thin film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for efficiently producing an amorphous silicon-based thin film exhibiting high stability, which is used as a solar cell or the like and which provides more excellent photodegradation suppressing performance. .

[Prior Art] Conventionally, as a method for forming an amorphous silicon (a-Si) -based film, a plasma CVD method, an optical CVD method, or the like has been performed, but even today, a sufficient optical deterioration suppressing performance is obtained. It is difficult to obtain the above-mentioned film and the film has not been satisfied.

On the other hand, as an example of the CVD method using xenon gas, for example, in JP-A-1-294866, in a plasma CVD method, Xe gas is used as a raw material gas for forming an amorphous silicon film, and its addition amount is the above. 2 Vol.% Against source gas
A method for forming an amorphous silicon film is described below, which promotes decomposition and activation of a raw material gas by using the following, and improves the film formation rate of the film without deteriorating the film characteristics. ing. In addition, special fair 1
JP-A-32652 describes a method for producing an amorphous silicon film by adding an inert gas such as xenon gas as a photosensitizer to a silane-containing gas mixture in the photo-CVD method.

[Problems to be solved by the invention]

Regarding the amorphous silicon film formed by the method described in JP-A-1-294866 mentioned above, 2 Vol%
Even if it is possible to improve the film formation rate by the addition of the following Xe gas, it is not described at all that it has a photodegradation suppressing ability in that range, and that the improvement can be achieved. In addition, the method described in Japanese Patent Publication No. 1-232652 is intended to increase the photosensitivity of a reactant to absorption of photons, and it Although it tries to increase the reliability of solid-state devices by preventing corrosion and device deterioration due to the adverse effects of environmental pollution caused by both, it is not described at all that it also has optical deterioration suppressing performance, and its improvement is It is hard to say what can be done.

[Means for Solving Problems] The present invention has been made in view of the above-mentioned drawbacks of the related art, and a sufficient amount of xenon (Xe) gas is specified for the raw material gas for forming amorphous silicon film. By using the mixed gas mixture to form a film on the substrate by the plasma CVD method, it is possible to sufficiently suppress photodegradation by the action effect that is considered to be a physical xenon gas, especially its physical form. The present invention provides a method for manufacturing an amorphous silicon thin film.

That is, the present invention is a plasma CVD method using a mixture of raw material gas for forming amorphous silicon film and xenon gas.
A method of forming an amorphous silicon-based film on a substrate by a method, wherein a mixed gas of xenon gas / amorphous silicon-based film forming raw material gas ≧ 1 is used in volume display. The present invention provides a method for manufacturing the same.

Here, in terms of volume, the above-mentioned mixture gas of xenon gas / amorphous silicon-based film forming raw material gas ≧ 1 is used. If it is less than 1, a sufficient effect of suppressing photodegradation can be obtained. Because it will not be possible,
Preferably, 30 ≧ xenon gas / amorphous silicon-based film forming raw material gas ≧ 2. In this case, even if it is less than 1, the effect of suppressing the photodegradation gradually increases as it approaches 1, but it must be 1 or more in order to obtain the desired suppression of photodegradation.

Further, regarding the raw material gas for forming an amorphous silicon film, for example, silane (SiH ₄ ), disilane (Si ₂ H ₆ ), a mixture gas of germane (GeH ₄ ) and silane or disilane, methane (CH ₄ ) and silane or It is a mixture gas of disilane and the like, and as the ordinary raw material for forming amorphous silicon film, especially those used in the plasma CVD method can be used.

Further, regarding the amorphous silicon-based thin film, the amorphous silicon thin film and various amorphous silicon-based alloy thin films such as amorphous silicon silicon germanium (a-SiGe) and amorphous silicon carbon (a-SiC) are collectively referred to. It is a representation.

Furthermore, the reason why the plasma CVD method is used is that the plasma CVD method is used to obtain the action and effect of the xenon, and the method is applied to another amorphous silicon thin film forming method. It goes without saying that it is also possible to apply the above to obtain the above-mentioned effects. The substrate is glass, aluminum, stainless steel or the like, and is not particularly limited.

[Action]

As described above, the method for producing an amorphous silicon-based thin film according to the present invention uses a mixture gas of xenon gas / amorphous silicon-based film forming raw material gas of ≧ 1 in volume display, and therefore, an excellent light What was able to be formed with the above thin film having deterioration suppressing performance, and as the action of xenon mixing when forming an amorphous silicon based thin film in the plasma CVD method, the energy of the long-lived excited species of Xe is 8.32 eV. Therefore, SiH ₃ can be increased as a film forming reaction species, and so-called good film quality can be expected. Ie Si
The excitation energy of H ₄ → SiH ₃ is 8.75 eV, and SiH ₄ → SiH ₂
Since the excitation energy of is 9.47eV, it requires an excitation energy of 9.47eV or more for the production of SiH ₂ that induces a bad film quality. It is possible to prevent SiH _{2 from} being generated near the film growth surface by the collision between the excited species and the source gas, and to
The presence of a large diameter substance such as Å) on the film growth surface, and in particular by interspersing a certain amount of it, suppresses the radical motion on the surface of the film-forming radical SiH ₃ , which prevents crystallization and also prevents hydrogen. While considering and confirming that voids, which are composed of atoms, can be incorporated in the network, these actions and effects are displayed in volume.
It has been found that Xe gas / a-Si-based film forming raw material gas ≧ 1 is effective for exhibiting photodegradation suppressing performance, and is an amorphous silicon-based thin film formed by the method of the present invention. Has a sufficiently long-term photodegradation suppressing performance, and is useful in a wide range of fields such as solar cells and various electronic articles employing amorphous silicon thin films.

[Embodiment] An embodiment of the present invention will be described below with reference to the drawings. However, the present invention is not limited to such embodiments.

FIG. 1 is a parallel plate type plasma for forming an amorphous silicon thin film on a glass substrate using the manufacturing method of the present invention.
FIG. 1 is a schematic view showing an example of a CVD device, the plasma CVD device
Reference numeral 1 denotes a reaction vessel 2 which can be decompressed and serves as a vacuum chamber, flat discharge electrodes 3 and 3 which are concentric with the vessel 2 and arranged in parallel vertically, and a high frequency wave connected to the upper side of the electrodes. Power supply 10
And a heater 5 which can mount the glass substrate 4 and which is provided in the lower electrode on which the glass substrate 4 is mounted and which heats the glass substrate from the inside to, for example, about 200 to 300 ° C.
A mixture gas, such as H ₄ , Si ₂ H ₆ , and GeH ₄ , which is supplied from an amorphous silicon film forming raw material gas supply source 6 and a xenon gas supply source 7, and is mixed in the above-mentioned specific volume ratio is used in the reaction vessel. It is composed of an introduction pipe 8 introduced into the inside of the reactor 2, and an exhaust port 9 connected to an exhaust pump for maintaining the pressure of the supply gas at a predetermined value after the reaction container 2 is once evacuated to a high vacuum.

In the plasma CVD apparatus 1 , after the glass substrate 4 is mounted on the lower electrode 3, the reaction vessel 2 is sealed and evacuated to a high vacuum (for example, 1 × 10 ⁻⁶ to 1 ×). Ten
^The pressure is reduced to about ⁻⁸ Torr), and the glass substrate 4 is heated to about 200 to 300 ° C. (for example, by the heater 5 provided in the electrode) (for example,
After heating to a predetermined temperature (about 250 ° C), SiH ₄ gas is supplied from the amorphous silicon film forming raw material supply source 6 to about
1 SCCM, Xe gas from the xenon gas supply source 7 was flowed by controlling the flow rate by about 30 SCCM respectively, and the mixed gas was introduced into the reaction vessel 2 through the introduction pipe 8 and the pressure in the vessel was adjusted to about
100 to 15 by high frequency power supply 10 while holding at 30mTorr
By applying electric power of 0 mW / cm ² (13.56 MHz, for example, about 130 mW / cm ² ) to the discharge electrode 3, the glass substrate 4
An amorphous silicon thin film having a film thickness of about 5000 to 6000Å is formed on the surface of.

About the amorphous silicon thin film obtained as described above, for example, the photoconductivity is measured and evaluated by a conductivity automatic measuring system manufactured by Spandonyx Co., Ltd., and the photodegradation is simulated by sunlight (AM-1, 100mW / c
m ^2, and measuring the light irradiation afterglow conductivity of up to about about 500 hours by a solar simulator light irradiation) was evaluated by comparing the optical conductivity of before the light irradiation. Various other measurements were made as described in detail below.

As a result, the amorphous silicon thin film was formed so as to suppress photodegradation for a sufficiently long period of time.

FIG. 2 shows the measurement results obtained by changing the film forming conditions using the plasma CVD apparatus shown in FIG.
The relationship between Xe / SiH ₄ and the ratio of the photoconductivity after light irradiation to the first photoconductivity, that is, the change in photoconductivity (σ _(∞) / σ _(o) ), is 0.03 W at high frequency power output. / cm ² shows the data when changing the ～0.53W / cm ^2. In either case, as the proportion of Xe increases, the amount of change in photoconductivity (σ _(∞) / σ
_It can be seen that _(o) ) is reduced and photodegradation is suppressed. That is, when Xe / SiH _{4 is set} to 1 or more, the change in photoconductivity is reduced and photodeterioration is suppressed. A more preferred range of Xe / SiH ₄ is _{30 ≧ Xe / SiH 4 ≧ 1} .

FIG. 3 is a diagram showing the relationship between light irradiation time and change in photoconductivity, Is the case of an a-Si thin film produced only with SiH ₄ , and the solid lines of □ and ■ are the a-Si thin films produced with Xe / SiH ₄ = 5, and the high frequency power output is 0.39 W / cm ² , ■ are for the case where the output is 0.53 W / cm ² .

By mixing a predetermined amount of Xe gas to produce an a-Si thin film, a thin film with a small change in photoconductivity with long-term light irradiation is obtained, and photodegradation of the a-Si thin film is suppressed. You can see that

〔The invention's effect〕

According to the present invention, since the xenon gas is supplied and mixed sufficiently in the volume ratio specified in the plasma CVD method to form the amorphous silicon-based thin film, the amorphous silicon-based thin film having substantially no photodegradation is formed. It can be made into a thin film, for example, it will be possible to suppress photodegradation, which is one of the biggest problems in amorphous silicon solar cells, and the useful amorphous silicon thin film that can contribute to popularization A manufacturing method is provided.

[Brief description of drawings]

FIG. 1 is a schematic view showing an example of a parallel plate type plasma CVD apparatus for carrying out the method for producing an amorphous silicon-based thin film of the present invention, and FIG. 2 is a schematic view showing an a-Si thin film obtained by the production method of the present invention. FIG. 3 is a diagram showing the relationship between the mixing ratio of xenon gas and the change in photoconductivity (σ _(∞) / σ _(o) ) upon irradiation, and FIG. 3 is an a-Si-based thin film obtained by the production method of the present invention. FIG. 5 is a diagram showing a relationship between a light irradiation time and a change in photoconductivity in FIG. 1 ... Parallel plate type plasma CVD apparatus 2 ... Reactor, 3,3 ... Discharge electrode 4 ... Glass substrate, 6 ... Amorphous silicon film forming source gas supply source, 7 ... Xenon gas supply source

Claims (1)

[Claims] 1. A method for forming an amorphous silicon-based film on a substrate by plasma CVD using a mixture gas of an amorphous silicon-based film forming raw material gas and xenon gas, wherein xenon gas / amorphous gas is displayed in volume. A method for producing an amorphous silicon thin film, characterized in that a mixture gas of an assilicon-based film forming raw material gas ≧ 1 is used.