JP2850047B2 - Doping method of a-SiC film - Google Patents

Description

The present invention relates to a method for doping a p-type or n-type a-SiC film.

[Conventional technology]

In a photovoltaic device mainly composed of a-Si, which is an amorphous semiconductor, an a-SiC having a wider band gap than a-Si is usually provided in a p-layer on the light incident side for effective use of sunlight. A thin film is used.

Conventionally, this p-type a-SiC film is formed by a radio frequency (RF) glow discharge method in which a doping gas such as B ₂ H ₆ (sibolane) is mixed into a source gas containing SiH ₄ (silane).

Here, in order to use sunlight more effectively, it is conceivable to widen the band gap of the p-type SiC film more than the current situation. J. Electrochem. Soc., 130 (8) (1983)
As described in 1749, C in the film is
If the band gap is widened by increasing the amount of (carbon), the conductivity is also lowered at the same time, so that it has been difficult to obtain a p-type a-SiC film having a wide band gap.

[Problems to be solved by the invention]

As described above, the band gap of the p-type a-SiC film increases as the amount of C in the film increases, but at the same time, the conductivity decreases, so that a p-type a-SiC film having a wide band gap can be formed. There is a problem that can not be.

In RF glow discharge, doping gas (source gas)
To decompose, the processing temperature must be increased,
In this case, there is also a problem that the underlying layer is exposed to a high temperature and impurity diffusion from the underlying layer occurs, and the photoelectric conversion efficiency is reduced.

The present invention has been made in consideration of such problems of the prior art, and the purpose thereof is to:
P-type (n-type) a with wide band gap and high conductivity
An object of the present invention is to make it possible to obtain a SiC-doped film in a short time by efficient post-doping at a low processing temperature so as to prevent diffusion of impurities from an underlayer.

[Means for solving the problem]

In order to achieve the above object, in the method of doping an a-SiC film of the present invention, a non-doped a-SiC film having a C content of 20% or more is formed in advance and formed by an ECR discharge method or a microwave discharge method. The non-doped a-SiC film is exposed to the plasma of the doped gas to be doped.

[Action]

Therefore, according to the a-SiC film doping method of the present invention, a non-doped a-SiC film having a large C content (20% or more) is used.
Higher gas decomposition efficiency than ordinary RF glow discharge method
Since the doping process is performed by exposing to a plasma of a doping gas (raw material gas) formed by an ECR discharge method or a microwave discharge method, the doping efficiency is increased, the p-type (n-type) a− having a wide band gap and high conductivity is used. A SiC doping film can be formed, in which case the doping gas decomposition efficiency by the ECR discharge method or the microwave discharge method is high, post-doping can be performed efficiently at a low processing temperature, and the processing time can be shortened. There is no impurity diffusion or the like from occurring.

〔Example〕

An embodiment for forming a p-type a-SiC film will be described with reference to the drawings.

First, in the ordinary parallel plate RF glow discharge method, RF
An electromagnet is provided below the electrodes, and a magnetic field is applied to increase the decomposition efficiency of the source gas to form a non-doped a-SiC film having more Si-C bonds than usual.

 Table 1 shows the conditions for forming the non-doped film.

Next, the non-doped film previously formed as described above is post-doped by processing with a plasma of a doping gas formed under the post-doping conditions shown in Table 2 to form a p-type a-SiC film. .

For this formation, a conventional RF glow discharge method (magnetic field intensity 0)
And a method by applying a magnetic field used for forming a non-doped film.

FIG. 1 shows the p-type a thus formed.
-P-type a-SiC formed by conventional method
This is shown together with the result of the film.

Table 3 shows conditions for forming a conventional p-type a-SiC film.

The first, second, in Table 3, CH ₄ is diluted with H ₂ to 10%, B ₂
H ₆ is H ₂ dilution of 0.1%.

As is apparent from FIG. 1, when a doping film is formed by post-doping a previously formed non-doped film, a p-type a-SiC film having a conductivity higher by at least two orders of magnitude than that of a conventional film can be obtained. I understand.

Further, it can be seen that, in the post-doping treatment, the treatment time can be shortened by using a method by applying a magnetic field having higher gas decomposition efficiency than the ordinary RF glow discharge method.

Further, when the light absorption characteristics of the doped film subjected to the post-doping process using the method by applying a magnetic field as described above and the film formed by the conventional method were examined, the results shown in FIG. 2 were obtained.

As is clear from FIG. 2, the film formed by the method of the present invention can obtain a film having the same conductivity (3 × 10 ⁻⁷ Ω ⁻¹ · cm ⁻¹ ) and low absorption.

Next, FIG. 3 shows the result of comparing various methods as a method of the post doping treatment.

The figure shows the conventional RF glow discharge method (square mark) with the post-doping time set to 30 minutes (constant), the method by applying a magnetic field shown in Tables 1 and 2 (square mark), the microwave discharge method (square mark). △)
And electron cyclotron resonance (ECR) discharge method (●)
The relationship between the processing temperature and the dark conductivity when each is used is shown.

As is clear from FIG. 3, the processing temperature required to obtain the same conductivity is the lowest in the ECR discharge method, and is higher in the order of the microwave discharge method, the method by applying a magnetic field, and the conventional method.

This is because conventional ECR and microwave discharge methods use the conventional R
This is because the decomposition efficiency of the source gas is higher than that of the F glow discharge method, and post-doping can be performed efficiently at a lower processing temperature.

This means that when applied to the formation of a doping film of an actual photovoltaic device, if the post-doping treatment is performed by the ECR discharge method or the microwave discharge method, the underlying layer of the p-type a-SiC film is not exposed to high temperatures. This indicates that the processing time is short as well as that the diffusion of impurities from the underlayer does not occur.

And, especially, the amount of C is 20% or more (C / (Si + C)
≧ 20%) by exposing the non-doped a-SiC film to a plasma of a doping gas formed by an ECR discharge method or a microwave discharge method, so that the band gap is wide and the high conductivity is short at a low processing temperature. An a-SiC doping film is obtained. At this time, diffusion of impurities from the underlying layer does not occur, and when this doping film is used as a window layer of a photovoltaic device, its photoelectric conversion characteristics are significantly improved.

In the above embodiment, the case of the p-type a-SiC film has been described. However, the present invention can be similarly applied to the case of forming the n-type a-SiC film.
The non-doped C film may be exposed to a plasma of a doping gas of PH ₃ (phosphine) formed by an ECR discharge method or a microwave discharge method.

〔The invention's effect〕

As described above, according to the doping method of the a-SiC film of the present invention, the non-doped a- film having a previously formed C content of 20% or more (C / (Si + C) ≧ 20% or more in the film).
Since the doping film was formed by exposing the SiC film to the plasma of the doping gas formed by the ECR discharge method or the microwave discharge method, the doping efficiency was improved, and the a-SiC film having a wider band gap and higher conductivity than before was formed. At that time, the doping gas is efficiently decomposed by the ECR discharge method or the microwave discharge method, the post-doping process can be performed efficiently at a low processing temperature, the processing time can be shortened, and the There is no diffusion of impurities.

Therefore, by using this film as a window layer of a photovoltaic device, its photoelectric conversion characteristics can be significantly improved.

[Brief description of the drawings]

The drawings show the case where the present invention is applied to the formation of a p-type a-SiC film. FIG. 1 is a characteristic diagram of dark conductivity, FIG. 2 is a light absorption characteristic diagram, and FIG. FIG. 4 is a relationship diagram between a doping temperature and dark conductivity.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Shinya Tsuda 2-18-18 Keihanhondori, Moriguchi-shi, Osaka Sanyo Electric Co., Ltd. (56) References JP-A-64-11317 (JP, A) JP-A Sho 64-22027 (JP, A) JP-A-2-162719 (JP, A) JP-A-61-26219 (JP, A) JP-A-1-196815 (JP, A) JP-A 64-53462 (JP, A A) JP-A-63-194326 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) H01L 21/265 H01L 21/22

Claims (1)

(57) [Claims] A non-doped a-SiC film having a C content of 20% or more is formed in advance, and said non-doped a-SiC film is exposed to a plasma of a doping gas formed by an ECR discharge method or a microwave discharge method. A method for doping an a-SiC film, comprising doping.