JPH0760802B2 - Method for producing p-type amorphous silicon - Google Patents

Description

TECHNICAL FIELD The present invention relates to a method for producing p-type amorphous silicon, and more particularly to a method for producing p-type amorphous silicon having a wide optical band gap.

2. Description of the Related Art Conventionally, p-type amorphous silicon (pa-Si) has been used as an incident side conductive amorphous silicon layer of a glass / transparent electrode / Pin / metal electrode type solar cell. However, in the conventional method for producing p-type amorphous silicon, for example, a plasma CVD method using a mixed gas of SiH ₄ (monosilane) and B ₂ H ₆ (diborane) as a source gas is used, and a low-resistance p-type layer is formed. In order to obtain the above, the substrate temperature was heated to 200 ° C. or higher. In this case, since the optical band gap is 1.6 to 1.7 eV, which is narrower than 1.7 to 1.8 eV of intrinsic type or n-type amorphous silicon, it is difficult to obtain a high light utilization rate. Therefore, CH ₄ and C ₂ H ₄ are mixed as a raw material gas to form p-type amorphous silicon carbide (pa-SiC), and the optical band gap is expanded to 1.9 to 2.0 eV. It was

Problems to be Solved by the Invention However, although the light utilization efficiency is improved by this method, carbon element is mixed into the intrinsic (i) type amorphous silicon deposited on the p-type layer as a contamination impurity element, Since the performance of the intrinsic layer as a photoactive layer is deteriorated and the p-i junction interface characteristics are deteriorated, the conversion efficiency as a solar cell cannot be improved for the light utilization efficiency.

The present invention aims to solve the problems in the prior art.

Means for Solving the Problems In order to solve the above problems, in the present invention, an ECR plasma CVD method (hereinafter referred to as μ wave ECR plasma CVD method) using p-type amorphous silicon using microwave and electron cyclotron resonance absorption is used. Is used to deposit the substrate at a temperature of 60 ° C. or lower, and then heat treatment is performed at the deposition temperature or higher.

Action Using this method, SiH ₄ and B ₂ H ₆
After depositing the mixed gas of
It has been found that p-type amorphous silicon having a low resistance and a wide optical band gap can be realized by carrying out the heat treatment of.

Using this method, p-type amorphous silicon deposited at 60 ° C. or lower originally has an optical gap of about 1.9 eV, but has a large resistance of about 10 ⁷ Ωcm. However, when this p-type amorphous silicon is heat-treated at a temperature of about 200 ° C. to 300 ° C., it is increased to about 2.0 eV due to structural relaxation, and the impurity element in the film is activated to reduce the resistance to about 10 ⁴ Ωcm. Of.

Examples Representative examples of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic diagram of a μ wave ECR plasma CVD apparatus used in this embodiment. A vacuum chamber 11 is evacuated to a vacuum through an exhaust hole 12. Microwaves are introduced from the microwave oscillator 14 into the plasma generation chamber 15 through the waveguide 13. Electromagnet 16
As a result, a magnetic field is applied to the plasma generation chamber 15. Reference numeral 17 is a gas inlet, into which raw material gas such as SiH ₄ and B ₂ H ₆ is introduced. By setting the strength of the magnetic field so as to satisfy the electron cyclotron resonance condition, plasma with a high degree of dissociation is generated. The generated plasma passes through the plasma extraction window 18 and reaches the substrate holder 19, and p-type amorphous silicon is formed on the substrate on the holder 19.

FIG. 2 shows the change in electrical conductivity and the change in optical band gap when the amorphous silicon formed at a substrate temperature of 60 ° C. or lower is heat-treated to 300 ° C. in the apparatus shown in FIG. . Optical bandgap of 1.9 eV due to heat treatment
Shows a change in electrical conductivity at the same time as increasing from 1.0 to 2.0 eV. This value is superior to the electrical conductivity ˜10 ⁻⁶ to 10 ⁻⁵ (Ωcm) ⁻¹ at the optical band gap of 2.0 eV obtained with p-type amorphous silicon carbide in the prior art.

The p-type amorphous silicon produced by the conventional plasma CVD method is S
It is produced by plasma CVD method using iH ₄ and B ₂ H ₆ mixed gas as source gas, but when the mixing ratio of B ₂ H ₆ gas is increased, it enters into p-type amorphous silicon and bonds with silicon atoms. The amount of hydrogen decreases sharply, resulting in a narrow optical gap. This means that substrate temperature 20
The same is true even if it is manufactured at 0 ° C to 300 ° C.

However, according to the above-mentioned method of the present invention, Si is sufficiently contained in p-type amorphous silicon formed at a temperature close to room temperature of 60 ° C. or less.
There is hydrogen bound to. Therefore, in the untreated state, the optical gap is reduced due to structural stress, but is relaxed by heat treatment at a deposition temperature or higher, and according to the present invention, an optical gap of ~ 2.0 eV or higher is obtained and the electrical conductivity is also improved. is there. Although a film having a wide optical gap can be obtained by forming the film at room temperature in the conventional plasma CVD method, p-type amorphous silicon having sufficient electric conductivity could not be obtained even by heat treatment. In addition, in the present invention, it is desirable that the substrate is not usually heated, but even if the substrate is not heated, the substrate is generally heated to about 60% by deposition.
Although it rises to about 0 ° C, there was no particular problem at this temperature. If the temperature is further increased, the above effect disappears, so it is necessary to cool the substrate to about 60 ° C. by cooling.

Effects of the Invention The effects of the present invention are as follows.

It was possible to realize a p-type layer having a sufficiently wide optical band gap and a sufficiently high electric conductivity as compared with the p-type layers of amorphous silicon and amorphous silicon carbide obtained by the conventional technique.
In particular, when an amorphous silicon solar cell having a substrate / transparent electrode / Pin / metal electrode structure is manufactured, it is convenient because there is no diffusion of carbon element contamination from the p-type layer to the i-type layer. Although heat treatment is required, it is usually 200 at the time of subsequent deposition of i-type layer and n-type layer.
Since the substrate is heated to 300 ° C., this heating can be utilized, and it is not necessary to actually perform the heat treatment, which is convenient in the manufacturing process.

[Brief description of drawings]

FIG. 1 is a schematic view of a μ wave ECR plasma CVD apparatus used in the present invention, and FIG. 2 is an example of the present invention in which SiH ₄ and B ₂ H ₆ are used as source gases and are formed by the apparatus shown in FIG. It is a figure which shows the electric conductivity of p-type amorphous silicon, and the change of the optical band gap by heat processing. 11 ... vacuum chamber, 12 ... exhaust hole, 13 ... waveguide,
14 ... Microwave oscillator, 15 ... Plasma generation chamber, 16 ...
… Electromagnet, 17 …… Gas inlet, 18 …… Plasma extraction window.

Claims (1)

[Claims] 1. A method for forming p-type amorphous silicon, in which a substrate is held at a temperature of 60 ° C. or lower by plasma decomposition utilizing microwave electron cyclotron resonance absorption to obtain SiH ₄
A method for producing p-type amorphous silicon, which comprises depositing and forming a mixed gas of B ₂ H ₆ as a raw material on the substrate and then performing heat treatment at a temperature in the range of 200 ° C. to 300 ° C.