JPH05343713A - Manufacture of amorphous solar cell - Google Patents

Abstract

PURPOSE:To obtain an amorphous silicon carbide p-type semiconductor containing micro crystals for solar cells having a larger area by using a plasma CVD system and combining a process for forming a semiconductor thin film and a process for micro crystallizing the film. CONSTITUTION:Using a timer to control the operation of a compressed air valve 15 makes it possible to introduce material gas and doping gas into a p-type layer reaction chamber 13 for a preset time and only hydrogen gas for another preset time subsequent thereto. If high-frequency power is kept applied to an anode and cathode electrodes in such a system, material such a system, material gas and doping gas are decomposed by plasma and a film grows on the surface of a substrate for a period when they are being introduced into the reaction chamber; the film undergoes hydrogen plasma treatment and is micro crystallized for a period when only it is being introduced thereinto. Repeating this sequence obtains a micro crystal silicon carbide thin film having a desired thickness.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing an amorphous solar cell using a silicon carbon semiconductor thin film containing a microcrystalline phase.

[0002]

2. Description of the Related Art It is known that a silicon carbon semiconductor thin film containing a microcrystalline phase is used in a semiconductor thin film light emitting device, a light receiving device or a solar cell to improve the performance thereof.

Conventionally, as a film forming method thereof, an electron cyclotron resonance plasma chemical vapor deposition apparatus (hereinafter referred to as ECR) is used.
-Silicone (Si
A method of simultaneously decomposing a mixed gas of H ₄ ), methane (CH ₄ ), diborane (B ₂ H ₆ ), hydrogen (H ₂ ) and the like by electron cyclotron resonance plasma to form a film is widely known. The p-type layer of an amorphous solar cell was formed using the manufacturing method.

In a p-type silicon carbon film containing a microcrystalline phase, the optical band gap is 2.0 eV or more, and the activation energy of conductivity is 0.1 eV or less.
Excellent characteristics can be obtained as a mold layer. By using this for the p-type layer of an amorphous solar cell, the diffusion potential can be improved and therefore the open circuit voltage of the solar cell can be improved.

[0005]

However, in the method using the above-mentioned ECR-pCVD apparatus, not only the apparatus itself is not widely used in a general semiconductor manufacturing process, but also an element using a semiconductor thin film is manufactured. In this case, it is not easy to increase the area, which is a great advantage in the manufacturing process, as compared with a general plasma chemical vapor deposition (CVD) apparatus that has been widely used (for example, a high frequency plasma CVD apparatus). An object of the present invention is to use a plasma CVD apparatus,
It is to obtain an amorphous silicon carbide p-type semiconductor thin film containing a microcrystalline phase for a large area solar cell.

[0006]

In the present invention, a step of forming a p-type amorphous silicon carbon semiconductor thin film on a substrate by supplying a source gas and a doping gas to a reaction chamber using a plasma CVD apparatus, A step in which the gas is exhausted from the reaction chamber and hydrogen gas is supplied to the reaction chamber to microcrystallize the p-type amorphous silicon carbon semiconductor thin film is performed at least once.

[0007]

According to the present invention, in a normal plasma CVD (for example, high-frequency plasma CVD) apparatus, two lines of gas lines are provided in a reaction chamber for forming a p-type layer, and a pneumatic valve of an electromagnetic relay system is controlled by a timer. A p-type microcrystalline silicon carbon thin film can be obtained only by performing the above.

[0008]

1 is a schematic sectional view of an example of a film forming apparatus used in the present invention.

For example, in a general multi-chamber capacitively coupled high frequency plasma CVD apparatus, an n-layer reaction chamber 11, an i-layer reaction chamber 12 and a p-layer provided between a pretreatment chamber 9 and a posttreatment chamber 10 are provided. It is constituted by the reaction chamber 13. Electrodes are provided in the respective reaction chambers, and the substrate 1 passes through the respective electrodes to form n, i, and p amorphous semiconductor layers.

A gas line 17 supplies, for example, SiH ₄ and PH ₃ to the n-layer reaction chamber 11, and a gas line 18 supplies SiH ₄ to the i-layer reaction chamber 12.

The p-layer reaction chamber 13 is provided with two gas lines, a gas line 16a for introducing hydrogen gas and a gas line 16b for introducing source gas and doping gas, and the gas line 16b for introducing source gas and doping gas includes For example, an electromagnetic relay type compressed air valve 14 is provided. Further, an exhaust line 16c having a compressed air valve 15 is provided in the middle thereof.

When the compressed air valve 14 is open and the compressed air valve 15 is closed, the source gas and the doping gas are introduced into the p-layer reaction chamber 13, and conversely, when the compressed air valve 15 is open and the compressed air valve 14 is closed, the source gas is removed. The doping gas is exhausted from the exhaust line 16c by an exhaust pump. Open and close the pneumatic valves 14 and 15
By controlling with a timer, the raw material gas and the doping gas can be introduced into the p-layer reaction chamber 13 for a certain set time,
During the next certain set time, only hydrogen gas is introduced into the p-layer reaction chamber 13.

When high frequency power is applied between the anode electrode 21 and the cathode electrode 22 in such a system, the source gas and the doping gas are decomposed by the plasma 8 while being introduced into the reaction chamber, and the film is deposited on the substrate 1. During the time when the film grows on the surface and only the next hydrogen gas is introduced into the p-layer reaction chamber 13, the film is subjected to hydrogen plasma treatment and crystallized. By repeating this sequence, a microcrystalline silicon carbon thin film having a desired film thickness can be obtained.

Using such a device, the raw material gas is actually
Silane (SiH_Four) 1 sccm, methane (C
H_Four) 1 sccm, diborane (B as a doping gas)
₂H ₆) With a gas doping ratio of 1%, and hydrogen (H
₂) Flow rate is 100 sccm and 20Å per cycle
Growth time, hydrogen plasma treatment time per cycle
The film formation experiment was performed using the as a parameter.

FIG. 2 is a plot of the hydrogen plasma treatment time on the horizontal axis and the dark conductivity of the film on the vertical axis.
As shown in the graph, the dark conductivity of the film is rapidly improved by about 7 digits in the hydrogen plasma treatment time of about 50 seconds, and it is understood that the film is microcrystallized by this degree of hydrogen plasma treatment. In addition, the composition analysis, Raman spectroscopy or X-ray diffraction showed that the film contained silicon carbon (μ
It was confirmed that the film was a c-SiC: H) film.

FIG. 3 is a schematic sectional view of a solar cell prepared by using the apparatus shown in FIG. On the substrate 1, 300 Å n-type a
The -Si: H film 2 is deposited in the n-layer reaction chamber 11 of FIG. 1, and then in the i-layer reaction chamber 12, the i-type a-Si: H film 3 is deposited.
5000 Å was deposited. Subsequently, in the p-layer reaction chamber 13, 200 Å of the p-type μc-SiC: H film 4 was deposited under the above-mentioned film forming conditions and hydrogen plasma treatment for 50 seconds. On this, a transparent conductive film 5 was deposited by 600 Å by a sputtering method, and finally an aluminum electrode 6 as a collecting electrode was vapor-deposited by an electron beam apparatus.

When the solar cell having such a structure was measured with a solar simulator under AM 1.5, 100 mW / cm ² light, the data shown in Table 1 below was obtained. Table 1 shows a solar cell using a microcrystalline p-type layer and an amorphous p-type layer.
It is a comparison table of the characteristic with the solar cell using a layer.

[0018]

[Table 1]

As shown in Table 1, the solar cell using the microcrystalline p-type layer has an open circuit voltage of 0.97V, and an open circuit voltage of 0.84V when using a normal p-type amorphous silicon carbon thin film. It has improved. This value is ECR-pCVD
The value is equal to or higher than that of a similar solar cell using a μc-SiC: H film formed by using the device as a p-type layer.

In the above-described embodiment, the i-type layer has a-S.
Although the i: H film is used, the application to a solar cell using a hydrogenated or fluorinated amorphous alloy film of amorphous silicon germanium (a-SiGe), amorphous silicon carbon (a-SiC) or the like as the i-type layer, Of course it is possible. Further, it can be applied to a solar cell in which a pin layer is laminated. Since the light absorption of the microcrystalline layer is small, it is more advantageous to use it on the light incident side of the solar cell.
Even if it is used on the side opposite to the light incident side, there is an advantage that the open circuit voltage is improved.

[0021]

According to the present invention, a microcrystalline silicon carbon thin film can be easily obtained as a uniform film over a large area by a normal CVD apparatus, and the performance of an amorphous solar cell using this manufacturing method can be improved.

[Brief description of drawings]

FIG. 1 is a schematic sectional view of an example of a film forming apparatus used in the present invention.

FIG. 2 is a graph showing the relationship between hydrogen plasma treatment time and dark conductivity of a film.

FIG. 3 is a schematic cross-sectional view of a solar cell manufactured according to the present invention.

[Explanation of symbols]

 1 substrate 2 a-Si: H film 3 a-Si: H film 4 μc-SiC: H film 5 transparent conductive film 6 aluminum electrode 11 n-layer reaction chamber 12 i-layer reaction chamber 13 p-layer reaction chamber 14, 15 compressed air valve

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yukihiko Nakata 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (72) Inventor Hitoshi Sannomiya 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Incorporated (72) Inventor Manabu Ito 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Within Sharp Corporation (72) Inventor Akitoshi Yokota 22-22, Nagaike-cho, Abeno-ku, Osaka-shi, Osaka

Claims (1)

[Claims] 1. A step of forming a p-type amorphous silicon carbon semiconductor thin film on a substrate by supplying a source gas and a doping gas into a reaction chamber using a plasma enhanced chemical vapor deposition apparatus,
At least once in combination with the step of exhausting the gas from the reaction chamber and supplying hydrogen gas to the reaction chamber to microcrystallize the p-type amorphous silicon carbon semiconductor thin film. Method for manufacturing crystalline solar cell.