JPH10251856A - Method for deposition of amorphous silicon film and plasma enhanced cvd system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To form amorphous silicon films having a uniform film thickness distribution by a plasma enhanced CVD system. SOLUTION: A substrate 11 is placed in a CVD chamber 10 which is provided with a substrate heating heater 12 for heating the substrate 11. A deposition unit 13 is disposed to face the substrate heating heater 12. The deposition unit 13 is internally provided with an electrode 17 connected to one end of a high-frequency power source 16. The other end of the high-frequency electrode 16 is connected to the substrate heating heater 12. The deposition unit 13 is provided with a mesh heater for heating gases in its section facing the substrate heating heater 12. A DC power source 20 is connected to the ground of a heater heating power source 19 in order to impress a negative bias voltage on the mesh heater 18.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for forming an amorphous silicon film for forming an amorphous silicon thin film having a uniform in-plane film thickness distribution and a plasma CVD apparatus used for the film formation.

[0002]

2. Description of the Related Art An amorphous silicon film is formed by a plasma CVD apparatus using a silane gas (SiH ₄ ) or a disilane gas (Si ₂ H ₆ ). In the case of an amorphous silicon film formed by a plasma CVD apparatus in which a normal film forming substrate and a high-frequency electrode are simply arranged opposite to each other, the defect density in the film is assumed to be 10 ¹⁶ / cc due to dangling bonds or the like. Exists.

[0003] Recently, a plasma C for which the defect density has been reduced
A VD device has been proposed, and the device will be described with reference to FIG. The film forming substrate 11 is brought into contact with a substrate heater 12 which is also used as one high-frequency electrode provided in a CVD chamber 10 as a vacuum vessel, and the substrate 11 is heated to 100 to 200 ° C. Film forming unit 13
The other high-frequency electrode 17 and a gas supply pipe 14 are provided therein, and a reaction gas such as a SiH ₄ gas and a doping gas in a gas cylinder 15 is introduced into the film formation unit 13 from the gas supply pipe 14.

The high-frequency electrode 17 and the substrate heater 12 are
The CVD chamber 1 is connected to the high frequency power supply 16
Adjust the inside of 0 to a pressure of 50 mTorr to several Torr,
Discharge is caused to turn the SiH ₄ gas into plasma, and the substrate 1
An amorphous silicon film is formed on one surface. The pressure in the CVD chamber 10 is maintained by continuously exhausting gas by a vacuum pump 21.

In the above device, the substrate 11 and the high-frequency electrode 17
By heating the radicals generated by the mesh heater 18 disposed between them, the defect density in the film can be reduced to 10 < ¹⁴ > to 10 < ¹⁵ > / cc. Reducing the defect density in the film increases the effective absorption of light and lowers the band gap.

[0006]

However, this device also has the following problems. When a mesh heater is used, a film having a thick central portion is formed. When such a film is used for an amorphous silicon solar cell, the thickness of the amorphous silicon film affects the conversion efficiency, and the efficiency is high for a thick film and low for a thin film. When a module is formed as a solar cell, the efficiency is suppressed by the efficiency at a portion where the film thickness is small, and the performance of the module as a whole, that is, the power generation performance is reduced.

Further, when a laser is used in a cutting step when a solar cell is formed into a module, if the laser intensity is adjusted to a thick portion, there is a problem that a thin film portion is cut too much. In addition, there is a problem that when the thickness is adjusted to a thin portion, a problem occurs such that a thick portion cannot be cut, and the yield is deteriorated.

An object of the present invention is to provide a method of forming an amorphous silicon film and a plasma CVD apparatus capable of reducing the defect density in the film and at the same time making the thickness distribution of the amorphous silicon film uniform.

[0009]

Means for Solving the Problems The present invention is configured as follows to achieve the above object. (1) The method of manufacturing an amorphous silicon film according to the present invention (claim 1) includes: A gas permeable heater is provided between the high-frequency electrode and the substrate, and a film is formed on the substrate by applying a negative DC bias voltage to the heater. (2) The present invention (claim 2) provides a plasma CVD apparatus in which a high-frequency electrode connected to a high-frequency power supply and the substrate are arranged to face each other to form an amorphous silicon film on the substrate. And a gas permeable heater is provided between the heater and the heater, and the heater is connected to a means for applying a negative bias voltage.

The heater is for heating while allowing gas to pass therethrough. For example, a heater in which mesh or rod-shaped heaters are arranged in a parallel or staggered lattice, or a plate-shaped heater in which the heaters are arranged in parallel can be used.

According to the present invention, the following operations and operations are achieved by the above configuration.
Has an effect. Plasma is generated by ionizing a film-forming gas passing therethrough by electrons generated from an electrode to form plasma. In the conventional apparatus, as shown in FIG. 4A, since the electron generation region 31 is expanded at the center of the electrode 17, the plasma generation region 32 is changed to a mesh heater at the expanded region of the electron generation region 31. It is leaking beyond 18. Therefore, the amount of radicals reaching the substrate surface becomes non-uniform in the plane, so that the film forming speed becomes non-uniform in the plane. It should be noted that the arrows in the drawing represent the film forming gas flows.

As in the apparatus of the present invention, the mesh heater 18
When a negative bias is applied, as shown in FIG. 4B, the electron generation region 31 moves away from the mesh heater 18 so that the plasma generation region 32 does not leak beyond the mesh heater 18 and The plasma generation region 32 is confined between the mesh heater 18 and the high-frequency electrode 17.

Since there is no mesh heater around the periphery of the substrate, the Coulomb force applied to the electrons is smaller than that at the center, and the distance away from the center is smaller. In the central part, the deposition rate changes more greatly than in the periphery, and the deposition rate is lower than that formed by the conventional apparatus, and the deposition rate is equivalent to that in the peripheral part. As a result, a film having a uniform thickness distribution is formed. be able to.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to FIG.
This will be described with reference to FIG. A substrate 11 is fixedly mounted on a substrate heater 12 in a CVD chamber 10. A film forming unit 13 is provided to face the substrate heater 12.

A gas supply pipe 14 is provided in the film forming unit 13.
Is provided. A reactive gas such as a doping gas and a SiH ₄ gas is supplied from an external gas cylinder 15 to the gas supply pipe 14, and these gases are introduced into the film forming unit 13 from the gas supply pipe 14. Also, the film forming unit 1
An electrode 17 connected to one end of a high-frequency power supply 16 is provided in 3. The other end of the high frequency power supply 16 is connected to the substrate heater 12.

A mesh heater 18 for heating gas is provided at a portion of the film forming unit 13 facing the substrate heater 12. The mesh heater 18 has a heater heating power supply 1 for heating the heater 18.
9 is connected. Further, one end of a DC power supply 20 is connected to the mesh heater to apply a negative bias voltage to the mesh heater 18. The other end of the DC power supply 20 is connected to the ground.

A vacuum pump 21 for evacuating the inside of the CVD chamber 10 is connected to the chamber 10. The actual film formation will be described. Substrate heater 12
The substrate 11 is heated to 100 to 200 ° C. Then, a doping gas and a SiH ₄ gas are introduced from the gas supply pipe 14 into the film forming unit 13. Then, the inside of the CVD chamber 10 is continuously evacuated by the vacuum pump 21, and the pressure is maintained at 50 mTorr to several Torr. Then, a high frequency is applied from the high frequency power supply 16 and discharged,
The reaction gas is turned into plasma. In addition, mesh heater 1
8 is heated by a heater heating power supply 19 and at the same time, a negative bias voltage is applied by a DC power supply 20 to the mesh heater 18.
Is applied.

The radicals in the plasma heated when passing through the mesh heater 18 grow on the substrate 11 to form an amorphous silicon film. FIG. 2 shows the results of measuring the film thickness distribution in the diagonal direction on the substrate surface when using the mesh heater bias. When there was no bias voltage, the film thickness at the center was about 40% thicker than at the edges. By applying a bias voltage of −40 V to the mesh heater, the film thickness variation between the center and the edges was reduced by 10%.
It is kept below.

Since the amorphous silicon film formed by the conventional apparatus has a thickness variation of ± 20%, it has been considered difficult to improve the efficiency of the module such as the power generation performance. Since the amorphous silicon film has a uniform thickness distribution, the module performance can be improved.

Further, by making the film thickness distribution uniform, the yield in the laser etching step can be improved. Note that the present invention is not limited to the above embodiment. For example, the form of the heater is not limited to the mesh,
A heater in which bar heaters are arranged in parallel, a heater in which bar heaters are arranged in a staggered pattern, or a heater in which plate heaters are arranged in parallel may be used. In addition, the present invention can be variously modified and implemented without departing from the gist thereof.

[0021]

As described above, according to the present invention, by applying a negative bias voltage to the heater disposed between the high-frequency electrode and the substrate, the plasma is confined between the heater and the high-frequency electrode. In addition, the defect density in the film can be reduced, and the film thickness can be made uniform by making the film forming speed uniform within the plane.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of a plasma CVD apparatus according to an embodiment of the present invention.

FIG. 2 is a characteristic diagram showing an in-plane film thickness distribution of an amorphous silicon film.

FIG. 3 is a schematic diagram showing a configuration of a conventional plasma CVD apparatus.

FIG. 4 illustrates the principle of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Plasma CVD chamber 11 Substrate 12 Substrate heater 13 Film-forming unit 14 Gas supply pipe 15 Gas cylinder 16 High frequency power supply 17 High frequency electrode 18 Mesh heater 19 Heater power supply 20 DC power supply 21 Vacuum pump

Claims (2)

[Claims] When an amorphous silicon film is formed on a substrate by a parallel plate type plasma CVD apparatus in which a high-frequency electrode and a substrate are opposed to each other, a gas is permeable between the high-frequency electrode and the substrate. A method for forming an amorphous silicon film, comprising: providing a heater and applying a negative DC bias voltage to the heater to form a film on the substrate. 2. A plasma CVD apparatus in which a high-frequency electrode and said substrate are opposed to each other to form an amorphous silicon film on said substrate, wherein a gas permeable heater is provided between said substrate and said electrode. A plasma CVD apparatus connected to a means for applying a negative bias voltage.