JPH0547970B2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field to Which the Invention Pertains] The present invention involves generating a glow discharge by applying a voltage between a first electrode that also serves as a support for a substrate and a second electrode that is placed opposite to the first electrode. This invention relates to a plasma CVD device that decomposes a reactive gas to deposit a thin film of an amorphous semiconductor or insulator on a substrate.

[Prior art and its problems]

Amorphous semiconductor solar cells using amorphous semiconductors, particularly amorphous silicon, are being researched and developed as a promising candidate for reducing the cost of solar cells that directly convert light into electrical energy. Amorphous silicon (hereinafter referred to as a-Si) solar cells are made of a p-type a-Si layer, a non-doped a-Si layer, etc. The a-Si layer having a pin junction is formed as a photovoltaic layer by forming an n-type a-Si layer of several hundred Å, several μm, and several hundred Å, respectively. In each of these layers, there is also a well-known technology to improve efficiency by using a highly transparent a-SiC layer or a highly conductive microcrystalline a-Si layer as the p-type layer and n-type layer. .

A capacitively coupled glow discharge device shown in FIG. 1 is known as a device for forming this a-Si layer. Capacitively coupled glow discharge devices are suitable for manufacturing large area solar cells. Heater 2 is installed inside bell gear 1.
An electrode 3 is attached to the electrode 3, and an electrode 4 is arranged opposite to the lower surface of the electrode 3. The substrate 5 on which the a-Si layer is formed is attached to the upper electrode 3, and is maintained at a temperature of 200 to 300°C by the heater 2. The internal space of the bell gear 1 is connected to a gas supply line via a gas inlet pipe 6 and to an exhaust system via an exhaust pipe 7. For example, when forming a p-type a-Si layer, appropriate amounts of silane gas and diborane gas are mixed, introduced into the bell gear through pipe 6, and maintained at 1 to 10 Torr in balance with the exhaust system. Using a high frequency power source 8 from the outside, high frequency power is applied between both opposing electrodes 3 and 4 to decompose the internal gas and p
A type a-Si layer is deposited on the substrate 5. In the formation of a non-doped layer and an n-type a-Si layer, a gas of an appropriate composition is decomposed by glow discharge and deposited in a similar manner.

Figures 2a and 2b show enlarged views of the upper electrode. 1A is a view of the upper electrode 3 holding the substrate 5 viewed from below. As shown in a and cross-sectional view b, the electrode 3 is attached to a support 10 with a built-in heater 2 by a support claw 9, and the electrode 3 is fitted into the support 10 and supported by the support claw 9. It is becoming more and more popular. The substrate 5 is fitted into a hole made in the electrode 3, and in order to improve electrical contact and thermal contact between the substrate 5 and the electrode 3, a metal plate is held down and fixed from the top of the substrate. ing. The surface of the substrate faces the electrode 4 and is exposed to the electrode 4. When a high frequency voltage is applied between the electrodes 3 and 4 to generate a glow discharge, a-Si adheres to the electrode 3, the substrate 5, the counter electrode 4, and the vessel wall. If this a-Si adheres to parts other than the substrate, the film will peel off from this part as the film continues to be formed, and the inside of the glow discharge device will become dirty.
Pinholes were formed in the Si film, and the quality of the a-Si film deteriorated, resulting in a decrease in the efficiency of the solar cell. Electrode 3
There is no problem because the electrodes 4, the support 10,
It is necessary to frequently remove adhering a-Si from the supporting claws 9 or the vessel wall, and to perform cleaning work. In this case, not only the film growth operation is interrupted, but also it takes time to lower the temperature of the furnace, the furnace itself is subjected to unfavorable conditions such as wiping work, air exposure, etc. However, it was necessary to take measures such as dry firing, which caused many problems in terms of equipment stability and operation rate.

FIG. 3 shows an example of another device. This device has p
The purpose is to improve controllability of the film by forming type, non-doped, and n-type a-Si layers in different reaction chambers, suppressing the influence of forming other layers during the growth of each layer. Three reaction chambers 11, 12, 13
There are a front chamber 11 for mounting the substrate on the susceptor 3 and a rear chamber 15 for taking out the substrate on which the pin layer has been formed, and each chamber 11 to 15 has a valve 16.
Connected to the exhaust system via. The susceptor 3 has a hole 31, as shown enlarged in FIG. 4, into which the substrate 5 is dropped. The holes 31 are arranged as shown in FIG. 2a when viewed from below. The susceptor 3 with the substrate 5 mounted thereon is placed into the front chamber 14 by opening a gate valve (not shown). The susceptor 3 is carried in by moving it on the wheels 17 that are lined up. When the susceptor 3 reaches a predetermined position in the front chamber 14, the gate valve is closed and the chamber 14 is evacuated via the valve 16. Next, the susceptor 3 is heated in the front chamber 14 so that the temperature of the substrate is 200 to 300°C. After the temperature stabilizes at 200-300℃, the front chamber 1
4 and the reaction chamber 11 is opened, and the susceptor 3 is moved into the chamber 1 as the wheel 17 is driven.
1. When it comes to the designated position, chamber 14,1
1 is closed, a mixed gas of silane and diborane is introduced into the reaction chamber 11, and glow discharge decomposition is caused by a high-frequency electric field applied between the susceptor 3 and the counter electrode 4 at 1 to 10 Torr. conduct, p
A type a-Si layer is deposited on a substrate 5 mounted on a susceptor 3. When the deposition of a predetermined film thickness is completed, the reaction chamber 11 is evacuated, the gate valve between the reaction chambers 11 and 12 is opened, and the susceptor 3 is moved to the reaction chamber 12.
Thereafter, each a-Si layer is deposited in the same manner. Room 1
When the n-layer a-Si is formed in step 3, the susceptor 3 is connected to the chamber 1 through the gate valve between the reaction chamber 13 and the rear chamber 15.
Put it in 5. After the susceptor 3 is cooled to a certain temperature, for example, 100° C. or lower, N ₂ gas is introduced into the chamber 15 to bring it to normal pressure, the gate valve is opened, and the susceptor 3 is taken out.

In the reaction chambers 11 to 13, the distance between the susceptor 3 and the counter electrode 4 is the shortest when viewed three-dimensionally, and is 40 to 100 mm. Other distances, such as the distance between the susceptor 3 and the wall of the reaction chamber, the distance between the wheel 17 and the chamber wall, and the distance between the wheel 17 and the counter electrode 4, are larger than the distance between the susceptor 3 and the counter electrode 4, for example, 1.5 times. It has distance. Therefore, even if a high-frequency electric field is applied between the susceptor 3 and the counter electrode 4 to cause a discharge, the electric field is concentrated between these two poles, and most of the decomposed a-Si is deposited on the substrate 5 attached to the susceptor 3. adhere to. Since the susceptor 3 is taken out together with the substrate 5, processing such as cleaning can be performed at that time.
A large amount of a-Si will be deposited on the counter electrode 4 in the reaction chamber, and if the amount is large, it will peel off, scatter during glow discharge, and be trapped on the substrate, causing pinhole formation or film quality deterioration. Therefore, until now, when the amount of deposition on the counter electrode exceeds a certain amount, the film formation operation is interrupted for cleaning to remove the a-Si, and then a gas such as CF ₄ is introduced, and a method such as plasma etching is performed. The inside of the reaction chamber was cleaned by However, initial attempts to perform plasma etching required a long time, and the removed portions varied, making it impossible to perform an efficient cleaning operation. Furthermore, when the reaction chamber was opened, there were problems such as the inner walls of the reaction chamber being contaminated with outside air, etc., and there were also problems in terms of operating efficiency because the work was interrupted for a long time.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a plasma CVD apparatus that can remove reaction products deposited on a counter electrode in a reaction chamber in a short time without opening the reaction chamber.

[Key points of the invention]

In the reaction chamber, a voltage is applied between a first electrode that also serves as a support for the substrate and a second electrode placed opposite to it to generate a glow discharge to decompose the reactant gas, which is then supported by the first electrode. In an apparatus for depositing a thin film on a substrate, a reaction chamber includes a thin ribbon that is electrically insulated from the first electrode and the second electrode, and a feeding roll and a take-up roll for the ribbon;
A delivery roll and a take-up roll are arranged at one end of the second electrode and opposite to this so that the ribbon passes near the second electrode on the first electrode side of the second electrode and shields the second electrode from the first electrode. The above object is achieved by arranging them on both sides of the other end.

[Embodiments of the invention]

FIG. 5 shows a first embodiment of the present invention. It is wound around a roll 21 passing between a first electrode 3 which also serves as a susceptor and a counter electrode 4. For example, a thin strip 2 made of a polymer film such as fluororesin, polyimide, polyamideimide, polybismaleimide, etc.
0 is wound onto a roll 22. A flat surface of the polymer ribbon 20 is formed by the tension between the two rolls. When the distance between the electrode 3 and the electrode 4 was 40 to 100 mm, the distance between the ribbon 20 and the counter electrode 4 was set to within 30 mm. FIG. 5 is a sectional view of the apparatus shown in FIG. 4 in a direction perpendicular to the plane of the paper. Therefore, the susceptor 3 moves in a direction perpendicular to the paper plane of FIG. The rolls 21 and 22 may be made of metal or an insulator and have the same potential as the counter electrode 8. 1~ in the reaction chamber
A voltage was applied using a high frequency power source 8 in a gas atmosphere of 10 Torr to perform glow discharge decomposition. The a-Si was formed on the susceptor, the substrate mounted on the susceptor, the counter electrode 4, and the insulating band 20. Counter electrode 4
Since the distance between the ribbon 20 and the ribbon 20 was small, the amount deposited on the surface of the counter electrode 4 was small compared to the amount deposited on the ribbon 20. In order to reduce the amount deposited on the counter electrode 4, it is necessary to place the insulating band 20 as close to the electrode 4 as possible. When the a-Si deposited on the ribbon 20 exceeds a predetermined thickness, the roll 2
2 to provide a fresh surface insulation strip. The a-Si deposited by this winding is rolled into the roll 22 together. It is desirable that the width of the ribbon 20 in the roll length direction is larger than the width of the electrode 4;
By increasing the size by 5 cm or more, the amount of a-Si adhering to the counter electrode 4 could be reduced. After winding up with the roll 22, the reaction chamber was plasma etched using a gas such as CF ₄ , thereby making it possible to clean the reaction chamber without exposing it to the outside air.

FIG. 6 shows a second embodiment in which rolls 21 and 22 are arranged on the opposite side of the counter electrode 4 with respect to the susceptor 3. This is the direction change roll 23, 24
It is configured as shown in the figure. With this configuration, it is possible to reduce a-Si adhering to the roll 21 around which the clean band 20 is wound. Then, during winding by the roll 22, the insulating band 20 with less a-Si adhesion could be sent out from the roll 21.

FIG. 7 shows a third embodiment, in which a susceptor 3 and a counter electrode 4 are configured in a reaction chamber 18 as shown in the figure, and a take-up roll 22 of an insulating band 20 is installed in an exhaust port 7 connected to an exhaust system. It is something. Therefore, even if the a-Si film is slightly blown away due to winding, the reaction chamber 18
No more contamination inside.

FIG. 8 shows a fourth embodiment, and in the third embodiment, a certain amount of a
-Since the Si is peeled off, the number of direction changing rolls is reduced, and both the roll 24 and the take-up roll 22 are installed inside the exhaust port 7. Further, the roll 21 wrapped with a new insulating band was covered entirely with a cover 26 except for the pull-out hole 27, and the cover 26 and the roll 21 were held at the same potential as the electrode 4. Therefore, a
-Si is no longer attached.

In any of the above cases, the susceptor 3 and the counter electrode 4
The distance between the rolls and the like that are at the same potential as the counter electrode 4 should be kept at a sufficient distance from the susceptor or the chamber wall (at least 1.5 times the distance between the susceptor 3 and the counter electrode 4).
Configured.

FIG. 9 shows a fifth embodiment, and shows the relationship between the susceptor 3, the counter electrode 4, rolls, etc. when there is a wheel 17 for transporting the susceptor 3. All distances are 1.5 of the distance between the susceptor 3 and the counter electrode 4.
It was more than doubled.

In FIG. 10, direction changing rolls 28 and 29 are fixed to the opposing electrode 4. In this case as well, it is desirable to configure the positions of the rolls 28 and 29 so that the insulating band 20 does not come into close contact with the counter electrode 4.

In the above embodiments, a polymer film is used for the ribbon 20, but the same effect could be obtained even if a conductor foil was used instead of the polymer film. However, in this case, it was necessary to keep the conductor parts such as the conductor foil and the roll supporting it insulated from the first electrode and the counter electrode.

〔Effect of the invention〕

The present invention covers the surface of the opposing electrode, which does not support the substrate, among the two electrodes for generating glow discharge in a plasma CVD apparatus, with a thin strip that is insulated from the electrode and passes near the electrode. It comes out from a delivery roll and is wound up on a take-up roll. This allows reaction products such as a-Si to adhere to the ribbon rather than the counter electrode, and by winding up the ribbon, the reaction products can be quickly removed without opening the reaction chamber. It is now possible to clean the product without exposing it to the outside air. As a result, it is possible to stably form an a-Si film used particularly in solar cells, and the characteristics of solar cells, the manufacturing yield, and the operating rate of plasma CVD equipment are improved, so the present invention The effect is extremely large.

[Brief explanation of the drawing]

Figure 1 is a cross-sectional view of a conventional plasma CVD device.
Figures 2a and b show the susceptor and heater part,
3 is a sectional view of another conventional plasma CVD apparatus, FIG. 4 is an enlarged view of its essential parts, and FIG. 5 is a sectional view of an embodiment of the present invention. 6
Figures 1 through 10 are cross-sectional views of different embodiments. 3... Susceptor, 4... Counter electrode, 18... Reaction chamber, 20... Thin strip, 21... Delivery roll,
22... Winding roll.

Claims (1)

[Claims] 1 In the reaction chamber, a voltage is applied between a first electrode that also serves as a support for the substrate and a second electrode placed opposite thereto to generate glow discharge and decompose the reaction gas, and the first electrode In the apparatus for depositing a thin film on a substrate supported by the reaction chamber, a thin strip electrically insulated from the first front electrode and the second electrode, and a delivery roll and a take-up roll for the thin strip are built into the reaction chamber. The feed roll and the take-up roll are connected to one side of the second electrode so that the ribbon passes near the second electrode on the first electrode side of the second electrode and shields the second electrode from the first electrode. A plasma CVD apparatus characterized in that the plasma CVD apparatus is arranged on both sides of one end and the other end opposite thereto.