Semiconductor device manufacturing: process – Making device or circuit emissive of nonelectrical signal – Having diverse electrical device
Reexamination Certificate
1999-09-03
2001-03-13
Pham, Long (Department: 2823)
Semiconductor device manufacturing: process
Making device or circuit emissive of nonelectrical signal
Having diverse electrical device
C438S022000
Reexamination Certificate
active
06200825
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method of manufacturing a silicon-based thin film photoelectric conversion device, and particularly to a manufacturing method thereof to achieve a superior performance as the silicon-based thin film photoelectric conversion device as well as improved cost and efficiency in production.
In the specification, the terms “polycrystalline,” “microcrystalline” and “crystalline” refer not only to perfect crystalline state but also a state partially involving amorphous state.
2. Description of the Background Art
In recent years a photoelectric conversion device employing a thin film containing crystalline silicon such as polycrystalline silicon, mycrocrystalline silicon, has been increasingly developed. It has been developed in attempting to reduce the cost of the photoelectric conversion device and also enhance the performance of the same by forming a crystalline silicon thin film of good quality on an inexpensive substrate through a process at a low temperature, and such development is expected to be applied to a variety of photoelectric conversion devices, such as optical sensors other than solar cells.
Conventionally, as an apparatus for producing a solar cell, an in-line system apparatus in which a plurality of film deposition chambers (or simply referred to as chambers) are coupled in line as shown in the block diagram of
FIG. 4
, or a multi-chamber system apparatus in which a plurality of deposition chambers are arranged around a central middle chamber as shown in the block diagram of
FIG. 5
, has been employed.
For an amorphous silicon solar cell, a single chamber system in which all semiconductor layers are formed in one and the same deposition chamber has been used as a simple method. In order to prevent conductivity type determining impurity atoms doped in a p type semiconductor layer and an n type semiconductor layer from being undesirably mixed to a semiconductor layer of a different type, however, it is necessary to sufficiently replace gas in the deposition chamber before forming respective semiconductor layers, for example, by gas replacement for one hour using purge gas, such as hydrogen. Even when such a gas replacement process is performed, it has been impossible to attain superior performance of the amorphous silicon solar cell. Therefore, the single chamber system has been used only for experimental purpose.
Manufacturing of an nip type solar cell by successively depositing an n type semiconductor layer, an i type photoelectric conversion layer and a p type semiconductor layer in this order from the side of the substrate using the aforementioned in-line or multi-chamber system will be described in the following.
In the in-line system shown in
FIG. 4
, a structure is used in which an n layer deposition chamber
3
n
for forming the n type semiconductor layer, i layer deposition chambers
3
i
1
to
3
i
6
for forming the i type photoelectric conversion layer and a p layer deposition chamber
3
p
for forming the p type semiconductor layer are coupled in order. Here, as the n type semiconductor layer and the p type semiconductor layer are thinner than the i type photoelectric conversion layer, film deposition time for these layers is significantly shorter. For this reason, in order to improve production efficiency, a plurality of i layer deposition chambers are generally coupled, and until the film deposition time of the n and p type semiconductor layers attain a rate regulating state, the larger the number of i layer deposition chambers, the higher the productivity.
In the multi-chamber system shown in
FIG. 5
, a substrate on which films are to be deposited is moved to respective deposition chambers
4
n
,
4
i
1
to
4
i
4
and
4
p
through a middle chamber
4
m.
The in-line system as described above disadvantageously includes a plurality of i layer deposition chambers
3
i
1
to
3
i
6
which require maintenance most. Therefore, even if maintenance of only one i layer deposition chamber is required, it is necessary to stop the entire production line.
By contrast, in the multi-chamber system as shown in
FIG. 5
, a movable partition capable of maintaining air-tightness between each of the deposition chambers
4
n
,
4
i
1
to
4
i
4
and
4
p
and the middle chamber
4
m
is provided. Therefore, even when there is a failure in one deposition chamber, other deposition chambers are available, and therefore overall production halt can be avoided.
The multi-chamber production system, however, has a mechanism for moving the substrate between each of the deposition chambers
4
n
,
4
i
1
to
4
i
4
and
4
p
and middle chamber
4
m
while maintaining air-tightness which is complicated and expensive, and further, the number of deposition chambers arranged around middle chamber
4
m
is limited by space. Therefore, the production apparatus of this type is not widely used for actual production.
SUMMARY OF THE INVENTION
The present invention was made in order to solve the problems above. One object of the present invention is to provide a method of manufacturing a silicon-based thin film photoelectric conversion device to allow a photoelectric conversion device having excellent performance and quality to be produced at a low cost with high efficiency by using a simple apparatus.
According to the method of manufacturing a silicon-based thin film photoelectric conversion device of the invention, a silicon-based thin film photoelectric conversion device having a stacked structure composed of a p type semiconductor layer, an i type crystalline silicon-based photoelectric conversion layer, and an n type semiconductor layer is fabricated by plasma CVD. This method is characterized in that the p type semiconductor layer, the i type crystalline silicon-based photoelectric conversion layer, and the n type semiconductor layer are successively produced in the same plasma CVD reaction chamber and that the p type semiconductor layer is formed on condition that the pressure in the reaction chamber is at least 5 Torr.
The inventors have found that when p, i and n layers are formed in this order in one reaction chamber and the pressure in the reaction chamber when the p type semiconductor layer is formed is set as high as 5 Torr or higher, a photoelectric conversion device having superior quality and high performance can be obtained. Details are as follows.
As the p, i and n layers are formed in this order, mixing of the conductivity type determining impurity atoms into the i type photoelectric conversion layer is reduced than when n, i and p layers are formed in this order. This is because the p type impurity atoms (for example, boron atoms) are harder to be diffused as compared with n type impurity atoms (for example, phosphorus atoms). More specifically, the p type impurity atoms adhered on an inner wall surface of the reaction chamber or on a plasma discharge electrode while forming the p type semiconductor layer do diffuse into the i type photoelectric conversion layer when the i type photoelectric conversion layer is formed. The extent of diffusion, however, is smaller than the n type impurity atoms. Therefore, mixture or entrance to the i type photoelectric conversion layer is suppressed.
Further, as the p type semiconductor layer is formed under a high pressure condition of 5 Torr or higher, film deposition rate of the p type semiconductor layer is high, and therefore it becomes possible to complete formation of the p type semiconductor layer in a short period of time. Accordingly, the time necessary for introducing raw material gas for forming the p type semiconductor layer into the reaction chamber can be shortened, and hence accumulation of p type impurity atoms adhered on the electrode of the reaction chamber, for example, can be suppressed. This further suppresses mixture or entrance of p type impurity atoms into the i type photoelectric conversion layer.
From the foregoing, even when the photoelectric conversion device is manufactured by the single chamber system, mixture of the co
Okamoto Yoshifumi
Yamamoto Kenji
Yoshimi Masashi
Hogan & Hartson LLP
Kaneka Corporation
Pham Long
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