1. Field of the Invention
The present invention relates to a method of forming a semiconductor device.
2. Related Background Art
A radio-frequency (RF) plasma CVD method facilitates formation of a device with a large area or at a low temperature and thus has an advantage in that a process throughput is improved. Therefore, the method is regarded as promising as a method of forming a silicon thin film.
Taking a solar cell as an example of a semiconductor device having a semiconductor junction composed of silicon thin films, the solar cell formed of the silicon thin films is advantageous in terms of inexhaustible energy source and clean power generation process as compared with existing energy utilizing fossil fuels. However, the solar cell needs to, for its widespread use, attain a lower unit price per generated power. To that end, significant technical issues to consider are as follows: establishment of a producing technique capable of realizing a low cost, a technique of enhancing a photoelectric conversion efficiency, a technique regarding a uniformity for forming semiconductor devices having desired characteristics in a stable manner, and a technique of improving an environmental resistance in consideration of actual use conditions (in many cases, the solar cell is placed outdoors).
As a method of producing the semiconductor device having the semiconductor junction composed of the silicon thin films, there have been known a method of sequentially forming semiconductor layers of desired conductivity types in a single semiconductor forming vessel, and a so-called batch method in which a p-type layer, an i-type layer, and an n-type layer are formed in separate semiconductor forming vessels for preventing an impurity gas from mixing therein, and the like. In addition, disclosed in U.S. Pat. No. 4,400,409 as a production method capable of avoiding mixing of impurities and realizing cost reduction is a continuous plasma CVD method employing a roll to roll system. From the viewpoint of further improving characteristics and productivity, Japanese Patent Application Laid-Open No. 2002-170973 discloses a method of forming a semiconductor device characterized by including the step of exposing a semiconductor layer to an oxygen atmosphere at a semiconductor interface.
The disclosed RF plasma CVD method is an excellent semiconductor device forming method. However, in the case of including plural pin junctions and using a multi-layer structure of the p-type layer, the i-type layer, and the n-type layer, the method involves the increased number of requisite semiconductor forming vessels. Suppose a case where all the semiconductor forming vessels are continuously connected with one another to continuously form the semiconductor layers in a step of forming the semiconductor device. In such a case, an operation of the entire system needs to be stopped each time the need for maintenance, inspection, or repair arises in part of the semiconductor forming vessels. Further, when taking out it to the outside (in the air) midway through the semiconductor formation, lots may vary from one another in their characteristics, in particular, photoelectric conversion efficiencies, although depending on deposition conditions, environmental conditions, or storage conditions.