The Research Of Phosphorus Diffusion Process In P-type Silicon

Since we entered the21st century,the energy and environmental issues have become an increasing attention, To use the solar energy has been an important way to solve the energy and environmental issues.The silicon solar cell get full development and become the mainstream of today’s solar cells by using the mature technology of the semiconductor industry.In this case,the R&D of silicon solar cell technology to improve the conversion efficiency and reduce costs has become the center of reseach. PN junction is the heart of solar cells. It can be said that there’ll be no photovoltaic industry without the PN junction.Diffusion is an important mean to form a PN junction,so this paper is focused on the diffusion process and the relationship of other silicon solar cell process to optimize the diffusion process, improve the efficiency of solar cell and reduce costs.The principle of the solar cells and the process steps of solar cells are described firstly.Then this paper tells the development of diffusion furnace. According to different diffusion methods,there are two different types of diffusion furnace.They are chain diffusion furnace and tube diffusion furnace.Then this article talks about the development of the models of phosphorous difusing in crystalline silicon and tells the contributions of Yoshida, Fair, S.M.Hu and so on.In this paper, the theories about PN junction and diffusion in detail are analyzed. In order to optimize the production process, the relationship between temperature, time, the sheet resistance and diffusion uniformity is researched. As follows, this paper gives out some conclusions. 1. The sheet resistances of diffused silicon are discrete. But the average of the sheet resistances of diffused silicon satisfies the equation from the derivation of Constant-surface-concentration diffusion. So we can use the equation to design ideal process.The discovery can reduce the time and cost of debugging in the production.2. The sheet resistance after diffusion is related to the short-circuit current(Isc) and the series resistance(Rs). The sheet resistance increases or decreases, the short-circuit current(Isc) and the serise resistance(Rs) increase and decrease too.Form this we can know that the discrete sheet resistances have a significant impact on solar cell efficiency. Whether higher or lower sheet resistances, the solar efficiency is reduced. The spacing of5mm in diffusion furnace is not the best.The sheet resistances would be more evenly, if the spacing is improved.3. The simulation SiO2film by supremⅣ and the oxygen flow experiments tell that the oxygen flow can be excessive.When the flow of oxygen is reduced, not only the efficiency of diffusion is improved bu also the sheet resistances are more discrete. The excessive oxygen grows thicker SiO2film which will hinder the diffusion、 reduce the diffusion rate and make the sheet resistances more discrete.