Polysilicon Thin Film Deposition Process

Solar cell as one kind of green energy resource exhibits important role because of the resource crisis and environmental crisis. Polycrystalline silicon thin film possesses the excellences of both crystalline silicon and amorphous thin film silicon. It not only is immune from "optical-induced degradation" but also can be compatible with the existing solar cell technology. It is promising cheap and excellent material for solar cell.Plasma enhanced chemical vapor deposition (PECVD) is one of the matured and simple manipulated among the thin film deposition methods. It suits to be used depositing large area high-uniformity film. But now this method faces two big difficulties: one is the crystalline ratio of the deposited film should be improved, the other is the deposition velocity is slow. The crystalline ratio decides the electric character and the deposition velocity influence the cost. So preparing high quality thin film rapidly is key element for solar cell. Aiming at this target scientists try to optimize the deposition parameters and use recrystallization method.PECVD method is used to deposit polycrystalline silicon thin films at low temperature. The influences of deposition parameters include temperature, substrate, rf power, ratio of SiH₄ and doping on the crystalline and electric character was studied systematically. Solid Phase Crystallization was also carried out using the thin film had deposited. It shows that: 1) In some range increasing the temperature, rf power and decrease the ratio of SiH₄, will improve the crystalline ratio. But going on increase temperature and power will depress it; decrease the SiH₄ ratio will slow down the deposition. 2) Conductivity and surface condition influence the crystallization. 3) There is difference between the furnace annealing and the rapid thermal annealing. 4) Phosphorus doping degenerates the crystalline ratio of deposited film but benefits recrystallization. 5) Dark conductivity increases and optical energy gap decreases when the crystalline ratio increases. Holes were found on the film surface and model was given to explain their formation. It was also found that recrystallization can also make antireflecting surface.