Preparation Technology Effect On Properties Of Polycrystalline Silicon Thin Films By Aluminum-induced Crystallization

Polycrystalline silicon films are considered to be a kind of photovoltaic materials with excellent properties. This kind of materials possesses advantages of high conversation efficiency and low manufacturing cost. There are many approaches to prepare polycrystalline silicon films, among which aluminum-induced crystallization is a relatively novel method. In this thesis, we investigated the process of polycrystalline silicon films by aluminum-induced crystallization, and analyzed the influence of different preparation conditions on polycrystalline silicon films by aluminum-induced crystallization.300nm initial amorphous silicon films prepared by hot wire chemical vapor deposition were subjected to air oxidation for 50 hours. After 100nm initial Al films were deposited, a-Si/SiO₂/Al laminated membrane structure was formed. Then the a-Si/SiO₂/Al structure was annealed at 500℃in Ar atmosphere at different time. Polycrystalline silicon films with strong preferential (111) orientation were formed after annealing. The size of polycrystalline silicon grains increased as the prolonging of the annealing time. Large grains with average size of 100μm were obtained after annealing for 5 hours. Meanwhile the polycrystalline silicon films'crystalline quality and absorption ability of visible light were improved when the annealing time was prolonged. In addition, experiments proved the polycrystalline silicon films were heavily doped p-type semiconductors.The deposition process of initial aluminum films by magnetron sputtering changed to by vacuum thermal evaporation, while other preparation conditions of aluminum-induced crystallization were kept the same. After annealing, the result showed the initial aluminum films prepared by vacuum thermal evaporation also could induce large-grain polycrystalline silicon films (¹00μm) with strong preferential (111) orientation. As prolonging the annealing time, the grain size increased and the crystalline quality got better and better. However, as compared with magnetron sputtering, the polycrystalline silicon films induced by aluminum films deposited by vacuum thermal evaporation had smaller stress, higher crystalline quality, and faster crystallization rate.The a-Si/SiO₂/Al laminated membrane structure was annealed at three temperatures of 450℃, 475℃and 500℃. The results showed that the grain size, crystalline quality and crystallization rate of the polycrystalline silicon thin films were very sensitive to annealing temperature. When the annealing temperature was below 475℃, large-grain polycrystalline silicon with excellent crystalline quality could not be induced. Only when the annealing temperature rose to 500℃, the aluminum-induced crystallization phenomenon could be very obvious. Initial aluminum films in the a-Si/SiO₂/Al laminated membrane structure were deposited by magnetron sputtering. By varying the substrate temperature during deposition of aluminum films, we found that as the substrate temperature rose, the grain size of the polycrystalline silicon after annealing decreased and the crystallization ability and quality degraded. When the substrate temperature during deposition of aluminum films rose to above 200℃, aluminum-induced crystallization phenomenon would not occur.