Metal-induced Polysilicon Thin Film Preparation And Research

Polycrystalline Silicon (p-Si) thin films are widely used in solar cells, thin film transistors and other fields due to their high mobility, low cost and excellent opt-electric stability. As a cost-effective technique, metal induced crystallization (MIC) exhibits great importance in fabrication and research of p-Si thin films and related solar cells.In this dissertation, p-Si thin films were successfully fabricated using nickel induced crystallization (NIC). At the start, amorphous silicon (a-Si) thin films were prepared by plasma enhanced chemical vapor deposition (PECVD) on glass substrates, after that, a 51nm thick Ni film was deposited over a-Si thin films using a thermal evaporation system, then the samples were annealed in N2 atmosphere with various annealing parameters. SEM and XRD were used to investigate the structural behavior and film properties of those films after annealing. Influential factors including annealing time and annealing temperature were analyzed. Besides, the ultraviolet-visible spectrophotometer was used to test the optical properties of both thin films before and after annealing. Certain conclusions have been achieved as follow:1. The crystallization of a-Si thin films by NIC was observed when films were annealed at about 460℃. Samples remained amorphous if annealing temperature was 450℃or below even though the annealing time kept increasing.2. The strongly preferred orientation to Si (111) of grain growth during annealing were evidenced. Remained Ni and O were detected in the films after annealing, which would affect performances of p-Si thin films.3. The average grain size was mainly affected by annealing time. When annealing time was prolonged, the average grain size increased at the beginning while saturated after 4 hours, and decreased after being annealed for 8 hours; the crystallinity kept increasing slowly when the annealing time was extended. The optimized annealing time was determined to be 4 hours.4. The crystallinity was mainly affected by annealing temperature. When annealing temperature was enhanced, the average grain size first increased slightly, then decreased and again increased at 600℃; the crystallinity kept increasing rapidly when the annealing temperature was elevated. The optimized annealing temperature was determined to be 530℃.5. The transmittance difference between thin films before and after NIC and the low absorption coefficient in visible range of p-Si thin films prepared by NIC was caused by MIC inherent defect of structural inhomogeneous and heavy doping.6. Sample films shed when glass covered with ITO thin films was used as the substrate, which was proved to be induced by the thermal expansion coefficient mismatch between a-Si and ITO. While glass covered with AZO thin films was used as substrate, the shedding problem would be successfully solved.