Research On Preparation And Properties Of Polycrystalline Silicon Thin Films By Aluminum-induced Crystallization From Nanocrystalline Silicon

Polycrystalline Silicon (poly-Si) thin film, considered to be a highly efficient andlow-attenuation photovoltaic material, has a relatively high photosensitivity and absorbability ofvisible sunlight. In the meantime, it also possesses an advantage of illumination stability and simplemanufacture technique. On the other hand, Aluminum Induced Crystallization (AIC) is a newtechnique of producing high quality poly-Si films with large grains, which could greatly shorten thepreparation time and lower the processing temperature. In order to obtain high carrier mobility poly-Sithin films, we need to improve the grain size and the crystalline quality using AIC technique. In thisthesis, we successfully prepared the Glass/nc-Si/SiO2/Al stack by R.F. sputtering and HWCVD, andthen investigated the technology of processing poly-Si films from nanocrystalline silicon (nc-Si) usingAIC. In addition, based on the view of dynamics, the study of crystallization mechanism was carriedout and the morphology, structure, electrical and optical property of the poly-Si films were analyzedby various methods of characterization.Under the traditional annealing condition, the Glass/nc-Si/SiO2/Al structure stacks were annealedat different processes. The XRD result shows that the poly-Si thin films present a strong preferentialorientation in (111) direction and Raman Spectrum indicates a very high crystalline quality of poly-Sithin films. Moreover, the annealing temperature, annealing time and thickness ratio of Si to Al layersare all important factors that affect the AIC process. Specifically, the poly-Si grain size up to400μmwas formed, when the sample was treated at425℃in5hours. With the annealing temperature rising,the number of small grains increased and the crystalline quality became better, whereas the opticaltransmittance decreased. When the sample was annealed at425℃in7hours,the morphology of grainreflected a great change, accompanying with a reduce of square resistance and resistivity; On theother hand, with the rising of thickness ratio of Si to Al layers, the number of large grains increased,the square resistance and resistivity became higher, and the poly-Si film showed a better crystallinequality. Based on view of dynamics, the crystallization mechanism was analyzed.Under the plasma-enhanced annealing condition, the effects of annealing temperature, annealingtime and R.F. power on the AIC process of Glass/nc-Si/SiO2/Al stack were investigated. The resultsshow that with increasing the temperature, the grain size grew up to500μm, and the crystalline qualitybecame better and the optical transmittance increased. When the treat time prolonged, the morphologyof grain changed into polygon and the crystalline volume fraction gradually increased, reaching97% when annealed at450℃in5hours under30W R.F. power. When the R.F. power increased, thecrystalline quality became better, while the optical transmittance decreased. Through analyzing theresults, we considered that the passivating effect of hydrogen became much more remarkable withincreasing annealing temperature, annealing time and the R.F. power. Besides, because of thenanocrystalline silicon inducer, we finally obtained high crystalline quality poly-Si films with largergrain size.