Structure Study On Silicon Thin Films Crystallized By Laser

As a kind of rising carrier of energy, the solar cell with characters of good enviromentprotecting, high efficiency, non-exhausting, is widely used in the fields of military, aero,aviation and civilians. Polycrystalline silicon (p-Si) thin films solar cell becomes oneworth-expecting direction because of its good performance, and laser crystallization ofamorphous silicon (a-Si) thin films is an important method of preparing p-Si thin films.Thestructure and number of crystal phase has a decesive role on the performance,therefore thestudy on the structure of crystal phase and process parameters is needed to provide the theorybasis to the method.The a-Si thin films,as precursors, are deposited by RF magnetron sputtering system onquartz glasses, and then the phase transition from a-Si to p-Si is performed by lasercrystallization.The 3-D heat transference finite element model is used to compute thetemperature field of laser crystallization of a-Si thin films at different processparameters. Considering the crystallinity, grain size and other indexes, the Differential ThermalAnalyzer, the Raman spectroscopy, XRD and TEM are used to study the microstructure of thefilms.The temperature field simulation results indicate that there is a near linear relationsbetween the surface temperature of the samples with the laser power, the scanning speed andthe defocusing amount in the laser crystallization process. The laser heat source formed thewater-drop shape in the sample to heat up the region, and the corresponding temperature fielddistributions are obtained.The results indicate that the a-Si thin films gradually transfer into p-Si, and the grainsizes are nanometer order of magnitude, the With the process parameters increasing, theaverage grain size of the film deposited on the roughness of 0.01μm presents a complextendency.When the power is lower than 85W, the grain size increases slowly but increasesdramatically to 4.02rim when the power reaches 90W. However,when the power adds to 95W,the grain size begins to decrease to 1.49nm but increases again to 2.95nm at the power of100W, and the crystallinity has the similar tendency with the grain size, which reaches thehighest 87.18% at 90W.When the scanning speed is lower than 4mm/s, the gain size graduallydecreases to the least value 56.90(?) at 4mm/s and then increases sharply to the max value75.45(?), at 8mm/s but gradually decreases again; when the defocusing amount is variable, the gain size gradually extends to the max value 75.45(?) at 95mm and then decreases to 56.90(?),at 100mm.The crystallinities are all over 90%.Compared to the films on the roughness of 0.01μin smooth quartz substrate, the trends ofthe grain size of the films on the the roughness of 0.83μm flock quartz substrate are similar tothe former, but the XRD and Raman peaks of the latter are significantly weaker than theformer, and the grain size and crystallinity are all less than the former.