Polycrystalline silicon (polysilicon) films are formed from the recrystallization of microcrystalline silicon films with different crystalline nucleus densities. The films are deposited by plasma CVD using a gas mixture of SiH2F2, SiH4, and H2. The SiH2F2 flow rate can successfully control the crystalline nucleus density of an as-deposited film. The recrystallization is carried out by annealing at 600°C. The TEM observation shows that recrystallization proceeds from the nucleus until the neighboring grains face each other. Therefore, the grain size in the annealed films and the field effect mobility of thin film transistors using polysilicon films completely depend on the crystalline nucleus density in the starting films. The largest grain sizes and highest field effect mobilities can be obtained from microcrystalline silicon films with the lowest nucleus densities.
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