INSITU CHEMICALLY CLEANING POLY-SI GROWTH AT LOW-TEMPERATURE

We report a novel growth method of polysilicon thin films on glass substrates at a low temperature (450-degrees-C) by plasma chemical vapor deposition (PCVD) using SiH4/SiF4 mixture gases. In this method, the conventional low-cost glass substrates such as Corning 7059 may be used because of the low deposition temperature. Furthermore, the conventional vacuum chamber with its base pressure of approximately 1 x 10(-4) Pa, which is usually thought to be inadequate for high-quality Si growth because of its many impurities, can be used since the growing surface of polysilicon is in-situ chemically cleaned by SiF4 plasma. The polysilicon films obtained on glass show strong (100) preferred orientation. A grain size as large as 250 nm is obtained in a film with 700 nm thickness. The field-effect mobility of 44 CM2/V . s has been achieved in a thin-film transistor (TFT) using this polysilicon film.