Fabrication of polysilicon thin film on glass with low-temperature UV-assisted crystallization

Abstract

The amorphous silicon (a-Si) film was crystallized on glass by a simple method employed ultraviolet at temperatures as low as 400°C. The employ of ultraviolet enhanced the crystallization of amorphous silicon. This method is able to uniformly crystallized large-area amorphous silicon films. The polysilicon films crystallized by this way are suitable for the fabrication of thin film transistors on ordinary glass. Crystallization process is performed in a furnace. Amorphous silicon sample is placed on a hot plate and irradiated by a bank of ultraviolet lamps through a diffuser plate to improve the uniformity of light that irradiates the sample. Raman microscopy is used for analyzing the qualities of UV-assisted crystallized silicon films. By measuring the Raman spectra the effects of anneal temperature and process time on the crystallizing behavior, crystallinity and grain size of the processed films were obtained. There has a threshold temperature for crystallization of amorphous silicon film in the presence of ultraviolet irradiation with certain intensity, i.e. by ultraviolet irradiation with certain intensity only when the temperature is up to the threshold temperature, the crystallization can be triggered. The threshold temperature is 400°C when the intensity of ultraviolet irradiation is 1mW/cm². Above threshold temperature, the increase of anneal temperature increased the rate of crystallization. Crystallinity and grain size extracted from Raman spectra of samples increase with the extending of process time at certain temperature. Crystallization of amorphous silicon film with thickness of 50nm completed within 6 hours at 400°C irradiated by ultraviolet with intensity of 2mW/cm².