Akihiko Hiroe

Deposition of Microcrystalline Si1-xGex by RF Magnetron Sputtering on SiO2 Substrates

Microcrystalline Si1-xGex (x~0.8) films have been deposited by magnetron sputtering on SiO2 substrates. Crystallinity was evaluated by spectroscopic ellipsometry, Raman scattering, X-ray diffraction (XRD), transmission electron microscopy (TEM), and electron backscatter diffraction (EBSD). Detailed investigation of the deposition behavior revealed that crystalline phase begins to form at 300 °C, which roughly corresponds to half of the melting temperature of the material. At 300 °C, crystallinity changes with thickness, i.e., crystallinity improves as thickness increases. It was found out that this change in the crystallinity is not due to the heat up of the substrate, but is an essential phenomenon. At 350 °C, on the other hand, crystalline phase is formed almost from the beginning of the deposition. However, surface (<100 nm) crystallinity of the 300 °C sample is higher compared with 350 °C sample when the film thickness is more than 500 nm. Substrate bias effect was also investigated. Crystallinity of 300 °C sample improves while that of 350 °C sample degrades when RF bias power is applied to the substrate.

High Performance Bottom Gate μc-Si TFT Fabricated by Microwave Plasma CVD

Deposition trend of μc-Si was investigated using microwave (2.45GHz) plasma enhanced CVD. μc-Si films with the preferential orientation of (111) and (220) were deposited and compared. Raman scattering results show that the (111) preferentially oriented film has higher crystallinity while ESR measurements result in the fact that the (220) preferentially oriented film has smaller dangling bond density. Bottom gate thin film transistors (TFTs) were fabricated using these μc-Si films as channel layer and evaluated. H 2 plasma post-treatment has been found to be effective to improve the TFT characteristics. Mobility of about 1.4cm 2 /Vsec and on/off ratio of more than 10 5 have been achieved.