Role of Hydrogen Dilution in the Low-Temperature Growth of Nanocrystalline Si:H Thin Films from SiH4/H2 Mixture

Hydrogenated nanocrystalline silicon thin films were fabricated from SiH4 with H-2 dilution at a low substrate temperature of 200 degrees C by the conventional plasma enhanced chemical vapor deposition technique. A high deposition rate over 0.75nm/s can be achieved. Raman scattering spectral measurements revealed that the crystalline fraction and grain size increased with the increase in hydrogen dilution ratio. Fourier transform infrared spectrum measurements showed that the hydrogen content decreased and the Si-H bonding configuration changed mainly from SiH to SiH2 with the increase in hydrogen dilution ratio. This suggested that the hydrogen dilution played an important role in the low-temperature growth of nanocrystalline silicon thin film. The growth mechanism is discussed in terms of a surface diffusion model and hydrogen etching effects.