回転電極型大気圧プラズマCVD法による多結晶Siの成膜特性

抄録

Polycrystalline silicon (poly-Si) films were fabricated with high deposition rate using the atmospheric pressure plasma CVD (AP-PCVD) technique. The films were prepared on thermal oxidized Si(001) wafers at 500 °C in atmospheric pressure VHF (very high frequency) plasma of gas mixtures containing He, H₂ and SiH₄. Surface morphology, cross-sectional structure and crystallinity of the Si films were characterized by scanning electron microscopy (SEM), reflection high-energy electron diffraction (RHEED) and Raman scattering spectroscopy. Hydrogen content of the deposited films was also evaluated by Fourier transformation infrared (FTIR) absorption spectroscopy. It was found that the crystallinity was affected by the gas flow direction within the plasma area when the SiH₄ concentration was 0.1%. Amorphous Si (a-Si) grew at the upstream region, while poly-Si grew at the downstream region. It also became clear from FTIR spectra that hydrogen atoms that terminated the dangling bonds were excessively contained in the a-Si film. Those excessive bonded hydrogen atoms desorbed thermally during the film growth, and caused film peeling from the substrate. These results indicated that decomposition of SiH₄ molecules was not sufficiently enhanced at the upstream region due to lack of the input VHF power. By decreasing the SiH₄ concentration to 0.01%, however, poly-Si film could be deposited in the whole plasma area. It was found from SEM observation that columnar Si grain grew from the substrate surface, and the grain size increased as the film thickness increased. At the SiH₄ concentration of 0.01%, a poly-Si film was deposited in 100mm×100mm area by scanning substrate in twice at 0.3mm/s. The SEM observation revealed that the Si grain grew continuously at the interface between the first layer and the second layer, suggesting that crystallinity of the film was uniform in the whole plasma area. The deposition rates were 9nm/s for 0.1% SiH₄, and 4nm/s for 0.01% SiH₄, which values were more than 10 times faster than that by the conventional deposition techniques.