Influence of H₂/SiH₄ Ratio on the Deposition Rate and Morphology of Polycrystalline Silicon Films Deposited by Atmospheric Pressure Plasma Chemical Vapor Deposition

Using the atmospheric pressure plasma chemical vapor deposition (AP-PCVD) technique, polycrystalline silicon (poly-Si) films were deposited at high rates. The plasma was generated by 150 MHz very high frequency (VHF) power. Deposition rate, morphology, and structure of the poly-Si films were studied as a function of the H₂/SiH₄ ratio, using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). Plasma length and optical emission were also investigated to examine the reaction process in the plasma. The maximum value of deposition rate was 7.4 nm/s at an SiH₄ concentration of 0.1% (H₂/SiH₄=100). SEM and TEM observations revealed that the poly-Si films had a columnar structure, and that the crystallites in the films deposited at high H₂/SiH₄ ratios contained no visible defects except at the grain boundaries. It was also shown that the Si film prepared has a preferential orientation of (220) by XRD. In addition, it was found that the plasma length was sensitive to the H₂ concentration, while it was not affected by the SiH₄ concentration within the deposition conditions used. This fact suggested that almost all the VHF power was consumed in the decomposition of H₂ molecules.