Investigation on the Effect of in situ Plasma Supply During Growth of Polycrystalline Silicon Films by Low-Pressure Chemical Vapor Deposition, and on their Electric Conduction Properties

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Polycrystalline Si (poly-Si) films were prepared on a fused quartz substrate as a function of the rf power (0-30 W), deposition temperature (T_d = 620-770ﾟC) and hydrogen dilution ratio (H_2/SiH_4 = 0 to 8).1. Structural Changes and Stability against Foreign Contamination in Undoped Poly-Si films. As the rf power is increased, the preferential orientation to a random, <100> and <110> texture can be selected. The effect of rf plasma supply during the film growth on the structural properties was found to act as an equivalent effect to a decrease in T_d or a decrease in H_2/SiH_4 (an increase in the partial pressure of SiH_4). Furthermore, the plasma supply was found to have industrially useful effects for smoothing the film surface and improving the stability against foreign contamination such as oxygen. The structural change with the plasma supply was interpreted in terms of both of a change in deposition rate and a change in a surface-diffusion coefficient of SiH-related adsorbates. Th … More e improvement of surface roughness with the plasma supply was explained in terms of a sputtering effect which is likely to be also responsible for the structural change.2. Doping Efficiency. The doping efficiency for phosphorus and boron in poly-Si films deposited by plasma-enhanced chemical vapor deposition (PECVD) method was largely improved as compared with that in poly-Si films prepared by low-pressure CVD (LPCVD) without plasma supply. The structure of doped films was similar to that of undoped films. Also PECVD films had very smooth surface independent of doping level, though the roughness of LPCVD films largely increased in an intermediate doping range.3. Examination of Thin-Film transistors. The field-effect mobility for thin-film transistors fabricated on the undoped poly-Si films was investigated. The highest mobility was observed for PECVD films exhibiting a dominant <110> texture, while LPCVD films with a random texture had the lowest mobility. These results were discussed in terms of the crystallite size, preferential orientation and surface roughness. Less