Influence of hydrogen dilution and doping gas on the material properties of plasma-deposited polycrystalline silicon thin films

•Effects on plasma deposition process conditions of poly-Si films were studied.•Hydrogen promoted fully crystallized subsurface and denser bulk layer.•Heavily doped films showed decreased grain size and increased void fraction.•Dark conductivity saturated at high doping levels. We studied the effects of precursor gas composition and the addition of dopant gas, PH3, on polycrystalline silicon films deposited using plasma-enhanced chemical vapor deposition. Spectroscopic ellipsometry measurement and modeling results revealed that the poly-Si films consist of a subsurface layer and a bulk layer. The sample deposited under greater hydrogen dilution exhibited a fully crystallized subsurface layer and a denser bulk layer. We also studied the effects of various dopant gas flow rates on structural and electrical properties of the poly-Si films. Ellipsometry, X-ray diffraction, and Raman analyses revealed that the film deposited using a large dopant-gas flow rate exhibits decreased grain size and increased void fraction. Furthermore, the doped poly-Si films show a trend of Raman peak shift, which was attributed to tensile stress. The stress of the doped poly-Si films increases with higher dopant-gas flow rate. Measurement of the temperature-dependent dark conductivity shows saturation of the electrical conductivity of heavily doped films.