Improvement of transport properties for polycrystalline silicon prepared by plasma-enhanced chemical vapor deposition

The carrier transport property of polycrystalline silicon (poly-Si:H:F) thin films was studied in relation to film microstructure, impurity, in situ or post-annealing treatments to obtain better carrier transport properties. Poly-Si:H:F films were prepared from SiF4 and H-2 gas mixtures at temperatures < 300 degreesC. Dark conductivity of the films prepared at high SiF4/H-2 gas flow ratio (eg., 60/3 sccm) exhibits a high value for intrinsic silicon and its Fermi level is located near the conduction band edge. The carrier incorporation is suppressed well, either by in situ hydrogen plasma treatment or by post-annealing with high-pressure hot-H2O vapor. It is confirmed that weak-bonded hydrogen atoms are removed by the hot-H2O vapor annealing. In addition, evident correlation between impurity concentrations and dark conductivity is not found for these films. It is thought that the carrier incorporation in the films prepared at high SiF4/H2 alas flow ratios is related to grain-boundary defects such as weak-bonded hydrogen. By applying hot-H2O vapor annealing at 310 degreesC to a 1-mum-thick p-doped (400)-oriented poly-Si:H:F film, Hall mobility was improved from 10cm(2)/VS to 17 cm(2)/Vs.