Amorphous-to-Microcrystalline Silicon Transition in Hot-Wire Chemical Vapor Deposition

Abstract

The conductivity and the structural properties of thin films deposited by Hot-Wire Chemical Vapor Deposition (HW-CVD) from silane and hydrogen at a substrate temperature of 220 °C are shown to be strongly dependent on the filament temperature, T_fil, and process pressure, p. Amorphous silicon films are obtained at low pressures, p < 3 × 10⁻² Torr, for T_fil ∼ 1900 °C and F_H2 = F_SiH4. At this T_filJU, high deposition rates are observed, both with and without hydrogen dilution, and no silicon was deposited on the filaments. At T_fil ∼ 1500 °C, a transition from a-Si:H for p > 0.3 Torr to microcrystalline silicon (μc-Si:H) for p < 0.1 Torr occurs. In this temperature regime, silicon growth on the filaments is observed. /ic-Si:H growth both without hydrogen dilution and also in very thin films (∼ 0.05 μm) is achieved. Raman and X-Ray spectra give typical grain sizes of 10 – 20 nm, with a crystalline fraction higher than 50%. For both, Tju ∼ 1500 °C, p > 0.3 Torr and T_fil ∼ 1900 °C and p ∼ 2.7 × 10⁻² Torr, an increase of the crystalline fraction from 0 to ∼ 30% is observed when the hydrogen dilution, F_H2/F_SiH4, increases from 1 to > 4.