Low Temperature Growth of Amorphous and Polycrystalline Silicon Films from a Modified Inductively Coupled Plasma

Abstract

A conventional inductive rf discharge is modified by inserting a discharge antenna in a plasma vessel with magnetic multipole confinement, which gives a high-density (∼1011 cm-3) silane plasma at very low pressures (∼1 mTorr). This new type of inductively coupled plasma (ICP) enables high-rate deposition (∼1 nm/s) of a-Si:H films at low substrate temperatures of ∼100°C, which have the photoconductivity of 10-5–10-4 S/cm and the dark conductivity of 10-10–10-9 S/cm. Moreover, microcrystalline or polycrystalline silicon films are formed on glass substrates at moderate temperatures of 200–300°C where the dark conductivity becomes comparable to the photoconductivity and the X-ray diffraction pattern shows sharp peaks corresponding to the silicon crystalline surfaces. Mass spectrometric measurements of the highly dissociated silane plasma show unique radical compositions; ∼90% of ions are hydrogen species (H3+, H2+, H+) while the density of neutral radicals (SiH3, SiH2, SiH) is lower than that of ionic radicals (SiH3+, SiH2+, SiH+, Si+). Thus, the main precursor of film growth from high-density plasmas may be ionic radicals rather than neutral radicals.