Electron cyclotron resonance microwave plasma deposition of a-Si:H and a-SiC:H films

Abstract

Amorphous silicon and silicon carbon alloy thin films (a-Si:H, a-SiC:H) were deposited by electron cyclotron resonance (ECR) microwave plasmas using SiH₄, CH₄ and hydrogen gas mixtures. The ECR-deposited, photosensitive a-Si:H films show a light conductivity of $\text{5 × 10}{}^{\mathrm{-5}}\text{Ω}{}^{\mathrm{-1}}\text{cm}{}^{\mathrm{-1}}$, and a light-to-dark conductivity ratio of about $\text{2 × 10}{}^6$. Optical bandgaps of ECR-deposited a-Si:H films are in the range 1.75–1.85 eV. The integrated defect density in the mobility gap of the photosensitive a-Si:H film was determined by junction capacitance measurements to be $\text{1.6 × 10}{}^{16}\text{cm}{}^{\mathrm{-3}}$. A new type of conductive a-Si:H film, which may contain a microcrystalline phase, was also deposited by ECR PECVD. The p-type dopedECR-deposited, conductive a-Si:H films show a conductivity of $\text{5 × 10}{}^{\mathrm{-2}}\text{Ω}{}^{\mathrm{-1}}\text{cm}{}^{\mathrm{-1}}$.

The ECR-deposited a-SiC:H films show slightly higher optical bandgaps than those of r.f.-deposited a-SiC:H films. Hydrogen dilution in the ECR plasma with a dilution ratio up to 5 shows no significant effect on the optical bandgap of a-SiC:H films. The deposition rate of a-SiC:H films is found to be strongly dependent on the ECR magnetic field and the hydrogen dilution. The hydrogen dilution effect on the deposition rate indicates that the etching in ECR hydrogen plasmas plays an important role in the deposition of a-SiC:H films. The two-phase nature of ECR-deposited, microcrystalline silicon carbon films (μ-SiC:H) is shown by X-ray diffraction to consist of 1000 Å microcrystallites of α-SiC and amorphous network structures.