Distributed electron cyclotron resonance plasma: A technology for large area deposition of device-quality a-Si:H at very high rate

Distributed electron cyclotron resonance is a technique that combines low pressure, microwaves and magnetic confinement with a network of antennas to produce large area, remote, high-density plasmas in a simple reactor design. We are optimizing this promising technology for depositing intrinsic and doped a-Si:H layers for thin film solar cells. Operating in depletion mode, the growth rate is proportional to the silane flow rate and the layer quality is affected by the gas residence time, power/gas flow rate ratio, ion energy and substrate temperature. Fast deposition of device-quality hydrogenated amorphous silicon requires short gas residence time and large silane flow rate but also a well-controlled sheath potential, to induce surface re-organization without generating defects, as well as a deposition temperature larger than 250 °C. Rates up to 60 Å/s have been achieved, i.e. at least 5 times the industrial best. 300 nm-thick device-quality layers were produced with a minority carrier diffusion length larger than 150 nm. Using a single-point injection, we achieved an homogeneity of ± 6% (± 3 sigma) for the material bandgap, ± 10% for the dielectric function and ± 12% for the solar cell fill-factor, for an average deposition rate of 24 Å/s on a 20 × 20 cm² glass.