Large area deposition technique for PECVD of amorphous silicon [solar cells]

The production of amorphous silicon solar cells usually requires large area, high-deposition-rate plasma reactors. Increasing the radiofrequency from the conventional 13.56 MHz up to VHF has demonstrated higher deposition rates and lower particle generation. But the use of VHF leads to a nonuniformity of the film thickness due to the generation of standing waves (TEM wave) and evanescent waveguide modes (TE waves) at the electrode surface. The nonuniformity of the film (500×600 mm² size) decreases due to a homogenization of the electrode voltage distribution by using multiple power supplies and load impedances at the RF electrode. The nonuniformity decreases from ±20% to ±2.4% (27.12 MHz) and from ±40% to ±5.9% (54.24 MHz). The uniformity also depends on the deposition parameters, e.g. pressure, power and silane flow