The production of amorphous silicon devices usually requires large area, high-deposition-rate plasma reactors. Non-uniformity of the film thickness at high power and deposition rate is found to be an important factor for large area deposition.
Increasing the radio frequency from the conventional 13.56 MHz up to VHF has demonstrated advantages for the deposition of a-Si:H films, including higher deposition rates and lower particle generation. The use of VHF for large area deposition leads to the generation of standing waves and evanescent waveguide modes at the electrode surface and on the power feeding lines. Thereby increasing the non-uniformity of the film thickness. The uniformity of the film thickness for an excitation frequency strongly depends on the deposition parameters e.g. pressure, input power, silane flow and the value of load impedances. With increasing exciting frequencies the range of deposition parameters for obtaining uniform films narrows.
Subsequently it is shown that for a large-area plasma-box reactor (500 × 600 mm2 plate size) with a double-sided RF electrode, the non-uniformity of the film decreases due to a homoge-neization of the electrode voltage distribution by using multiple power supplies and load impedances on the end of the RF electrode. The uniformity errors decrease from ±20% to ±2.4% (27.12MHz) and from ±40% to ±5.9% (54.24MHz). Experimental results of the film uniformity will be discussed in dependence on excitation frequencies and the deposition parameters.