Fast deposition of a-Si:H layers and solar cells in a large-area (40x40cm2) VHF-GD reactor

Large-area deposition of hydrogenated amorphous silicon has been investigated in a single-chamber industrial reactor with electrode dimensions of 40x40 cm(2) in the plasma excitation frequency range of 60 to 120 MHz. The film thickness uniformity, analyzed by a light interferometry technique and a step profiler, has been compared with 2-dimensional interelectrode voltage measurements and calculations. The frequency of 80 MHz has been found to be a good compromise between the gain in deposition rate and the homogeneity requirements necessary for a-Si:H solar cells. Under these conditions and while using hydrogen dilution high deposition rates of 6-7 Angstrom/s with a film uniformity of +/-5% over a usable substrate size of 30x30 cm(2) have been obtained. In the same single-chamber deposition system at 80 MHz, 0.4 mu m thick single-junction a-Si:H solar cells with high performance were fabricated in a total process time of 16 minutes applying a continuous deposition process. Spectral response measurements indicate a minor boron contamination of the i-layer. Initial cell efficiencies of 7.1 % could be achieved for such a fast grown a-Si:H solar cell.