Plasma etching for industrial in-line processing of c-Si solar cells

Thinner wafers and the reduction of breakage losses make it attractive for solar cell manufacturers to use inline production systems. Closing the gap between diffusion and in-line silicon nitride deposition systems a plasma etching system has been designed suitable for a throughput of 1000 wafer/h with an automated transport system. Different plasma sources appropriate for etching large areas were tested and etch rates of around 13 μm/min for saw damage removal could be reached with sufficient homogeneity. For phosphorous glass (PSG) removal selectivities between PSG and silicon above 10 could be achieved with a CF4/C2H4 etch gas mixture with sufficient PSG etch rates of around 80 nm/min. Solar cells processed with the plasma PSG removal step show slightly decreased efficiencies attributed to the plasma induced damage to the emitter layer and the silicon bulk. Further process optimization is needed to reduce this damage.