Atmospheric pressure PECVD and atmospheric plasma chemical etching for continuous processing of crystalline silicon solar wafers

Atmospheric pressure gas phase technologies will become essential for future concepts of in-line manufacturing of crystalline solar cells because of cost considerations. Important process steps to be transferred to atmospheric preassure plasma are the etching steps including saw damage etching, surface texturizing, phosphorus silicate glass etching, and edge isolation as well as the deposition of silicon nitride as anti-reflective and passivation layer. The application of two innovative atmospheric pressure plasma sources for solar cell processing has been evaluated: a linearly extended DC arc discharge and a microwave plasma source. Both show high rates for silicon etching of up to 11 micron/min by use of NF3 and 7 micron/min for a mixture of SF6 and oxygen. The surface structure can be controlled by adjusting the etch chemistry and the etch rate. PSG etching with rates of about 60 nm/min by use of several carbon fluoride containing etch gases is demonstrated. Silicon nitride films with refractive index of 2.1 and hydrogen content of 10 to 20 % are deposited with rates of up to 300 nm/min.