Plasma Enhanced CVD and Plasma Chemical Etching at Atmospheric Pressure for Continuous Processing of Crystalline Silicon Solar Wafers

摘要

Atmospheric pressure plasma technologies are a potential substitution for wet chemical and vacuum processes for production of crystalline silicon solar cells, leading to a simplified in-line processing chain. Plasma chemical etching and deposition technologies are developed as a basis for a future continuous production process. At Fraunhofer IWS a linearly extended DC are discharge and a microwave plasma source are used for activation of the processing gases. An Ar-N_2 mixture is fed through the plasma source; etch gases or precursors are injected into the activated plasma gases outside of the plasma source, near the substrate. Controlled purge gas systems prevent the contamination of the reaction zone with air or moisture as well as the release of reaction products. Etching rates up to 12 μm/min are realized; in dependence of etch gas composition and plasma conditions. The texture of the wafer surface can be controlled; on nano-structured Si surfaces the diffuse reflection was reduced to 10 %. First industrial tests confirmed standard efficiencies of cells after edge isolation by atmospheric pressure plasma etching. Passivation properties of silicon nitride layers are comparable to low pressure PECVD reference films.