Dry processing of silicon solar cells in a large area microwave plasma reactor

We report a dry Si solar cell process that replaces all wet chemistry by various microwave-excited plasma treatments. The key steps are: (i) SF6 plasma etching to clean the wafer prior to the emitter diffusion, (ii) CHF3 plasma etching to remove the phosphor silicate glass (PSG) after diffusion, (iii) SF6 plasma treatment for mesa etching of the emitter, and (iv) the plasma deposition of an antireflection coating. We also avoid wet chemistry during the metallization. The best completely dry-processed float-zone Si cell shows a power conversion efficiency of 14.7%. The wet-processed reference has an efficiency of 15.1%.