A novel approach for single side wet chemical polishing of crystalline silicon solar cells
Single side etching processes, e.g. parasitic emitter etch and single side etching, are steps used in the fabrication of high efficiency solar cell concepts. For cost reduction the combination of process steps is preferable. Because chemical treatments produce reactive gases that are able to damage structures like the front side emitter, single side polishing needs to be done before the emitter diffusion. Due to this fact and ineffective exhausting systems, the combination of the emitter etch and the single side polishing step have not been achieved yet. Another factor influencing the etching is the shading of the etched surface due to the transport system or gas bubbles sticking between the wafer surface and the etching solution. With a newly developed single side etching tool the shading and the emitter damage has been reduced due to a novel transport system, a fluid flow concept and a high-performance exhaust system. Damage to the front side of the wafer due to reactive gasses produced during the etch process was investigated and the performance of the new exhaust system was tested. With etching mixtures containing different amounts of HF, HNO3 and H2SO4 when combined with the improved exhaust system, it was possible to limit the emitter damage while raising the etching rate. The fluid flow system in combination with the new transport system led to a homogeneous surface without shading effects. In addition the mechanism of fluid wraparound to the front side of the wafer was investigated.