Alkaline Polishing for PERC and TOPCon

Details

The alkaline polishing system combines several process steps into a modular system. On the one hand, the emitter layer on the rear side of the wafer, which is grown during the diffusion process, will be single-sided isolated from the front and on the other hand, the rear side of the cell is smoothed and prepared for a perfect surface passivation.

The machine can be converted at any time for the TOPCon process. This means that the doped glass on the front side is not removed for the TOPCon process. For the PERC process, the doped glass (PSG/BSG) on the front side will be removed. So, each PERC system is easily convertible into a TOPCon-ready production system.

Potassium hydroxide solution (KOH) is used instead of the expensive acid. The obvious advantages: No nitrogen oxide (NOX) is generated, which requires a complex exhaust and a subsequent costly disposal. This allows for easy compliance of increasingly strict environmental requirements. In addition, processing at approx. 80-90°C ensures a high Etching rate and a reduction of the footprint of the system with high throughput. During the edge isolation/polishing process, the emitter is protected by a water mask developed and patented by SCHMID.

Specially developed transport rollers ensure that the etching medium only wets the back of the cells, which leads to a reduction in chemical consumption. In addition, all necessary processes for polishing take place in one and the same machine. This makes it possible to dispense with further machinery with the associated automation and carriers.