Development and demonstration of a high throughput junction isolation process using picosecond lasers
Reduction of isolation groove depth due to less emitter drive-in when using ultra-short pulse lasers and thus a reduction of the impact on cell integrity
High throughput of 2000 wafers/h and throughput improvement by 25% compared to state-of-the-art
Main Project Achievements During the project junction isolation on the front side using various laser sources was studied. The focus was on ultra-short pulse lasers, which allow more shallow grooves. It was found that the groove depth can be reduced to 10 µm (instead of 25 µm for standard nanosecond isolation). However, laser isolation on the front side cannot compete with state-of-the-art single-sided etching, which has become state-of-the-art in recent years.
New back-contact cell concepts, like Solland's Sunweb MWT cell, require a laser isolation step on the rear side, which can only be realized using laser irradiation. This process was investigated using picosecond lasers. Good isolation was achieved with groove depth of about 10 µm at processing times of four seconds. This long processing time is due to the low volume removal rate of ultra-short pulse lasers (compared to nanosecond lasers). Benefits compared to the current production process in terms of improved groove quality and reduced depth using nanosecond lasers were not found. When going to considerably thinner cells (<100 µm) the picosecond process could be of interest again, because more shallow grooves are sufficient and laser-induced damage can thus be reduced.