UV fs-Laser System Pre-Evaluation for Passivation Layer Ablation

Abstract

In this work the laser ablation process on silicon nitride (SiNX) and silicon oxide (SiO2 / SiNX) layers using ultra-short pulses from 250 femtoseconds (fs) up to 4 picoseconds (ps) for infrared (IR), visible (VIS) and ultraviolet (UV) wavelength was investigated. Studies on re-passivation behavior of ablated areas with SiN X and screen printed aluminum (Al), lifetime reduction due to laser damage and laser spot size have been carried out. An unexpected non linear trend for spot sizes in the D2 versus ln (EP) plot for fs-pulses in the VIS and UV wavelength was observed just like a trend reversal in the statistical models comparing laser damage for fs-pulses between VIS and UV wavelength. A residual was observed in the ablation spot center which occurs only for UV wavelength in combination with very short pulses where the formation can be observed only on single SiN X but not on SiO2 / SiNX layers. Furthermore a difference in the re-passivation behavior with Al and SiNX is demonstrated and laser opened PERC solar cells without any damage etch have been processed showing results comparable to an etching paste opened reference group.