Effect of Laser Scanning Speed on the Ablation of SiNₓ/ SiO₂ Passivation Stacks for realization of Al local rear contacts in n-PERT RJ Si solar cells

This work investigates the effect of laser scanning speed on the ablation of the SiNₓ/SiO₂ passivation stack for the realization of Al local rear contacts in n-PERT silicon solar cells. For this, SiNₓ/SiO₂ passivation stack was realized on n-type Si wafer. The SiNₓ/SiO₂ passivation stack consisted of a 2-nm-thick SiO₂ layer formed by thermal oxidation in a tube furnace and an 80-nm-thick SiNₓ layer deposited by plasma-enhanced chemical vapor deposition (PECVD). Local openings of the SiNₓ/SiO₂ passivation stack were then performed by laser ablation using a nanosecond (ns) green laser with a wavelength of 532 nm and varying the scanning speed from 800 to 1400 mm/s in increments of 200 mm/s. Optical microscopy showed that the laser-treated surface consisted of both ablated and non-ablated regions. The width of the non-ablated SiNₓ/SiO₂ passivation stack decreases with increasing the laser scanning speed. Scanning electron microscopy (SEM) analysis revealed that laser-induced thermal damage in the ablated regions decreased with increasing the laser scanning speed. Energy-dispersive X-ray spectroscopy (EDS) indicated the presence of traces of residual SiNₓ/SiO₂ passivation stack in the ablated areas. X-ray photoelectron spectroscopy (XPS) analysis showed that the amount of these residual species decreased with increasing laser scanning speed. These results indicate that a complete removal of the SiNₓ/SiO₂ passivation stack requires optimization of additional laser-processing parameters, such as laser power, which will be investigated in future work