Laser ablation of AlOx and AlOx/SiNx backside passivation layers for advanced cell architectures

In this paper, we investigate laser ablation of aluminum oxide (AlOx) layers and AlOx/SiNx stacks. This laser ablation process is studied in order to be implemented in back side passivation ablation in PERC-type cell process flow. The objective of this work is to define laser conditions for selectively and locally ablating the layers and reducing the laser-induced damages in the Si and in the passivation layer. In addition, different laser ablation patterns have been tested in order to determine the best ablation conditions to reach high efficiency PERC-type cells. Different laser sources and parameters (pulse duration, wavelength, power...) were tested in order to ablate these layers. The quality of the openings was characterized by optical and electronic microscopies and the laser-induced damages were evaluated by QSSPC-calibrated lifetime mapping. Based on this characterization method, we have processed PERC-type cells with AlOx/SiNx back side passivation with different laser ablation patterns. This work allowed us to determine suitable laser conditions and ablation patterns for reaching higher efficiency for AlOx-backside passivated PERC-type cells.