Femtosecond vs Nanosecond: An Analysis on the Laser Ablation Properties of Dielectric Layers for Solar Cells

Abstract

This paper reports on the ablation and micro-structuring properties of dielectric layers using a high average power femtosecond and nanosecond laser sources. The dielectrics investigated include SiNx, AlOx/SiNx stack and thermal SiO 2 /SiNx stack deposited on planar n-type silicon wafer. Initially, single pulse ablation properties such as threshold fluence and energy penetration depth were determined for both laser sources. In femtosecond ablation, the presence of two different ablation regimes: gentle and strong ablation was identified. An analytical model has been developed to estimate the line width micro-machined at different pulse spacing. The modelled line width is in good agreement with the experimentally measured values for femtosecond ablation due to negligible debris deposition. As such, for line ablation using femtosecond laser, the reduction in the threshold fluence with respect to pulse overlap ratio has been estimated. These ablation properties are very useful in carrying out precise and low damage structuring of dielectrics for ablation intensive architectures such as interdigitated back contact (IBC) solar cells.