Selective laser ablation of SiNx layers on textured surfaces for low temperature front side metallizations

For an alternative front side metallization process without screen printing of metal paste the selective opening of the front surface anti‐reflection coating could be realized by laser ablation. A successful implementation of this scheme requires direct absorption of the laser light within the anti‐reflection coating, since the emitter underneath must not be damaged severely. Additionally, the ablation must be feasible on textured surfaces. In this paper, we show that laser light with a wavelength of 355 nm and a pulse length of approximately 30 ns is absorbed directly by a typical silicon nitride anti‐reflection coating. Based on lifetime measurements on ablated samples it is shown that a damage free laser ablation of SiNx layers on planar surfaces is possible. The characteristic ablation structure on textured surfaces is explained and quantified by rigorous coupled wave analysis (RCWA) simulations. Finally, high efficiency solar cells with a standard emitter (Rsh approx. 50 Ω/sq) have been processed using laser ablation of the silicon nitride anti‐reflection coating. These cells show efficiencies of up to 19·1%, comparable to the reference solar cells using photolithographically opened contact areas. Copyright © 2008 John Wiley & Sons, Ltd. In this paper we discuss the possibility of using laser ablation of a silicon nitride anti‐reflection coating as a key process for a novel low temperature metallization scheme. The characteristic ablation structure on textured surfaces is explained and quantified by RCWA simulations. High efficiency solar cells with a standard emitter (Rsh = 50/sq) have been processed using laser ablation of anti‐reflection coating, which show efficiencies of up to 19.1%, comparable to the reference cells using photo lithographically opened contact areas.