On the Reactivity of Silicon Nitride during the Electroless NiP Deposition for the Front Side Metallization of Crystalline Silicon Solar Cells

Narrow metallic structures to collect photocurrent in solar cells can be fabricated by copper electroplating and implementation of a barrier layer to prevent copper diffusion. Such barriers can be formed from electrolessly deposited Ni layers. In this work, the conditions to selectively deposit NiP on top of Si laser-patterned lines are investigated. With the conventional HF preclean, Pd activation and electroless reaction, parasitic deposition is observed on the surrounding insulating SiNx layer, activated by superficial Si-H bonds. An oxidizing treatment using Caro's acid is successfully introduced prior to Pd activation, yielding structures suitable for further integration with copper electroplating.