Compatibility of the alternative seed layer (ASL) process with mono-Si and poly-Si substrates patterned by laser or wet etching

An alternative seed layer (ASL) process is proposed in order to increase the efficiency of silicon solar cells by forming a low cost, front metal contact with reduced contact resistance and increased line conductivity and aspect ratio. A nickel seed layer is deposited directly on silicon to form a low resistivity nickel silicide (NiSi) ohmic contact and this contact is thickened by light induced plating (LIP) of nickel and copper. Unlike the traditional screen printing process currently used in industry, the ARC layer must be patterned to expose the silicon surface for nickel deposition. This paper investigates the compatibility of the ASL process with two different ARC patterning methods: 1) masking & wet chemical etching, and 2) laser ablation. In addition, the ASL process is demonstrated on both mono-crystalline and polycrystalline silicon substrates with ARC layers from different sources. The nickel seed layer and resulting NiSi layer are evaluated using scanning electron microscopy (SEM) with energy dispersive x-ray spectroscopy (EDS) and focused ion beam (FIB) cross section. X-ray photoelectron spectroscopy (XPS) is used to investigate the completeness of the ARC removal step. In addition, contact resistance testing will be performed to determine the quality of the ohmic contact formed from the ASL process. The importance of chemistry optimization in the development of a robust ASL process that is compatible with mono-Si and poly-Si substrates and exposed to two different ARC patterning methods will be discussed.