Characterization of electroless nickel as a seed layer for silicon solar cell metallization

Electroless nickel plating is a suitable method for seed layer deposition in Ni-Cu-based solar cell metallization. Nickel silicide formation and hence contact resistivity of the interface is largely influenced by the plating process and annealing conditions. In the present work, a thin seed layer is deposited from neutral pH and alkaline electroless nickel baths which are annealed in the range of 400-420(a similar to)C for silicide morphology and contact resistivity studies. A minimum contact resistivity of 7 m Omega cm(2) is obtained for seed layer deposited from alkaline bath. Silicide formation for Pd-activated samples leads to uniform surface morphology as compared with unactivated samples due to non-homogeneous migration of nickel atoms at the interface. Formation of nickel phosphides during annealing and the presence of SiO2 at Ni-Si interface creates isolated Ni2Si-Si interface with limited supply of silicon. Such an interface leads to the formation of high resistivity metal-rich Ni3Si silicide phase which limits the reduction in contact resistivity.