Electroless Deposition of CuNiP Alloys onto Silicon Surfaces

Abstract

We have investigated electroless deposition of CuNiP alloys onto silicon wafer surfaces. Initially, surfaces were pre-activated in a diluted hydrofluoric acid solution containing PdCl2. Following, it was used an alkaline chemical bath having NiSO4, CuSO4, Na2HPO2, Na3C6H5O7, NH4Cl and NH4OH as constituents diluted in DI water. The concentration of copper salt in the deposition solution greatly affects the Cu content of the CuNiP deposits and thus the Ni and P contents. A procedure to extract the film stoichiometry is presented and good quality CuNiP alloys were obtained. Areal concentration and composition were measured by Rutherford Backscattering Spectrometry (RBS) and surface morphology was characterized by Atomic Force Microscopy (AFM). For the studied range of CuSO4 concentrations, it was inferred that the sparsely distributed sites of Pd on Si act predominantly as local catalysts for Cu (and not for Ni) deposition and, therefore, "Cu islands" are being formed at these sites and its deposition far from them is not eased because the Ni concentration was chosen at least fifty times higher than the Cu concentration. As a result, Ni deposition dominates far from Pd sites, possibly, as a layer-by-layer deposition.