Refinement of electrodeposition mechanism for fabrication of thin nickel films on n-type silicon (111)

Electrodeposition of nickel on n-type silicon surface from sulfate, sulfate-chloride and Watts solutions has been investigated. Cyclic voltammograms obtained from different solutions reveal that nickel reduction is influenced by hydrogen evolution, adsorption of chloride ions and concentration of Ni2+ ions in the electrolyte. Electrochemical nucleation and growth of nickel from different solutions at a distinct deposition potential were monitored by ex-situ scanning electron microscopy (SEM) to determine size of electrodeposited nuclei or nucleation rate as measured by the number of nuclei per surface area. Results show that the size of nuclei formed at the critical time depends significantly upon a number of factors including the presence of chloride ions, pH and Ni2+ concentration in the solution. The addition of Cl- and reduction of pH have the most enhancing effects on the nucleation rate and thus the critical size of stable nuclei, but widen the size distribution of electrodeposited nickel granules. SEM and X-ray diffraction (XRD) indicate that electrodeposition of nickel on n-Si(1 1 1) is always associated with two stages: (i) formation of granules and (ii) coalescence until a continuous film is formed. XRD reveals that the crystallographic structure of nickel films highly depends on the composition of electrodeposition electrolyte, as nickel films electrodeposited from Watts bath at a pH of 2 exhibit a preferential growth orientation along (1 1 1) main Bragg diffraction at low nominal thickness below 50 nm. (C) 2012 Elsevier B.V. All rights reserved.