Influence of Surface Roughness and Current Efficiency on Composition Gradients of Thin NiFe Films Obtained by Electrodeposition

Abstract

The composition gradients of 5–500 nm thin NiFe films on Cu, Ru, and NiP substrates, obtained by electrodeposition in stirred plating solutions at pH 3.0 on 8 in wafers, were studied. It was found that the average elemental composition of NiFe, determined by ICP analysis, changes during electrodeposition with steep downturns of Fe-content in composition gradient zone near the substrate interface in the thickness range 5–250 nm depending on the electrode substrate (Cu, Ru, and NiP). The extent of anomalous co-deposition achieved at deposit thickness near the substrate (<100 nm) was found to be several times larger than in thicker NiFe films. The partial current densities for metals (Ni, Fe) deposited on Cu-substrates increase during the time of electrodeposition and gives rise to stable values at thickness >250 nm. The partial current density for hydrogen evolution decreases and becomes stable at the thickness>250 nm. The observations related to the experimental results could be explained through a modified Bockris-Drazic-Despic (BDD) reduction mechanism. It was found a strong correlation between the dynamics of surface roughening of NiFe films and the anomalous codeposition inside the composition gradient zone. The decrease of Fe-content with time inside the composition gradient zone-which is a special case of anomalous codeposition- was explained through surface roughening of the NiFe films and the surface H+ concentration dependent competitive adsorption of FeOH+ and NiOH+ electroactive species.