Effect of Electrolyte Composition on Cu Stripping of Pt Contact Pins in Semiconductor Cu Electroplating Process

Abstract

In Cu electroplating processes, the wet-contact pins are deposited with Cu films. The Pt contact pins should be stripped to remove extra Cu films to maintain contact quality and plating efficiency. However, the stripping behavior is affected by electrolyte composition. The proportion of copper sulphate and sulfuric acid changes the conductivity, pH, and cupric-ion concentration of the electrolyte solution. In this study, an electrochemistry analysis system is employed to characterize the behavior of the Pt stripping process in electrolytes having various electrolyte proportions. It was found that increasing the copper sulphate and sulfuric acid concentrations suppresses the Cu stripping current but enhances the water electrolysis reaction on the Pt surface. Copper sulphate decreased the rate of oxide dissolution and cupric diffusion. The dissolution rate was limited by denser cation layer. Sulfuric acid decreased the dissolubility of cupric ions and suppressed the electrode from releasing more cupric ions. There is no significant influence of additives such as leveler suppressor on the stripping. Minute quantity of HNO3 and H3PO4 were also added to the plating electrolyte. The additional acid HNO3 eliminated the inhibition form dense cupric layer and enhanced the stripping performance without changing the quality of the deposited films during the plating process.