Electrochemical study of the electroless deposition of Co(P) and Co(W, P) alloys

In this article, the results of the electrochemical investigation of the electroless Co alloy deposition systems for barrier/capping layer of copper interconnects means are presented. The sulfate baths for electroless deposition of Co-P and Co-W-P were studied. Pourbaix's diagrams for various aqueous systems were calculated to estimate thermodynamic capability of the electroless Co-alloy plating. Cobalt-, cobalt complex-, and tungstate-hypophosphite aqueous solutions at the working conditions were taken into account. Two plating solutions of Co-W-P with different tungsten source were investigated. Electrochemical study of the partial reactions of reducer oxidation and metal ions reduction using electroless plated Co-P and Co-W-P electrodes was carried out. In situ mixed potentials of the process for different electrolytes were measured. The deposition rate of cobalt alloys was measured gravimetrically. The test of the mixed potential theory was performed by comparison between direct experimental values of the mixed potential and deposition rate with those derived theoretically from the current-potential curves for partial reactions. The film composition was determined by using X-ray photoemission spectroscopy measurements.