Electrodeposition of CoWP film: IV. Effect of applied potential and current density

CoWP films were electrochemically deposited on copper-coated silicon wafers from citrate electrolytes containing cobalt sulphate, sodium tungstate and sodium hypophosphite by both potentiostatic and galvanostatic methods and the effects of applied potential and current density on composition and microstructure of the films were studied. Surface compositional analysis using XPS shows that the films contained elemental cobalt, tungsten and phosphorus, cobalt hydroxide, and oxides of cobalt and tungsten. The thickest film with highest amount of cobalt (65 at.%) was obtained at an applied potential of −1.0 V versus AgCl/Cl reference electrode. It was observed that larger variation of compositions (cobalt from 36 to 57 at.%, tungsten from 31 to 59 at.% and phosphorus from 5 to 12 at.%) could be achieved by changing the deposition current density between −1 and −9 mA cm−2. XRD and SEM examinations revealed that the films deposited at low cathodic potentials and current densities were crystalline with larger crystallites, whereas films plated at higher cathodic potentials and current densities were amorphous with smaller crystallites.