Adhesion studies of magnetron-sputtered copper films on chemically etched nickel substrates: Effects of the concentration and the temperature of the bath

Abstract

The adhesion strength of sputtered copper films to chemically etched nickel substrates has been studied using the scratch adhesion test. The effects of the concentration and the temperature of a nitric acid bath were investigated and it was found that the critical load was very weak unless the amorphous layer produced by mechanical polishing on the substrate surface was eliminated. A chemical etching at room temperature in a nitric acid bath was shown to have only a slight efficiency in the enhancement of the adhesion, whatever the bath concentration was. High critical loads could be obtained when the temperature of the bath was increased to 80 °C. Above this temperature, the critical load enhancement was largely lost. At room temperature, the addition to the bath of small quantities of nickel sulphate (1 gl −1) gave a strong increase in the values of the critical load. A larger addition of sulphate led to poorer results. The roughness of the etched surface was measured with a profilometer and observations were made by scanning electron microscopy. It was observed that, as a general rule, the critical load increases with increasing surface roughness. However, a very important factor in the adhesion strength seems to be the morphology of the surface.