Influence of ultrasound and cathode rotation on formation of intrinsic stress in Ni films during electrodeposition

Abstract

The influence of 25 kHz ultrasound and cathode rotation during electroplating of Ni films on Si wafers has been studied with respect to intrinsic stress formation. Current densities from 1·6 up to 28·3 A dm⁻² were used in an additive free Ni sulphamate electrolyte. In general, more efficient agitation by either ultrasound or cathode rotation was found to reduce intrinsic stress towards compressive levels compared with conventional agitation with an electrolyte circulation pump. Furthermore, intrinsic stresses become less dependent on changes in current density. The latter effect is most pronounced for ultrasonic agitation. Structure analysis of samples deposited by ultrasonic agitation shows dense deposits with initially smaller grains at high ultrasonic effect. Locally increased temperature at the substrate surface could be an important effect of ultrasound agitation.

Keywords:

• Intrinsic stress
• Electrodeposition
• Ultrasound
• Nickel
• Electroforming

The authors acknowledge the Ultraplate project (no. GRD1-2000-25735) under the European Commission and the Institute doctoral programme at the Swedish Knowledge Foundation for financial support.