Abstract
The effects of halide anions on the crystal growth, deposition mechanism and internal stress in copper deposits during electroplating from an acid copper sulfate bath were investigated. The cross-section morphology of deposits was observed using a scanning electron microscope, and the internal stress was in-situ measured using a copper electrode with a resistance-wire type strain gauge setup on its reverse side.
The strength of internal tensile stress in a copper deposit of 5μm thick was in the order of F− > no additive > Cl− > Br− > I− in the additive concentration of 50ppm. This order was compared with solubility products of cuprous halide in the plating solution. In particular, chloride ions added in a concentration range of 0 to 200ppm were inclined to make the copper deposits promote epitaxial growth to the crystal orientation of copper substrate, and the internal tensile stress decreased along with an increase in the concentration of chloride ions. Howerver, addition of chloride ions in excess of the solubility products of cuprous chloride always resulted in the precipitation of cuprous chloride onto the copper electrode. Cuprous chloride might bring about the remarkable suppression of cathodic current for copper deposition.
