Effects of chloride, bromide and iodide ions on internal stress in films deposited during high speed nickel electroplating from a nickel sulfamate bath

Abstract

The effects of chloride, bromide and iodide additions on the internal stress developed in nickel films deposited during high speed electroplating from nickel sulfamate baths operated close to the nickel ion limiting current density were investigated. The variations in internal strain in the films were detected in situ using a resistance wire-type strain gauge placed on the reverse side of the copper substrate. The film resistance on the as-plated electrodes was measured using an electronic current interrupter technique. The effects of chloride, bromide, and iodide additions could be classified into two groups: (a) chloride and bromide ions, and (b) iodide ions. For chloride and bromide additions over the concentration range of 0.1 to 0.5 M, the nickel deposits exhibited a block- and pyramid-like texture with a (200) crystal orientation. The internal tensile stress developed in 20 μm thick nickel films deposited in the presence of these two halides was as low as 140–170 MPa. Conversely, for additions of iodide, at iodide concentrations greater than 0.1 M the deposited nickel exhibited a fine granular texture of disordered crystal orientation. The internal tensile stress developed in 20 μm thick nickel films deposited from these latter baths tended to rise with increasing iodide concentration to values considerably higher than those observed at similar concentrations of NiCl₂ or NiBr₂.