Deposition of gold from an organic immersion plating bath for microelectronic applications.

摘要

A novel process utilizing an organic immersion plating bath (OIPB) was developed for depositing gold films onto nickel films by a galvanic displacement reaction. The bath was prepared with poor electrically conductive organic solutions that are commonly used for the liquid-liquid extraction of metal ions from aqueous solutions.;The objectives of this study were to identify bath parameters that would result in the deposition of uniform, continuous gold films. The parameters investigated included: gold concentration (0.1 to 3.0 g/L); amount of metal extractant (1.7 to 50 vol. %); type of metal extractant; type of diluent; deposition time (0.5 to 30 minutes); and deposition temperature (20 to 40°C). The effect various additives (HCl, H2SO4, KC1, water, glacial acetic acid, acetone, decanol, methanol) and sparging gases (N2, 5%H2/Ar forming gas, compressed air) had on the morphology of the deposited gold films was also considered.;It was found that the type of metal extractant and diluent had a substantial effect on the morphology of the deposited gold film; an addition of HC1 to the OIPB was required to obtain gold films composed of uniform gold particles. The deposition rate was self-limiting which is characteristic of a galvanic displacement reaction. First-order reaction rate constants were determined; the reaction rate was found to be mixed chemical/diffusion controlled.;Characterization of the deposited gold films demonstrated that they were crystalline and composed of nanometer sized particles. Furthermore, it was found that the gold films were typically 18-35 nm thick and composed of pure metallic gold with no co-deposited nickel or carbon detected in the gold film.