Copper deposition onto silicon by galvanic displacement: Effect of Cu complex formation in NH4F solutions

Copper was deposited onto rotating Si substrates by galvanic displacement in 6.0M NH4F to determine the effects of Cu complex formation on deposition rates. Deposition rates decreased with increasing rotation speed, indicating that Cu(I) intermediates, stabilized by NH3, diffuse away from the Cu surface before they reduce to Cu(0). UV–visible spectra of contacting solutions and direct measurements of mass changes resulting from Cu deposition and Si removal confirmed this proposal. These findings contrast those reportedpreviously for deposition fromHF solutions, inwhichCu(I) species are unstable and reduce rapidly to Cu(0). These data andmixed-potential theorywere used to develop a reaction-transportmodel alvanic displacement lectroless deposition pen-circuit potential (OCP) otating-disk electrode etallization that accurately describes the effects of mass transfer and electrochemical reaction rates on Cu deposition dynamicsandopen-circuitpotential (OCP)values. Theeffectsof ascorbic acidand tartrateadditivesonfilm properties and formation rates were also examined. Cu reduction kinetics decreased significantly when ascorbic acid (0.01M) was present. Adhesion of Cu films was improved when ascorbic acid was used, but internal stresses caused films to distort when their thicknesses exceeded 100nm. Adding potassium sodium tartrate to solutions containing ascorbic acid decreased film stresses and led to robust films with excellent adhesion.