Immersion Deposition of Metal Films on Silicon and Germanium Substrates in Supercritical Carbon Dioxide

Abstract

A low-temperature CO2-based technology, supercritical fluid immersion deposition (SFID), has been developed for producing Pd, Cu, Ag, or other metal films on Si-based substrates in supercritical CO2 solutions. The reaction is most likely initiated by oxidation of elemental silicon to SiF4 or H2SiF6 with HF, causing the reduction of a metal chelate precursor to the metallic form on silicon surface in CO2. Using this method, only the substrate surfaces exposed to CO2 solutions are coated with metals, and the metal films (Pd, Cu, and Ag) exhibit good coverage, smooth and dense texture, and high purity. Preliminary experiment indicates that palladium films deposited on silicon by SFID can be converted to palladium silicide by annealing treatment. Metal films can also be deposited onto germanium substrates using SFID. The gaslike properties and high pressure of the supercritical fluids, combined with the low reaction temperature, make this SFID method potentially useful for fabricating thin films of metal or metal silicide in small features, which is difficult to accomplish by conventional metal deposition methods.