Chemical Fluid Deposition of Metals from Supercritical Fluids

Chemical Fluid Deposition (CFD) involves the chemical reduction of organometallic compounds in SCFs to yield high purity deposits.[4] Typically, the reaction is initiated upon the addition of H2 or other reducing agent. The advantages of CFD over conventional deposition techniques are a consequence of the unique properties of SCFs, which lie intermediate to those of liquids and gases. Supercritical CO2 (scCO2) has been used in most of the depositions because it is non-flammable, non-toxic and it has convenient critical parameters (Tc=31 oC, Pc=73.8 bar).[5] Furthermore, many organometallic compounds dissolve appreciably in scCO2.[6, 7] The presence of scCO2 facilitates desorption of ligand decomposition products, which reduces contamination of the metal film. Although CFD is a solution-based technique, the transport properties of scCO2 (low viscosity and high diffusivity relative to liquids), the absence of surface tension and its miscibility with gaseous reducing agents such as H2 promote infiltration into complex geometries and mitigate mass transfer limitations common to liquid phase reductions. To date, high purity Pt, Pd, Au, Rh, Ni, Cu and other metal films have been deposited by CFD from scCO2 using appropriate precursors.[1, 2, 8-11] CO2 technology is also under development for other applications in the microelectronics industry [12-14] Nevertheless our technique is not limited to scCO2 and we have deposited Cu films by CFD from supercritical C2F6 (scC2F6)[2] and supercritical CF3H (scCF3H).