Thermal dry-etching of copper using hydrogen peroxide and hexafluoroacetylacetone

A new thermal dry etch process for copper (Cu) is reported which results in isotropic removal of Cu at high rates, does not involve the use of halogens such as chlorine, and results in formation of a volatile etching product. Applications include cleaning of chemical vapor deposition reactors and the back-side of wafers. The process involves oxidation of copper by hydrogen peroxide (H2O2) vapor to form either copper(I) or copper(II) oxide depending on the etch temperature and removal of the copper oxides by reaction with hexafluoroacetylacetone (hfacH) to form volatile copper(bis-hexafluoroacetylacetonate) (Cu(hfac)(2)) and water. Copper was etched at temperatures as low as 150 degrees C and at rates of up to similar to 1 mu m min(-1) at 190 degrees C by simultaneous flow of H2O2 and hfacH over a heated substrate. The etch rate increased with substrate temperature, etchant flow rates, and chamber pressure over the range of the parameters studied. The rate-limiting regime was identified by observing the film color during etching; a dark-brown color suggested fast oxidation with slow removal of copper oxide as the rate limiting step while a copper color suggested fast removal of copper oxide from the surface with oxidation as the rate-limiting step. The partially etched copper films were less reflective and exhibited higher surface roughness compared with the sputter-deposited copper used for etching.