Oxidation state of cobalt oxide in thermal-cyclic atomic layer etching of cobalt by plasma oxidation and organometallization

Thermal-cyclic atomic layer etching of Co blanket film and a fine pattern by plasma oxidation and organometallization were investigated. To obtain a smoothly etched surface and self-limiting etching, a two-step temperature-etching process was used. Co was first oxidized using O2 plasma at a low temperature of 25 °C. Then, the Co oxide formed in the first step was organometallized with acetylacetone (acacH) and sublimed at a high temperature of 210 °C, which is appropriate for organometallization and sublimation. The etched amount per cycle was 0.6 nm. This value is the same as the saturated oxidation amount. The root-mean-square roughness after 20-cycle etching was 0.53 nm, and an atomically smooth etched surface was obtained. From the x-ray photoelectron spectroscopy (XPS) analysis, the oxidation state of Co oxide with a 530-eV O1s peak was dominant for organometallization with acacH. As the temperature increased, the O1s XPS peak of the Co oxide shifted lower to 529 eV and formed a columnar-shaped oxide. However, with acacH, oxide was organometallized when the O1s peak was at 530 eV.