Low Temperature Cu Etching Using CH4-Based Plasmas

Methane-(CH4) based subtractive plasma etching of Cu was investigated at low temperature. The Cu etch rate using a CH4 plasma (17 nm/min) was higher than that of an H-2 plasma (13 nm/min) under the same plasma conditions, despite the fact that hydrocarbon deposition was evident with CH4. The higher Cu etch rate is ascribed to increased momentum transfer due to the heavier mass of CH+ and C+ relative to H+ and to the more thermodynamically stable etch products of CH3Cu or CH3CuH- relative to CuHx. Methyl-containing Cu etch product species were not detected by optical emission spectroscopy, most likely because Cu-CH3 was readily dissociated by energetic electron impact collisions after desorption from the Cu surface. Patterns generated in Cu displayed a sidewall angle of similar to 80 degrees, similar to that of H-2 plasma patterning, but unlike the result in an H-2 plasma, a photoresist mask was not significantly degraded during the etch process. (C) 2013 The Electrochemical Society. All rights reserved.