Kinetics of photoresist etching in an electron cyclotron resonance plasma

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Abstract
An electron cyclotron resonance plasma processing system was used to etch hardbaked KTI‐820 photoresist from single crystal silicon wafers, silicon dioxide films and patterned multilayer structures. Etch rates of 1500 nm/minute were observed at a substrate temperature below 373 K in a Pforward=750 W, 0.13‐Pa ECR oxygen plasma with no applied substrate bias. The etch rate increased linearly with increasing power from Pforward=300–750 W. Etch rate was a complicated function of pressure and residence time, but a modified adsorption‐reaction‐ion‐stimulated desorption rate expression could be used to fit the data. Etch rates decreased for increasing oxygen residence time at low operating pressures due to a combination of polymeric film formation of reaction products and reactant (atomic oxygen) depletion. Maximum etch rates were observed at approximately 0.13 Pa for all residence times. Multilayer photoresist structures were etched at various pressures as well as at a 45° angle to the incident plasma stream. Etch profiles for the variable angle runs indicated that the etch rate was strongly dependent on ion flux. Etch anisotropy increased with decreasing pressure, consistent with increased ion bombardment energy. The degree of anisotropy was, however, limited due to a non‐normal component of ion energy, which has been interpreted previously as an ion temperature.