Aspect ratio dependent metal etching studied for high density plasmas

Aspect Ratio Dependent Etching (ARDE) is an important issue in etching deep sub-micron metal interconnect structures. ARDE describes the observation that the etch rate depends on the aspect ratio (depth:width) of the microstructure. A model has been built to account for the ARDE behaviour in a high density plasma etcher. This model is based on chemical surface etch reactions and etch inhibitor deposition versus desorption processes. These processes depend on chemical reaction-and desorption rates as well as on the aspect ratio dependent reactant and inhibitor flux. Good agreement is found between experimental and model data. The model can account for the inverse RIE lag at low aspect ratios and normal RIE lag at high aspect ratios. Inverse RIE lag increases with an increase in process pressure and a decrease in gas flow. Inverse RIE lag results, like sidewall tapering, from etch inhibitor deposition on the wafer surface.