FLOW AND TRANSPORT MODELING OF A LOW-PRESSURE PLASMA-ETCHING SYSTEM

Plasma etching of aluminum-copper alloys is performed at high densities and low pressures (10 mTorr) in a modified parallel plate plasma etching system with a Cl2/BCl3 gas chemistry. In this study, flow modeling is used to characterize the etching environment. The flow distribution and transport of chemical species within the reactor is modeled by the commercially available fluid dynamic software package, FLUENT, to predict metal etch rate and uniformity patterns on 6 in. aluminum wafers. Flow velocity vectors and chemical species distributions are presented. Cl2 is considered as the primary etchant by the single step surface reaction 3Cl2 + 2Al = 2AlCl3. [D. Smith and R. Bruce, J. Electrochem. Soc. 129, 2045 (1982).] A good fit is achieved between the measured etch pattern and the predicted pattern. The etching is determined to be primarily transport limited, with diffusion as the dominant transport mechanism. Theoretical comparisons diffusive to convective transport in this pressure region are made.