BACKSCATTERED DEPOSITION IN AR SPUTTER ETCH OF SILICON DIOXIDE

Detailed mechanisms of sputter etch of silicon dioxide in argon plasma are studied using a novel test structure. We have found that a significant amount of the sputtered material (up to 50% of the sputter flux) returns, as an isotropic backscattered flux to the wafer. This backscattered flux results in significant deposition that cannot be accounted for by redeposition, i.e., line-of-sight deposition of the sputtered material, alone. A profile simulator is used to demonstrate a new physical model for the Ar sputter-etch process, based on the interaction of three simultaneous processes: (1) sputtering, (2) direct (i.e., line-of-sight) redeposition of sputtered material, and (3) isotropic deposition of sputtered material backscattered from the gas phase. Simulated profiles show good agreement with experimental results on the test structure and a common device structure.