REDEPOSITION KINETICS IN FLUOROCARBON PLASMA-ETCHING

The redeposition kinetics of plasma etching products have been measured as a function of ion and free-radical fluxes which are representative of the fluorocarbon etching environment. Silicon and SiO2 surfaces were exposed in a multibeam etching tool to energetic ions (Ar+), etchant radicals (F), and depositing carbonaceous species (CF2), the relative fractions of which were independently varied to alter the etching product distributions. The rate of product redeposition (i.e., the deposition rate on nonbombarded surfaces such as trench or via sidewalls) was measured using a quartz crystal microbalance (QCM) which could be rotated around the etching sample face. While redeposition rates of Ar+ sputtering products from Si and SiO2 were characteristically high, the addition of F suppressed redeposition by nearly an order of magnitude. The mechanisms for this reduction involve the passivation of the nonbombarded QCM surface by atomic F, the chemical etching of the redeposited material, and the production of volatile products which do not readily stick to sidewall surfaces. Redeposition rates during ion-enhanced F etching of Si and SiO2 surfaces are largely determined by the fraction of physical sputtering, which emits unsaturated ''sticky'' products. Accordingly, redeposition rates are observed to increase with decreasing F/Ar+ ratio and increasing ion energy. Addition of CF2 radicals during ion bombardment was observed to suppress redeposition rates measured during pure physical sputtering, but had no significant effect on redeposition in the presence of atomic F.