REDEPOSITION KINETICS IN FLUOROCARBON PLASMA-ETCHING

The redeposition kinetics of plasma etching products have been measure d as a function of ion and free-radical fluxes which are representativ e of the fluorocarbon etching environment. Silicon and SiO2 surfaces w ere exposed in a multibeam etching tool to energetic ions (Ar+), etcha nt radicals (F), and depositing carbonaceous species (CF2), the relati ve fractions of which were independently varied to alter the etching p roduct distributions. The rate of product redeposition (i.e., the depo sition 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, t he addition of F suppressed redeposition by nearly an order of magnitu de. The mechanisms for this reduction involve the passivation of the n onbombarded QCM surface by atomic F, the chemical etching of the redep osited material, and the production of volatile products which do not readily stick to sidewall surfaces. Redeposition rates during ion-enha nced F etching of Si and SiO2 surfaces are largely determined by the f raction of physical sputtering, which emits unsaturated ''sticky'' pro ducts. Accordingly, redeposition rates are observed to increase with d ecreasing F/Ar+ ratio and increasing ion energy. Addition of CF2 radic als during ion bombardment was observed to suppress redeposition rates measured during pure physical sputtering, but had no significant effe ct on redeposition in the presence of atomic F.