Etching of SiO2 in C4F8/Ar plasmas. II. Simulation of surface roughening and local polymerization

In this article the SiO2 surface morphology in C4F8/Ar plasma etching was simulated using a three-dimensional Monte Carlo profile simulator. The complete surface kinetics model was previously developed, incorporated, and tested for accuracy within the simulator as reported in the companion paper [Guo et al., J. Vac. Sci. Technol. A 28, 250 (2010)]. The simulated planar surface roughening at ion incidence angles from 0 degrees to 82 degrees and flux ratios of 5 and 20 were compared to the experimental results that were etched in reactive ion beam experiments and characterized by atomic force microscopy. Distinctively different patterns were obtained with varying ion incidence angle. The surface remained smooth at normal ion incidence up to 45 degrees off-normal and transformed to striations perpendicular to the ion beam at 60 degrees-75 degrees. The transverse striation was explained with the local curvature dependence based on the sputtering theory. The surface became smooth again at grazing angle of 82 degrees. The simulated transition of surface morphology was qualitatively consistent with the experimental observations. Surface composition was mapped out to disclose the roughening mechanism. At low flux ratio, the surface composition indicated the formation of polymer islands around the roughened area. Greater polymer formation on the shadowed edge of features and enhanced the roughening, in agreement with the micromasking mechanism proposed previously based on other experimental observations. At high flux ratio, the simulation showed a higher extent of polymerization with a uniform distribution. The surface passivation together with other factors led to a smooth surface. The simulated polymer distribution provided insights to the surface roughening process. (C) 2010 American Vacuum Society. [DOI: 10.1116/1.3290766]