Kinetics modeling and 3-dimensional simulation of surface roughness during plasma etching

[摘要] (cont.) The kinetics of SiO2 etching in C4Fs/Ar plasma was first developed in a similar fashion to that for poly-Si etching, with the additional assumption of equal reaction rates among all ionic or neutral radicals. All the ionic and neutral species experimentally measured were taken as inputs and the etching yield were predicted over a range of neutral-to-ion flux ratios and ion energies. Angular dependence on etching yield was also modeled to take into account the etching at off-normal angles. Then the kinetics was incorporated into the 3-D simulator and a good match was found between the experimental and profile simulation results in terms of etching yield and surface composition at various conditions, suggesting the kinetics after incorporation is capable of predicting complex surface chemistry of oxide substrate with fluorocarbon plasma. Then SiO2 surface roughness was simulated as functions of ion bombardment angle and neutral-to-ion flux ratio. The surface patterns, preferential orientation with respect to the ion beam and spatial frequency of the simulated surface showed a qualitative match with the experimental observations. The transition from coarsening to smooth surface with the increase of neutral-to-ion flux ratio was captured and related to the extent of polymerization on the surface. At low neutral-to-ion flux ratio, the modeled surface composition contour confirmed the formation of polymer islands around the roughened area, leading to etching inhomogeneity on the leading and shadowing side of features. The formation of polymer patchiness according to the simulation verified the polymer-induced micro-masking mechanism people proposed mechanistically to explain roughening on dielectric films. At high neutral-to-ion flux ratio, the simulation showed a higher extent of polymerization and yet the polymer deposit fairly uniformly and result in a smooth surface. The 3-D simulator coupled with detailed kinetics provided insights to the surface roughening mechanism on a microscopic basis.

[发布机构] Massachusetts Institute of Technology