Numerical study of the etch anisotropy in low-pressure, high-density plasma etching

Evolution of etched profiles has been numerically studied during low-pressure, high-density (LPHD) plasma etching of Si in Cl2. The surface etch rates were calculated using a reaction model of synergism between incoming ions and neutral reactants, including the spread of ion angular distributions due to their thermal motions and the transport of neutrals arising from the reemission on surfaces in a microstructure. Etched profiles were then simulated using a so-called two-dimensional string algorithm to examine the effects of ion temperature kTi and energy (or sheath voltage) eVs on the etch anisotropy for different neutral-to-ion flux ratios Γn/Γi toward the substrate. Numerical results indicated that in typical Cl2 LPHD plasma etching environments, where the neutral-to-ion flux ratio is Γn/Γi∼1 and the ratio of sheath voltage to ion temperature is eVs/kTi∼100, the chlorinated surface coverage is microscopically nonuniform in etched features: The coverage is very low at the bottom (α∼0.1), whereas the sid...

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