Pulse-time modulated plasma discharge for highly selective, highly anisotropic and charge-free etching

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Abstract
Highly selective, highly anisotropic, notch-free and charge-build-up damage-free polycrystalline silicon etching is performed by using electron cyclotron resonance plasma modulated at a pulse timing of a few tens of microseconds. A large quantity of negative ions is produced in the afterglow of the pulse-time modulated plasma. The decay times of electron density, electron temperature and sheath potential are considerably reduced, which is attributable to negative ion generation. Furthermore, the pulse-time modulated plasma reduces the time-averaged sheath potential. As a result of these effects, charged particles in the sheath are strongly modified from the continuous discharge, and they should improve selective etching in the pulsed ECR plasma and elimination of charge accumulation on the substrate.