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

Highly selective, highly anisotropic, notch-free, and charge-build-up damage-free silicon etching is performed by using Electron Cyclotron Resonance (ECR) Cl₂ plasma modulated at a pulse timing of a few tens of microseconds. A large quantity of negative ions are 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 the selective etching in the pulsed ECR plasma and eliminates charge accumulation on the substrate.