MECHANISM OF CHARGING REDUCTION IN PULSED PLASMA-ETCHING

Numerical simulations of charging and etching in time-modulated high-d ensity plasmas suggest a new mechanism for the reduction of pattern-de pendent charging, which is based on low energy positive ions. During t he power-off period and before the sheath collapses, the electron temp erature and plasma potential decrease rapidly, resulting in low energy ions which can be deflected by smaller local electric fields. The nux of deflected ions to the upper mask sidewalls increases enabling neut ralization of the negative charge accumulated there due to the electro n shading effect. Current balance at the trench bottom surface is achi eved at lower charging potentials, which lead to significantly reduced notching and gate oxide degradation. Pulsing period and duty ratio ar e examined as parameters to control the performance of pulsed plasmas.