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Mechanism of Charging Reduction in Pulsed Plasma Etching

Numerical simulations of charging and etching in time-modulated high-density plasmas suggest a new mechanism for the reduction of pattern-dependent charging, which is based on low energy positive ions. During the power-off period and before the sheath collapses, the electron temperature and plasma potential decrease rapidly, resulting in low energy ions which can be deflected by smaller local electric fields. The flux of deflected ions to the upper mask sidewalls increases enabling neutralization of the negative charge accumulated there due to the electron shading effect. Current balance at the trench bottom surface is achieved at lower charging potentials, which lead to significantly reduced notching and gate oxide degradation. Pulsing period and duty ratio are examined as parameters to control the performance of pulsed plasmas.