Strong variation of average ion energy in oscillation frequency of sheath potential

In a modern plasma etching device, the plasma sheath potential is usually s uperposed by an externally driven oscillating voltage to enhance and contro l the bombarding ion energy. A collisionless particle simulation is used to study the variation of average kinetic energy < K >(nu(rf)) of bombarding ions as a function of a wide range of sheath oscillation frequency nu(rf) ( 0.1 nu(pi)less than or equal to nu(rf)less than or equal to 10 nu(pi), wher e nu(pi) is the ion plasma frequency). It is found that a resonance phenome non between the ion transit motion and the sheath oscillation can yield a s trongly peaked enhancement of < K >(nu(rf)) near nu(rf)similar or equal to 0.5 nu(pi). Ion species with different mass show the peaks at different nu( rf). The relative importance of different ion molecules in an ion-enhanced etching process will be sensitive to nu(rf). This phenomenon may allow a re duction of the undesirable capacitive coupling by optimizing nu(rf) to yiel d an enhanced < K > of desired ion species at low applied voltages. (C) 200 0 American Institute of Physics. [S1070-664X(00)03702-2].