Velocity Distribution of Ions Incident on a Radio-Frequency Biased Wafer.

摘要

The ion velocity distribution (IVD) is important in plasma etching of microfeatures. IVD at a rf biased wafer is studied, first analytically using probability theory and then numerically by using a particle simulation method. The analytic expression shows that IVD is governed by the parameter (qVrf/miU)l, where q is the charge of ion, VTf is the rf bias amplitude, uj is the rf bias angular frequency, / is the penetration depth of bias potential, and mi is the mass of ion. The analytical expression is applicable to the case when the ion collisions in the penetration depth are negligibly few and the rf period of biasing is much shorter than the time that ions take in traversing the depth I. The IVDs for general conditions are also examined using the self-consistent particle-in-cell/Monte Carlo simulation.