Sheath collision processes controlling the energy and directionality of surface bombardment in 0 sub 2 reactive ion etching.

The effect of sheath collision processes on the energy and directionality of surface bombardment in reactive ion etching is modeled. Although the methods used are generally applicable, all the numerical examples are for a low pressure high frequency oxygen plasma. Charge transfer is shown to be the dominant process controlling bombardment energies. The effect of momentum transfer collisions on bombardment energies is shown to be negligible under the conditions considered. Equations are derived for the average energy ions and neutrals, the average ion energy, the average neutral energy, and the ion energy distribution function. The average ion velocity at a point in the sheath is related to the voltage distribution by an equation that provides a rigorous basis for a self consistent theory of the sheath voltage distribution. These equations are generally applicable to high frequency, low pressure plasmas where charge transfer is the dominant collision process.