CONTROL OF ION ENERGY IN A CAPACITIVELY COUPLED REACTIVE ION ETCHER

The energy of ions bombarding the wafer is proportional to the potenti al difference between the plasma and the powered electrode in reactive ion etching systems. This work seeks to control the ion energy withou t altering the applied radio-frequency power or the chamber pressure s ince these variables are closely tied to other important quantities, s uch as reactive chemical species concentrations in the plasma and wafe r etch uniformity. a variable resistor placed in parallel with the blo cking capacitor allows the plasma self-bias voltage (V-bias) to be arb itrarily varied between its nominal value and zero. Optical emission s pectroscopy for a CF4 plasma reveals that the nominal plasma chemical concentrations do not change under this control method. The use of a L angmuir probe to measure the plasma potential shows that the ion energ y changes by approximately one-half of the change in V-bias. The poten tial uses of this ion energy control technique to plasma self-bias vol tage regulation, etch selectivity, and plasma cleaning of chamber wall s are demonstrated. A potential drawback, namely, decreased plasma sta bility, is also indicated.