EXPERIMENTS WITH BACK SIDE GAS-COOLING USING AN ELECTROSTATIC WAFER HOLDER IN AN ELECTRON-CYCLOTRON-RESONANCE ETCHING TOOL

Wafer temperature, etch rate, and etch uniformity measurements of SiO2 wafers were made to characterize the use of back side helium cooling with an electrostatic wafer holder in an electron cyclotron resonance etching tool. The etch rate was found to be independent of the wafer t emperature in the range between 20 and 110-degrees-C. A 7% increase in etch nonuniformity (3sigma) at higher backside pressures was attribut ed to helium, which leaked around the edge of the wafer, displacing th e etchant gas. A back side pressure of 2-3 Torr provides a balance bet ween wafer temperature control and helium leak rates.