High-selectivity plasma etching of silicon dioxide on single-wafer etchers

Etching of silicon dioxide with CHF3 /CF4 chemistry has been investigated on single-wafer etchers with both high-frequency and low-frequency plasma discharge. A simple kinetic model emphasizing surface reaction and desorption is proposed to explain the selectivity mechanism, polymer control, and process trends. A reproducible single-step plasma etch process with a high selectivity of thermal oxide to polysilicon is then developed employing effective temperature controls on both electrodes as well as the wafers being etched. It is demonstrated that the plasma etching mode is capable of etching submicron geometries.