Ion bombardment energy and SiO2/Si fluorocarbon plasma etch selectivity

Abstract

The role of ion bombardment in the plasma etch selectivity of silicon dioxide to silicon has been investigated in a CHF3/H2 plasma using a method that produces a narrow ion energy distribution (IED) at the substrate surface. The effects of the narrow IED is compared with the broad, bimodal IED produced by the conventional sinusoidal bias voltage wave form (at 5 and 20 MHz). A comparison of the etch rate versus the average ion bombardment energy shows a higher ion energy threshold for etching, a larger gap between the thresholds for the two materials, and a high selectivity over a wider range of bias voltage with the narrow IED. A physical explanation of the observed phenomena is proposed. Additionally, reported models of the reactive sputter etch rate as a function of ion energy are used to show that the etch rate in this regime is higher for a narrow IED than for a broad one.