Etching characteristics of ZnO thin films in chlorine-containing inductively coupled plasmas

Abstract

This study examined the plasma etching characteristics of ZnO thin films etched in BCl 3/Ar, BCl 3/Cl 2/Ar and Cl 2/Ar plasmas with a positive photoresist mask. The ZnO etch rates were increased in a limited way by increasing the gas flow ratio of the main etch gases in the BCl 3/Ar, BCl 3/Cl 2/Ar and Cl 2/Ar plasmas at a fixed dc self-bias voltage ( V dc). However, the ZnO etch rate was increased more effectively by increasing the V dc. Optical emission spectroscopy (OES) and X-ray photoelectron spectroscopy (XPS) analyses of the ZnO surfaces etched at various Cl 2/(Cl 2 + Ar) mixing ratios revealed the formation of the ZnO x Cl y reaction by-products as a result of the increased etch rate with increasing Cl 2 addition, compared with 100% Ar + sputter etching. This suggests that at Cl 2/Ar flow ratios ⩾20%, the ZnO etch process is controlled by an ion-assisted removal mechanism where the etch rate is governed by the ion-bombardment energy under the saturated chlorination conditions.