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

This study examined the plasma etching characteristics of ZnO thin films etched in BCl3/Ar, BCl3/Cl2/Ar and Cl2/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 BCl3/Ar, BCl3/Cl2/Ar and Cl2/Ar plasmas at a fixed dc self-bias voltage (Vdc). However, the ZnO etch rate was increased more effectively by increasing the Vdc. Optical emission spectroscopy (OES) and X-ray photoelectron spectroscopy (XPS) analyses of the ZnO surfaces etched at various Cl2/(Cl2 + Ar) mixing ratios revealed the formation of the ZnOxCly reaction by-products as a result of the increased etch rate with increasing Cl2 addition, compared with 100% Ar+ sputter etching. This suggests that at Cl2/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.