Dry Etching Characteristics of Zinc Oxide Thin Films in Cl2-Based Plasma

Abstract

We investigated the etching characteristics of zinc oxide (ZnO) and the effect of additive gases in a <TEX>$Cl_2$</TEX>-based inductively coupled plasma. The inert gases were argon, nitrogen, and helium. The maximum etch rates were 44.3, 39.9, and 37.9 nm/min for <TEX>$Cl_2$</TEX>(75%)/Ar(25%), <TEX>$Cl_2$</TEX>(50%)/<TEX>$N_2$</TEX>(50%), and <TEX>$Cl_2$</TEX>(75%)/He(25%) gas mixtures, 600 W radiofrequency power, 150 W bias power, and 2 Pa process pressure. We obtained the maximum etch rate by a combination of chemical reaction and physical bombardment. A volatile compound of Zn-Cl. achieved the chemical reaction on the surface of the ZnO thin films. The physical etching was performed by inert gas ion bombardment that broke the Zn-O bonds. The highly oriented (002) peak was determined on samples, and the (013) peak of <TEX>$Zn_2SiO_4$</TEX> was observed in the ZnO thin film sample based on x-ray diffraction spectroscopy patterns. In addition, the sample of <TEX>$Cl_2$</TEX>/He chemistry showed a high full-width at half-maximum value. The root-mean-square roughness of ZnO thin films decreased to 1.33 nm from 5.88 nm at <TEX>$Cl_2$</TEX>(50%)/<TEX>$N_2$</TEX>(50%) plasma chemistry.