Research on property and wet etch of ZnO films grown by radio-frequency magnetron sputtering

Abstract

ZnO is a wide band gap semiconductor material and has a large electromechanical coupling coefficient. ZnO has great potential for photoelectronic devices, acousto-optic devices and SAW devices. In this paper, ZnO films were deposited on quartz substrates by RF magnetron sputtering, with depositing and annealing parameters optimized through the orthogonality method. High-purity (99.999%) ZnO target, O2 and Ar were used in the deposition process. Base pressure was 3times10-5 mTorr and sputtering pressure was 10~15 mTorr, O2 and Ar partial pressure ratio was changed according to the flow rate. The influence of substrate temperature, grown atmosphere and annealing on the crystallization of ZnO films were investigated by X-ray diffraction (XRD). Results show that substrate temperature and annealing efficiently reduce FWHM of ZnO (002) peak. In the deposition period of ZnO film, larger O2 partial pressure is availed to improve the crystallization of the films. Deposition parameters for preferred c-axis orientation are: O2 and Ar partial pressure ratio, 1:9; substrate temperature, 400square; sputtering power, 200 W; and deposition time, 30 minutes. ZnO film was annealed in air at 900square for 1.5 hours. Three ZnO diffraction peaks were found: (002), (004) and (103). The intensity of (002) diffraction peak was 2477. Wet etch of ZnO film was also investigated. The proposed etch solution provided a rational etch rate, and a good selectivity between ZnO and resist was observed. Etch profile was measured by Alpha-step 500 profiler. Result shows that etch profile was moderate with little lateral etching activity, according to the request.