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

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.