Study on Effects of Hydrogen Flow Rates on the Properties of ZnO Thin Film Deposited by Facing Targets Sputtering System

Abstract

Zinc oxide (ZnO) thin film was synthesized using the low processing temperature facing targets sputtering (FTS) system with change in the low and high H2 gas flow rates. In this study, an FTS system was adopted, in which the substrate is significantly less thermally damaged by impinging high-energy particles due to the confining magnetic field between the two facing magnetron sources. To monitor the process condition, the substrate temperature change was monitored and an optical emission spectroscopy (OES) diagnostic was performed. According to the structural property analysis, the grain size and crystallization had not changed significantly at a low H2 flow rate change. The grain size is 15.27–17.97 nm at a low H2 flow regime (O2: 0.4 sccm, H2: 0–1.0 sccm) and 16.85–21.36 nm at a high H2 flow regime (O2: 6 sccm, H2: 0–30 sccm). In optical property analysis, the transmittance is over 87% and the optical band gap increased with blue shift from 3.22 to 3.28 eV at a high flow regime. X-ray photoelectron spectroscopy (XPS) analysis showed that the OH/ZnOx ratio changed from 0.605 to 0.694 at a low H2 flow regime and from 0.386 to 0.554 at a high H2 flow regime. Sheet resistance changed from 100 to 10-3 MΩ/sq. with an H2 flow rate at a low H2 flow regime and from 107 to 8×10-2 MΩ/sq. with an H2 flow rate at a high H2 flow regime. From the results, it is suggested that the H2 flow rates could act as an effective control of the electrical property of the ZnO thin film.