2. Experiment details
SnO2 thin films were deposited by PEALD (iSAC Co. Ltd., iOV d100) on Si (100) wafers between 150 and 350 °C using SnCl4 (Mecaro Co. Ltd., 99.995%) and O2 (99.999%) plasma. One deposition cycle of PEALD-SnO2 consists of a SnCl4 pulse, an Ar (99.999%) purging, a 20 sccm O2 plasma and a second Ar purging. Each purging process lasted for 10 sec to allow for a sufficient exhaust of residual gases and physisorbed precursors. During the SnCl4 pulse, the precursor with high vapor pressure was remained at room temperature, was supplied to the chamber with a 20 sccm Ar gas. A radio frequency plasma was used at powers from 100 to 400 W. The deposition pressure was 3 Torr, and 100 sccm Ar gas was continuously supplied to the chamber during the PEALD process.
The thickness and refractive index (nr) of thin films were measured by ellipsometer (J. A. Woollam, alpha-SE) at 632.8 nm, and the film crystallinity was analyzed by grazing incidence X-ray diffraction (GIXRD, Rigaku, Ultima IV) using Cu Kα radiation (λ=0.15405 nm) with an incident angle of 1.5°. The density and composition of the film were measured using Rutherford backscattering spectroscopy (RBS, NEC) using He2+ion with 2 MeV energy. The electrical properties of the films deposited on Corning XG glass were investigated by the van der Pauw method using Hall-effect measurement (Ecopia/HMS-3000). The corrosion potential (Ecorr) and corrosion current density (icorr) of the films on SS316L were measured by a potentiodynamic polarization test using an electrochemical workstation (Princeton, VersaSTAT 4) and a conventional three-electrode cell in 3.65 wt% NaCl solution [12]. For a precise analysis, all the chemical and physical properties such as crystallinity, composition, electrical properties, and corrosion properties were conducted to 40-nm-thick SnO2 samples through careful control of the number of repeated deposition cycles.