Helium and Oxygen Plasma Treatment on ZnO Thin Films Fabricated Using Atmospheric Cold Plasma

Abstract

Under atmospheric pressure, homogeneous non-equilibrium barrier discharge was generated stably using high voltage pulsed power (1 kV, 20 kHz) excitation of helium and oxygen gases. Source material Zn-MOPD (2-methoxy-6-methyl-3, 5-heptanedionate Zinc) was fed into this glow discharge cold plasma. Transparent uniform ZnO films about 172 nm of thickness were fabricated on glass slides at the substrate temperature of 400℃. In this paper, we investigate the effects of He and O₂ plasma treatment or He plasma treatment on ZnO thin films. The average transmittance of as-deposited film and the films after plasma treatment was about 90% with wavelengths ranging from 400 to 800 nm. X-ray diffraction measurement revealed that ZnO films had a c-axis oriented poly-crystalline structure. Their crystallinity improved by plasma treatment. By increasing the time of He and O₂ plasma treatment, electrical resistivity increased from 0.50 Ωm to 7.9 Ωm at 60 min. However, by increasing the time of He plasma treatment, electrical resistivity decreased into 0.053 Ωm at 60 min. FE-SEM observations show a change in the grain size of the columnar microstructure of the film. These results suggest that He plasma treatment or He and O₂ plasma treatment change the microstructure of the film and then electrical resistivity changes.