AFM observation of ITO thin films deposited on polycarbonate substrates by sputter type negative metal ion source

Abstract

Early stages of indium tin oxide (ITO) thin film deposition on room temperature polycarbonate (PC) substrates using d.c. magnetron sputter type negative metal ion source (SNMIS) were investigated by comparing them with those ITO films prepared at same PC substrate by conventional magnetron sputter deposition. The optical and electrical properties were also investigated as they grew from 12 to 150 nm. The electrical resistivity of ITO films decreased with increased thickness. The ITO films prepared by SNMIS had lowest resistivity of 5.1×10 −4 Ω cm, whereas the lowest resistivity of ITO film prepared by conventional magnetron sputtering was 1.3×10 −3 Ω cm. For films deposited by SNMIS, the optical transmittance decreased with thickness from 96 to 84% in visible spectrum, the ITO films showed higher optical transmittance in a visible region than those of the films prepared by a d.c. sputter deposition. According to a result obtained by atomic force microscope, root mean square (RMS) roughness of the ITO films prepared with SNMIS showed remarkable change with increasing thickness initial nucleation at 50 nm and continuous grain growth process at 150 nm in thickness. Whereas in the case of d.c. magnetron sputtering process, RMS roughness was almost constant and the ITO films with thickness of 150 nm were still amorphous. In X-ray photoelectron spectroscopy (XPS) analysis of the ITO films the elements of In, Sn, O, C and Cs are found in the spectra. Although the Cs 3d 5 peak is observed in the typical XPS survey spectrum the Cs concentration was less than 0.1 at.%. In this study, we were able to obtain ITO films (100 nm thick) on the PC substrate with 5.1×10 −4 Ω cm and high optical transmittance of 84% at 550 nm using SNMIS.