Effects of CH 4 addition to Ar–O 2 discharge gases on resistivity and structure of ITO coatings

Abstract

It is known empirically that the resistivity of indium–tin–oxide (ITO) coatings is sometimes affected by the base pressure of the process chamber prior to the film deposition. This implies that a small amount of an impurity gas affects the resistivity of the coatings. In this study, to investigate effects of CH 4 addition as an impurity gas to Ar–O 2 discharge gases, ITO films have been deposited in Ar–O 2–CH 4 mixtures onto borosilicate glass substrates by d.c. magnetron sputtering, using a sintered ITO ceramic target with a base pressure of lower than 1.0×10 −5 Pa. By optimizing the discharge gas composition, the film with resistivity of 5.1×10 −4 Ω cm was obtained on an unheated substrate. The addition of CH 4 decreased the film resistivity by more than one order and transmittance in the visible range by a few % under an optimized O 2 condition. Without O 2 in the discharge gas, the films showed more absorption in the visible range and did not provide a low resistivity. Films deposited in Ar–O 2 were crystalline with the 〈111〉 orientation. With the addition of CH 4, films became non-crystalline with a weak and broad peak of (222). The results suggest that the addition of CH 4, producing a higher pressure than the chamber base pressure, may be effective in stabilizing an ITO deposition process.