Effects of CH4 addition to Ar-O2 discharge gases on resistivity and structure of ITO coatings

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 CH4 addition as an impurity gas to Ar-O-2 discharge gases, ITO films have been deposited in Ar-O-2-CH4 mixtures onto borosilicate glass substrates by dc. magnetron sputtering, using a sintered ITO ceramic target with a base pressure of lower than 1.0 x 10(-5) Pa. By optimizing the discharge gas composition the film with resistivity of 5.1 x 10(-4) Omega cm was obtained on an unheated substrate. The addition of CH4 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 move 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 CH4. films became non-crystalline with a weak and broad peak of (222). The results suggest that the addition of CH4, producing a higher pressure than the chamber base pressure, may be effective in stabilizing an ITO deposition process. (C) 1998 Elsevier Science Ltd. All rights reserved.