In-Situ X-Ray Photoelectron Spectroscopy of Reactive-Ion-Etched Surfaces of Indium-Tin Oxide Film Employing Alcohol Gas

Reactive ion etching (RIE) of the In-Sn oxide (ITO) film has been studied employing methyl alcohol (CH3OH). The ITO etch rate depends strongly on ion energy, and the etching results show a directional feature for a wide region of pressure. The activation energy is a relatively high value of 4.0 kcal/mol. Therefore, ITO etching with CH3OH is likely to follow the ion-induced chemical reaction. The reaction kinetics which were also studied using in-situ X-ray photoelectron spectroscopy (XPS) and mass analysis implied that at first the ITO bonds were broken or weakened by hydrocarbon and hydrogen ions, thereby being reduced to metallic Sn and In. These metals are changed to volatile alkyls or alkoxys as a consequence of the reaction with hydrocarbon species. In fact, M/e=104 of the double-charge ion of In(OCH3)3 with M/e=208 is detected by a mass analyzer in the range of M/e=1-200. The advantage of using CH3OH is the suppression of the photoresist etch rate. The photoresist exposed by CH3OH plasma was ashed easily by oxygen radicals.