TECHNIQUES FOR THE SPUTTERING OF OPTIMUM INDIUM-TIN OXIDE-FILMS ON TOROOM-TEMPERATURE SUBSTRATES

New ion-assisted, successive-layer plasma anodisation processes are de scribed for the preparation of indium-tin oxide films. They use unbala nced planar magnetron sputtering to provide controlled argon-ion bomba rdment of the growing film, and also use room-temperature substrates. In both processes the magnetron was used both to deposit the metal and to provide the activated reactive atmosphere, either by moving the su bstrate between different units or by controlled pulsing of the admiss ion of the oxygen to change the function of the magnetron, These proce sses have been used to determine the optimum stoichiometry through con trol of the amount of oxygen incorporated into the metal oxide, and th e optimum doping of the indium oxide with tin to produce films with th e highest electrical conductivity and visible transparency. The experi ments confirm results which were obtained with continuous deposition p rocesses, which demonstrated that the addition of any tin will result in a loss of performance as compared to that achieved with control of the stoichiometry. The continuous processes used both oxide and metal targets with the supply of oxygen being carefully controlled, when nec essary, from process parameters. We generally used plasma-emission mon itoring (PEM) of the radiation emitted by the sputtered indium, when e xcited by the plasma, to indicate the partial pressure of oxygen and t he state of the target. The continuous sputtering of a compacted oxide target was the least critical of the processes: only a small amount o f flow-controlled oxygen had to be added to the sputtering atmosphere to give adequate electrically conducting and visibly transmitting film s. Better films could be made more quickly reactively from metal targe ts, but were much more critical in the control of the conditions which they required. The use of successive ion-assisted plasma anodisation techniques made this a much less critical process, while in all cases the limiting resistivity was found to be around 4 x 10(-6) Ohm.m. This was obtained via control of the stoichiometry through the oxygen cont ent of an indium film. The role of tin was to make the achievement of optimum films more easily attainable. (C) 1998 Elsevier Science S.A.