Reactive ion-plating at low ion energies with an unbalanced magnetron

An unbalanced magnetron uses changes in the configuration of the magnetic field, which confines the plasma close to the sputtering cathode, to allow some of it to ‘leak’ out to impinge on the substrate. A device which can produce ion bombardment of an isolated surface at a bias ofover 100 V with a current density of 100 mA cm −2 is described. The dependence of the surface bombardment on process parameters such as magnetron power and gas pressure is reported; a general diminution of the bombardment occurs as the pressure is increased beyond 0.2 Pa, but the effect becomes greater when oxygen replaces argon as the sputtering gas. The operation of the magnetron under conditions using extra electron injection is shown to result in additional ion current, whilst the bias potential is maintained. Reactive sputtering with such a source allows the growing film to be improved in structure whilst the reactive gas is made more reactive which allows a lower partial pressure to be used for the creation of stoichiometric films. Electron injection allows the pressure of the inert sputtering gas to be low, so that operation is possible at pressures giving mean-free paths greater than the source to substrate distance. Line of sight transfer of material having energies appropriate to sputtered material is then possible. The application of such a device to the preparation of thin films of indium-tin oxide and diamond-like carbon and the etching of a polymer surface is described.