A NEW METHOD FOR FILM DEPOSITION IN THE DISCHARGE OF TARGET METAL VAPOR

A new method for generation of a discharge in its own metal vapour of an r.f.-excited electrode is described. The method is based on the r.f. plasma jet (RPJ) system utilizing a small size r.f. nozzle in which a hollow cathode-type discharge is generated. The nozzle outlet (target) is sputtered and/or evaporated by the ion bombardment from the jet discharge. The power density at the nozzle outlet reaches the order of hundreds of watts per square centimetre even at reasonably low r.f. power supply levels (above 100 W). A dense plasma containing a large amount of the nozzle metal ions can be generated inside the nozzle. Depending on the nozzle material, at a definite critical value of the r.f. power the discharge character can change to a particular kind of arc (RPJ arc) in which metal ejection inside the self-heated nozzle is sufficient to generate a sustained discharge without any auxiliary gas. Experiments indicate that the generation of the RPJ arc can be considered as a combination of a distributed discharge (diffuse) arc and a high voltage arc. Optical emission spectra from an Mg RPJ generated plasma exhibit only Mg emission lines and Mg film growth rate reaches values above 4 mum min-1. Conditions for generation of self-sustained discharges in Ti and Cu nozzles are also discussed. The effect of the nozzle geometry on the generation of stable self-sustained discharges for deposition of thin films is explained. In most cases an enhanced thermionic electron emission from the metallic surface contributes to a positive feedback to maintain the dense metal vapour plasma discharge. Deposition of Ti films in a plasma containing Ti vapours, Ti+ ions and low partial pressure of Ar at regimes close to the RPJ arc is described.