New Approach to rf-Sputter Power Supply Design

Abstract

rf transmission line and matching network have been eliminated. The rf generator with primary coil is detachably mounted directly on the feedthrough flange for the target which is connected directly to the secondary coil. This results in a much more compact unit, eliminating rf-power losses, thereby increasing the overall efficiency and reducing substantially the number of components in the power supply. The final amplifier tube anodes are operated at de ground potential. This allows water cooling of the anodes by feeding the cooling water through a double helical resonant coil terminating both water inlet and outlet at ground potential. Water cooling furthermore reduces the size of the rf generator. No dc potential is superimposed on the rf potential. Therefore, relatively low voltage breakdown rf components can be used. rf arc-over, if it should occur, will not cause dc arcing. Rugged low cost medium power tubes are used in parallel connections for high power at low impedance. This also contributes to the usability of low voltage breakdown components. For lower power requirements, filaments of parallel tubes may be de-energized. This provides coarse matching of impedance to smaller targets while reducing rf power to desired levels. Fine control of impedance matching is obtained by variable inductive coupling.