R.F. Sputtering apparatus including multi-network power supply

Apparatus for supplying power efficiently to the discharge plasma load in a sputtering chamber by means of r.f. energy of a predetermined frequency in the megahertz range which comprises:

• A. a source of megahertz r.f. power having an impedance of the order of 50 ohms at its output terminals,
• B. electrodes of the type adapted to function as cathode means and anode means during the sputtering process to produce sputtering plasma between them,
• C. a pressure chamber including grounded metallic walls having said electrode means mounted therein and including grounded metallic structure surrounding and in relatively close proximity to a substantial portion of at least said cathode means for confining said plasma when generated, the input impedance of said electrode means including deleterious power transfer effects produced by the said surrounding structure and the metallic walls during sputtering operation of said apparatus, said effects being brought about principally by a first capacitive reactance parallel with said plasma having an impedance ohmage of the same order as that of said source impedance but which is a substantial number of times less than the impedance of the resistive component of said plasma, the electrodes being electrically coupled to said plasma during operation of said apparatus,
• D. said apparatus including means to provide for transporting a substrate member relative to said anode means within said chamber between the anode means and the cathode means so that the plasma will sputter material derived from said cathode means upon said substrate member during operation of said apparatus and
• E. means for coupling said source to said electrodes to transfer power from said source to said plasma which comprises:
• i. a string of three inductor and capacitor combination networks each being resonant at the frequency of said source and being connected seriatim between said source and electrodes, the first network following the source being an impedance transfer network effective to raise the voltage and impedance of the source, the second network following the impedance transfer network being an idler network, said idler network being effective substantially to raise the voltage of the impedance transfer network and
• a. having an output terminal at a certain voltage and impedance and
• b. a coupling line extending from said output terminal to said cathode means so that the output terminal voltage of said idler network is applied to said coupling line at the impedance of said output terminal of said idler network,
• the third network being a load network also connected to said coupling line and whose total capacitive reactance participating in the resonance condition of said load network includes the said first capacitive reactance parallel with said plasma,
• ii. at least the second and third network inductors being transformers,
• iii. each of the networks being constructed and arranged to have a ratio of Q/QL which is at least of the order of ten to provide efficient power transfer under load.