Three-coil inductively coupled plasma source with individually controlled coil currents from a single rf power generator

A method of individually controlling currents in three coil antennas of a plasma reactor supplied from an RF generator through an RF impedance match, comprising:

• providing respective current divider branches between said impedance match and respective ones of said coil antennas, each of at least two of said current divider branches comprising a respective variable impedance element;
• providing a model comprising a first set of equations defining voltage drops in said current divider branches in accordance with mutual inductances of said coil antennas and corresponding portions of a plasma in said reactor and a second set of equations defining voltage drops in said corresponding portions of said plasma in accordance with said mutual inductances;
• solving said first and second sets of equations for currents in said coil antennas relative to total current as 3-dimensional functions of impedance values of said variable impedance elements in said at least two current divider branches;
• correlating information corresponding to said functions to a user-defined apportionment of currents in said coil antennas.

A plasma reactor for processing a workpiece, comprising:

• an Pop power generator and an impedance match coupled to said RF power generator;
• three coil antennas having respective driven ends and return ends, said return ends being connected to a common potential;
• a pair of current divider branches each comprising respective series and parallel impedance elements, the series impedance element of each of said pair of current divider branches being of an impedance value other than zero or infinity and being coupled between said impedance match and the driven end of a respective one of said, coil antennas, the parallel impedance element of each of said pair of current divider branches being of an impedance value other than zero and being coupled in parallel with a respective one of said coil antennas;
• a third current divider branch coupled between said impedance match the driven end of a third one of said three coil antennas;
• and
• a current apportionment controller controlling impedances of either (a) said series impedance elements of said pair of current divider branches or (b) said parallel impedance elements of said pair of current divider branches, in response to a user-specified apportionment of currents to said three coil antennas received from said user interface.