Patent ID: 8617351

Claim:
A method of processing a wafer in a plasma reactor comprising a workpiece support surface and an overhead source power applicator overlying a ceiling of the reactor and facing said workpiece support surface, comprising: generating a plasma in a process region over said workpiece support surface while supporting the workpiece on said workpiece support surface; generating a DC magnetic field in said process region by applying respective DC current levels to concentric inner and outer DC coils above and displaced by different distances from said RF source power applicator and to a bottom DC coil at an axial location below said wafer; determining an uncorrected plasma ion density distribution at said workpiece support surface; determining changes in plasma ion density distribution as functions of D.C. current applied one at a time to respective ones of said inner, outer and bottom electromagnets; mathematically adding said functions with said uncorrected plasma distribution for different combinations of D.C. currents applied to said inner, outer and bottom electromagnets, so as to compute plural trial plasma ion density distributions; searching said trial plasma ion density distributions for at least one corresponding to a desired correction in plasma ion density distribution, and determining a corrective set of currents corresponding to coil currents associated with the one trial density distribution; and performing the desired correction by applying said corrective set of currents to respective ones of said inner, outer and bottom electromagnets.