EXPERIMENTAL INVESTIGATION OF THE MATCHING AND IMPRESSED ELECTRIC-FIELD OF A MULTIPOLAR ELECTRON-CYCLOTRON-RESONANCE DISCHARGE

The experimental performance of an end excited, internally tuned, mult ipolar electron cyclotron resonance plasma source is investigated vers us several independent input variables: (1) incident power (185-350 W) , (2) discharge pressure (1-7 mTorr), and (3) microwave matching (appl icator length, L(s), varies from 65-170 mm). Plasma source performance in argon gas is determined from measurements of (1) absorbed microwav e power, (2) the magnitude, and (3) the spatial variation of the impre ssed electric field, and the output (4) plasma density and (5) electro n temperature. The nonlinear experimental relationships between variat ions in the input variables and performance variables are established. Two well-matched stable discharge operational regions or modes are id entified as L, is varied. Using the measured impressed electric field patterns, these two modes are identified as TM, Phi symmetric, lambda( g), and lambda(g)/2 standing wave modes. As L(s), pressure and power v ary, considerable hysteresis in absorbed power and density is observed . However, it is shown that this complex input/output discharge behavi or can be approximately explained using simple global plasma models. D espite the multiple steady states and hystereses, it is shown that the discharge can be easily maintained in well-matched, high density (n(e ) > 3 x 10(11)/cm(3)) stable operating conditions. The impressed elect ric field varies between 3 and 4.5 kV/m. An equivalent circuit of the plasma loaded cavity applicator is developed and provides important in sights for the plasma matching process. The microwave coupling efficie ncies are greater than 98% and the ion production costs vary between 3 00 and 450 eV/ion versus the experimental inputs. The data presented i s useful for plasma source optimization and in developing intelligent plasma processing control strategies. (C) 1997 American Vacuum Society .