CONTROL OF MULTIPOLAR ELECTRON-CYCLOTRON-RESONANCE DISCHARGES USING INTERNAL CAVITY IMPEDANCE MATCHING

Recently, electron cyclotron resonance (ECR) discharges have been succ essfully applied to numerous ion source applications. These range from accelerator to etching and thin film deposition applications, and hav e strong potential for application in several commercial/industrial pr ocesses. Thus, new design requirements related to process automation a nd control are now imposed on plasma source design. Internal cavity tu ning methods for excitation and impedance matching and ECR discharge c ontrol are presented. These impedance matching methods utilize a varia ble cavity end plate and an adjustable coupling probe to provide the t wo independent adjustments required to match the discharge loaded cavi ty applicator. Both end feed and side feed coupling create a well matc hed plasma source but the end feed excitation produces the most effici ent (approximately 220-230 eV/ion) and most uniform (1sigma=2.5%) disc harge. Control of internal tuning can serve not only to match discharg e impedance, but with the proper control can also avoid hysteresis and multiple steady states and jumps in plasma source outputs. Adjusting the internal cavity tuning to always produce a slight mismatch helps i nsure a stable and repeatable discharge operation.