J. Asmussen et P. Mak, CONTROL OF MULTIPOLAR ELECTRON-CYCLOTRON-RESONANCE DISCHARGES USING INTERNAL CAVITY IMPEDANCE MATCHING, Review of scientific instruments, 65(5), 1994, pp. 1753-1760
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.