AVS 49th International Symposium
    Plasma Science Tuesday Sessions
       Session PS-TuP

Paper PS-TuP2
A Comparison of the Performance Between Low Pressure Magnetized and Non-magnetized Microwave Discharges

Tuesday, November 5, 2002, 5:30 pm, Room Exhibit Hall B2

Session: Plasma Applications
Presenter: J. Asmussen, Michigan State University
Authors: M. Perrin, Michigan State University
T.A. Grotjohn, Michigan State University
J. Asmussen, Michigan State University
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Microwave discharges can be created and maintained at low pressures both with and without the application of static (ECR and non-ECR) magnetic fields. Thus important microwave plasma source design issues are (1) when is the application of a static magnetic field advantageous, (2) what are the differences between the output performance of similar magnetized and non-magnetized microwave discharges, (3) what microwave heating mechanisms maintain the two different microwave discharges at low pressure? This investigation attempts to answer these questions by experimentally measuring the performance of a 13cm diameter microwave plasma source operating in argon gas from 1-50 mTorr with and with out a set of multipolar permanent magnets. Specifically, differences between magnetized and non-magnetized discharges are noted by comparing measured electron densities, electron distribution functions and effective electron temperatures versus pressure,i.e. 2-50 mTorr, and absorbed microwave power from 200-500W. The discharge stability of each configuration is also noted. The experimental results indicate that at pressures above 6 mTorr the non-magnetized discharge is superior in all aspects of performance to the magnetized discharge. Thus above a specific pressure ;i.e. 6 mtorr in this case, the application of static magnetic fields is not required to efficiently maintain microwave plasma processing sources. In fact the application of a magnetic field may reduce source efficiency. However at very low pressures ,i.e.below 4mtorr in this case, magnetized discharges are more efficient and stable and have lower electron temperatures and plasma potentials. The experimental measurements suggest that the non-magnetized discharge is maintained by non-collisional mechanisms at pressures below 15-20 mTorr. The similarity between discharge configurations also then suggests that similar non-collisional heating mechanisms are present in the magnetized discharge.