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Applied Science and Convergence Technology 2002; 11(1): 68-75

Published online April 1, 2002

Copyright © The Korean Vacuum Society.

Characteristics of Microwave Air Plasma With a Wide Range of Operating Pressures

Jung-Hyun Cho,Bong-Chul Jang,Bong-Kyung Park,Yun-Hwan Kim,Yong-Ho Jung,Gon-Ho Kim


It is observed the characteristic of the microwave air plasma in the wide range of the operating pressure, 1 mTorr~760 Torr. The microwave air plasma was generated by an AC-type microwave source manufactured with a magnetron taken from a commertial microwave oven and the input power was fixed at 370 W. Characteristics of the plasmas were observed by an injection Langmuir probe and an OES(Optical Emission Spectroscopy). The breakdown electric field is drastically changed at 500 mTorr. For < 500 mTorr, the ratio of the breakdown electric field and the pressure decreased inversely to the pressure, 5.7×10⁴ V/m-Torr. However, the ratio increased linearly as 43 V/m-Torr for the operating pressure, > 500 mTorr. The minimum breakdown electric field was observed about 12.5 ㎸/m at 500 mTorr. It corresponds that the input frequency equals to the collision frequency. The effective collision cross section of the air at this pressure was calculated as 9.23×10^(-16) ㎠. The results of the OES measurement revealed that the ain ions were composed of the oxygen, argon, and nitrogen for > 500 mTorr. In contrast, only oxygen and argon ions were dominated for < 500 mTorr. Ion temperature of oxygen (O(Ⅱ)) in the air was decreased from about 1.2 eV to 0.5 eV as the pressure increased. Langmuir probe data shows that the plasma density for < 500 mTorr was higher that for > 500 mTorr.

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