AVS 51st International Symposium
    Plasma Science and Technology Wednesday Sessions
       Session PS-WeA

Paper PS-WeA3
Monitoring Electron Density of Processing Plasmas Using a Transmission-line Type Microwave Sensor

Wednesday, November 17, 2004, 2:40 pm, Room 213A

Session: Plasma Diagnostics
Presenter: K.C. Leou, National Tsing Hua University, Taiwan
Authors: C.H. Hseih, National Tsing Hua University, Taiwan
K.C. Leou, National Tsing Hua University, Taiwan
C. Lin, National Tsing Hua University, Taiwan
Correspondent: Click to Email
The purpose of this study@footnote 1@, was to develop an electron density sensor for applications in process real-time feedback control of plasma based semiconductor fabrication tools, such plasma etchers or PECVDs. The sensor was a dielectric waveguide based transmission-line where microwave propagates at a phase velocity determined by the structure and the plasma density (electron density) surrounding the structure. Thus the variation of plasma density can be estimated from the phase shift of the transmitted microwave from one to the other end of the transmission-line. For the proof-of-principle study, a coaxial type transmission-line was adopted with a Teflon outer dielectric and a copper inner conductor operated at a freqeuncy of 2-3 GHz. Analytical analysis of dispersion characteristics of the transmission line structure was carried and the resulting propagation constants were in good agreement with results from calculation using a commercial high frequency structure simulation code (HFSS by ANSOFT). Experimental demonstration have been performed with an inductively-coupled plasma. The sensor was mounted on the inner wall of plasma chamber with a coaxial line length of 8 cm and a distance of 5 cm between input and output ports. Measurement results show that the dependence of electron density of plasma source RF power predicted by the sensor agrees well with the Langmuir probe measurements. Compared to conventional microwave interferometers where line-averaged plasma density is measured, the trainsmission-line type microwave sensor will be less susceptive to the interference caused by multi-passes reflection/refraction effect resulting from nonuniformity of plasma density profiles. Therefore, it provides a measurement of higher sensitivity and wider dynamic range. @FootnoteText@ Work supported by the grant from the National Science Concil of R.O.C. under contract #92-2218-E-007-018.