AVS 53rd International Symposium
    Plasma Science and Technology Thursday Sessions
       Session PS-ThP

Paper PS-ThP7
A Transmission Line Microwave Interferometer for Monitoring of Electron Density in Plasma Processing Tools

Thursday, November 16, 2006, 5:30 pm, Room 3rd Floor Lobby

Session: High Pressure Discharges and Novel Diagnostics & Sources Poster Session
Presenter: C.H. Chang, National Tsing Hua University, ROC
Authors: C.H. Chang, National Tsing Hua University, ROC
J.Y. Jeng, National Tsing Hua University, ROC
C. Lin, National Tsing Hua University, ROC
K.C. Leou, National Tsing Hua University, ROC
Correspondent: Click to Email
We developed a transmission line microwave interferometer for monitoring of electron density for applications in process real-time feedback control of plasma based semiconductor fabrication tools, such plasma etchers or PECVDs. The sensor was a dielectric transmission-line where microwave propagates at a phase velocity determined by the structure and the electron density of the surrounding plasma. 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 2.4 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 6 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.