AVS 53rd International Symposium
    Plasma Science and Technology Friday Sessions
       Session PS2-FrM

Paper PS2-FrM10
Monitoring of Electron Density in Plasma Reactor with Frequency Shift Probe

Friday, November 17, 2006, 11:00 am, Room 2011

Session: Diagnostics
Presenter: K. Nakamura, Chubu University, Japan
Authors: K. Nakamura, Chubu University, Japan
H. Sugai, Nagoya University, Japan
Correspondent: Click to Email
A plane type of frequency shift (FS) probe for monitoring electron density in reactive plasmas was developed with modification of the hairpin probe.@footnote 1@ The FS probe is connected to a network analyzer to detect reflection from the probing plane antenna located at an inner surface of the chamber. The reflection becomes minimum at a certain frequency due to resonance at the antenna, and the resonant frequency shifts from f0 for vacuum without plasma to higher frequency f in the presence of the plasma because of a decrease in permittivity. The frequency blue shift (f-f@sub 0@) gives the absolute electron density ne according to ne (x10@super 10@cm@super -3@) =[f@super 2@-f@sub 0@@super 2@]/0.81 in unit of GHz for f and f@sub 0@. In principle, the FS probe is based on volume wave resonance while a previouly-proposed surface wave (SW) probe relies on surface wave resonance.@footnote 2@ In comparison to the SW probe, the plane FS probe has various advantages. The FS probe can be installed on a reactor wall surface, thus minimizing the disturbance to processing plasmas. Furthermore, since the resonance cavity of the FS probe is formed at the plane antenna itself, the resonance frequency can be measured easily in a wide range of the discharge conditions. The characteristics of FS probe were examined in an ICP reactor as functions of the RF power and the discharge pressure, and the experiments revealed that the wall-installed FS probe could monitor relative variations of electron densities in the bulk plasma.@FootnoteText@ @footnote 1@ R. B. Piejak et al. J. Appl. Phys. 95 (2004) 3785.@footnote 2@ H. Kokura et al: Jpn. J. Appl. Phys. 38 (1999) 5262.