69th Annual Gaseous Electronics Conference
Volume 61, Number 9
Monday–Friday, October 10–14, 2016;
Bochum, Germany
Session RR1: Electrical Diagnostics II
11:00 AM–12:30 PM,
Thursday, October 13, 2016
Room: 1
Chair: Alan Howling, Swiss Plasma Center
Abstract ID: BAPS.2016.GEC.RR1.1
Abstract: RR1.00001 : Development and Miniaturization of RF based probes for Electron Density Measurements
11:00 AM–11:30 AM
Preview Abstract
Abstract
Author:
Keiji Nakamura
(Chubu University)
To make a diagnostics on plasmas for materials processing plasmas
accompanying with deposition of non-conducting films in etching and/or CVD
processes, curling probe (CP) with a spiral slot antenna has been recently
developed as a compact diagnostic tool which enables the local electron
density measurement. The electron density is obtained from a shift of the
probe resonance frequency in discharge ON and OFF monitored by a network
analyzer (NWA). A conventional CP has a diameter larger than \textasciitilde
15 mm typically, because a slot length of the CP is as long as several tens
millimeters for its resonance frequency less than several GHz. Further
miniaturization of the CP was required to expand applicable range to various
plasma sources like a narrow-gap parallel plate discharge. We tried
miniaturization of the CP down to less than \textasciitilde 3 mm in the
probe diameter by fabricating narrow spiral slot antenna, and experimentally
and numerically the miniaturized probe was investigated how much influence
the slot width has on probe resonance characteristics and electron density
measurements. In the case of the conventional CP made of stainless steel,
\textasciitilde 0.3-mm-wide normal slot antenna, the resonance spectra was
clearly observed regardless of antenna materials of copper or stainless
steel (SS). However, when the slot width was reduced down to \textasciitilde
0.03 mm, the slot resonance was strongly dependent on the antenna materials.
Namely the resonance peak was almost vanished for the SS antenna, whereas
clearly appeared for the copper antenna. In general, the narrower the slot
is, the higher attenuation factor the slot has for electromagnetic wave
propagating along the slot. In such an attenuated transmission line of the
narrow slot, high electric conductivity of the antenna seems preferable for
the slot resonance. Furthermore, the miniaturized CP with the copper antenna
was also introduced into low pressure (\textless \textasciitilde 1Pa) Ar
plasma. The resonance frequency was confirmed to changes sensitively with
electron density, suggesting the miniaturized CP will be available to
electron density measurements. Numerical simulation showed that localization
of electromagnetic fields near the slot was remarkably enhanced by
decreasing in the slot width, suggesting that the miniaturized CP suffers
from more significant sheath effects compared to the conventional CP.
To cite this abstract, use the following reference: http://meetings.aps.org/link/BAPS.2016.GEC.RR1.1