| AVS 59th Annual International Symposium and Exhibition | |
| Plasma Science and Technology | Wednesday Sessions |
| Session PS1-WeA |
| Session: | Plasma Diagnostics, Sensors and Control 2 |
| Presenter: | A. Pandey, Chubu University, Japan |
| Authors: | A. Pandey, Chubu University, Japan Y. Liang, Chubu University, Japan S. Ikezawa, Chubu University, Japan K. Nakamura, Chubu University, Japan H. Sugai, Chubu University, Japan |
| Correspondent: | Click to Email |
A new type of microwave resonator probe, curling probe, has recently been proposed [1] which employs mono-pole excitation of spiral slot antenna. This probe enables direct measurement of electron density in reactive plasmas, based on a quarter-wavelength resonance at the frequency f=b(c/4L)[2/(ein+eout)]1/2. Here, b is the finite-size correction factor, L is the antenna length, ein and eout are the relative permittivities of two dielectrics inside and outside the slot antenna, respectively. When the probe is inserted into plasma, the outer dielectric constant eout is expressed as ep =1-(fp/f)2 with the electron plasma frequency fp=(e2n/me0)1/2. Thus, measuring the resonance frequency of curling probe, one can determine fp, and hence the electron density n. The finite-difference time-domain (FDTD) simulation of 11-mm-diam curling probe of 35-mm antenna length shows a sharp resonance at the frequency from 1 GHz to 6 GHz uniquely determined by the electron density. The sheath formed in front of the probe surface was modeled as a vacuum layer of ~5lD in thickness. The resonance frequency was hardly influenced by the sheath at the density higher than 1011 cm-3. Basic experiments of electron density measurement by the curling probe were performed in an argon (1~20 Pa) low-power (<2 kW) discharge in ICP device for 300-mm-wafer process. The power dependence of the resonance frequency observed by the curling probe was explained well by the FDTD simulation result as well as the analytical formula. The radial distribution of electron density was measured by a movable curling probe.
When a polymer layer (permittivity ed) is deposited on the probe surface, the resonance frequency decreases with the increasing layer thickness. Using this probe characteristic, one can in situ monitor the thickness of dielectric layer deposited onto a wall of plasma vessel, where the curling probe is positioned to just the same surface of inner wall. The FDTD simulation shows ~10 MHz shift in the resonance frequency for 15-mm-thick deposition of polymer (ed =3.2), in good agreement with the experimental observation. Thus, the wall deposition layer during chamber cleaning or CVD process can be monitored by the curling probe. In fact, amorphous carbon layer formed on the vessel wall was in situ monitored by the curling probe in a 1-kW surface-wave plasma in CH4/Ar deposition discharge and in O2/Ar cleaning discharge. This model experiment successfully demonstrated an applicability of curling probe to monitoring the dielectric layer deposited on the plasma vessel wall.
[1] I. Liang, K. Nakamura, and H. Sugai, Appl. Phys. Express 4, 066101 (2011).