Recent innovations in microwave probes for reactive plasma diagnostics

Abstract

Conventional Langmuir probe cannot be used in most reactive plasmas for materials processing, owing to the insulating layers that are deposited on the probe surface. To address this issue, a novel variety of microwave probes has been recently developed for the purpose of monitoring local electron density, which is a key parameter for plasma control. The probe diagnostic must be stable, compact, easy, exhibiting negligible disturbance to a plasma and materials processing. This article presents a review of the diagnostic principle, characteristics and applications of representative probes such as the plasma oscillation probe, surface wave probe (plasma absorption probe), multi-pole resonance probe, hairpin probe and curling probe. The merits and demerits of each probe are presented from a reactive plasma diagnostic point of view. Innovations in the applications of microwave probes to optical emission spectrometry and the monitoring of wall deposits are also presented.

Mass spectroscopic measurement of time-varying ion composition in a pulse-modulated Ar/C4F8/O2 dual-frequency capacitively coupled plasma

“…In the SW probe measurement, the network analyzer is often used, and n e is measured by finding the absorption dip frequency of the reflected signal. The absorption dip frequency is close to the SW resonant frequency ( f sw ), and the electron density is obtained from the dip frequency by the following equation: 25) p Here, ε 0 , m e , and e denote vacuum permittivity, electron mass, and elementary charge, respectively. In the timeresolved measurement, however, the time dependence of the reflected signal via an RF-bridge unit was measured by a spectrum analyzer at various signal frequencies.…”

Crossing Frequency Method Applicable to Intermediate Pressure Plasma Diagnostics Using the Cutoff Probe

“…Hence, microwave probes are seen as useful tools in deposition processing, and various types of probes have been developed. Details of these probes, such as the curling probe (CLP), the multipole resonance probe (MRP), the cutoff probe (CP), etc., are well explained in [42,43].…”

Science-based, data-driven developments in plasma processing for material synthesis and device-integration technologies

“…Invasive diagnostics of plasma properties are obtained using microwave probes. 33) These methodologies are based on the detection of the resonant frequency of the surface- Itatani (1990). 31) ].…”