Frequently Asked Questions about the Curling Probe |
Q1. If the curling probe is damaged, do we have to replace the whole curling probe?A. It depends on the damaged part. It is possible to repair a damaged part only. |
Q2. If we already have a network analyzer (NWA), is it possible to buy a system without NWA?A. Basically, you can buy each part separately. (We once sold an inlet tube of the curling probe only to a domesticcustomer. However, our NWA is installed with "software for data analysis", it is convenient because
the electron density is automatically calculated. |
Q3. Can we select a material of the inlet tube or the head part of CP?A. We have some experiences to provide the curling probes with stainless steel (SUS304) and aluminum (A5052).Aluminum surface is generally treated with anodizing or alumina coating.
Please consult about a specific material and coating method for CP. |
Q4. After purchasing the curling probe in Japan, is it possible to use it in a foreign contries?A. It is OK to use the curling probe in any country who is a member of the WA. (Wassenaar Arrangement, NewCOCOM) |
Q5. The most classical plasma diagnostic technique is a probe method (Langmuir probe method).Single probe, double probe, and triple probe method are known as probe methods. Which of these is aneffective method for RF discharge plasma?A. First, single probe method has been developed for a DC power supply. In a RF discharge, the plasma potential isoscillating in the RF (the reference potential fluctuates), which makes it difficult to use as it is. In order to removethe RF noise, a noise filter is connected to the probe.
When using a double probe, it is sometimes possible to measure the RF plasma even without filter, but themeasurement with high accuracy will be very difficult because of the RF inductionsignal.
The triple probe method is not generally used even for a DC discharge and has the same problem as a single probemethod for a high-frequency discharge.
On the other hand, the curling probe can be used without any problems even at high frequency discharge. Ingeneral, plasma potential is oscillating in a RF discharge due to the nature of RF,which may cause a negative effecton the plasma measurement. Inductively coupled high-frequency discharge (ICP) and capacitively coupleddischarge plasma (CCP) are well known as RF discharge plasmas. In case of ICP, the curling probe can measureplasma without any problem because RF oscillation is so small in ICP plasma. However, in ICP having a RF bias tothe substrate or in CCP, the plasma potential is strongly oscillating. This oscillating signal might get into the networkanalyzer and damage it. It is recommended to use a protective circuit to prevent the damage. For example, apower limiter (N9355C) from Agilent (now, Keysight) or other by-pass filter are recommended. |
Q6. Should the curling probe be always used as single?A. Single curling probe is enough to measure electron density of plasma. If you want to measure electrontemperature, you will need one more curling probe with a different size. Please refer to the following papers aboutdetailed measurement method.
K.Nakamura, M.Ohta, and H.Sugai, J.Vac.Sci.Technol A21 (2003) 32 However, the measurement accuracy is notgood enough and we don't have much experiences for further comments. |
Q7. Are plasma parameters measured by Langmuir probe the same as ones measured by the curlingprobe?A.The measurable range of plasma density (usually equal to electron density) is approximately same for bothLangmuir and the curling probe in the range of 109/cm3 - 1012/cm3. Langmuir probe first measures electrontemperature and then calculate plasma density from the measured electron density.
The measuring range of electron temperature is about 0.2 ~ 10 eV. While the curling probe can directly measureplasma density without measuring electron temperature.
Two different sizes of the curling probe can measure electron temperature with the same measuring range asLangmuir probe. (See Q6) |
Q8. When plasma density is changing over time by a pulsed discharge or power modulation, is itpossible to measure plasma parameter over time?A. When plasma density is constant over time, it can be measured easily by a simple network analyzer (NWA). Incase of periodically changing at a certain frequency by applying a pulse discharge or power modulation, the use of ahigh performance NWA with a trigger function can measure electron density at any time. Please refer to thefollowing article about the method.
A.Pandy, W. Sakakibara, H. Matsuoka, K. Nakamura, and H. Sugai: Appl. Phys. Lett.104(2014) 024111
This paper described an examples of pulsed discharge at a low frequency of 400 Hz. A recent study showed that itcan measure even at 20 kHz of pulsed discharge using on-Point method of NWA. |
Q9. What classification of plasma measuring methods can the curling probe be correspond to?A. In the Japan Society of Plasma Science and Nuclear Fusion Research, it is classified into five measurementmethods; probe, microwave, laser, spectroscopic and particle measurement.
The curling probe is a microwave measurement method. In addition, microwave measurement has been classified tothree methods; absorption measurement, interference measurement and cyclotron radiation. However, the curlingprobe is a new method and it should be considered as the fourth method called "resonance method". |
Q10. What are the differences between Langmuir probe and the curling probe?A. The biggest difference as a measurement technique is that Langmuir probe measures a plasma's response toDC power while the curling probe measures plasma response to microwave and derive the plasma of informationwith it. From this difference, when an insulating film is covered on the surface of Langmuir probe, it becomesimpossible to measure because there is no electrical current through Langmuir probe due to the insulating layer. Incontrast, an insulating film can have little effect even to curling probe. Please refer to the answer of the previous Q5and Q7 for others. |
Q11. Is there any references or books?A. For a basic knowledge of plasma and its applications, Hideo Sugai al., "Plasma Electronics"(Ohm Co., 2000) isrecommended. In addition, for a plasma of measurement method,"Fundamentals and Applications of PasmaDiagnostics" (Corona Publishing Co., 2006) from Plasma Fusion Society is recommended. |
Q12. What about the intellectual property of curling probe?A. A Japanese patent application has been filed already.
It should also be noted that "curling probe" and "opto-curling probe" is registered trademarks of Noa Leading Co.,Ltd in Japan. |
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