A microwave probe is known to be a suitable method to measure plasma density, even in the processing condition and is widely used in various environments of lowtemperature processing plasmas. Various types of microwave probes have been researched and developed to measure the precise plasma density. Extensive research has been conducted to investigate each probes characteristic responding to the plasma parameters (plasma density, electron temperature, pressure, sheath width, and so forth) based on both experiments and simulations. However, a comparative study elucidating the relative characteristics of each probe has not been completed yet, despite the wide applications of the probes in processing plasma. We conduct a comparative study among the microwave probes using the numerical method of threedimensional finitedifference timedomain simulation. In this study, the microwave probes are compared by investigating the precision of plasma density measurement under a comprehensive range of plasma parameters (plasma density, pressure, and sheath width).
A new method for time-resolved measurement of pulsed plasmas is suggested for reducing the measurement time. A short impulse has a broadband spectrum, and it can be used to make a spectrum in a short time. The use of a cutoff probe with a Fourier analysis (Fourier Cutoff Probe, FCP) provides the absolute electron densities with high speed. The measurement results from the FCP show good agreement with Langmuir probe's measurement results. However, it took only 1 minute 45 seconds using the FCP to make the temporal profile of electron densities in a pulsed plasma, versus 46 minutes for the Langmuir probe. The FCP's measurement was about 26 times faster than that by the Langmuir probe. This method will provide researchers a faster and convenient diagnostic method for pulsed plasmas.
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