Article
Automated control of an actively compensated Langmuir probe system using simulated annealing
DOI:Nolle, L., Goodyear, A., Hopgood, A., Picton, P. and Braithwaite, N. (2002) Automated control of an actively compensated Langmuir probe system using simulated annealing. Knowledge-Based Systems. 15(5-6), pp. 349-354. 0950-7051.
Source: OAI
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Article: Self Bias of an R.F. Driven Probe in an R.F. Plasma
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ABSTRACT: An effect of sinusoidal r.f. voltages between a plasma and a floating Langmuir probe (or other electrode) is to produce a d.c. self bias voltage. This effect has previously been studied with r.f. applied to probes in d.c. plasmas, and the results have often been referred to in connection with d.c. probes in r.f. plasmas, although the situation is slightly different. In the current work a ‘d.c.’ probe in an r.f. plasma is examined. However, the r.f. potential difference between probe and plasma is first compensated for by superimposing a synchronous signal of appropriate amplitude and phase on to the d.c. circuit. Thus the probe can perform essentially d.c. type measurements on the r.f. plasma. The deliberate reintroduction of a measure of r.f. between probe and plasma is accomplished by overdriving the compensation signal thereby generating a controlled amount of self bias.The observed variation of probe bias with r.f. overdrive is in good agreement with analytic theory based upon modified Bessel functions as used for d.c. generated plasmas. This work is of general interest in probe diagnostics of r.f. generated plasmas, and understanding the self bias of isolated electrodes.MRS Proceedings. 12/1987; 117. -
Article: Multiple harmonic compensation of Langmuir probes in rf discharges
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ABSTRACT: We report on the use of an active Langmuir probe with three-harmonic compensation to diagnose rf discharge plasmas driven at 13.56 MHz. The plasma generates many harmonics on the fundamental, the first few being strongest. This gives a multi-harmonic rf voltage across the probe sheath that is removed by applying a rf signal to the probe that is matched both in amplitude and in phase for each harmonic. The probe I-V characteristic can then be analysed using dc theory. We show here that only when the rf harmonic amplitude approaches about 2Te is it necessary to compensate for that harmonic. For the commercial processing rig used this only occurs for the second harmonic at low pressures, < 5×10-3 mbar. Here the addition of second-harmonic compensation shifts the probe I-V curve, making it markedly more positive than for fundamental-only compensation. Despite this the values obtained for the electron density ne and temperature Te changed by less than 10%. For most plasmas in which the harmonics have amplitudes below Te the use of fundamental-only compensation is adequate for all but the most precise measurements.Measurement Science and Technology 05/2000; 11(5):554. · 1.49 Impact Factor -
Article: Electrical characterization of radio‐frequency discharges in the Gaseous Electronics Conference Reference Cell
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ABSTRACT: Measurements of the electrical characteristics of radio‐frequency (rf) discharges can be subject to large errors due to limitations in the measurement instruments and the stray impedance of the discharge cell. This study reports electrical measurements of argon discharges in the GEC Reference Cell in which special care has been taken to identify and minimize these sources of error. Careful calibration of current and voltage probes was found to be essential. In addition, parasitic impedances in the cell were found to be large, sensitive to minor changes in electrical connections, and not adequately described by simple a priori models. A general technique for characterizing the stray impedance, including an analysis of the propagation of errors, is presented here. This technique assures accurate results with specified uncertainties. Error analysis demonstrated that large gains in the precision of the measurements can be obtained using an inductive shunt circuit. Together, these techniques should improve the utility of electrical measurements for gauging the reproducibility of plasma conditions among rf discharge cells, for testing theoretical results, and for monitoring plasma processing.Journal of Vacuum Science & Technology A Vacuum Surfaces and Films 12/1992; · 1.25 Impact Factor
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Keywords
automated control system
deduce 14 Fourier terms
possible solutions
radio frequency waveform
reliable
required waveform
resulting search space
simulated annealing
skilled human operators
solutions
waveform