Bergamini, S

Kenyon, AJ

Law, VJ

Lea, L

Thornhill, NF

English

UCL Discovery

-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.04th harmonic amplitude (V)Amplitude fundamental (V) 0.3 mbar 0.4 mbar 0.15 mbar-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.05th harmonic amplitude (V)Amplitude fundamental (V)-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.06th harmonic amplitude (V)Amplitude fundamental (V)-1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0-1.0-0.8-0.6-0.4-0.20.00.20.40.60.81.07th harmonic amplitude (V)Amplitude fundamental (V)020406080 100120140160180200220240260 2803003203401502002503003504004505001502002503003504004505000.150.2 0.3 0.40.50.6   Amplitude (mV) oxygen 4th harmonicPlasma Harmonics Lissajous MeasurementsS.Bergamini*, V. Law*, T. Kenyon*, N. Thornhill*, L. Lea**.*Electronic & Electrical EngineeringUniversity College London, Torrington Place WC1E 7JE London (UK)** STS-plc Newport, Gwent, Wales NP1 9UJ UK-105-100-95-90-85-80-75-70-65-60-55-50-45-40-35-3025 35 45 55 65 75 85 95 105 115Frequency (MHz)Signal (50 ohm) dBm-130-125-120-115-110-105-100-95-90-85-80-75-70-65-60-55Signal (plasma tool) dBmThe instrumentNon-invasive analogue instrument for real-time detection of plasma generated harmonics of the fundamental drive frequency of 13.56 MHz.  It allows the simultaneous measurement of the amplitude and relative phase of incident and plasma-generated  waveforms, by simply connecting the instrument to the 50 Ohm input of the matching network of the plasma tool [1].  Noise figure =1.7Lissajous figures are obtained by plotting one harmonic versus the fundamental.  It is possible to extract information about the amplitudes and relative phase of the two waves by analysing the Lissajous features [2].The  changes in phase and amplitude reflect a variation in the plasma impedance, which is shown to be very sensitive to changes of plasma parameters like pressure and power. 02468 1 0 1 2 1 4 1 6 1 8 2 0 2 2 2 4 2 6 2 8-20020406080100120140160180200Phase (deg)Time (min) non-conditioned chamberinstrumental noise-2 0 2 4 6 8 10121416182022242628-20020406080100120140160180200instrumental noise Phase (deg)Time (min) conditioned chamber The evolution of the state of the plasma can be monitored real-time by displaying changes in phase and amplitude.As an example (left) the chamber conditioning is monitored by measuring phase changes in time. This measurement technique is very sensitive to the state of the plasma, showing a distinct exponential variation of the phase during the outgassing process and a settling to steady-state for conditioned chamber. Transient spikes in the phase up to 8 times larger than the background noise may reveal some important event occurring at the time-scale typical of the mean gas residence time. Diplexer provides -30 dB isolation between the harmonic channel and the fundamentalHarmonic Filters (n=2 to n=9) 1 MHz BW @-3 dBAmplifier adjustable gain up to 35 dBLissajous figuresReal-time phase measurementsPhase and amplitude measurements can be used to identify a unique plasma state as an evolving 2-dimensional vector, which can be visualized  in a polar plotPhase (deg)HP Gas13.56-MHzGeneratorFundamentalDiplexerComm LPLPmTDS 5052OscilloscopeAmplifiersFiltersMatching NetworkHarmonics[1] V. J. Law, A. J. Kenyon, N. F. Thornhill, V. Srigengan, I. Batty. Vacuum 57(1), 351 (2000)[2] V. J. Law, A. J. Kenyon, N. F. Thornhill, A. J. Seeds, I. Batty. J. Phys. D 34, 2726 (2001)Contact e-mail: s.bergamini@ee.ucl.ac.uk. Published in TPP7 "Progress in Plasma Processing of Materials", Strasbourg, France, June 18-June 21, 2002. pp. 127-134 (Begell House Inc, New York. 2003).Spikes on the 7thchannel reveal that the plasma-tool has poor electromagnetic immunity to the FM radio broadcast band 

Plasma harmonics Lissajous measurements

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