PHYSICS OF PLASMAS 18,
053503 (2011)
Temporally resolved ion velocity distribution
measurements in a radio-frequency plasma sheath.
B. Jacobs,1, a)
W. Gekelman,1 P. Pribyl,1 and M. Barnes2
1 University
of California, Los Angeles, California 90095, USA
2 MS
Barnes Engineering, San Ramon, California 94583, USA
Abstract
The ion velocity distribution function (IVDF)
above and within a radio-frequency (RF) biased plasma sheath is studied experimentally with a
pulsed laser-induced fluorescence diagnostic in an industrial plasma etch tool. Temporally
resolved measurements taken at eight different phases of the 2.2 MHz bias waveform show that the ion
dynamics vary dramatically throughout the RF cycle (the ratio of the average ion transit time
through the sheath to the RF period is sion=sRF¼0.3).
The position of the presheath=sheath
edge is constant throughout the RF cycle and the time-averaged ion flux is conserved within the sheath
region. The characteristic bimodal structure of the time-averaged ion distributions found in
previous experiments is observed to arise from the time-dependent ion dynamics, in accord with
existing theory. The large temporal variation of the IVDF has implications for the plasma
chemistry and etching quality.
VC 2011 American Institute of Physics. [doi:10.1063/1.3577575]
References
31 S. L. Gulick, B. L. Stansfield,
Z.
Abou-Assaleh, C. Boucher, J. P. Matte, T. W. Johnston, and R. Marchand,
J. Nucl.
Mater. 176,
1059 (1990).
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