Relative calibration of a retarding field energy analyzer sensor array for spatially resolved measurements of the ion flux and ion energy in low temperature plasmas

Ries, S. and Schroeder, M. and Woestefeld, M. and Corbella, C. and Korolov, I. and Awakowicz, P. and Schulze, J.

Volume: 92 Pages:
DOI: 10.1063/5.0059658
Published: 2021

A calibration routine is presented for an array of retarding field energy analyzer (RFEA) sensors distributed across a planar electrode surface with a diameter of 450 mm that is exposed to a low temperature plasma. Such an array is used to measure the ion velocity distribution function at the electrode with radial and azimuthal resolutions as a basis for knowledge-based plasma process development. The presented calibration procedure is tested by exposing such an RFEA array to a large-area capacitively coupled argon plasma driven by two frequencies (13.56 and 27.12 MHz) at a gas pressure of 0.5 Pa. Up to 12 sensors are calibrated with respect to the 13th sensor, called the global reference sensor, by systematically varying the sensor positions across the array. The results show that the uncalibrated radial and azimuthal ion flux profiles are incorrect. The obtained profiles are different depending on the sensor arrangement and exhibit different radial and azimuthal behaviors. Based on the proposed calibration routine, the ion flux profiles can be corrected and a meaningful interpretation of the measured data is possible. The calibration factors are almost independent of the external process parameters, namely, input power, gas pressure, and gas mixture, investigated under large-area single-frequency capacitively coupled plasma conditions (27.12 MHz). Thus, mean calibration factors are determined based on 45 different process conditions and can be used independent of the plasma conditions. The temporal stability of the calibration factors is found to be limited, i.e., the calibration must be repeated periodically. © 2021 Author(s).

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