Fundamentals and Applications of energy-selective Ion Mass Spectrometry for the Analysis of low-pressure radio-frequency Plasmas
The majority of plasma-surface interactions utilized in technological applications are initiated by the ion flux onto the substrate surface. Therefore, energy-selective mass spectrometry (ESMS) has become the standard diagnostic for the analysis of the ion flux at the substrate, as it allows for versatile and flexible access to the energy- and mass-resolved ion flux. In this work, comprehensive simulations of the ion trajectories within the ion optics and the cylindrical Bessel-Box energy filter of a prevalent mass spectrometer, the Hiden Analytical PSM, are presented. The results provide insight into the fundamental working principle of the mass spectrometer, the impact of each electrode voltage on the ion trajectory and ion transmission and suggestions to minimize distortions in the measurements. Furthermore, a typical monitoring application of an ESMS is presented. When the mass spectrometer’s sampling orifice is integrated into the grounded electrode of a capacitively coupled plasma (CCP) with inverted electrode geometry, it allows to obtain the ion energy distribution function (IEDF) without the distortions typical for CCPs with classical electrode geometry. Strategies for tailoring the ion flux distribution with the dilution of the Ar gas with He are discussed. The addition of an inductively coupled plasma (ICP) turns the setup into an RF-biased ICP that allows for independent control over ion flux and ion energy. Lastly, a new technique for the determination of secondary electron emission and electron reflection coefficients by the comparison of measured and computed IEDFs is presented. The different influence of the secondary electron yield and the electron reflection probability on the plasma density and plasma potential allows the unambiguous determination of both surface parameters. The particle-in-cell (PIC) simulations offer a detailed insight into the reasons for the individual influence of each parameter on the discharge.
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