Physics-informed selection of non-Maxwellian EEDF models for reliable OES-based plasma diagnostics

Abstract

In low-temperature plasma diagnostics, optical emission spectroscopy (OES) is widely employed as a non-invasive technique for analyzing electron energy distribution functions (EEDFs). Conventional OES methods typically assume a pre-selected EEDF model, chosen in advance based on domain knowledge of the electron heating physics of the target plasma. However, such assumptions limit diagnostic accuracy and may introduce errors when the actual electron heating physics deviates from the assumed model. This study proposes a physics-informed model-selective diagnostic method that identifies the most appropriate non-Maxwellian EEDF by quantitatively comparing emission line ratios predicted by a collisional-radiative model with experimental OES spectra. Three analytic EEDF models—generalized Maxwellian, bi-Maxwellian, and beam-shifted Maxwellian—are considered as candidates. The method was applied and validated in inductively coupled plasma and VHF-CCP systems exhibiting distinct electron heating characteristics. The validity was confirmed through comparison with Langmuir probe measured EEDF and a physics-based analytic model within 10%. The proposed method significantly improves diagnostic accuracy by reducing EEDF estimation error by more than a factor of five and lowering reaction rate uncertainty by over an order of magnitude.