Seong-Bin Park (Korea Research Institute of Standards and Science (KRISS), Daejeon 34113, Republic of Korea; Department of Mechanical Engineering, Yonsei University, Seoul 03722, Republic of Korea)

Young-Joo Kim (Department of Mechanical Engineering, Yonsei University, Seoul 03722, Republic of Korea)

Hyo-Chang Lee (Department of semiconductor science, Engineering and Technology, Korea Aerospace University, Goyang 10540, Republic of Korea)

Jung-Hyung Kim (Korea Research Institute of Standards and Science (KRISS), Daejeon 34113, Republic of Korea)

Seong-Bin Park (Korea Research Institute of Standards and Science (KRISS), Daejeon 34113, Republic of Korea; Department of Mechanical Engineering, Yonsei University, Seoul 03722, Republic of Korea)

Wooram Kim (Korea Research Institute of Standards and Science (KRISS), Daejeon 34113, Republic of Korea)

Young-Joo Kim (Department of Mechanical Engineering, Yonsei University, Seoul 03722, Republic of Korea)

Hyo-Chang Lee (Department of semiconductor science, Engineering and Technology, Korea Aerospace University, Goyang 10540, Republic of Korea)

Jung-Hyung Kim (Korea Research Institute of Standards and Science (KRISS), Daejeon 34113, Republic of Korea)

Electron ionization mass spectrometry has been widely used for the identification and quantitative analysis of diverse chemical species. However, its hard ionization method induces extensive fragmentation; fragment ions generated by dissociative ionization within the ion source may overlap with analyte-derived ions at the same mass-to-charge ratio, compromising quantitative interpretation of mass spectra. In this study, a signal decomposition method was established that separates the measured ion signal into direct and dissociative ionization contributions, enabling reliable radical density estimation in plasma environments. As the basis of this correction, the fragment ion extraction efficiency was characterized for the plasma processing gases O₂, N₂, H₂, and CF₄, identifying general trends applicable across gas species as well as gas-specific behavior. The atomic oxygen density in O₂ plasma was then estimated from the signals of O⁺ and O₂⁺ measured by mass spectrometry at different electron energies. The estimated densities with and without the correction for the dissociative ionization contribution were compared to quantify its impact. We demonstrated that this correction is essential for reliable radical density estimation. These findings provide a basis for reliable in situ sensing of reactive species in plasma processes such as etching and deposition.

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