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Quantitative analysis of helium by post‐ionization method using femtosecond laser technique
Author(s) -
Yurimoto Hisayoshi,
Bajo Kenichi,
Sakaguchi Isao,
Suzuki Taku T.,
Jurewicz Amy J. G.,
Itose Satoru,
Uchino Kiichiro,
Ishihara Morio
Publication year - 2016
Publication title -
surface and interface analysis
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.52
H-Index - 90
eISSN - 1096-9918
pISSN - 0142-2421
DOI - 10.1002/sia.6119
Subject(s) - ionization , fluence , chemistry , analytical chemistry (journal) , mass spectrometry , helium , femtosecond , ion , detection limit , reproducibility , laser , atomic physics , optics , chromatography , physics , organic chemistry
Helium has the largest ionization potential of all elements; thus, it is difficult to ionize for measurement by mass spectrometry. In order to analyze He, a tunnel‐ionization time‐of‐flight sputtered neutral mass spectrometry system (called LIMAS) has recently been developed. LIMAS uses a femtosecond laser technique and can ionize He. We quantified the effectiveness of this method for He analysis from a 2.5 × 4 µm 2 area of He‐implanted silicon. The amount of He in an implant was quantified by measuring the ion current, giving a nominal implant fluence per unit area. Thus, the fraction of total He measured by LIMAS during depth profiling could be quantified by comparison with the He concentration of the reference implant. The He + intensities normalized by host ions of Si linearly correlated with the known He concentrations with a reproducibility of 10% at concentrations less than 10 21 cm −3 . The detection limit was down to 10 18 He cm −3 (20 ppm). For concentrations exceeding 10 21 cm −3 , the He intensities are smaller than those expected from the lower concentration range. This non‐linearity may reflect the limit of retention of He in the Si lattice, because He is chemically inert. Copyright © 2016 John Wiley & Sons, Ltd.