Quantitative analysis of helium by post-ionization method using femtosecond laser technique

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• 作者：Hisayoshi Yurimoto ; Ken-ichi Bajo ; Isao Sakaguchi ; Taku T. Suzuki ; Amy J. G. Jurewicz ; Satoru Itose ; Kiichiro Uchino and Morio Ishihara
• 刊名：Surface and Interface Analysis
• 出版年：2016
• 出版时间：November 2016
• 年：2016
• 卷：48
• 期：11
• 页码：1181-1184
• 全文大小：424K
• ISSN：1096-9918

文摘

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 µm² 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 10²¹ cm⁻³. The detection limit was down to 10¹⁸ He cm⁻³ (20 ppm). For concentrations exceeding 10²¹ 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