2004 Fiscal Year Final Research Report Summary
HIGHLY SENSITIVE DETECTION OF HAZARDOUS GASES PRODUCED IN THE PLASMAS OF PERFLUOROCARBON ALTERNATIVES
| Project/Area Number |
15540476
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| Research Category |
Grant-in-Aid for Scientific Research (C)
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| Allocation Type | Single-year Grants |
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| Section | 一般 |
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| Research Field |
Plasma science
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| Research Institution | KYUSHU UNIVERSITY |
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Principal Investigator |
FURUYA Kenji Kyushu University, Department of Molecular & Material Sciences, Accociate Professor, 大学院・総合理工学研究院, 助教授 (70229128)
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| Project Period (FY) |
2003 – 2004
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| Keywords | Perfluorocarbon plasma / SiO2 etching process / Mass spectrometry / Dication of CF3 / Growth of gaseous molecule / Lithium ion |
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| Research Abstract |
Making use of CF_3^<2+> as a specific product ion to quantify selectively CF_4 produced in the SiO_2 etching process by plasmas of perfluorocompounds(PFCs), such as c-C_4F_8,C_3F_8,and C_2F_6,has been proposed and investigated in the present experiments by measuring mass spectra in and out of the plasmas. It is known that the CF_3^<2+> ion does not appear in the mass spectra of any stable PFCs, except for CF_4. This dication has a characteristic mass of 34.5 amu and is easy to find in mass spectrometry. There are many kinds of unstable chemical species in the plasmas, such as neutral free radicals, ions, and excited atoms/molecules, as well as stable compounds. However, the quantity of CF_3^<2+> originated from the CF_3 radical in the mass spectra measured in situ has been found to be negligible by measuring the mass spectra of the pyrolysis products of CF_3I. The quantity of CF_3^+ in the plasma is too small to explain the intensity of CF_3^<2+> appearing in the mass spectra measured
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in situ, even if CF_3^+ could produce stable CF_3^<2+> by ionization. A stable compound of CHF_3 may also be formed in PFC plasmas due to a trace amount of water as an impurity. A very weak peak of CF_3^<2+> has been observed in the mass spectrum of CHF_3 in the present experiments, although there has been no report of the CF_3^<2+> formation by the ionization of CHF_3. It has been confirmed, however, that the contribution of CF_3^<2+> originated from CHF_3 to the observed mass spectra of the PFC plasmas is practically negligible. It is therefore concluded that CF_3^<2+> can be used as the fingerprint of CF_4 in mass spectrometry. Application of this new method to the quantitative analysis of CF_4 produced in the SiO_2 etching process by PFC plasmas may result in the fact that the CF_4 production advances significantly not only in the SiO_2 etching region of the plasmas and but also downstream in the plasmas.
In addition, the growth of gaseous neutral species and positive ions was investigated in the downstream region of Ar/CF_4 plasmas by mass spectrometry. As a result, there were several series of C_nF_<2n+1>^+(n=1-7),C_nF_<2n-1>^+(n=3-8) and C_nF_<2n-3>^+(n=4-9) for the positive ions and C_nF_<2n+2>(n=2-7) and C_nF_<2n>(n=4-8) for the neutral species. The intensity dependence of the positive ions on the partial pressure of CF_4 was quite different from that of the neutral species, demonstrating that their growth mechanisms are independent of each other. Less
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