Radiant energy – Ionic separation or analysis – With sample supply means
Reexamination Certificate
2000-12-15
2003-01-14
Anderson, Bruce (Department: 2881)
Radiant energy
Ionic separation or analysis
With sample supply means
C250S282000, C250S281000, C423S489000, C423S490000, C423S491000, C423S495000, C423S496000, C423S497000
Reexamination Certificate
active
06507020
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a mass spectrometry method and a mass spectrometry apparatus for d halide compound, and more particularly relates to a mass spectrometry method and a mass spectrometry apparatus for a halide compound using soft ionization utilizing ion attachment in ionizing the halide compound for the purpose of mass spectrometry.
2. Description of the Related Art CF
4
, C
4
F
6
, and other perfluoro compounds (PFC), CH
3
and other hydrofluorocarbons (HFC), and SF
3
, NF
3
and other gases are utilized in various industries. These fluoride compounds are extremely stable, but have an extremely large effect on global warming. There have therefore been calls for reducing the amount of their emission on a global scale. In particular, in semiconductor and electronic component manufacturing facilities, gases are inevitably being discomposed and emitted Therefore, emphasis is currently being placed on precisely measuring what types of ingredients of the gases are being emitted in exactly what amounts.
In the past, the general practice had been to use mass spectrometry for measuring the ingredients and amounts of gas. Mass spectrometry measures the mass of the gas (or molecular weight) to identify the ingredients of the gas and measure the amount of the gas. In mass spectrometry, a positive charge or negative charge is given to the neutral gas molecules to Ionize them, then the gas molecules are led into a specific electrical field or magnetic field space and the electrical force or magnetic force applied to the ions is changed to obtain a mass spectrum with mass as its abscissa and the amount of tons as its ordinate. For this mass spectrometry, there have conventionally been several methods in accordance with the means of ionization used, that is, (1) the method of utilizing electron impact, (2) the method of utilizing electron attachment, and (3) the method of utilizing cation (positive ion) attachment. These mass spectrometry methods will be explained in brief below and their problems are pointed out.
(1) Electron Impact Mass Spectrometry:
In a mass spectrometry method utilizing electron impact (EI), electrons having an energy of, for example, 50 to 100 eV or so are made to collide with gas molecules to strip electrons from the gas molecules and convert the gas molecules to positive ions. This Is the most generally used method because the hardware is simple.
(2) Electron Attachment Mass Spectrometry;
This mass spectrometry method has been developed in recent years and uses the action of electron attachment (EA). That is, electrons having a low energy of not more than 10 eV are made to attach to the gas molecules to give the gas molecules a negative charge as a whole and ionize them. This method has the advantage of involving less excess energy and resulting in less dissociation compared with electron impact. The method was developed with the intent of precise mass spectrometry of fluoride compounds. As a technical reference of the related art,
Oyo Butsuri
(
Applied Physics
). vol. 68. no. 10, p. 1148 (1999) and
Review of Scientific Instruments
, vol. 69, no. 1., p. 116 (1998) may be mentioned.
(3) Cation Attachment Mass Spectrometry
This mass spectrometry method causes cations (or positive ions) to be attached to the gas molecules for ionization Instead of the afore-mentioned electron attachment. This method has been in existence for a comparatively long time, therefore has been mainly used in the field of organic spectrometry. The method alms at precise mass spectrometry of gas molecules without causing dissociation. The method of using positive charge metal ions of an alkali metal is effective. In practice, the efficacy has been confirmed for hydrocarbons with small electron affinity. Up until now, various systems have been proposed by Hodge, Bombick, Fujii, etc. These systems will be explained in brief next.
The Hodge system is described in
Analytical Chemistry
, vol. 48, no. 6. p. 825 (1976). The system proposed by Hodge utilizes Li
+
as the alkali metal ions. Li
+
is generated by heating an emitter including an Li oxide. The Li
+
generated from the emitter moves to the flight region, then is guided to the reaction chamber containing the gas molecules to be detected. Therefore, the emitter is placed in a region outside the reaction chamber. The ionization is performed in the reaction chamber. The gas molecules with the Li
+
attached as a result of the ionization are withdrawn from the reaction chamber and transported to a quadrapole mass spectrometer for mass spectrometry. This system is an indirect attachment method which causes Li
+
to be attached to the gas molecules being detected. It is said that direct attachment is difficult with this system. In indirect attachment. the Li
+
is first attached to a reaction gas, then the Li
+
is moved from the reaction gas, with the Li
+
to the gas being detected. In direct attachment. the Li
+
is attached directly to the gas molecules being detected without interposition of a reaction gas. The above reference gives working data to explain the indirect attachment in the above way. The reasons given are that there is little difference in the sensitivity by the detected gas (ease of attachment of cations) and there Is little dissociation. As opposed to this, it indicates that when using direct attachment, dissociation occurs when the detected gas is a fluoride compound etc. so, direct attachment is difficult. In the above configuration, a large amount of reaction gas (isobutane or other hydrocarbon) is introduced into the reaction chamber.
The system of Bombick is described in
Analytical Chemistry
, vol. 56, no. 3, p. 396 (1984). The system proposed by Bombick utilizes K+ as the alkali metal ions. An emitter containing potassium (K) oxide is placed in the reaction chamber. Only the gas being detected is introduced into the reaction chamber. No other reaction gas is introduced. Therefore, the K+ released from the emitter in the reaction chamber directly attaches to the molecules of the detected gas. That is, the system of Bombick is a direct attachment system.
Problems in Electron Impact Mass Spectrometry:
In this method, the electron impact is a physical action, so a high energy is given to the detected gas. Therefore, if electron impact is used for gas molecules of a fluoride compound or other halide compound, since the binding energy of atoms in the gas molecules is usually small, the excess energy of the electron impact will cause the gas molecules to dissociate into fragments along with the ionization. Therefore, the peak due to the gas molecules not dissociating in the mass spectrum is called the molecule peak (or parent peak), while the peaks of the dissociated fragments are called the fragment peaks. With molecules with large number of atoms such as the above halide compounds, however, fragment peaks appear due to dissociation and the inherent molecule peak cannot be discerned well at all.
FIG. 4
shows an example of a mass spectrum obtained by ionization of molecules of a fluoride compound, that is. C
4
F
8
, by electron impact by an electron energy of 70 eV. In
FIG. 4
, the abscissa indicates the mass, while the ordinate indicates the amount of ions. The mass of the C
4
F
8
molecule is 200 amu (atomic molecular units), but the molecule peak does not appear much at all in the mass spectrum. Only the fragment peaks of C
3
F
5
, C
2
F
4
, CF, etc. appear. In the past, the practice had been to deduce the inherent molecule peak, that is, the mass and amount of the molecules, based on the state of appearance of these fragment peaks. In this way, precise mass spectrometry of a halide compound was difficult with mass spectrometry using electron impact.
Problems in Electron Attachment Mass Spectrometry:
This method has currently reached a level of measurement sensitivity practical for halide compounds. Compared with the method of utilizing electron impact, there is Indeed less dissociation. Even so
Fujii Toshihiro
Shiokawa Yoshiro
Anderson Bruce
Anelva Corporation
Oliff & Berridg,e PLC
Wells Nikita
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