JPH0363174B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to an ion microanalyzer that irradiates a sample with primary ions and analyzes secondary ions released from the sample.

[Background of the invention]

Figure 1 shows the configuration of a conventional ion microanalyzer (hereinafter referred to as IMA), where 1' is a dual plasmatron primary ion source, 2 is a convergent lens system, 3 is a sample, and 4 is a mass spectrometer. It shows. In this IMA, the primary ions 5 generated in the primary ion source 1' are transferred to the convergent lens system 2.
The beam is focused to a predetermined beam diameter and irradiated onto the sample 3. The composition of the sample 3 can be determined by analyzing the secondary ions 6 emitted from the sample 3 by the irradiation with the primary ions 5 using the mass spectrometer 4.
The size of this primary ion source 1' is approximately 0.1 to 0.2 mmφ
With this, it is possible to analyze the μ-order range of sample 3.

In this way, IMA detects the sputtered secondary ions by irradiating the sample with primary ions, but the amount of secondary ions of a specific element m contained in the sample is
I _n is, I _n = I _l・η・K _n・C _n・S _n …(1) Here, I _l : Primary ion current η : Secondary ion yield of the device K _n : Secondary of element m Ionization rate C _n : Concentration of element m S _n : Sputtering rate of element m, so when I _l , η, and C _n are constant, I _n is
Depends on K _n and S _n . Both K _n and S _n have values specific to the element, and the larger the K _n value, the lower the detection limit.

Figure 2 shows the relative secondary ion concentration intensity ratio of positive secondary ions when various elements are irradiated with 13.5 KeV O ^- primary ions (HAStorms
et al Anal.Chem.2023.1977). The horizontal axis of this figure shows the atomic number, and the vertical axis shows the relative secondary ion intensity ratio.
Cr, Ru, In, Ba, etc. have high detection sensitivity in IMA, and C, N, S, As, Se, Cd, Te, Pt, Au,
It can be seen that elements such as Hg have low detection sensitivity in IMA. In other words, as shown in this figure, when O ^- primary ions are used, the sensitivity difference between elements is as much as 10 ⁴ to 10 ⁵ orders of magnitude, which not only makes it difficult to quantify from analysis results, but also However, it has the disadvantage of low detection sensitivity.

To solve this problem, a method using a Cs ion gun has been proposed. This heats the metal Cs in the Cs reservoir to a certain temperature and evaporates the Cs.
The sample is irradiated with the ionized material that is passed through the porous W which is kept at a high temperature.
The detection sensitivity is increased by increasing the value of K _n .

However, the source of this Cs ion gun has a size of, for example, approximately 2 mmφ, and the irradiation range of the sample is several.
As the diameter reached 10μ, it was not possible to analyze microscopic parts of about μ. Therefore, it was not possible to use this as an IMA with reduced sensitivity differences between elements.

[Purpose of the invention]

The present invention aims to eliminate these problems and make it possible to provide an IMA with reduced sensitivity differences between elements.

[Summary of the invention]

The present invention provides a dual plasmatron type first primary ion source that irradiates a sample with primary ions and sputters secondary ions, a means for analyzing the secondary ions, a filament type surface ionization type ion gun,
and irradiation ion switching means for changing the polarity of the potential of the surface ionization type ion gun with respect to the sample and switching between emitting ions of an element belonging to a group of the periodic table and ions of an element belonging to a group of the periodic table. , a second primary ion source that irradiates the analysis section of the sample with primary ions from the first primary ion source in a single phase.

In the present invention, the sensitivity difference between elements in FIG.
The reason why there are five orders of magnitude is because the ionization rate K _n and the sputtering rate S _n as mentioned above, and the fact that the sputtering rate S _n is usually 1 to 10 atoms/ion. In order to improve the ionization rate _Kn and reduce the difference in sensitivity between elements, we installed a second primary ion source to improve the ionization rate, and a dual plasmatron type first ion source _. By operating the first primary ion source and the second primary ion source simultaneously, the desired objective can be achieved.

[Embodiments of the invention]

FIG. 3 is an explanatory diagram of one embodiment, and the same parts as in FIG. 1 are given the same reference numerals. In this diagram, 1
1 is a dual plasmatron type first primary ion source, 7 is an acceleration power source for the mass spectrometer 4, 8 is a second primary ion source, 9 is a filament of the second ion source 8, 10 is a current source, and 11 is a Ion acceleration power supply, 12
indicates primary ions from the second ion source 8. The ion accelerating power source 11 makes the primary ions 5 generated from the first primary ion source 1 have a high energy of several keV or more, and the primary ions 12 generated from the second primary ion source have a lower energy than this. selected.

This second primary ion source 8 is a filament-type surface ionization ion source, in which an element applied onto a filament 9 is heated and ionized by a filament heating current from a current source 10, resulting in primary ions 1.
Releases 2. The primary ions 12 are irradiated in a superimposed manner at the position of the sample 3 that is irradiated with the focused primary ion beam 5.

In this embodiment, an ion accelerating power source 11 connected between the sample 3 and the filament 9
However, if the filament 9 is set to have a positive potential with respect to the sample 3, positive primary ions will be superimposed on the irradiation, and if it is set to have a negative potential, negative primary ions will be superimposed. irradiated. Primary ions generated from the primary ion source 1 generally include
Gas species ions such as O ^- , O ₂ ⁺ , Ar ⁺ are used,
Sample 3 is sputtered. Then, the primary ions 5 are emitted from the second primary ion source 8.
The primary ions 12 irradiated in a superimposed manner have an ionization rate of
Used to increase K _n . The primary ions emitted from this second primary ion source 8 are halogen element ions or alkali metal ions.

Next, the relationship between the type of primary ions 12 emitted from the second primary ion source 8 and the ionization rate K _n will be explained.

When an unknown sample M _x is irradiated with primary ions, the state shown in the following equation is obtained.

M _x゜M _x ⁺ +e ...(2) Here, M _x゜ is a neutral atom M ⁺ is a positive ion e is an electron In the process of sample atoms repeatedly colliding and ejected from the surface, positive ions M of the unknown sample When _x ⁺ captures electron e again, the positive ion M _x ⁺ of the unknown sample becomes a neutral atom
M _x゜. Therefore, if a halogen element exists on the sample, the probability that the electron e in equation (2) will be absorbed by the halogen element and neutralize the positive ion M _x ⁺ of the unknown sample decreases. In other words, the presence of the halogen element increases the positive secondary ion yield. Also, if alkali metals are present on the unknown sample,
Contrary to the case of halogen elements, they themselves have the property of emitting electrons and becoming positive ions, which increases the negative secondary ion yield of elements with high electron affinity.

For example, when CsCl of the second primary ion source is used, positive and negative ions are generated by heating the filament as shown in CsCl→C _s ⁺ +Cl ⁻ (3). Therefore, as mentioned above, when the potential of the unknown sample is positive with respect to the filament, Cl ^- in equation (3) is irradiated to the unknown sample, increasing the positive secondary ion yield, and the potential of the unknown sample is positive with respect to the filament. When it is negative, Cs ⁺ is irradiated onto the unknown sample, increasing the negative secondary ion yield.

FIG. 4 shows the effect of improving the secondary ion yield, with the horizontal axis plotting the atomic number and the vertical axis plotting the rate of increase in the secondary ion yield. As is clear from the comparison between this figure and Figure 2, in Figure 2, C, S, As, Se, Te, and
The secondary ion yields of Au and Pt have increased significantly. Therefore, by irradiating ion species that improve the secondary ion yield with low energy from the second primary ion source, it is possible to improve the secondary ion yield that cannot be detected by conventional IMA or has low sensitivity. , This makes it possible to reduce sensitivity differences between elements.

Since this IMA uses a duoplasmatron type ion source as the first primary ion source, the irradiation range of the sample with primary ions can be on the μ order, and the primary ion source from the second primary ion source As a result, it is possible to increase the ionization rate of primary ions in the irradiation range of the sample by the primary ions from the first primary ion source, and as a result, it is possible to analyze a minute part of the sample with a high secondary ion yield. It can be made possible.

In addition, when using a filament-type surface ionization type ion gun, it is possible to apply an ionizing substance to the filament so that the mode of generating positive and negative primary ions and the mode of emitting thermoelectrons can be combined. Thermionic electrons emitted by heating can also be used to neutralize charges during dissociation of an insulator.

〔Effect of the invention〕

The present invention is an IMA that reduces sensitivity differences between elements.
This has great industrial effects.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram of a conventional ion microanalyzer, Fig. 2 is a diagram showing the relationship between atomic number and relative secondary ion intensity ratio when using a conventional ion microanalyzer, and Fig. 3 is a diagram of the present invention. FIG. 4 is a diagram showing the relationship between the atomic number and the rate of increase in the secondary ion yield, which also shows the effect. 1... First primary ion source (duoplasmatron type), 2... Convergent lens system, 3... Sample,
4...Mass spectrometer, 5...Primary ion, 6...2
Secondary ion, 8... (second) primary ion source, 9...
... filament, 10 ... current source, 11 ... ion acceleration power source, 12 ... primary ions (from the second primary ion source).

Claims (1)

[Claims] 1. A first dual-plasmatron primary ion source that irradiates a sample with primary ions and sputters secondary ions, and means for analyzing the secondary ions;
A filament-type surface ionization type ion gun, and changing the polarity of the potential of the surface ionization type ion gun with respect to the sample, and switching between emission of ions of an element belonging to a group of the periodic table and ions of an element belonging to a group of the periodic table. and a second primary ion source that superimposes and irradiates the analysis section of the sample with primary ions together with the primary ions from the first primary ion source. Ion micro analyzer.