JPH04138648A - Neutral particle mass analyzer - Google Patents

Abstract

PURPOSE:To improve mass resolution by constituting an ionizing chamber of a three-dimensional electrode, provided with an opening part for light to permeate and an opening part for an ion of ionizing a neutral particle to permeate, and a draw out electrode provided in parallel to the ion permeating opening part. CONSTITUTION:When a sample surface 3 is irradiated by a primary ion 2 from an ion gun 1, a neutral particle 5 or the like is generated. Next, the neutral particle 5 passes through an opening part 8 to advance into the inside of a cylindrical electrode 7. Then, laser light 14 is irradiated to light-ionize the neutral particle 5. Potential distribution is generated in the electrode 7 to decrease a spread of initial energy given to the ion, and an ion 15, generated in accordance with the potential distribution formed by the electrode 7 and a draw out electrode 16, is guided to a mass analyzing part 17. Thereafter, the ion 15 is converted into an electrical signal to analyze a sample element. In this way, mass resolution is improved, and deterioration of sensitivity by slight fluctuation of a converging point of laser light can be prevented by collecting the ion on the center axis.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention is directed to a method in which a sample to be analyzed is irradiated with ions, neutral particles sputtered from the sample surface are post-ionized, and the ions are subjected to mass spectrometry. particle mass spectrometers, especially
Regarding the ionization chamber.

[Prior art] Neutral particle mass spectrometry (SNMS) is expected to compensate for the shortcomings of secondary ion mass spectrometry (SIMS), which is currently widely used as a method for trace analysis of elements, and to replace SIMS in the future. The method is attracting attention. When the sample surface is irradiated with an ion beam, particles such as secondary ions, neutral particles, and electrons are emitted from the sample surface, and elemental analysis of the sample can be performed by mass spectrometry of these particles.

The amount of secondary ions generated at this time changes sensitively depending on the sample type and the state of the sample surface, making measurement unstable and lacking in reproducibility. On the other hand, the ease with which neutral particles come out from the sample surface is a characteristic of the element, and is influenced by other coexisting elements. Mass spectrometry of neutral particles is considered more advantageous than mass spectrometry of secondary ions because the amount of radiation is larger than that of secondary ions.

A conventional neutral particle mass spectrometer will be explained with reference to FIG.

In Fig. 4, 1 is an ion gun, 2 is a primary ion, 3 is a sample to be analyzed, 4.5 is a generated secondary ion and neutral particles, 6 is an ionization chamber, and a uniform electric field is generated by plate electrodes 61 and 62. is occurring. Reference numeral 13 indicates a condensing lens, and reference numeral 14 indicates a laser beam, and an excimer laser having ultraviolet light with high photon energy and high peak power is often used. 15 is a multiphoton ionized ion, 17 is a mass spectrometer, 18
19 is an ion detector, 19 is a preamplifier, and 20 is a measurement and data processing device. Note that the ion gun 1 to the ion detector 18 are all placed in a high vacuum or ultrahigh vacuum atmosphere.

Next, the operation of this device will be explained.

When the sample surface 3 is irradiated with primary ions 2 from the ion gun 1, the sample surface 3 is sputtered with the irradiated primary ions 2, and secondary ions 4 and neutral particles 5 are generated. The generated secondary ions 4 are reflected and removed by applying an appropriate potential to the electrode 61. The neutral particles 5 pass through as they are, and are irradiated with the laser beam 14 focused by the lens 13 between the electrodes 61 and 62 to be multiphoton ionized, and the electric field between the electrodes 61 and 62 is is accelerated by Then, the multiphoton ionized and accelerated ions 15 pass through the mass spectrometer 17 and are detected by the ion detector 18.
After being converted into an electrical signal, the signal is guided to a measurement and data processing device 20 via a preamplifier 19, where the sample elements are analyzed.

[Problem to be solved by the invention] A conventional neutral particle mass spectrometer is configured as described above,
Post-ionization is performed by arranging plate electrodes facing each other in parallel to generate a uniform electric field, and irradiating this spatial region with a high-power pulsed laser to produce multiphoton ionization. It has a spread approximately equal to the diameter of the condensed light. Therefore, in the structure of the ionization chamber of a conventional neutral particle mass spectrometer, an initial energy distribution of accelerated ions corresponding to the spread of the ionization region inevitably occurs as shown in Figure 3a, and the initial energy distribution of accelerated ions in the subsequent mass spectrometer This is one of the causes of lower mass resolution.

The present invention was devised to eliminate the drawbacks of the prior art as described above, and provides a neutral particle mass spectrometer that can suppress the spread of initial energy in the ionization chamber and improve mass resolution. The purpose is to provide.

[Means for Solving the Problems] In order to achieve the above object, the neutral particle mass spectrometer of the present invention has an ionization chamber that has an aperture through which light passes and an aperture through which neutral particles pass. and an aperture through which ions obtained by ionizing neutral particles pass, and an extraction electrode provided in parallel to the ion-passing aperture.

[Function] The neutral particle mass spectrometer of the present invention is configured as described above, and when a predetermined voltage is applied to the three-dimensional electrode and the extraction electrode, the interior of the three-dimensional electrode is similar to a conventional ionization chamber. Instead of a linearly sloped distribution, a potential distribution with gradual potential changes near the ionization region is obtained. Therefore, the initial energy distribution given to ions is also reduced, and mass resolution can be improved.

[Example] Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a diagram showing an embodiment of the present invention, in which 1 is an ion gun, 2 is a primary ion, 3 is a sample to be analyzed, 4.5 is a generated secondary ion and neutral particles, 6 is a shield electrode, 7 is a cylindrical electrode, which has openings 8-11. 12 is an insulator, 13 is a focusing lens, 14 is an excitation laser beam 1.1
5 is a multiphoton ionized ion, 16 is an extraction electrode,
17 is a mass spectrometer, 18 is an ion detector, 19 is a preamplifier, and 20 is a measurement and data processing device. Incidentally, the ion gun device or the ion detector 18 are all placed in a high vacuum or ultrahigh vacuum atmosphere.

When a predetermined voltage is applied between the cylindrical electrode 7 and the extraction electrode 16, a nonlinear potential distribution as shown in FIG. 2 is generated inside the cylindrical electrode.

The operation of analyzing sample elements using this analyzer will be explained.

When the sample surface 3 is irradiated with primary ions 2 from the ion gun 1, the sample surface 3 is sputtered with the irradiated primary ions 2, and secondary ions 4 and neutral particles 5 are generated. The generated secondary ions 4 are reflected and removed by the reflected electric field created by the shield electrode 6 and the cylindrical electrode 7. On the other hand, the generated neutral particles 5 enter the inside of the cylindrical electrode through the opening 8.
The laser beam 14 focused by the lens 13 is irradiated through the aperture 9 and photoionized. The used laser light exits the cylindrical electrode 7 through the aperture 10. At this time, as described above, a potential distribution with a nonlinear change as shown in FIG. 2 is generated inside the cylindrical electrode 7, so that the potential distribution is applied to the ions as shown in FIG. 3. The initial energy spread becomes very small. The generated ions 15 are guided to the mass spectrometer 17 through the aperture 11 according to the potential distribution formed by the cylindrical electrode 7 and the extraction electrode 16. The ions that have passed through the mass spectrometer 17 are converted into electrical signals by the ion detector 18, and then guided to the measurement and data processing device 20 via the preamplifier 19, where the sample elements are analyzed.

Although a cylindrical electrode was used in the above embodiment, the same effect can be obtained by using a cubic or rectangular parallelepiped electrode.

[Effects of the Invention] As described above, in the present invention, since the ionization chamber is constituted by a three-dimensional electrode and an extraction electrode, there is no linear gradient distribution inside the three-dimensional electrode unlike in the conventional ionization chamber. Therefore, a potential distribution with gradual potential changes is obtained in the vicinity of the ionization region. Therefore, the initial energy distribution given to the ions becomes smaller, and mass resolution can be improved.

In addition, the shape of the potential distribution has the effect of concentrating ions on the central axis, and even if the focal point of the laser beam changes somewhat and the ion generation point is not on the central axis, it is possible to prevent a decrease in sensitivity.

[Brief explanation of the drawing]

Figure 1 is a diagram showing the neutral particle mass spectrometer of the present invention, Figure 2 is a diagram showing the neutral particle mass spectrometer of the present invention.
The figure shows the potential distribution inside the cylindrical electrode. Figure 3 shows the relationship between the potential distribution inside the cylindrical electrode and the spread of ion initial energy. Figure 4 shows the conventional neutral particle mass spectrometer. FIG. 1...Ion gun, 2...-Next ion,
3... Sample to be analyzed, 4... Secondary ions, 5... Neutral particles, 6... Shield electrode, 7... Cylindrical electrode, 8-11...
Opening portion, 12... Insulator, 13... Focusing lens, 14... Excitation laser beam, 15...
...Ions that are ionized neutral particles, 16...
... Extraction electrode, 17 ... Mass spectrometry section, 18
...Ion detector, 19 ...Preamplifier, 20 ...Measurement and data processing device

Claims (1)

[Claims] (1) In a neutral particle mass spectrometer that irradiates the sample to be analyzed with ions, post-ionizes the neutral particles sputtered from the sample surface, and performs mass spectrometry on the ions, there is an opening through which light passes. , a three-dimensional electrode provided with an aperture through which neutral particles pass, an aperture through which ions obtained by ionizing the neutral particles pass, and an extraction electrode provided in parallel to the ion-passing aperture. A neutral particle mass spectrometer comprising an ionization chamber.