JP3055159B2 - Neutral particle mass spectrometer - Google Patents

Description

The present invention relates to a method for irradiating a sample to be analyzed with ions, post-ionizing neutral particles sputtered from the sample surface, and performing mass analysis of the ions. TECHNICAL FIELD The present invention relates to a neutral particle mass spectrometer, particularly to an ionization chamber thereof.

[Prior art] The secondary ion mass spectrometry (SIMS) method, which is now widely used as a trace analysis method for elements, has been compensated for in the future.
Attention is focused on neutral particle mass spectrometry (SNMS) methods that are expected to replace MS. 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 the particles can be subjected to mass analysis to perform elemental analysis of the sample. The amount of secondary ions generated at this time varies sensitively depending on the type of sample and the state of the sample surface, making measurement unstable and poor in reproducibility. On the other hand, the easiness of neutral particles coming out of the sample surface is a characteristic of the element, is not easily affected by other coexisting elements, is released from the sample in proportion to the concentration of that element in the sample, and secondary ions It is believed that mass spectrometry of neutral particles is more advantageous than mass spectrometry of secondary ions because of the greater radiation.

A conventional neutral particle mass spectrometer will be described with reference to FIG. In FIG. 4, 1 is an ion gun, 2 is a primary ion,
Reference numeral 3 denotes a sample to be analyzed, reference numerals 4 and 5 denote generated secondary ions and neutral particles, and reference numeral 6 denotes an ionization chamber, in which plate electrodes 61 and 62 generate uniform electric fields. Reference numeral 13 denotes a condensing lens, and reference numeral 14 denotes a laser beam. An excimer laser having high peak power and ultraviolet light having high photon energy is often used. 15 is a multiphoton ion, 17 is a mass spectrometer, 18 is an ion detector, 19 is a preamplifier, and 20 is a measurement and data processing device. The ion gun 1 to the ion detector 18 are all placed in a high vacuum or ultra high vacuum atmosphere.

 Next, the operation of this device will be described.

When the sample surface 3 is irradiated with the primary ions 2 from the ion gun 1, the sample surface 3 is sputtered by 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 increased. Accelerated by
Then, the multiphoton ionized and accelerated ions 15 pass through the mass spectrometer 17 and are converted into electric signals by the ion detector 18, and then are measured and data-processed through the preamplifier 19.
Guided to 20, the sample elements are analyzed.

[Problem to be Solved by the Invention] The conventional neutral particle mass spectrometer is configured as described above, and generates a uniform electric field by facing the plate electrodes in parallel, and irradiates a high-power pulse laser in this space region. Then, multi-photon ionization is performed to perform post-ionization, and the region to be ionized has a width approximately equal to the converging diameter of laser light condensed by a lens. Therefore, in the structure of the ionization chamber of the conventional neutral particle mass spectrometer, the initial energy distribution of the accelerating ions corresponding to the expansion of the ionization region is inevitably generated as shown in FIG. This contributes to a decrease in mass resolution.

The present invention has been made in order to solve the above-mentioned drawbacks of the prior art, and has a neutral particle mass spectrometer capable of suppressing the spread of the initial energy in the ionization chamber and improving the mass resolution. The purpose is to provide.

[Means for Solving the Problems] To achieve the above object, a neutral particle mass spectrometer of the present invention comprises an ionization chamber, an opening through which light passes, and an opening through which neutral particles pass. And a three-dimensional electrode provided with an opening through which ions obtained by ionizing neutral particles pass, and an extraction electrode provided in parallel with the ion passing opening, and an opening through which the light passes The part is formed on the three-dimensional electrode so that light passes through a part where the potential change formed in the three-dimensional electrode is gradual.

[Operation] 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 formed like a conventional ionization chamber. Instead of a linear gradient distribution, a potential distribution having a gradual potential change near the ionization region is obtained. Therefore, the initial energy distribution given to the ions is also reduced, and the mass resolution can be improved.

Embodiment An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 is a view showing an embodiment of the present invention, wherein 1 is an ion gun, 2 is a primary ion, 3 is a sample to be analyzed, 4 and 5 are secondary ions and neutral particles generated, 6 is a shield electrode, Reference numeral 7 denotes a cylindrical electrode having openings 8 to 11. 12 is an insulator, 13 is a condenser lens, 14 is an excitation laser beam, 15 is multiphoton ionized ions, 16 is an extraction electrode, 17 is a mass spectrometer, 18 is an ion detector, 19 is a preamplifier, 20 Is a measurement and data processing device. The ion gun 1 to the ion detector 18 are all placed in a high vacuum or ultra high vacuum atmosphere.

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

The operation of analyzing a sample element using this analyzer will be described. Sample surface 3 by primary ions 2 from ion gun 1
Is irradiated, 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 shielded electrodes 6 and cylindrical electrodes 7.
The light is reflected and removed by the reflected electric field created by. On the other hand, the generated neutral particles 5 enter the inside of the cylindrical electrode through the opening 8, and are photoionized by being irradiated with the laser beam 14 condensed by the lens 13 through the opening 9. . The used laser light exits the cylindrical electrode 7 through the opening 10. At this time, since a potential distribution having a non-linear change as shown in FIG. 2 is generated inside the cylindrical electrode 7 as described above, the potential distribution is given to the ions as shown in FIG. 3b. The spread of the initial energy is very small. The generated ions 15 pass through the opening 11 according to the potential distribution formed by the cylindrical electrode 7 and the extraction electrode 16 and
Led to. The ions that have passed through the mass spectrometer 17 are converted into electrical signals by an ion detector 18 and then guided to a measurement and data processor 20 via a preamplifier 19, where the sample elements are analyzed.

Although a cylindrical electrode is used in the above embodiment, a similar effect can be obtained by forming the electrode in a cubic or rectangular parallelepiped shape.

[Effects of the Invention] As described above, in the present invention, since the ionization chamber is constituted by the three-dimensional electrode and the extraction electrode, a linear gradient distribution is formed inside the three-dimensional electrode as in the conventional ionization chamber. Not
In the vicinity of the ionization region, a potential distribution having a gradual potential change is obtained. Therefore, the initial energy distribution given to the ions is reduced, and the mass resolution can be improved. In addition, the shape of the potential distribution has an effect of collecting ions on the central axis, and the focal point of the laser beam fluctuates somewhat, so that a decrease in sensitivity can be prevented even if the ion generating point is not on the central axis.

[Brief description of the drawings]

FIG. 1 is a diagram showing a neutral particle mass spectrometer of the present invention, and FIG.
The figure shows the potential distribution inside the cylindrical electrode, FIG. 3 shows the relationship between the potential distribution inside the cylindrical electrode and the spread of the ion initial energy, and FIG. 4 shows the conventional neutral particle mass spectrometer. FIG. DESCRIPTION OF SYMBOLS 1 ... Ion gun, 2 ... Primary ion, 3 ... Analyte sample, 4 ... Secondary ion, 5 ... Neutral particles, 6 ... Shield electrode, 7 ... Cylindrical electrode, 8-11 ... … Opening, 12 ……
Insulator, 13: Focusing lens, 14: Excitation laser beam, 15
...... Ions with neutral particles ionized, 16 ... Extraction electrode, 17 ... Mass spectrometer, 18 ... Ion detector, 19 ... Preamplifier, 20 ... Measurement and data processing device

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01J 49/14 G01N 27/62 H01J 49/26

Claims (1)

(57) [Claims] 1. A neutral particle mass spectrometer for irradiating a sample to be analyzed with ions, post-ionizing neutral particles sputtered from the surface of the sample, and performing mass analysis of the ions. Part, an opening through which neutral particles pass,
An ionization chamber is formed by a three-dimensional electrode provided with an opening through which ions obtained by ionizing neutral particles pass, and an extraction electrode provided in parallel with the ion passage opening, and an opening through which the light passes A neutral particle mass spectrometer, wherein a hole is formed in the three-dimensional electrode so that light passes through a part of the three-dimensional electrode where the change in potential is gradual.