JP3140577B2 - Laser ionization neutral particle mass spectrometer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to laser ionization for measuring the mass spectrum of photoexcited ions generated by irradiating a neutral particle generated by irradiating an ion beam on an area to be analyzed on a solid surface with an ultraviolet pulse laser. The present invention relates to a neutral particle mass spectrometer, and more particularly, to a laser ionization neutral particle mass spectrometer capable of performing a depth analysis with good sensitivity under conditions of good depth resolution.

[0002]

2. Description of the Related Art As a typical method for trace analysis of a solid sample, there is a secondary ion mass spectrometry for detecting secondary ions sputtered from the surface by an ion beam. However, since secondary ions have low generation efficiency and large element dependence and sample dependence, the secondary ion intensity is not proportional to the element concentration in the sample, and there is a problem in quantitativeness. On the other hand, the amount of neutral particles sputtered at the same time as the secondary ions is almost proportional to the element concentration. Therefore, the neutral particle mass spectrometry for detecting this is an analytical method with good quantitative properties. In particular, laser ionization neutral particle mass spectrometry, in which neutral particles are ionized by a high-intensity laser and mass analysis is performed, is known as a method with high ionization efficiency. However, since lasers that can be ionized are limited to pulsed lasers, the ion intensity obtained per second is smaller than that of secondary ion mass spectrometry, and laser ionization neutral particle mass spectrometry is used for secondary ion mass spectrometry. Often inferior in sensitivity. As a laser ionization neutral particle mass spectrometer capable of depth direction analysis, there is an apparatus (laser ionization neutral particle mass spectrometer) described in JP-A-3-291559. This device can also be used as a secondary ion mass spectrometer. Hereinafter, the principle and configuration of the present device will be described.

FIG. 4 shows a schematic configuration of the present apparatus. In the figure, first, a continuous ion beam 2 is generated from an ion beam generator 1. Next, after the continuous ion beam 2 is focused using the electrostatic lens 3, the continuous ion beam 2 is vibrated by the scanning electrode 4 to apply an impact while scanning the surface of the solid sample 5. Neutral particles 6 and secondary ions 7 are sputtered from the surface of the solid sample 5 by the impact of the continuous ion beam 2. Here, the neutral particles 6 are ionized by an ultraviolet pulse laser 9 generated from an ultraviolet laser
Becomes Secondary ions 7 and photoexcited ions 10 are extracted electrodes 11
Mass spectrometer using magnetic and electric fields
After being mass-separated by an ion detector 13, it is converted into an electric pulse by the ion detector 13 and counted by the pulse counter 14. This device can be used also as a secondary ion mass spectrometer by cutting off the ultraviolet pulse laser 9 and changing the setting of the extraction electrode 11.

In this apparatus, since the continuous ion beam 2 is used for sputtering, the secondary ions 7 detected by the mass analyzer 12 are continuously generated. On the other hand, the photoexcited ions 10 generated by ionization by the ultraviolet pulse laser 9 have a higher peak value than the secondary ions 7, but generate only the number of times equal to the repetition frequency of the ultraviolet pulse laser 9 per second. Is discrete in time. When detecting the photo-excited ions 10 with the present apparatus by utilizing the difference in the temporal generation method of the secondary ions 7 and the photo-excited ions 10, the photo-excited ions 10 Detection is performed only during the time when 10 arrives at the ion detector 13.

The reason why the continuous ion beam 2 is scanned in the present apparatus is to perform a depth direction analysis as in the secondary ion mass spectrometry. In general, in the depth direction analysis in the secondary ion mass spectrometry, as shown in FIG. 5, a method of scanning an ion beam over a wide range of the surface of a solid sample and detecting only secondary ions from near a flat center is adopted. Can be This makes it possible to remove the influence of the non-flat end portion, and obtain a good depth resolution.

[0006]

When the technique of the depth direction analysis in the secondary ion mass spectrometry described in the preceding section is directly applied to the depth direction analysis in the laser ionization neutral particle mass spectrometry, Such a problem arises. First, FIG. 6 shows a region where the ion beam irradiates the surface of the solid sample when the depth analysis in the secondary ion mass spectrometry is directly applied to the depth analysis in the laser ionization neutral particle mass spectrometry. And the relationship between the region near the center where the neutral particles serving as the source of the photoexcited ions are sputtered and the position where the neutral particles serving as the source of the photoexcited ions are generated. As can be seen from the figure, as in the case of performing the depth direction analysis in the secondary ion mass spectrometry, neutral particles generated only from the vicinity of the center, which is flat, are ionized and detected as photoexcited ions, and the edge of the non-flat edge is detected. By removing the influence of the portion, it is possible to improve the resolution in the depth direction.

On the other hand, since the generation of photoexcited ions by an ultraviolet pulse laser is discrete in time, the generation position of the neutral particles that are the source of the photoexcited ions is determined by scanning the ion beam with the solid sample. Will exist discretely above. At this time, if the technique of the depth direction analysis in the secondary ion mass spectrometry is directly applied to the depth direction analysis in the laser ionization neutral particle mass spectrometry, all the generated photoexcited ions cannot be used. For example, in the case where 9% near the center of the region scanned by the ion beam is used for depth direction analysis, even if the repetition frequency of the ultraviolet pulse laser is 100 Hz, the photoexcitation ions actually used are It is limited to those generated by only nine laser pulses.

As can be seen from the above description, when the technique of the depth direction analysis in the secondary ion mass spectrometry is directly applied to the depth direction analysis in the laser ionization neutral particle mass spectrometry, the resolution in the depth direction is improved. In this case, the number of photoexcited ions detected in one second is reduced to about 1/10, and as a result, the sensitivity is reduced. Therefore, when the technique of the depth direction analysis in the secondary ion mass spectrometry is directly applied to the depth direction analysis in the laser ionization neutral particle mass spectrometry, the sensitivity is good under the condition that the depth direction resolution is good. It is difficult to perform depth analysis.

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art and to provide a laser ionized neutral particle mass capable of performing a sensitive depth analysis under conditions of good depth resolution. An object of the present invention is to provide an analyzer.

[0010]

The object of the present invention is to irradiate an area to be analyzed on the surface of a solid sample with an ion beam in a vacuum to sputter neutral particles from the area to be analyzed.
An ultraviolet pulse laser that ionizes the neutral particles to generate photoexcited ions, a mass analyzer that mass separates the photoexcited ions, and a laser that detects the photoexcited ions mass separated by the mass analyzer In the ionized neutral particle mass spectrometer, the time required for the ion beam to scan the region to be analyzed once is equal to the emission interval of the ultraviolet pulse laser, and the pulse laser is moved from the central portion of the region to be analyzed. This can be achieved by a laser ionization neutral particle mass spectrometer characterized by having means for irradiating sputtered neutral particles.

[0011]

FIG. 7 shows an example of the distribution of the concentration of the trace element M in the solid sample to be analyzed in the depth direction. FIG. 8 shows the depth analysis in the secondary ion mass spectrometry as it is for laser ionized neutral particles. FIG. 9 shows an example of a result expected to be obtained when the sample is analyzed by applying to the depth direction analysis in the mass spectrometry, and FIG. 9 shows the result when the sample is analyzed by the laser ionization neutral particle mass spectrometer of the present invention. An example of the expected results is shown. In the case of FIG. 8, since the sensitivity is poor, the ion intensity is small even at the same concentration, and the minimum detectable concentration, that is, the detection limit is high. On the other hand, in the case of FIG. 9, all the laser pulses can be used and all the photoexcited ions generated can be used, so that the depth direction analysis method in the secondary ion mass spectrometry of FIG. Sensitivity can be improved about 10 times as compared with the case of application to depth direction analysis in ionized neutral particle mass spectrometry, and the minimum detectable concentration, that is, the detection limit can be lowered.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The laser ionization neutral particle mass spectrometer of the present invention will be specifically described below with reference to embodiments.

[0013]

Embodiment 1 FIG. 1 is a diagram showing an example of the relationship between the emission of an ultraviolet pulse laser and the voltage sweeping a scanning electrode in a laser ionization neutral particle mass spectrometer of the present invention. In the apparatus of the present invention, the ion beam scans the region to be analyzed once by sweeping the voltage between the scan electrode in the X direction and the scan electrode in the Y axis direction in synchronization with the emission of the ultraviolet pulse laser. The time required for the irradiation is set to be equal to the light emission interval of the pulse laser, and further, the ultraviolet pulse laser is applied to the neutral particles generated from the central part in the ion beam irradiation area. Specifically, when the repetition frequency of the ultraviolet pulse laser is f and the number of scanning lines is n,
As shown in FIG. 1, a sawtooth voltage of fHz and n × fHz is swept across the scanning electrodes in the X direction and the scanning electrodes in the Y axis direction. As a result, first, the ultraviolet pulse laser emits light only when the voltage of the scanning electrode in the X direction reaches a certain predetermined value. At this time, as shown in FIG. 2, the ultraviolet pulse laser emits light only when the ion beam reaches a certain position in the region to be analyzed. Since neutral particles have a finite velocity, it takes a finite time to reach a spatial region to be ionized after being sputtered. This time is defined as t seconds. The emission phase of the ultraviolet pulse laser is adjusted so that the ultraviolet pulse laser emits light t seconds after the time when the center portion of the analysis area is sputtered.

In this way, it is possible to ionize neutral particles only from the flat central portion and detect them as photoexcited ions, to improve the depth direction resolution and to generate an ultraviolet pulse laser. Since all the photoexcited ions obtained can be used, the sensitivity can be improved.

[0015]

[Embodiment 2] FIG. 3 shows that an ion beam is scanned in a spiral in synchronization with the emission of an ultraviolet pulse laser, and neutral ions generated from the central part of the analysis area are also used in the same manner as in the first embodiment. FIG. 4 is a diagram showing a state in which particles are irradiated with an ultraviolet pulse laser. Thus, similarly to the case of the first embodiment, the neutral particles only from the flat central portion are ionized and detected as photoexcited ions, thereby improving the depth direction resolution, and generated by the ultraviolet pulse laser. Since all the photoexcited ions can be used, the sensitivity can be improved.

In the case of this embodiment, even if there is a slight fluctuation in the emission timing of the ultraviolet pulse laser, the ion beam is scanned in a spiral shape, so that the ion beam is generated from the true center of the region to be analyzed. The neutral pulse generated from a position very close to the true center portion is irradiated with the ultraviolet pulse laser even if it is not a neutral particle. Therefore, even if the synchronization between the emission of the ultraviolet pulse laser and the scanning of the ion beam is not perfect, the depth direction analysis with good sensitivity can be performed under the condition that the depth direction resolution is good, as in the case of the first embodiment. It is.

[0017]

As described above, by using the laser ionization neutral particle mass spectrometer according to the present invention, the problems of the prior art can be solved and the resolution in the depth direction can be improved. A laser ionization neutral particle mass spectrometer capable of performing sensitive depth analysis under a variety of conditions was provided.

[Brief description of the drawings]

FIG. 1 is a diagram showing an embodiment of a relationship between emission of an ultraviolet pulse laser and a sweep voltage applied to a scanning electrode in the laser ionization neutral particle mass spectrometer of the present invention.

FIG. 2 is a diagram showing a relationship between a part of a trajectory of an ion beam scanning a surface of a solid sample and ultraviolet pulse laser emission in the apparatus of the present invention.

FIG. 3 is a diagram showing an example of the relationship between the trajectory of an ion beam scanning a region to be analyzed and the emission of an ultraviolet pulse laser in the apparatus of the present invention (when the ion beam is scanned spirally).

FIG. 4 is a diagram showing a configuration of a conventional laser ionization neutral particle mass spectrometer.

FIG. 5 is a diagram showing a relationship between a region where an ion beam is scanned and a region where a secondary ion is detected when a depth direction analysis is performed using a secondary ion.

FIG. 6 shows a region where an ion beam scans on the surface of a solid sample when a depth direction analysis method in secondary ion mass spectrometry is directly applied to a depth direction analysis in laser ionization neutral particle mass spectrometry. The figure which shows the relationship between the area | region which detects a photoexcitation ion, and the neutral particle generation position which is the source of a photoexcitation ion.

FIG. 7 is a diagram showing an example of a depth direction distribution of the concentration of a trace element M in a solid sample to be analyzed.

FIG. 8 is a diagram showing an example of an analysis result expected to be obtained when the technique of the depth direction analysis in the secondary ion mass spectrometry is directly applied to the depth direction analysis in the laser ionization neutral particle mass spectrometry. .

FIG. 9 is a diagram showing an example of an analysis result expected to be obtained when analysis is performed by the laser ionization neutral particle mass spectrometer of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Ion beam generator, 2 ... Continuous ion beam, 3
... electrostatic lens, 4 ... scanning electrode, 5 ... solid sample, 6 ... neutral particles, 7 ... secondary ion, 8 ... ultraviolet laser generator, 9 ... ultraviolet pulse laser, 10 ... photoexcited ion, 11 ... extraction electrode,
12… Mass analyzer, 13… Ion detector, 14… Pulse counter.

──────────────────────────────────────────────────続 き Continuation of front page (72) Inventor Yoshikazu Honma Nippon Telegraph and Telephone Corporation, 1-6-1, Uchisaiwaicho, Chiyoda-ku, Tokyo (56) References JP-A-1-265154 (JP, A) JP-A Sho 49-66396 (JP, A) JP-A-4-56057 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01J 49/10 H01J 49/26 H01J 37/252

Claims (2)

(57) [Claims] 1. A means for irradiating an ion beam to a region to be analyzed on a surface of a solid sample in a vacuum to sputter neutral particles from the region to be analyzed, and an ultraviolet ray for ionizing the neutral particles to generate photoexcited ions. In a laser ionization neutral particle mass spectrometer comprising a pulse laser, a mass analyzer for mass-separating the photoexcited ions, and a detector for detecting photoexcited ions mass-separated by the mass analyzer, the ion beam is The time required to scan the area to be analyzed once is equal to the emission interval of the ultraviolet pulse laser,
A laser ionization neutral particle mass spectrometer comprising means for irradiating the pulse laser to neutral particles sputtered from a central portion of the region to be analyzed. 2. The laser ionization neutral particle mass spectrometer according to claim 1, further comprising means for spirally irradiating the ion beam.