JP3643917B2 - Microscopic laser mass spectrometer - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a microscopic laser mass spectrometer for analyzing a substance at a specific location on a sample, and in particular, a microscopic laser mass for analyzing a minute region in a semiconductor, a liquid crystal display, a memory disk, a circuit board, etc. with high sensitivity and high resolution. Related to analyzers.
[0002]
[Prior art]
A conventional microscopic laser mass spectrometer has a system diagram shown in FIG. 12 as described in JP-A-63-146339. In FIG. 12, 1 is a mass spectrometer, 2 is a sample, 6 is a laser light source, 14 and 16 are dichroic mirrors, 22 is a condensing lens, 24 is an ion extraction electrode, and 34 is an ion detector. Laser light generated from the laser light source 6 passes through the dichroic mirrors 14 and 16 and is collected on the sample 2 by the condenser lens 22 and the reflection lens 24. The atomic or molecular ions excited by the laser light are accelerated by the extraction electrode 28, pass through the ion passage hole 24 a provided in the center of the reflection mirror 24, and subjected to mass analysis by the mass analysis unit 1.
[0003]
In the prior art, the laser light source 6 and the condenser lens 22 are usually provided separately from the mass spectrometer. The laser light 6 generated from the laser light source 6 is condensed by the condenser lens 22 and the sample 2 is collected. In order to irradiate the lens, a reflecting mirror 24 is necessary, and the position of the reflecting mirror 24 is between the condenser lens 22 and a lens having a large numerical aperture (hereinafter referred to as NA). There were restrictions on using. For this reason, it has not been possible to observe the sample 2 with high precision like a microscope or to narrow the laser beam to a specific location on the sample.
[0004]
In the prior art, atoms and molecular ions generated in the sample are accelerated by the extraction electrode 28, pass through the ion passage hole 24a of the reflection mirror 24, and enter the detector 34. However, it has not been sufficiently considered to converge on the passage hole 24a and pass the mirror 24.
[0005]
Insufficient examination has been conducted on the fact that the ions collide with the reflecting mirror 24 and most of them are lost and the sensitivity is lowered.
[0006]
[Problems to be solved by the invention]
In a conventional microscope laser mass spectrometer, as described above, the reflecting mirror is arranged between the sample and the condenser lens, because of the long optical path between the sample and the condenser lens, N. of the condenser lens A. Had to use a lens system with a small focal length and a long focal length.
In order to increase the resolution of the observation image by narrowing down the laser beam, A. It is necessary to use a lens with a large focal length of the lens.
For this reason, if the reflecting mirror is arranged between the sample and the condenser lens as in the conventional example, the laser beam cannot be reduced to a small size and the resolution of the observation image cannot be increased.
N. A. There is an objective lens used in a microscope as a lens having a large focal length and a short focal length. By using such a lens, the laser beam can be narrowed down and a good observation image with high resolution can be obtained.
However, atom and molecular ions generated from the sample upon irradiation with laser light cannot be transmitted through the objective lens unlike light.
For this reason, it is necessary to devise so that a hole is made in the center of a lens and an ion is allowed to pass through. In addition, it is necessary to devise so that atoms and molecular ions can be accelerated to a speed necessary for analysis with a laser mass spectrometer. In addition, it is necessary to devise so that ion particles are not lost by colliding with a wall or the like when passing through a hole formed in the lens system.
[0007]
By solving this problem, the present invention makes it possible to narrow down the laser beam and to observe the measurement part of the sample with sufficient resolution, and to detect atoms and molecular ion particles generated at a specific observed position. An object of the present invention is to provide an apparatus capable of mass spectrometry with high sensitivity.
[0008]
[Means for Solving the Problems]
In order to achieve the above object, a microscopic laser mass spectrometer according to the present invention includes a stage on which a sample is mounted, an optical system that irradiates the surface of the sample with laser light, and atoms vaporized from the surface of the sample by irradiation with the laser light. In a microscopic laser mass spectrometer equipped with an ion detector for detecting ions or molecular ions,
The optical system includes a lens in which a hole through which atomic ions or molecular ions pass is opened at the center of the optical axis, and an ion control composite electrode structure disposed in the hole.
The ion control composite electrode structure has a triple tubular member composed of a conductive outer tube, an electrically insulating middle tube, and a conductive inner tube. It is positioned on the sample side with respect to the member and is provided separately from this, and a tip electrode having a tubular shape concentric with the optical axis is provided,
Further, a microscopic laser mass spectrometer characterized in that an extraction electrode made of a conductive film having a hole concentric with the optical axis is disposed between the sample and the tip electrode.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
N. A. As a lens having a large focal length and a short focal length, an objective lens used in a microscope has been conventionally used. However, the diameter of the lens that can not open a large hole through the ion particles in the small center. If the hole is opened, the resolution of the image is deteriorated, and the laser beam cannot be condensed so that the hole is very small to be opened without such influence. In the present invention, the objective lens of the microscope is made as large as possible without degrading the resolution and resolution, and the hole through which atoms and molecular ion particles are passed is made as small as possible at the center of the optical axis of this lens. Then, an ion permeable pipe electrode was formed to allow atomic and molecular ions to pass through the hole.
[0010]
The resulting atoms by the excitation of the laser beam, the molecular ion particles, it is necessary to highly accelerated at a high voltage in a short time only Ru can.
Moreover, it is necessary to pass through the hole so that the ion particles accelerated at high speed do not collide with the “wall of the hole opened in the lens” and cause a loss.
For this purpose, a voltage is applied so that the particle ions do not collide with the wall, and preferably a voltage that can pass through the center of the hole is applied . More preferably, it is preferable to provide a structure including an electrode group that can focus ions at a specific location.
As the above structure, an Einzel lens composed of three groups of electrodes has been conventionally used. Maybe only a small work can be such an Einzel lens in the present invention, it was to be placed in a hole drilled in the center of the microscope objective lens.
[0011]
However, the high-resolution objective lens is composed of a plurality of lenses, and the smaller the lens closer to the sample , the larger the hole cannot be made.
For this reason, the tip part of the structure for converging the ions is formed in a pipe shape that is as simple as possible.
Since the central portion of the objective lens can have a larger hole than the tip portion, the Einzel lens electrode structure is set in the central portion.
[0012]
In such an optical system, the numerical aperture of the objective lens on the surface of the sample is reduced by irradiating the surface of the sample with laser light through the objective lens of the microscope. A. And can be narrowed down to the diffraction limit determined by the wavelength.
[0013]
As a result, it is possible to easily select specific minute portions on the sample surface and generate atoms and molecular ions of the optical system from the sample. By using an objective lens for a microscope, it is possible to irradiate with a smaller spot size with a large numerical aperture and to keep the aberration of the optical system small, and to selectively generate atomic and molecular ions of the optical system in a fine area. be able to. Moreover, analysis can be performed by opening a hole at the tip of the lens and introducing atomic and molecular ion particles to the analyzer through the hole.
[0014]
(Condensed diameter) = 1.22 × (wavelength) / (NA) (1)
A conductive pipe is provided in the hole formed in the center of the objective lens, and ions are taken in by applying a high voltage between the sample and the pipe.
[0015]
In addition, by providing a cover glass coated with a conductive light-transmitting film between the pipe and the sample, and applying a voltage to the cover glass to form an ion extraction electrode, the distance between the sample and the extraction electrode can be shortened. Improve ion uptake efficiency.
[0016]
The tip of the objective lens has a pipe structure with a simple structure as much as possible, and an electrode structure including an Einzel lens is set at the rear of the lens where a hole can be made slightly larger than the tip of the center of the objective lens. This converges the ion beam.
[0017]
This electrode structure is composed of an Einzel lens in which the inner, upper, middle, and lower three conductive pipes are arranged with an insulator therebetween, and the outside of the Einzel lens is surrounded by an insulating intermediate pipe, Further, the outside is covered with a conductive outer pipe. By applying a shield voltage to the outer pipe, the electric field in the Einzel lens is prevented from being disturbed, and the ion trajectory becomes the axis target.
[0018]
Further, the insulator and the intermediate pipe are made of polyimide, so that the withstand voltage can be increased even if the space between the electrodes is narrow, and the electrode structure can be incorporated into the narrow space in the objective lens.
[0019]
In manufacturing this composite electrode structure, the outer pipe is divided into two upper and lower pipes, and wiring to the Einzel lens is routed between the two pipes. Wiring is removed from the electric field to prevent disturbance of the electric field.
[0020]
FIG. 1 is a schematic configuration diagram of a mass spectrometer according to an embodiment of the present invention.
1 is a mass spectrometer, 2 is a sample , 6a and 6b are laser light sources, 7a and 7b are laser light, 8 is observation illumination light, 10 is a TV camera, 15 is a camera lens, 14 and 16 are light reflecting mirrors, and 17 is An optical path, 19 is a vacuum vessel, 21 is an ion beam, 22 is an objective lens, 26 is a sample stage, 30 is an ion reflector, and 34 is an ion detector.
1, the ion electrode composite disposed in the objective lens 22 and the extraction electrode disposed between the ion electrode composite and the sample stage 26 cannot be drawn. Will be described later with reference to FIG.
[0021]
At the time of mass analysis, the laser light 7a from the laser light source 6a is condensed on the center of the sample 2 by the objective lens 22. The ion beam 21 thus excited is incident on the mass analyzer 1. The ion beam 21 is reflected by the ion reflector 30 and enters the ion detector 34. By measuring the time from when the laser beam 7 is irradiated until the ions reach the ion detector 34, the flight time of the ions can be determined. Thereby, the mass of the ion was able to be analyzed.
[0022]
At the time of sample observation, light from the observation illumination light source 8 is incident on the sample by the objective lens 22. The sample image is observed by the TV camera 10.
[0023]
In this embodiment, the objective lens 22 is a Cassegrain type lens with a magnification of 36 times, N.P. A. Of 0.5 was used. At the center of this, a hole was made and an ion electrode structure was attached. When the laser beam 7a was 355 nm of YAG laser, the spot diameter could be narrowed down to 0.8 μm according to Equation (1). Thus, according to the present invention, the N.I. A. The laser beam could be reduced to a very small diameter.
[0024]
The ion electrode structure of this example is shown in FIG. 2 is a sample, 28 is an extraction electrode, 29a, 29b, and 29c are upper electrodes, middle electrodes, lower electrodes, and 29d are tip electrodes. The dimensions of each part are shown in the figure. Thus, by making the electrode structure thin at the tip and thick at the rear, the area where the tip blocks the incident light can be reduced. In addition, a lead electrode 28 formed by forming a conductor film on a cover glass having a hole in the center was provided between the electrode structure and the sample 2. The conductor film was made thick enough to transmit incident light. Thereby, the N.I. A. The extraction electrode can be provided in the vicinity of the sample without limiting the above, and the emitted ions from the sample can be extracted with a large acceleration.
[0025]
The potentials of the sample 2, the extraction electrode 28, the tip electrode 29d, the lower electrode 29c, the middle electrode 29b, and the upper electrode 29a were 0 V, −3000 V, −3000 V, −3000 V, −8000 V, and −3000 V, respectively. Ions emitted from the sample 2 are drawn into the holes of the extraction electrode 28 by the electric field between the sample 2 and the extraction electrode 28. Since the extraction electrode 28, the tip electrode 29d, and the lower electrode 29c are equipotential, the ions are not accelerated during this time but travel straight. In this embodiment, by extracting ions with a large acceleration of 3000 eV, the velocity component moving away from the central axis can be made smaller than the velocity component along the central axis. As a result, it was possible to prevent ions from colliding with the electrode wall and lowering the sensitivity. The ions after passing through the tip electrode 29d were focused by an Einzel lens composed of the lower electrode 29c, the middle electrode 29b, and the upper electrode 29a.
[0026]
Insulation between the middle electrode 29b of the Einzel lens of FIG. 4 and the upper electrode 29a and the lower electrode 29c was performed by polyimide intermediate pipes 101a and 101b. By using polyimide as the insulating material, it was possible to prevent discharge when a voltage of several thousand volts was applied in a narrow space in the objective lens. The outside of the pipes 101a and 101b was covered with conductive outer pipes 102a and 102b. These pipes were connected to the upper electrode 29a and the lower electrode 29b so as to have the same potential. This shielded the Einzel lens from an external electric field. The pipes 101a and 101b and the pipes 102a and 102b were separately manufactured, and the lead wire 103 from the joint portion to the middle electrode 29b was led. As a result, the lead wire 103 was prevented from disturbing the electric field inside the Einzel lens, and ions could be efficiently sent to the mass analyzer 1.
[0027]
FIG. 7 is a laser mass spectrum of polystyrene beads in Example 1. Measurement of polystyrene beads having a diameter of 0.3 μm was possible, and a polystyrene spectrum was obtained as shown in FIG. As described above, in the present invention, it is possible to analyze minute foreign matters by narrowing incident light to a minute region and increasing ion collection efficiency.
[0028]
Example 2
The enlarged view of the ion excitation part of Example 2 of this invention was shown in FIG. In this embodiment, a transmissive lens is used as the objective lens 22 instead of the Cassegrain type objective lens of the first embodiment. The objective lens has a magnification of 100 times. A. Used 0.8. The laser beam 7a was 355 nm. From the formula (1), the spot diameter of the laser beam could be reduced to 0.5 μm. Even if a transmission type objective lens is used in this way, N.I. A. The laser beam can be reduced to a very small diameter, and the same effect as in Example 1 was obtained.
[0029]
Example 3
Example 3 is shown in FIG. This eliminates the tip electrode portion 29d of FIG. 4 and provides an Einzel lens at the tip of the objective lens. As in Example 1, ions from the sample 2 could be extracted at a high acceleration of −3000 eV, and ions could be collected with high efficiency.
[0030]
Example 4
Example 4 is shown in FIG. In this example, the outer pipes 101a and 101b in the first to third embodiments are cut off from the upper electrode 29a and the lower electrode 29c, and -3000V is applied so that the middle electrode 29b can be omitted even if the middle electrode 29b is omitted. It is. As in the first and second embodiments, the outer pipe 101 serves as a shield and can prevent disturbance of the electric field inside the Einzel lens. As a result, ions can be collected efficiently, and the ion exciter can employ other configurations as shown in FIGS.
[0031]
【The invention's effect】
According to the present invention, a laser beam can be narrowed down, focused on a specific part of a sample and irradiated to generate a trace amount of ion particles that can be focused and analyzed with high sensitivity, and a microscopic image that can finely analyze a foreign object image with high resolution. A laser time-of-flight mass spectrometer can be obtained.
[0032]
More specifically, there is no disposing member that is physically and optically obstructed between the objective lens and the sample, the focal length is small, and N.I. A. Since a large objective lens is used, a specific part on the sample can be irradiated with laser light, and ion particles are generated.
[0033]
In addition, since the passage hole is provided in the central portion of the objective lens, the ion particles can be led to the central passage through the extraction electrode, the tip electrode, and the Einzel lens, and Efficient introduction into the mass spectrometer.
[0034]
In addition, since the Einzel lens is provided in the objective lens, the ion particles can be focused and guided to the passage hole in the central portion even if there is a gap between the objective lens and the sample, and Efficient introduction into the mass spectrometer.
[0035]
Thus, it is possible to provide a microscopic laser time-of-flight mass spectrometer that can obtain a mass spectrum of an extremely minute portion having a good S / N.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of a microscopic laser mass spectrometer using a microscope objective lens incorporating an ion control combined electrode structure according to an embodiment of the present invention.
FIG. 2 is an enlarged view of an ion excitation unit of a laser mass spectrometer according to Embodiment 2 of the present invention.
FIG. 3 is an enlarged view of an objective lens of Example 2.
4 is an enlarged view of the composite electrode structure of Example 1. FIG.
5 is an enlarged view of an Einzel lens of Example 3. FIG.
6 is an enlarged view of an electrode of Example 4. FIG.
FIG. 7 shows an example of mass spectrum measurement.
FIG. 8 is an enlarged view showing another configuration of the composite electrode structure.
FIG. 9 is an enlarged view showing still another configuration of the composite electrode structure.
FIG. 10 is an enlarged view showing still another configuration of the composite electrode structure.
FIG. 11 is an enlarged view showing still another configuration of the composite electrode structure.
FIG. 12 is a schematic diagram for explaining a main part of a conventional microscopic laser mass spectrometer.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Mass analyzer 2 ... Sample 6 ... Laser light source 7 ... Laser light 8 ... Sample illumination light source 9 ... Sample illumination light 10 ... TV camera 11 ... Half mirror 13 ... Beam expander 14 ... Reflection mirror 14a ... Reflection mirror 14 Ion particle passage hole 17 ... Optical path 18 ... Ion particle 19 ... Vacuum container 21 ... Ion beam 22 ... Objective lens 22a, 22b, 22c ... Perforated lens 23 ... Perforated glass plate 25a ... X-axis deflection electrode 25b ... Y-axis deflection electrode 26 ... Sample stand 27 ... Shield plate 28 ... Ion extraction electrode (cover glass)
DESCRIPTION OF SYMBOLS 29 ... Tip part electrode 30 ... Composite electrode structure 30a, 30b, 30c ... Einzel lens 31 ... Ion reflector 32, 33 ... Ion trajectory curve 34 ... Ion detector 35 ... Electrostatic potential distribution curve

Claims (2)

Microscopic laser mass comprising a stage on which a sample is mounted, an optical system for irradiating the surface of the sample with laser light, and an ion detector for detecting atomic ions or molecular ions vaporized from the surface of the sample by the irradiation of the laser light In the analyzer
The optical system includes a lens in which a hole through which atomic ions or molecular ions pass is opened at the center of the optical axis, and an ion control composite electrode structure disposed in the hole.
The ion control composite electrode structure has a triple tubular member composed of a conductive outer tube, an electrically insulating middle tube, and a conductive inner tube. It is positioned on the sample side with respect to the member and is provided separately from this, and a tip electrode having a tubular shape concentric with the optical axis is provided,
Further, a microscopic laser mass spectrometer characterized in that an extraction electrode made of a conductive film having a hole concentric with the optical axis is disposed between the sample and the tip electrode.   The conductive inner tube of the ion control composite electrode structure is divided into three in the optical axis direction, and an electrical insulator is interposed between the divided inner tubes. The microscopic laser mass spectrometer according to Item 1.

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