JPH0619973B2 - Electrostatically corrected time-of-flight secondary ion microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention irradiates a sample with a pulsed primary ion beam to extract secondary ions generated from the sample to obtain an enlarged image of the sample with an ion species having a specific mass. Time-of-flight secondary ion microscope.

[Conventional technology]

As a method for analyzing the components on the sample surface, there is a secondary ion microscope that obtains an elemental image of the sample by irradiating the sample surface with an ion beam to extract secondary ions generated from the sample surface. As a method for obtaining an elemental image with this secondary ion microscope, two types, a scanning type and a mapping type, have been put into practical use.

FIG. 4 is a diagram for explaining a scanning type secondary ion analyzer, FIG. 5 is a diagram for explaining a mapping type secondary ion analyzer, and FIG. 6 is a diagram showing an example of ion species detection. And 2
1, 24 are samples, 22 and 26 are mass spectrometric systems, 23 and 27
Is a display device, 25 is an electrostatic lens system, 31 is a magnetic field, 32 is a detector, and 33 is a fluorescent screen.

As shown in FIG. 4, the scanning ion analysis apparatus narrows the primary ion beam i and scans it on the sample 21, and the secondary ions generated from the sample 21 are extracted to cause the mass analysis system 22 to extract the secondary ions. A sample image is obtained after fixing to the ion species to be analyzed.

In addition, as shown in FIG. 5, the mapping type secondary ion analyzer does not narrow the primary ion beam i and keeps the sample 24
The secondary ions that have been extracted and radiated onto the electrostatic lens system 2 are
The image is formed as a magnified image in 5, and an ion image of a specific element is obtained by combining the lens system with the mass spectrometric system 26.

In the mass spectrometric system used in these secondary ion analyzers, the ion species are made to have a constant energy and run in the magnetic field 31, as shown in FIG. Then, the ion species draws an arc having a different radius in the magnetic field 31 due to the difference in mass. That is, since a heavy ion species draws a large diameter and a light ion species draws a small diameter, a detector 32 is arranged at one point as shown in FIG. The ion species can be detected, and by disposing the fluorescent plate 33 as shown in FIG. 6 (b), the ion species can be detected within a predetermined mass number range.

[Problems to be solved by the invention]

However, the above-mentioned conventional methods have various drawbacks.
For example, the scanning type requires a long analysis time because the sample surface is scanned by irradiating a finely focused ion beam, and the stability of the apparatus is strictly required. That is, there is a problem that it cannot be used for a sample that undergoes changes in a long analysis time. Further, although it is a problem common to the mapping type, it is difficult to bake out since each has a large electromagnet, and it is difficult to obtain an ultra-high vacuum, which is essential for such an apparatus.

The present invention solves the above problems, and an object thereof is to provide an electrostatically corrected time-of-flight secondary ion microscope that is compatible with ultra-high vacuum and is capable of analyzing a sample by ion irradiation with high accuracy. It is what

[Means for solving problems]

To this end, the present invention provides a time-of-flight type ion beam that irradiates a sample with a pulsed primary ion beam and extracts secondary ions generated from the sample to obtain an enlarged image of the sample with an ion species of a specific mass corresponding to the flight time in free space. A secondary ion microscope,
A cathode lens system for extracting secondary ions generated from the sample, an electrostatic sector for time-focusing the secondary ions extracted by the cathode lens system, and a sample for each ion species time-focused by the electrostatic sector An electrostatic magnifying lens system for obtaining a magnified image and image detecting means for detecting an image of the magnified image of the sample obtained by the magnifying lens system by a gate pulse are provided, and the ion species is selected by controlling the timing of the gate pulse. It is characterized by doing.

[Action]

In the electrostatic correction time-of-flight secondary ion microscope of the present invention, the secondary ions generated from the sample are extracted and accelerated by the cathode lens system, so the image detection means corresponds to the flight time through the electrostatic magnifying lens system. A sample image is formed for each ion species. In this flight space, energy variations are corrected by the electrostatic selector time convergence action.
Therefore, the image of the specific ion species can be selectively detected with high resolution by controlling the timing of the gate pulse by the image detecting means.

〔Example〕

 Hereinafter, embodiments will be described with reference to the drawings.

First, before describing the present invention, a time-of-flight secondary ion microscope, which is the basis of the present invention, will be described.

FIG. 7 is a diagram showing the configuration of one embodiment of a time-of-flight secondary ion microscope, FIG. 8 is a diagram for explaining the relationship between mass and flight time, and FIG. 9 is a diagram for explaining detection peaks. Is.

The operation of the time-of-flight secondary ion microscope shown in FIG. 7 will be described. In FIG. 7, 41 is a sample, 42 and 43 are lenses, 44 is a channel plate, 45 is a fluorescent plate, and 46 is a video camera. Now, when the sample 41 is irradiated with a pulsed (generally about 1 n ″) primary ion beam i ⁺ , secondary ions having various mass numbers are generated at that moment. If the voltage is V, these extracted secondary ions have energy of eV if the initial energy is ignored, so the mass number of the ion is M, the sample 41 and the channel plate 44.
When the distance between them is L, the time of flight (TOF) t _M required to reach the channel plate 44 after the secondary ions are generated is Becomes However, k is a constant. As is clear from this equation, the flight time t _M is proportional to the square root of the mass number M.
Therefore, as shown in FIG. 8, the ion species 53 having a small mass number M travel in the free space at a faster speed than the ion species 54 having a large mass number M and reach the channel plate 44.

For example, assuming that a secondary ion peak as shown in FIG. 9 (a) appears on the channel plate 44 with time after the sample is irradiated with the pulsed primary ion beam, the relationship between the peak and the mass M is shown in FIG. It can be seen as the relationship shown in (b). Therefore, during pulsed ion beam irradiation,
If a gate pulse V _G (up to 1 nsec) is applied to the channel plate 44 at time t _{M, the} channel plate 44 has an amplifying function only within this pulse supply time. Image (enlarged image of the analysis area of the sample) will appear. That is, if the flight time t _M is reselected according to the desired analysis ion, an image of the ion species suitable for each case can be obtained.

The channel plate 44 is of a secondary tandem type, for example, and a positive voltage V ₂ is applied to the output end thereof, and a positive gate voltage V _G is applied in a pulsed manner. The image signal multiplied by the channel plate 44 illuminates the fluorescent plate 45 in the subsequent stage, and the final image detection is performed by, for example, a CCD (Charge Coupled Devic).
e) and the like are carried out by the video camera 46 or the CPU. The mechanism for forming the magnified image is similar to that of a general electron emission microscope.

By the way, in the time-of-flight secondary ion microscope, the initial energy eU ₀ of the secondary ions was ignored, but the energy E of the extracted ions is actually E = e (U ₀ + V), and As a result, the flight time becomes blurred due to the influence of, and the mass resolution deteriorates. The electrostatically corrected time-of-flight secondary ion microscope of the present invention is an improvement of the above time-of-flight secondary ion microscope for the purpose of reducing the influence of this initial energy.

FIG. 1 is a diagram showing the configuration of one embodiment of an electrostatically-corrected time-of-flight secondary ion microscope according to the present invention, FIG. 2 is a diagram for explaining the time focusing action in an electrostatic sector, and FIG. FIG. 4 is a diagram showing an energy distribution of secondary ions.

In FIG. 1, 1 is a sample, 2 and 3 are lenses, 4 is a channel plate, 5 is a fluorescent plate, 6 is a video camera, and 7 is an energy sector. Here, the positive high voltage H.V. V is applied and the primary ion beam is irradiated in pulses. There is an extraction electrode in the immediate vicinity of the sample 1, and a so-called cathode lens (lens 2) system is formed including the sample 1. Then, when secondary ions are generated from the sample 1 by irradiation with the pulsed primary ion beam,
The secondary ions are extracted from the lens 2 and enlarged through the electrostatic energy sector 7 and the electrostatic lens 3 to form an image on the input surface of the channel plate 4.

As described above, the electrostatic correction time-of-flight secondary ion microscope of the present invention has the electrostatic energy sector 7 in the middle of the optical path.
Is provided. Ions that pass through the energy sector 7 and contribute to image formation are only those having a constant energy width and an energy width determined by the operating conditions of the energy sector 7. Therefore, it is possible to avoid a decrease in resolution due to energy variations. The energy sector 7 also serves as a so-called Poscherieder type analyzer. That is, as shown in FIG. 2, the one with a large energy runs with a diameter larger than that with a small energy and converges at time at a certain point. Therefore, as shown in FIG. 3, even if the energy width of the secondary ions is large, the time focusing, that is, the flight time width becomes almost zero.

The present invention is not limited to the above embodiment, and various modifications can be made. For example, the number of lenses may be appropriately increased in consideration of the enlargement ratio, or the gate pulse may be supplied to a blocking mesh placed in front of the channel plate. Further, the video camera may be any image detection as long as it is a simultaneous capture type such as CCD.

〔The invention's effect〕

As is clear from the above description, according to the present invention, a third new method of a secondary ion analyzer having an image function is provided, which is composed of a simple electrostatic lens or an electrostatic energy sector. Therefore, it is easy to manufacture and adapts to ultra-high vacuum. Further, both image resolution and mass resolution are equivalent to those of the conventional two types, and switching of positive and negative ions is also possible. Furthermore, since an ion image of the entire surface is simultaneously acquired with an extremely short pulse (about 1 ns), it can be used for analysis of a sample which has a rapid decomposition time and is easily changed.

[Brief description of drawings]

FIG. 1 is a diagram showing the configuration of one embodiment of an electrostatically-corrected time-of-flight secondary ion microscope according to the present invention, FIG. 2 is a diagram for explaining the time focusing action in an electrostatic sector, and FIG. Is a diagram showing energy distribution of secondary ions, FIG. 4 is a diagram for explaining a scanning type secondary ion analyzer, FIG. 5 is a diagram for explaining a mapping type secondary ion analyzer, FIG. 6 is a diagram showing an example of detection of ion species, FIG. 7 is a diagram showing the configuration of one embodiment of a time-of-flight secondary ion microscope, and FIG. 8 is a diagram for explaining the relationship between mass and time of flight, FIG. 9 is a diagram for explaining the detected peaks. 1 ... Sample, 2,3 ... Lens, 4 ... Channel plate, 5 ... Fluorescent plate, 6 ... Video camera, 7 ... Energy sector.

Claims (1)

[Claims] 1. A time-of-flight secondary in which a sample is irradiated with a pulsed primary ion beam and secondary ions generated from the sample are extracted to obtain an enlarged image of the sample by an ion species of a specific mass corresponding to the flight time in free space. An ion microscope, in which a cathode lens system for extracting secondary ions generated from a sample, an electrostatic sector for time-focusing the secondary ions extracted by the cathode lens system, and time-focusing for the electrostatic sector An electrostatic magnifying lens system for obtaining a magnified image of the sample for each ion species, and an image detecting means for performing an image detection operation on the magnified image of the sample obtained by the magnifying lens system by a gate pulse are provided, and the timing of the gate pulse is controlled. An electrostatically compensated time-of-flight secondary ion microscope characterized in that the ion species are selected accordingly.