JP3331245B2 - Scanning soft X-ray microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning soft X-ray microscope.

[0002]

2. Description of the Related Art In recent years, with the advent of SOR light sources and laser plasma for laboratory use, development of various systems using soft X-ray optical elements has been proposed. In particular, research on X-ray microscopes capable of observing a transmission image of a sample with high resolution is being vigorously pursued by various research institutions. Among them, the scanning type, which forms an image by scanning a sample by obtaining a minute beam with an imaging optical element, observes a biological sample in a living state, analyzes various materials, etc. Attention has been paid to those suitable for the use of A scanning X-ray microscope that forms an X-ray micro-beam by scanning a sample by reducing an image of a light source of a finite size by an X-ray optical system measures a transmission microscope or fluorescent X-rays and secondary electrons. It is convenient because it can be applied to surface analysis.

[0003]

The problem shown in FIG. 2 is as follows.
An attempt is made to realize a scanning X-ray microscope as follows. In this example, a laser plasma light source is used as an X-ray light source, and a Schwarzschild type optical system is used as an X-ray optical system for creating a micro beam.

In FIG. 1, reference numeral 1 denotes an Nd: YAG laser, reference numeral 2 denotes a lens, and reference numeral 3 denotes a target, which generate laser plasma. X-rays emitted by laser irradiation on the target 3 pass through a pinhole 11 arranged in front of the light source, and are spectrally and reducedly imaged by the Schwarzschild type optical system 21. Then, the light-converging point is two-dimensionally scanned by the target sample (sample). At this time, if this microscope is used as a transmission microscope for observing a transmission image of the sample as mentioned above, Like
A filter 24 and a detector 25 are placed behind the focal point to monitor the intensity. When used as a surface analyzer, an electron spectrometer or an X-ray detector denoted by reference numeral 30 in the figure is arranged in front of the sample.

Here, the scanning is performed by moving the sample in a raster shape. A sample stage 22 is provided for such movement, and the target sample is arranged here and moved. The sample scanning uses a high-precision XY stage using PZT or the like to increase the spatial resolution, and such a stage is used as the sample scanning stage 22.

Here, focusing on the spatial resolution of the scanning X-ray microscope, the spatial resolution of the scanning X-ray microscope is generally determined by the size of the pinhole, the magnification of the X-ray optical system, and the spatial resolution. . Here, the Schwarzschild type optical system has particularly excellent spatial resolution, and the spatial resolution is several tens of nanometers.
m, which is very high. Therefore, when the optical system related to the X-ray imaging optical system is used, the size of the microbeam is mainly determined by the magnification of the pinhole and the optical system. As a specific example, for example, if a microhole is formed by a 200-fold X-ray imaging optical system using a pinhole of 10 μmφ with respect to a used pinhole and an X-ray imaging optical system, the beam size is approximately It is about 50 nm.

In this case, in order to realize a scanning X-ray microscope having such a resolution of the size of a microbeam, a two-dimensional stage having a spatial resolution of at least 50 nm is used as a means for scanning a sample. Is required.

When designing a scanning X-ray microscope, one of the most problematic is the stage (sample scanning stage) 22 for scanning a sample.
This is because it has excellent linearity as a sample scanning stage to be prepared in that case, as described above or including the following considerations, and has several tens of nm.
This is because it is necessary to produce a stage having a high spatial resolution. In general, when a reduced image is formed by an optical system, the depth of focus is very shallow (the numerical aperture on the reduction side is, for example, about 0.2). Therefore, if the used scanning stage has poor linearity, defocus occurs when scanning the sample, and the spatial resolution is significantly deteriorated. Therefore, to avoid this, a very expensive and highly accurate scanning stage is required for the sample scanning stage.

The present invention has been made on the basis of the above-mentioned considerations, and can solve the above-mentioned disadvantages, does not require a high-precision stage for scanning, and is excellent in spatial resolution. This is to realize microscopic observation.

[0010]

SUMMARY OF THE INVENTION The present invention provides a pinhole for defining the size of a soft X-ray micro-beam using X-rays from an X-ray light source, and a soft X-ray for reducing and imaging an incident X-ray beam. An X-ray microscope that irradiates a sample with an imaging optical system, wherein the pinhole is disposed between the X-ray light source and the soft X-ray imaging optical system, and the pinhole is positioned at an optical axis. A means for moving the pinhole in a vertical plane, whereby scanning is performed by moving the pinhole with an accuracy equal to or higher than a value obtained by multiplying a required spatial resolution by a magnification of the soft X-ray imaging optical system. It is characterized by having done. Furthermore, the present invention uses a X-ray from an X-ray light source to form a soft X-ray microbeam with a pinhole that defines the size of the microbeam, and a soft X-ray imaging optical system that reduces and forms an incident X-ray beam on a sample. An X-ray microscope for irradiating the X-ray, wherein the pinhole is arranged between the X-ray light source and the soft X-ray imaging optical system, and the pinhole is moved in a plane perpendicular to the optical axis. Means is provided, whereby scanning is performed by moving the pinhole with an accuracy higher than the size of the pinhole.

[0011]

According to the present invention, a method in which the sample is fixed and the pinhole is scanned in a plane perpendicular to the optical axis to scan the micro beam itself is effectively realized. When scanning the sample with the size of the microbeam, when scanning with the sample stage on the reduction side, it is necessary to scan with a high required positional resolution. When the microbeam itself is scanned by allowing the microhole to move in a plane perpendicular to the optical axis, the pinhole itself may be two-dimensionally scanned with the size of the pinhole. In addition to this, even when the pinhole is two-dimensionally scanned, even if the scanning is performed with the fluctuation in the optical axis direction,
The position of the focal point in the imaging optical system moves much less than the amount of movement of the pinhole in the optical axis direction. Therefore, deterioration of the spatial resolution due to defocus hardly occurs. Therefore, for example, a stage using a stepping motor for scanning has sufficient accuracy, and required spatial resolution can be easily secured. Further, in the present invention, any of the SOR light source and the laser plasma light source can be applied.

[0012]

An embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows an embodiment of the present invention. FIG. 3 shows an overall configuration image of the light source and the microscope system according to the present embodiment, and the basic configuration may be the same as that shown in FIG. This system consists of an X-ray light source, a pinhole for defining the size of a soft X-ray microbeam, a soft X-ray imaging optical system for forming a soft X-ray beam, a sample, an ultraviolet filter, an X-ray detector, and the like. Specifically, here, the case of a scanning X-ray microscope using a laser plasma light source as a light source and using a Schwarzschild optical system is taken as an example.

The Nd: YAG laser 1 irradiates a target 3 placed in a vacuum. That is, the laser light from the laser 1 is condensed on the target 3 by the condensing lens 2 to generate white laser plasma. Thus, a soft X-ray light source is obtained.

The X-rays emitted as described above form a soft X-ray microbeam in order to irradiate the sample with the microbeam as probe light, and are required to be placed near the light source so as to define the size of the beam. The light passes through a pinhole 11 having a hole size, travels toward a Schwarzschild optical system 21, and is incident thereon. Schwarzschild optical system 21
Comprises a spherical mirror coated with a multilayer film having a reflectance distribution with respect to a predetermined wavelength, and the X-ray imaging optical system is configured to include this.

An ultraviolet light cut filter 24 and a detector 25 composed of a micro channel plate (MCP) are arranged behind the light collecting point. The present filter 24 plays a role of cutting off ultraviolet stray light not related to image formation. The X-ray detector 25 is used for performing a transmission microscope observation for observing a transmission image of the sample, and is used by being connected to a display monitor or the like outside the container. When a photoelectron spectroscope or X-ray detector 30 for detecting secondary electrons or the like generated by irradiating a sample with a microbeam is also arranged in a container and used together, the present system uses a transmission microscope and display analysis. Can be used properly with the machine. Optical system as above,
The detection system is also placed in a vacuum to avoid absorption of soft X-rays by air.

The present system includes the above-described light source, optical system, and detection system. In the present embodiment, the pinhole 11 having the predetermined size between the laser plasma light source unit and the Schwarzschild optical system 21 is provided. Means are provided so that the pinhole 11 can move in a plane perpendicular to the optical axis so as to scan the microbeam itself by scanning in a plane perpendicular to the optical axis. The means is provided with a pinhole forming member 12 in which a pinhole 11 is set.
Stage 13 that can move in a plane perpendicular to the optical axis
Can be provided.

This is based on the following points (the principle of solution). Assuming that the size of the pinhole used is s and the magnification of the X-ray optical system is m, the microbeam size is s / m. Therefore, when scanning the sample with the size of the microbeam, when scanning with the sample stage on the reduction side, it is necessary to scan with a positional resolution of s / m.

However, in scanning, the sample is fixed,
If the method scans the microbeam itself by scanning the pinhole 11 in a plane perpendicular to the optical axis, this method requires (s / m) · m = s, that is, the size of the pinhole 11 ( In step s), the pinhole 11 itself may be two-dimensionally scanned. According to this, the scanning may be rough. In addition, the pinhole 1
In one two-dimensional scan, even if the pinhole moves in a direction originally undesirable for the two-dimensional scan, a large deterioration in spatial resolution due to defocus can be avoided. In other words, when the pinhole 11 is two-dimensionally scanned, even if the pinhole 11 is scanned with fluctuations in the optical axis direction, it works at the vertical magnification (that is, 1 / m ² ) on the condensing point side. If the magnification is, for example, 100 times (= m), even if the pinhole 11 moves about 100 μm in the optical axis direction, the position of the condensing point moves only about 10 nm. , Which means that scanning does not require such high precision). Therefore, deterioration of the spatial resolution due to defocus hardly occurs.

As described above, scanning need not be high-precision, and a required spatial resolution can be ensured. This system is based on the pinhole 11
Is provided with a stage 13 for scanning in a plane perpendicular to the optical axis.

In the above case, the following can be said with respect to the relationship with the used X-ray light source. That is, at this time, an important point is whether or not the X-ray light source has a sufficiently large and uniform luminance.
In the case of OR light, the beam is 1 mm × 1 mm in size and has relatively uniform brightness. Therefore, 10 μm
Even if a pinhole of φ (= s) is used, a two-dimensional image composed of 100 × 100 pixels can be obtained. On the other hand, the laser plasma light source has a light source size of 200 to 300 μm when the laser light is condensed to about several tens of μm. However, if the laser beam diameter is increased and the intensity is increased, the plasma size is also about 1 mm. Can be formed. Therefore, the present invention can be applied to a laser plasma light source as in the system of this embodiment. In the case of using a laser plasma light source, when obtaining an image of a sample and observing it with a microscope, or when performing surface analysis, a light source that can be easily used in a laboratory can be used.

In a preferred embodiment, the stage 13 provided for scanning the pinhole 11 in accordance with the above is specifically a microstage using a simple stepping motor having a moving mechanism. In the system of this embodiment, the laser plasma light source and the Schwarzschild optical system 21 are used as described above. In this case, the Schwarzschild type optical system has a wide field of view, so that it has several tens μm (image side: reduction side). In the area (), the size of the microbeam is smaller than 0.1 μm. Under such conditions, an area with a resolution better than (higher than) 0.1 μm is realized in a 10 μm × 10 μm (100 × 100 pixel) area. When the position is controlled in steps of about 100 nm on the image plane side, on the object side, the pinhole side, the value is multiplied by the magnification (= m) of the optical system. So, for example,
When using a 100 × objective, 100 nm × 100 =
The pinhole 11 may be moved with an accuracy of 10 μm.

Therefore, the moving mechanism becomes extremely simple. Therefore, for example, as a moving mechanism for realizing this, even a microstage using a stepping motor has sufficient accuracy. Of course, a stage using high-precision PZT such as an inchworm stage may be used.

Thus, in the present system, the stage 13 for the pinhole 11 is preferably a micro stage using a stepping motor. More preferably, this is not only a two-dimensional stage but also a three-dimensional XYZ microstage that can scan the pinhole 11 in the optical axis direction in addition to the two-dimensional scanning of the pinhole 11. Also, preferably, the microstage comprises:
This is a pinhole stage whose position can be controlled by controlling a stepping motor and the like from the atmosphere side (outside the vacuum vessel).
However, as mentioned above, it does not prevent using a stage using high-precision PZT such as an inchworm stage as the pinhole stage 13. Even in this case, the microbeam itself can be scanned by scanning the pinhole 11 in a plane perpendicular to the optical axis.

Here, a three-dimensional microstage is used, and therefore, the pinhole forming member 12 having the pinhole 11 is fixed on the three-dimensional microstage 13 of XYZ. The position of the micro stage 13 can be controlled by controlling a stepping motor or the like from the atmosphere side.

The scanning of the sample is performed under such a configuration, and the Schwarzschild optical system 21 and the pinhole 1 are used.
For example, if a 200 × (= m) Schwarzschild optical system and a pinhole of 10 μmφ (= s) are used, if a spatial resolution of 50 nm is required on the image plane, the pinhole 11 has a size of about 10 μm. It suffices if two-dimensional scanning can be performed in a plane orthogonal to the optical axis with high accuracy. In the one according to FIG.
In the case of a similar optical system magnification and a pinhole size, it is much rougher than the precision required when realizing a lens having the same resolution.

The X-rays having passed through the pinhole 11 moved in a plane perpendicular to the optical axis by the three-dimensional microstage 13 are incident on a Schwarzschild optical system 21 and split by a multilayer film of the optical system. An image is formed by an optical system. In this embodiment, the transmission sample is kept fixed, and the focusing point and the sample are aligned by moving the pinhole 11 in the optical axis direction. With the three-dimensional micro stage 13, such a thing can be realized. The sample stage 22a
Can be used for applications such as insertion and removal of a sample from the optical axis. At the time of scanning, the sample is scanned by scanning the microbeam itself, and the X-rays that have passed through the sample pass through the ultraviolet light cut filter 24 that cuts off the ultraviolet stray light,
The transmitted image of the sample detected by the detector 25 using the CP can be observed with high resolution on a display or the like.

Thus, a laser plasma light source,
The sample includes a pinhole 11, a Schwarzschild optical system 21, an ultraviolet filter 24, and a detector 25. The sample 13 is fixed and moves the pinhole 11 in a plane perpendicular to the optical axis. Scanning soft X that can effectively realize the method of scanning itself
Obtain a line microscope. Even when reducing and forming an image with an optical system having a very shallow depth of focus, the quality of the linearity of the stage 13 to be used greatly affects performance such as occurrence of defocus during scanning of a sample and remarkable deterioration of spatial resolution. Can also be avoided. An extremely expensive scanning stage having excellent linearity and high spatial resolution can be manufactured, and the above-mentioned scanning soft X-ray microscope can be realized without using it.

Further, the present embodiment will be described including specific numerical values. In the present embodiment, it is now assumed that the numerical aperture on the image plane side of the used Schwarzschild optical system 21 is 0.3, and in that case, the defocus amount w on the image plane and the blur due to the defocus of the micro beam are reduced. Estimate.

The degree of blurring due to defocus of the micro beam is the area where the image plane crosses the micro beam.
Therefore, in an optical system having a numerical aperture on the image plane side of 0.3, the diameter a of the area crossing the microbeam in this case is 2 · w
・ It is given by tan0.3 ≒ 0.6w. Then, when the spatial resolution is required to be 0.1 μm or more in such a microscope,
w needs to be 0.15 μm or less. Therefore, it is necessary to scan the sample on the image plane side with a microbeam with a planar accuracy of w = 0.15 μm or less. According to the present invention, since the pinhole itself is scanned, the pinhole may be two-dimensionally scanned with an accuracy of m ² w. Specifically, in this embodiment, m = 200, w = 0.15 μm, and 200 ²
× 0.15 μm = about 6 mm. As described above, also from this point, it can be understood that a scanning X-ray microscope can be realized using a stage with extremely rough accuracy.

The present invention is not limited to the above embodiment. For example, in the illustrated example, the light source has been described as a laser plasma light source, but as mentioned earlier, S
An OR light source may be used. Further, the imaging optical system may be implemented by a system other than the Schwarzschild optical system. Also,
The present invention also includes a case where it is exclusively used as a surface analyzer.

[0031]

According to the present invention, the scanning can be performed by moving the pinhole in a plane perpendicular to the optical axis while the sample is fixed, and the microbeam itself can be scanned. However, rough accuracy is sufficient and sufficient spatial resolution can be easily secured even in such a case.

[Brief description of the drawings]

FIG. 1 is a diagram showing one embodiment of the present invention.

FIG. 2 is a diagram of a comparative example of a scanning soft X-ray microscope using a laser plasma light source unit and a Schwarzschild type optical system, which is shown in comparison with FIG.

[Explanation of symbols]

 Reference Signs List 1 Nd: YAG laser 2 Lens 3 Target 11 Pinhole 12 Pinhole forming member 13 Pinhole stage 21 Schwarzschild type optical system 22a Stage 24 Filter (ultraviolet light cut filter) 25 Detector (micro channel plate) 30 Photoelectron spectroscope or X-ray detector

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-50-98773 (JP, A) JP-A-3-246500 (JP, A) JP-A-5-273400 (JP, A) JP-A-5-273400 164987 (JP, A) JP-A-5-54500 (JP, A) JP-A-62-126334 (JP, A) JP-A-5-142400 (JP, A) JP-A-2-181639 (JP, A) JP-A-63-163278 (JP, A) JP-A-5-75719 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G21K 7/00

Claims (2)

(57) [Claims] An X-ray from an X-ray light source is used to form a soft X-ray microbeam on a sample by a pinhole for defining the size of a soft X-ray microbeam and a soft X-ray imaging optical system for reducing and imaging an incident X-ray beam. An X-ray microscope for performing irradiation, wherein the pinhole is arranged between the X-ray light source and the soft X-ray imaging optical system, and the pinhole is moved in a plane perpendicular to an optical axis. Wherein the scanning is performed by moving the pinhole with an accuracy equal to or more than a value obtained by multiplying a required spatial resolution by a magnification of the soft X-ray imaging optical system. Soft X-ray microscope. 2. An X-ray from an X-ray light source, a pinhole for defining the size of a soft X-ray microbeam, and a soft X-ray imaging optical system for reducing and imaging an incident X-ray beam to a sample. An X-ray microscope for performing irradiation, wherein the pinhole is arranged between the X-ray light source and the soft X-ray imaging optical system, and the pinhole is moved in a plane perpendicular to an optical axis. A scanning soft X-ray microscope, wherein the scanning is performed by moving the pinhole with an accuracy equal to or greater than the size of the pinhole.