JP2010160034A - Soft x-ray spectrometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a soft X-ray spectrometer for applying soft X rays, which go toward the soft X-ray spectrometer from a sample, to a diffraction lattice as much as possible to enhance the intensity of the detected soft X rays. <P>SOLUTION: In the soft X-ray spectrometer equipped with: the diffraction lattice for diffracting incident soft X rays; and a detector for detecting the soft X rays diffracted by the diffraction lattice, a pair of mirrors are provided, which sandwich the center rays of the soft X rays entering the diffraction lattice and the curvatures of which in the direction parallel to the plane vertical to the diffraction lattice and containing the center rays, and vertical to the center rays, is zero. The mirrors reflect the soft X rays going toward the side of the diffraction lattice to make them enter the diffraction lattice. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a soft X-ray spectrometer, and more particularly to a spectrometer that improves the utilization efficiency of incident soft X-rays in a soft X-ray spectrometer.

  Soft X-ray emission spectroscopy is a method in which a sample is irradiated with X-rays or an electron beam and the generated soft X-rays are spectroscopically analyzed, and the electronic state of a substance contained in the sample can be known. However, soft X-ray emission in the sample is a light emission phenomenon that occurs isotropically, that is, optically becomes a divergent light source. For this reason, in the soft X-ray spectrometer used for the analysis, only a part of the soft X-rays emitted from the sample that travels in a limited direction is detected.

  The soft X-ray spectrometer includes a diffraction grating for performing spectroscopy and a detector for detecting soft X-rays after the spectroscopy (see, for example, Patent Document 1). The configuration of a conventional soft X-ray spectrometer is shown in FIG. The soft X-ray spectrometer includes a diffraction grating 91 and a detector 92, and the sample S is irradiated with X-rays or electron beams. 9A is a plan view taken along a plane perpendicular to the diffraction grating 91, and FIG. 9B is a side view. As shown in FIG. 9B, the diffraction grating 91 for soft X-rays (wavelength of about 1 nm) having a wavelength much shorter than that of visible light has an extremely large incident angle (close to 90 °). It is necessary to make the incident arrangement.

  Although not shown, in order to increase the resolution, a slit that restricts the width of the soft X-ray beam bundle in the diffraction direction (direction perpendicular to the diffraction grating) is arranged in the optical path of the soft X-ray from the sample to the diffraction grating 91. Or an optical system that converges an X-ray or electron beam irradiated for excitation into a minute spot is arranged in front of the sample. The latter is called a slitless spectroscopic device, and has high resolution in the use of soft X-rays from a sample, and therefore has high detection sensitivity, while having the same resolution as that of a configuration having slits.

JP-A-6-186178

  In a soft X-ray spectrometer, the diffraction grating must be arranged at an oblique incidence as shown in FIG. 9B. However, in such an arrangement, the diffraction efficiency is low in principle, and soft X-ray emission in the sample does not occur. Combined with being isotropic, the intensity of the soft X-rays after entering the detector becomes low. This decrease in intensity is an obstacle to analysis with high sensitivity, and further improvement in sensitivity is desired also in slitless spectroscopic devices.

  The present invention provides a soft X-ray spectrometer capable of increasing the intensity of detected soft X-rays and increasing the detection sensitivity by making as many soft X-rays as possible directed from the sample toward the soft X-ray spectrometer enter the diffraction grating. The purpose is to provide.

  The present invention is a soft X-ray spectrometer comprising a diffraction grating that diffracts incident soft X-rays and a detector that detects soft X-rays diffracted by the diffraction grating, and is a soft X-ray spectrometer that is incident on the diffraction grating. A soft X-ray spectrometer comprising a pair of mirrors sandwiching a central ray of X-rays, having a curvature of 0 in a direction perpendicular to the diffraction grating and parallel to a plane including the central ray and perpendicular to the central ray.

  According to the present invention, the pair of mirrors are cylindrical concave mirrors having an axis in a direction parallel to the plane and perpendicular to the central ray.

  Furthermore, the present invention is characterized in that the pair of mirrors are symmetrical with respect to the plane.

  According to the soft X-ray spectroscopic device of the present invention, the curvature in the direction perpendicular to the central ray and perpendicular to the diffraction grating is sandwiched between the central rays of the soft X-rays incident on the diffraction grating. Since a pair of zero mirrors is provided, it is possible to make the soft X-rays that go to the side of the diffraction grating and not enter the diffraction grating without the mirror be reflected by the mirror and enter the diffraction grating. is there. Therefore, the amount of soft X-rays incident on the diffraction grating increases, and the intensity of soft X-rays that are diffracted by the diffraction grating and detected by the detector increases.

  Further, according to the present invention, the pair of mirrors has no curvature in a direction perpendicular to the diffraction grating and parallel to the plane including the central ray and perpendicular to the central ray. Is not changed in a direction parallel to the plane. Therefore, the mirror does not affect the diffraction by the diffraction grating. For this reason, even when a pair of mirrors is added to the existing soft X-ray spectroscopic apparatus to form the soft X-ray spectroscopic apparatus of the present invention, it is not necessary to change the design of the optical system.

  According to the invention, in the configuration in which the pair of mirrors is a cylindrical concave mirror having an axis in a direction parallel to the plane and perpendicular to the central ray, the soft X-rays that are being diverged can be converged by the mirror. This is possible, and it becomes easy to make all the reflected soft X-rays incident on the diffraction grating while enlarging the mirror to increase the number of reflected soft X-rays.

  In the configuration in which the pair of mirrors are symmetrical with respect to the plane, the design is easy.

It is a figure which shows typically the structure of the soft X ray spectroscopy apparatus of one Embodiment of this invention. It is a figure which shows the parameter which prescribes | regulates the whole optical system, diffraction grating, and detector of the soft X ray spectroscopy apparatus of one Embodiment of this invention. It is a figure which shows the parameter which prescribes | regulates a pair of mirror of the soft X ray spectroscopy apparatus of one Embodiment of this invention. It is a figure which shows the variable factor in installation of the soft X ray spectroscopy apparatus of one Embodiment of this invention. It is a figure which shows the relationship between the difference | error of the variable factor in installation of the soft X-ray spectrometer of one Embodiment of this invention, and the intensity | strength and peak width of the soft X-ray to be detected. It is a figure which shows the result of the resolution calculation by the ray trace about the soft X ray spectroscopy apparatus of one Embodiment of this invention. In the soft X-ray spectrometer of one embodiment of the present invention, it is a figure showing an image of soft X-rays on a detector when water is used as a sample. It is a figure which shows intensity distribution in the area | region A of FIG. It is a figure which shows the structure of the conventional soft X-ray spectrometer.

  Hereinafter, the soft X-ray spectrometer of the present invention will be described with reference to the drawings. FIG. 1 schematically shows the configuration of a soft X-ray spectrometer 1 according to an embodiment of the present invention. This soft X-ray spectroscopic apparatus 1 constitutes a part of a soft X-ray emission spectroscopic system together with a soft X-ray emission apparatus that irradiates a sample S with an electron beam or X-rays to generate soft X-rays from the sample S. . The soft X-ray spectrometer 1 includes a diffraction grating 2 and a detector 3. The soft X-ray from the sample S is diffracted by the diffraction grating 2 and the diffracted soft X-ray is detected by the detector 3. Although the soft X-ray spectrometer 1 of the present embodiment is a slitless spectrometer, the present invention is also applied to a soft X-ray spectrometer equipped with a slit on the soft X-ray optical path from the sample S to the diffraction grating 2. Applicable.

  1A is a plan view seen along a plane perpendicular to the diffraction grating 2, and FIG. 1B is a side view. As shown in the drawing, the traveling direction of the central ray X0 of the soft X-ray incident on the diffraction grating 2 is the Z direction, and the in-plane perpendicular to the diffraction grating 2 includes the central ray X0 of the soft X-ray incident on the diffraction grating 2. Thus, the direction perpendicular to the Z direction is defined as the Y direction, and the direction perpendicular to the Z direction and the Y direction is defined as the X direction.

  The diffraction grating 2 is designed to diffract soft X-rays having an energy in the range of 200 to 1400 eV (corresponding to a wavelength of 6 to 0.9 nm). Each grating (scored line) of the diffraction grating 2 extends in the X direction, and the diffraction grating 2 has diffractive power only in the Y direction. The soft X-rays incident on the diffraction grating 2 are diffracted at a diffraction angle corresponding to the energy (wavelength), thereby performing spectroscopy.

  The detector 3 has sensitivity to soft X-rays in the above energy range, and a number of minute elements that convert incident soft X-rays into electric charges are two-dimensionally arranged on the soft X-ray incident surface. This is a CCD type detector. The detector 3 is connected to a signal processing device (not shown) that processes the output signal.

  The soft X-ray spectrometer 1 includes a pair of mirrors 5. The mirror 5 is arranged between the sample S and the diffraction grating 2 so as to sandwich the central ray X0 of soft X-rays incident on the diffraction grating 2. These mirrors 5 have a curvature of 0 in a direction perpendicular to the diffraction grating 2 and parallel to a plane including the central ray X0 (YZ plane) and perpendicular to the central ray X0. That is, the mirror 5 has no curvature in the Y direction. The mirror 5 is symmetric with respect to the plane (YZ plane) perpendicular to the diffraction grating 2 and including the central ray X0. The mirrors 5 are arranged in a generally opposing manner so that the distance between the end portions near the diffraction grating 2 is wider than the end portions near the sample S.

  The mirror 5 reflects soft X-rays directed to the side of the diffraction grating 2 in the X direction and makes the diffraction grating 2 enter. Therefore, soft X-rays that should not enter the diffraction grating 2 if the mirror 5 is not present are reflected by the mirror 5 and enter the diffraction grating 2. As a result, the intensity of soft X-rays diffracted by the diffraction grating 2 and detected by the detector 3 is improved as compared with the configuration in which the mirror 5 is not provided.

  The reflection surface of the mirror 5 is curved so that all soft X-rays reflected in the range from the end near the sample S to the end near the diffraction grating 2 enter the diffraction grating 2. However, the mirror 5 does not have a curvature in the Y direction as described above, and is a cylindrical mirror. For this reason, the angle in the Y direction of the soft X-rays with respect to the diffraction grating 2 is not changed by being reflected by the mirror 5. Therefore, the soft X-rays that are directly incident on the diffraction grating 2 without passing through the mirror 5 and the soft X-rays that are reflected by the mirror 5 and incident on the diffraction grating 2, and the incident position on the diffraction grating 2 in the Y direction. And the incident angle with respect to the diffraction grating 2 is the same. Accordingly, the diffraction characteristics of the diffraction grating 2 including the resolution are theoretically unchanged regardless of the presence of the mirror 5.

  This means that the mirror 5 can be attached to the existing soft X-ray spectrometer without design change, and provides a simple improvement method for the existing soft X-ray spectrometer.

  Parameters defining the entire optical system, the diffraction grating 2 and the detector 3 of the soft X-ray spectrometer 1 are shown in FIG. 2, and parameter values are shown in Table 1. 2 and Table 1, r represents the distance from the sample S to the center of the diffraction grating 2 (the optical path length of the soft X-ray central ray X0 incident on the diffraction grating 2), and r ′ represents the center of the diffraction grating 2. To the center of the detector 3. The center of the detector 3 is set so that 450 eV soft X-rays enter.

  α represents an angle between a straight line connecting the sample S and the center of the diffraction grating 2 (the optical path of the central ray X0 of the soft X-ray incident on the diffraction grating 2) and a normal line at the center of the diffraction grating 2, and β0 is Represents an angle formed by a straight line connecting the center of the diffraction grating 2 and the center of the detector 3 and a normal line at the center of the diffraction grating 2. θ represents an angle formed by a straight line connecting the center of the diffraction grating 2 and the center of the detector 3 and the normal line of the detector 3.

The diffraction grating 2 is a cylindrical non-uniformly spaced scored diffraction grating defined according to the following formula (1).
d (w) = d0 / {1+ (2b ₂ / R) w + (3b ₃ / R) w ²
+ (4b ₄ / R) w ³ } (1)

  Here, w is the distance from the center in the arrangement direction of the score lines (the direction perpendicular to the individual score lines) (exit side is positive, incident side is negative), and d (w) is the position of the distance w. Where d0 is the number of score lines at the center and R is the radius of curvature. Further, h represents the height difference (the depth of the score line) of the diffraction grating 2. The parameters of the diffraction grating 2 are optimized including the incident angle to the detector 3.

  The parameters that define the mirror 5 are shown in FIG. 3, and the parameter values are shown in Table 2. 3 and 2 in the table, rm represents the distance from the sample S to the midpoint between the centers of the pair of mirrors 5, αm represents the inclination of the tangent at the center of the mirror 5 in the X direction, and D represents , The distance between the mirrors 5 at the center. Rm represents a radius of curvature.

  In the present embodiment, the mirror 5 is a cylindrical mirror having an axis in the Y direction, but a pair of plane mirrors may be employed instead of the mirror 5. However, a cylindrical mirror is preferable because the amount of soft X-rays incident on the diffraction grating 2 can be increased even if the size is the same.

  The influence of the installation error of the mirror 5 and the sample S on the detection by the detector 3 will be described. The variable factors in the installation of the mirror 5 and the sample S are shown in FIG. The position ΔX of the sample S in the X direction, the angle Δθy around the Y direction of the mirror 5 and the angle Δθz around the Z direction can be adjusted. Since resolution and detection efficiency are insensitive to errors of other factors, factors other than position ΔX, angles Δθy, and Δθz are fixed. FIG. 5 shows the relationship between the error of the above three factors and the intensity and peak width of soft X-rays detected by the detector 3.

  As shown in FIG. 5A, the error ΔX in the position of the sample S in the X direction has a large effect on the efficiency, and the intensity is halved by an error of ± 1.0 mm. By adjusting with an accuracy of ± 0.5 mm, it is possible to secure a strength of about 85%.

  As shown in FIG. 5B, the error Δθy of the angle around the Y direction of the mirror 5 has a great influence on the efficiency. The intensity is halved with an error of ± 0.3 °. By adjusting with an accuracy of ± 0.25 °, a strength of about 85% can be secured.

  As shown in FIG. 5C, the angle error Δθz around the Z direction of the mirror 5 has a large influence on the peak width, that is, the resolution. With an error of ± 0.4 °, the peak width doubles (resolution is halved). By adjusting with an accuracy of ± 0.1 °, it is possible to almost prevent a decrease in resolution.

  The above three factors can be adjusted while observing the light amount and image detected by the detector 3. The mirror 5 is fixed after adjusting the angle.

  The result of resolution calculation by ray tracing is shown in FIG. 6A shows the energy resolution when the spot size is 10 μm, 5 μm, and 1 μm with and without the mirror 5, and FIG. 6B shows the spot with the mirror 5. The relationship between the distance on the detector 3 and the intensity distribution when the size is 1 μm (condition of curve B in (a)) is shown. As is clear from FIG. 6A, there is no significant reduction in resolution due to the provision of the mirror 5 except when the resolution is particularly high. Further, as apparent from FIG. 6B, although the aberration appears, sufficient resolution is achieved.

An image of soft X-rays on the detector 3 when water is used as the sample S is shown in FIG. 7A shows a case where the mirror 5 is provided, and FIG. 7B shows a case where the mirror 5 is not provided. In the region A, emission of 1s orbital of oxygen atoms of water molecules appears. Appearing in the region B is light emission of 1s orbital of nitrogen atoms of Si ₃ N ₄ which is a constituent material of the window of the sample container. The intensity near the straight line C in FIG. 7A is high, and it can be seen that the soft X-rays reflected by the mirror 5 are concentrated here.

  FIG. 8 shows the intensity distribution in the region A of FIG. In FIG. 8, the curve (a) corresponds to FIG. 7 (a) with the mirror 5, and the curve (b) corresponds to FIG. 7 (b) without the mirror 5. The intensity represented by the area under the curve is about four times higher in (a), and the effect of providing the mirror 5 is noticeable.

DESCRIPTION OF SYMBOLS 1 Soft X-ray spectrometer 2 Diffraction grating 3 Detector 5 Mirror S Sample X0 Center ray

Claims (3)

A soft X-ray spectrometer comprising a diffraction grating that diffracts incident soft X-rays and a detector that detects soft X-rays diffracted by the diffraction grating,
A pair of mirrors having a curvature of 0 in a direction perpendicular to the central ray and parallel to a plane including the central ray perpendicular to the diffraction grating and sandwiching the central ray of soft X-rays incident on the diffraction grating are provided. A soft X-ray spectrometer.   The soft X-ray spectrometer according to claim 1, wherein the pair of mirrors are cylindrical concave mirrors having axes in a direction parallel to the plane and perpendicular to the central ray.   3. The soft X-ray spectrometer according to claim 1, wherein the pair of mirrors are symmetrical with respect to the plane.