WO2003036677A1

WO2003036677A1 - Electron microscope having x-ray spectrometer

Info

Publication number: WO2003036677A1
Application number: PCT/JP2002/001899
Authority: WO
Inventors: Masami Terauchi
Original assignee: Jeol Ltd.
Priority date: 2001-10-24
Filing date: 2002-02-28
Publication date: 2003-05-01

Abstract

An electron microscope having an X-ray spectrometer of high resolution with a compact optical system. The X-ray spectrometer (10) has a spectrometer chamber (11) from which air is exhausted by vacuum pumps (18, 19, 20). In the spectrometer chamber (11), diffraction grating at different intervals (12) is arranged and at its end, an X-ray detector (14) is mounted. The X-ray spectrometer (1) is mounted on the side wall of the electron microscope via a gate valve (4). Characteristic X-rays emitted from a sample (3) to which an electron beam is applied is incident at a great angle (α) with respect to a normal of the diffraction grating at different intervals and diffracted X-rays from the diffraction grating reach the X-ray detector (14) and are detected by it.

Description

Specification

Electron microscope equipped with X-ray spectrometer

The present invention relates to an electron microscope equipped with an X-ray spectroscope. Background art

Conventionally, a wavelength-dispersive spectrometer (WDS) is attached to a scanning electron microscope (SEM), and the characteristic X-rays generated when the sample is irradiated with an electron beam in the electron microscope are detected by the WDS. An electron probe microanalyzer (EPMA) for performing line analysis (elemental analysis) is known. This WDS requires a mechanism that aligns the three points of the X-ray generation point (sample), the center point of the spectral crystal, and the center point of the slit of the detector with predetermined positions on the Rowland circle. Because it is several meters long, it becomes a large-scale optical system. In addition, since the angle of incidence on the spectroscopic crystal (the angle relative to the normal to the crystal plane) is small, the detector approaches the electron microscope column side, making the overall arrangement difficult. On the other hand, an energy dispersive spectrometer (EDS) is combined with a transmission electron microscope (T EM) or SEM to detect characteristic X-rays from a sample by EDS. Energy-energy resolution is not enough compared to WDS for PMA.

The present inventor has been developing an electron microscope capable of performing high-resolution energy analysis by combining an energy filter with a transmission electron microscope (TEM). Using this device, it is possible to know the dielectric function and the conduction band density distribution in the 30 nm φ region of the sample. For detailed electronic state studies It is necessary to know not only the conduction band but also the valence band state density. As described above, in a transmission electron microscope (TEM) equipped with an EDS, elemental analysis can be performed using characteristic X-rays generated from a region irradiated with an electron beam. If Torr can be measured with an energy resolution of less than leV, the valence band density of states distribution can be obtained. However, the energy resolution of current EDS using semiconductor detectors is about 100-200 eV, which is not enough for studying electronic states. Also, WDS has a higher resolution (about 10 eV) than EDS, but does not have sufficient energy resolution to obtain the valence band state density. Disclosure of the invention

An object of the present invention is to provide an electron microscope having an X-ray spectrometer having a compact optical system and capable of obtaining high energy resolution.

An electron microscope equipped with the X-ray spectrometer of the present invention is an X-ray spectrometer which is evacuated by a vacuum pump, has a non-equidistant diffraction grating, and has a spectroscopic chamber having an X-ray detector attached to an end. Electron microscope attached to the side wall of an electron microscope via a gate valve.The characteristic X-ray emitted from the sample irradiated with the electron beam is oblique at a large angle with respect to the normal to the irregularly spaced diffraction grating surface. The X-ray detector detects the diffracted X-rays with an X-ray detector.

As the X-ray detector, a back-illuminated CCD detector can be used. It is preferable that the emission angle of the X-ray diffracted by the unequally spaced diffraction grating is 75 to 87 degrees with respect to the normal to the diffraction grating surface.

In addition, the characteristic X-rays emitted from the sample are focused toward the irregularly spaced diffraction grating. An X-ray focusing mirror can be provided.

Further, it is possible to equip a plurality of unequally spaced diffraction gratings having different measurement energy ranges and provide a diffraction grating exchange mechanism capable of selectively arranging one of the unequally spaced diffraction gratings at the characteristic X-ray incident position.

Characteristics It is possible to provide a grating tilt adjustment mechanism that adjusts the tilt of unequally spaced diffraction gratings selectively set at the X-ray incidence position.

It is preferable that the CCD detector is connected to the spectroscopic chamber via a bellows so as to be movable with respect to the diffraction grating.

The bellows has a structure in which a plurality of bellows with different expansion and contraction directions are connected in cascade, and the CCD detector can be moved two-dimensionally with respect to the diffraction grating by combining expansion and contraction of multiple bellows. It is preferably provided in BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a diagram showing an example of a transmission electron microscope equipped with an X-ray spectrometer.

Figure 2 shows the Boron K emission spectrum of] 3 polon. FIG. 3 is a conceptual diagram illustrating another example of the transmission electron microscope of the present invention. FIG. 4 is a diagram showing an X-ray focusing mirror.

FIG. 5 is a diagram showing a grating exchange mechanism.

FIG. 6 is a diagram showing a grating tilt adjusting mechanism.

FIG. 7 is a diagram showing another example of the X-ray focusing mirror. BEST MODE FOR CARRYING OUT THE INVENTION

Fig. 1 shows an example of a transmission electron microscope equipped with an X-ray spectrometer according to the present invention. FIG. In FIG. 1, the inside of the lens barrel 2 of the TEM 1 is maintained at a vacuum. The sample 3 placed in the lens barrel 2 is irradiated with an electron beam from above through an electron lens, and is projected on a fluorescent screen through an electron beam lens transmitted through the sample. As a result, a transmitted electron image is formed on the phosphor screen. A hole for taking out characteristic X-rays generated from the sample to the outside of the lens barrel 2 is formed in the side wall of the room in which the sample 3 of the lens barrel 2 is disposed, and a connection pipe having a gate valve 4 in this hole is provided. X-ray spectroscope 10 is attached via 60. The gate valve 4 is arranged between the spectroscope 10 and the lens barrel of the TEM 1 and can separate the vacuum of both. Spectroscope (spectrometer chamber 1) 11 A diffraction grating 12 arranged in the chamber 1 and a back-illuminated CCD detector 14 attached to the end of the spectroscopic chamber via a bellows 13 14 Spectroscope 10 Is configured.

The diffraction grating 12 has grooves formed at irregular intervals for aberration correction. It is known that such unequally spaced diffraction gratings can realize an image plane perpendicular to the diffracted light when light is incident at a large incident angle. Therefore, in this embodiment, the characteristic X-ray emitted from the sample 3 when irradiated with the electron beam in the TEM 1 has a large incident angle α (normally parallel to the diffraction grating plane) with respect to the normal to the diffraction grating plane. ), The incident angle a to the diffraction grating is selected. Due to this oblique incidence, the focal point of the diffracted X-rays is created not on the Rowland circle but on a plane (CCD plane) almost perpendicular to the light rays. Dispersion due to this diffraction grating is smaller than that of a normal grooved diffraction grating, so that a wide energy range can be detected using a fixed CCD detector 14.

The spectrometer chamber 11 is provided with a turbo molecular pump (TMP) 19 and a sputter ion pump (SIP) 18 combined with a single pump 20 through valves 15, 16 and 17. It has been evacuated to a vacuum. CCD Since the detector 14 is attached to the spectrometer chamber 11 via the bellows 13 ·, fine adjustment of the distance from the diffraction grating is possible. The signals from the CCD detector 14 taken out under the control of the CCD controller 21 are transferred to the data processor 22 for data processing, and the spectrum is displayed on the monitor 23. .

The diffraction grating of the present embodiment has 1200 grooves / mm, and is arranged so that the interval gradually changes from one to the other along the traveling direction of the light beam (X-ray). The diffraction grating has a concave surface with a radius of 6549 mm, a width (in the direction perpendicular to the light beam direction) of 30 mm, and a length (in the light beam direction) of 50 mm. A gold layer is formed on the surface by surface treatment.

The incident angle α to the normal of the diffraction grating surface is 87 degrees, the emission angle 3 is 77 to 83 degrees, and the length of the arm (the distance from the sample to the diffraction grating irradiation point and the distance from the diffraction grating to the CCD) is , Are set to 237mm and 235mm respectively. The back-illuminated CCD has a size of 1100X330 pixels, size 26.4mm x 7.9mm, and one pixel size of 24µm x 24xm (resolution corresponding to an emission angle of 77 to 83 degrees).

The spot size of the diffracted X-ray focused on the CCD detector is the superposition of the size of the electron beam on the sample and the spread due to the aberration of the diffraction grating. The size of the electron beam focused on the sample is approximately 500ηm in the experiment. It has been reported that the spot spread due to the diffraction grating aberration is 40 m at 248 eV and 20 μm at 124 eV, so the spread for Boron K emission energy of about 185 eV is almost It is estimated to be 30 / xm. Therefore, the spot size of the diffracted X-ray focused on the CCD detector is mainly determined by the aberration. The energy dispersion of the diffraction grating is λ = σ (sin CK -f- sin β) (1)

(Is wavelength, σ is groove interval, α is incident angle and diffraction angle)

Is evaluated as about 0.3 eV per pixel size. Therefore, the energy resolution of the Boron K emission spectrum is estimated to be about 0.6 eV (0.3 eV x 2 pixels).

Figure 2 shows a Boron K emission spectrum of 3 pols obtained from a 600 nm diameter single crystal sample surface at a probe current of about 70 ηA. The detection time is about 1 hour. The horizontal axis represents the number of channels of the CCD detector. The stalls show one peak and two shoulders, each indicated by an arrow and a vertical line. The energy of the peak is 185 eV and the width of the peak is about 10 eV when referring to the previously reported spectrum by the diffraction spectrometer. FIG. 2 shows that the device of the present invention has a high energy resolution and an excellent SZN ratio.

Next, another embodiment of a transmission electron microscope equipped with the X-ray spectrometer according to the present invention will be described with reference to FIGS.

FIG. 3 is a conceptual diagram illustrating another example of the transmission electron microscope of the present invention. On the side wall of the room where the sample 3 of the TEM lens barrel 2 is placed, a hole is made to take out the characteristic X-rays generated from the sample to the outside of the lens barrel 2, and a metal connection pipe 6 is formed in this hole. 0—1 is entered. One end of the connection pipe 60-1 extends into the room toward the sample 3, and the other end is connected to the gate valve 4. An X-ray spectroscope 10 is connected to the other end of the gate valve 4 via a metal connection pipe 60-2.

An X-ray focusing mirror 30 for collecting X-rays emitted from the sample 3 is mounted inside the distal end of the connection tube 60-1. The X-ray focusing mirror 30 focuses the X-rays to increase the intensity of X-rays incident on the diffraction grating. The fixed time can be shortened and the SZN ratio of the spectrum can be improved. The collected X-rays are unequally spaced in the spectrometer chamber 11 through slits 31 and 32 arranged in the connecting pipes 60-1 and 60-2 before and after the gate valve 4. The light enters the diffraction grating 12. Slits 33 are also arranged immediately above the incident surface of the unequally spaced diffraction grating 12 with a small distance from the incident surface (a distance that does not hinder X-ray incidence and emission). The light emitted from the electron irradiation point on the sample and traveling in a direction other than the X-ray optical path from the sample to the diffraction grating reaches the CCD detector 14 by these multiple slits 31, 32, and 33. It can be prevented from being detected as a ground. This improves the S / N ratio of the spectrum.

The unequally spaced diffraction grating 12 is attached to a grating exchange mechanism 40 described later. The grating exchange mechanism 40 holds and holds a plurality of unequally spaced diffraction gratings having different measurement energy regions. One of the unequally spaced diffraction gratings is set at the X-ray incident position and diffracts X-rays. The tilt of the diffraction grating set at the X-ray incident position is adjusted by the grating tilt adjusting mechanism 50.

A CCD detector 14 for detecting diffracted X-rays is attached to the end of the spectrometer chamber 11 via a bellows 13. The spectrometer chamber 111 of the present embodiment includes two divided cylinders 111, 112 and a bellows 34 connecting the two cylinders. As shown in FIG. 3, the two cylinders 1 1—1, 1 1 and 1 2 are arranged with their center axes shifted, and the bellows 3 4 The cylinder 1 1 1 1 and 1 1-2 are connected. As a result, by combining the expansion and contraction of the two bellows 13 and 34, the CCD detector 14 can be moved up and down, left and right (two-dimensional direction), and the position can be finely adjusted. As mentioned above, When light is incident at a large angle of incidence, an unequally spaced diffraction grating forms an image plane perpendicular to the diffracted light, so the light-receiving surface of the CCD detector 14 must be aligned with that image plane. Need to be In the present embodiment, the position and direction of the light receiving surface with respect to the diffracted X-rays are adjusted by moving the cylinder 1 1-2 and the CCD detector 14 using two bellows having different expansion and contraction directions. Can be.

As a result, for example, it is possible to detect a deviation of the CCD position due to an assembly error, and it is possible to set an optimal position. At this time, the incidence of the diffracted X-rays on the CCD detector can be optimized by combining the adjustment of the grating inclination adjusting mechanism 50.

FIG. 4 is a diagram illustrating the X-ray focusing mirror 30. The X-ray focusing mirror 30 is a pair of two mirrors facing each other, and the surface facing each mirror is flat in the direction perpendicular to the plane of the paper, and in the direction parallel to the plane of the paper, the angle of incidence of X-rays on the mirror gradually decreases. A curved surface is drawn on the sample, and the distance between the mirrors is such that the sample side is narrow and the diffraction grating side is wide.

X-rays generated from the electron beam irradiation point of the sample tilted toward the X-ray focusing mirror are radiated in all solid angle directions, and XI and X2 in the figure (the electron beam irradiation point of the sample and the diffraction grating). The range within the straight line connecting the ends) represents the X-rays incident on the diffraction grating when no mirror is used. By setting the focusing mirror, the X-rays in the range between XI and X3, X2 and X4 in the figure (X3 and X4 are straight lines connecting the sample and the front end of the mirror) The light is condensed and enters the diffraction grating. As a result, the intensity of X-rays incident on the diffraction grating increases (the solid angle of X-ray detection increases), so that the measurement time can be reduced and the SZN ratio of the spectrum can be improved.

FIG. 5 is a diagram illustrating an example of the grating exchange mechanism. Fig. 5 (a) In the example, unequally spaced diffraction gratings I, II, and III having different measurement energy ranges are fixed to a rotating table 41 that can rotate in a vertical plane, and the rotation angle of the rotating table can be adjusted from outside the vacuum. As a result, any one of the three diffraction gratings can be set at the X-ray incident position by the slit 33 without breaking the vacuum. Of course, a turntable that rotates in a horizontal plane may be used.

In the example of Fig. 5 (b), unequally spaced diffraction gratings I, II, and II with different measurement energy ranges are fixed to the horizontal moving table 42, and the position of the horizontal moving table 42 is adjusted from outside the vacuum. Can be. Thus, any one of the three diffraction gratings can be set at the X-ray incident position by the slit 33 without breaking the vacuum.

By using three unequally spaced diffraction gratings I, II and I II with different measurement energy ranges in this way, a wider energy range (60-1200 eV) can be measured. Furthermore, by installing a large number of unequally spaced diffraction gratings with different energy ranges to be measured, it is possible to measure a wider energy range by replacing the diffraction grating without breaking vacuum. FIG. 6 is a diagram illustrating a grating tilt adjustment mechanism. In this example, the inclination of the diffraction grating set at the X-ray incident position by the slit 33 can be detected by the grating exchange mechanism using the turntable 41 shown in FIG. 5 (a). . That is, the straight line introducer 51 is configured so that the rod in contact with one end of the diffraction grating moves up and down by converting the rotational movement into linear movement, and the height of one side of the diffraction grating at the tip of the aperture Can be adjusted. As a result, it is possible to correct the tilt of the diffraction grating due to an assembly error or the like, and realize an optimal X-ray optical system.

FIG. 7 is a view showing another example of the condensing mirror 30. As shown in FIG. In the example of Fig. 4, two X-ray focusing mirrors with curved surfaces were used facing each other. A total of four rat focusing mirrors are used in combination. Each mirror is composed of a silicon substrate, and a gold thin film is formed on the facing surface (X-ray incident surface) by sputtering. By forming a thin gold film, the reflection efficiency of X-rays on the mirror surface can be increased.

It should be noted that the present invention is not limited to the above-described embodiment, and can be modified. For example, to prevent secondary electrons generated from the electron beam irradiation point on the sample from reaching the CCD detector 14 and generating some noise, for example, insulate the slit 31 or 32 from the surroundings. The voltage may be applied to repel secondary electrons. Alternatively, a trapping electrode to which a voltage for attracting secondary electrons is applied may be arranged in the connection tubes 60-1 and 60-2.

In the above embodiment, the X-ray spectrometer is combined with the TEM column. However, the X-ray spectrometer may be combined with another electron microscope (SEM, EPMA or Auger microprobe). good. In this case, an X-ray spectrometer may be attached to the side wall of the sample chamber of SEM, EPMA or Auger microprobe. In short, the term “electron microscope” as used in the present invention is not limited to TEM or SEM, but encompasses all devices having a function of acquiring an image of a sample based on electron beam irradiation on the sample. is there.

As described above, according to the present invention, it is possible to achieve a higher resolution with a more compact optical system than conventional WDS, and to obtain a partial state density of a valence band from a specific small sample region. An electron microscope equipped with an X-ray spectrometer can be realized.

In addition, X-rays from the sample are condensed by a condenser mirror and made incident on the diffraction grating, thereby increasing the intensity of X-rays incident on the diffraction grating, shortening measurement time, The SZN ratio of the spectrum can be improved.

In addition, by making X-rays incident on the diffraction grating through a plurality of slits, the background due to stray light can be reduced, and the SZN ratio of the spectrum can be improved.

In addition, by attaching the CCD by combining bellows with different expansion and contraction directions, fine adjustment of the CCD position in the vertical and horizontal directions can be performed. Can be set.

In addition, by providing a grating exchange mechanism equipped with a plurality of diffraction gratings with different measurement energy regions, it is possible to measure a wider energy region by exchanging diffraction gratings without breaking vacuum.

In addition, by providing a grating tilt adjustment mechanism, it is possible to correct the tilt of the diffraction grating due to an assembly error or the like, and to realize an optimal X-ray optical system. Industrial applicability

As described above, the electron microscope equipped with the X-ray spectrometer according to the present invention is useful as an apparatus that can obtain a valence band state density distribution.

Claims

The scope of the claims

1. An X-ray spectrometer, which is evacuated by a vacuum pump, has a non-uniformly spaced diffraction grating, and has a spectroscopic chamber with an X-ray detector mounted at the end, is attached to the side wall of the electron microscope via a gate valve. A characteristic X-ray emitted from an electron beam-irradiated sample at an oblique angle at a large angle with respect to the normal to the irregularly spaced diffraction grating surface, and the diffracted X-ray is detected as an X-ray An electron microscope equipped with an X-ray spectrometer, which is characterized by detection with an instrument.

2. The electron microscope according to claim 1, wherein the X-ray detector is a back-illuminated CCD detector.

3. The electron microscope according to claim 1, wherein an emission angle of the X-ray diffracted by the unequally spaced diffraction grating is 75 to 87 degrees with respect to a normal to the diffraction grating surface.

4. The transmission electron microscope according to claim 1, wherein the characteristic X-rays emitted from the sample are condensed by an X-ray condensing mirror and incident on a non-equidistant diffraction grating.

5. Equipped with a plurality of unequally spaced diffraction gratings with different measurement energy ranges, and equipped with a diffraction grating exchange mechanism that can selectively arrange one of the unequally spaced diffraction gratings at the characteristic X-ray incident position. 2. The transmission electron microscope according to claim 1, wherein:

6. Characteristics The transmission electron microscope according to claim 5, further comprising a grating tilt adjusting mechanism for adjusting the tilt of the unequally spaced diffraction grating selectively set at the X-ray incident position.

7. The electron microscope according to claim 1, wherein the CCD detector is connected to the spectroscopic chamber via a bellows so as to be movable with respect to the diffraction grating. .

8. The bellows cascade connects a plurality of bellows with different expansion and contraction directions. 8. The electron microscope according to claim 7, having a structure, wherein the CCD detector is provided so as to be two-dimensionally movable with respect to the diffraction grating by combining expansion and contraction of a plurality of bellows.