JP2014044967A - Scanning electron microscope and sample holder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sample holder for a scanning electron microscope in which a slide glass used for observation by an optical microscope can be used as an observation sample as it is, and also to provide the scanning electron microscope mounting the sample holder thereon.SOLUTION: A scanning electron microscope according to an embodiment includes an evacuation system 13 enabling low vacuum control, an energy dispersion type X-ray detector 14, and a sample holder 15 capable of mounting a slide thereon. Thereby, the slide used for observation by a polarization microscope becomes possible to be mounted on an electron microscope as it is, and the same sample makes it possible to provide the scanning electron microscope capable of observation and analysis.

Description

  The present invention relates to a scanning electron microscope, and more particularly to an observation and analysis method for a thin film (thin piece) sample fixed on a slide glass.

  One of the electron microscopes is a scanning electron microscope (hereinafter referred to as SEM) and an energy dispersive X-ray analyzer (hereinafter referred to as EDX) that processes a signal from a semiconductor X-ray detector attached to the SEM. There is a combination of. This EDX is a device that performs elemental analysis of a micro area of several μm, and performs qualitative analysis, quantitative analysis, element distribution analysis by X-ray image, etc. at the same time as image observation by SEM It is.

  In addition, in recent SEMs, a charging phenomenon (hereinafter referred to as the following) occurs when a non-conductive sample is irradiated with an electron beam by maintaining the sample chamber of the SEM at a pressure higher than usual (hereinafter referred to as low vacuum control). There are low-vacuum SEMs that can reduce image obstruction due to charge-up) and can observe and analyze not only conductive samples but also non-conductive samples. Here, the pressure in the vacuum sample chamber used in the low vacuum SEM is about 1 to 270 Pa.

  In recent years, there is a need to bring a sample that has been observed with an optical microscope into the sample chamber of an SEM as it is, and perform observation with higher magnification, higher resolution, and deeper depth of focus.

  In Patent Document 1 (Japanese Patent Application Laid-Open No. 2007-335237), a vacuum vessel equipped with an electron optical system is arranged with the electron beam emission direction facing upward, and a preparation is applied to an opening provided on the upper surface of the vacuum vessel. An invention for observing a sample by irradiating an electron beam onto the sample fixed to the back surface of the substrate is disclosed. The preparation is fixed to the vacuum container via a preparation holder provided on the upper surface side of the vacuum container, and the vacuum seal between the preparation and the preparation holder and the vacuum container is maintained by an O-ring. The preparation holder is provided with four feed screws in the XY two-axis direction two by two, and can be manually finely moved in the XY direction while maintaining a vacuum seal with an O-ring.

JP 2007-335237 A

  In the scanning electron microscope described in Patent Document 1, the preparation is vacuum-sealed with an O-ring and directly brought into contact with the vacuum vessel. The preparation itself is moved with the moving screw. Therefore, there is a high possibility that the preparation is damaged during the movement, and if the preparation is damaged, the vacuum seal of the vacuum container is broken and the electron optical system in the container is damaged.

  The present invention is suitable for observing a sample mounted on a slide glass and a sample (hereinafter referred to as a slide, which is synonymous with a slide) in which the sample is fixed on the slide glass and thinned to a spectroscopic state. An object of the present invention is to provide a scanning electron microscope or a sample holder provided with a holder.

  In the present invention, the sample holder held in the scanning electron microscope is constituted by a plate-like member having a slide mounting surface constituted by a recess having a depth substantially equal to the thickness of the slide, and further the sample holder However, the said subject is solved by providing the pressing member which fixes the slide mounted in the said slide mounting surface by pressing against the level | step-difference part of the said recessed part from a side surface.

  ADVANTAGE OF THE INVENTION According to this invention, it becomes possible to implement | achieve the scanning electron microscope which can perform SEM observation simply using the slide used for observation with an optical microscope, without changing the structure of a SEM main body.

It is a SEM schematic diagram of a 1st embodiment. It is the schematic of the sample holder which can mount a slide. It is a SEM schematic diagram of a 2nd embodiment. Example 1 of an optical image obtained by imaging a slide set in a sample holder. Example 2 of an optical image obtained by imaging the slide set on the sample holder. Example 3 of an optical image obtained by imaging the slide set on the sample holder.

  DESCRIPTION OF EMBODIMENTS Hereinafter, modes for carrying out the present invention (hereinafter referred to as embodiments) will be described in detail with reference to the drawings.

<First Embodiment>
The first embodiment will be described in detail with reference to FIGS. 1 and 2.

  FIG. 1 is an SEM schematic diagram of the first embodiment.

  The SEM 1 of the first embodiment includes an electron source 2, an electron beam 3 emitted from the electron source, a condenser lens 4 for converging the electron beam 3, a deflection coil 5 for scanning, and an objective lens 6 for focusing. An electron optical column 7, a control device for adjusting the conditions of the electron optical column, and a secondary electron detector 9 for detecting secondary electrons emitted from the sample 8 by irradiation of the electron beam 3 on the sample 8. A sample for holding a vacuum, comprising: a semiconductor detector 10 for detecting reflected electrons; a control device for processing a signal from the detector; and a sample micro-moving device 11 capable of moving the sample to an arbitrary position. The chamber 12 is constituted by a vacuum exhaust system 13 and the like, and an EDX X-ray detector 14 is combined therewith. The electron optical column 7 is provided with a differential exhaust diaphragm for maintaining the sample chamber 12 in an environment lower in vacuum than the vacuum in the electron optical column. It has a configuration capable of low vacuum control. In addition, the detector for detecting the signal emitted from the sample 8 with the sample chamber 12 under low vacuum control includes not only the secondary electron detector 9 and the semiconductor detector 10 but also an ion current detection electrode. .

Conventionally, as a method for adjusting the sample when observing or analyzing the sample, a method of fixing the sample to a dedicated sample table with carbon tape or the like has been used. However, since the slide is made of quartz glass, the If fixed, it may be damaged when it is removed from the sample stage.
Therefore, a sample holder 15 on which a slide can be mounted is prepared.

  FIG. 2A is a schematic view of a sample holder 15 on which a slide can be mounted.

  The sample holder 15 includes a plate-like member 17 having a slide placement surface 16 constituted by a recess having a depth substantially equal to the thickness of the slide, and a slide placed on the slide placement surface 16 in the recess. A pressing member 18 that presses against the stepped portion from the side surface, an attaching / detaching mechanism that fixes and releases the pressing member 18 at a predetermined mounting position by a pressure of a spring or the like, and a foot portion 22 that supports the plate-like member are provided. As a result, the slide can be easily set in the sample micro-movement device 11 without damaging the slide and the sample 8 on the slide.

  FIGS. 2B and 2C show schematic views of the attachment / detachment mechanism in a state where the slide is fixed and a state where the slide is released. The pressing member 18 has a crank shape, and one end of the pressing member 18 forms a pressing portion of the slide. Further, the pressing member 18 is fitted to the plate-like member 17 through a groove provided on the lower surface of the plate-like member 17. On the other hand, a hole for attaching the spring 23 is formed on the back side of the foot 22. One end opposite to the slide pressing portion of the pressing member 18 is fixed to the spring 23, and the slide pressing portion is pressed against the side surface of the plate-like member 17 by the elastic force of the spring. Thereby, a slide is fixed to the level | step-difference part of the said recessed part.

  When the slide is released, the vicinity of the fixing portion between the pressing member 18 and the spring 23 is pushed by hand as indicated by an arrow in FIG. Thereby, the slide pressing portion is released from the pressing position, and the slide can be removed from the sample holder.

  If the purpose is simply to fix the slide, both ends of the slide may be pressed from the upper surface with a spring-type clamp or the like, but the sample may be placed on the entire upper surface of the slide. In such a case, the sample may be damaged if it is fixed with a clamp from above. Therefore, the risk of damaging the sample is less when the slide is fixed with a fixing tool from the side like the sample holder of this embodiment. In addition, as a method of fixing the slide from the side surface, a method of providing pressing members on both side surfaces of the sample table without forming a recess in the sample table may be used. However, this method requires two or more pressing members, which increases the cost of manufacturing the sample stage. Therefore, the sample holder shown in FIG. 2A is superior from the economical viewpoint.

In addition, the shape of the slide glass is roughly classified into two types according to standards: general use and mineral use. Here, the size standards of major glass slides in the world are shown below.
・ General use (Japan (JIS standard) ... 76mm x 26mm, USA ... 3inch x 1inch (76.2mm x 25.4mm), Europe ... 75mm x 25mm)
・ For mineral ... (48mm × 28mm)

  As described above, the shape of the slide glass is roughly classified into two types, general use and mineral use, and the thickness is approximately 0.5 mm to 1.5 mm. Moreover, the size of the general-purpose slide glass is almost the same in any standard in Japan, the United States and Europe. Therefore, in the sample holder of the present embodiment, the shape of the concave portion formed on the upper surface of the sample table is configured to be able to place the above-mentioned two types of standard and slide glasses for minerals. Specifically, as shown in FIG. 2, in addition to a mounting surface (shown by a dotted line on the slide mounting surface 16 in FIG. 2) for mounting a general-purpose slide glass, a mineral is formed on the step portion of the recess. The slide concave portion 20 is provided to secure the width of the placement surface on which the mineral slide glass can be placed. As a result, the single sample holder 15 can handle all the slide glasses manufactured according to the world's major standards.

  Further, the sample holder of the present embodiment includes a Faraday cup element 19 for measuring the sample current at a position different from the slide mounting surface 16 on the upper surface of the sample holder. At the time of quantitative analysis of EDX, calibration by sample current measurement is necessary, and conventionally, a dedicated Faraday cup device is attached to the SEM. According to the sample holder of this embodiment, the sample current required for calibration can be obtained simply by moving the irradiation position of the electron beam from the observation position of the slide to the position of the Faraday cup element 19 using the sample micro-movement device 11 of the SEM. Can be measured. That is, it is possible to obtain an accurate quantitative analysis result without requiring a dedicated Faraday cup device.

  As described above, the SEM of the present embodiment includes the sample holder 15 on which the slide can be mounted, so that the slide used for observation with the optical microscope can be mounted on the SEM as it is, and the optical microscope using the same sample is used. SEM suitable for observation and SEM observation is realized.

<Second Embodiment>
When observing the same sample with an optical microscope and a separate device called SEM, searching for a visual field becomes a problem. Conventionally, when an image taken with an optical microscope (hereinafter referred to as an observation position designation image) is taken into an SEM and a field of view is searched, the characteristics of the observation designation image are used for alignment adjustment between the observation position designation image and the sample micro-movement device. It is necessary to find a point from the SEM observation image and associate a plurality of feature points serving as the respective references with complicated operations. Therefore, in the present embodiment, an SEM incorporating a visual field search support function will be described.

  FIG. 3 is a schematic diagram of a main part of the SEM of the present embodiment, in which the sample holder 15 on which a slide can be mounted and the imaging device 21 are incorporated in the sample chamber of the SEM 1 described in the first embodiment. (The other parts are the same as those of the SEM 1 described in the first embodiment, and the description thereof is omitted). Here, the imaging device 21 is an optical imaging device (CCD camera or the like) or an optical microscope. Note that the imaging device 21 may be incorporated into the sample chamber 12 including the sample micro-movement device 11 or may be placed outside.

  At the start of imaging of the SEM shown in FIG. 3, first, the sample holder 15 is moved directly below the imaging device 21 by the sample micro-movement device 11, and an image of the entire slide or the entire sample on the slide glass is captured. At this time, if the magnification and field of view of the imaging device 21 are fixed in advance, the movement correction value (alignment value) of the sample micro-movement device 11 for performing imaging of the same field of view with the imaging device 21 and the electron optical column 7. Can be calculated automatically. Thereafter, by designating an arbitrary position of the observation position designation image picked up by the image pickup device 21, it becomes possible to move the sample micro-movement device 11 to the observation position by the electron optical column 7, and at the time of observation and analysis The visual field search can be easily performed. The alignment value calculation process is performed by executing a program stored in a memory on a computer by a calculation means (processor or the like) in the computer.

  Now, the problem is that the imaging device 21 is an optical imaging device.

  FIG. 4 shows an example of an optical image obtained by picking up an image of the slide set on the sample holder 15 on which the slide mounting surface 16 is not processed with the image pickup device 21.

  In general, since the sample on the slide is a thin film, when the image is picked up by the imaging device 21, the optical image transmits not only the shape of the sample on the slide but also the shape of the slide mounting surface 16 of the sample holder 15 through the slide. Therefore, when the slide mounting surface 16 of the sample holder 15 has an extra shape (in the case of FIG. 4 of the present embodiment, the screw head is imaged in the sample shape), the field of view is searched. Therefore, an effective image cannot be obtained as the observation position designation image. Therefore, the slide mounting surface 16 of the sample holder 15 needs to be a uniform flat surface having no excessive shape.

  FIG. 5 is an example of an optical image in which white paper is sandwiched between the slide and the slide mounting surface 16 and the slide set on the sample holder 15 is imaged by the imaging device 21.

  Although the shape of the slide placement surface 16 was not imaged, the sample shape on the slide had poor contrast, and it was not an effective image as an observation position designation image for visual field search.

  Therefore, in this embodiment, the slide mounting surface 16 of the sample holder 15 is a flat surface having a uniform metallic luster. Such a plane can be obtained, for example, by mirror-finishing the slide mounting surface. FIG. 6 shows an example of an optical image obtained by a sample holder in which the slide mounting surface 16 is mirror-finished. From FIG. 6, it can be seen that the shape of the slide mounting surface 16 is not imaged, the sample shape on the slide has good contrast, and an effective image is obtained as an observation position designation image for visual field search.

  As described above, by setting the slide mounting surface of the sample holder to a flat surface having a uniform metallic luster, it is possible to capture the sample shape on the slide in more detail, and therefore, observation And the search for the visual field of analysis is facilitated.

  Instead of mirror-finishing the slide mounting surface, an optical image may be taken by inserting a glossy thin metal plate between the slide and the slide mounting surface 16. Further, in the present embodiment, the sample holder of the present embodiment has been described using an SEM incorporating a visual field search support function as shown in FIG. 3 as an example, but the sample holder of the present embodiment is generally used. It is clear from the comparison of FIGS. 4 to 6 that the present invention has an effect even when applied to an optical microscope.

<Third Embodiment>
As an application target of the sample holder according to the first embodiment to the second embodiment, there is a mineral sample. As a method of observing and analyzing mineral samples, it is common to observe with a polarizing microscope and to analyze with EPMA (Electron Probe MicroAnalyser: an apparatus that performs elemental analysis from the wavelength of characteristic X-rays generated by electron beam irradiation). Is. However, the pretreatment methods are different from each other. In the polarization microscope, the specimen is observed with a slide, and in EPMA, the specimen is embedded in a resin and analyzed with a sample polished to be analyzed. Therefore, a series of operations from observation to analysis is complicated, and there is a problem that observation and analysis using the same sample cannot be performed.

  By using the sample holder of the first embodiment or the second embodiment, it is possible to carry the SEM observation or EDX analysis by directly bringing the slide used for the observation with the polarizing microscope into the SEM, and the analysis by the conventional EPMA Can be replaced with SEM + EDX.

  Here, the merit of replacing the analysis from EPMA to SEM + EDX is not only the realization of the observation and analysis by the same sample as in the first and second embodiments. In general, a wavelength dispersive X-ray analyzer (hereinafter referred to as WDX) employed in EPMA is superior in wavelength resolution as compared to EDX, but requires a large irradiation current of about two orders of magnitude, resulting in large damage to the sample. Simultaneous analysis of multiple elements is not possible. On the other hand, since EDX is superior to WDX in detection sensitivity, it can be analyzed in a short time, and a plurality of elements can be analyzed simultaneously. EDX is inferior in wavelength resolution compared to WDX, but when the object of analysis is a thin film such as a slide, the background caused by the diffusion of the electron beam in the sample and the bremsstrahlung of the sample is greatly reduced. The features of EDX with high sensitivity can be exhibited more. In general, EPMA cannot control a low vacuum in the sample chamber, and therefore cannot analyze a non-conductive slide.

  Therefore, by replacing the analysis from EPMA to SEM + EDX, analysis using the same sample as that observed with the polarizing microscope and damage to the sample due to irradiation current can be reduced, and multiple elements can be analyzed simultaneously in a short time. It is possible to provide an analytical device that can be used.

  Needless to say, the present invention can be applied not only to SEMs equipped with SEMs and EDXs but also to similar devices in the observation and analysis of slides of various samples.

1 Scanning electron microscope (SEM)
2 Electron source 3 Electron beam 4 Condenser lens 5 Deflection coil 6 Objective lens 7 Electron optical column 8 Sample 9 Secondary electron detector 10 Semiconductor detector 11 Sample micro moving device 12 Sample chamber 13 Vacuum exhaust system 14 X-ray detector 15 Sample holder 16 Slide mounting surface 17 Plate-shaped member 18 Pressing member 19 Faraday cup device 20 Slide concave portion 21 for mineral Imaging device 22 Foot 23 Spring

In the present invention, the sample holder held in the scanning electron microscope is configured by a plate-like member having a step portion having a depth substantially equal to the thickness of the slide and a slide mounting surface , thereby achieving the above-described problem. Solve.

Claims (19)

A scanning electron microscope capable of observing a sample placed on a slide glass,
An electron optical column that scans the primary electron beam on the sample placed on the sample holder;
A sample chamber for storing the sample holder;
A detector for detecting a signal obtained by scanning the primary electron beam,
The sample holder is
A plate-like member having a slide glass placement surface on which the slide glass is placed, and a stepped portion that contacts a side surface of the slide glass when the slide glass is fixed,
The scanning electron microscope according to claim 1, wherein the step portion is a step substantially equal to the thickness of the slide glass with respect to the slide glass placement surface. The scanning electron microscope according to claim 1,
The scanning electron microscope characterized in that the slide glass mounting surface is a surface having a metallic luster. The scanning electron microscope according to claim 1,
A scanning electron microscope characterized in that the slide glass is used for observation with an optical microscope. The scanning electron microscope according to claim 1,
A scanning electron microscope, wherein the slide glass is observed with an optical imaging device or an optical microscope in a state of being mounted on the sample holder. The scanning electron microscope according to claim 1,
A scanning electron microscope comprising a pressing member that fixes the slide glass by pressing the slide glass from a side surface of the slide glass. The scanning electron microscope according to claim 5, wherein
The scanning electron microscope, wherein the pressing member is pressed against the slide glass by an elastic force of a spring. The scanning electron microscope according to claim 1,
The scanning electron microscope according to claim 1, wherein the slide glass mounting surface corresponds to a plurality of slide glasses having a size. The scanning electron microscope according to claim 1,
A scanning electron microscope characterized in that the sample is a thin film. The scanning electron microscope according to claim 1,
A scanning electron microscope comprising: a sample micro-movement device that is stored in the sample chamber and moves the sample holder. The scanning electron microscope according to claim 1,
A scanning electron microscope characterized in that the inside of the sample chamber is maintained at a lower vacuum than in the electron optical column. The scanning electron microscope according to claim 3 or 4,
A sample micro-movement device that is stored in the sample chamber and moves the sample holder;
A scanning electron microscope characterized in that a movement correction value of the sample micro-movement device is obtained so that the optical microscope or the optical imaging device and the electron optical lens barrel perform imaging of the same field of view. In a sample holder capable of holding a slide glass on which the sample is placed, which is used in a scanning electron microscope that detects a signal obtained by scanning a primary electron beam on a sample placed on the sample holder,
The holder is
A slide glass placement surface on which the slide glass is placed;
A plate-like member having a step portion that contacts the side surface of the slide glass when the slide glass is fixed,
The step portion is a step substantially equal to the thickness of the slide glass with respect to the slide glass placement surface. The sample holder according to claim 12,
A sample holder, wherein the slide glass mounting surface is a surface having a metallic luster. The sample holder according to claim 12,
A sample holder, wherein the slide glass is used for observation with an optical microscope. The sample holder according to claim 12,
The slide glass is observed with an optical imaging device or an optical microscope while being mounted on the sample holder. The sample holder according to claim 12,
A sample holder, comprising: a pressing member that fixes the slide glass by pressing the slide glass from a side surface of the slide glass. The sample holder according to claim 16,
The sample holder, wherein the pressing member is pressed against the slide glass by an elastic force of a spring. The sample holder according to claim 12,
The sample glass mounting surface corresponds to a plurality of slide glasses having a plurality of sizes. The sample holder according to claim 12,
The sample holder is a thin film.