JP2004319518A - Scanning electron microscope device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a scanning electron microscope device enabled to effectively use an inner space of a sample chamber by eliminating an occupied space in the sample chamber, indicating a scanning center position by a laser beam, capable of easily specifying an observation point. <P>SOLUTION: A long-focal-distance optical microscope 19 having a light axis capable of crossing that of the scanning electron microscope 3 on a sample 5 is installed outside the sample chamber 4 fitted to the scanning electron microscope 3. A movement direction of images by the long-focal-distance optical microscope is made to conform with that by the scanning electron microscope, and a laser beam irradiation means 36 is provided for irradiating a laser beam toward the sample by coinciding it with the light axis of the scanning electron microscope halfway from the axis. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a scanning electron microscope apparatus, and more particularly to a scanning electron microscope apparatus provided with an optical microscope capable of easily selecting a visual field in observation.

  2. Description of the Related Art As a scanning electron microscope apparatus provided with a conventional optical microscope, for example, there is one disclosed in Patent Document 1. The scanning electron microscope device will be described with reference to FIG.

  An electron gun 1 that emits an electron beam, and a lens barrel 3a having a scanning mechanism 2 that scans the electron beam emitted from the electron gun 1 on the sample surface are erected on the upper surface of an airtight sample chamber 4 to be a scanning type. An electron microscope 3 is configured, a sample 5 is placed inside the sample chamber 4, a sample stage 6 movably provided, and secondary electrons generated by scanning the sample 5 with an electron beam are captured. The secondary electron detector 7 is accommodated.

  Further, a cylindrical adapter 8 is provided diagonally above the sample chamber 4, and an optical microscope 9 is provided on the cylindrical adapter 8 via a bellows 10 so as to be movable in the optical axis direction and airtight. The optical microscope 9 is moved in the optical axis direction by a moving mechanism (not shown), and the optical axis of the optical microscope 9 matches the center of the observation position of the scanning electron microscope.

  The case where the sample 5 is observed by the above scanning electron microscope will be described.

  The optical microscope 9 is moved by a moving mechanism (not shown) as shown by a two-dot chain line, the sample stage 6 is moved, the surface of the sample 5 is observed by the optical microscope 9, and the position to be observed is specified by the scanning electron microscope. I do. When the position to be observed can be specified, the optical microscope 9 is retracted so that the optical microscope 9 does not block the electron beam scanning of the scanning electron microscope or the secondary electrons generated from the sample 5 do not collide with the optical microscope 9. To Thereafter, an electron beam is generated from the electron gun 1, scanned by the scanning mechanism 2, and an image obtained based on the secondary electrons captured by the secondary electron detector 7 is displayed and observed on a CRT (not shown). Was.

  However, in the above-mentioned conventional scanning electron microscope, since the optical microscope has a short focus, it is necessary to bring the optical microscope close to the sample, and the optical microscope 9 is housed in the sample chamber 4. However, the effective space of the sample chamber 4 is narrowed down to the vicinity of the sample 5, and the space in which the sample 5 is installed, the distance for moving the sample 5, or the inclination of the sample 5 is limited, and secondary electrons and reflected electrons are generated. A detector for detection cannot be provided at the same time, and secondary electrons and reflected electrons cannot be captured at the same time, and an image based on each electron cannot be created and used for observation.

  Furthermore, in the above-mentioned conventional example, since the scanning center position of the scanning electron microscope 3 (the position where the electron beam is irradiated on the sample surface) cannot be specified, the observation site cannot be specified.

JP-A-4-3088639

  In view of such circumstances, the present invention eliminates the space occupied in the sample chamber of the optical microscope, and effectively uses the internal space of the sample chamber, and indicates the scanning center position of the scanning electron microscope with a laser beam. This facilitates the operation of specifying the observation site.

  The present invention provides a long focal length optical microscope having an optical axis capable of intersecting with the optical axis of the scanning electron microscope on a sample outside a sample chamber provided in the scanning electron microscope. The moving direction of the image coincides with the moving direction of the image by the scanning electron microscope, and a laser beam is aligned with the optical axis of the scanning electron microscope from the middle of the optical axis of the scanning electron microscope and irradiated toward the sample. The present invention relates to a scanning electron microscope apparatus provided with a laser beam irradiation means.

  According to the present invention, the optical microscope is provided outside the sample chamber, and the space occupied by the optical microscope in the sample chamber is removed, so the effective space in the sample chamber is greatly increased, and the sample table, the sample, etc. The restriction is relaxed, and the laser beam indicates the scanning center position of the scanning electron microscope, so that the operation of specifying the observation site is facilitated.

  Hereinafter, the best mode for carrying out the present invention will be described with reference to the drawings.

  FIG. 1 shows a first embodiment, in which the same components as those shown in FIG. 11 are denoted by the same reference numerals.

  A column 3a whose lower end protrudes into the sample chamber 4 is provided upright on the upper surface of the sample chamber 4, and the electron gun 1, the first condenser lens 11, the second condenser lens 12, and the scanning are provided inside the lens barrel 3a from above. A coil 13 and an objective lens 14 are sequentially provided. A sample stage 15 is provided below the lower end of the lens barrel 3a so as to be freely tiltable in any direction via a moving mechanism in the X, Y axis directions, rotation, inclination, and vertical direction. The sample 5 is placed on the sample table 16 provided, and the sample stage 15 is located immediately below the lower end of the lens barrel 3a.

  A movable mirror 35 is provided at a required position on the optical axis of the lens barrel 3a, for example, between the second condenser lens 12 and the scanning coil 13, and a laser beam emitting means 36 for emitting a laser beam toward the movable mirror 35 is provided. Provide. The movable mirror 35 has an elliptical mirror, and is provided with an insertion / extraction mechanism and a centering mechanism, or provided with a hole sufficient for passing an electron beam. Before the irradiation of the electron beam, the movable mirror 35 is inserted and the center is adjusted so as to be coaxial with the optical axis of the electron beam. The laser beam emitted from the laser beam emitting means 36 is adjusted by the movable mirror 35 so as to be coaxial with the optical axis of the electron gun 1 and is reflected toward the sample 5. The laser beam irradiating means of the movable mirror 35 and the laser beam emitting means 36 indicates the scanning center position of the scanning electron microscope by the laser beam. At the time of irradiation with the electron beam, the movable mirror 35 is pulled out, and the electron beam is irradiated at the scanning center position of the aligned sample 5. Alternatively, the movable mirror 35 is provided with a hole sufficient to allow an electron beam to pass therethrough, and the scanning center position of the scanning electron microscope is indicated by a laser beam without providing an insertion / extraction mechanism. The sample 5 is irradiated with a laser beam by the elliptical mirror of the movable mirror 35.

  A secondary electron detector 7 is provided in a side wall of the sample chamber 4 in a gas-tight manner, and a secondary electron detector 7 a of the secondary electron detector 7 is located on a side of the sample 5. A reflected electron detector 17 is provided in the other side wall of the sample chamber 4 in an airtight manner, and the reflected electron detector 17a of the reflected electron detector 17 interferes with the electron beam emitted from the lens barrel 3a. And extends above the sample 5 at a position that does not block the visual field of the optical microscope.

At the upper corner of the sample chamber 4, there is provided an optical microscope mounting window 18 airtightly stretched with lead glass for preventing leakage of X-rays generated during electron beam irradiation. A microscope 19 is provided upright. As the optical microscope 19, one having a long focal length, for example, one having a focal length of 100 mm or more is used, and the focal position coincides with the surface of the sample 5. Also, the visual field of the optical microscope 19 has a size that can cover the entire area of the sample holder 16, since the closer to observation with the naked eye, and a ^15mm φ ~30mm φ about a region as the maximum field of view. Further, the optical microscope 19 has a zoom mechanism.

  The field of view of the optical microscope 19 is illuminated by a coaxial illumination system. That is, a half mirror 20 is provided inside the optical microscope 19, and a coaxial illumination unit 21 is continuously provided to face the half mirror 20. Illumination light from a cold light illumination light source 22 having a light source such as an incandescent lamp is guided to the coaxial illumination unit 21 via a fiber cable 23 and reflected by the half mirror 20 in a direction coinciding with the optical axis of the optical microscope 19. The sample 5 is illuminated.

  An image pickup means such as a color CCD camera 24 and a television camera is provided on the eyepiece side of the optical microscope 19, and an image obtained by the optical microscope 19 is picked up by the color CCD camera 24 and further signalized. The image is formed on the color monitor 25 and input to the image processing device 26. The image processing device 26 has an image storage circuit (not shown), and can store an image obtained by the optical microscope 19. Therefore, the stored past image can be appropriately displayed on the color monitor 25.

  The secondary electron detector 7 and the backscattered electron detector 17 are connected to a signal amplifier 28 via a switching circuit 27. The signals from the secondary electron detector 7 and the backscattered electron detector 17 are transmitted to the signal amplifier 28, The image data is input to the color monitor 25 and the image display means such as the CRT 29 via the image processing device 26. The scanning circuit 30 of the CRT 29 also drives the scanning coil 13 and scans the CRT 29 in synchronization with the scanning of the scanning coil 13.

  Here, in the work of setting the position of the sample 5 by the optical microscope 19, the fact that the moving direction on the image of the scanning electron microscope 3 and the moving direction of the image obtained by the optical microscope 19 coincide with each other facilitates the work. Is important.

  In order to make the moving direction on the image of the scanning electron microscope coincide with the moving direction of the optical microscope, the following conditions (1) and (2) are satisfied.

Optical microscope conditions (1)
The relationship between the optical microscope image and the scanning electron microscope image will be described with reference to FIG.

  Let A be the intersection of the optical axis (scanning center) O1 of the scanning electron microscope and the optical axis O2 of the optical microscope, and let D1 be the working distance of the scanning electron microscope when the sample surface is aligned with point A. The focal length D2 of the optical microscope is set so that point A is focused. The scanning electron microscope image is an image when the sample is viewed from above, that is, from the electron gun side. On the other hand, the optical microscope image is obliquely upward θ when the angle between the sample surface and the optical axis O2 of the optical microscope in FIG. It becomes an observation image from an angle. To approach both images, it is necessary to make θ as large as possible structurally. However, the angle .theta. Is limited by the shape of the objective lens, the working distance D1, and the maximum visual field size of the optical microscope. In this embodiment, a value of 30.degree. Was adopted.

Optical microscope conditions (2)
The mounting position of the optical microscope may be anywhere if the conditions shown in FIG. 2 are applied. Rather, a predetermined mounting position is determined to satisfy the following restrictions.

  As described above, since the two observation directions are different from each other, it is impossible to completely match the images of the optical microscope image and the scanning electron microscope image, but it is desirable that at least the following requirements be satisfied. That is, 1) the top and bottom of the image, the left and right should be matched, 2) the optical microscope image can be obtained even under the tilt observation condition with the scanning electron microscope using the tilt function of the scanning electron microscope sample device, 3 ) The relationship between the moving direction of the sample and the moving direction of the image is the same between the optical microscope image and the scanning electron microscope image.

  This state will be described with reference to FIG. FIG. 3 is a view of the sample chamber as viewed from above, and FIG. 4 shows a cross section of the sample section.

  When the moving direction of the sample is X +, X-, Y +, Y- as shown in FIG. 3, the image of the scanning electron microscope is set as shown in FIG. For this reason, in the optical microscope, in order to obtain the same vertical and horizontal relationship as the scanning electron microscope image, in FIG. 3, the optical microscope is placed on the sample Y moving axis passing through the scanning electron microscope scanning center (A). It turns out that it is necessary to set. Thus, on the Y movement axis, an optical microscope can be mounted on either the Y + side or the Y- side.

  First, when the optical microscope is mounted on the Y- side, the optical microscope image is as shown in FIG. 6, and the moving direction of the image with respect to the movement of the sample also matches the scanning electron microscope. However, in the sample tilting function of the scanning electron microscope, the Y + side is lowered and the Y− side is raised when the tilt is +. For this reason, when the optical microscope is mounted on the Y- side, an optical microscope image of the sample surface cannot be obtained if the tilt angle exceeds the angle θ in FIG. 2 due to the sample tilt. Therefore, mounting on the Y- side in FIG. 3 is not preferable.

  Next, when an optical microscope is mounted on the Y + side position, the optical microscope image is obtained by inverting the top, bottom, left and right of the scanning electron microscope image as shown in FIG. The problem caused by the sample inclination as in the case of mounting on the Y− side is eliminated, but rather the value of the angle θ in FIG. 2 can be varied by the sample inclination, and the constraint 2) can be satisfied.

  Next, to satisfy the constraints 1) and 3), the following two methods are used.

(A) Matching by Rotating CCD Camera The CCD camera can be mounted by rotating it by 180 ° so that the left and right sides of the optical microscope image can be matched with the scanning electron microscope image.
(B) Rotating the Scanning Axis of the Scanning Electron Microscope The scanning axis rotating function (scan rotation) of the scanning electron microscope rotates the 180 ° scanning axis to match the optical microscope image.

  Either of the above two methods can satisfy the constraints 1) and 3).

  In the present embodiment, the optical microscope is mounted at the position shown in FIG. 2, and the top and bottom sides of the image of the optical microscope are matched with the moving direction of the sample by the methods (A) and (B).

  Hereinafter, the operation will be described.

  First, the observation position of the sample 5 is specified by setting the optical microscope 19 to a low magnification. Next, the optical microscope 19 is zoomed up to set the position of the sample 5 at the center of the screen, which is the observation position of the observation site by the scanning electron microscope, accurately. In setting the observation position of the sample 5 by the optical microscope 19, since the laser beam from above the scanning coil 13 irradiates the scanning center position of the scanning electron microscope 3, the setting of the site by the optical microscope 19 is extremely simple and accurate. It becomes.

  During illumination light irradiation for image observation with an optical microscope, image observation with a scanning electron microscope (SEM) cannot be performed. This is because the photomultiplier tube (PMT) built in the detector for the scanning electron microscope image detects the illumination light for the optical microscope, and the image cannot be displayed. Therefore, simultaneous display and observation of the optical microscope image and the scanning electron microscope image can be achieved by using one of the images as a stored image via the image processing device 26.

  Next, observation with a scanning electron microscope will be described.

  The electron beam emitted from the electron gun 1 is reduced by the first condenser lens 11 and the second condenser lens 12 to form a sharp electron probe, and the electron probe is converged on the surface of the sample 5 by the objective lens 14. At the same time, irradiation is performed on the sample surface by the scanning coil 13. At this time, secondary electrons or reflected electrons emitted from the sample surface are captured by the secondary electron detector 7 or the reflected electron detector 17, converted into an electric signal, and further amplified.

  Signals from the secondary electron detector 7 and the backscattered electron detector 17 are selected by the switching circuit 27 and input to a signal amplifier 28. The secondary electron detector 7 is mainly connected to the signal amplifier 28 when information on the unevenness of the sample 5 is obtained, and the reflected electron detection is performed when information on the composition, crystallinity, etc. is obtained in addition to the unevenness information of the sample. The device 17 is connected to the signal amplifier 28.

  A signal from the signal amplifier 28 is input to the CRT 29. The CRT 29 is driven by the scanning circuit 30 in synchronization with the scanning coil 13 to form an image.

  The switching circuit 27 selects the secondary electron detector 7 or the backscattered electron detector 17 according to the observation conditions, and scans the part specified by the optical microscope 19 with a scanning electron microscope. Then, the scanning result can be observed by the CRT 29.

  The second embodiment will be described with reference to FIG.

  The optical microscope mounting window 18 is provided vertically, a triangular slide block 31 is provided so as to be vertically slidable with respect to the optical microscope mounting window 18, and the optical microscope 19 is provided on the triangular slide block 31. 19 is movable in the vertical direction together with the triangular slide block 31. A sufficiently large slide surface is formed so that the vacuum is not broken when the optical microscope 19 is moved.

  By moving the optical microscope 19 in the vertical direction and in a direction intersecting the optical axis of the optical microscope 19, the intersection of the optical axis of the optical microscope 19 and the optical axis of the scanning electron microscope is changed from A to A '. Go to Accordingly, even if the thickness of the sample changes and the working distance D1 of the scanning electron microscope changes, it can be easily coped with. The moving direction of the optical microscope may be oblique to the optical axis as shown in FIG. 8, or may be a direction perpendicular to the optical axis.

  A third embodiment will be described with reference to FIG.

  As another mechanism for moving the intersection A, an optical microscope mounting window 18 having a convex seat is provided at a corner of the sample chamber 4, and the optical microscope mounting window 18 is slidably engaged with the convex surface of the optical microscope mounting window 18. A concave slide seat 32 to be provided, an optical microscope 19 is provided on the concave slide seat 32, and the optical microscope 19 is tilted to move in a direction intersecting the optical axis of the optical microscope 19, and the intersection A is moved in the vertical direction. You may make it move.

  Further, as another mechanism for moving the intersection point A, as shown in FIG. 10, the optical microscope mounting window 18 may be formed in a concave surface, and a convex slide seat 33 which slidably engages the optical microscope mounting window 18 may be provided. .

It is a schematic structure figure showing one embodiment of the present invention. FIG. 2 is an explanatory diagram showing a positional relationship between a scanning electron microscope and an optical microscope in the embodiment. FIG. 3 is an explanatory diagram of a moving direction of a sample and a moving direction of an image of an optical microscope. It is a figure showing the relation between a sample and a sample stand. It is explanatory drawing regarding a scanning electron microscope image. It is explanatory drawing regarding an optical microscope image. It is explanatory drawing regarding an optical microscope image. It is an explanatory view showing another embodiment of the present invention. It is an explanatory view showing another embodiment of the present invention. It is an explanatory view showing another embodiment of the present invention. It is explanatory drawing which shows a prior art example.

Explanation of reference numerals

REFERENCE SIGNS LIST 1 electron gun 3 scanning electron microscope 4 sample chamber 5 sample 7 secondary electron detector 16 sample table 17 backscattered electron detector 19 optical microscope 21 coaxial illumination unit 22 cold light illumination light source 23 fiber cable 24 color CCD camera 25 color monitor 26 image Processing unit 27 Switching circuit 29 CRT
31 Triangular slide block 32 Concave slide seat 35 Movable mirror 36 Laser beam emitting means

Claims (1)

  A long focal length optical microscope having an optical axis that can cross the optical axis of the scanning electron microscope on the sample is provided outside a sample chamber provided in the scanning electron microscope, and a moving direction of an image by the long focal length optical microscope is provided. And the direction of movement of the image by the scanning electron microscope coincides, and the laser beam is irradiated from the middle of the optical axis of the scanning electron microscope to the optical axis of the scanning electron microscope and irradiated toward the sample. A scanning electron microscope apparatus comprising means.

Images