US3714422A

US3714422A - Scanning stereoscopic electron microscope

Info

Publication number: US3714422A
Application number: US00025656A
Authority: US
Inventors: S Hosoki; H Okano; K Kamijo
Original assignee: Hitachi Ltd
Current assignee: Hitachi Ltd
Priority date: 1970-04-06
Filing date: 1970-04-06
Publication date: 1973-01-30
Anticipated expiration: 1990-01-30

Abstract

A charged particle beam apparatus provided with an adjusting device to change an impinging angle of charged particle beams to be irradiated onto a specimen, thereby enabling a stereo-image thereof without tilting the same.

Description

United States Patent 11 1 Hosoki et al.

[54] SCANNING STEREOSCOPIC ELECTRON MICROSCOPE [75] Inventors: Shigeyuki Hosoki; Hiroshi Okano;

Kazuaki Kamijo, all of Tokyo,

Japan [73] Assignee: Hitachi Limited, Tokyo-to,.lapan [22] Filed: April 6, 1970 [21] Appl. No.: 25,656

[52] U.S. CI. ..250/49.5 A, 250/495 PE, 250/6l [51] Int. Cl. ..I-I0lj 37/26, GOln 23/04 [58] Field of Search ..250/49.5 A, 49.5 PE

[56] References Cited UNITED STATES PATENTS 3,585,382 6/l97l Sugzmuma ..25(l/49.5 A

1 51 Jan. 30, 1973 1 2,436,676 2/19411 Smith .250/495/1 2,617,041 11/1952 Fleming... ..250/49.5A 2,627,589 211953 121115 ..250/49.5A

Primary Examiner-James W. Lawrence Assistant Examiner-C. E. Church Attorney-Robert E. Burns and Emmanuel J. Lobato [57] ABSTRACT A charged particle beam apparatus provided with an adjusting device to change an impinging angle of charged particle beams to be irradiated onto a specimen, thereby enabling a stereo-image thereof without tilting the same.

8 Claims, 9 Drawing Figures PATENTEDJAN 30 I973 SHEET 10F 3 FIG-J PATENTEU JAN 30 I975 SHEET 2 OF 3 FIG.6

PATENTEuJ/mao I973 SHEET 3 [IF 3 FIG.?

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a charged particle beam apparatus, and, more particularly, it is concerned with a novel means which enables observation of a stereoimage of a specimen in a scanning-type electron microscope, for instance, without tilting the same.

2. Discussion of Prior Art In the case of observing a stereo-image of a specimen in a scanning-type electron microscope, it has heretofore been a practice that an image of the specimen is first photographed at a certain position, and then another photograph thereof is taken from another position by tilting the specimen for a certain angle. A pair of photographs thus taken are disposed at left and right positions to be observed simultaneously through a stereoscope. (vide: Theory and Application of Electron Microscope, pages 292 to 301, published from Maruzen Kabushiki Kaisha, Japan, Oct. 25, 1959) Such conventional method of observing a stereoimage, however, has various disadvantages arising from the necessity of tilting the specimen, as follows. First, it is difficult to cause the rotating center of the specimen at the time of its tilting and the center of the viewing field of the specimen to be observed (i.e., a focal point of electron beams on the specimen disposed in a horizontal position) to perfectly coincide. This, more or less, results in discrepancy between the center of the specimen tilting and the center of the viewing field, which inevitably necessitates adjustment of the focus at every time the specimen is to be tilted to various positions, because the center of the viewing field becomes different depending on the respective tilt positions. Secondly, on account of the center of the viewing field becoming different at every tilt position of the specimen, it is not possible to select the same viewing field when the specimen is tilted. Furthermore, as an image of the specimen needs be photographed at every SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a charged particle beam apparatus which enables a stereo-image of a specimen to be observed without tilting the specimen.

It is another object of the present invention to provide a charged particle beam apparatus which enables a stereo-image of a specimen in changing state to be observed in an easy manner.

It is another object of the present invention to provide a charged particle beam apparatus, in which a stereo-image ofa specimen can be observed by an electricalexpedient only.

According to the present invention, there is provided a charged particle beam apparatus comprising means to generate charged particle beams, means to focus the beams and irradiate the same onto a specimen, means to convert an electron pattern of the specimen to be obtained by irradiation of the charged particle beams into an observable image, and means to adjust an impinging angle of the charged particle beams with respect to the specimen to be irradiated thereby.

The foregoing objects of the present invention will become more apparent by the following detailed description of the invention taken in conjunction with the accompanying drawing.

BRIEF EXPLANATION OF THE DRAWING In the drawing:

FIG. 1 is a schematic diagram of a scanning-type electron microscope;

FIGS. 2 and 3 are respectively schematic diagrams showing a conventional method of observing a stereoimage of specimen;

FIGS. 4 through 8 are schematic diagrams respectively showing embodiments of the present invention; and

FIG. 9 is a graphical representation to explain operations of the embodiment shown in FIG. 8.

DETAILED DESCRIPTION OF THE INVENTION The charged particle beam apparatus according to the present invention is applicable in various ways. In the present invention, however, a scanning-type electron microscope is taken as an example of application of such apparatus, the construction and operations of which are outlined as follows.

Referring to FIG. 1, the scanning-type electron microscope, in which the apparatus according to the present invention is to be incorporated is constructed by an electron gun I, focusing lenses 2, 3 (the lens may be of a single unit in some case), an aperture plate 4, a scanning device 5, a detector 7, a scanning oscillator 8, and an oscilloscope 9.

Electron beams e generated in and emanated from the electron gun I are focused by the focusing

lenses

2, 3, and irradiated onto a specimen 6 disposed in an observation plane at a position opposite the electron gun 1. The focused electron beam then scans over the specimen 6 by means of the scanning device 5, whereupon secondary electrons are emanated from the specimen 6 to form an electron pattern. The secondary electrons are then detected by a detector 7 such as a scintillator, and a photomultiplier, which provides a corresponding detecting signal which is fed to the oscilloscope 9 to modulate the intensity of the electron beam for the oscilloscope 9. The oscilloscope 9 and the scanning device 5 are fed with scanning signals from the .scanning oscillator 8. Accordingly, the electron pattern of the specimen 6 is converted to an observable image, and the image becomes observable on the oscilloscope 9. r

The conventional method of stereo-image observation has been carried out in such a manner as shown in FIG. 2, wherein the specimen 6 placed at a horizontal position III-I is tilted to a position of either AA or BB,

' to change an impinging angle of electron beams with whereby stereo-image of the specimen can be observed without tilting the specimen.

The present invention as explained above has been accomplished on the basis of the following considerations. As shown in FIG. 4, electron beams which have passed a point of an image plane are necessarily focused on one point F of a specimen surface 6 by a focusing lens 3. in this case, in order to utilize the electron beam in its sufficiently focused state, an aperture plate 4 provided with an appropriate size of electron beam passage hole (or aperture) is disposed in the vicinity of the optical axis. Accordingly, when the aperture plate is moved in a transverse direction within a range of irradiation of the electron beam e with respect to the aperture, the impinging angle of the electron beam with respect to the specimen can be changed or varied without tilting the specimen, as shown by the solid lines in the Figure. Therefore, if the aperture plate 4 is made movable, the impinging angle of the electron beam e with respect to the specimen becomes changeable by shifting the aperture plate to an opposite side of the optical axis, whereby alternate irradiation of electron beam onto the specimen becomes possible, hence the stereo-image of the specimen is made observable.

Thus, according to the present invention, it is possible to observe a stereo-image of a specimen, but frequent shifting of the aperture plate 4 is not so preferable. From the practical standpoint, therefore, use of an adjusting device is considered more convenient.

Referring to FIG. 5 which shows a schematic construction of the adjusting device according to the present invention, an aperture plate is provided with two apertures, which makes the aperture plate of the present invention different from the conventional type aperture plate. In order to alternately open and close the two apertures of the aperture plate 1 0, a shutter 11 having a single aperture is provided at the aperture plate 10. By shifting the shutter 11 in the transverse direction, focused electron beam of different impinging angles may be irradiated alternately on the specimen and the same region covering SS can be scanned. In this case, in order to enable not only a stereo-image of the specimen but also an ordinary two-dimensional image to be observed, the aperture plate 10 may be provided with three apertures, one of which is made the center of the optical axis and the remaining two of which are disposed at both sides of this central aperture. According to this construction, the aperture plate 10 needs not be shifted. While the apertures of the plate 10 require high precision, the aperture of the shutter ll needs not be so high in its precision as that of the plate 10, hence a stereo-image of the specimen can be well observed.

in the above construction of the adjusting device, it is necessary to provide the apertures within the range of the electron beam irradiation, so that the degree of the impinging angle of the electron beam with respect to the specimen is limited to some extent. The embodiment shown in FIG. 6 is so constructed that this restriction can be eliminated. In FIG. 6, numeral 12 designates an electrode for dividing the electron beam into two beam portions and numerals l3 and 14 designate deflecting devices. A predetermined negative voltage -E is applied to the dividing electrode 12 by means ofa very thin metal wire, etc. The electron beam focused on an image plane of the focusing lens 3 is divided by the dividing electrode 12 into two beam portions. The two electron beam portions pass respectively through the

deflecting devices

13 and 14 and then enter into two passage holes of the aperture plate. Accordingly, by deflecting one of the divided electron beams, one of the beams does not reach its corresponding passage-hole on the aperture plate. For example, when the electron beam portion passing through the deflecting device 13 is properly deflected through the left side passage-hole, the other electron beam portion is not allowed to pass through the right side passagehole of the aperature plate 10. In this case, if the deflecting device 14 is not operated, an electron beam portion is only radiated through the left side passagehole of the aperture plate 10. Thus, radiation of a specimen with an electron beam is made possible by utilizing the electron beam passed through either the right side or the left side passage-hole of the aperture plate 10. It is thereby possible to vary the impinging angle of the electron beam radiated onto the specimen, as shown in FIG. 6 by solid line or dotted line. Therefore, the impinging angle of the electron beam can be taken at a considerably large degree, and it becomes possible to observe a stereo-image of the specimen by an electrical operation alone and yet with a widened impinging angle of the electron beam.

Furthermore, according to this embodiment, highspeed scanning of the specimen due to the electron beam is possible, hence the desired stereo-image of the specimen can be directly observed through the oscilloscope 9 without taking photographs but by merely carrying out, for example, alternate scanning for every one scanning line on the same region SS, of the specimen with two electron beams of different impinging angles. Consequently, stereo-image observation of a specimen in changing state, which has heretofore been impossible, can be done successfully. That is, two detectors for the above-mentioned secondary electron emanated from the scanning region SS are provided, and the outputs of the respective detectors are switched for every scanning by the respective electron beams, after which these outputs are impressed on each of electron guns in color television receiving sets, for instance, for brightness modulation, whereby a stereoimage of the specimen in changing state can be directly observed. In this case, in order that an ordinary image may be made observable, the adjusting device is so constructed that the aperture plate 10 be provided with three apertures, the electrode 12 be made movable outside of the electron beam path, and the deflecting devices l3, 14 be made not to hinder passage of the electron beams.

FIG. 7 indicates another embodiment of the present invention, wherein a deflecting device 15 is provided at a position of an image plane of the focusing lens 3, and the electron beam focused on the image plane is deflected by the deflecting device 15.

Consequently, it is possible to feed the electron beam into the focusing lens 3 by such variation of the deflecting angle of the electron beam by means of the deflecting device 15 as shown in FIG. 7 by solid line or dotted line, to thereby vary the impinging angle of the electron beam radiated on the specimen. Consequently, when the region SS on the specimen 6 is alternately scanned by the electron beam deflected as shown by solid line and then is scanned by the electron beam deflected as shown by dotted line, a stereo-image can be obtained. In such a manner mentioned above, the above embodiment accomplishes substantially equal functions and effect to the embodiment shown in FIG. 6.

In the embodiment shown in FIG. 7, the deflecting device is provided at the position of the image plane. The device, however, can be disposed below the image plane as shown in FIG. 8. In this case, an aperture plate 16 is interposed between the image plane and the deflecting device 15. This deflecting device operates so as to deflect the electron beam passed through the passage hole of the aperture plate 16 in a similar manner as in the case of the deflecting device in the embodiment of FIG. 6. The scanning device 5 is applied with a superposed voltage composed of a deflecting voltage V, for scanning and a voltage V for cancelling the undesirable deflection component on the specimen .due to the deflecting device 15, as shown in FIG. 9.

In this embodiment, as the electron beams are not to be deflected at the image plane of the focusing lens, when there is no scanning, the electron beams comes out of the center of the viewing field and is focused. in order therefore to offset a certain definite deflection component corresponding to the deflecting voltage V a voltage V of opposite phase to V is superposed as mentioned in the foregoing. In FIG. 9, the deflecting voltage V, and the offsetting voltage V are in perfect synchronism. Actually, such synchronism is not always necessary.

Also, for the sake of convenience in explaining the construction shown in FIG. 8, the scanning device 5 is shown to be provided at the central position within the focusing lens 3. This may of course be provided at the bottom part of the scanning lens.

As explained in the foregoing, the present invention makes it possible to perform desired observation of a stereo-image of a specimen without tilting the specimen whatsoever as has been practiced heretofore, the effect of which is therefore outstanding.

Although the foregoing embodiments are all related to a scanning-type electron microscope as an example, the invention is of course not limited to such electron microscope, but canbe applied all types of apparatuses such as X-ray microanalyzers, electron microscopes of ordinary type, ion microanalyzers (having means for obtaining an image by detecting secondary electron obtained by scanning a specimen with ion beams), and so forth, wherein charged particle beams emanating from a charged particle beam source are focused by a focusing lens or any other analogous means, then the focused charged particle beams are irradiated on the same portion of a specimen, and the charged particle beams are scanned or directly enlarged to detect permeated electron beams, secondary electrons, reflected electrons, X-ray, light beams, etc., thereby to observe a magnified image of the specimen.

What we claim is:

1. In a scanning-type electron microscope comprising an electron source operable to emit an electron beam; focusing means for focusing the electron beam; scanning signal generating means for providing a dary electrons; detecting means for detecting secondary electrons emitted from the specimen and providing a corresponding detecting signal; and indicating means receptive of both said scanning signal and said detecting signal for providing a visual image of the specimen; the improvement comprising angle varying means disposed upstream from said scanning means for selective varying the angle at which the focused electron beam impinges upon the specimen to accordingly vary the secondary electron emission from the specimen in such a manner that said indicating meansprovides a visual stereoscopic image of the specimen.

2. A scanning-type electron microscope according to claim I; wherein said angle varying means comprises an aperture plate having means therein defining one passage-hole, and means mounting said aperture .plate for alternate movement in a direction substantially transverse to the electron beam to effect selection of only a desired portion of said electron beam.

3. A scanning-type electron microscope according to claim 1; wherein said angle varying means comprises an aperture plate having means therein defining at least two passage-holes, a shutter plate having means therein defining one passage-hole, and means mounting said shutter plate for alternate movement on said aperture plate to alternately open and close said two passageholes.

4. A scanning-type electron microscope according to claim 1; wherein said angle varying means comprises an aperture plate having means therein defining at least two passage-holes, an electrode connectable to a source of electrical potential for dividing the electron beam into two beam portions, and deflecting means for deflecting one of the divided electron beam portions to prevent same from passing through one of said two passage-holes.

5. A scanning-type electron microscope according to claim 1; wherein said angle varying means comprises deflecting means disposed at the image plane of said focusing means for alternately deflecting the electron beam in two directions towards said focusing means.

6. A scanning-type electron microscope according to claim 1; wherein said angle varying means comprises an aperture plate having means therein defining one passage hole disposed below an image plane of said focusing means, and deflecting means disposed downstream from said aperture plate having means therein defining one passage-hole for alternately deflecting the electron beam passing therethrough in two directions towards said focusing means.

7. A method for obtaining a stereoscopic image of a specimen comprising: providing a specimen to be observed and placing same in an observation plane; emitting an electron beam and directing same towards the specimen; focusing the electron beam on the specimen located in said observation plane; scanning the focused electron beam across the specimen in a predetermined scanning pattern causing the specimen to emit secondary electrons; selectively varying the angle at which the focused electron beam impinges upon the specimen while same is located in said obserhaving an electron beam movable in synchronization with the scanning of said focused electron beam across the specimen, and modulating the intensity of the oscilloscopic electron beam in accordance with saiddetecting signal whereby said oscilloscope provides a stereoscopic image of the specimen.

v I UNITED STATES PATEN' I OFFK F: QRTEFf CATE 0% QGRECTEON;

Patent No- 3,714,422 Dated Januery 30, 1-973 lnvefitofls) SHIGEYUKI-HOSOKI-7' VIQIIIROSHI OKANO. andhK AZ UAKI KAMIJo It is certified that error appears in' the above-Fidehtified patent and that said Letters 'Patent are herebycorrected as shown 'below:

In the Heading to the Patent insert the follcmi w I I Foreign-A-pplication Priority Data April 9, 1969 Japan 26838/69-' si ned and sealed this 12th ja of March 197A, v

( SEAL) Attest: t v H EDWARD M-.FLETCHIER, JB c. MARSHALL AN Attesting Officer Commissionerof Patents DRM Po-wso (1069) v I Q I uscd m-oc 6Q376-P69 GOVER NMENT PRINTING OFFICE i969 0-366-334,

Claims

1. In a scanning-type electron microscope comprising an electron source operable to emit an electron beam; focusing means for focusing the electron beam; scanning signal generating means for providing a scanning signal; scanning means receptive of said scanning signal for scanning the focused electron beam across a specimen to be observed in accordance with said scanning signal whereby the specimen emits secondary electrons; detecting means for detecting secondary electrons emitted from the specimen and providing a corresponding detecting signal; and indicating means receptive of both said scanning signal and said detecting signal for providing a visual image of the specimen; the improvement comprising angle varying means disposed upstream from said scanning means for selective varying the angle at which the focused electron beam impinges upon the specimen to accordingly vary the secondary electron emission from the specimen in such a manner that said indicating means provides a visual stereoscopic image of the specimen.

2. A scanning-type electron microscope according to claim 1; wherein said angle varying means comprises an aperture plate having means therein defining one passage-hole, and means mounting said aperture plate for alternate movement in a direction substantially transverse to the electron beam to effect selection of only a desired portion of said electron beam.

3. A scanning-type electron microscope according to claim 1; wherein said angle varying means comprises an aperture plate having means therein defining at least two passage-holes, a shutter plate having means therein defining one passage-hole, and means mounting said shutter plate for alternate movement on said aperture plate to alternately open and close said two passage-holes.

7. A method for obtaining a stereoscopic image of a specimen comprising: providing a specimen to be observed and placing same in an observation plane; emitting an electron beam and directing same towards the specimen; focusing the electron beam on the specimen located in said observation plane; scanning the focused electron beam across the specimen in a predetermined scanning pattern causing the specimen to emit secondary electrons; selectively varying the angle at which the focused electron beam impinges upon the specimen while same is located in said observation plane to accordingly vary the secondary electron emission from the specimen; detecting secondary electrons emitted from the specimen and providing a corresponding detecting signal; and providing a stereoscopic visual image of the specimen in response to said detecting signal.