DE2105455A1 - SLR electron microscope - Google Patents

Description

Patent attorney Dipl.-Phys. Gerhard Liedl 8 Munich 22 Steinsdorfstr. 21-22 Tel. 29 84

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NIHON DENSHI KABUSHIKI KAISHA 1418 Nakagami-cho, Akishima-shi, Tokyo, Japan

SLR electron microscope

The invention relates to a mirror reflex electron microscope.

In U.S. Patent 2,901,627 there is a mirror reflex electron microscope described, in which a parallel electron beam on the object to be observed

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to which a negative potential is applied, directed, reflected and then projected onto a fluorescent screen. However, if the diverging beam serves as a parallel beam in this arrangement, the brightness of the beam is the The electron image projected on the screen is very small. In addition, in the known electron microscopes this is on the Screen projected image a silhouette, what an effective one Analysis made considerably more difficult.

The object of the invention is therefore to provide a mirror reflex electron microscope to create a greater image brightness than the known ones without reducing the field of view Electron microscopes allowed. This is achieved by the features specified in claim 1. Advantageous configurations of the invention are specified in the subclaims.

In the electron microscope of the present invention, the scanning method is used used in such a way that the incident Electron beam focused before reaching the object to be observed and then the object to be observed is scanned with the electron beam. An additional benefit of this method is that it can it is possible to generate a dark field image with the help of the reflected electrons.

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The electron microscope according to the invention allows the object to be examined in a wide field of view to observe. In an advantageous embodiment of the Invention, the potential distribution on the surface of the object to be examined can be quantitatively observed will*

Preferred embodiments M of the invention are explained in more detail with the aid of the drawings.

Figure 1 is a schematic view of a mirror reflex electron microscope according to the invention, in which the object to be examined by an impacting one Electron beam is scanned,

Figures modified embodiments of the shown in Figure 1

2, 3, 4

showed electron microscope,

FIG. 5 another embodiment of the invention,

FIG. 6 shows a cross-section and an end view of a semiconductor diaphragm as used in the embodiment of FIG.

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« Ia 'MagFwm _f das the distribution of the output voltages caused by. the semiconductor aperture of the J? ig «6 is measured, represents,

Figure B is a circuit diagram for analyzing the surface image of the object to be examined,

a modified embodiment of the electron microscope according to I ¹ Ig. 5, with which an obliquely exposed silhouette of the object to be examined can be generated on a display device,

Figure 10 shows a cross-section and an end view of the object to be examined,

figuren in a schematic way the pictures, which with the u. 12

Electron microscope as shown in Fig. 9 can be produced.

In the embodiment of the invention shown in FIG. 1 an electron beam arrives from an electron gun is generated, through an opening 2a in a fluorescent screen 2; it is controlled by a projection lens 3

13 ** 3 *

. focused, so that a reduced image S of the opening is produced. The electron beam then passes through the center of a diaphragm 5 »which is arranged in the rear focal plane of an objective lens 4, and is then focused by the objective lens 4, so that a reduced image S ¹ of S is produced. Two pairs of deflection coils 7a and 7b, to which vertical and horizontal scanning signals are fed from a signal generator 8 via an amplifier 9, are arranged between the projection lens 3 and the diaphragm 5. The electron beam may thus by controlling the intensity "of the scanning signals deflected in an arbitrary manner and be guided thereby in any desired direction and with any angle of deflection by the shutter 5; herein, the said beam-forming electrons which extend more or less parallel to each other, at a Focused on point r in the vicinity of the object to be examined 6. By now varying the intensity of the above-mentioned scanning signals, the focal point r _{Q can be} shifted, ie the object to be observed is scanned.

Furthermore, a large negative voltage is applied to the object to be examined with the aid of an energy source 20, so that in the vicinity of the object an electric retardation field arises which the electrons of the electron beam in the opposite direction, reflected and

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accelerated before they reach the surface of the object · You calibrate through the diaphragm 5 moving electrons are taken out of the electron path by the deflection coils 7a and 7b and focused in the same plane as S f, to create an electron spot S ". The electron spot S" is then enlarged and with the aid of the projection lens 3 is projected onto the fluorescent screen 2.

The shape of the electric field generated in front of the object is determined according to the potential distribution and the non-uniformity of the surface of the object to be examined. As a result, the reflected electrons are "scattered" _f accelerated by the electric field and captured by the diaphragm 5, thereby reducing the number of reflected electrons that pass through the diaphragm corresponding to the form of the electric field that is located in front of the object to be observed. The magnification coefficient M of this image results from:

M = j (I ₁ + I ₂ + I ₃ ) Mp

where f is the focal length of the objective lens, I _{1 is} the distance between the diaphragm 5 and the second deflection coils 7b,

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2 distance between the first deflection coils 7m »ad second deflection coils 7b, 1 ~ the distance between the first deflection coil 7a and the projection lens 3 and Mp of the YergröSeruagskoefflzient of the projection lens 3 is ·

At the same time Sekundgu are: _electron-f caused by the gene of the reflected electrons to the diaphragm 5, multiplied by a secondary electron multiplier 10 m and perceived. The resulting signal is then amplified by an amplifier 11 and fed to the grid of a display device 12. In addition, the scanning signal sound generated by the signal generator 8 is sent through an amplifier H to a pair of deflection coils 1? output which form part of the display device 12. As a pole merger, a dark field image is generated in the display device 12, the brightness areas of which are opposite to those of the image appearing on the fluorescent screen 2. ™

Since in the embodiment described above on electron image projected on the fluorescent screen 2 is focused, "the picture is so bright that it can be easily can be evaluated. Furthermore, since the electron beam is deflected like a caterpillar, eich lets the "u investigate" Object within a large field of view

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observe «The dark field image, which corresponds to the variable number of those impinging on the aperture 5 Electrons are generated, arises in the display device at the same time that the bright field image is formed on the fluorescent screen.

In the embodiment according to FIG. 2, the scanning is carried out with only a pair of deflection coils, an intermediate lens 15 for deflecting the electron beam being arranged between the deflection coils 7 and the diaphragm 5. With this arrangement, the magnification coefficient M of the image emerging on the fluorescent screen 2 is given by:

2 I ₁ -I,

M = Mp

fl ₂

In the embodiment of Figure 3, the reflected electrons by means of a Hagnetfeldes 16 are deflected out of the path of the incident electron beam and moved out to be ¹¹ · The electrons scattered by the electric field in front of the object to be observed, "meet at the aperture 5, and are fed directly to the amplifier 11

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In the embodiment of FIG. 4, the fluorescent screen is replaced by a diaphragm 21 serving as a detector, similar to the diaphragm 5, which is arranged somewhere between the deflection coils and the electron gun. Furthermore, a switch 22 is provided so that the bright field blower . which originates from the electrons focused on the diaphragm 2t and guided through the Yei> stronger 25, as well as the dark field image, which originates from the electrons focused on the diaphragm 5 and discharged by the amplifier 11, is shown in the display device 12 at will can be.

In the embodiment of FIG. 5, a diaphragm 25 is provided with a number of detector elements which provide quantitative information with regard to the potential distribution and / or topographical unevenness of the surface to be observed. The incident electron beam EB, which is focused by the objective lens 4, is reflected at an angle γ , corresponding to the shape of the electric field formed in front of the object, which is determined by the potential distribution and / or topographical irregularity of the surface to be observed. The reflected electrons then migrate through the objective lens 4 and hit the diaphragm 25, which from a

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plate-shaped R-semiconductor and one immigrant. Sends from P-semiconductors 27a, 27b, 27c, ... 27a (Fig. 6 A and B) "consists, whereby, several detector elements with formed by a PN junction

The thickness of the semiconductor layer is such that the buoyant electrons reach the base of the layer. Furthermore, since the P semiconductors that form the semiconductor layer are separated from each other, signals can be obtained from terminals 28a, 28b, 2Sc, ·· -Transition detector element to meet, be discharged. If, for example, the reflected electrons EB ¹ hit the diaphragm 25, output voltages V ₁ , V ₂ , V *, ··· Y _n (Pig «7) are measured by the PH transition detector elements · Da the sum Y of the output voltages , which are measured by the detector elements, the reflection ^{angle V * s} VYX ^ + yy2 of ^the impinging electron beam, the size of the reflection angle γ can be determined without difficulty by measuring the total voltage.

The azimuth θ of the maximum value V _{113x of the output voltages measured by the detector elements is known from the approximation curve of} the output voltage distribution according to FIG. 7 and can be represented as follows:

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Tangent θ »

where jfy «jfcos θ and ^ x β / sin θ holds.

Ba furthermore / corresponds to / value Y, / x and jy express as follows:

yx is V cos θ yy = s V sin θ

As shown in FIG. 8, the output signals of the detector elements 27a, 27b,... 27n are fed to a comparison stage 29 and an integrating stage 30. The comparison stage 29 compares the intensity values of the output signals and selects the output signal with the maximum intensity value in order to determine the azimuth 9. The integration stage 50, on the other hand, integrates the output voltages measured by the detector elements, the integral corresponding to the total sum V. Comparison stage 29 and integrating stage 30 are fed to a computer 31 in which Vcosö, Vsinö, γχ and yy are calculated. The values yx and yy calculated in this way are then stored in a memory 32, and the information signals γχ and yy relating to of each point of the object to be examined are entered into a computer 33 in which

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the image of the surface to be examined is quantitatively analyzed in accordance with the surface scan.

In the embodiment of FIG. 9, the Detector elements 27a-h converted electrical signals measured into two groups of signals, with the help of a switch 40, which with the respective detector moment terminals 41a-h connected in series, two electrically conductive ones Plates 42, 43 and a rotatable insulating plate 44 has. The ends of the insulating plate 44 are at the electrically conductive Plates attached. V / if the electron beam impinging on a point A 'of the object to be examined (FIGS. 10 A and B) are directed by the plates 42 and 43 generates signals Ia and Ib, respectively. The signal Ia, which reflects the number of the detector elements 27b, c, d, e that hit Electrons is greater than the signal Ib, which corresponds to the number of the detector elements 27a, h, g, f striking corresponds to reflected electrons. These signals are fed to a differentiating or subtracting stage 45, which subtracts the signal Ib from the signal Ia; the difference is then reported as a positive signal to the display device 12 supplied.

When the incident beam hits a point B of the investigated Object is directed, is the size of the

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Signal Ia is equal to the size of the signal Ib, with the result that the output signal of the differentiating stage 45 2iull is.

If the incident electron beam is directed at a point C of the object to be examined, the The size of the signal Ia is smaller than the size of the signal Ib, with the difference in this Pail as a negative signal in the display device 12 is input.

As a result of the above, it is found that a shadow image corresponds to a certain exposure condition (see Fig. 11), because of the irregularity of the to surface to be examined depends, arises in the display device when the object to be examined is scanned will.

When the insulating plate 44 is rotated 90 °, the v / ground signals measured by the detector elements 27d, e, f, g and 27h, a, b are grouped, differentiated and displayed, whereby a shadow image as shown in Fig. 12 is created.

In the embodiments described above, a semiconductor with a PN junction was used as a detector for the reflected electrons. However, these means could be replaced by a spark counter or some other detector .

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Claims (10)

Claims f 1. j single-lens reflex electron microscope with an Ulel-ctronon cannon, characterized by an electrical delay field for delaying the electron beam generated by the electron cannon (1), which is arranged in front of the object to be observed and preferably by a strong negative potential applied to the object to be observed is generated, a lens (4) which focuses the electron beam in the vicinity of the object to be observed, a deflection device (7) for deflecting the electron beam and for scanning the object to be observed with (2.12) Using the electron beam, and a display device / with the aid of at least some of the electrons of the electron beam reflected by the electric deceleration field generates an image of the surface to be examined. 2. Electron microscope according to claim 1, characterized in that the display device has a fluorescent screen (2) which is arranged in the path of the electron beam. B 4996 109834/1167 91 η - 15 - 3 · Electron microscope according to claim. 1 or 2, thereby characterized in that the display device includes a detector (10) for detecting the reflected electrons and an am Has detector connected image device (12,13). 4. Electron microscope according to one of the preceding claims, characterized by a magnetic field (16) with whose help the reflected electrons are removed from the path of the electron beam. 5. Electron microscope according to claim 1, characterized in that a diaphragm (5) is provided with an opening through which the incident electron beam passes, and that the display device shows the image of the surface to be examined with the aid of both the image through the diaphragm generated reflected electrons passing through as well as being captured by the diaphragm. 6. Electron microscope according to claim 5, characterized in that the display device has a detector (10) for detecting the reflected electrons captured by the diaphragm (5), an image device (12, 13) connected to the detector and a fluorescent screen (2), the one between the electron gun (1) and the 109834/1 167 ..fei. Aperture (5) is arranged in the path of the impinging electron beam in order with the aid of the passing through the aperture reflected electrons to generate the image of the surface to be examined. 7. Electron microscope according to claim 5, characterized in that the display device zv / egg detectors (10,21) -, one of which is the reflected electrons passing through the end and the other that of the diaphragm captured reflected electrons detected, a switch connected to the detectors (22) and an image device (12) connected to the switch to v / eist. 8. Mirror reflex electron microscope with an electron gun, characterized by an electrical retardation field to delay the electron beam generated by the electron gun (1) that is in front of the object to be observed is arranged and preferably by a strong negative potential applied to the object to be observed is generated, a lens (4) that focuses the electron beam in the vicinity of the object to be observed, a deflection device (7) for deflecting the electron beam and for scanning the object to be observed with the aid of the electron beam, and detector elements (27) for detecting 109834/1167 the electrons reflected by the electric field, which are arranged in the area of the rear focal plane of the lens. 9. Electron microscope according to claim 8, characterized by an integrating stage (30) for integrating the output voltages of the detector elements and a comparison stage (29) for comparing the magnitudes of the output voltages the detector elements (Pig. 8). 10. Electron microscope according to claim 8, characterized by one connected in series with the detector elements (27) Switch (40) which converts the output signals of the detector elements into two signals, one stage (45) for generating the difference from these two signals, and a display device (12) which, with the aid of the difference signal an image of the surface to be examined is generated (Fig. 9). 109834/1167 Blank page