JPH0620634A - Scanning electron microscope - Google Patents

Abstract

PURPOSE:To enable observation of atomic arrangement by providing an electrode for applying positive voltage on the reverse side of a detection means for sandwiching a sample when an electron beam is focused to scan the sample surface, and the secondary electron obtained at the time is put into the detection means, and the signal fro the detection means is displayed being synchronized with beam scanning to provide a scan image. CONSTITUTION:An electron beam 2 emitted from a field emission type electron gun 1 is focused by a condenser lens 3, deflected by a deflection coil 4, focused again by an objective lens 5, and is applied on the surface of a sample 7 put on a sample stage 6. A secondary element 8 is generated thereby from the surface of the sample 7, which is detected by a secondary electron detector 9, which is positioned in the side of the sample stage 6, and to which positive high voltage is applied, and the detection intensity is displayed on a CRT 1 while synchronizing with the scanning by the coil 4 of the beam 2, to provide a scan image. The same voltage as the drawing voltage of the detector 9 is supplied to an electrode 10 provided on the symmetric position of the detector 9 by which the sample 7 is sandwiched, to make the electric field around the sample 7 symmetric in terms of face.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention relates to a scanning electron microscope for observing the surface of a crystalline material.

[0002]

2. Description of the Related Art Conventionally, a reflection electron microscope or a scanning reflection electron microscope has been used as a method of observing the distribution of atomic arrangement on the surface of a single crystal substrate of semiconductor, metal or the like as an image in real space. In a backscattered electron microscope, an electron beam is incident on the surface of the sample and an image of the surface is formed by using the electrons diffracted by the atomic sequence on the sample surface (Yagi, Tanijo, Takayanagi: "Surface electron microscopy" applied physics). 55 (198
6) 1036). Further, in the scanning backscattered electron microscope, similarly, diffracted electrons generated when an electron beam is made to impinge on the sample surface are used, but the electron beam is made to scan the sample surface in the same manner as a scanning electron microscope, and The surface scanning image is obtained by displaying the intensity of the diffracted electrons on the cathode ray tube in synchronism with (Ichikawa, Doi, Hayakawa: "Observation of crystal surface by microprobe backscattered electron diffraction method" Applied Physics 54 (1985) 1187). . All of them are means of being sensitive to the atomic arrangement on the crystal surface, and a surface rearrangement structure in which a heteroatom layer adsorbed on the surface or a crystal constituent atom has an atomic arrangement different from the inside (bulk) of the crystal in the surface 1 to 3 atomic layers. (For example, a 7 × 7 structure or Si (10
It is possible to observe the spatial distribution of the 1 × 2 structure in the 0) plane as a clear image. However, in each case, the electron beam must be incident on the surface of the sample (a few degrees or less) in order to use the reflected and diffracted electrons from the surface, and the image obtained will be extremely small in the incident direction of the electron beam. It causes clogging (aspect ratio of several tens to one).

There is also an attempt to obtain a scanning image of the crystal surface by secondary electrons without using reflected diffraction electrons (Ichinokawa: “Low Energy Scanning Electron Microscope”, Journal of the Crystal Society of Japan 29 (19).
87) I30 and Ino: "Observation of surface adsorption layer by ultra-high vacuum scanning electron microscope", Preparatory Lecture 2nd Volume P. 460). In this case, a vertically incident electron beam can be used and the scanning image is not clogged. However, this method can identify a layer of atoms different from the substrate atoms existing on the surface, but cannot distinguish the difference in the atomic arrangement of the substrate atoms themselves as in the surface rearrangement layer. This, as described below,
This is because the conventional method detected the generated secondary electrons irrespective of the emission direction, and could not distinguish the difference in atomic arrangement.

FIG. 6 shows the structure of a conventional scanning electron microscope. Electron beam 2 generated from field emission type electron gun 21
2 is converged by the condenser lens 23, and the deflection coil 2
After being deflected by 4, the sample 27 is further converged by the objective lens 25 and mounted on the sample table 26 placed therein.
Is irradiated on the surface of. As a result, secondary electrons 28 are generated from the surface of the sample 27. The secondary electrons 28 are attracted to the electric field of the secondary electron detector 29 while moving in the cyclotron motion in the magnetic field of the objective lens and trace upward, and the secondary electron detector 2
9, a scanning image is obtained by displaying the detected intensity on the display means 30 such as a CRT in synchronization with the scanning of the electron beam 22 by the deflection coil 24. FIG. 7 is a view showing the structure of another type of conventional scanning electron microscope. The electron gun, condenser lens, and deflection coil are the same as in FIG. The electron beam 32 is converged by the objective lens 35 and irradiated on the surface of the sample 37 mounted on the sample table 36 placed outside the objective lens 35. As a result, secondary electrons 38 are generated from the surface of the sample 37. Secondary electrons 38 are secondary electron detectors 39
Of the electric field (typically 10 kV) and is detected by the secondary electron detector 39. And electron beam 3
A scanning image is obtained by displaying the detected intensity on the display means 40 such as a CRT in synchronization with the scanning by the second deflection coil 34.

The reason why the image reflecting the atomic arrangement cannot be obtained by the conventional apparatus is that the generated secondary electrons are detected regardless of the emission direction in the sample surface. That is, in the secondary electron detection method as shown in FIG. 6, the information on the emission direction of the secondary electrons is lost due to the cyclotron motion of the secondary electrons, and the secondary electrons emitted in any direction on the sample surface are evenly distributed. Had detected. Further, in the secondary electron detection method as shown in FIG. 7, between the secondary electrons emitted in the direction of the secondary electron detector 39 and the secondary electrons emitted in the opposite direction to the secondary electron detector 39. Although there was a difference in the pulling efficiency, the emission direction selectivity was very weak due to the effect of the strong pulling electric field. This is because the conventional device focuses on increasing the efficiency of drawing secondary electrons, and rather employs a detection method that does not provide selectivity in the emission direction.

As a detection method having a selective emission direction, there is a method using a Banbury-Nixon cage (L. Reimer: Scanning Elec).
tron Microscopy, Springer
-Verlag (Berlin, 1985) pp. Two
37-38). As shown in FIG. 8, in the scanning electron microscope of the type shown in FIG. 7, a cylindrical electrode 41 having a window with a grid and an upper electrode 42 are installed under the objective lens 35 and around the sample 37. Therefore, a positive voltage is applied to the cylindrical electrode 41, and a negative voltage is applied to the upper electrode 42. As a result, before the secondary electrons generated from the sample are drawn into the secondary electron detector 39, they can be extracted while maintaining the initial emission direction. However, when the sample is surrounded by such a cage, the electron beam backscattered from the sample generates secondary electrons on the cage surface, which causes background noise. This is a great obstacle when observing a delicate contrast due to a difference in atomic arrangement. In addition, in the scanning electron microscope, when performing backscattered electron image observation, characteristic X-ray analysis, or Auger electron analysis often used together with secondary electron image observation, the cage becomes an obstacle. In particular, in order to focus the electron beam finely to 10 nm or less for high-resolution observation, it is advantageous to make the distance between the objective lens 35 and the sample 37 as close as possible, so that the cage as shown in FIG. 8 becomes an obstacle.

[0007]

SUMMARY OF THE INVENTION The present invention has been proposed in order to improve the above-mentioned drawbacks of the conventional scanning electron microscope, and its object is a scanning electron microscope capable of observing the real spatial distribution of the surface atomic arrangement. To provide.

[0008]

In order to achieve the above object, the present invention provides a scanning electron microscope having an electrode capable of applying a positive voltage on the opposite side of the secondary electron detecting means with a sample interposed therebetween, and a sample. The gist of a scanning electron microscope is characterized in that a plurality of electrodes capable of applying a positive voltage are arranged on the same plane including the secondary electron detector around the.

[0009]

【Example】

(Embodiment 1) FIG. 1 shows a scanning electron microscope according to a first embodiment of the present invention. The electron beam 2 generated from the field emission type electron gun 1 is converged by the condenser lens 3, deflected by the deflection coil 4, further converged by the objective lens 5, and the surface of the sample 7 mounted on the sample stage 6. Is irradiated.
As a result, secondary electrons 8 are generated from the surface of the sample 7.
The secondary electrons 8 are placed beside the sample stage 6 and are drawn into the secondary electron detector 9 to which a positive high voltage (typically 10 kV) is applied for detection. Then, the display means 1 such as a CRT is synchronized with the scanning of the electron beam 2 by the deflection coil 4.
A scan image is obtained by displaying the detected intensities on 1. At this time, the same voltage as the pull-in voltage of the secondary electron detector 9 is applied to the electrode 10 placed at a position symmetrical to the secondary electron detector 9 with the sample 7 interposed therebetween. The shape of the electrode 10 is the same as that of the high voltage application part of the secondary electron detector 9. As a result, as schematically shown in FIG. 2, the electric field around the sample 7 becomes close to plane symmetry with the sample in between. Therefore, the secondary electrons 81 emitted at an angle close to the direction perpendicular to the straight line connecting the irradiation point of the electron beam 2 and the secondary electron detector 9 on the sample 7, and the secondary electrons 82 emitted in the opposite direction. Is the secondary electron detector 9
Does not reach

At this time, the reason why the scan image reflects the surface atomic arrangement distribution will be described below. The emission direction of secondary electrons is not completely isotropic and has a spatial distribution that reflects the anisotropy of atomic arrangement. This state is S with two-fold symmetry
The l × 2 structure of i (100) will be described as an example with reference to FIG. Looking at the atomic arrangement of the 1 × 2 structure from the side, A
The atomic arrangement differs between the direction shown as the direction and the B direction perpendicular to the direction. Therefore, the emission intensity of secondary electrons also has a slight difference between the A direction and the B direction. Therefore, when the emitted secondary electrons that are emitted only within the azimuth angle of less than ± 90 ° are detected, the secondary electron intensity has the same two-fold symmetry as the atomic arrangement. The intensity difference between the peak and the valley in the two-fold symmetry of the emission intensity of the secondary electrons is only the secondary electrons emitted at a low angle with respect to the surface, rather than detecting the secondary electrons in the direction perpendicular to the surface. Is larger when detected. In the case where two regions (domains) whose atomic directions in the atomic arrangement of FIG. 3 differ by 90 ° coexist (1 × 2 on the Si (100) plane)
Area and 2 × l area), using the device of the present invention
When the secondary electrons emitted in the B direction or in the B direction are selectively detected, each domain is divided into bright or dark, and an image reflecting the domain distribution can be obtained.

The electrode 10 has the same shape as the high voltage application portion of the secondary electron detector 9 as described above.
It is desirable that the secondary electron detector 9 is installed at a symmetrical position with the sample 7 in between and the same voltage as the pull-in voltage of the secondary electron detector 9 is applied, but the shape, position, and applied voltage are not limited to this. It is not done. For example, the position of the electrode 10 is brought closer to the sample 7 side than the position symmetrical with the secondary electron detector 9,
In addition, it is possible to make the electric field on the surface of the sample 7 plane-symmetric by reducing the applied voltage.

(Embodiment 2) FIG. 4 shows an electrode arrangement of a scanning electron microscope according to a second embodiment of the present invention. The other parts are the same as those in the first embodiment and therefore omitted. In this embodiment, a plurality of electrodes capable of applying a positive voltage are arranged on the same plane including the secondary electron detector 9 around the sample 7. FIG. 4 shows the same shape as the high voltage application part of the secondary electron detector 9.
An example is shown in which the electrodes 101 to 103 are arranged at the other three vertices of a square with the secondary electron detector 9 as one vertex with the sample 7 as the center. The applied voltage to each electrode is made equal to the pull-in voltage of the secondary electron detector 9. The secondary electrons 81 emitted on the sample 7 at an angle close to the direction perpendicular to the straight line connecting the irradiation point of the electron beam 2 and the secondary electron detector 9 are the electrodes 101.
The secondary electrons 82 that are drawn into the electrodes 103 and 103 and emitted in the opposite direction do not reach the secondary electron detector 9 because they are drawn into the electrode 102. For this reason, the angle limiting property of the secondary electrons that can be detected more than in Example 1 is enhanced, and the domain contrast can be improved. The number of electrodes, the shape, the distance from the sample, and the applied voltage are not limited to those in the example of FIG. 4, and the secondary electrons 81 are directed to the direction other than the secondary electron detector 9 on the surface of the sample 7. It suffices if it can generate an electric field for extraction. For example, it is possible to use without using the electrode 102. Further, the applied voltage can be lowered by bringing the electrodes 101 and 102 closer to the sample 7 than in the example of FIG.

Here, 1 × of the Si (100) surface is used.
The description has been made for a structure having a 2-fold symmetry such as 2, but when observing the domain contrast for a structure having a 3-fold symmetry, a 4-fold symmetry, or a higher-order symmetry. May have an electrode arrangement according to the symmetry of the observation target.

(Embodiment 3) FIG. 5 shows the arrangement of electrodes and detectors of a scanning electron microscope according to a third embodiment of the present invention. The other parts are the same as those in the first embodiment and therefore omitted. In this embodiment, some secondary electron detectors 91 and 92 arranged on the same plane including the secondary electron detector 9 around the sample 7 and capable of applying a positive voltage are replaced with other secondary electron detectors 91 and 92. ing. FIG. 5 shows three electrodes 104 to 106 having the same shape as the high voltage application part of the secondary electron detector 9 and a secondary electrode newly added for the purpose of observing an atomic arrangement structure having three-fold symmetry. An example is shown in which the electron detectors 91 and 92 are arranged at the apex of a regular hexagon with the sample 7 as the center and the secondary electron detector 9 as one apex. Each electrode and additional secondary electron detector 9
The applied voltage to Nos. 1 and 92 is set equal to the pull-in voltage of the secondary electron detector 9. Secondary electrons 82 to 86 emitted at an angle larger than an angle close to 60 ° with the straight line connecting the irradiation point of the electron beam 2 and the secondary electron detector 9 on the sample 7 are
04-106, and added secondary electron detectors 91, 9
The secondary electron detector 9 detects only secondary electrons emitted within an angle of less than ± 60 ° because the secondary electrons are pulled to 2.
On the other hand, for the same reason, the secondary electron detector 91 has a 6-axis centered on a direction forming an angle of 120 ° with the secondary electron detector 9.
Secondary electrons 84 emitted at an angle larger than 0 ° and not exceeding 180 ° are detected. Similarly, the secondary electron detector 92
The emitted secondary electrons 85, which are larger than 180 ° and not larger than 300 °, are detected centering on a direction forming an angle of 240 ° with the secondary electron detector 9. As a result, each secondary electron detector can separately detect three types of domains having different atomic arrangements with three-fold symmetry. Therefore, by displaying the signals from the respective detectors on different display means, the distributions of the three types of domains can be observed simultaneously. In addition,
The number and shape of the secondary electron detectors and electrodes, the distance from the sample, and the applied voltage are not limited to the example of FIG. 5, and only the secondary electrons generated in a desired direction on the surface of the sample 7 are detected. It is only necessary to generate an electric field that can be selectively detected. For example, in Example 2 shown in FIG. 4, by replacing the electrode 101 with another secondary electron detector, two domains of the surface atom arrangement having two-fold symmetry can be observed at the same time.

[0015]

As described above, the scanning electron microscope having an electrode capable of applying a positive voltage to the side opposite to the secondary electron detecting means with the sample sandwiched between the scanning electron microscope and the secondary electron detector around the sample is included. By using a scanning electron microscope characterized by arranging multiple electrodes that can apply a positive voltage on the same plane, it becomes possible to observe the real space distribution of the surface atomic arrangement with a scanning electron microscope, which was difficult in the past. There is no doubt that it will make great progress in the research of the surface structure of semiconductors and metals, and will make a great contribution to material development and device development.

[Brief description of drawings]

FIG. 1 is a diagram illustrating a scanning electron microscope according to a first embodiment of the present invention.

FIG. 2 is a diagram for explaining an electric field distribution near a sample in the first embodiment.

FIG. 3 is a diagram for explaining the anisotropy of the atomic arrangement of the 1 × 2 structure on the Si (100) plane.

FIG. 4 is a view for explaining an electrode arrangement in the second embodiment of the present invention.

FIG. 5 is a view for explaining the arrangement of electrodes and the arrangement of secondary electron detectors in the third embodiment of the present invention.

FIG. 6 is a diagram illustrating a conventional scanning electron microscope.

FIG. 7 is a diagram illustrating a conventional scanning electron microscope.

FIG. 8 is a diagram illustrating a detection unit having a selectivity in the emission direction of secondary electrons in a conventional scanning electron microscope.

[Explanation of symbols]

1 electron gun, 2 electron beam, 3 condenser lens, 4 deflection coil, 5 objective lens, 6 sample stage, 7 sample, 8 secondary electron emitted in the direction of secondary electron detector 9, 9 secondary electron detector 81 secondary electrons emitted in a direction nearly perpendicular to the secondary electron detector 9, 82 secondary electrons emitted in a direction opposite to the secondary electron detector 9, 83 60 ° to the secondary electron detector 9 Secondary electron emitted in the direction close to the direction 84, secondary electron emitted in the direction close to 120 degrees to the secondary electron detector 9 84, emitted in the direction close to 240 degree to the secondary electron detector 85. Secondary electrons, 86 secondary electrons emitted from the secondary electron detector 9 in a direction close to 300 °, 91 secondary electron detectors, 91 secondary electron detectors, 10 electrodes, 101 electrodes, 102 electrodes, 103 electrodes, 104 electrodes, 105 electrodes 106 electrodes, 11 display means, 21 electron gun, 22 electron beam, 23 condenser lens, 24 deflection coil, 25 objective lens, 26 sample stage, 27 sample, 28 secondary electron, 29 secondary electron detector, 30 display means, 31 electron gun, 32 electron beam, 33 condenser lens, 34 deflection coil, 35 objective lens, 36 sample stage, 37 sample, 38 secondary electron, 39 secondary electron detector, 40 display means, 41 cylindrical electrode, 42 upper electrode .

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Masato Tomita 1-1-6 Uchisaiwaicho, Chiyoda-ku, Tokyo Nippon Telegraph and Telephone Corporation

Claims (3)

[Claims] 1. The electron beam is converged finely to scan the surface of the sample, secondary electrons generated at that time are drawn into the secondary electron detection means, and the signal from the secondary electron detection means is synchronized with the scanning of the electron beam. A scanning electron microscope, wherein a scanning image of the surface of a sample is obtained by displaying the scanning electron microscope, wherein the scanning electron microscope has an electrode capable of applying a positive voltage on the side opposite to the secondary electron detecting means with the sample interposed therebetween. 2. The electron beam is converged finely to scan the sample surface, secondary electrons generated at that time are drawn into the secondary electron detection means, and the signal from the secondary electron detection means is synchronized with the scanning of the electron beam. In the scanning electron microscope, which obtains a scanning image of the sample surface by displaying the same, a plurality of electrodes capable of applying a positive voltage are arranged on the same plane including the secondary electron detector around the sample. Scanning electron microscope. 3. The scanning electron microscope according to claim 2, wherein any one of the electrodes to which a plurality of positive voltages can be applied is replaced with a secondary electron detector.