JPH08203460A - Scanning electron beam diffraction apparatus - Google Patents

Abstract

PURPOSE: To provide scanned images with high resolution from low magnification to high magnification and which display the distribution of crystalline states of a sample. CONSTITUTION: A two-stage scanning coil 5 is installed between two objective lens 4, 6 arranged in the direction of an optical axis. At the time of scanning observation, at low magnification, electron beams are converged only by (on) the objective lens 4 and beams are made to run in parallel by the scanning coil 5 and at the time of scanning observation at high magnification, electron beams are converged only by (on) the objective lens 6 and the beams are scanned in a common way by the scanning coil 5.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a scanning electron beam diffractometer for observing and analyzing a sample using a diffracted electron beam secondarily generated from the sample by scanning the sample surface with a finely focused electron beam. In particular, it relates to improvement of electron beam focusing and scanning mechanism. The scanning electron diffraction apparatus referred to here is sometimes called a scanning electron diffraction microscope.

[0002]

2. Description of the Related Art In an apparatus for irradiating a sample while scanning a finely focused electron beam, an arrangement of an objective lens and a scanning coil as shown in FIG. 3 has been conventionally used. Among them, in the scanning electron diffraction apparatus in which the direction of irradiating the sample with the electron beam is important, the arrangement shown in FIG. 3 (a) is mainly used (see JP-A-2-216746). This arrangement is for the objective lens 51.
The two-stage scanning coil 52 is disposed below (on the sample side), and the electron beam 53 is converged by the objective lens 21 and then the scanning coil 52 scans the electron beam in parallel. The beams can be emitted from the same direction.

The arrangement shown in FIG. 3B is mainly used in a scanning electron microscope. In order to make the electron beam thinner, the distance between the objective lens and the sample is shortened to increase the reduction ratio. The scanning coil is arranged above the objective lens (on the side of the electron gun). At this time, if the electron beam does not pass through the center of the objective lens, aberration due to the objective lens becomes large and the electron beam cannot be focused, so that the electron beam is always scanned so as to pass through the center of the objective lens.

[0004]

The arrangement shown in FIG. 3 (a) is suitable for a scanning electron beam diffractometer because the electron beam can be scanned while being kept parallel and the sample can be irradiated with the electron beam from the same direction. However, since the distance between the objective lens and the sample is relatively large, the diameter of the electron beam is about 100n.
It is difficult to make it less than m. Therefore, since the resolution is insufficient, a high-magnification scan image cannot be obtained.

On the other hand, in the arrangement shown in FIG. 3 (b), the diameter of the electron beam can be reduced to about 10 nm or less, so that a high-magnification scanning image can be obtained. It is generally not preferable to apply this arrangement to a scanning electron diffractometer because the direction of impact changes with scanning. However, since the change in the direction in which the electron beam impinges on the sample is very small only when observing at high magnification, this arrangement can be applied to the scanning electron diffraction apparatus.

It is an object of the present invention to provide a scanning electron diffraction apparatus capable of observing from low magnification to high magnification.

[0007]

According to the present invention, in order to solve the above problems, a scanning type having an electron gun for generating an electron beam, an objective lens for narrowing down the electron beam, and a scanning coil for scanning the electron beam. In the electron beam diffractometer, two objective lenses for focusing the electron beam on the sample surface are provided separately from each other in the optical axis direction, and a two-stage scanning coil is provided between the two objective lenses.

[0008]

Since the objective lenses are provided above (on the side of the electron gun) and below (on the side of the sample) the two-stage scanning coils, the operations of the objective lens and the scanning coil are set at low magnification and high magnification, respectively. By doing so, an operation suitable for both conditions can be obtained. That is, as shown in FIG. 2A, when the magnification is low, the lower objective lens is not operated and is operated in the same manner as in FIG.
As shown in (b), the upper objective lens does not work and is operated in the same manner as in FIG. 3 (b). By doing so, it is possible to realize a scanning electron beam diffractometer having appropriate resolution from low magnification to high magnification and an irradiation direction to the sample.

[0009]

1 is a schematic diagram of a scanning electron diffraction apparatus, which is an embodiment of the present invention. The electron beam 10 is generated by the electron gun 1, and the beam current is adjusted by the condenser lens 2 and the diaphragm 3. When the sample 7 is irradiated with an electron beam that is narrowly converged by the objective lens (upper) 4 or the objective lens (lower) 6, the diffracted electron beam 11 is reflected according to the crystal state of the sample 7, and the diffracted electron beam 11 is reflected on the fluorescent plate 8. A diffraction pattern is drawn, and the brightness of one of the diffraction spots is detected by the detector 9
Is detected by The signal from the scanning power supply 13 is supplied to the scanning coil 5 to scan the electron beam on the sample surface. In synchronization with this, the luminance signal from the detector 9 is given to the CRT 12 to display the sample on the screen of the CRT 12. A scan image representing the distribution of crystalline states is obtained.

The current from the objective lens power supply 14 is switched by the switch 1.
The objective lens 4 or 6 through which the current flows is selected by 5. However, this is the objective lens (top) 4
And the objective lens (bottom) 6 may be provided with separate objective lens power supplies, and the currents flowing through the two objective lenses may be controlled individually. Although the condenser lens is drawn in one stage in the figure, this may be two stages or more. Further, the scanning coil 5 is provided with an X-axis coil and a Y-axis coil in each of two stages, and can scan the electron beam two-dimensionally.

FIG. 2 shows the arrangement of the beam focusing objective lens and the beam deflecting scanning coil, which is the main part of the present invention. A two-stage scanning coil 5 is arranged between two objective lenses (upper) 4 and objective lenses (lower) 6 arranged side by side in the optical axis direction. To obtain a low-magnification scan image, the electron beam is scanned as shown in FIG. 2A (this is called a low-magnification mode). In this mode, the switching device 15 is set so that no current is passed through the objective lens (lower) 6 so that it does not work, and only the objective lens (upper) 4 is used.
0 is focused on the surface of the sample 7. Electron beam
The beam is scanned by the two-stage scanning coil so that the sample surface is irradiated with electrons from a certain direction while keeping the parallel state. For this purpose, if a current I is applied to the upper coil 5a of the two-stage scanning coil, a current -I having the same direction but the opposite direction may be applied to the lower coil 5b. When the magnification is low, a relatively wide range is scanned on the sample surface, but as described above, the electron beam is always irradiated from a fixed direction on the sample surface, so that the diffraction condition is not disturbed. Further, since it is a low-magnification image, there is no problem in the resolution of the observed image even if the diameter of the electron beam is slightly larger.

As the magnification of the scanning image is increased, FIG.
In the operation of (a), since the distance between the objective lens (upper) 4 and the sample 7 is relatively large, the diameter of the electron beam cannot be reduced, so that the resolution is insufficient and the image becomes blurred. When a scan image is obtained at such a high magnification, the operation is switched to that shown in FIG. 2B (this is called a high magnification mode). At this time, by switching the switching device 15, no current is passed through the objective lens (upper) 4 so that it does not work.
The electron beam 10 is focused on the surface of the sample 7 using only the objective lens (lower) 6. Since the distance between the objective lens (lower) 6 and the sample 7 is short, the reduction rate can be increased and the diameter of the electron beam can be reduced. Therefore, even at high magnification, a clear image can be obtained without blurring the scanned image. The scanning method at this time is that the electron beam is the objective lens (lower) 6
It is deflected by a two-stage scanning coil so as to pass through the center of. This is because unless the electron beam passes through the center of the objective lens, the aberration becomes large and a high-magnification image cannot be obtained. To this end, the distance between the coil 5a and the coil 5b and the coil 5
Assuming that the distance between b and the objective lens (bottom) 6 is equal, the current I flows through the upper coil 5a of the two-stage scanning coil.
If the current is passed through, the lower coil 5b may be supplied with a current −2I having a direction opposite to that of the coil 5b. When scanning is performed in this way, the irradiation direction of the electron beam on the sample surface slightly changes as the scanning is performed. However, when a high-magnification image is obtained, the scanning range on the sample surface is extremely small. Is extremely small and does not matter.

In the embodiment of FIG. 2, the objective lens (lower) 6 is not provided with a diaphragm, so that the central portion thereof has an opening of several mm. The actual size is a value determined by the design of the lens yoke. A diaphragm for reducing spherical aberration of the objective lens may be placed in the central portion of the objective lens (upper) 4, or may be located upstream of the scanning coil 5 (on the electron gun side) and downstream of the diaphragm 3 attached to the condenser lens. If it is the sample side), it may be placed anywhere on the electron beam axis.

Although it has been stated in the above description that the objective lens (upper) 4 is not operated in the high magnification mode, when the objective lens power sources for the two objective lenses are separately provided as described above, Of course, both the upper and lower objective lenses may be operated to focus on the sample surface.

The present invention includes the following configurations. In a scanning electron diffraction microscope having an electron gun for generating an electron beam, an objective lens for narrowing the electron beam and a scanning means for irradiating a sample while scanning the electron beam, two stages of XY biaxial scanning means and scanning thereof A first objective lens is provided on the electron gun side of the means, and a second objective lens is provided on the sample side of the scanning means. The first objective lens is operated in the low magnification mode, and the first objective lens is operated in the high magnification mode. 2. A scanning electron diffraction microscope, characterized in that an operation switching means for actuating both objective lenses of 2 is provided.

[0016]

According to the present invention, two objective lenses are prepared,
Since the two-stage scanning coil is provided between them, it is possible to select the operation in both the low magnification mode and the high magnification mode. In the low-magnification mode, the distribution image of the correct crystalline state is obtained by focusing on irradiating the sample with the electron beam from the same direction rather than increasing the resolution determined by the diameter of the electron beam. Further, in the high magnification mode, the electron beam irradiation direction is sacrificed with an emphasis on increasing the resolution, but since it is used only in the high magnification mode, the influence is small. Therefore, the apparatus of the present invention can realize a scanning electron beam diffraction apparatus in which the irradiation directions of electron beams on a sample are aligned and observation can be performed with good resolution from low magnification to high magnification.

[Brief description of drawings]

FIG. 1 is an embodiment of a scanning electron diffraction apparatus of the present invention.

FIG. 2 shows an arrangement of an objective lens and a scanning coil, which is a main part of the present invention.

FIG. 3 shows a conventional arrangement of an objective lens and a scanning coil.

[Explanation of symbols]

1 ... Electron gun 2 ... Condenser lens 3
... Aperture 4 ... Objective lens (upper) 5 ... Scanning coil 6
… Objective lens (bottom) 7… Sample 8… Fluorescent plate 9
… Detector 10… Electron beam 11… Diffraction line 1
2 ... CRT 13 ... Scanning power supply 14 ... Objective lens power supply 1
5 ... Switching device 51 ... Objective lens 52 ... Scanning coil 5
3 ... Electron beam 54 ... Sample

Claims (1)

[Claims] 1. A scanning electron diffraction apparatus comprising an electron gun for generating an electron beam, an objective lens for narrowing the electron beam, and a scanning coil for scanning the electron beam.
A scanning electron beam, characterized in that two objective lenses for converging an electron beam on a sample surface are provided apart from each other in the optical axis direction, and two-stage scanning coils are arranged between the two objective lenses. Diffraction device.