JPH02250252A - Scanning type reflection and diffraction electron microscope - Google Patents

Abstract

PURPOSE:To irradiate specimen surface with an electron beam always in constant circular form by adjusting the focal distance of an electron beam and its profile in accordance with the inclining angle of the specimen. CONSTITUTION:A magnetification adjusting circuit 5 adjusts the ratio of the Y-direction scan amount of an electron beam scan signal given by a scan signal generator 10 to its scan amount in the X direction in conformity to a specimen inclination angle signal sensed by an inclining angle sensor 4 so that the electron beam scans over the specimen surface in its zone approximated to the display screen of a CRT 3. A focal point adjusting circuit 7 controls an electron lens 8 so that the focus of electron beam lies in the measuring center of the specimen S surface and moves the focal point in accordance with the specimen inclination angle signal, while an astigmatism correction circuit 9 feeds a convergent intensity adjusting signal according to the specimen inclination signal to an astigmatism correction coil 11, and thus the convergent intensity in Y direction is adjusted. This ensures that the irradiation spot of the electron beam on the specimen S surface becomes genuine circle at all times.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Field of Application) The present invention relates to a scanning reflection diffraction electron microscope (prior art) In a scanning reflection diffraction electron microscope, an electron beam is When observing a sample that has been scratched, if the scanning amount of the electron beam is the same in both the X and Y directions, the scanning range of the sample surface will be extended in the Y direction.
The amount of scanning in the direction must be smaller than the amount of scanning in the Since the electron beam is separated from the surface, unless the focal length of the -order electron beam is changed, the size of the irradiation spot of the electron beam that irradiates the sample changes, making it impossible to obtain a clear image.

In addition, ideally the focus of the electron beam is a point, but in reality it has a size due to the effects of aberrations and diffraction, and the sample surface is inclined, so the focus of the electron beam is Even if the surface is irradiated with a primary electron beam with a perfect cross section, the irradiation spot P of the electron beam irradiated onto the sample surface becomes an oval shape, and the degree of blurring in the measurement image differs in the vertical and horizontal directions. If there is a problem and you try to project a perfectly circular primary electron beam irradiation spot onto the sample surface, as shown in Figure 2B, the irradiation beam will have a horizontally oblong cross section, depending on the inclination angle of the sample surface. The sample must be irradiated.

As a method to solve such problems, a method for correcting image distortion and blur caused by the specimen tilt angle was proposed in Japanese Patent Publication No. 63.
-36110, the scanning range of the −order electron beam,
Proposals have been made in which the focal position can be adjusted.

In this method, the scanning amount of the electron beam in the Y direction is made smaller than the scanning amount in the By manually adjusting the amplification degree of the scanning signal in the Y direction and superimposing the adjusted scanning signal in the Y direction on the focusing coil of the electron lens, the focus value 1 of the electron beam is constantly positioned at the sample surface. However, in this method, the size of the irradiation spot of the electron beam that scans the tilted sample surface was kept constant. However, in this method, the size of the irradiation spot of the electron beam that scans the tilted sample surface is The scanning signal must be adjusted manually, which is very cumbersome to operate, and since the irradiation spot is an ellipse extending in the direction of the sample inclination, the measurement image has a high resolution in both the vertical and horizontal directions. The problem remained that different blurring occurred and the degree of blurring varied depending on the tilt angle of the sample.

(Problems to be Solved by the Invention) The present invention adjusts the focal length and beam shape of the electron beam in accordance with the inclination angle of the sample, so that the sample surface is always irradiated with the same circular electron beam. The purpose is to

(A means to solve issues) In the scanning -type reflection times, in the electron microscope device, the inclination angle detection means to detect the inclined angle of the sample surface and the sample tiled signal from the above -sled angle detection means means for controlling the convergence strength of the electron lens in accordance with the sample tilt signal from the tilt angle detection means in conjunction with the scanning signal in the Y direction; Astigmatism correction means for controlling the convergence strength of the astigmatism correction coil in the X or Y direction or in the X and Y directions is provided.

(Function) In order to obtain an image without distortion or blur in a scanning reflection diffraction electron microscope device, a circular electron beam of a certain size is irradiated onto a rectangular area similar to a CRT screen on the sample surface. The spot must be scanned. Furthermore, if the sample surface is tilted, the focal position of the electron beam must be adjusted in conjunction with scanning in the tilt direction (Y direction). Moreover, the above adjustment must be changed in response to a change in the inclination angle of the sample with respect to the -order electron beam.

The present invention is a method for scanning a rectangular range similar to a CRT screen on a sample surface by detecting the tilt angle of the sample surface and adjusting the electron beam to match the shape of the CRT screen according to the sample tilt signal. As a method of making the scanning amount in the Y direction smaller than the scanning amount in the The scanning signal was superimposed on the focus control signal of the electronic lens. Therefore,
In conjunction with the scanning signal in the Y direction, the focal position of the electron lens moves according to the inclination angle of the sample, so that the focal position of the electron lens is constantly located on the sample surface. Furthermore, as a method of making the electron beam irradiation spot irradiated onto the sample surface a perfect circle, as shown in Figure 2B, the electron beam is made into an astigmatic beam, and the X-direction convergence line of the beam is placed on the sample surface. The astigmatism correction circuit is driven by the sample inclination signal to control the convergence strength of the astigmatism correction coil in the Y direction, the X direction, or the X and Y directions, and Correspondingly, the ratio of the major axis to the minor axis in the cross-sectional shape of the electron beam was changed so that the irradiation spot of the electron beam on the sample surface was always a perfect circle, so the measurement image could be maintained regardless of the inclination of the sample surface. In, X
The resolution in both the direction and the Y direction is always the same.

(Example) FIG. 1 shows an example of the present invention. In Figure 1, S
diffracts the electron beam irradiated from the electron gun onto the sample. 1 is a diffraction electron detector that detects diffraction electrons from the sample S. 2
detects secondary electrons emitted from the sample S with a secondary electron detector. 3 is a CRT for displaying a signal detected by the diffraction electron detector 1 or the secondary electron detector as an image. 4 is an inclination angle detector, which is linked to the inclination angle adjustment mechanism of the sample.
Detect the tilt angle of the sample. Reference numeral 5 denotes a magnification adjustment circuit that adjusts the ratio of the scanning amount in the Y direction and the scanning amount in the X direction of the electron beam scanning signal from the scanning signal generator 10 using the sample tilt angle signal detected by the tilt angle detector 4. Then, the electron beam scans the sample surface in an area that is in phase with the display screen of the CRT 3.

7 is a focus adjustment circuit that focuses the electron beam on the measurement center of the surface of the sample S. Specifically, it focuses the electron beam at a point near the X-direction convergence line of the astigmatic beam, and the width of the irradiation spot in the X-direction is equal to the scanning pitch. The electron lens 8 is controlled by transmitting a focus control signal so that the point of equalization) is located, and the Y amplified according to the sample tilt angle signal detected by the tilt angle detector 4 is transmitted.
A direction scanning signal is superimposed on the focus control signal, and the focus position is moved in accordance with the sample tilt angle signal in conjunction with the Y direction scanning signal. 9 is an astigmatism correction circuit which applies a convergence strength adjustment signal corresponding to the sample tilt signal to the astigmatism correction coil 11;
By adjusting the convergence intensity in the Y direction, the length of the irradiation spot in the Y direction is changed according to the sample tilt signal, so that the electron beam irradiation spot P that irradiates the sample surface is constantly made into a perfect circle. .

<Effects of the Invention> According to the present invention, the focal length and beam shape of the electron beam can be adjusted in accordance with the inclination angle of the sample, and the sample surface can always be irradiated with the same circular electron beam. This made it easier to adjust the scanning control of the electron beam relative to the sample angle, eliminating distortion and blurring of the display screen, and further improving resolution.

[Brief explanation of drawings]

FIG. 1 is a configuration diagram of an embodiment of the present invention, and FIG. 2 is an explanatory diagram of scanning of an electron beam in the X direction. S... Sample, 1... Diffraction electron detector, 2... Secondary electron detector, 3... CRT, 4... Tilt angle detector, 5m magnification adjustment circuit, 6... Scanning Coil, 7... Focus adjustment circuit, 8... Electronic lens, 9... Astigmatism correction circuit, 10... Scanning signal generator, 11... Astigmatism correction coil.

Claims (1)

[Claims] an inclination angle detection means for detecting the inclination angle of the sample surface; an adjustment means for adjusting the ratio of the scanning amount in the X direction and the Y direction according to the sample inclination signal from the inclination angle detection means; means for controlling the convergence strength of the electron lens in accordance with the sample tilt signal from the tilt angle detection means;
A scanning reflection diffraction electron microscope characterized in that it is provided with astigmatism correction means for controlling convergence strength in the X and Y directions of the astigmatism correction coil in accordance with the sample tilt signal.