JPH1069870A - electronic microscope - Google Patents

Abstract

(57) [Object] To provide an electron microscope capable of detecting a magnetic field of a sample without error. Kind Code: A1 A shift of a spot formed on a detector by an electron beam transmitted through a sample is determined by calculation of signals from a plurality of detectors constituting the detector. An electron microscope that detects the Lorentz deflection caused by the magnetic field of the sample 4 when transmitting light through the sample 4. The shape of the spot is such that the length across the boundary between the detectors is always constant within the range of the movement required for observation. To be.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to an electron microscope.

[0002]

2. Description of the Related Art In order to observe a magnetic image with an electron microscope, Lorentz electron microscopy, which detects electron beam deflection (Lorentz deflection) due to a magnetic field, is used. In this Lorentz electron microscopy, for example, as described in Japanese Patent Application Laid-Open No. 5-13033, a converged electron beam is transmitted to an observation portion, and a shift of a spot formed by the transmitted electron beam on a detector is described. Detects the direction and magnitude of Lorentz deflection from. The direction of Lorentz deflection is perpendicular to the magnetic field, and the magnitude is proportional to the magnetic field. Therefore, the direction and strength of the magnetic field can be known by detecting the shift of the spot position on the detector with respect to the absence of the magnetic field.

In conventional Lorentz electron microscopy, FIG.
As shown in FIG. 2, in order to detect the shift of the circular spot 8 formed on the detector 6 by the transmitted electron beam, the detector 6 is divided into four parts, and each detector (A, B, C,
An operation was performed on the signal from D). For example, in FIG.
In order to obtain the shift of the circular spot 8 in the X-axis direction, signals from the detection units A, B, C, and D (only A,
B, C, D), (A-B-C + D) / (A +
B + C + D). The result of this operation (referred to as I) is proportional to X when the shift of the circular spot 8 in the X-axis direction (referred to simply as X) is sufficiently smaller than the radius (R) of the circular spot 8 (I). = 4 / (π
R) X). However, in the general case where X does not have such a condition, the range until the circular spot 8 completely moves to one side of the Y axis and I becomes a constant value (this is set to 1 in FIG. 2). Since the relationship between I and X becomes non-linear, error could not be avoided if X was mechanically derived from I using the proportional coefficient (4 / (πR)). Moreover,
The above-mentioned nonlinear equation describing the relationship between I and X is complicated, and it has been difficult to automatically solve this nonlinear equation to easily obtain X from I. For this reason, the conventional Lorentz electron microscopy requires a range in which X is sufficiently smaller than R and a proportional relationship between I and X is established, that is, when the magnetic field to be observed is relatively weak (Lorentz deflection is small). Was used for observation.

[0004]

The problem to be solved by the present invention is to solve the above-mentioned problem in the prior art of Lorentz electron microscopy that the error increases as the magnetic field becomes stronger.

[0005]

According to the present invention, there is provided:
Attention is paid to the cause of the increase in error when the magnetic field is increased in the above-described conventional technology. This is because the spot of the electron beam is circular as is apparent from FIG. More specifically, there is a problem in that the area of a portion that moves from one detection unit to the other detection unit in the spot due to the spot shift is not constant for the same shift amount.

In order to keep the area of the moving portion constant, the spot shape should not be a simple circular shape but a shape in which the length of the portion straddling the boundary between the detecting portions at the time of moving is always constant. Good. FIG. 3 shows a specific example of such a spot shape. First, FIG. 3A shows spots whose upper and lower boundaries (boundaries intersecting the Y axis) are parallel to each other. In the spot having such a shape, when moving in the X-axis direction, the length across the Y-axis is always constant. Therefore, even if the electron beam undergoes a large Lorentz deflection in the X-axis direction due to the magnetic field, no error occurs in the deflection amount detection.

However, in such a spot shape, the detection of the spot shift in the Y-axis direction is represented by (A + B-
If the value is obtained from (CD) / (A + B + C + D), a detection error may occur. To avoid this, the shape of the spot may be parallel not only to the upper and lower boundaries but also to the left and right boundaries (boundaries intersecting the X axis). With such a spot shape, no error occurs in the deflection amount detection even if the electron beam undergoes a large Lorentz deflection in any of the X-axis and Y-axis directions.

Further, in order to make the signal change amounts corresponding to the same amount of spot shift in the X-axis direction and the Y-axis direction coincide with each other, as shown in FIG. It is preferable that the lengths of the portions are the same (a). By employing such a spot shape, the direction and relative intensity of Lorentz deflection can be detected without error.

[0009]

FIG. 1 shows an embodiment of the present invention. In FIG. 1, an electron beam 1 supplied from an electron source (not shown) passes through a stop 2 having a square opening, is converged by a converging lens system 3, and passes through a sample 4. The electron beam 1 transmitted through the sample 4 reaches the detector 6 through the magnifying lens system 5. The magnifying lens system 5 has a function of forming an image of the aperture of the stop 2 on the detector 6 at a desired magnification and orientation.

[0010] The detector 6 is of a four-split type, and is composed of four split parts separated by orthogonal boundaries. The signals (referred to as A, B, C, and D) from each of the division units are guided to the arithmetic unit 7, and the arithmetic unit 7 performs the arithmetic shown in FIG. The result of the operation (Ix and I in FIG. 1)
y) corresponds to a shift amount of a spot formed by the electron beam 1 on the detector 6 in directions orthogonal to each other (referred to as an X-axis direction and a Y-axis direction). The shift of the electron beam 1 in the two directions bears knowledge on the direction and relative strength of the magnetic field in the portion of the sample 4 through which the electron beam 1 has passed. Therefore, if a scan image is obtained using the calculation results Ix and Iy as luminance signals while scanning the electron beam 1 on the sample 4, the electron beam 1 of the sample 4 can be obtained.
This means that a magnetic image in the scanning area has been obtained.

In order to obtain this scanning image, the present embodiment uses a scanning coil installed on a surface including the stop 2 on the optical axis or a surface conjugate with the stop 2 in a range from the stop 2 to the sample 4. And a scanning circuit for driving the scanning circuit, a scanning image generating circuit for generating a scanning image by using a signal from the scanning circuit as a position signal, and a signal from the arithmetic unit 7 as a luminance signal. Are omitted in FIG. 1 because they have the same configuration as the device required for normal scanning image generation.

Next, the spot of the electron beam 1 formed on the detector 6 in this embodiment, and the relationship between the shift on the detector 6 and the calculation result in the arithmetic unit 7 will be described with reference to FIGS. ,
This will be described with reference to FIG.

In this embodiment, since the image of the square opening of the stop 2 is formed on the detector 6, the spot of the electron beam 1 formed on the detector 6 is square. Further, in this embodiment, since this spot can be rotated to a desired angle, each side of this square spot (referred to as a rectangular spot 9) as shown in FIG. It can be parallel to the X axis and Y axis defined by the boundary of the section.

Considering the case where the rectangular spot 9 moves in the X-axis direction under such conditions, for example, as shown in FIG. 4, the signal strength (Ix in FIG. 1, but here, for simplicity, The movement amount (referred to simply as X) is the movement amount (referred to simply as X).
Is proportional to X exactly until it becomes half the length (a) of the side of the rectangular spot 9. Then, when X exceeds this, the rectangular spot 9 completely moves to one side of the Y axis, and I becomes a constant value (this is set to 1 in FIG. 4).

In practice, each side of the rectangular spot 9 is defined by the X axis,
Since it may be difficult to make an adjustment parallel to the Y-axis accurately, the signal intensity (I) and the moving amount (X) when the side of the rectangular spot 9 is tilted with respect to the X-axis and the Y-axis next. ) Will be described with reference to FIGS.

As shown in FIG. 5, the rectangular spot 9 is X
When the axis is tilted with respect to the axis and the Y axis (an angle of inclination is θ), an intermediate area is generated between an area where I is proportional to X and an area where a constant value (in FIG. 5, this is 1) is obtained. Here I
And X are no longer linear (similar to the case of FIG. 4, it is assumed that the rectangular spot 9 moves in the X-axis direction).

FIG. 5 shows that the proportional area decreases and the intermediate area increases as θ increases. However, on the other hand, it can be understood that, when θ increases, the amount of change of I with respect to X in this proportional region increases, that is, the sensitivity to X improves. FIG. 6 shows the relationship between I and X more quantitatively. Thus, in the intermediate region (shown as quadratic in FIG. 6) between the proportional region (shown as linear in FIG. 6) and the region where I is constant (shown as constant in FIG. 6), I is X
It can be seen that there is a quadratic relationship to Also,
It is also apparent that the widths of these regions and the relationship between I and X in the proportional region and the intermediate region depend on θ. Here, in practice, it is easy to adjust θ within 5 degrees (0.087 radians), so the intermediate region is 0.45 ≦ X / a
≤0.55, and I and X are almost in the same range as when θ shown in FIG. 4 is exactly 0 degrees.
Can be maintained.

In the above description, not only when the rectangular spot 9 moves in the X-axis direction but also when the rectangular spot 9 moves in the Y-axis direction, (A + B−C−D) /
The same applies by using (A + B + C + D). This is because the rectangular spot 9 in this embodiment is square. That is, in the square rectangular spot 9, the length of the portion straddling the Y-axis and the X-axis at the same movement amount in the X-axis direction and the Y-axis direction is always constant at an arbitrary θ. If it can be assured that θ is always constant, for example, as shown in FIG. 3B, the length of the portion that crosses the X-axis and the Y-axis is the same, and this is the Y-axis direction. A spot having a shape that does not change with movement in the X-axis direction may be used.

In other words, if a spot having a shape such that the length of the portion straddling the boundary between the detection units constituting the detector 6 is always constant within the range of the movement amount required for observation is used, This can be done without compromising the essence of the invention.

[0020]

According to the present invention, the position of the electron beam 1 on the detector 6 can be detected without error, and the Lorentz deflection of the electron beam 1 by the magnetic field of the sample 4 can be obtained accurately. High-precision observation of the magnetic field distribution of No. 4 became possible.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of one embodiment of the present invention.

FIG. 2 is an explanatory diagram of a problem of the conventional device.

FIG. 3 is an explanatory diagram of a solution to the problem of the conventional device.

FIG. 4 is an explanatory diagram of the operation of the electron microscope according to the present invention.

FIG. 5 is an explanatory diagram of the operation of the electron microscope according to the present invention.

FIG. 6 is an explanatory diagram of the operation of the electron microscope according to the present invention.

[Explanation of symbols]

1 ... Electron beam, 2 ... Aperture, 3 ... Converging lens system, 4 ... Sample,
5 magnifying lens system, 6 detector, 7 arithmetic unit, 8 circular spot, 9 rectangular spot.

Claims (3)

[Claims] An electron gun comprising an electron source, a high-voltage power supply, an accelerator, etc., an aperture for extracting only a desired portion of the electron beam emitted from the electron gun, and an electron beam passing through the aperture. A converging lens system for converging and irradiating the observed portion, a magnifying lens system for adjusting the cross section of the electron beam after passing through the observing portion to a desired size and direction, and an electron beam passing through the magnifying lens system. A split-type detector composed of a plurality of detectors for detection, and corresponds to an arrival position of an electron beam on the split-type detector by an operation using a signal from the detector of the split-type detector as a variable. An arithmetic circuit for outputting an arithmetic result, a scanning coil for moving a converged electron beam irradiation position in an observation portion in a scanning manner, a scanning circuit for driving the scanning coil, and a signal from the scanning circuit as a position signal. In an electron microscope including a scanning image generating circuit for generating a scanning image using a signal from the arithmetic circuit as a luminance signal, when an aperture of the stop is formed on the split type detector by the magnifying lens system. An electron microscope characterized in that, even when an image moves on the split-type detector, the length of an image portion straddling the boundary between the detection portions does not change in a practically important image movement range. 2. The method according to claim 1, wherein the split type detector comprises:
An electron microscope configured to include a portion in which the four detection units having a right-angled boundary occupy the first, second, third, and fourth quadrants of the orthogonal coordinate axes. 3. An electron microscope according to claim 2, wherein said aperture of said aperture has a square shape.