JP3131265B2 - Focus adjustment method for electron microscope - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron microscope, and more particularly to a focus adjustment method in a transmission electron microscope (TEM).

[0002]

2. Description of the Related Art In a TEM, a focus adjusting means is usually mounted in order to obtain a clear electron microscope image on a fluorescent screen or to take a good photograph. Although various focus adjustment methods have been proposed, one of them is a focus adjustment method called an image wobble method. The principle is described below with reference to FIG. In the drawings, 1 denotes a deflection coil, 2 denotes a sample, 3 denotes an objective lens (OL), 4 denotes an imaging lens, 5 denotes a fluorescent plate, and O denotes an optical axis.

When the focus adjustment by the image wobble method is started, a predetermined deflection current is supplied to the deflection coil 1 from a control device (not shown) including a microprocessor or the like. And a gradient indicated by a broken line 7 are given at a predetermined cycle. Here, the inclination angles of the solid line 6 and the broken line 7 are each θ with respect to the optical axis O, but the solid line 6 and the broken line 7 are set to be axially symmetric with respect to the optical axis O. Hereinafter, the solid line 6 is used for convenience.
Is referred to as (+) tilt, and tilted as indicated by the broken line 7 is referred to as (-) tilt. Sample 2 is a pole piece of OL3 (not shown).
Needless to say, the imaging system lens 4 is shown as a block, but is constituted by an intermediate lens and a projection lens of about 2 to 4 steps.

Now, assuming that a solid line 8 in FIG. 3 shows an enlarged image at the time of (+) inclination, and a broken line 9 shows an enlarged image at the time of (-) inclination, the image is enlarged when the object is out of focus. Since the images 8 and 9 do not coincide with each other, a fluctuation of the enlarged image is observed on the fluorescent screen 5 in response to the (+) inclination and the (-) inclination being repeated at a predetermined cycle. , 9 coincide with each other, and no fluctuation of the enlarged image is observed. Therefore, the focus adjustment can be performed by adjusting the excitation of the OL 3 or other lens by the focus adjustment knob so that the fluctuation of the enlarged image on the fluorescent screen 5 is not observed.

[0005]

However, even if the enlarged image on the fluorescent screen 5 is observed with the naked eye,
When observing with the loupe arranged in the EM, it is not only one point of the focus adjustment knob but also a certain range that the fluctuation of the enlarged image is not observed. There was a problem that it was difficult.

That is, when the focus adjustment knob is rotated from the under-focus side to the over-focus side at the time of focus adjustment, it is assumed that the fluctuation of the enlarged image is no longer observed at the position indicated by A in FIG. If the focus adjustment knob is rotated from the overfocus side to the underfocus side, and the fluctuation of the enlarged image is no longer observed at the position indicated by B in FIG.
Usually, the position A and the position B do not coincide with each other, and there is a range G between which the fluctuation of the enlarged image is not observed. The size of the range G can be reduced by further enlarging and observing the enlarged image on the fluorescent screen 5 with a loupe or the like, but it is almost impossible to match the position A with the position B anyway. It is possible.

Therefore, the operator who performs the focus adjustment memorizes the position A and the position B, and performs the focus adjustment by positioning the focus adjustment knob at an intermediate position between them. However, such an operation is very troublesome.

An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to provide a focus adjustment method for an electron microscope that can easily perform focus adjustment.

[0009]

In order to achieve the above object, a focus adjustment method for an electron microscope according to the present invention comprises a focus adjustment means for performing focus adjustment by an image wobble method, and the focus adjustment means. When the focus is changed from the under-focus side to the over-focus side, the first setting switch for instructing that the image is not shaken, and the focus adjusting means shifts the focus from the over-focus side to the under-focus side. A second setting switch that indicates when the image is no longer shaken when the image is changed; a focus adjustment amount by a focus adjustment unit at a time pointed by the first setting switch; Average value of the focus adjustment amount by the focus adjustment means at the time point indicated by the setting switch Based on, characterized in that it comprises a control means for determining an adjustment amount of the focus giving focus.

[0010]

According to the present invention, since the focus adjustment means for performing focus adjustment by the image wobble method and the first and second setting switches are provided, the image wobble method is used from the under focus side. When the focus is adjusted to the overfocus side and from the overfocus side to the underfocus side, when the image of the electron microscope is no longer shaken, the first and second setting switches may be used to indicate the focus, and the focus is adjusted accordingly. Since the position is automatically obtained, the operator is released from troublesome operations as in the related art, and can easily perform focus adjustment, thereby contributing to improvement of operability.

[0011]

Embodiments will be described below with reference to the drawings.
FIG. 1 is a diagram showing a configuration of an embodiment of a focus adjustment method for an electron microscope according to the present invention. Side setting switch, 1
4 is a focus setting switch, 15 is a focus adjustment knob, and 16 is a driving means.

In FIG. 1, a control device 10 is composed of a microprocessor and its peripheral circuits, and is responsible for processing for focus adjustment according to the present invention. ,
A deflection current for giving a (+) tilt and a (-) tilt to the electron beam is instructed to a deflection coil (not shown in FIG. 1). Thus, the electron beam repeats the (+) tilt and the (-) tilt at a predetermined cycle.

After the focus adjustment is started, the operator operates the focus adjustment knob 15. When the focus adjustment knob 15 is operated, the control device 10 applies a predetermined exciting current according to the rotation angle to OL ( An instruction is given to a lens for performing other focus adjustment (not shown in FIG. 1). Assuming that the focus adjustment knob 15 is to be rotated from the underfocus side to the overfocus side, the operator observes the enlarged image on the fluorescent screen, and when the fluctuation of the enlarged image cannot be detected, the operator moves the underside. Press the setting switch 12.

The control device 10 includes an under-side setting switch 1
When it is detected that the button 2 has been pressed, the rotation angle θ _U of the focus adjustment knob 15 when the under-side setting switch 12 is pressed is captured. The capture of this rotation angle θ _U
For example, it can be performed by detecting the position of the notch of the focus adjustment knob 15.

When the above operation is completed, the operator rotates the focus adjustment dial 15 from the overfocus side to the underfocus side, and presses the over-side setting switch 13 when the fluctuation of the enlarged image cannot be detected. . As a result, the control device 10 controls the focus adjustment knob 1 when the over-side setting switch 13 is pressed.
Taking the rotation angle theta _O 5.

Next, the operator presses the focus setting switch 14. When the control device 10 detects that the focus setting switch 14 has been pressed, the rotation angle θ _U of the focus adjustment knob 15 captured when the under-side setting switch 12 is pressed and the over-side setting switch 13
(Θ _U + θ _O ) / 2 is calculated from the rotation angle θ _O of the focus adjustment knob 15 captured when is pressed, the angle obtained by this calculation is determined as the position of the focal point, and the angle is determined. Notify the driving means 16. As a result, the drive unit 16 positions the focus adjustment knob 15 at the angle specified by the control device 10. Then, the control device 10
The excitation current corresponding to the final position of the focus adjustment knob 15 is notified to the focus adjustment lens. In the above description, the underside setting switch 12 is pressed first,
Next, the over-side setting switch is pressed, but this order may be reversed.

An embodiment of the present invention has been described above. Next, another embodiment of the present invention will be described with reference to FIG. In the embodiment shown in FIG. 1 described above, the underside setting switch 12 is used to set a position at which no fluctuation of the enlarged image is observed on the underside, and the overside setting switch 13 is set at a position at which no fluctuation of the enlarged image is observed on the overside. FIG. 2 differs from the configuration shown in FIG. 1 in that a near-focus point setting switch 17 and a swing range setting switch 18 are provided.

An in-focus point setting switch 17 is used by an operator to operate the focus adjustment knob 15 to indicate a position at which the operator recognizes the in-focus point position. The apparatus 10 captures the rotation angle θ _J of the focus adjustment knob 15 when the near-focus point setting switch 17 is pressed.

The swing range setting switch 18 is for the operator to observe a magnified image and indicate a range in which the shake cannot be observed. For example, the operator presses the swing range setting switch 18 at the positions A and B in FIG. . This allows the control device 10 to set the focus adjustment dial 15 at the position A.
Taking the rotation angle theta _B of the focus control knob 15 in the rotation angle theta _A and position B. When the focus setting switch 14 is pressed thereafter, the control device 10
(Θ _A + θ _B ) / 2 is calculated, the angle obtained by this calculation is determined as the position of the focal point, and the angle is notified to the driving means 16. This allows the driving means 16 to control the control device 1
The focus adjustment knob 15 is positioned at an angle designated from 0. Then, the control device 10 notifies the focus adjustment lens of the excitation current corresponding to the final position of the focus adjustment knob 15.

The focus adjustment is performed by executing the above processing. However, when both θ _A and θ _B are on the under focus side of θ _J ,
Alternatively, when θ _A and θ _B are both on the overfocus side of θ _J , the calculation for finding the in-focus position is not performed ignoring the acquired rotation angle. This is because the angle θ _{J of the in-} focus position set by the near-focus point setting switch 17 should be between the rotation angles θ _A and θ _B indicating the swing range.

Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible. For example, in the above embodiment, the focus setting switch 14 is provided. However, if the control device 10 automatically calculates the in-focus position when all necessary data is taken in, the focus setting switch 14 is used.
Need not be provided. In the above embodiment, the control device 10 automatically rotates the focus adjustment knob 15. However, the operator may be instructed by displaying the angle of focus on a display device such as a CRT. Things.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing a configuration of another embodiment of the present invention.

FIG. 3 is a diagram for explaining the principle of focus adjustment by an image wobble method.

FIG. 4 is a diagram for explaining a method of obtaining an in-focus position.

[Explanation of symbols]

1: Deflection coil, 2: Sample, 3: Objective lens (OL),
4 imaging lens, 5 fluorescent plate, 10 control device, 11
... Focus adjustment start switch, 12 ... Under setting switch, 13 ... Over setting switch, 14 ... Focus setting switch, 15 ... Focus adjustment knob, 16
... Drive means, O ... Optical axis.

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) H01J 37/21 H01J 37/26

Claims (1)

(57) [Claims] 1. A focus adjusting means for performing focus adjustment image Wo bra scheme, by the focus adjusting means, when changing the focus from the under-focus side to over-focused side, when no longer sway of an image A second setting switch for instructing when the image is no longer shaken when the focus is changed from the overfocus side to the underfocus side by the focus adjustment means; Based on the average value of the focus adjustment amount by the focus adjustment unit at the time pointed by the first setting switch and the focus adjustment amount by the focus adjustment unit at the time pointed by the second setting switch. Control means for determining an amount of focus adjustment for providing a focal point, Electron microscope focus adjustment method of that.