JPH08321274A - Active vibration resisting device of electron microscope - Google Patents

Abstract

PURPOSE: To enhance the vibration resisting performance and reduce the costs through omission of a horizontal direction sensor by controlling an actuator member using a two-dimensional dislocation amount acquired from the vibration data from sensor and the image data. CONSTITUTION: The vertical vibration data acquired from a vibration sensor 12 fixed on a surface reference plate 5 is fed to a DSP member 17 via an A/D converter 16a. The horizontal dislocation amount acquired from the image data taken in by a scanning image sensor 13 of an electron microscope 23 is also fed to the DSP member 17 via another A/D converter 16b and an image processing device 22. The control signal calculated at a high speed by the member 17 is passed through a D/A converter 18 and amplifier 19 to control an actuator member 3. Thereby the sensing data of dislocation amount is made accurate to lead to enhancement of the vibration resisting performance. Sensing points in the horizontal direction are lesser required to allow decreasing the number of sensors in provision.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active vibration isolator for an electron microscope.

[0002]

2. Description of the Related Art In a precision instrument such as an electron microscope, image accuracy or performance may be deteriorated due to vibration of a floor on which the instrument is installed. Is installed in. The vibration isolation device is a passive member such as an elastic spring member having low rigidity in the vertical and horizontal directions, such as a coil spring, an air spring, or a vibration damping rubber, and a vibration damping member such as a viscous damper having a damping effect. A combination of is often used. The vibration isolation device is a device for reducing (vibrating) the absolute acceleration of the response of the surface plate and the equipment mounted on the surface plate by vibrating and insulating minute vibrations from the floor surface. However, the passive vibration isolator always has a natural frequency, and there is a limit to lowering the natural frequency. Generally, the natural frequency of the passive vibration isolation device is about 1 to 3 Hz, and the vibration isolation effect of the passive isolation device cannot be obtained for floor vibrations of 1.5 to 4 Hz or less, and it may rather be amplified. There is a problem with the passive vibration isolator.

Therefore, as a method of solving such a problem, a method of actively suppressing the vibration of the surface plate against a slight vibration of the floor vibration is considered, and the conventional technique of this method is, for example, As described in Japanese Patent Application Laid-Open No. 2-246382, there is an active vibration isolation device that uses an actuator to feed back the amount of vibration of the surface plate to actively suppress the vibration of the surface plate and equipment.

[0004]

When an active vibration isolator is applied to an electron microscope, not only the surface plate but also the vertical and horizontal vibration amounts of the equipment are detected to improve the accuracy, and the detected vibration is detected. By feeding back the amount, the effect of suppressing the vibration of the electron microscope can be improved. However, in the active vibration isolator of this method, it is impossible to directly attach the detector for obtaining the acceleration data and the displacement data to the electron beam, so that the detector is attached at an approximate measurement point. Therefore, the accuracy of the data obtained from the detector becomes poor. Further, since a plurality of detectors are required to obtain these data, the cost of the active vibration isolator increases.

[0005]

In order to solve the above-mentioned problems, the present invention provides an actuator member provided between a surface plate and a mount of an electron microscope, a spring member which is an elastic body, or this spring. Member and vibration damping member, and a detector that is placed on the surface plate to detect the acceleration or displacement of these members, and the data detected by these detectors and the horizontal between the beam and the sample stage. An active vibration isolation device including a controller that controls an actuator member based on image data indicating a deviation amount in a direction is provided.

[0006]

According to the present invention, the two-dimensional shift amount between the electron beam and the sample obtained from the vibration data of the surface plate and equipment supported by the active vibration isolator and the image data is fed back to the controller to activate the active vibration isolator. Control the actuator member of. This displacement amount is highly accurate displacement data directly obtained from the image data of the electron microscope, so that the vibration isolation performance is improved. Further, since the detector in the horizontal direction can be omitted, the cost of the active vibration isolator can be reduced.

[0007]

Embodiments of the present invention will now be described with reference to the drawings.

First, an embodiment of the present invention will be described with reference to FIG. In the embodiment shown in FIG. 1, active vibration isolation is performed in which the electron microscope 23 directly takes in the two-dimensional shift amount between the electron beam and the sample, which is obtained from the digitized image data of the present invention, and feeds back this amount for control. It is an example to which the device is applied. In this embodiment, a plurality of actuator members 3 and a passive vibration isolation member 4 which is an elastic body are provided in parallel with a pedestal 2 installed on the floor 1. The actuator member 3 and the hash vibration damping member 4 support the surface plate 5. Further, the main body of the electron microscope 23 is mounted on the surface plate 5. In the electromagnetic lens holder 6 of the electron microscope 23,
An electron gun 7 that emits an electron beam and an electromagnetic lens that converges the electron beam are provided, and the inside of the electromagnetic lens holder 6 is evacuated by a vacuum pump 8b. Further, a stage 10 for moving the sample stage 11 in the chamber 9 from outside the chamber 9 in any horizontal and vertical directions is provided in the chamber 9, and the chamber 9 includes a vacuum pump 8
A vacuum is applied by a. Moreover, in order to control the actuator member 3, for example, as shown in FIG. Provide one. Further, a scanning image detector 13 for detecting the deviation amount of the horizontal component obtained from the captured image data is provided. The data obtained from the detector 12 is passed through the A / D converter 16a,
Further, the shift amount of the horizontal direction component obtained from the image data captured by the scanning image detector 13 is calculated by the A / D converter 16b,
Through the image processing device 22, both are input to the DSP member 17, and an execution program for controlling the actuator member 3 is written in the DSP member 17,
The signal calculated at high speed by the member 17 is the D / A converter 18,
The actuator member 3 is controlled via the amplifier 19. The ROM member 20 has a function of sending the command signal to the DSP member 17 when starting or ending the control of the actuator member 3.

FIG. 2 is an explanatory view showing the concept of the deviation amount detecting method according to the present invention. When the image O point moves to the image O ′ point after a short time, the displacement amount OO ′ in the X direction is ΔX, and the displacement amount in the Y direction is ΔY. The method of detecting these deviation amounts ΔX and ΔY is as follows. That is, the pixel number (i) and the line number (j) are determined in the X-axis and Y-axis directions on the screen when capturing image data,
The original position is compared with the position after a short time, and the product of the amount of the shifted scale and the size between pixels or lines is calculated by X.
By performing each in the axis and Y-axis directions,
X and ΔY are obtained.

FIG. 3 shows a specific example of the method of detecting the amount of deviation according to the present invention. An image when the electron microscope 23 is not affected by floor vibration is shown by a dotted line. Then, when the electron microscope 23 is affected by floor vibration, an image shown by a solid line is obtained. That is, the boundary line of the image becomes jagged under the influence of floor vibration. This jaggedness deteriorates the image accuracy in the electron microscope 23. Therefore, the horizontal width of this jagged surface can detect the image shift amount δ, and ΔX, Y in the X-axis direction.
It is used as ΔY in the axial direction. Then, the true shift amount can be detected by dividing by the magnification of the electron microscope 23 currently used. The vibration direction in FIG. 3 is the direction of the arrow shown in FIG. In this method, the entire image is not required, and the deviation amount is detected from the portion where the deviation amount is generated, whereby the deviation amount detection time can be shortened.

The operation of the embodiment will be described with reference to FIGS. The surface plate 5 supported by the actuator member 3 and the passive member 4 by the floor vibration and the electron microscope 23 main body are
Since the electron microscope 23 is oscillated horizontally and vertically, and the electron microscope 23 is not generally supported by the center of gravity, a mode is added to the surface plate 5 that is inclined with respect to the horizontal plane. As a result, for example, relative displacement tends to occur between the electron gun 7 in the electromagnetic lens holder 6 and the sample table 11. At this time, the detector 1 that detects the amount of vibration at each point of the surface plate 5 on which the actuator member 3 is arranged
The output signal of 2 is applied to the low-pass filter 21 and the A / D converter 1
6a, the scanning image signal detected by the scanning image detector 13 is passed through the A / D converter 16b and the image processing device 22, and the horizontal deviation amounts ΔX and ΔY are both DS.
Input to the P member 17, and these horizontal deviation amounts ΔX,
The squared value of each of ΔY and the power of the actuator member 3 is used as an evaluation function, and the DSP member 17 is used by using the feedback gain determined so as to minimize this evaluation function.
Instantaneously calculates a voltage corresponding to the control force by the actuator member 3, and the calculated control voltage drives the actuator member 3 through the D / A converter 18 and the amplifier 19. The control force of the actuator member 3 suppresses the electron microscope 23 so as to reduce the horizontal shift amounts ΔX and ΔY of the image of the electron microscope 23.

In FIG. 4, instead of the detector 12 for detecting the amount of vibration in the vertical direction, a laser measuring device 14 is used as an electromagnetic lens holder 6.
It is an example attached to. The method of detecting the amount of vibration in the vertical direction is as follows. First, a laser measuring device is attached to the electromagnetic lens holder 6 and the laser measuring device 1 is used when it is not affected by floor vibration.
Set the distance between 4 and the sample. Next, the distance between the laser measuring device 14 and the sample under the influence of this and the floor vibration is measured, and the value to be corrected is determined by comparison and the actuator member 3 is controlled. The laser measuring device 14 can output three lasers at one time, and since the laser measuring device 14 controls the lasers by the three lasers, the parallelism between the electromagnetic lens holder 6 and the sample is not affected by the floor vibration. It is possible to keep the same inclination as when.

In FIG. 5, instead of the detector 12 for detecting the amount of vertical vibration, a laser measuring device 14 is used for the electromagnetic lens boulder 6.
It is an example in which the inclinometer 15 is attached to the stage 10 as well as to. The method of detecting the amount of vibration in the vertical direction is as follows. First, the laser measuring device 14 when not affected by floor vibration is used.
And the distance between the samples and the tilt angles of the inclinometers 15a and 15b are set. Next, the tilt angle of the inclinometers 15a and 15b when it is influenced by this and the floor vibration is measured, and the value to be corrected is determined by comparing with the tilt angle set in the initial stage. Alternatively, the inclinometer 15 when not affected by floor vibration
a and 15b are compared to set the difference between the inclination angles. Next, this and the inclinometer 15a when affected by the vibration from the floor,
The value to be corrected is determined by measuring the difference in the inclination angle of 15b and comparing them. With this control, the electron beam and sample stage 11
The inclination angle between them becomes the same as when not affected by vibration, and the laser measuring device 14 attached to the electromagnetic lens holder 6 determines a value for correcting the distance between the electromagnetic lens holder 6 and the sample, and the actuator member 3 To control. The laser measuring device 14 used in this embodiment emits one laser at a time.

[0014]

According to the present invention, in an active vibration isolator for an electron microscope which vibrationally isolates a floor vibration input, control can be performed by using a shift amount obtained from image data to achieve high accuracy and horizontal level. Since the number of detection points in the direction is reduced, the number of detectors can be reduced, and a low-cost active vibration isolation device for an electron microscope can be provided.

[Brief description of drawings]

FIG. 1 is a block diagram of an embodiment in which an active vibration isolation device of the present invention is applied to an electron microscope device.

FIG. 2 is an explanatory view of the principle of the horizontal shift amount detecting method of the present invention.

FIG. 3 is an explanatory diagram showing an example of a horizontal shift amount detection method of the present invention.

FIG. 4 is an explanatory diagram showing an example of measuring a vertical vibration amount using a laser measuring device.

FIG. 5 is an explanatory diagram showing an example in which the amount of vertical vibration is measured using a laser measuring device and an inclinometer.

[Explanation of symbols]

1 ... Floor, 2 ... Stand, 3 ... Actuator member, 4 ... Passive member, 5 ... Surface plate, 6 ... Electromagnetic lens holder, 7 ... Electron gun, 8 ... Vacuum pump, 9 ... Chamber, 10 ... Stage,
11 ... Sample stand, 12 ... Detector, 13 ... Scan image detector,
16 ... A / D converter, 17 ... DSP member, 18 ... D / A
Converter, 19 ... Amplifier, 20 ... ROM member, 21 ... Low-pass filter, 22 ... Image processing device, 23 ... Electron microscope.

Claims (4)

[Claims] 1. An active vibration isolator comprising an actuator member provided between a floor and a surface plate on which equipment is mounted, and a detector and a controller provided for controlling the actuator member, wherein the actuator member is controlled. An active vibration isolation device for an electron microscope, which feeds back a two-dimensional shift amount between an electron beam and a sample obtained from image data. 2. An electronic device according to claim 1, wherein the actuator is controlled by feeding back a two-dimensional shift amount between the electron beam obtained from the image data and the sample in the horizontal direction and the data obtained from the vibration detector in the vertical direction. Active vibration isolation device for microscopes. 3. The active vibration isolation device for an electron microscope according to claim 2, wherein a laser measuring device is used as a vibration detector provided to detect vertical vibration data. 4. An active vibration isolation device for an electron microscope according to claim 2, wherein a laser measuring instrument and an inclinometer are used in combination as a vibration detector provided to detect vertical vibration data.