JPH09204894A - Electron beam micro analyzer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the sufficient quantity of light required to auto-focus control by feedback controlling with a slope correction means and making the sample surface vertical to an optical axis in an auto-focus. SOLUTION: When the quantity of light is judged as insufficient for auto- focus control in the judgement of the quantity of light, a control device 5 performs inclination correction control to supply the required quantity of light to a CCD camera 4. A detector 71 has detecting regions 71a-71d in positive and negative directions of the X axis and Y axis directions, and outputs a signal indicating the distance to each axis direction from the center. An inclination correction control circuit 53 generates an inclination correcting signal based on the outputted signal, and corrects the sample 1 horizontally with a gyro mechanism 21. When the sufficient quantity of light required for auto- focus control is obtained, an auto-focus detecting circuit 51 receives the photo image of the CCD camera, and focuses the image through a Z direction control circuit 52 by driving an XYZ stage. The sample surface is horizontally set in real time, and a microscope with high reflection efficiency can be obtained.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electron beam microanalyzer, and more particularly to autofocus control of an optical microscope of an electron beam microanalyzer.

[0002]

2. Description of the Related Art An electron beam microanalyzer is equipped with an optical microscope for observing the surface of a sample and observes an image of the surface of the sample to determine the analysis position. Focus adjustment of the optical microscope is performed by moving the sample table on which the sample is placed by autofocus control. Normally, this autofocus control uses an optical image obtained from the sample in CC
An image is received by a light receiving device such as a D camera, and the XYZ stage is driven in the optical axis direction (Z axis direction) so that an optimum focus can be obtained based on the received image signal.

[0003]

In the conventional electron beam microanalyzer, there is a problem that the autofocus control is not sufficiently performed when the sample surface is inclined. In the autofocus control of the optical microscope, control is performed based on the optical image obtained by reflecting from the sample surface. Therefore, when the amount of reflected light is small and the amount of light received by the CCD camera is small, a sufficient autofocus operation can be performed. It will be difficult.

The analysis sample surface may not necessarily be perpendicular to the optical axis of the irradiation light but may be inclined. When the tilt angle with respect to the optical axis of the irradiation light becomes smaller, the amount of reflected light reflected on the sample surface decreases, making it difficult to perform autofocus control. FIG. 9 is a diagram for explaining the inclination of the analysis sample surface.

In FIG. 9A, the sample 1 on the sample table 2 is
When the surface of is perpendicular to the optical axis of the irradiation light (Z axis), the reflected light reflected on the sample surface is reflected in the optical axis direction of the irradiation light. A light receiving means such as a CCD camera installed on the optical axis receives the reflected light and performs autofocus control. On the other hand, as shown in FIG. 9B, when the analysis sample surface of the sample 1 is inclined with respect to the irradiation light optical axis, the reflected light reflected on the sample surface is the irradiation light light. The light is reflected in a direction deviated from the axial direction, and the light receiving means cannot receive the reflected light, which makes it difficult to perform autofocus control.

Therefore, the present invention solves the problems of the conventional electron beam microanalyzer described above, and in the autofocus control of the electron beam microanalyzer, the inclination correction of the sample is performed so that a sufficient light amount required for the autofocus control can be obtained. It is an object of the present invention to provide an electron beam microanalyzer capable of performing.

[0007]

The present invention comprises an optical microscope having at least a sample stage whose movement can be controlled in the optical axis direction, and an optical microscope having an optical focus position on the optical axis direction of the sample stage. In an electron beam microanalyzer equipped with an autofocus control means for controlling the focus position by moving the sample stage based on the image, an inclination mechanism that allows the sample to incline with respect to the optical axis and a sample surface perpendicular to the optical axis. By providing the tilt correction means for applying the feedback control to the tilt mechanism, the tilt correction of the sample is performed and a sufficient light amount required for the autofocus control is obtained.

In the autofocus control of the optical microscope in the electron beam microanalyzer, when a sufficient light quantity for performing the autofocus control cannot be obtained, the tilt correction means feedback-controls the tilt mechanism so that the sample surface is illuminated. Control is performed so that it is perpendicular to the axis.
By this control, when the sample surface becomes perpendicular to the optical axis as shown in FIG. 9C, the autofocus control means can obtain a sufficient amount of light for performing the autofocus control. As a result, the autofocus control means can automatically adjust the focus position of the optical microscope by the autofocus control.

In the first embodiment of the present invention, the tilt correction means includes a detection means for detecting the tilt amount and the tilt direction of the sample surface, and the optical axis is detected based on the detection amount and the detection direction obtained from this detection means. Feedback control is applied to the tilt mechanism so that the deviation from the sample surface is reduced. By this tilt correction of the sample surface, the autofocus control means obtains a sufficient amount of reflected light from the sample surface for performing the autofocus control. You can

In the second embodiment of the present invention, the detecting means for detecting the inclination amount and the inclination direction of the sample surface includes a light receiving means for receiving the reflected light from the sample surface, and the sample surface is perpendicular to the optical axis. At this time, the tilt amount is obtained from the distance from the light spot on the light receiving means to the detection light spot, and the tilt direction is detected from the direction of the detection light spot.

According to a third embodiment of the present invention, the light receiving means in the detecting means has a light receiving surface divided into four in the X-axis direction and the Y-axis direction, and the inclination direction depends on which divided surface the light is received. Can be detected.

Further, according to a fourth embodiment of the present invention, the light receiving means in the detecting means includes a concentric circle centered on a light spot on the light receiving means when the sample surface is perpendicular to the optical axis, and the light spot. It can be configured by a plurality of pixels divided into a fan shape divided at an arbitrary angle as a center, and an inclination amount and an inclination direction can be detected from the received light pixel.

[0013]

Embodiments of the present invention will be described below in detail with reference to the drawings. A configuration example of the embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram illustrating the configuration of an embodiment of an electron beam microanalyzer of the present invention. In FIG. 1, a sample 1 is mounted on a tilt mechanism 2 that constitutes a sample stage, and the tilt mechanism 2 is a sample stage 3 that is movable at least in the optical axis direction.
Supported above. The sample stage 3 can be configured by an XYZ stage, and the controller 5 controls the X axis,
Movement control in the Y-axis direction and Z-axis direction is possible. Normally, movement in the X-axis and Y-axis directions moves the analysis point on the sample surface, and movement in the Z-axis direction controls autofocus. To do. This autofocus control is
The sample 1 is irradiated from the control device 5 side or a separately prepared light source through the half mirrors 11 and 13, and the optical image of the sample surface is detected again by the CCD camera 4 through the half mirrors 13 and 11, and based on the detection signal. This is performed by controlling the Z axis on the sample stage 3 side from the control device 5. Since this autofocus control is well known in the optical microscope system of the electron beam microanalyzer, its details are omitted.

Further, the electron beam microanalyzer of the present invention is provided with a structure for compensating the amount of light detected by the CCD camera 4 so that the amount of light detected by the CCD camera 4 is sufficient in performing the autofocus control. ing. The mechanism for compensating for this light quantity includes a tilt mechanism 2 that allows the sample 1 to tilt with respect to the optical axis 9 and a tilt mechanism that performs feedback control on the tilt mechanism 2 so that the sample surface is perpendicular to the optical axis 9. Compensation means. This tilt correction means supplies a laser light source 6 for irradiating the sample 1 with light, a detector 7 for detecting reflected light from the sample 1, and a feedback signal based on a detection signal of the detector 7 to the tilt mechanism 2. It can be configured with an output control device 5 (here, a control device for autofocus control is also included).

The tilt correction control signal from the control device 5 to the tilt mechanism 2 includes signals relating to the tilt amount (tilt angle θ) and tilt direction α of the tilt mechanism 2, whereby the surface of the sample 1 is moved to the optical axis 9. Control to be perpendicular to.

In the structure shown in FIG. 1, in order to improve the accuracy of inclination detection, the laser light source 6 is used to irradiate the sample 1 with light with a small divergence of the irradiation light, but other light sources are used. It can also be used. Further, in the configuration of FIG. 1, the autofocus control and the tilt correction control (light amount control) are controlled by the common control device 5, but they may be configured by separate control devices.

Next, in the electron beam microanalyzer having the configuration shown in FIG. 1, autofocus control will be described with reference to FIG. 2, and tilt correction control will be described with reference to FIG. The optical paths shown in FIGS. 2 and 3 show only the parts related to each control, and the optical paths related to other controls are omitted.

In the autofocus control, as shown in FIG. 2, the sample 1 is irradiated from the control device 5 side through the half mirrors 11 and 13, and the light reflected on the sample surface is again detected by the CCD camera 4 through the half mirrors 13 and 11. To do.
The control device 5 uses the Z axis with respect to the sample stage 3 so that the optical focus position on the optical axis direction of the sample stage is focused on the basis of mainly the change in the light amount of the light image received by the CCD camera 4. A direction control signal is sent to perform autofocus control.

On the other hand, in the tilt correction control, as shown in FIG. 3, the sample is irradiated from the laser light source 6 through the half mirrors 12 and 13, and the light reflected on the sample surface is detected by the detector 7 through the half mirror 13. To do. Control device 5
Based on the position of the reflected light received by the detector 7 on the detector 7, the information about the inclination amount (θ) and the inclination direction (α) of the sample surface with respect to the optical axis 9 is obtained. A tilt correction signal that is perpendicular to the axis 9 is sent to the tilt mechanism 2 to perform tilt correction control.

By the tilt correction control, the sample surface is controlled to be perpendicular to the optical axis 9. When the amount of light received by the CCD camera 4 in the autofocus control is insufficient because the sample surface is tilted, the CCD camera 4 is sufficient to perform the autofocus control by performing this tilt correction control. It is possible to obtain a large amount of light and to perform auto focus control.

Next, the procedure for performing the autofocus control and the tilt correction control will be described with reference to the flowchart of FIG. When the optical microscope in the electron beam microanalyzer obtains an optical image, the control device 5 first determines whether or not a sufficient amount of light for performing autofocus control is obtained. This light amount determination can be performed, for example, by presetting a light amount range in which autofocus control is possible and determining whether the light amount received by the CCD camera 4 is within the set range (step S1). .

In this light amount determination, if the light amount is sufficient for performing the autofocus control, the control device 5
Performs normal autofocus control (step S
2).

On the other hand, when the amount of light is not sufficient for performing the autofocus control in the light amount determination in step S1 and the amount of light is insufficient (step S3), the control device 5 performs tilt correction control and the CCD camera. 4 is irradiated with a sufficient amount of reflected light to make it possible to perform autofocusing (step S4). On the other hand, when the amount of light is excessive (step S3), the control device 5 causes the CCD camera to perform other adjustments such as sensitivity adjustment. The amount of light is adjusted so that autofocus is possible (step S5).

The processes of steps S3 and S4 can be carried out a plurality of times, or the autofocus control can be proceeded to after one process. Usually 1
By performing the tilt correction control once, it is possible to set the light amount range in which auto focus is possible.

Next, the tilt amount (tilt angle θ) and tilt direction (α) of the sample surface will be described with reference to FIG. FIG.
(A) is a case where the sample surface is perpendicular to the optical axis (Z axis in the figure), and at this time, the CCD camera 4 is irradiated with reflected light of a sufficient light amount for autofocus control. On the other hand, FIGS. 5B to 5D show the case where the sample surface is inclined with respect to the optical axis. 5 (b) to FIG.
In (d), only the sample surface where the X axis and the Y axis are positive is shown.
Other aspects are omitted.

FIG. 5B shows the case where the sample surface is tilted in the X-axis direction, the angle α representing the tilt direction is 0, and the tilt amount is represented by the tilt angle θ, and FIG. Is the case where the sample surface is tilted in the Y-axis direction, and α representing the tilt direction
Is π / 2, and its inclination amount is represented by an inclination angle θ. In addition, in FIG. 5C, the sample surface is in the X-axis direction and Y direction.
In the case of tilting between the axial directions, the angle α representing the tilting direction is 0 <α <π / 2, and the tilt amount is the tilt angle θ.
Represented by When light is incident on the inclined sample surface shown in FIGS. 5B to 5D from the Z-axis direction, the reflected light proceeds in a direction symmetrical to the incident light about the vertical axis.
The detector irradiates the sample surface at a position corresponding to the tilt direction and the tilt amount.

Next, the position of the reflected light on the detector will be described with reference to FIG. 6, and the relationship between the position of the reflected light on the detector and the tilted state of the sample surface will be described with reference to FIG. FIG.
In (a), a point P indicates the irradiation position of the reflected light on the detector, and when the sample surface is tilted with respect to the Z axis, the tilt direction is represented by an angle ω from the X axis, for example. The tilt amount is represented by the distance d from the Z-axis axis. When the detector is divided into four parts in the X-axis and Y-axis directions, the tilt directions are, for example, (X +), (X-), (Y +) as shown in FIG. 6B. , (Y-)
Is represented by each divided portion, and the inclination amount is represented by a distance d from the axis of the Z axis.

The relationship between the amount of tilt and the distance d from the axis of the Z axis can be expressed by the relationship shown in FIG. 7 (a), where L is the distance between the sample surface and the detector. The relationship between the amount of tilt (tilt angle θ) and the distance d from the axis of the Z axis is expressed by the following equation (1).

D = L · tan 2θ (1) Further, the relationship between the tilt direction of the sample surface and the irradiation position on the detector can be expressed by, for example, the relationship shown in FIG. Represented by 2). α = ω + π (2) where α is the angle of the normal to the sample surface when viewed from the X-axis direction on the XY plane, and ω is the angle when viewed from the X-axis direction on the surface of the detector.

The control device 5 can detect the inclination amount and the inclination direction of the sample surface by using the relationship between the position of the reflected light on the detector and the inclination state of the sample surface as shown in FIG. . For example, the above relational expression is built in the control device 5 and the tilt amount and the tilt direction are calculated based on the detection signal from the detector 7, or the tilt amount with respect to the detector signal is calculated in the control device 5. The inclination direction may be stored in the storage means, and the inclination amount and the inclination direction may be read according to the detector signal.

Next, a configuration example using a detector divided into four parts will be described with reference to FIG. In FIG. 8, the detector 71 of the tilt correction means is divided into four in the X-axis and Y-axis directions,
The detection area 71a is arranged in the positive direction of the X axis, the detection area 71c is arranged in the negative direction of the X axis, the detection area 71b is arranged in the positive direction of the Y axis, and detection is performed in the negative direction of the Y axis. Area 71d
Has been arranged. Each of these detection areas sends an output indicating the distance from the center to the tilt correction control circuit 53, and the tilt correction control circuit 53 generates a correction signal for correcting the tilt based on the output to horizontally correct the sample surface. Gyro mechanism 2
1 or send it to a tilt correction mechanism such as a tilt mechanism.

For example, when a detection signal is obtained from the detection area 71a of the detector 71, it indicates that the sample surface is inclined in the direction in which the positive direction of the X axis is downward.
The tilt correction control circuit 53 generates a control signal that raises the positive direction of the X axis or lowers the negative direction of the X axis. As a result, the gyro mechanism 21 corrects the sample surface so that it is perpendicular to the Z axis.

When the amount of light reflected by the CCD camera 4 is sufficient to perform autofocus control by the tilt correction mechanism, the autofocus detection circuit 51 causes the C
The optical image of the CD camera 4 is received, and the XYZ stage is driven through the control circuit 52 that corrects the Z-axis direction to perform focusing. The autofocused optical image is displayed on the monitor 8 of the optical microscope.

According to the embodiment of the present invention, since the sample surface can be horizontally set in almost real time, it is possible to stably obtain a microscopic image having excellent reflection efficiency and reduce the surface analysis time. can do. Further, even when the sample surface is tilted and the amount of reflected light is small, autofocus control can be performed within the tilt correction range, and the range in which autofocus control can be performed can be expanded.

[0035]

As described above, according to the present invention,
In the autofocus control of the electron beam microanalyzer, it is possible to provide the electron beam microanalyzer capable of correcting the inclination of the sample so that a sufficient amount of light required for the autofocus control can be obtained.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a configuration of an embodiment of an electron beam microanalyzer of the present invention.

FIG. 2 is a diagram for explaining autofocus control in a block diagram of an electron beam microanalyzer.

FIG. 3 is a diagram for explaining tilt correction control in a block diagram of an electron beam microanalyzer.

FIG. 4 is a flowchart illustrating a procedure for performing autofocus control and tilt correction control.

FIG. 5 is a diagram for explaining a tilt amount (tilt angle θ) and a tilt direction (α) of a sample surface.

FIG. 6 is a diagram for explaining the position of reflected light on a detector.

FIG. 7 is a diagram for explaining the relationship between the position of reflected light on the detector and the tilted state of the sample surface.

FIG. 8 is a block diagram of a configuration example of an electron beam microanalyzer using a detector divided into four parts.

FIG. 9 is a diagram for explaining the inclination of the analysis sample surface.

[Explanation of symbols]

1 ... Sample, 2 ... Tilt mechanism, 3 ... Sample stage, 4 ... CC
D camera, 5 ... Control device, 6 ... Laser light source, 7 ... Detector, 8 ... Monitor, 9 ... Optical axis, 11, 12, 13 ... Half mirror.

Claims (1)

[Claims] 1. A sample stage, which is capable of controlling movement in at least an optical axis direction, and an optical microscope having an optical focal point position on the optical axis direction of the sample stage, wherein the sample stage is moved based on an optical microscope image. In an electron beam microanalyzer provided with an autofocus control means for controlling a focus position, a tilt mechanism for tilting the sample with respect to the optical axis and a tilt mechanism for feedback control with the sample surface perpendicular to the optical axis. An electron beam micro-analyzer, comprising: an inclination correcting means for applying the electron beam.