JP2738322B2 - Autofocus control method and observation device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image processing type autofocus control method and apparatus, and more particularly to an autofocus control method and an observation apparatus which are optimal for use in an observation apparatus or a processing apparatus having an XY stage.

[0002]

2. Description of the Related Art Conventionally, an autofocus control method performed in optical equipment such as a microscope is disclosed in
No. 15, JP-A-5-236315, and a method of detecting a focus position by image processing.

Here, a conventional auto focus control method will be described with reference to FIGS. 4, 5 and 6. FIG.

FIG. 4 is a diagram showing the configuration of a general observation device in which autofocus control is to be performed.
FIG. 6 is a flowchart showing a procedure of a conventional autofocus control method, and FIG. 6 is a diagram showing a relationship between the operation of the Z stage and contrast data.

When the sample 13 placed on the XY stage 14 is observed by the observation optical section 22, the objective lens 1
It is necessary to move the Z stage 15 on which the 2 is installed in the Z-axis direction for focusing, that is, to arrange the Z stage 15 at the focal point position. Automatically performing this focusing is called auto focus control.

In the observation apparatus shown in FIG. 4, in order to execute autofocus control, first, the Z stage 15 is returned to the AF origin position 24 (S201). The initial installation position of the Z stage where auto focus can be executed is
It is necessary to be within the auto focus capture range 26 shown in FIG. That is, unless the AF origin position 24 is set within the autofocus capture range 26, the contrast peak 27 cannot be detected, and as a result, the in-focus position 25 cannot be detected. Next, the Z stage 15 is moved in the Z-axis direction by driving the stepping motor 16 (S202). The sample 1 obtained by the observation optical unit 22 sequentially while moving the Z stage 15
The image of No. 3 is picked up by the CCD camera 17, and the image processing unit 18 samples the contrast data of the video signal obtained by the CCD camera 17 (S203). The control unit 23 detects the position of the Z stage 15 where the contrast reaches the peak 27 as the focal point position 25 based on the contrast data sampled in the image processing unit 18 (S204). Then, the controller 23 drives the stepping motor 16 to set the Z stage 15 at the detected focal point position 25 (S20).
5).

[0007] The detection accuracy of the focal point position of the Z stage deteriorates when the autofocus capture range is widened.
In order to improve the accuracy of the focus position, the capture range of the autofocus must be narrowed. Therefore,
Normally, the required focusing accuracy is different between a case where a low magnification objective lens of about 5 to 10 times is used and a case where a high magnification objective lens of 50 times or more is used. Are different. That is, when a low-magnification objective lens is used, the depth of focus is large, so that the accuracy of the in-focus position is not so required. Therefore, the autofocus capture range is 25 to 75 μm
The focus position is detected by roughly calculating the luminance level while moving the Z stage up and down as much as possible (hereinafter, the execution mode of the autofocus control is referred to as a coarse movement mode). In addition, when a high-magnification objective lens is used, since the depth of focus is small, the accuracy of the focal point must be within ± 1 μm. Therefore, in order to achieve this accuracy, the autofocus capture range is made as small as ± 6 μm or less, and the Z stage is finely moved up and down to calculate the luminance level and detect the in-focus position ( Hereinafter, the execution mode of the autofocus control is referred to as a fine movement mode.

[0008]

Generally, the width of irregularities on the surface of a sample to be observed is limited to about ± 25 μm due to problems in machining and assembly of the sample holder and polishing accuracy of the sample surface. Yes, it is very difficult to make it smaller. For this reason, when observing the observation point A on the sample having a concavo-convex width of 25 μm as shown in FIG. 7 using a high-magnification objective lens and then observing the observation point B by the conventional autofocus control method, Has the following problems.

In the fine movement mode in the conventional auto focus control method, the auto focus capture range is ± 6 μm.
It is necessary to set it within
5 μm cannot be covered. In other words, the focus position M can be accurately determined by the auto-focus control in the fine movement mode.
0 is detected, the Z stage is set at that position, and the observation point A
Observe. Then, move the XY stage to observe point B
Is placed below the objective lens. Next, the autofocus control in the fine movement mode is performed as described above.
Referring to FIG. 7, since the observation point A and the observation point B have a height difference of 25 μm, the installation position N1 (= M0) of the Z stage at the time of observing the observation point A is the observation point B. This is about 25 μm away from the in-focus position. Therefore, even if the autofocus control in the fine movement mode is executed in order to observe the observation point B in a state where the Z stage is set at the position N1, the initial position of the Z stage is set to the aforementioned autofocus capture range (± 6μ
m), the in-focus position cannot be detected. As described above, there is a region on the sample surface where the autofocus control cannot be executed, and the operability is very poor.

When actually observing the observation point B, the operator manually moves the Z stage to the autofocus capture range, that is, a position within ± 6 μm from the in-focus position when observing the observation point B. And then the auto focus control is executed again. This operation procedure has a problem that workability, throughput, and the like are significantly reduced. In addition, it is more difficult for the operator to return the AF origin position of the Z stage as the magnification of the objective lens used increases.

[0011]

In order to solve the above-mentioned problems, in an auto-focus control method according to the present invention, an objective lens is moved up and down within a first movement range larger than the unevenness width of a surface to be observed. An image of the observation target is captured by the imaging device, contrast data is calculated by the image processing device based on the image, the first in-focus position is detected based on the contrast data, and the objective lens is set at that position. The auto-focus control in the coarse movement mode is performed. Subsequently, the object to be observed is moved by the imaging device while moving the objective lens from the first in-focus position within a second movement range smaller than the unevenness width of the surface of the object to be observed. Image, an image processing apparatus calculates contrast data based on the image, detects a second in-focus position based on the contrast data, Finally autofocus control of the fine movement mode of installing the objective lens is executed position.

The range of movement of the objective lens in the autofocus control in the coarse movement mode is also affected by the magnification of the objective lens. However, if the unevenness of the surface of the observation object is about ± 25 μm, it is about 25 to 75 μm. And The moving range of the objective lens in the autofocus control in the fine movement mode is also affected by the magnification of the objective lens. However, if the detection accuracy of the focused position needs to be within ± 1 μm, 3 About 6 μm.

Further, even when observing a plurality of observation points on the observation object, it is not necessary to return the objective lens to the AF origin by manual operation each time, so that the observation object is mounted on the XY stage. It is also easy to place and observe a plurality of observation points continuously.

Further, when the movement of the object to be observed has not been performed for a certain period of time or more, the automatic focusing control may be automatically executed.

[0015]

Next, an embodiment of the present invention will be described in detail with reference to the drawings.

The autofocus control method of the present embodiment is as follows.
It is optimally executed when the unevenness width of the sample surface to be observed is larger than the autofocus capture range necessary for obtaining the required accuracy of the in-focus position. In the control procedure, first, a first autofocus control (coarse movement mode) for roughly detecting an in-focus position by setting an autofocus capture range larger than a concavo-convex width of a sample surface is performed.
Next, the Z stage is installed at the focal point detected by the first autofocus control, and the position is set as the AF origin position, and the second autofocus control (fine movement mode) for detecting the focal point with high accuracy is performed. It is to do.

The configuration of the observation apparatus in which the autofocus control method of the present embodiment is executed is the same as the configuration of a general observation apparatus in which the conventional autofocus control is performed as shown in FIG. Since only the procedure is different, a detailed description thereof will be omitted. However, hereinafter, the reference numbers given to the configuration of the observation device use the numbers given in FIG.

FIG. 1 is a flowchart showing the control procedure of the present embodiment. FIG. 2 is a diagram for explaining the operation of the present embodiment. FIG. 1A shows the operation of the autofocus control in the fine movement mode. It is a figure which shows, and (b) is a figure which shows the operation | movement of the auto focus control of a fine movement mode.

It is assumed that a high-magnification objective lens is set on the Z stage, and that any observation point on the sample surface is observed using this objective lens. First, the first auto focus control (coarse movement mode) (S10) is executed. That is, after returning the Z stage 15 to the first AF origin position 1 (S101), the Z stage 15 is moved to 25-7.
While moving up and down about 5 μm (S103), the CCD
An image of the surface of the sample 13 is captured by the camera 17 through the objective lens 12. In the image processing unit 18, C
The contrast of the image obtained by the CD camera 17 is roughly sampled. Then, the position of the Z stage 15 at which the contrast reaches the peak 5 is detected as the first focal point position 2, and the Z stage 1 is located at the focal point position 2.
5 is set (S104). Here, the first set Z
The position of the stage 15, that is, the first AF origin position 1
However, if it is out of the autofocus capture range 3 in the coarse movement mode (S102), a focus error occurs (S105), and the autofocus control is not executed.
After returning the position 5 to the position within the auto focus capture range 3, the auto focus control is executed.

However, at this point, only the autofocus control in the coarse movement mode (S10) is performed, so that the first focus position 2 is included in the autofocus capture range 4 in the fine movement mode. However, the detection accuracy of the first in-focus position 2 has not reached the level required when the high-magnification objective lens 12 is used, and the sample 13 cannot be observed as it is.

Then, next, the second auto focus control (fine movement mode) (S20) is executed. At this time, the autofocus control in the coarse movement mode (S1
The Z stage 15 is set at the first focal point position 2 detected in step (0), and this position 2 is set as the AF origin position 6 in the fine movement mode. Move the Z stage 15 to this position 6
While moving it up and down by about 3 to 6 μm (S10
6) An image of the surface of the sample 13 is captured by the CCD camera 17 through the objective lens 12. Z stage 1 at this time
The moving range of 5 is smaller than the width of the irregularities on the surface of the sample 13. More specifically, the moving range of 5 is desired in order to set the detection accuracy of the second in-focus position described later to a value corresponding to the magnification of the objective lens 12. Is within the autofocus capture range. Next, in the image processing unit 18, the CCD camera 17
The contrast of the image obtained by is sampled finely. Then, the position of the Z stage 15 at which the contrast reaches the peak 8 is detected as the second in-focus position 7, and the Z stage 15 is set at the in-focus position 7 (S
107). Thus, finally, by performing the autofocus control (S20) in the fine movement mode, the in-focus position can be detected with an accuracy within ± 1 μm required when the high-magnification objective lens 12 is used. Can be.

As described above, in the present embodiment, first, the Z stage is moved to the AF origin in order to execute the auto-focus control in the coarse movement mode in comparison with the case of executing the auto-focus control in the fine movement mode from the beginning. The manual operation for returning to the position is greatly simplified. In other words, the in-focus position can be detected even if the AF origin position at which the Z stage should be set by manual operation exceeds a certain degree of ± 6 μm from the in-focus position.

Further, once the in-focus position is detected, the Z stage is set at that position, and then the sample is moved by the XY stage to observe another observation point on the sample surface. If the surface unevenness width is about ± 25 μm, the autofocus control in the coarse movement mode is performed first, so that the autofocus control can be performed on all the regions on the sample surface. That is, since the moving range of the Z stage (in other words, the autofocus capture range) is set to be as wide as 25 to 75 μm, if the unevenness width of the sample surface is within this autofocus capture range,
It is always possible to detect the position of the Z stage at which the contrast is maximum. Therefore, the in-focus position can be detected for all regions of the sample surface.

Thus, if the in-focus position can be detected by executing the auto-focus control for a certain point on the sample surface, even if the sample is moved by the XY stage and the observation point is changed, any other Without performing the processing of
Auto focus control can be executed.

Next, a case where the autofocus control method of the present invention is applied to laser repair will be described with reference to FIG.

FIG. 3 is a diagram showing the configuration of one embodiment of the laser repair. A laser beam 21 emitted from a laser oscillator 9 is shaped by a processing optical system 10 comprising a beam expander, a variable slit, and the like. After being reflected by the dichroic mirror 11, it passes through the objective lens 12 and irradiates the surface of the substrate 13. A wiring pattern made of a conductive substance is formed on the surface of the substrate 13, and the wiring pattern is processed into a desired shape by the irradiated laser beam 21. Therefore, the irradiation position of the laser beam 21 is
Since very high precision is required, high magnification, for example, 8
It is necessary to position the irradiation position of the laser beam 21 while observing the surface of the substrate 13 using the objective lens 12 of about 0 ×. Therefore, by applying the autofocus control method of the present invention, the substrate 13 can be moved with high accuracy and high speed.
Can be observed. Since the observation method based on the autofocus control has already been described, it will not be repeated here.

After focusing at an arbitrary position on the substrate 13 by the autofocus control of the present invention, an image of the surface of the substrate 13 taken through the objective lens 12 by the CCD camera 17 is displayed on the display 20. The substrate 13 is moved by the XY stage 14 while observing the displayed image, and the irradiation position of the laser beam 21 is determined. Here, in the present embodiment, once the in-focus position has been detected, it is not necessary to manually return the Z stage 15 to the AF origin position in all regions on the substrate 13, and the auto-focus control is performed. In order to be able to perform, the first observation point is
Need not be set near the irradiation position. Also, the substrate 13
Even when the laser repair is performed for the above plurality of positions, the auto focus control is performed without manually returning the Z stage 15 to the AF origin position every time the irradiation position of the laser beam 21 is changed. Operability is greatly improved because it is executed.

When the time during which the XY stage 14 is not driven is measured and the autofocus control is automatically executed when the time exceeds a predetermined time, the autofocus control is further performed. The operation for starting is also unnecessary.

The apparatus to which the autofocus control method of the present invention is to be applied is not limited to the laser repair described above. In order to process a sample moving by an XY stage by some means, the surface of the sample is processed. The effect is exhibited by being applied to a device that needs to be observed with high precision.

Although the detection of the in-focus position and the like has been described with reference to the position of the Z stage, it may be considered that the position of the objective lens that moves up and down is the same as the Z stage.

[0031]

As described above, according to the autofocus control method of the present invention, even when a plurality of observation points on an observation object are continuously observed, the installation position of the objective lens is always maintained. Since it is within the autofocus capture range, autofocus control can be easily performed. In particular, when a high-magnification objective lens is used, it is necessary to detect the in-focus position with high accuracy.
The autofocus capture range must necessarily be small. However, by executing the auto-focus control in the coarse movement mode first as in the present invention, the auto-focus capture range can be expanded without lowering the detection accuracy of the in-focus position, and the operability is greatly improved.

[Brief description of the drawings]

FIG. 1 is a flowchart showing a control procedure of the present invention.

FIG. 2 is a diagram for explaining the operation of the present invention.
It is a figure explaining operation of auto focus control of coarse movement mode, and (b) is a figure explaining operation of auto focus control of fine movement mode.

FIG. 3 is a diagram showing a configuration of a laser processing apparatus to which the autofocus control method of the present invention is applied.

FIG. 4 is a diagram illustrating a configuration of a general observation device in which autofocus control is performed.

FIG. 5 is a flowchart showing a conventional auto focus control procedure.

FIG. 6 is a diagram illustrating an operation of a conventional auto focus control.

FIG. 7 is a diagram illustrating a problem of the conventional auto focus control.

[Explanation of symbols]

 1 First AF origin position 2 First in-focus position 3 Autofocus capture range (for coarse movement mode) 4 Autofocus capture range (for fine movement mode) 5, 8 (Contrast) peak 6 Second AF origin position 7 Second Focusing Position 9 Laser Oscillator 10 Processing Optical System 11 Dichroic Mirror 12 Objective Lens 13 Substrate (Sample) 14 XY Stage 15 Z Stage 16 Stepping Motor 17 CCD Camera 18 Image Processing Device 19 Control Unit 20 Display

Claims (7)

(57) [Claims] 1. A method according to claim 1, wherein the first surface is larger than the width of the irregularities on the surface of the observation target.
Capturing the image of the observation target while moving the objective lens up and down within the moving range of, and detecting a first in-focus position based on contrast data obtained from the image;
A first step of installing the objective lens at that position; and performing the observation while moving the objective lens within a second movement range smaller than the unevenness width of the observation target surface from the first focal point position. Taking a target image, detecting a second focus position based on contrast data obtained from the target image, and setting the objective lens at the second focus position. Control method. 2. The apparatus according to claim 1, wherein the second movement range is within a capture range determined based on accuracy of the second focus position defined by a magnification of the objective lens. 2. The autofocus control method according to 1. 3. The unevenness width of the observation surface is at least ± 2.
5 μm or more, the first movement range is a value selected from the range of 25 to 75 μm based on the magnification of the objective lens, and the second movement range is based on the magnification of the objective lens. 2. The autofocus control method according to claim 1, wherein the value is selected from a range of 3 to 6 μm. 4. The autofocus control method according to claim 1, wherein the observation target is placed on an XY stage. 5. The method according to claim 5, further comprising: measuring a time when the observation target is stationary, and when the measured time reaches a preset time,
2. The autofocus control method according to claim 1, wherein the first step is automatically executed, and subsequently, the second step is executed. 6. A Z stage for moving an objective lens up and down within a predetermined moving range, an image pickup device for picking up an image of an observation target mounted on an XY stage through the objective lens, and an image pickup device obtained by the image pickup device. An image processing device that calculates contrast data based on the obtained image data; and a focus position of the objective lens that is detected based on the contrast data calculated by the image processing device. A control device for installing the objective lens in the observation device, wherein the imaging device moves the objective lens up and down in a first movement range larger than the unevenness width of the surface of the observation target, and An image is taken, and a first focus position is set based on contrast data calculated by the image processing apparatus based on the image. Out, and after installing the objective lens at that position, the imaging device moves the objective lens from the first focal point position in a second movement range smaller than the unevenness width of the observation target surface. Capturing an image of an observation target, detecting a second focus position based on contrast data calculated by the image processing apparatus based on the image, and installing the objective lens at that position. Observation device. 7. The observation object is mounted on an XY stage, and means for measuring a time during which the observation object is not moved by the XY stage, and the measured time is set in advance. At that time,
The observation apparatus according to claim 5, wherein the movement of the objective lens within the first movement range is automatically started.