JPH08190045A - Automatic focusing control method and observation device - Google Patents

Abstract

PURPOSE: To provide an automatic focusing control method capable of easily detecting a focal position for all regions on the surface of a sample. CONSTITUTION: The image of a sample is picked up by an image pickup device while an objective lens is moved vertically within a first moving range larger than the rugged width of the surface of the sample (S103), the contrast is calculated from the image by an image processor, a first focal position is detected based on the contrast, the objective lens is mounted on the position (S104), then, while the objective lens is moved from the first focal position within a second moving range smaller than the rugged width of the surface of the sample (S106), the image of the sample is picked up by the image pickup device, the contrast is calculated from the image by the image processor, a second focal position is detected based on the contrast and the objective lens is finally installed on the position.

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 therefor, and more particularly to an autofocus control method and observation apparatus optimum for use in an observation apparatus or processing apparatus having an XY stage.

[0002]

2. Description of the Related Art A conventional autofocus control method performed in an optical instrument such as a microscope is disclosed in Japanese Patent Laid-Open No. 63-986.
This is performed by the method for detecting the in-focus position by image processing disclosed in Japanese Patent Laid-Open No. 15 and Japanese Patent Laid-Open No. 5-236315.

A conventional autofocus control method will be described with reference to FIGS. 4, 5 and 6.

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

When the sample 13 mounted 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 No. 2 is installed in the Z axis direction to focus, that is, to arrange the Z stage 15 at the in-focus position. The automatic focus adjustment is called autofocus control.

In the observation apparatus shown in FIG. 4, in order to execute the autofocus control, first, the Z stage 15 is returned to the AF origin position 24 (S201). The initial installation position of the Z stage that can execute auto focus is
It must 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). While moving the Z stage 15, the sample 1 sequentially obtained by the observation optical unit 22
The image of No. 3 is picked up by the CCD camera 17, and the contrast data of the video signal obtained by the CCD camera 17 is sampled by the image processing section 18 (S203). The control unit 23 detects the position of the Z stage 15 where the contrast becomes the peak 27 as the focus position 25 based on the contrast data sampled by the image processing unit 18 (S204). Then, the control unit 23 drives the stepping motor 16 to set the Z stage 15 at the detected focus position 25 (S20).
5).

The detection accuracy of the in-focus position of the Z stage deteriorates when the capture range of the autofocus is widened, and conversely,
In order to improve the precision of the in-focus position, it is necessary to narrow the capture range of autofocus. Therefore,
Usually, the accuracy of the focusing position required is different between the case of using a low-magnification objective lens of approximately 5 to 10 times and the case of using a high-magnification objective lens of 50 times or more, so the capture range of autofocus is different. Is different. That is, when a low-magnification objective lens is used, since the depth of focus is large, accuracy of the in-focus position is not so required. Therefore, the autofocus capture range is 25 to 75 μm.
The Z stage is moved largely up and down, and the brightness level is roughly calculated to detect the in-focus position (hereinafter, the execution mode of the autofocus control is referred to as a coarse movement mode). Further, when a high-magnification objective lens is used, the focus depth is required to be within ± 1 μm because the depth of focus is small. Therefore, in order to achieve this accuracy, the autofocus capture range is made as small as ± 6 μm, and the Z stage is slightly moved up and down to finely calculate the brightness level to detect the in-focus position ( Hereinafter, the execution mode of this autofocus control is referred to as a fine movement mode).

[0008]

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

In the fine movement mode in the conventional autofocus control method, the autofocus capturing range is ± 6 μm.
Since it is necessary to set it within the range, the uneven width of the sample surface is 2
It cannot cover 5 μm. That is, the in-focus position M can be accurately adjusted by the autofocus control in the fine movement mode.
0 is detected, the Z stage is installed at that position, and the observation point A
To observe. After that, the XY stage is moved to the observation point B.
Is located below the objective lens. Next, the fine focus mode autofocus control 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 when the observation point A is observed is the observation point B. This means that it is about 25 μm away from the in-focus position when performing. Therefore, even if the autofocus control in the fine movement mode is executed in order to observe the observation point B in the state where the Z stage is installed at the position N1, the initial position of the Z stage is the above-mentioned autofocus capture range (± 6μ
Since it is not within m), the focus position cannot be detected. Thus, there is a region on the sample surface where the autofocus control cannot be executed, and the operability was very poor.

When actually observing the observation point B, the operator manually places the Z stage in the autofocus capturing range, that is, within ± 6 μm from the in-focus position when observing the observation point B. Then, the auto focus control was executed again. This operation procedure has a problem that workability, throughput, etc. are significantly reduced. Further, the difficulty in returning the AF origin position of the Z stage by this operator increases as the magnification of the objective lens used increases.

[0011]

In order to solve the above problems, in the autofocus control method of the present invention, the objective lens is moved up and down within a first moving range which is larger than the uneven width of the surface to be observed. While the image of the observation target is taken by the image pickup device, the contrast data is calculated by the image processing device by the image, the first in-focus position is detected based on the contrast data, and the objective lens is installed at that position. The coarse focus mode autofocus control is performed, and subsequently, the observation target is moved by the imaging device while moving the objective lens from the first focus position within a second movement range that is smaller than the uneven width of the observation target surface. Image is captured, an image processing device calculates the contrast data from the image, and the second focus position is detected 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 affected by the magnification of the objective lens, but if the uneven width of the surface of the observation object is about ± 25 μm, it is about 25 to 75 μm. And Further, the range of movement of the objective lens in the autofocus control in the fine movement mode is also influenced by the magnification of the objective lens, but if the detection accuracy of the in-focus position is required to be within ± 1 μm, then 3 Approximately 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 observation target is not moved for a certain period of time or longer, the autofocus control may be automatically executed.

[0015]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, one embodiment of the present invention will be described in detail with reference to the drawings.

The autofocus control method of this embodiment is
It is most suitable when it is performed when the unevenness width of the sample surface to be observed is larger than the autofocus capture range necessary to obtain the required precision of the in-focus position. As the control procedure, first, the first autofocus control (coarse movement mode) is performed in which the autofocus capturing range is set larger than the uneven width of the sample surface to roughly detect the in-focus position.
Next, the Z stage is set at the in-focus position detected by the first auto-focus control, and the second auto-focus control (fine movement mode) for detecting the in-focus position with high accuracy is set by using the Z stage as the AF origin position. It is to do.

The structure of the observation apparatus in which the autofocus control method of this embodiment is executed is the same as the structure of the general observation apparatus in which the conventional autofocus control shown in FIG. 4 is performed. Since only the procedure is different, detailed description thereof will be omitted. However, hereinafter, the reference numbers given to the configuration of the observation apparatus shall use the numbers given in FIG.

FIG. 1 is a flow chart showing the control procedure of this embodiment, and FIG. 2 is a diagram for explaining the operation of this embodiment. FIG. 1 (a) shows the operation of the fine focus mode autofocus control. FIG. 9B is a diagram showing an operation of autofocus control in a fine movement mode.

It is assumed that a high-magnification objective lens is installed on the Z stage and an arbitrary observation point on the sample surface is observed using this objective lens. First, the first autofocus control (coarse movement mode) (S10) is executed. That is, after the Z stage 15 is returned 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), CCD
The camera 17 captures an image of the surface of the sample 13 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 focus position 2, and the Z stage 1 is set at the focus position 2.
5 is set (S104). Here, the Z that was initially set
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. Therefore, the Z stage 1 is manually operated again.
After returning 5 to the position within the autofocus capture range 3, the autofocus control is executed.

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

Therefore, next, the second autofocus control (fine movement mode) (S20) is executed. At this time, the autofocus control (S1
The Z stage 15 is set at the first in-focus position 2 detected by 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 up and down about 3 to 6 μm (S10
6) The CCD camera 17 captures an image of the surface of the sample 13 through the objective lens 12. Z stage 1 at this time
The moving range of 5 is a range smaller than the uneven width of the surface of the sample 13, and more specifically, it is desired in order to make the detection accuracy of the second focus position, which will be described later, a value according to the magnification of the objective lens 12. The value is within the auto-focus capture range of. 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 where the contrast reaches the peak 8 is detected as the second focus position 7, and the Z stage 15 is set at the focus position 7 (S).
107). Thus, finally, by performing the autofocus control (S20) in the fine movement mode, it is possible to detect the in-focus position with an accuracy within ± 1 μm required when the high-magnification objective lens 12 is used. You can

As described above, in this embodiment, first, in order to execute the autofocus control in the coarse movement mode, the Z stage is set to the AF origin as compared with the case where the autofocus control in the fine movement mode is executed from the beginning. The manual operation for returning to the position is greatly simplified. That is, even if the AF origin position where the Z stage should be set manually exceeds ± 6 μm from the in-focus position to some extent, the in-focus position can be detected.

Further, when the focus position is detected once and the Z stage is set at that position, the sample is moved by the XY stage to observe other observation points on the sample surface. When the uneven width of the surface is about ± 25 μm, the autofocus control in the coarse movement mode is first performed, so that the autofocus control can be performed for all the regions of the sample surface. That is, since the moving range of the Z stage (in other words, the autofocus capturing range) is as wide as 25 to 75 μm, if the uneven width of the sample surface is within this autofocus capturing range,
The position of the Z stage that maximizes the contrast can be detected without fail. Therefore, the in-focus position can be detected for all the areas on the sample surface.

As a result, if autofocus control can be executed for one point on the surface of the sample to detect the in-focus position, even if the sample is moved by the XY stage and the observation point is changed, nothing else happens. Without processing
Autofocus 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 construction of an embodiment of the laser repair. The laser light 21 emitted from the laser oscillator 9 is shaped by a processing optical system 10 including a beam expander and a variable slit. After being reflected by the dichroic mirror 11, it passes through the objective lens 12 and is irradiated onto the surface of the substrate 13. A wiring pattern made of a conductive material 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 light 21 is
Since a considerably high precision is required, a high magnification, for example, 8
It is necessary to position the irradiation position of the laser light 21 while observing the surface of the substrate 13 using the objective lens 12 of about 0 times. Therefore, by applying the autofocus control method of the present invention, the substrate 13 can be accurately and rapidly processed.
The surface of can be observed. Since the observation method by the autofocus control has already been described, the description will not be repeated here intentionally.

After focusing on 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 by the CCD camera 17 through the objective lens 12 is displayed on the display 20. While observing the displayed image, the substrate 13 is moved by the XY stage 14 to determine the irradiation position of the laser light 21. Here, in this embodiment, once the in-focus position is detected, it is not necessary to manually return the Z stage 15 to the AF origin position in all the areas on the substrate 13, and the auto focus control is performed. In order to be able to carry out the first observation point laser light 21
It is not necessary to set near the irradiation position of. Also, the substrate 13
Even when laser repair is performed on a plurality of positions above, autofocus control can be performed without returning the Z stage 15 to the AF origin position by manual operation every time the irradiation position of the laser light 21 is changed. As it is executed, the operability is greatly improved.

Further, if 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. There is no need for the operation to start.

The apparatus to which the autofocus control method of the present invention is applied is not limited to the above laser repair, and the surface of the sample is processed in order to process the sample moving by the XY stage by some means. The effect is exhibited by being applied to an apparatus that requires highly accurate observation.

The detection of the in-focus position and the like has been described with reference to the position of the Z stage, but this may be considered with reference to the position of the objective lens that moves up and down as with 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, the autofocus control can be easily executed. In particular, when using a high-magnification objective lens, it is necessary to detect the in-focus position with high accuracy.
The autofocus capture range must necessarily be small. However, by performing the autofocus control in the coarse movement mode first as in the present invention, the autofocus capturing range can be expanded without lowering the detection accuracy of the in-focus position, and the operability is dramatically improved.

[Brief description of 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, in which (a) is
It is a figure explaining the operation of the autofocus control of the coarse movement mode, and (b) is a figure explaining the operation of the autofocus control of the 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 showing a configuration of a general observation device in which autofocus control is performed.

FIG. 5 is a flowchart showing a conventional autofocus control procedure.

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

FIG. 7 is a diagram illustrating a problem of conventional autofocus control.

[Explanation of symbols]

 1 First AF origin position 2 First in-focus position 3 Auto focus capture range (for coarse movement mode) 4 Auto focus capture range (fine movement mode) 5, 8 (Contrast) peak 6 Second AF origin position 7 Second Focus Point 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 Controller 20 Display

Claims (7)

[Claims] 1. A first device which is larger than a width of irregularities on a surface to be observed.
While moving the objective lens up and down within the movement range of, the image of the observation object is captured, the first focus position is detected based on the contrast data obtained by the image,
A first step of installing the objective lens at that position; and the observation while moving the objective lens within a second movement range smaller than the uneven width of the observation target surface from the first focus position. A second step of picking up an image of an object, detecting a second in-focus position based on the contrast data obtained by the image, and installing the objective lens at that position. Control method. 2. The second moving range is within a capture range determined based on the accuracy of the second in-focus position defined by the magnification of the objective lens. 1. The autofocus control method described in 1. 3. The uneven width of the observation surface is at least ± 2.
5 μm or more, the first moving range is a value selected from the range of 25 to 75 μm based on the magnification of the objective lens, and the second moving 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 the 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 time when the observation target is stationary is measured, and when the measured time reaches a preset time,
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 object placed on the XY stage through the objective lens, and an image pickup device provided 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 based on the contrast data calculated by the image processing device. In the observation device including a control device that installs the objective lens on the observation target of the observation target while moving the objective lens up and down in a first movement range that is larger than the uneven width of the surface of the observation target. An image is taken, and the first focus position is determined based on the contrast data calculated by the image processing device based on the image. Then, after the objective lens is installed at that position, the image pickup device is used to move the objective lens from the first focus position in a second movement range smaller than the uneven width of the observation target surface. An image of an observation target is picked up, a second focus position is detected based on contrast data calculated by the image processing device based on the image, and the objective lens is installed at that position. Observation device. 7. The observation target is placed on an XY stage, and means for measuring the time during which the observation target is not moved by the XY stage, and the measured time are preset. When the time is reached,
The observation apparatus according to claim 5, wherein the movement of the objective lens within the first movement range is automatically started.