JP4418205B2 - Autofocus method - Google Patents

Description

The present invention relates to autofocus how put the plate-like device under test to the apparatus for inspecting the imaging means such as a CCD camera.

Conventionally, the reflected light from the object to be inspected is divided into three or more light beams, a light detector is provided for each of the divided light beams, and the light detectors are arranged so that the focus positions are different from each other. An autofocus device is known in which the depth of focus of the device is increased by the sum of the signals from (see, for example, Patent Document 1).
In addition, a first image sensor for displaying an image of the object to be inspected, and second and third image sensors that are arranged at an equal distance from each other in the focus direction with respect to the first image sensor. By moving the first to third imaging elements relative to the object to be inspected to positions where the variances of the data relating to the brightness of the object to be inspected obtained by the second and third imaging elements become equal, the first There is known an autofocus device in which the image pickup device is set at an optimum focus position with respect to an object to be inspected (see, for example, Patent Document 2).
Japanese Patent Laid-Open No. 3-12827 JP-A-4-260015

  In the above-described conventional autofocus device, the focus detection light detector or image sensor and the image display or other (photographing) light detector or image sensor are functionally independent, and a pair of focus detection light beams. Since a photodetector and an image sensor for image display are installed at an intermediate position in the focus direction of the detector and the image sensor, the photodetector and the image are picked up due to changes in the temperature environment where the device is placed. If the initial mounting position of the element causes a misalignment in the focus direction, the optimum focus position obtained by the photodetector for focus detection or the image sensor, the photodetector for image display, or the inspected object of the image sensor There is a case where the optimum focus position for does not match. In this case, in order to adjust the optical detector for image display and the image sensor to the optimum focus position with respect to the object to be inspected, the moving direction of whether to move or adjust them toward or away from the object to be inspected is unknown. Therefore, the optical detector and image sensor for image display and the optical detector and image sensor for focus detection are simultaneously inspected from the optimum focus position obtained by the optical detector and image sensor for focus detection. It has to be moved back and forth with respect to the body to check the optimum focus position of the image display photodetector and image sensor, and there is a problem that it takes time to detect the optimum focus position.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an autofocus method with a simple structure that can quickly adjust an imaging unit to an optimum focus position with respect to an object to be inspected. .

The present invention is characterized by the following points in order to solve the above problems.
That is, an autofocus method according to a first aspect of the present invention is a first imaging unit that faces the object to be inspected, and is disposed at a position spaced apart from the first imaging unit by a certain distance in the focus direction and faces the object to be inspected. Second imaging means, an optical system for guiding reflected light from the object to be inspected to the first imaging means and the second imaging means, and image data of the first imaging means and the second imaging means Based on the control means for obtaining the dispersion of the data relating to the brightness of the object to be inspected, and operated by a command of the control means, the first imaging means, the second imaging means and the optical system in the first imaging using the automatic focusing device provided with a driving means for moving means or the focusing direction of the second imaging means, combining said first image pickup means or the second image pickup means to the optimum focus position for the object to be inspected auto In Okasu method,
After obtaining the maximum value of the data relating to the brightness obtained based on the image data of the first imaging means and the second imaging means in at least one set location of the inspection object, the first imaging means The first imaging means or the second imaging means is moved to a position in the focus direction where the data relating to the brightness obtained based on the image data of the second imaging means becomes equal, and the first imaging means The first imaging unit, the second imaging unit, and the second imaging unit from the set location to the examination location of the object to be inspected while maintaining the same brightness data obtained based on the image data of the second imaging device. After moving the optical system relative to the object to be inspected,
Either one of the first imaging means or the second imaging means is used as an imaging imaging means, and the optimum focus position is the fixed distance with the first imaging means and the second imaging means separated in the focus direction. It is characterized in that it is moved in the direction approaching the object to be inspected by 1/2.

An autofocus method according to a second aspect is the autofocus method according to the first aspect , wherein the autofocus method is obtained based on image data of the first imaging means and the second imaging means at the inspection location of the object to be inspected. Further, the first imaging means or the second imaging means on the side moving so as to approach the position in the focus direction where the data regarding brightness is equal is used as the imaging means for photographing.

The present invention has the following excellent effects.
According to the autofocus method of the first aspect, since one of the two imaging units also serves as the imaging unit for imaging, the conventional imaging unit for focus detection and the imaging unit for imaging are separate. As described above, it is not necessary to determine the focusing direction of the imaging means for photographing caused by a mechanical position shift due to a change in the time between the imaging means for focus detection and the imaging means for photographing. Can be done.

In addition, when moving each imaging means to the inspection location of the inspected object, each imaging means follows the focus direction so that the surface of the inspected object is always at the center of the optimum focus position of each imaging means. Since it is moved, the imaging means can be focused at the inspection location in a short time, and the inspection object can be inspected quickly and reliably in the optimum focus state.

According to the autofocus method of the second aspect , in order to maintain the state where the surface of the object to be inspected is located at the center of the optimum focus position of each imaging means at the inspection location, the imaging means is moved in the focus direction. In addition, since the moving-side imaging means is used as the imaging imaging means so as to approach the surface of the object to be inspected, each imaging means is placed on the surface of the object to be inspected after the state of being positioned at the center is completed. It is not necessary to move again for focusing, and the imaging means can be moved to the optimum focus position in a short time.

Hereinafter, an autofocus device according to an embodiment of the present invention will be described with reference to the accompanying drawings.
1 to 3, reference numeral 1 denotes an inspection apparatus for inspecting a flat plate-like object W provided with an autofocus device 2 according to an embodiment of the present invention. The inspection apparatus 1 includes a table 4 horizontally supported by a gantry 3 and an X-axis beam portion 5b at the upper end of a pair of legs 5a and 5a erected at both ends in the X-axis direction x of the table 4. Are connected to each other, and a portal-shaped X-axis frame 5 provided so as to straddle the flat plate-like object W placed on the table 4, and the X-axis beam portion 5 b of the X-axis frame 5 in the X-axis direction and an X-axis slider 6 that supports the autofocus device 2 on the front surface side.
The X-axis frame 5 is supported by two guide rails 7, 7 whose legs 5 a, 5 a are arranged along the Y-axis direction y at both ends in the X-axis direction x of the table 4. A ball nut (not shown) fixed to the lower ends of 5a and 5a is disposed between the guide rails 7 and 7 and screwed into the ball screw 8, and is installed on the table 4 as a Y-axis drive motor (Y-axis). When the ball screw 8 is rotated by a drive device 9, it is moved in the Y-axis direction y.
The X-axis slider 6 has upper and lower end portions in the Z-axis direction z on a pair of guide rails 10, 10 provided along the X-axis direction x on the upper and lower end portions in the Z-axis direction z of the X-axis beam portion 5b. A ball nut (not shown) that is supported and fixed to the rear surface (rear surface) is screwed into a ball screw 11 disposed between the guide rails 10 and 10 along the X-axis direction x, and the ball screw 11 is It is moved in the X-axis direction x by being rotated by an X-axis drive motor (X-axis drive device) 12 fixed to one end portion (right end portion in FIG. 1) of the axial beam portion 5b.

  The autofocus device 2 is supported by a pair of guide rails 6a, 6a provided on the front surface of the X-axis slider 6 along the Z-axis direction z, and is fixed to the X-axis slider 6 (Z-axis drive). Device) Z-axis slider 15 provided movably in the Z-axis direction z by a screw mechanism composed of a ball screw 14 and a ball nut rotated by 13, and a front surface of Z-axis slider 15 along Z-axis direction z. It is supported by a pair of guide rails 16 and 16 and is moved in the Z-axis direction z by a screw mechanism comprising a ball screw 18 and a ball nut rotated by a focusing motor (driving means) 17 fixed to the Z-axis slider 15. A freely provided focus head 19 is provided. The screw pitch of the ball screw 18 is set to be smaller than the screw pitch of the ball screw 14, and the focus head 19 can be finely moved in the Z-axis direction z rather than the Z-axis slider 15.

The focus head 19 is attached to the base 19a in the interior thereof with a predetermined interval in the X-axis direction x, with the optical axis aligned with the Z-axis direction z, and with the objective lens side facing the inspected object W side. The first imaging unit 20 and the second imaging unit 21 such as a CCD camera, and the reflected light B from the surface of the object W to be inspected are received and both sides in the X-axis direction x (left and right sides in FIG. 2) The beam splitter 22 is divided and sent, and the light sent from the beam splitter 22 is reflected to the opposite side (upper side in FIG. 2) of the inspected object W in the Z-axis direction z. A pair of reflecting mirrors 23 a and 23 b inclined in opposite directions to be received by the imaging means 20 and 21, and an objective lens 24 for guiding the reflected light B to the beam splitter 22.
The first imaging means 20 and the second imaging means 21 use the same CCD camera having a focal depth of several μm (preferably around 2 μm, in this example 1.72 μm), and the first imaging means 20 A position separated by a certain distance L in the Z-axis direction z (focus direction perpendicular to the surface of the object W to be inspected) with respect to the second imaging means 21 (in the example of FIG. 2, the first imaging means 20 is the second imaging means 20). Are separated in the direction lower than the imaging means 21 of the image pickup device 21). The fixed distance (separation distance) L is preferably several tens of μm, and is set to 20 μm in this example. The fixed distance L is a distance included in a numerical range obtained by adding or subtracting the depth of focus of the first and second imaging means 20 and 21 to the set numerical value.
The beam splitter 22, the reflecting mirrors 23a and 23b, and the objective lens 24 constitute an optical system 25 for guiding the reflected light B from the object W to the first and second imaging means 20 and 21.

  Further, as shown in FIG. 3, the control device 26 of the inspection apparatus 1 including the autofocus device 2 converts the analog image signals obtained by the first and second imaging means 20 and 21 into digital signals A. / D converters 27a and 27b, image memories 28a and 28b for storing image data of digital signals output from the A / D converters 27a and 27b, and image data stored in the image memories 28a and 28b. An image processing unit 29 that reads and creates data relating to the brightness in the image of the object W from the image data, and calculates the variance of the data relating to the brightness based on the data obtained by the image processing unit 29 Then, an arithmetic processing unit 30 for obtaining the maximum value, and an operation based on an output from the arithmetic processing unit 30, the Y-axis drive motor 9, the X-axis drive motor 12, the Z-axis drive motor 13, Motor controller 31 for operating the focus motor 17; input means 32 for setting and inputting a command necessary for operating the control device 26; a program for operating the control device 26; and various settings input by the input means 32 And a memory 33 in which numerical values, data obtained by the calculation means, and the like are registered. The A / D converters 27a and 27b, the memories 28a and 28b, the image processing unit 29, the arithmetic processing unit 30, and the like constitute a focus control device (control means) 34 that calculates dispersion of data relating to the brightness of the object W to be inspected. is doing.

Next, an autofocus method using the autofocus device 2 together with the operation of the autofocus device 2 having the above-described configuration will be described with reference to FIGS.
First, as shown in FIG. 4, the initial position of the focus head 19 in the Z-axis direction z is set by a teaching operation (step S1). The Y-axis drive motor 7 and the X-axis drive motor 12 are operated, the focus head 19 is moved in the X and Y axis directions x and y, and the objective lens 24 is placed and fixed on the table 4. The inspection object W is moved above one arbitrarily selected set point (teaching position) in the plane direction. Then, after the Z-axis drive motor 13 is operated in accordance with the thickness of the object W to be inspected and the focus head 19 is lowered to a predetermined height in the Z-axis direction z, the focus motor 17 is operated and the teaching is performed. At the position, the focus head 19 is lowered toward the surface of the inspection object W at a constant fine speed, and the focus position search processing operation by the first and second imaging means 20 and 21 is performed.

  In this search processing operation, the image data obtained from each imaging means 20, 21 is converted into a digital signal via each A / D converter 27a, 27b of the focus control device 34 and stored in the image memories 28a, 28b. Corresponding to the focus position Z (see FIG. 5) in the Z-axis direction z of the focus head 19 detected by a Z-axis encoder (focus position detector) 17a (see FIG. 3) provided in the focus motor 17 is stored. The Then, the image data for each focus position of the focus head 19 stored in the image memories 18a and 28b is read by the image processing unit 29, and the surface of the object W to be inspected from the image data by the image processing unit 29. Data on the brightness of the is created. Thereafter, the variance of the data relating to the brightness is calculated by the arithmetic processing unit 30, and the maximum value is obtained as the optimum focus position with respect to the surface of the object W to be inspected of the imaging means 20 and 21.

The data relating to the brightness is obtained by processing the image data of the object W to be inspected at each focus position Z in the Z-axis direction z obtained by the imaging units 20 and 21 by the image processing unit 29, and Data obtained by quantifying the contrast difference between a bright part and a dark part existing in the image (hereinafter referred to as a focus value (AFV)). Further, as shown in FIG. 5, the variances a and b of the brightness data (AFV) obtained based on the image data of the imaging means 20 and 21 are determined by the respective imaging means 20 and 21 in the focus direction (Z-axis). In the z-axis direction z focus positions Z1 and Z2 indicated by the numerical values of the encoder 17a of the focus motor 17, the sizes are respectively separated in the direction z) by the fixed distance L (offset). The maximum (AFVmax) appears, and the focus positions Z1 and Z2 are the optimum focus positions of the imaging means 20 and 21, respectively. The difference between the focus position Z2 and the focus position Z1 in the Z-axis direction z coincides with a certain separation distance L set in the focus direction of the first imaging unit 20 and the second imaging unit 21.
A focus position (initial focus setting position) Zo at which the difference between the AFVs based on the respective imaging means 20 and 21 obtained as described above becomes zero is calculated by the arithmetic processing unit 30 to obtain the initial focus. The focus head 19 is moved to the set position Zo by the operation of the focus motor 17. As shown in FIG. 6, the initial focus setting position Zo is in a state where the optimum focus positions Z1 and Z2 of the imaging means 20 and 21 sandwich the object to be inspected W at the center thereof.

  Next, the focus head 19 is moved from the teaching position by moving the X axis slider 6 in the X and Y axis directions x and y by the X and Y axis drive motors 12 and 9 by the following operation (step S2). The surface of the object W to be inspected is translated horizontally to the actual measurement location (inspection location) to be inspected. During this movement, each data (AFV) relating to the brightness obtained based on the image data of each imaging means 20, 21 is created by the image processing unit 29. At that time, when the object to be inspected W is tilted upward as shown in FIG. 7, for example, the data (AFV) relating to the brightness obtained based on the image data of the imaging means 20 and 21 are different from each other. Therefore, the focus head 17 moves the focus head 19 upward in FIG. 7 so that the difference between the AFVs is calculated by the arithmetic processing unit 30 and the difference becomes zero. The state where the optimal focus positions Z1, Z2 of 21 hold the object W to be inspected at the center is maintained. When the object to be inspected W is tilted in the opposite direction, the focus head 19 is moved downward to a position where the difference between the AFVs is zero, and when the object to be inspected W is not tilted, The focus head 19 does not move in the Z-axis direction z and maintains the initial focus setting position Zo at the teaching position, and the optimum focus positions Z1 and Z2 of the imaging means 20 and 21 are always in the center as described above. A state in which the object W is sandwiched is maintained.

  Next, when the surface of the inspected object W is inspected at the actual measurement location by the detailed search operation (step S3), one of the imaging means 20 and 21 is used for imaging on the surface. Focusing is performed as an imaging means. In this case, since the optimum focus positions Z1 and Z2 of the imaging means 20 and 21 exist at the equidistant focus positions Z above and below the subject W, the focus directions of the imaging means 20 and 21 are present. By moving the focus head 19 up or down in the Z-axis direction z by half of the mutual separation distance L at, each optimum focus position Z1 (Z2) is quickly and reliably aligned with the surface of the inspection object W. be able to. In this way, it is possible to accurately inspect the state of a defect or the like on the surface of the inspection object W by the one imaging means 20 (21) for focusing which is focused on the surface of the inspection object W.

In the follow-up operation (step S2), the optimum focus positions Z1 and Z2 are inspected while the object W is sandwiched between the optimum focus positions Z1 and Z2 of the imaging means 20 and 21. The imaging means 20 (21) moving to the side closer to the body W is selected as the imaging imaging means (first imaging means 20 in FIG. 7), and the optimum focus position Z1 (Z2) thereof is the inspection object. When the movement of the focus head 19 is continued until the surface of the body W coincides with the surface of the body W, the inspection object W is positioned at the center of the optimum focus positions Z1 and Z2 of the imaging means 20 and 21 ( The focus head 19 is focused on the surface of the inspection object W after the optimum focus positions Z1 and Z2 are in a state in which the surface of the inspection object W is positioned and sandwiched between them. Therefore, it is not necessary to move the focus head 19 again, so that the time required for acceleration / deceleration during the movement of the focus head 19 is small, and the imaging means 20 (21) is moved to the optimum focus position Z1 (Z2) in a short time. The inspection object W can be inspected.
When the detailed search operation (step S3) completes the focusing operation (autofocus operation) and the inspection with respect to the surface of the inspection object W of each imaging means 20, 21 at one actual measurement location of the inspection object W, Whether or not there is another measurement location to be inspected in the inspected object W (whether or not the focus head 19 is moved to the next measurement location) is determined by the arithmetic processing unit 30 from the registered contents of the memory 33 ( Step S4) If there are other measurement points to be measured, the operations of steps S2 and S3 are repeated, and then the focusing operation and the inspection for all the measurement points on the surface of the object W to be inspected are completed.

  According to the autofocus device 2 according to the above-described embodiment, the first imaging unit 20 facing the object to be inspected W, and the first imaging unit 20 with the constant distance L in the Z-axis direction (focus direction) z. Second imaging means 21 arranged at a distance from the object to be inspected W and the reflected light B from the object to be inspected W are guided to the first imaging means 20 and the second imaging means 21. An optical system 25, a control unit 34 for obtaining dispersion of data AFV relating to the brightness of the object W to be inspected based on image data of the first imaging unit 20 and the second imaging unit 21; A driving unit 17 that is operated by a command and moves the first imaging unit 20 or the second imaging unit 21 and the optical system 25 in the focus direction z of the first imaging unit 20 or the second imaging unit 21; It is configured with Therefore, since one of the two image pickup means 20 and 21 also serves as an image pickup means, the conventional autofocus image pickup means and the image pickup image pickup means are prepared separately as in the apparatus. It is not necessary to determine the focusing direction of the photographing imaging means caused by a mechanical positional shift caused by a change in the autofocus imaging means and the photographing imaging means with time, and the autofocus operation can be performed in a very short time.

  According to the autofocus method according to the embodiment, the brightness obtained based on the image data of the first imaging means 20 and the second imaging means 21 in at least one set location of the object W to be inspected. After the maximum value AFVmax of the data AFV is obtained by the control means 34, the position in the focus direction at which the data AFV relating to the brightness obtained based on the image data of the first imaging means 20 and the second imaging means 21 becomes equal. In addition, the first imaging means 20 or the second imaging means 21 is moved, and the brightness data AFV obtained based on the image data of the first imaging means 20 or the second imaging means 21 is equal. The first imaging means 20 or the second imaging means 21 is relatively moved in parallel with the inspection object to other inspection locations of the inspection object W while maintaining After that, the first imaging means 20 or the second imaging means 21 is moved in a direction approaching the object to be inspected by ½ of the fixed distance L separated in the focus direction. When the imaging means 20 and 21 are moved to the measurement location (inspection location) of the inspection subject W, the surface of the inspection subject W is always positioned at the center position Zo of the optimum focus positions Z1 and Z2. Since the focus head 19 (each imaging unit 20, 21) is moved following the Z-axis direction (focus direction) z, each imaging unit 20, 21 can be focused in a short time at the measurement location. , 21 is used as an imaging means for photographing, and the inspection object W can be inspected in the optimum focus state.

In the inspection device 1 according to each of the above embodiments, the X-axis frame 5, the X-axis slider 6, the Z-axis slider 15, and the focus head 19 are respectively ball screws 8, 11, A drive device is used in which the drive motors 9, 12, 13, and 17 are rotated by drive motors 9, 12, 13, and 17 to move relative to the object W in the X, Y, and Z axis directions x, y, and z. Not limited to this, a linear motor driving device or other driving means may be used as the X, Y, Z axis driving device.
In the autofocus device 2, the focus head 19 is attached to the X-axis slider 6 via the Z-axis slider 15, and the focus head 19 is moved in the Z-axis direction (focus direction) by the Z-axis drive motor 13 and the focus motor 17. ), The Z-axis slider 15 and the Z-axis drive motor 13 are omitted, and the focus head 19 is directly supported by the X-axis slider 6 in the Z-axis direction z. You may make it move.

It is a perspective view showing an inspection device provided with an autofocus device concerning a 1st embodiment of the present invention. It is a front view which shows the principal part of the auto-focus apparatus which concerns on the 1st Embodiment of this invention. FIG. 2 is a control block diagram of the autofocus device according to the first embodiment of the present invention. It is an operation | movement flowchart of the autofocus apparatus which concerns on the 1st Embodiment of this invention. It is a diagram which shows dispersion | distribution of the data regarding the brightness of a to-be-inspected object based on the image data of an imaging means. It is explanatory drawing which shows the initial setting state of the focus position with respect to a to-be-inspected object at the time of teaching operation | movement of an imaging means. It is explanatory drawing which shows the setting state of the focus position with respect to the to-be-inspected object at the time of the tracking operation | movement of an imaging means. .

Explanation of symbols

2 Autofocus device 4 Table 5 X-axis frame 6 X-axis slider 12 X-axis drive motor (X-axis drive device)
13 Z-axis drive motor (Z-axis drive device)
15 Z-axis slider 17 Focus motor (drive means)
DESCRIPTION OF SYMBOLS 19 Focus head 20 1st imaging means 21 2nd imaging means 22 Beam splitter 23a, 23b Reflector 24 Objective lens 25 Optical system 29 Image processing part 30 Arithmetic processing part 34 Focus control apparatus (control means)
B Reflected light L Fixed distance W Inspected object

Claims (2)

A first imaging means facing the object to be inspected; a second imaging means disposed at a position spaced apart from the first imaging means by a fixed distance in the focus direction; and facing the object to be inspected; Data relating to the brightness of the object to be inspected based on the optical system for guiding the reflected light from the first imaging means and the second imaging means and the image data of the first imaging means and the second imaging means And a control means for obtaining the dispersion of the first and second imaging means, and the optical system is moved in the focus direction of the first imaging means or the second imaging means. In an autofocus method using an autofocus device provided with a driving means for adjusting the first imaging means or the second imaging means to an optimum focus position with respect to an object to be inspected,
After obtaining a maximum value of data relating to brightness obtained based on the image data of the first imaging means and the second imaging means at at least one set location of the object to be inspected, the first imaging means And the first imaging means or the second imaging means are moved to a position in the focus direction where the brightness-related data obtained based on the image data of the second imaging means is equal to the first imaging means. The first imaging unit, the second imaging unit, and the second imaging unit from the set location to the examination location of the object to be inspected while maintaining the same state of the brightness data obtained based on the image data of the second imaging device. After moving the optical system relative to the object to be inspected,
Either one of the first imaging unit or the second imaging unit is used as a photographing imaging unit, and the optimum focus position is the fixed distance with the first imaging unit and the second imaging unit separated in the focus direction. The autofocus method is characterized in that it is moved in a direction approaching the object to be inspected by 1/2 of the above. At the inspection location of the object to be inspected, on the side that moves closer to the position in the focus direction where the data on the brightness obtained based on the image data of the first imaging means and the second imaging means are equal. 2. The autofocus method according to claim 1 , wherein the first image pickup means or the second image pickup means is used as an image pickup image pickup means.

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