JP4875354B2 - Autofocus device and autofocus method - Google Patents

Description

The present invention relates to an autofocus device and an autofocus method for an object to be measured, and more specifically, at least two or more projection patterns having different imaging positions in the optical axis direction of an objective lens on the object to be measured. The present invention relates to an autofocus apparatus and an autofocus method which are controlled so that the contrast difference of a projected image in the above range is within a predetermined range, and have a simple configuration and realize high-speed autofocus.

Conventionally, in an autofocus device using a contrast method, a first image sensor for displaying an image of an object to be measured, and a second image sensor arranged at an equal distance from the first image sensor in the focus direction, A third image sensor, and the first to third image sensors are moved relative to the object to be measured at positions where the variances of data relating to the brightness of the object measured by the second and third image sensors are equal. Thus, an autofocus device is known in which the first image sensor is set to the optimum focus position with respect to the object to be measured (see Patent Document 1).
On the other hand, there is known an autofocus device that includes a projection unit that projects a predetermined pattern on the measurement surface and a single observation optical system (CCD camera) in order to increase the contrast of the measurement surface of the object to be measured ( Patent Document 2).
JP-A-4-260015 Japanese Patent Laid-Open No. 9-304685

In the above-described prior art (Patent Document 1), the image sensor for focus detection and the image sensor for image display or the like are functionally independent, and are positioned at an intermediate position between the focus direction positions of the pair of image sensors for focus detection. Since image sensors for image display etc. are installed, if the initial mounting position of these image sensors is displaced in the focus direction due to changes in the temperature environment where the device is placed, etc. There is a case where the optimum focus obtained with the image pickup device does not coincide with the optimum focus position with respect to the object to be measured of the image display image pickup device.

In this case, in order to adjust the image sensor for image display to the optimum focus position with respect to the object to be measured, it is unclear whether the image sensor for photographing should be adjusted to move toward or away from the object to be measured. Therefore, the image sensor for photographing and the image sensor for focus detection are simultaneously moved back and forth with respect to the object to be measured from the optimum focus position obtained by the image sensor for focus detection. There was a problem that the focus position had to be confirmed, and it took time to detect the optimum focus position.

On the other hand, in the prior art (Patent Document 2), since the pattern image formation position and the focus position of the observation optical system (CCD camera) are the same, if the observation optical system moves relatively, the measurement surface of the object to be measured is moved. There is a possibility that the focus cannot be adjusted due to the influence of contrast.
In this method, when the object to be measured moves, if the measurement surface of the object to be measured is tilted or wavy, even if the focus is first adjusted at the measurement position, the focus is greatly shifted at the next measurement point. As a result, the direction of movement of the observation optical system for focusing is completely unknown, and there is a problem that the control speed of autofocus is slowed down.

The present invention has been made in view of the above circumstances, and an object thereof is to provide an autofocus apparatus and an autofocus method that have a simple structure and are intended to realize high-speed autofocus.

The present invention is characterized by the following points in order to solve the above problems.
That is, an autofocus device according to a first aspect of the present invention includes an imaging optical system having an objective lens that faces the object to be measured, and one imaging unit that captures an image of the object to be measured via the objective lens, and the imaging An autofocus device comprising: a drive mechanism that displaces an optical system in the optical axis direction of the objective lens; and a control unit that drives and controls the drive mechanism based on an image of the object to be measured captured by the imaging optical system A projection optical system for projecting two projection patterns onto the measurement surface of the object to be measured via the objective lens, and the imaging positions of the two projection patterns to be projected are both the imaging a upward or downward of the focus position of the optical system, wherein a different positions in a direction perpendicular to the optical axis and the optical axis of the objective lens, wherein, the two obtained by the imaging optical system Comparing the magnitudes of the contrasts of the projection images of the projection pattern, between the first imaging position where the contrast of one of the two projection images is maximum and the second imaging position where the contrast of the other is maximum Search operation means for controlling the displacement of the imaging optical system so that the measurement surface is located, and a focus for displacing the imaging optical system in one direction so that the position of the measurement surface matches the focus position of the imaging optical system And an operating means .

According to a second aspect of the present invention, there is provided an autofocus method for using the autofocus device according to the first aspect of the invention to focus the imaging optical system with respect to an object to be measured, wherein at least one set location of the object to be measured Is positioned directly below the objective lens, and the two projection patterns are projected onto the measurement surface, and the imaging means moves the imaging optical system along the optical axis direction while the two projection patterns The imaging optical system such that the setting portion is sandwiched between a step of obtaining each maximum value of data relating to brightness and an optical axis direction position of the objective lens corresponding to each maximum value. a step of the Before moving to the optical axis direction while maintaining a state where the setting portion is sandwiched between the optical axis position of the objective lens, the measurement point or from the setting position The imaging optical system, wherein the steps of Ru is relatively moved parallel to the object to be measured moves the imaging optical system in the focus position of the imaging optical system from a position on the optical axis of the imaging optical system at that time The process is performed sequentially .

The present invention has the following excellent effects.
According to the first aspect of the invention, two projection patterns having different imaging positions in the optical axis direction of the objective lens are automatically used so that the contrast difference of the projected image on the object to be measured falls within a predetermined range. By controlling, the optical distance between the surface of the object to be measured and the objective lens of the imaging means can be easily maintained within a predetermined range.

And since each image formation position of the two projection patterns is above or below the focus position of the imaging optical system, the imaging optical system is in the defocused state relative to the measurement surface of the object to be measured. The contrast between the two projection patterns on the surface can be acquired, and the optical distance between the imaging optical system and the measurement surface can be maintained within a predetermined range without being affected by the contrast of the measurement surface.

According to the invention of claim 2, the control of the displacement of the imaging optical system by the control means is executed while the object to be measured and the imaging optical system are relatively moving, The optical distance between the imaging optical system and the measurement surface can be maintained within a predetermined range by causing the imaging optical system to follow the undulation of the measurement surface of the object. Therefore, even when the measurement range is wide, autofocus can be executed at high speed.

Hereinafter, an autofocus device and an autofocus method according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.
First, FIG. 1 is a conceptual diagram showing an autofocus device according to an embodiment of the present invention. The autofocus device 1 automatically controls the focus on the object 7 to be measured, and particularly enables automatic control of the focus following the displacement of the measurement surface 7a accompanying the movement of the object 7 to be measured. The autofocus device 1 includes an imaging optical system 2, a projection optical system 3, an illumination optical system 4, a drive mechanism 5, and a control unit 6.

The imaging optical system 2 is provided, for example, above the XY stage 1a of the inspection apparatus, and images the measurement surface 7a of the measurement object 7 placed on the XY stage 1a , and faces the measurement surface 7a. In addition to an image pickup means (CCD camera) 9 that photoelectrically converts and outputs an image of the measurement surface 7a acquired via the lens unit 8 including the objective lens 8a and the imaging lens 8b arranged coaxially, and a lens A first half mirror 10 disposed above the unit 8 and separating an optical path of the imaging optical system 2 and an optical path of the projection optical system 3 described later, and provided between the half mirror 10 and the CCD camera 9 and separated by the half mirror 10. a first mirror 11 that deflected the light path to the CCD camera 9 side, is arranged between the objective lens 8a and the imaging lens 8b be described later and the optical path of the imaging optical system 2 and the projection optical system 3 And a second half-mirror 12 for separating the optical path of the illumination optical system 4. The photographing optical system 2 is provided on a base 14 that can be displaced in the optical axis direction of the lens unit 8 by a driving mechanism 5 described later.

The base 14 is provided with a projection optical system 3. This projection optical system 3 projects two projection patterns having the same shape with different imaging positions in the optical axis direction of the lens unit 8 onto the measurement surface 7a of the object 7 to be measured via the lens unit 8. The optical path from the second half mirror 10 through the lens unit 8 to the measurement surface 7a of the object 7 to be measured is made common with the optical path of the imaging optical system 2, and is separated by the second half mirror 10 and extends straight from the measurement surface 7a. First and second masks 15 and 16 each having the projection pattern formed thereon are arranged at different positions on the optical path. A pattern projection light source 17 is provided above the first and second masks 15 and 16.

Further, as shown in FIG. 2, the first and second masks 15 and 16 form a light-shielding film 26 in a region on one side obtained by dividing the rectangular transparent substrate 25 in the longitudinal direction. Circular projection patterns 26a and 26b that transmit light are formed substantially at the center. The masks 15 and 16 are arranged at positions shifted from each other in the lateral direction (direction perpendicular to the optical axis) so that the projection patterns 26a and 26b do not overlap in the optical axis direction. Further, the projection images Ia and Ib of the projection patterns 26a and 26b are respectively formed in the visual field of the CCD camera 9 at a predetermined distance in the horizontal direction as shown in FIG. Predetermined areas α and β including the projected images Ia and Ib in the field of view of the CCD camera 9 are set, and the areas α and β are used as areas for calculating contrast values.

Furthermore, the imaging positions (Z2, Z3) on the optical axis of the lens unit 8 of the projection patterns 26a, 26b of the masks 15, 16 are below the focus position Z1 of the CCD camera 9, as shown in FIG. And when the CCD camera 9 is in the focus position with respect to the measurement surface 7a, the image Ia3 of the projection image Ia of the first mask 15 and the projection image Ib of the second mask 16 are displayed. The image Ib3 is unfocused with respect to the measurement surface 7a.

Conversely, when the projection image Ia of the projection pattern 26a of the first mask 15 is imaged on the measurement surface 7a as the image Ia2, the image Ib2 of the projection image Ib of the projection pattern 26b of the second mask 16 is in the state of the unfocused to the measuring surface 7a, CCD camera 9 also becomes unfocused to the measurement surface 7a.
When the projection image Ib of the projection pattern 26b of the second mask 16 is imaged on the measurement surface 7a as the image Ib1, the image Ia1 of the projection image Ia of the projection pattern 26a of the first mask 15 is measured. in the state of the unfocused to the plane 7a, CCD camera 9 also becomes unfocused to the measurement surface 7a.

Therefore, with the CCD camera 9 unfocused with respect to the measurement surface 7a, the projection images Ia and Ib of the projection patterns 26a and 26b of the masks 15 and 16 are picked up by the CCD camera 9, and the projection images in the areas α and β are captured. By comparing the contrast values of Ia and Ib and displacing the imaging optical system 2 to a position where the magnitude relationship falls within a predetermined range (FIG. 6), the measurement surface 7a is not affected by the measurement surface 7a. It can be maintained between the imaging positions Z2 and Z3 of the projection patterns 26a and 26b.

Further, the base 14 is provided with an illumination optical system 4 for illuminating an inspection pattern or the like formed on the measurement surface 7a of the object 7 to be measured so that the CCD camera 9 can take an image. The illumination optical system 4 shares the optical path from the second half mirror 12 through the objective lens 8A to the measurement surface 7A with the optical path of the imaging optical system 2, and the optical axis of the imaging optical system 2 by the second half mirror 12. The second mirror 13 and the observation light source 18 are disposed on the optical path separated from the light source.

In addition, the base 14 is provided with a drive mechanism 5, which displaces the base 14 in the direction of the optical axis of the lens unit 8, and a moving mechanism 5 a that allows the base 14 to move, The motor 5b drives the moving mechanism 5a, and the motor 5b is driven by a motor driver 5c.

The CCD camera 9, the pattern projection light source 17, the Z-axis sensor 5 d for detecting the position of the lens unit 8 of the base 14 in the optical axis direction, and the motor driver 5 c are connected to the control means 6. The control means 6 calculates the contrast values of the areas α and β including the projection images Ia and Ib of the projection patterns 26a and 26b obtained by the CCD camera 9 independently. The contrast values are compared, and the motor 5b of the drive mechanism 5 is driven and controlled so that the difference between the contrast values is within a predetermined range. Two projection images acquired by the CCD camera 9 are controlled. An autofocus unit (hereinafter referred to as “AF unit”) 27 that controls the drive of the drive mechanism 5 based on the contrast of Ia and Ib, and a control PC 20 that issues various commands to the AF unit 27 are configured. Yes.

Here, the AF unit 27 converts the analog image information acquired by the CCD camera 9 into digital and outputs the digital image and the above-mentioned image information that has been digitally converted, and performs image processing on the areas α and β. Based on the data output from the image processing unit 22 that outputs data enabling comparison of the contrast values and the data output from the image processing unit 22, the difference between the contrast values of the areas α and β is calculated. Of the control PC 20 that outputs a control signal for driving the motor 5B, a motor controller 28 that controls the motor driver 5c based on the control signal, and the control PC 20 via the control unit 23. And a light controller 19 for turning on / off the light source 15 for paran projection according to a command.

Next, the operation and autofocus method of the autofocus device having the above configuration will be described with reference to the flowchart of FIG.
First, in step S1 (first search operation), the driving means of the XY stage 1a of the measuring apparatus on which the object to be measured 7 is placed is driven to select one set position (teaching position) of the object 7 to be measured. ) So that it is positioned directly below the objective lens 8A.
Then, after the observation light source 18 and the CCD camera 9 of the illumination optical system 4 are operated, the motor 5b of the drive mechanism 5 is operated, and the base 14 is directed toward the surface of one selected setting location of the object 7 to be measured. Is lowered at a constant speed, and the first search processing operation for the focus position of the CCD camera 9 is performed.

In the first search processing operation, the surface of the set point is continuously provided by the CCD camera 9 while the base 14 is lowered at a constant slow speed toward the surface of the selected set point of the object 7 to be measured. The Z-axis of the base 14 is detected by the control unit 23 by the Z-axis direction position detector 5d of the base 14 through the A / D converter 21 and the image processing unit 22. A contrast value corresponding to the direction position (see FIG. 5) is calculated, and data relating to the brightness of the surface of the set location of the DUT 7 is created.

Thereafter, the distribution of the data relating to the brightness (FIG. 5) is further calculated from the data relating to the brightness of the surface of the set location of the object 7 to be measured, and the maximum value (AFVmax1) is further calculated. It is calculated | required as an optimal focus position with respect to the measurement surface 7a .
The data relating to the brightness is obtained by processing the image data of the measurement surface 7a of the measurement object 7 at each imaging position in the Z-axis direction of the base 14 obtained by the CCD camera 9 with the AF unit 27, and measuring the measurement object. It means data (hereinafter referred to as “AFV”) in which the contrast difference between the bright part and the dark part existing in the image of the object 7 is digitized.

Next, in step S2 (second search operation), after displacing the base 14 to the optimum focus position, the observation light source 18 is turned off, the pattern projection light source 17 is turned on, and the motor 5b of the drive mechanism 5 is turned on. , The base 14 is raised at a constant speed, and the second search processing operation of the second focus position by the masks 15 and 16 is performed.
In this second search processing operation, the projection pattern 26a of the masks 15 and 16 projected onto the measurement surface 7a of the DUT 7 by the CCD camera 9 while the base 14 is raised at a constant fine speed in the Z-axis direction. , 26b, the image data obtained by continuously photographing the areas α, β including the projected images Ia, Ib is transmitted to the base 14 in the control unit 23 via the A / D converter 21 and the image processing unit 22. A contrast value corresponding to the Z-axis direction position (see FIG. 6) of the base 14 detected by the Z-axis direction position detector 5d is calculated, and data relating to the brightness of the surface of the set location of the DUT 7 is obtained. Created.

Further, the distribution of the data (AFV) relating to the brightness of the areas α and β obtained based on the image data of the CCD camera 9 is such that the first mask 15 and the second mask 16 of the objective lens are as shown in FIG. The projections of the first mask 15 and the second mask 15 in the Z-axis direction indicated by the numerical values of the Z-axis direction position detector 5d of the base 14 in the relationship of being separated by the constant distance γ in the optical axis direction. At the image forming positions Z2 and Z3 of the patterns 26a and 26b, the maximum (AFVmax2) appears, and these Z2 and Z3 are the image forming positions of the first mask 15 and the second mask 16 . .

Next, the motor 5b of the drive mechanism 5 is operated to displace the base 14, and the measurement surface 7a of the object 7 to be measured is positioned between Z2 and Z3 .

Next, in step S3 (follow-up operation), the device to be measured 7 is moved by the driving means of the XY stage 1a of the measuring device so that the measurement location of the device to be measured 7 is located directly below the objective lens 8a. .
During this movement, the AFV unit 27 obtained based on the image data of the areas α and β of the CCD camera 9 is used, and the measured object 7 is tilted upward as shown in FIG. 8, for example. Since the AFVs obtained based on the image data of the areas α and β of the CCD camera 9 are different from each other (the AVF in the area α is larger than the AVF in the area β), the difference between the AFVs is the image. The motor 5b of the drive mechanism 5 is operated by an instruction from the control unit 23 so that the difference calculated by the processing unit 24 falls within a predetermined range, and the base 14 moves upward in FIG. The measurement surface 7a is maintained between the imaging positions Z2 and Z3 .

On the other hand, when the DUT 7 is inclined to the right, the AVF in the area α is smaller than the AVF in the area β, contrary to the above, and the base 14 is in the direction opposite to the above case. When the object 7 to be measured is not tilted, the base 14 is not moved in the Z-axis direction but is maintained at the initial position, and the measurement surface 7A of the object 7 to be measured is always at the imaging positions Z2 and Z3. Maintained during.

Further, in step 4 (detailed focus operation), in order to optimally focus the CCD camera 9 on the inspection pattern on the measurement surface 7a at the measurement location of the object 7 to be measured, first, the projection light source of the pattern projection means 3 is used. 17 is turned off, and then the illumination light source 18 of the illumination optical system 4 is turned on to irradiate the surface of the DUT 7 with illumination light.
Then, the base 14 is lowered toward the measurement surface 7a of the object 7 to be measured, and the focus position of the CCD camera 9A is adjusted to the surface of the pattern to be inspected.
In this case, since the measurement surface 7a of the object 7 to be measured is maintained between the imaging positions Z2 and Z3 , the base 14 is lowered toward the measurement surface 7a of the object 7 to be measured.

At that time, the image data of the surface of the pattern to be inspected on the measurement surface 7 a irradiated with the light from the observation light source 18 by the CCD camera 9 is continuously taken while the base 14 is lowered toward the measurement surface 7 a of the object 7 to be measured. Then, based on the image data, AFVmax1 is obtained in the same manner as in step S1 described above, and the base 14 is displaced to a position where AFVmax1 is obtained, so that the focus position of the CCD camera 9 can be measured more accurately. The operation of matching the surface 7a with the surface of the pattern to be inspected is completed.

In step 4, the measurement device 7 is maintained while the measurement surface 7a of the object 7 to be measured is maintained between the imaging positions Z2 and Z3 of the projection patterns 26a and 26b of the first mask 15 and the second mask 16. The XY stage 1a driving means moves the measured object 7 so that the measurement location of the measured object 7 is positioned directly below the objective lens 8A. Therefore, the measured object 7 is positioned directly below the objective lens 8A. Since the optical distance between the CCD camera 9 and the measurement surface 7a of the object 7 to be measured is measured by the Z-axis sensor 5d when the measurement location is located, the distance of the focus position of the CCD camera 9 is subtracted from that value. Accordingly, the surface of the pattern to be inspected on the measurement surface 7 a of the object to be measured 7 can be easily positioned at the optimum focus position of the CCD camera 9 by moving the base 14 closer to the object to be measured 7. Kill.

Furthermore, in step 5 (end operation), after the focusing operation (autofocus operation) and photographing of the CCD camera 9 at one measurement location of the object 7 to be measured, another measurement of the object 7 to be measured should be performed. Whether or not there is a location is determined from the command of the control PC 20, and when there are other measurement locations, after step 2 and step 3 are repeated, the focusing operation for all measurement locations of the object 7 to be measured is performed. Shooting ends.

According to the autofocus device 1 according to the above-described embodiment, the CCD camera 9 that captures an image of the object 7 to be measured via the objective lens 8a of the lens unit 8 that faces the object 7 to be measured, and the CCD camera 9 are provided. The drive mechanism 5 for displacing the objective lens 8a in the optical axis direction, the control means 6 for driving and controlling the drive mechanism 5 based on the image of the object 7 taken by the CCD camera 9, and the light of the lens unit 8 The projection optical system 3 for projecting the projection patterns 26 a and 26 b of the two masks 15 and 16 having different imaging positions in the axial direction onto the measurement surface 7 a of the object 7 to be measured is acquired by the control unit 6 with the CCD camera 9. The contrast levels of the two projection patterns 26a and 26b are compared, and the CCD camera 9 is displaced integrally with the base 14 so that the contrast relationship is within a predetermined range. For and has a configuration,
Since the AFV can be obtained without being influenced by the surface of the measurement surface 7a even while the object to be measured 7 is moving, the optical distance between the measurement surface 7a and the CCD camera 9 can be maintained within a predetermined range. Focus can be done quickly and accurately.

In the autofocus device 1 according to the present embodiment, the base 14 is displaced by the operation of the motor 5b of the drive mechanism 5, but the objective lens 8a of the lens unit 8 is measured on the measurement surface 7a of the object 7 to be measured. You may make it displace with respect to.
Moreover, although the projection pattern of the filters 15 and 16 is circular, the shape of the pattern may be a shape sufficient to achieve the object of the present invention, and the shape is not particularly limited.
In the autofocus method according to the present embodiment, the observation light source 18 is turned on or off in each step (S1 to S5), but the observation light source 18 is turned on in each step. In (S1 to S5), it may be constantly lit.
further,

It is a conceptual diagram which shows embodiment of the autofocus apparatus by this invention. It is explanatory drawing which shows the structural example of the two masks which formed the pattern for projection used for the said auto-focus apparatus. It is a conceptual diagram which shows the image on the to-be-measured object of the pattern for each projection of the said mask. It is explanatory drawing which shows the relationship between each image formation position of each pattern for projection of the said mask, and the focus position of an imaging means. It is explanatory drawing which shows distribution of the contrast value of a to-be-measured object. It is explanatory drawing which shows the relationship between distribution of the contrast value of to-be-measured object, and distribution of the contrast value of each pattern for projection of the said mask. It is a flowchart explaining the operation | movement of the autofocus apparatus and autofocus method by this invention. FIG. 8 is an explanatory diagram showing particularly a follow-up operation in the autofocus operation of FIG. 7.

DESCRIPTION OF SYMBOLS 1 Autofocus apparatus 2 Imaging optical system 3 Projection optical system 4 Illumination optical system 5 Drive mechanism 6 Control means 7 Measured object 8 Lens unit 9 Imaging means 15 1st mask 16 2nd mask 26a, 26b 1st, 2nd Mask projection patterns Ia, Ib Projected images

Claims (2)

An imaging optical system having an objective lens facing the object to be measured and one imaging means for capturing an image of the object to be measured via the objective lens, and displacing the imaging optical system in the optical axis direction of the objective lens An autofocus device comprising: a driving mechanism for controlling the driving mechanism based on an image of the measurement object imaged by the imaging optical system;
A projection optical system for projecting two projection patterns onto the measurement surface of the object to be measured via the objective lens;
The imaging positions of the two projected patterns to be projected are both above or below the focus position of the imaging optical system, and are different positions in the optical axis direction of the objective lens and in the direction perpendicular to the optical axis. And
The control means includes
Comparing the magnitudes of the contrasts of the projection images of the two projection patterns acquired by the imaging optical system, the first imaging position where the contrast of one of the two projection images is maximum and the contrast of the other are maximum Search operation means for controlling the displacement of the imaging optical system so that the measurement surface is located between the second imaging positions to be
An autofocus device comprising: a focus operation unit that displaces the imaging optical system in one direction to adjust a position of the measurement surface to a focus position of the imaging optical system . A method of using the autofocus device according to claim 1 to focus the imaging optical system with respect to an object to be measured,
Projecting the two projection patterns onto the measurement surface by positioning at least one set point of the object to be measured directly under the objective lens ;
A step of determining the respective maximum values of the data relating to the brightness of the two projection pattern by the imaging means while moving along the imaging optical system in the optical axis direction,
As a state where the setting portion is sandwiched between the optical axis position of the objective lens corresponding to the maximum value of said respective, a step Before moving the imaging optical system in the optical axis direction,
While maintaining the state where the setting portion is sandwiched between the optical axis position of the objective lens, the imaging optical system to the measurement point from the set point, a step of Ru is parallel to the relative movement to said object to be measured,
And a step of sequentially moving the imaging optical system from a position on the optical axis of the imaging optical system at that time to a focus position of the imaging optical system.