JPH11352392A - Focus controller and focus controlling method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make an object to be measured movable to a focal position in optical measurement in a short time. SOLUTION: A pixel line PL including the edge part E of an image picked up in a state where a specified optical distance is kept is scanned while making plural operators OP having different size respectively act on the pixel line PL. The difference between pixel values at positions corresponding to both ends of the operator is arithmetically calculated by using the operators. An operator including one or more and the smallest number of values Rmax being a difference between the maximum value Pmax (15) and the minimum value Pmin (0) of a variable density value in the arithmetically calculated results R1, R2,... by the operator is specified as the optimum operator which is the most appropriate for deciding the focusing degree of the image, whereby a focus evaluated value is obtained. By referring to corresponding relation between the various focus evaluated values previously obtained and the focal position, the measured object is moved to the focal position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a focus control device and a focus control method for bringing an object and an imaging optical system into focus.

[0002]

2. Description of the Related Art When some kind of optical measurement is performed on a sample, such as inspection of a pattern on a semiconductor substrate, inspection of a biological sample, etc., the sample to be measured is moved to a focal position of an imaging optical system. It is necessary to arrange.

In a typical prior art, a predetermined pattern is projected on a sample, and the projected pattern is sequentially imaged while intermittently changing the distance between the sample and the imaging optical system. The position of the sample when the sharpness (sharpness) of the projection pattern in the captured image is maximized is detected as the focal position.

[0004]

However, in this prior art, since it is necessary to move and stop the sample stage or the imaging optical system every time each image is taken, it is often necessary to complete the detection of the focal position. It took time.

Further, in this conventional technique, it is necessary to take these images a plurality of times each time the focus position is detected. Since these multiple images need to be performed by changing the distance between the sample and the imaging optical system, there is a limit to speeding up the detection of the focal position. There was a problem that it was difficult to move.

In view of the above problems, an object of the present invention is to provide a focus control device and a focus control method that can move an object to a focus position of an imaging optical system in a short time.

[0007]

In order to achieve the above object,
The focus control device according to claim 1, wherein the focus control device sets the target and the imaging optical system in a focused state, and sets a relative optical distance between the imaging optical system and the target. A distance changing unit for changing, an image obtaining unit that captures an image of the object through the imaging optical system to obtain an image signal, and the object based on the image signal of a predetermined area in the image. Evaluation value calculation means for obtaining an evaluation value relating to the degree of focus between an object and the imaging optical system; and storage means for storing in advance a correspondence relationship between a plurality of the optical distances and the evaluation values corresponding thereto. Obtaining a difference between the optical distances to a focus position based on the evaluation value obtained by the evaluation value calculation means and the correspondence stored in the storage means, and calculating the optical distance by the difference. To change the distance Characterized in that it comprises a control means for controlling the.

[0008] The focus control device according to claim 2 is
2. The focus control device according to claim 1, wherein the evaluation value calculation unit obtains the evaluation value based on a degree of a gradient of the image signal corresponding to an edge portion included in the acquired image. 3. .

According to a third aspect of the present invention, there is provided a focus control device,
3. The focus control device according to claim 2, wherein the evaluation value calculation unit has a plurality of operators each adapted to a plurality of image signals having different inclinations, and when the operator acts on the image signals, The evaluation value is obtained based on the most suitable operator.

[0010] The focus control device according to claim 4 is
The focus control device according to any one of claims 1 to 3, further comprising a projection unit configured to project patterns having different projection angles on the object corresponding to a predetermined area in the image. .

A focus control method according to a fifth aspect of the present invention
A focus control method for bringing an object and an imaging optical system into a focused state, wherein an image of the object is captured via the imaging optical system to obtain an image signal, and the image acquiring step An evaluation value calculating step of obtaining an evaluation value relating to a degree of focusing between the object and the imaging optical system based on an image signal of a predetermined area in the target area; and a plurality of the optical distances and the evaluation values corresponding thereto. A preparatory step of previously obtaining a correspondence relationship between the evaluation value and the evaluation value obtained in the evaluation value calculation step, and the correspondence obtained in the preparatory step. And moving the optical distance by the difference.

The focus control method according to claim 6 is
6. The focus control method according to claim 5, wherein in the evaluation value calculating step, the evaluation value is obtained based on a degree of inclination of the image signal corresponding to an edge portion included in the acquired image. .

According to a seventh aspect of the present invention, there is provided a focus control method comprising:
7. The focus control method according to claim 6, wherein the evaluation value calculating step includes preparing a plurality of operators each adapted to a plurality of image signals having different inclinations. 8.
Obtaining the evaluation value based on the most suitable operator when the operator operates on the image signal.

The focus control method according to claim 8 is
The focus control method according to any one of claims 5 to 7, further comprising a step of projecting patterns having different projection angles on the object corresponding to a predetermined area in the image.

[0015]

Embodiments of the present invention will be described below with reference to the drawings.

<A. Apparatus> FIG. 1 is a schematic view showing a configuration of an optical measuring apparatus 1 according to a first embodiment of the present invention. The optical measurement device 1 detects a focal position where the sample 9 to be measured is to be placed prior to optical measurement of the sample 9 (for example, measurement of the thickness of a thin film formed on a semiconductor substrate), and determines the focal position. This device has a focusing function of arranging the sample 9 at the focal position after detection (more precisely, a function of arranging the observation surface of the sample 9 at the focal position).

The optical measuring apparatus 1 includes a light source unit 11 for emitting illumination light 11L illuminated on a sample 9, an illumination optical system 20a for guiding illumination light 11L from the light source unit 11 to the sample 9, and a reflection from the sample 9. An imaging optical system 20b for guiding the light 31L to a predetermined light receiving position, an image generating unit 31 for receiving the reflected light 31L and generating an image signal of the sample 9, a stage 41 on which the sample 9 is placed, and the stage 41 Is provided with a stage drive unit 42 which can be driven to move in the vertical direction (Z direction) and the horizontal direction. The driving amount of the stage driving unit 42 (the moving amount of the stage 41)
Is installed.

The illumination optical system 20a has a lens 21, a selective light-shielding part 22, a half mirror 23, and an objective lens 24. The illumination light 11L emitted from the light source part 11 receives the lens 21 and the selective light-shielding part 22. The illumination light 11 </ b> L reflected on the half mirror 23 via the objective lens 24 irradiates the sample 9 via the objective lens 24. In addition, the selective light shielding unit 22
Is located at a position that is optically conjugate with the focal position to be located.

The selective light blocking unit 22 includes a field stop 22a,
A disk-shaped light-transmitting pattern member 22b that rotates about the rotation axis AX1 is provided.
As shown in (a), a stripe pattern 15 in which stripe-shaped transparent regions 15T and light-shielding regions 15B are alternately arranged.
(In FIG. 2A, the light-shielding area 15B is drawn by hatching, but is actually a solid black area). FIG. 3 is a diagram showing the light transmitting pattern member 22b. A plurality of (three in the figure) patterns 15a, 15b, and 15c are drawn on the translucent pattern member 22b, and one of the patterns 15a, 15b, and 15c is rotated by rotating about the rotation axis AX1. It can be selectively located near the center of the central opening 22c of the field stop 22a. Then, the selected pattern 15 is projected on the sample 9 by the illumination optical system 20a as a projection pattern 15P (see FIG. 2B). The patterns 15a, 15b, and 15c are formed such that when projected onto the sample 9, the angles of the patterns (directions of the boundaries between the black and white stripes) are different from each other. As will be described later, the sample 9 can be moved to the focal position by calculating the focus evaluation value for the region including the projection pattern 15P. Further, after the focus position is detected and the sample 9 is moved to the focus position, the projection pattern 15 is positioned outside the field of view by rotating the translucent pattern member 22b so that the projection pattern 15P It is possible not to interfere with the optical measurement for the measurement object.

The imaging optical system 20b has an objective lens 24, a half mirror 23, and a lens 25, and its optical axis Lb and the optical axis La of the illumination optical system 20a intersect at the half mirror 23. That is, in the optical measurement device 1, the illumination optical system 20 a and the imaging optical system 20
The form of coaxial epi-illumination in which b shares the optical axis Lb is adopted. The reflected light 31L from the sample 9 is
The light is guided to the image generation unit 31 via the half mirror 23 and the lens 25 in this order.

The image generating section 31 has a CCD camera having light receiving elements arranged two-dimensionally, and receives the reflected light 31L to generate an image signal of the sample 9.
At this time, the generated image includes an image obtained by projecting the pattern 15 of FIG. 2A onto the sample surface (that is, the projected pattern 15P of FIG. 2B).

Further, the optical measuring device 1 also includes a selective light shielding control unit 14, a camera control unit 30, a memory 32, an evaluation value calculation unit 33, a stage drive control unit 40, and a focal position calculation unit 60.

The selective light-shielding control unit 14 controls the light-transmitting pattern member 22b to realize selective light-shielding using the pattern 15, and a desired projection pattern 15P is projected on the sample 9.

The camera control section 30 controls the generation of image signals in the image generation section 31, transfers the generated image signals to the memory 32, and stores them as digital image signals in the memory 32. The evaluation value calculation unit 33 stores the memory 3
2 is to calculate a focus evaluation value of a predetermined portion with respect to the image stored in 2.

The stage drive control unit 40 sends a control signal to the stage drive unit 42,
The stage 41 and the sample 9 placed on the stage 41
Can be moved up and down in the vertical direction (the Z direction shown in FIG. 1) and also in the horizontal direction. Stage 41
Is moved in the Z direction, the sample 9 and the imaging optical system 20b can be relatively moved along the optical axis Lb, and thereby, the optical distance between the sample 9 and the imaging optical system 20b is continuously set. Can be changed.

Further, the focus position calculating section 60 calculates the focus position based on the focus evaluation values of the images picked up at a plurality of positions, as will be described later.

The optical measuring device 1 also includes a light source control unit 10 for controlling the light amount of the light source unit 11 and the like, and an input / output unit 50 for performing a human interface such as key input of various conditions and display output of an image. I have.

Further, the optical measuring device 1 includes an overall control unit 1
00 is also provided. The general control unit 100 gives a rough control command to each control unit such as the light source control unit 10, the camera control unit 30, the evaluation value calculation unit 33, and the stage drive control unit 40, and controls the transmission timing of the control command.
On the other hand, each of the control units 10, 30, 33, and 40 actually performs individual specific control according to a control command from the overall control unit 100.

In the present embodiment, each of the control units is configured using a computer system (hereinafter, referred to as a "computer").
3. The focus position calculation unit 60 and the overall control unit 100 are configured to operate by executing a program.
The camera control unit 30 and the stage drive control unit 40 are configured as electric circuits provided in a computer. All of these configurations may be configured as software, or all may be configured as hardware. Further, it may be constructed only partially as software. The adjustment of the operation relationship between the components by the overall control unit 100 may be ensured between the components, and any one of the components may also serve as the role of the overall control unit 100. Also, as described later, the evaluation value calculation unit 33
In the above, arithmetic processing by a plurality of operators can be performed in parallel on a predetermined area of the acquired image. In this case, the parallel processing operation for a plurality of operators in the evaluation value calculation unit 33 can be achieved, for example, by using a separate CPU or a separate dedicated hardware circuit as the evaluation value calculation unit 33. Yes, and when using a single CPU for them, it can also be achieved by utilizing the multitasking function of that CPU.

<B. Operation> The operation of the optical measuring device 1 will be described with reference to FIG. Here, FIG. 4 is a flowchart illustrating the operation of the optical measurement device 1.

After the start of the operation, the measurement site of the sample 9 is positioned substantially at the center of the field of view, and first, the stage 41 is driven in the Z direction (see FIG. 1) to move the sample 9 to the initial position (step SP110). ). The initial position is preferably set so as to be located as close as possible to a place where the sample 9 is almost assumed to be the focal position, by taking the thickness of the sample 9 into consideration.

The overall control unit 100 includes a stage 41
Is obtained (step SP120). This position acquisition can be performed using, for example, an output pulse signal from an encoder 42E attached to the stage drive unit 42 as a position detection signal. In this embodiment, since the imaging optical system 20b is at a fixed position, the current position of the stage 41 is determined by the change in the optical relative distance between the imaging optical system 20b and the observation surface (upper surface) of the sample 9. It is information that expresses. Here, the position of the stage 41 in the Z direction is used as an index indicating the optical relative distance relationship between the focal position and the sample 9.

Next, the pattern 15 is projected onto the sample 9 (step SP210). This is the projection pattern 15
P is projected onto the surface of the sample 9 to create an artificial edge.
Of the projection pattern 15P
And calculates and evaluates a focus evaluation value (described later) relating to an edge portion included in.
Although it is possible to obtain the focus evaluation value not for the projection pattern 15P but for the edge portion existing on the sample 9 itself, in order to obtain the focus evaluation value as little as possible in the state of the sample 9, the projection pattern 15P Preferably, it is used.

Then, in response to the imaging command of the overall control unit 100, the camera control unit 30 performs imaging by the image generation unit 31 and obtains an image including the projection pattern 15P (step SP220). CCD (Charge coupled dev
After the charge is accumulated in ice) and an image is generated, the generated image is transferred to the memory 32 and stored in the memory 32 as a digital image signal. Thus, the image I0 at the initial position is obtained. The image I0 taken at this initial position
Is associated with the current position Z0 of the stage 41 (described above).

Thereafter, the evaluation value calculation section 33 calculates a focus evaluation value F0 for the image I0 in response to a focus evaluation value calculation command from the overall control section 100. The image I0 generated by the image generation unit 31 includes the projection pattern 15P, and the focus evaluation value F0 is obtained for an area including the projection pattern 15P. Hereinafter, a method of obtaining the focus evaluation value F0 will be described.

<Regarding Focus Evaluation Value> FIG. 5 is a diagram for explaining the degree of focus (degree of focus). The image I0 has a projection pattern 15 as shown in FIG.
5B is an enlarged view of one pixel row PL in the X direction included in the edge portion 15E, and the pixel value Pi of each pixel is represented by light and shade, light and dark, etc. . Further, in the pixel row PL, at the edge portion, each pixel value Pi is set in the X direction.
Changes rapidly. FIG. 5C is a conceptual diagram showing the rapid change in the pixel value. When the degree of focusing is ideal, that is, when the sample 9 is located at the focal position,
The edge portion 15E in the captured image I0 changes stepwise as in the gradation distribution E1, and the pixel value of each pixel in the pixel array PL is the pixel at the position corresponding to the step position C in the gradation distribution E1. The maximum value Pmax of the contrast with respect to
And the minimum value Pmin. On the other hand, when the sample 9 is located at a position shifted from the focal position, the gradation distribution is in a so-called “blurred” state, and is smaller than 90 degrees as shown by the gradation distributions E2 to E5 in the figure. It will have a slope. Therefore, each pixel of the pixel column PL has a pixel value corresponding to the inclination. Note that, as the degree of focusing gradually deteriorates, the gradation distribution changes from E2 to E2.
Gradually lean to 5.

The degree of focusing is evaluated using an operator as shown in FIG. FIG. 6 shows a plurality of operators OP0 to OP5 (the symbol "OP" is used when these are collectively referred to). Here, first, the basic type operator OP1 will be described with reference to FIG. I do. FIG. 7A shows the value of each pixel in the pixel row PL when the gradation distribution of the edge E on the image I0 has a predetermined inclination. Each pixel value Pi has the smallest pixel value Pmin (0 in the figure) in the portion BR where the light-shielding region 15B of the pattern 15 is projected, and in the portion ER in which the edge has a slope, from the left side of the diagram. The pixel value gradually increases toward the right side, and the transparent area 1
The portion TR corresponding to 5T has the maximum value Pmax (15 in the figure). Here, the pixel column PL in the figure
0, 0, 0, 5, 10, 1 from the left for 8 pixels
The values of 5, 15, and 15 are assumed. Note that the pixel values in the figure do not indicate actual values, but are index values indicating the relative relationship between the densities of the pixels.

The arithmetic processing is performed on the pixel array PL having such pixel values by operating the operators OP0 to OP5 (step SP310 in FIG. 4). The result of the operation is
In FIG. 7 (a), this is shown as a calculation result R1 for one operator OP1. For example, 0, 0, 5
Operator O for a row of pixels having each pixel value of
When P1 acts, 0 × (−1) + 0 × 0 + 5 × (+
By the operation of 1), 5 is obtained. Also, 5, 10,
When the operator OP1 acts on a row of pixels having each pixel value of 15, 5 × (−1) + 10 × 0 + 1
An operation of 5 × (+1) yields 10. As described above, by operating the operator OP1 having a width of three pixels on three consecutive pixels of the pixel row PL, 1
.., 0, 5, 10, 10, 5, 0... By calculating relative results by shifting the pixel row PL one by one. The result R1 will be obtained.

FIG. 7B shows the calculation result R2 when the operator OP2 (see FIG. 6) is operated.
The operator OP1 and the operator OP2 have -1 at both ends.
The number of 0 (zero) pixels sandwiched between +1 and +1 is different (see FIG. 6). The operation result R2 is obtained by operating the operator OP2 having a width of four pixels on four consecutive pixels of the pixel row PL, and obtaining one result, and shifting the result by one for the pixel row PL. ... 5, 1
0, 15, 10, 5,...

FIG. 7C shows the operation result R3 when the operator OP3 (see FIG. 6) is operated. This calculation result R3 is obtained by operating the operator OP3 having a width of 5 pixels on five consecutive pixels of the pixel row PL, and obtaining one calculation result, and shifting this one by one for the pixel row PL. , 10, 15, 1
The results are 5, 10, ... By performing such a calculation for all of the prepared operator OPs, the calculation result for each operator OP can be obtained.

As described above, the plurality of operators O
P1 to OP5 differ in the number of 0 (zero) pixels sandwiched between −1 and +1 at both ends, disregard the pixel value of the pixel row PL in a portion corresponding to zero of the operator OP, and The difference between the pixel values in the pixel row PL at the positions corresponding to both ends is calculated. Therefore, when the width of zero of the operator OP is sufficiently large, the pixel values at the positions corresponding to −1 and +1 at both ends of the operator OP are the minimum value Pmin (0) and the maximum value Pmax of the pixel value, respectively. (1
5), Pmi is included in the operation result of the operator OP.
n × (−1) + Pmax × (+1) = Pmax−Pmin value 15
Exists. Here, the value 15 of Pmax-Pmin becomes the maximum value in the calculation result R, and is hereinafter represented as Rmax. On the other hand, when the width of the zero pixel row of the operator OP is not so large, the operator O
The pixel values at the positions corresponding to -1 and +1 at both ends of P are the minimum value Pmin (0) and the maximum value Pmax of the pixel values, respectively.
Since it does not become (15), the calculation result of the operator OP does not include the maximum value Rmax (15).

FIG. 8 shows the calculation results R obtained by operating a plurality of operators OP in the X direction of the pixel row PL. The calculation results R1, R2, R3,.
Is a graph. As shown in the figure, the calculation result (for example, R0) by the operator OP having a small number of zero pixels does not include the maximum value Rmax. And a plurality of operators OP in which the number of zero pixels is gradually increased
Is applied, the maximum value of the pixel values included in the operation result R gradually increases, and when the operator OP including a specific number of zeros is applied, the operation result (R2 in FIG. ) Includes the maximum value Rmax. Then, once the maximum value Rmax is included in the calculation result, thereafter, the number of the maximum values Rmax included in the calculation result increases. Therefore, among the plurality of operators OP, the operator including the least maximum value Rmax in the calculation result R is specified as the operator most suitable for determining the degree of focusing of the image I0 (hereinafter, “optimum operator”) ( Step SP320 in FIG. 4),
The degree of the gradient of the gradation distribution, that is, the degree of focusing can be determined. For example, in the example of FIG. 8, the operator OP2 corresponding to the calculation result R2 is specified as the optimal operator.
The number of zeros (= 2) included in 2 can be used as the focus evaluation value F (step SP33 in FIG. 4).
0). In this way, by operating a plurality of operators having different numbers of zeros, the degree of focus can be determined. In this case, the focus evaluation value F is a discrete value, but can be a continuous focus evaluation value F by interpolation in consideration of the degree of conformity to the operator OP. The value can also be changed by performing appropriate scaling.

In this way, the arithmetic processing by each of the plurality of operators OP is performed (step SP3 in FIG. 4).
10), the optimum operator OP is specified based on the result of the arithmetic processing by each operator OP (Step S)
P320), the focus evaluation value F can be obtained (step SP330).

<Comparison with Reference Table and Movement to Focus Position> FIG. 9 is a graph in which the focus evaluation value F obtained for the image of the reference sample in the same manner as above is plotted against the position Z. Note that the crosses indicate the value of the position Z. The correspondence between the focus evaluation value F and the position Z in the Z direction of the stage 41 as shown in FIG. 9 is obtained by performing a predetermined measurement in advance before the start of the focusing operation, and is stored in the memory as reference data. 32. The correspondence is that an operation is performed in which a plurality of operators OP each act on an image captured at one value of the position Z of the stage 41 to obtain a focus evaluation value F indicating the degree of focus thereof. To position Z
Are obtained by repeatedly changing the value of This preliminary correspondence acquisition operation is preferably performed automatically by operating each unit in FIG. 1 under the control of the overall control unit 100 in FIG. 1 in order to save labor and increase the speed.

The focus position calculating section 60 calculates the focus evaluation value F obtained for the sample 9 as a measurement object,
By comparing with the reference data, the shift amount between the current position Zp (not shown) of the stage 41 at the time of acquiring the image I0 and the focus position Zf is obtained (step SP4 in FIG. 4).
10). Here, the focus position Zf of the stage 41 is a position where the focus evaluation value F is the best (minimum in the example of FIG. 9), and when the stage 41 is at the focus position Zf,
The observation surface of the sample 9 is located at the focal position of the imaging optical system 20b. For example, if the operator OP2 is specified as the most suitable operator for determining the degree of focus of the image I0, and the focus evaluation value F has the value F2 in FIG. The amount of deviation between them can be obtained as the absolute value of (Zp-Zf) in the figure.

Here, the stage drive control section 40 sets the amount of movement to the absolute value of (Zp-Zf) and moves the stage 41. However, it is unclear in which direction the shift between the current position Zp and the focus position Zf exists. This is because, as shown in FIG. 9, there are two positions corresponding to the focus evaluation value F2, the position Z2 and the position Z2 ', and thus the current position Zp is changed to the position Z2 and the position Z2.
This is because it is not possible to specify which of 2 ′.

Therefore, first, the stage 41 is moved in a predetermined direction (for example, the direction of arrow AR2) (step SP420 in FIG. 4). Then, after the movement, the image Ix is acquired again, and the same operation (steps SP120 to SP330) as that performed on the image I0 is repeated for the acquired image Ix. When the focus evaluation value Fx thus obtained is improved (decreased in FIG. 9) from the focus evaluation value F0, the position before the movement is Z2, and the position after the movement is the focus position Zf. It can be seen that it is. On the other hand, when the focus evaluation value Fx is deteriorated, it can be seen that the position before the movement is Z2 'and the position after the movement is (Zf + 2 * Z2'). In the latter case, the Z position is corrected by performing the movement again in the direction opposite to the previous movement (in the direction of arrow AR3) with the movement amount as the absolute value of (2 × (Zp−Zf)). Thus, the stage 41 can be moved to the focus position Zf (step SP430 in FIG. 4).

Then, the position Z obtained as described above is obtained.
After the stage 41 is moved to f, optical measurement is performed. Thereby, the observation surface of the sample 9 can be arranged at the focal position of the imaging optical system 20b, and the optical measurement can be performed.

As described above, by calculating the focus evaluation value for the two images I0 and Ix acquired in the focusing operation, the stage 41 is set to 1 or 2
Since the sample 9 can be moved to the focus position only by rotating the focus, the focusing operation can be performed in a very short time.

It is sufficient that the focus position obtained in the focus detection operation is within the depth of focus for the required resolution. By determining the magnification of the image, the number of the operators OP, the positioning accuracy of the stage 41, and the like so as to satisfy such a condition, it is possible to perform the focus position detection with sufficient performance.

<C. Other Embodiments> In the above embodiment, any one of the patterns 15a, 15b, and 15c is selectively positioned near the center of the central opening 22c of the field stop 22a by rotating the light transmitting pattern member 22b. Although the projection pattern 15P is projected on the sample 9 by this, the invention is not limited to this. For example, the light-transmitting pattern member 22b
Above, it can be fixed and arranged at a position away from the center of the opening 22c so as not to disturb the optical measurement. In this case, a rotation mechanism is not required and a simple configuration is provided.

In the above embodiment, the focus evaluation value is obtained for the image on which the pattern 15 is projected. However, the present invention is not limited to this. For example, when there is an object corresponding to the pattern 15 in the sample 9 itself to be measured (for example, when a wiring pattern is already created on a semiconductor substrate), an image including the pattern portion is displayed. On the other hand, a focus evaluation value can be obtained.

Further, in the above embodiment, the sample 9 placed on the stage 41 is moved, but when the optical distance between the sample 9 and the imaging optical system 20b is continuously changed, the imaging optical system is changed. The system 20b may be moved.

In the above embodiment, the arithmetic processing is performed for all of the plurality of operators OP (step S in FIG. 4).
P310) Then, the optimum operator OP most suitable for the determination of the in-focus state of the image I0 has been specified (Step S).
P320) is not limited to this, and it is only necessary that the operator OP including the smallest maximum value Rmax in the calculation result R can be specified as the most suitable operator for determining the degree of focus of the image I0. For example, the operator OPs that gradually include a large number of zeros are sequentially applied (in the order of operators OP0, OP1, OP2,... In FIG. 6), and the operation results are saturated and the image becomes saturated. When the optimum operator OP of I0 can be specified, the calculation for a plurality of operators OP can be completed. This eliminates the need to perform the operation for all of the plurality of operators OP, thereby enabling higher-speed processing. Alternatively, it is also possible to specify the optimum operator OP most suitable for determining the in-focus state of the image I0 by using a kind of a binary search method. Again, in this case,
Since the calculation process needs to be performed only for a smaller number of operators OP, higher-speed processing can be performed.

Further, as shown in FIG. 10, the speed can be further increased by performing the arithmetic processing in parallel for each of the plurality of operators OP. FIG.
, Each of the plurality of arithmetic units Xi (i = 0 to M) performs an operation on each of the operators OP on the pixel array PL in parallel, and based on those results, the determination unit 33J
A configuration is shown in which the optimum operator OP most suitable for determining the in-focus state of the image I0 including the pixel row PL is specified and the focus evaluation value F is calculated. Since the arithmetic processing of each operator OP is performed in parallel, further higher speed can be realized.

In the above embodiment, the image I0
Although one pixel column PL included in the image I0 has been extracted to evaluate the degree of focus of the image, the present invention is not limited to this. For example, as shown in FIG. 11, a pixel row obtained by adding each pixel value of a plurality of pixel rows PLj (j = 1,..., J) included in a two-dimensional image area in the Y direction in the drawing is referred to as a pixel. It can also be used as column PL. In this case, the effect of reducing the influence of noise and the like can be obtained.

Further, in the above embodiment, the operator OP as shown in FIG. 6 is used, but the present invention is not limited to this. For example, an operator as shown in FIG. 12 can be used. Each operator in FIG. 12 has a configuration in which −1 and +1 are further added to both ends of each operator in FIG. By using such an operator, the influence of noise can be reduced.

Alternatively, an operator as shown in FIG. 13 can be used. Each operator in FIG.
, And -2 and +2 are added to both ends of each operator. According to this, the influence of noise can be reduced and the degree of edge change can be reflected in more detail.

[0059]

As described above, according to the focus control apparatus according to the first and second aspects and the focus control method according to the fifth and sixth aspects, an evaluation value for a predetermined area in an image and an evaluation value obtained in advance can be obtained. The in-focus state can be obtained by obtaining the difference in the optical distance to the in-focus position based on the corresponding relationship and changing the optical distance by the difference. Therefore, the focusing operation on the target object can be realized with a small number of movements.

According to the focus control apparatus of the third aspect and the focus control method of the seventh aspect, since the evaluation value is obtained by causing a plurality of operators to act on the image signal, it is necessary to use a complicated calculation. Absent.

According to the focus control device of the fourth aspect and the focus control method of the eighth aspect, it is possible to project a pattern having a different projection angle on an object corresponding to a predetermined area in an acquired image. Therefore, the evaluation value can be appropriately obtained without depending on the surface state of the object.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing a configuration of an optical measurement device 1 of the present invention.

FIG. 2 is a view showing a pattern 15;

FIG. 3 is a view showing a light transmitting pattern member 22b.

FIG. 4 is a flowchart illustrating an operation of the optical measurement device 1.

FIG. 5 is a diagram illustrating a degree of focus.

FIG. 6 is a diagram showing a plurality of operators OP0 to OP5.

FIG. 7 is a diagram illustrating an operation of an operator OP.

FIG. 8 is a graph showing a calculation result R by a plurality of operators OP.

FIG. 9 is a graph showing a relationship between a position Z of a stage 41 and a focus evaluation value F.

FIG. 10 is a diagram showing a configuration in a case where arithmetic processing of an operator OP is performed in parallel.

FIG. 11 is a diagram showing a pixel column PL.

FIG. 12 is a diagram illustrating an example of another operator.

FIG. 13 is a diagram showing another example of an operator.

[Explanation of symbols]

 Reference Signs List 1, 1B Optical measuring device 9 Sample 11 Light source unit 11L Illumination light 15 Pattern 20a Illumination optical system 20b Imaging optical system 21, 25 Lens 22 Selective light shielding unit 22b Light transmission pattern member 23 Half mirror 24 Objective lens 31 Image generation unit 31L Reflected light 41 Stage 42 Stage drive section La, Lb Optical axis PL Pixel array OP Operator R Calculation result F Focus evaluation value Z (stage 41) position

Claims (8)

[Claims] 1. A focus control device that focuses an object and an imaging optical system, wherein the distance changing unit changes a relative optical distance between the imaging optical system and the object. An image acquisition unit configured to capture an image of the object through the imaging optical system to acquire an image signal; and the object and the imaging optics based on the image signal of a predetermined area in the image. Evaluation value calculation means for obtaining an evaluation value related to the degree of focusing with a system; storage means for storing in advance a correspondence relationship between a plurality of the optical distances and the evaluation values corresponding thereto; and the evaluation value calculation means. The difference between the optical distance to the in-focus position is obtained based on the evaluation value obtained by the above and the correspondence stored in the storage means, and the distance is changed to change the optical distance by the difference. Control means for controlling the change means; Focus control apparatus comprising: a. 2. The focus control device according to claim 1, wherein the evaluation value calculation unit obtains the evaluation value based on a degree of inclination of the image signal corresponding to an edge portion included in the acquired image. A focus control device, comprising: 3. The focus control device according to claim 2, wherein said evaluation value calculating means has a plurality of operators each adapted to a plurality of image signals having different inclinations, and operates said operator on said image signals. A focus control device that obtains the evaluation value based on a most suitable operator when the control is performed. 4. The focus control device according to claim 1, further comprising: a projection unit configured to project a pattern having a different projection angle on the object corresponding to a predetermined area in the image. A focus control device, comprising: 5. A focus control method for bringing an object and an imaging optical system into a focused state, comprising: acquiring an image of the object via the imaging optical system to acquire an image signal. And an evaluation value calculating step of obtaining an evaluation value relating to a degree of focusing between the object and the imaging optical system based on an image signal of a predetermined area in the image, and a plurality of the optical distances and A preparatory step of previously obtaining a correspondence relationship with the corresponding evaluation value; focusing on the basis of the evaluation value obtained in the evaluation value calculation step and the correspondence relation obtained in the preparation step. A moving step of determining a difference in the optical distance to a position and changing the optical distance by the difference. 6. The focus control method according to claim 5, wherein the evaluation value calculating step obtains the evaluation value based on a degree of inclination of the image signal corresponding to an edge portion included in the acquired image. And a focus control method. 7. The focus control method according to claim 6, wherein the calculating of the evaluation value includes preparing a plurality of operators respectively corresponding to a plurality of image signals having different inclinations, and A step of obtaining the evaluation value based on the most suitable operator when is applied. 8. The focus control method according to claim 5, further comprising a step of projecting patterns having different projection angles on the object corresponding to a predetermined area in the image. A focus control method characterized by the following.