JPH11326745A - Focal position detecting device and method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a focal position detecting device and a focal position detecting method for detecting a focal position in optical measurement at high speed. SOLUTION: By consecutively driving a stage 41 in a direction Z, a sample 9 placed on the stage 41 is moved in the direction of the optical axis Lb of an image formation optical system 20b and plural images are acquired during the consecutive movement. The image acquiring operation includes image pickup operation by an image forming part 31 and transfer operation to a memory 32. An evaluated value calculation part 33 calculates the focus evaluated values F of the respective images concurrently with the image acquiring operation, so that total processing time is shortened. A focal position calculation part 60 calculates the focal position based on plural focus evaluated values F.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a focal position detecting device and a focal position detecting method for detecting a focal position at which an object to be measured is to be placed during optical measurement.

[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 prior art, each time one imaging is completed, an evaluation calculation of sharpness is performed based on the imaging result, and after such a set of processing is completed, the image is moved to the next imaging position. Therefore, there is a problem that it takes more time to complete the detection of the focal position.

In view of the above problems, it is an object of the present invention to provide a focus position detecting device and a focus position detecting method capable of detecting a focus position in optical measurement at high speed.

[0007]

In order to achieve the above object,
The focus position detection device according to claim 1 is a focus position detection device that detects a focus position in optical measurement,
(a) an imaging optical system that guides light from a measurement target to a predetermined light receiving position, and (b) a distance that continuously changes a relative optical distance of the measurement target with respect to the imaging optical system. Changing means, (c) detecting means for detecting a change state of the optical distance, and (d) sequentially changing the image of the measurement object at the light receiving position when the optical distance is continuously changed. Image capturing means for sequentially capturing a plurality of images, and (e) focusing the measurement target at the time when each image is captured in parallel with the sequential image capturing operation of the plurality of images. Evaluation value calculation means for sequentially calculating the evaluation value of the state from the acquired images, and (f) the change state of the optical distance when each of the plurality of images is acquired, and for each of the plurality of images Focus for obtaining the focus position based on the relationship with the evaluation value of Characterized in that it comprises a 置算 out means.

According to a second aspect of the present invention, in the focus position detecting apparatus according to the first aspect, the image obtaining means is configured to continuously change the optical distance at a constant speed. A feature is to acquire a plurality of images.

According to a third aspect of the present invention, in the focus position detecting device according to the first or second aspect, the evaluation value calculating means is provided in parallel with each other; Receiving two or more images alternately or cyclically,
It is characterized by comprising a plurality of unit calculation means for calculating the evaluation value for each received image.

According to a fourth aspect of the present invention, in the focal position detecting device according to any one of the first to third aspects, the focal position calculating means is configured to determine the focal position. It is characterized in that the change state of the optical distance when each of the plurality of images is obtained is corrected according to the required imaging time of each image and used.

According to a fifth aspect of the present invention, there is provided a focal position detecting method for detecting a focal position in an optical measurement, wherein (a) light from a measuring object is guided to a predetermined light receiving position. A distance changing step of continuously changing a relative optical distance of the object to be measured with respect to an image optical system, (b) a detecting step of detecting a change state of the optical distance, and (c) the optical distance An image acquisition step of sequentially taking an image of the measurement object a plurality of times at the light receiving position in synchronization with the continuous change of the image, thereby sequentially acquiring a plurality of images,
(d) in parallel with the image obtaining step, an evaluation value calculating step of sequentially calculating the evaluation value of the in-focus state of the measurement object at the time when each image is obtained, from the obtained images, and (e) A focus position step for determining the focus position based on a relationship between the change in the optical distance when each of the plurality of images is acquired and the evaluation value for each of the plurality of images, It is characterized by having.

According to a sixth aspect of the present invention, in the focus position detecting method according to the fifth aspect, in the image acquiring step, the optical distance is continuously changed at a constant speed. The method is characterized in that the plurality of images are obtained.

According to a seventh aspect of the present invention, in the focus position detecting method according to the fifth or sixth aspect, the evaluation value calculating step includes the step of calculating (d-1) 2 or more images by a plurality of images. The method further comprises the step of alternately or cyclically providing the evaluation value to the unit calculation means and calculating the evaluation value for each of the two or more images by the plurality of unit calculation means.

According to an eighth aspect of the present invention, in the focus position detecting method according to any one of the fifth to seventh aspects, in the calculating of the focal position, the determining of the focal position is performed. It is characterized in that a change state of the optical distance when each of the plurality of images is acquired is corrected according to a required imaging time of each image and used.

[0015]

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

<A. First Embodiment><Apparatus> FIG. 1 is a schematic diagram showing a configuration of a focus detection apparatus 1 according to a first embodiment of the present invention. The focus detection device 1 has a sample 9
Is a device for detecting the focal position where the sample 9 to be measured is to be placed prior to the optical measurement (for example, measuring the thickness of a thin film formed on a semiconductor substrate). It also has a function of focusing at the focal position (more precisely, a function of arranging the observation surface of the sample 9 at the focal position).

The focus detecting device 1 includes a light source section 11 for emitting illumination light 11L radiated to the sample 9, an illumination optical system 20a for guiding illumination light 11L from the light source section 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 part 22 includes a field stop 22.
a and a light-transmitting pattern member 22b disposed at the center thereof, and the light-transmitting pattern member 22b has stripe-shaped transparent regions 15T and light-shielding regions 15B alternately arranged as shown in FIG. The striped pattern 15 is drawn (in FIG. 2A, the light-shielding area 15B is drawn by hatching, but is actually a solid black area). This pattern 15 is projected onto the sample 9 by the illumination optical system 20a. It is preferable that the pattern 15 is disposed at a position slightly shifted from the center of the visual field so that the pattern 15 does not disturb the optical measurement after the focus position is detected. Alternatively, the pattern 15 is moved by moving the light-transmitting pattern member 22b after the focus position is detected.
Out of the field of view.

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 focus detection 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 generator 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).

The focus detecting device 1 further includes a camera control unit 30, a memory 32, an evaluation value calculation unit 33, a stage drive control unit 40, and a focus position calculation unit 60.

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 section 40 sends a control signal to the stage drive section 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 focus detection device 1 further 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 focus detection 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 control unit actually performs individual specific control according to a control command from the overall control unit 100, and each control unit 1
0, 30, 33, and 40 perform processing in parallel with each other.

For example, the stage drive control section 40 receives the movement command (control command) sent by the overall control section 100 and actually controls the stage drive section 42. The stage 41 can be moved in the Z direction by driving a motor of a stage driving unit 42 or the like. After sending the control command to the stage drive control unit 40, the overall control unit 100 does not participate in the actual drive control of the stage drive unit 42, and performs another process (for example, the camera control unit 30) during that time.
Can be performed.

The camera control section 30 receives the imaging command (control command) sent by the overall control section 100 and performs imaging with the image generation section 31. The overall control unit 100
After sending the control command to the camera control unit 30, it does not participate in the operation of the camera control unit 30, and it is possible to perform another process during that time. Here, the camera control unit 30 and the stage drive control unit 40 can perform processing in parallel.

The overall control unit 100 includes the image generation unit 3
After the imaging operation in 1 is completed, a control command (focus evaluation value calculation command) for calculating the focus evaluation value is transmitted to the evaluation value calculation unit 33. Thus, the evaluation value calculation unit 33 calculates a focus evaluation value of a predetermined portion of the image stored in the memory 32. Similarly to the above, after transmitting the control command to the evaluation value calculation unit 33, the overall control unit 100 can perform another process during the period without being involved in the operation of the evaluation value calculation unit 33. That is, the camera control unit 30 that controls the imaging operation of the image generation unit 31 and the evaluation value calculation unit 33 can operate in parallel.

In the present embodiment, each of the above-mentioned 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. The parallel operation of the camera control unit 30 and the evaluation value calculation unit 33 described above is achieved, for example, by using a separate CPU or a separate dedicated hardware circuit for the camera control unit 30 and the evaluation value calculation unit 33. It can also be achieved by using a single CPU for them, and by using the multitasking function of that CPU.

<Operation> Referring to FIGS. 3 and 4,
The operation of the focus detection device 1 will be described. Here, FIG. 3 is a flowchart illustrating the operation of the focus detection device 1, and FIG. 4 is a timing chart illustrating the operation of each control unit.

First, as shown in FIG. 3, after the operation starts (step SP10), the stage 41 is driven to move the sample 9 to the initial position (step SP20). The initial position is set so that the sample 9 passes through the focal position by the movement of the stage 41 in the Z direction (see FIG. 1).
Is set to be a position sufficiently far or close to.

Thereafter, the overall control unit 100 controls the stage 4
A movement command to move 1 in the Z direction is sent to the stage drive controller 40 (step SP30). The stage drive control unit 40 drives and controls the stage drive unit 42 so as to continuously move in a predetermined moving section at a predetermined speed in response to the movement command. After the initial acceleration period, an initial acceleration period for achieving a substantially constant speed has been confirmed in advance by actual measurement and the like, and after the initial acceleration period has elapsed, during this continuous movement, images at a plurality of positions are obtained. (Sample images) are sequentially acquired, and a focus evaluation value is obtained for each of the acquired images. The reason why the image acquisition is preferably performed while the stage 41 moves at a predetermined constant speed is to reduce the influence of the speed change on the imaging operation and the position measurement.

Next, the overall control section 100 sends an imaging command S1 to the camera control section 30 after the elapse of the initial acceleration period (step SP40). In response to the imaging command S1, the camera control unit 30 causes the image generation unit 31 to start imaging. As shown in FIG. 4, from time t10 to time t1
In the period P11 leading to the period No. 1, the CCD (Charge coupled)
device) to generate an image.
Thereafter, in a period P12 from time t11 to time t12, the generated image is transferred to the memory 32 and stored in the memory 32 as a digital image signal. In this way, an image at one position is obtained.

The overall control unit 100 includes a stage 41
Is obtained (step 50). 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, such a stage 41
The current position is information expressing the state of change in the optical relative distance between the imaging optical system 20b and the observation surface (upper surface) of the sample 9. In the example of FIG. 4, the current position at time t10 is associated with the first image Ik (k = 1: not shown). That is, 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, and the current position of the stage 41 in the Z direction at the time when the image is captured is referred to as “k-th position”. As the sampling position Zk ”(k = 1 at the time of the first image capturing) and is associated with the captured image Ik. This association can be performed, for example, by putting information on the address where the sampling position Zk is stored in the header of the file storing the image Ik. As described above, the image Ik generated by the charge accumulation in the CCD is transferred to and stored in the memory 32. The time width required for generating and transferring this image is Δt1 in FIG. .

Thereafter, a focus evaluation value calculation command for calculating the focus evaluation value Fk for the image Ik is sent by the overall control unit 100 to the evaluation value calculation unit 33 (step SP60).

In response to the focus evaluation value calculation command, the evaluation value calculation unit 33 calculates the focus evaluation value Fk (k = 1) in a period P14 (time width Δt2) from time t13 to time t14. The image Ik generated by the image generation unit 31 includes the projection pattern 15P, and the focus evaluation value Fk can be obtained for an area including the projection pattern 15P. Here, the focus evaluation value Fk may be any value as long as the value indicates the degree of focus such as contrast and sharpness (sharpness).

On the other hand, the overall control unit 100 executes step SP
After a lapse of a predetermined time Δt0 from the first execution start time of Step 40, the process returns to Step SP40, and the next imaging command S
2 to the camera control unit 30. This imaging command S2
Is transmitted without waiting for the end of the processing of the evaluation value calculation unit 33 in the period P14, and the imaging operation in the period P21 (described below) is performed in parallel with the processing of the evaluation value calculation unit 33.

The camera control section 30 performs an image acquiring operation in the same manner as described above in response to the imaging command S2. That is, in the period P21 from the time t20 to the time t21, the charge is stored in the CCD and the next image Ik + 1
Is generated. Thereafter, in a period P22 from time t21 to time t22, the generated image Ik + 1 is stored in the memory 3
2 and stored in the memory 32 as a digital image signal. Such an imaging operation is performed during the period P1.
The processing is performed in parallel with the processing of the evaluation value calculation unit 33 for the previous image Ik performed in 4.

Further, similarly to the above, the sampling position Zk + 1 of the stage 41 is obtained (step 50).

Thereafter, the image Ik + stored in the memory 32
1, the focus evaluation value F for the image Ik + 1
A focus evaluation value calculation command for calculating k + 1 is sent by the overall control unit 100 to the evaluation value calculation unit 33 (step SP60). In response to the focus evaluation value calculation command, the evaluation value calculation unit 33 calculates the focus evaluation value Fk + 1 in a period P24 from time t23 to time t24.

In this way, the image Ik + 1 corresponding to the imaging command S2 is obtained, and the focus evaluation value Fk + 1 for the obtained image Ik + 1 is obtained.

The above-described image acquisition operation and evaluation value calculation operation are repeatedly performed, and it is determined whether the operation has been completed a predetermined number of times (step SP70). To the focus position calculation operation (step SP80).

In step SP80, a plurality of images {Ik} (k = 1, 2,..., N) obtained by sequentially repeating steps 40 to SP60.
Is calculated based on the information of the focus evaluation value {Fk} and the sampling position {Zk} corresponding to each of the above (the symbol {} is a set of k = 1, 2,..., N Represents).

FIG. 5 shows sampling positions {Zk} and focus evaluation values {Fk} for a plurality of images {Ik}.
Are plotted on the horizontal axis and the vertical axis, respectively. Open circles indicate the values at the measurement points. The value between the sampling positions {Zk} can be given by interpolation, which can be done using quadratic and higher order curve approximations, etc., so that the focus evaluation changes substantially continuously. The value (focus evaluation curve) F can be obtained. The focus position calculation unit 60 obtains the position Zf of the stage 41 corresponding to the focus position at which the focus evaluation value F is optimal by such interpolation. Conversely, when the stage 41 is at this position Zf, the observation surface of the sample 9 is located at the focal position. For example, FIG.
In the case where the ratio of the density of the dark part to the density of the bright part (the reciprocal of the contrast) of the striped pattern in FIG.
Is a state where the observation surface of the sample 9 coincides with the focal position Zf. Thus, focus evaluation positions {Zk} corresponding to each of the plurality of images {Ik} and focus evaluation values {F
The focus position can be detected based on k｝, and the focus detection operation ends (step SP90).

Further, 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 and the optical measurement can be performed.

The above measurement operations such as the image acquisition operation and the focus evaluation value calculation operation need only be performed for at least three positions over and under the position Zf. Further, the detection error of the focus position obtained by the above-described focus detection operation is sufficient if it is within the depth of focus for the required resolution. By determining the interval between the sampling positions, the positioning accuracy of the stage 41, and the like so as to satisfy such conditions, it is possible to perform the focus position detection with sufficient performance.

<Characteristic Effects of Embodiment> As described above,
The focus detection device 1 according to the present embodiment continuously moves the stage 41 to continuously change the optical relative distance of the sample 9 with respect to the imaging optical system 20b while the plurality of images ΔI
k}, and calculates a plurality of focus evaluation values {Fk} corresponding to the respective images {Ik}. It should be noted that the focus detection device 1 can perform the image acquisition operation and the focus evaluation value calculation operation in parallel. For example, the imaging command S2 is transmitted without waiting for the end of the processing of the evaluation value calculation unit 33 in the period P14, and the imaging operation in the period P21 is performed by the evaluation value calculation unit 33.
Is performed in parallel with the processing of. Such parallel processing can reduce the overall processing time.

FIG. 8 is a diagram showing an example of a conventional focus position detection technique in order to clarify the advantages of this embodiment. Conventionally, in response to the imaging command S1 ', the control unit 30' performs imaging of the image by the CCD in the period P11 ', and transfers the captured image to the memory 32' (not shown) in the period P12 '. Control to acquire an image, and the focus evaluation value for the image is calculated in the period P14 ′. And period P1
After the calculation of the focus evaluation value in 4 ′ is completed, the next imaging command S2 ′ is issued, and in response to the imaging command S2 ′, the image acquisition operation in the periods P21 ′ and P22 ′ and the period P
The focus evaluation value calculation operation of 24 'was performed. That is, since the image acquisition operation and the focus evaluation value calculation operation are performed sequentially (in series), there is a limit to speeding up the focus position detection operation.

On the other hand, in the apparatus 1 according to the embodiment of the present invention, as described above, a certain imaging instruction S (for example, S2)
Can be performed in parallel with the calculation operation of the focus evaluation value Fk for the image Ik acquired by the imaging command S (for example, S1) earlier than that. Therefore, it is possible to reduce the overall processing time.

The transmission intervals of the imaging commands S1, S2, S3... In the apparatus 1 of the embodiment have a fixed time width Δt0.
However, the time width Δt0 is determined in accordance with the condition that it is equal to or more than the maximum value of the period Δt1 for acquiring the image and the period Δt2 for the focus evaluation value calculation operation.
This is a condition for enabling the parallel processing as shown in FIG. 4 to be repeated. In the example of FIG. 4, this maximum value is the time interval Δ
t1.

Looking at this situation from another viewpoint, in the case of the example of FIG. 4, the transmission interval Δ of each imaging command S1, S2, S3.
The difference between t0 and the period Δt1 for image acquisition, ie,
Since .DELTA.tm = (. DELTA.t0-.DELTA.t1) is only a time margin, by setting the imaging command transmission interval .DELTA.t0 so that the margin .DELTA.tm becomes substantially zero, the theoretical maximum processing speed can be reduced. Obtainable.

A case in which a plurality of evaluation value calculation sections 33 and the like are provided in parallel will be described in the second embodiment.

<B. Second Embodiment> FIG. 6 is a schematic diagram showing a configuration of a focus detection device 1B according to a second embodiment.
The focus detection device 1B according to the second embodiment has a plurality of
) Memories 33A and 33B and an evaluation value calculation unit 33A,
The configuration is the same as that of the focus detection device 1 of the first embodiment except that the focus detection device 1 includes a focus detection device 33B. Hereinafter, based on such a configuration, by performing processing with higher parallelism than the focus detection device 1 of the first embodiment, it is possible to perform the focus position detection operation at higher speed with reference to FIG. I will explain while.

FIG. 7 is a diagram showing parallel processing in the camera control unit 30 and the evaluation value calculation units 33A and 33B of the focus detection device 1B.

First, the overall control unit 100 sends an imaging command S1 to the camera control unit 30. Camera control unit 3
0 corresponds to the time t10 from the time t10 in response to the imaging command S1.
During a period P10 (time width Δt1) leading to 12, an image acquisition operation including image generation and transfer to the memory 32A is performed. Then, for the acquired image, the evaluation value calculation unit 33A calculates the focus evaluation value F in a period P14 (time width Δt2) from time t13 to time t14.

In addition, the overall control unit 100 sends an imaging command S2 to the camera control unit 30 in parallel with the focus evaluation value calculation operation in the period P14. In response to the imaging command S2, the camera control unit 30 performs an image acquisition operation including generation of an image and transfer to the memory 32B during a period P20 from time t20 to time t22. Then, in a period P24 from time t23 to time t24, the focus evaluation value F is calculated in the evaluation value calculation unit 33B.

In the above operation, the camera control unit 30
Is performed not only in parallel with the process in the evaluation value calculation unit 33A, but also in the camera control unit 30 and the process in the evaluation value calculation unit 33B in parallel. The processing in the unit 33A and the processing in the evaluation value calculation unit 33B are also executed in parallel. Therefore, the degree of parallelism of processing is increased, and the overall processing time can be reduced.

Since the period P14 and the period P24 can be more quantitatively overlapped with each other, the "repetition period Δt0 of the imaging command must be longer than the calculation period Δt2 of the focus evaluation value in the first embodiment. In the second embodiment, the condition "repetition period Δt0
Must be 以上 or more of the focus evaluation value calculation period Δt2 ”.

Therefore, the effect of shortening the processing time is particularly large when the calculation period Δt2 of the focus evaluation value is longer than the image acquisition period Δt1. When the calculation period Δt0 of the focus evaluation value is longer than the image acquisition period Δt1, the total processing time can be further reduced by further increasing the number of memories and evaluation value calculation units to increase the degree of parallelism of processing. Can be shortened.

Generally, M (M is an integer of 2 or more) memories and an evaluation value calculation unit (unit for calculating a focus evaluation value) are arranged, and these can be operated in parallel.
When a plurality of images are alternately or cyclically received and the focus evaluation value is calculated for each image, the repetition period Δt0 of the imaging command is (1/1) of the image acquisition period Δt1 and the focus evaluation value calculation period Δt2. N) or more, and the maximum efficiency (maximum speed) is obtained when the repetition period Δt0 of the imaging command is substantially equal to the maximum value among the above.

<C. Other Embodiments> In the above embodiment, the focus evaluation value calculation command is transmitted to the overall control unit 100.
Is transmitted to the evaluation value calculation unit 33, but the camera control unit 30 can also transmit the evaluation value to the evaluation value calculation unit 33.

In the above embodiment, each imaging command S is transmitted at a predetermined time interval. However, the present invention is not limited to this. For example, the next imaging command S may be transmitted when the stage 41 reaches a predetermined position.

Further, in the above embodiment, the sampling position {Zk} of the stage 41 is the current position at the time when the imaging command S is sent, but the present invention is not limited to this. More preferably, the position may be a position corresponding to a time at which the generation time of an image actually captured by the CCD camera is more reflected. For example, CC
Period P1 during which an image is generated by accumulating charges in D
A position corresponding to an intermediate time of 1 (a period from time t10 to time t11 in FIG. 4) can be set as the sampling position Zk. As described above, by correcting the position in consideration of the moving speed, the CCD charge accumulation time, and the like, the measurement accuracy of the focal position can be further improved.

That is, in this case, the correction means for correcting the optical relative distance relationship between the imaging optical system and the sample when a plurality of images are generated in accordance with the time required for capturing each image is provided by the correction means. The focal position is calculated in consideration of the correction result provided by the correction unit provided in the calculation unit 60.
For example, the required imaging time is represented by Δtd (not shown), during which the relative distance between the imaging optical system and the sample becomes Δtd.
If the distance changes by L, the distance Δ
The value (Zk + ΔL) obtained by adding L is used as a new corrected relative distance. In this case, the graph of FIG. 5 is shifted to the right by ΔL as a whole.

In the above embodiment, the focus evaluation value is calculated 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 calculated.

When the optical distance between the sample 9 and the image forming optical system 20b is continuously changed, the image forming optical system 20
b may be moved.

[0068]

As described above, according to the focus position detecting apparatus according to the first aspect and the focus position detecting method according to the fifth aspect, a plurality of images of the object to be measured are measured with respect to the imaging optical system. When the relative optical distance of the object is continuously changed, the image is acquired by being sequentially imaged a plurality of times, so that a plurality of images can be quickly captured without stopping the relative movement of the measurement object. Can be obtained. In addition, in parallel with the sequential acquisition operation of a plurality of images, the evaluation value of the in-focus state of the measurement target at the time when each image is acquired is sequentially calculated from the acquired images, so that it is necessary for focus position detection. The influence of the evaluation value calculation time on the entire time can be reduced. Since the focus position is obtained based on the evaluation value of each of the plurality of images obtained in this way and the change state of the optical distance when each image is obtained,
The focus position can be detected at high speed.

According to the focal position detecting device of the second aspect and the focal position detecting method of the sixth aspect, a plurality of images are acquired while the optical distance is continuously changed at a constant speed. Therefore, a stable image can be obtained.

According to the focus position detecting device according to the third aspect and the focus position detecting method according to the seventh aspect, since the evaluation values for each of the two or more images are obtained in parallel with each other, the speed is further increased. Can be detected.

According to the focal position detecting device of the fourth aspect and the focal position detecting method of the eighth aspect, when determining the focal position, the optical distance at the time when each of a plurality of images is acquired is determined. Since the change status is used after being corrected according to the required imaging time of each image, the focal position can be more accurately obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating a configuration of a focus detection device 1 according to a first embodiment of the present invention.

FIG. 2 is a view showing a pattern 15;

FIG. 3 is a flowchart illustrating an operation of the focus detection device 1.

FIG. 4 is a timing chart illustrating an operation in each control unit.

FIG. 5 is a graph showing a relationship between a sampling position Zk and a focus evaluation value F.

FIG. 6 is a schematic diagram illustrating a configuration of a focus detection device 1B according to a second embodiment.

FIG. 7 shows a camera controller 30 and an evaluation value calculator 33A;
It is a figure showing parallel processing in 33B.

FIG. 8 is a diagram showing a conventional example.

[Explanation of symbols]

 Reference Signs List 1, 1B focus detection device 9 sample 11 light source unit 11L illumination light 15 pattern 20a illumination optical system 20b imaging optical system 21 lens 22 light shielding unit 22b light transmitting member 23 half mirror 24 objective lens 25 lens 31 image generation unit 31L reflected light 41 Stage 42 Stage drive unit La, Lb Optical axis S, S1, S2 Imaging command

Claims (8)

[Claims] 1. A focal position detecting device for detecting a focal position in an optical measurement, comprising: (a) an imaging optical system for guiding light from an object to be measured to a predetermined light receiving position; Distance changing means for continuously changing a relative optical distance of the object to be measured with respect to an image optical system; (c) detecting means for detecting a change state of the optical distance; (d) the optical distance In the case of continuous change, the image of the measurement object is sequentially imaged a plurality of times at the light receiving position,
Image acquisition means for sequentially acquiring a plurality of images, (e) in parallel with the operation of sequentially acquiring the plurality of images, the evaluation value of the in-focus state of the measurement object at the time when each image is acquired Evaluation value calculating means for sequentially calculating the acquired images, (f) the change state of the optical distance when each of the plurality of images is acquired, and the evaluation value for each of the plurality of images And a focus position calculating means for calculating the focus position based on the relationship between the focus position and the focus position. 2. The focus position detecting device according to claim 1, wherein the image acquiring unit acquires the plurality of images while the optical distance is continuously changed at a constant speed. Focus position detecting device. 3. The focal position detecting device according to claim 1, wherein the evaluation value calculating means is provided in parallel with each other, and alternately or cyclically switches two or more images. A focus position detecting device comprising: a plurality of unit calculating means for calculating the evaluation value for each of the received images. 4. The focal position detecting device according to claim 1, wherein said focal position calculating means determines each of said plurality of images when determining said focal position. A focus position detection device, wherein the change state of the optical distance is corrected according to a required time for capturing each image. 5. A focus position detection method for detecting a focus position in an optical measurement, comprising: (a) the relative position of the measurement object with respect to an imaging optical system for guiding light from the measurement object to a predetermined light receiving position; A distance change step of continuously changing the optical distance, (b) a detection step of detecting the change state of the optical distance, (c) synchronous with the continuous change of the optical distance, The image of the object to be measured is sequentially imaged a plurality of times at the light receiving position, whereby an image acquiring step of sequentially acquiring a plurality of images, (d) In parallel with the image acquiring step, each image is acquired. An evaluation value calculating step of sequentially calculating the evaluation value of the in-focus state of the measurement object at the time from the acquired image, and (e) a change situation of the optical distance when each of the plurality of images is acquired And, for each of the plurality of images, Based on the relationship between the value, the focus position detection method characterized by and a focus position steps stage of determining the focal position. 6. The focus position detecting method according to claim 5, wherein in the image obtaining step, the plurality of images are obtained while the optical distance is continuously changed at a constant speed. Characteristic focus position detection method. 7. The focus position detecting method according to claim 5, wherein the evaluation value calculating step includes: (d-1) alternately or cyclically giving two or more images to a plurality of unit calculating means. And a step of calculating the evaluation value for each of the two or more images by the plurality of unit calculation means. 8. The focal position detecting method according to claim 5, wherein in the focal position calculating step, each of the plurality of images is obtained when determining the focal position. A focus position detecting method, wherein the change state of the optical distance at that time is corrected and used according to the required imaging time of each image.