JPH1140491A - Detection of focusing position - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain the focusing position of an optical system in a short measuring time independently of the vibration of a stage by imaging an object at plural times during the movement of the object from one side to the other side of a predetermined range provided by the stage movable in the direction of the optical axis of the optical system to obtain the focusing position of the optical system from a plurality of images for different stage positions. SOLUTION: When a wafer stage is driven from Z1 to Z2, a drive target value in the Z-direction is denoted by 31, an actual position in the Z-direction is denoted by 32, an acceleration is denoted by 33, and an error component between the target value 31 and the actual position 32 is denoted by 34, and for the error components 34, the drive start and end periods, wherein the error is large, are excluded and the uniform motion period is used as a focusing measurement range 35. Measurement for the focusing detection is carried out in the range of ±h μm from a temporary focus center Zc. The data obtained during the part of image capture timing is processed during the period of transfer timing in an image processing part, and the contrast is calculated from the image in the image processing part. This processing is repeatedly carried out in the range of ±h μm from Zc, and a quadratic functional approximation curve is obtained, the peak of which being the focusing position.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for detecting a focal position of an optical system, and for example, a circuit pattern such as an IC or LSI formed on a reticle in a semiconductor manufacturing exposure apparatus is projected onto a wafer surface by a projection lens. The present invention relates to an in-focus position detecting method suitable for obtaining position information of a wafer by observing an alignment mark formed on a wafer surface via a projection lens before projecting.

[0002]

2. Description of the Related Art Conventionally, in a projection exposure apparatus, an alignment mark formed on a wafer surface is observed through a projection lens to obtain positional information of the wafer, and the alignment between the wafer and a reticle engraved with a pattern to be exposed is performed. I do. As an observation method of the wafer alignment mark for this purpose,
A method that mainly uses non-exposure light and does not pass through a projection lens (O
FF-AXIS method), a method using exposure light and passing through a reticle and a projection lens (exposure light TTR method), and a method using non-exposure light and passing through a projection lens (non-exposure light TTL method). Was used. In particular, recently, an imaging element is used for an alignment light detection system, and the obtained one-dimensional or two-dimensional image signal is converted into a digital signal, which is subjected to filtering and template matching so as to correspond to wafers of various processes. It has become.

[0003]

As the miniaturization of ICs and LSIs progresses year by year and higher alignment accuracy is required, defocusing of alignment marks with respect to the image sensor during alignment becomes a problem. It has become. This is because defocus is not a problem if the alignment scope is an ideal telecentric optical system.However, in practice, there are restrictions on the adjustment of the scope and aberrations including the projection lens when measuring wafer marks via the projection lens. Is not an ideal telecentric optical system because it is not easy to correct the image.When defocusing occurs, the image height of the wafer mark on the image sensor changes, which results in a measurement error and alignment. An error occurs.

In order to solve this problem, there is a case where a focus position of a wafer mark on an image pickup device of an alignment detection system is obtained before performing wafer alignment. For example,
When the alignment mark on the wafer enters the alignment scope detection area and the wafer stage position enters the tolerance, a temporary focus center is set, and the wafer is moved from that position in the direction of the projection lens optical axis (hereinafter, Z direction) to the projection lens side. (Hereinafter, the projection lens side is the + direction of Z, and the opposite side is
Direction), a certain amount of defocusing is performed to obtain an alignment mark image, and a certain amount of Z is again defocused in the + direction to obtain an alignment mark image. This is repeated until the defocus amount reaches a certain amount. Driving and measurement are similarly repeated in the negative Z direction from the temporary focus center, and the in-focus position is obtained from the obtained wafer mark images at a plurality of different Z positions.

[0005] However, this method has a disadvantage that it takes time to find the in-focus position of one mark.
This is mainly because the settling time of the stage associated with the driving of the Z stage is long and it is necessary to wait for the Z stage position to fall within a certain tolerance. FIG. 5 shows this state. When the drive profile output by the control system is step drive as indicated by 61, the difference between the profile and the actual position, that is, the error 62 increases at the rising edge (jerk) of the profile 61. In order for the vibration to converge, several cycles of the natural frequency of the stage are required. Since the frequency is usually several tens of Hz, it takes about 100 msec for the stage to enter the tolerance of 50 nm, for example. Since the measurement is started after a certain period of time after entering the tolerance, the time required for the measurement becomes longer. Assuming that a total of 12 shots of wafer alignment marks are measured during wafer global alignment, the in-focus position is determined for each mark measurement. The mark is driven ± 10 μm in the Z direction from the temporary focus center position for each mark, and the total is calculated for each 1 μm. Assuming that 21 points of images are captured, it is assumed that it takes 150 msec from the start of 1 μm driving in the か ら direction to settling, and 66 msec including a waiting time to capture an image, and (150 + 66) msec × 21 per shot.
= 4536 msec, 4.536 sec per wafer
× 12 = 54.432 sec. In this case, a time corresponding to a time for exposing one wafer is required for the detection of the focus position of the alignment, and the throughput is reduced.

A first object of the present invention is to provide a method of determining a focal point of an optical system in a short measurement time without being affected by the vibration of the stage accompanying the step driving of the stage. It is an object of the present invention to provide an in-focus position detecting method capable of performing the following.

A second object of the present invention is to provide a focusing position detecting method capable of determining the focusing position of the optical system with high accuracy in the method of determining the focusing position of the optical system.

A third object of the present invention is to provide a method for determining the focal point of an optical system, which is simple and highly accurate without being affected by the vibration of the stage accompanying the step driving of the stage. It is an object of the present invention to provide a focus position detection method capable of obtaining a position.

A fourth object of the present invention is to provide a method of obtaining an image plane of an optical system in a short measurement time without being affected by the vibration of the stage accompanying the step driving of the stage. It is to provide a possible image plane detection method.

A fifth object of the present invention is to provide an image plane detecting method capable of obtaining an image plane of an optical system with high accuracy in a method of obtaining an image plane of an optical system.

A sixth object of the present invention is to provide an image plane detecting method capable of determining the image plane of the optical system with high accuracy when the light irradiated to the optical system is pulsed light. is there.

A seventh object of the present invention is to provide a method for obtaining an image plane of an optical system, which is capable of accurately and accurately detecting an image plane of an optical system by a simple method without being affected by vibration of a stage accompanying step driving of the stage. An object of the present invention is to provide an image plane detection method that can be obtained.

[0013]

In order to achieve the first object, according to a first aspect of the present invention, an object is connected to a stage by a stage movable in the optical axis direction of the optical system. Moving from one side of the predetermined range including the image plane to the other, capturing the image of the object observed through the optical system a plurality of times by the image sensor during the movement period, and obtaining a plurality of different stage positions. The in-focus position of the optical system is obtained from the above image.

In order to achieve the second object, in the first aspect, a measurement timing signal is generated during the movement period, and the position of the stage is synchronized with the measurement timing signal. Measure and monitor the accumulation period of the image sensor to determine the position error of the stage during the accumulation period, and correct the position of the stage corresponding to the image obtained by the image sensor based on the position error. I just need. Further, when the observation light is pulsed light, a measurement timing signal is generated during the movement period, the position of the stage is measured in synchronization with the measurement timing signal, and an accumulation period of the imaging element is measured. And monitoring the light emission timing of the pulse light to determine the position error of the stage before or after light emission during the light emission during the accumulation period, and determine the position of the stage corresponding to the image obtained by the imaging device. What is necessary is just to correct based on this position error.

[0015] In order to achieve the third object, in the first aspect, the storage period of the image sensor is set to have a maximum power among vibration components of a control system of a movement direction of the stage. It is preferable to make the frequency substantially equal to an integral multiple of the period of the frequency component.

In order to achieve the fourth object, according to a second aspect of the present invention, in the optical axis direction of the optical system, or in the direction parallel to the axis orthogonal to the optical axis direction and a plane normal to the optical axis. An object which is moved from one side of a predetermined range including the image forming surface of the optical system to the other by a stage movable in a rotational direction about an axis, and which is observed via the optical system during the moving period; Is captured by a single or a plurality of image sensors, and an image plane of the optical system is obtained from a plurality of obtained images having different stage positions or postures and different image heights.

In order to achieve the fifth object, in the second aspect, a measurement timing signal is generated during the movement period, and the position and the position of the stage are synchronized with the measurement timing signal. The posture is measured and the accumulation period of the image sensor is monitored to determine the position and orientation error of the stage during the accumulation period, and the position and orientation of the stage corresponding to the image obtained by the image sensor are determined by the position. The correction may be made based on the position error and the posture error.

In order to achieve the sixth object, in the second aspect, a measurement timing signal is generated during the movement period, and the position and the position of the stage are synchronized with the measurement timing signal. The position of the stage and the position error of the stage before or after the light emission during the accumulation period and the light emission timing of the pulse light are monitored by measuring the posture and monitoring the accumulation period of the image sensor and the light emission timing of the pulsed light. The position and orientation of the stage corresponding to the image obtained by the above may be corrected based on the position and orientation errors.

In order to achieve the seventh object, in the second aspect, the accumulation period of the image pickup device is set to a frequency having a maximum power of a vibration component of a control system of a moving direction of the stage. It is good to make it substantially equal to an integral multiple of the cycle of the component.

[0020]

Next, an embodiment of the present invention will be described. According to a first embodiment of the present invention, in a method of determining a focal point position of a lens, a stage, which is disposed near an imaging plane of the lens and is movable in at least an optical axis direction of the lens, is moved. An image of an object placed on the stage, which is observed through the lens during the constant velocity period during the moving period, is observed by the imaging device, and the in-focus position of the lens is obtained from the obtained images. Thus, the in-focus position of the lens can be obtained in a short measurement time without being affected by the vibration of the stage accompanying the step driving of the stage.

In the second embodiment of the present invention, the substrate on the stage can be moved to a position near the image forming plane of the lens in order to obtain the focal point of the lens. Moving a possible stage, the focal point position of the lens is determined from a plurality of images at different stage positions obtained by observing an image of an object placed on the stage observed through the lens by an image sensor. In the method for detecting the in-focus position to be obtained, a measurement timing generator for measuring the position of the stage is provided, the position of the stage is measured in synchronization with a signal from the timing generator, and an accumulation period of the image sensor is stored. Is monitored to determine the position error of the stage during the accumulation period, and the stage position corresponding to the image obtained by the image pickup device is corrected, so that the lens position can be accurately determined. It is obtained by enabling the determination of the focal position.

In a third embodiment of the present invention, in order to obtain an image plane of a lens, a substrate on a stage can be moved to a position near an imaging plane of the lens. Moving a stage movable in a rotation direction about an axis parallel to an orthogonal axis on a plane having a normal to the axial direction and the optical axis, and moving the stage through the lens during a constant velocity period in the moving period of the stage. By obtaining the image plane of the lens from a plurality of images obtained by observing an image of an object placed on the stage observed by the one or more imaging devices, the stage of the stage accompanying the step driving of the stage is observed. The in-focus position of the lens can be obtained in a short measurement time without being affected by vibration.

Further, in the fourth embodiment of the present invention, in order to obtain the image plane of the lens, the substrate on the stage can be moved to the vicinity of the imaging plane of the lens. An object placed on the stage that moves through a stage that is movable in a direction of rotation about an axis parallel to an orthogonal axis on a plane having a normal to the axial direction and the optical axis, and that is observed through the lens Measurement timing for measuring the position of the stage in the in-focus position detection method for obtaining the image plane of the lens from a plurality of images at different stages obtained by observing the image of the stage with one or more imaging devices A timing generator for measuring the position of the stage in synchronization with the signal from the timing generator, and monitoring the accumulation period of the image sensor to determine the position error of the stage during the accumulation period; It is obtained by possible to obtain the image surface of the lens with high accuracy by correcting the stage position corresponding to the obtained image by the element.

In a fifth embodiment of the present invention, in order to obtain an image plane of a lens, a substrate on a stage can be moved to a position near an imaging plane of the lens. An object placed on the stage that moves through a stage that is movable in a direction of rotation about an axis parallel to an orthogonal axis on a plane having a normal to the axial direction and the optical axis, and that is observed through the lens In the in-focus position detection method for obtaining the image plane of the lens from a plurality of images at different stage positions obtained by observing the image by one or a plurality of imaging devices, light irradiated to the lens is pulsed light. A measurement timing generator for measuring the position of the stage; measuring the position of the stage in synchronization with a signal from the timing generator; By monitoring the light emission timing to determine a position error of the stage at the time of the light emission or before or after the light emission during the accumulation period, and correcting the stage position corresponding to the image obtained by the imaging device. ,
This makes it possible to obtain the image plane of the lens with high accuracy.

According to a sixth embodiment of the present invention, there is provided a method for determining a focal point position of a lens, wherein at least an optical axis direction of the lens or an optical axis capable of moving a substrate on a stage near an imaging plane of the lens. Moving a stage movable in a rotation direction about an axis parallel to an orthogonal axis on a plane having a normal to the axial direction and the optical axis, and moving the stage through the lens during a constant velocity period in the moving period of the stage. An image of an object placed on the stage observed by the imaging device, the accumulation period of which substantially coincides with an integral multiple of the cycle of the frequency component having the maximum power among the vibration components of the control system in the moving direction of the stage. The in-focus position of the lens is obtained from a plurality of images obtained by observation, and the lens can be measured in a short time with a simple configuration without being affected by the vibration of the stage accompanying the step driving of the stage. It is obtained by enabling the determination of the focus position.

In a seventh embodiment of the present invention, in order to obtain an image plane of a lens, a substrate on a stage can be moved to a position near an imaging plane of the lens. Moving a stage movable in a rotation direction about an axis parallel to an orthogonal axis on a plane having a normal to the axial direction and the optical axis, and moving the stage through the lens during a constant velocity period in the moving period of the stage. The accumulation period of an image of an object placed on the stage observed by one or more of the vibration components of the control system for the movement direction of the stage substantially coincides with an integral multiple of the cycle of the frequency component having the maximum power. By obtaining the image plane of the lens from a plurality of images obtained by observation by a plurality of image sensors, the lens can be measured in a short time with a simple configuration without being affected by the vibration of the stage accompanying the step driving of the stage. It is obtained by enabling the determination of the focal position.

[0027]

Embodiments of the present invention will be described below with reference to the drawings. First Embodiment FIG. 1 is a partial schematic view of a projection exposure apparatus to which a focus position detecting method according to a first embodiment of the present invention is applied.

In FIG. 1, reference numeral 1 denotes a reduction projection lens whose optical axis is indicated by AX in the figure, and whose image plane is perpendicular to the AX direction in the figure. The illumination system 11 emits ultraviolet light such as i-line and excimer laser light.

The reticle 2 is held on a reticle stage 3, and the pattern of the reticle 2 is reduced and projected to 1/5 to 1/2 at the magnification of the reduction projection lens 1 to form an image on its image plane. Reference numeral 4 denotes a wafer having a surface coated with a resist, on which a plurality of exposure regions (shots) formed in the previous exposure step are arranged.

Reference numeral 5 denotes a stage on which the wafer is placed, a chuck for attracting and fixing the wafer 4 to the wafer stage 5, an XY stage which can be moved horizontally in the X-axis direction and the Y-axis direction,
Ζ-axis actuator 7 and Z-direction position detection sensor 6
A leveling stage that is controlled by the optical axis of the projection lens 1 and is rotatable about an axis that is horizontal in the X-axis and Y-axis directions, and is rotatable about an axis that is horizontal to the axis. And a six-axis correction system for matching a reticle pattern image to a region to be exposed on a wafer. A stage mark 8 having an alignment mark or the like is formed on the wafer stage.

In FIG. 1, there are three alignment scopes, and a TTR alignment scope 10 is provided on a wafer 4 via a reticle 2 and a projection lens 1 by light from a TTR alignment illumination system 12 having the same or substantially the same wavelength as exposure light. Wafer mark or stage mark 8
And the reflected light from the mark follows the same path as TT
Return to the R alignment scope 10. Since a polarizer is contained in the TTR alignment scope 10, the illumination light and the reflected light do not interfere with each other. The reflected light forms an image on the image sensor 13 and is taken into the image processing unit 20 as an image. The switching mirror 17 escapes outside the exposure area of the illumination system during wafer exposure,
Only when observing the wafer stage 5 from the TTR alignment scope 10 via the projection lens 1, it moves into the exposure area. The off-axis alignment scope 9 captures an image of a wafer mark or a stage mark 8 on the wafer 4 illuminated by non-exposure light from a light source (not shown).
4. This image is taken into the image processing unit 20 as an image. The TTL off-axis alignment scope 15 forms an image of the wafer mark or the stage mark 8 on the wafer 4 illuminated by the non-exposure light from a light source (not shown) via the projection lens 1 on the image sensor 16. This image is similarly captured by the image processing unit 20 as an image.

The main control unit 24 shown in FIG.
Is placed in a predetermined area of the wafer 4 at a position in the XY plane (the position of X and Y, and {rotation around an axis parallel to the axis}) and the position in the Ζ direction (of the axis parallel to each of the X and Y axes). The entire system is controlled so as to perform exposure while adjusting the rotations α, β and {height on the axis}). That is, the alignment of the reticle pattern in the XY plane is performed by the position data of the interferometer (not shown) on the reticle stage 3 and the interferometer (not shown) on the wafer stage 5 and the alignment scopes 9, 10, and 10.
This is realized by calculating control data from the position data of the wafer 4 obtained from 15 and controlling the reticle position control system 23 and the wafer position control system 22.

Hereinafter, a method of detecting the focus position of the off-axis alignment scope 9 by the focus position detection method according to the first embodiment of the present invention will be described. FIG. 2 shows that the wafer stage 5 is moved in the Ζ direction by Ζ1 when the horizontal axis represents time.
Drive target position 31 and ウ エ ハ direction position sensor 6 generated by wafer stage control system 22 when driven from to Ζ2
, The actual position 32 in the Ζ direction, the acceleration 33 based on the sensor detection, the target position 31, and the position 3 actually driven.
2 shows an error component 34. Looking at the error component 34, since the error is large at the start and end of driving, the constant velocity movement period excluding this part is used as the in-focus measurement range 35 for measurement. Assuming that the temporary focus center is Δc, ± h from this Δc
It is assumed that measurement for focus detection is performed in the range of μm.
FIG. 3 is an enlarged view of the portion A in FIG. 2, in which an image capture timing Ig and a transfer timing It by the image sensor are additionally written. The data obtained in the Ig part is I
The image data is transferred to the image processing unit 20 and processed in the period of t. In this case, the Ζ-direction position Ζk of the wafer stage corresponding to the image accumulated in Ig is determined by measuring the error at each Ζ-direction position measurement sampling position on the assumption that the Ζ-direction position measurement system measures n times at intervals of td between Ig. If δi,

[0034]

(Equation 1) Given by A contrast calculation is performed by the image processing unit 20 from the image obtained during the Ig period. The contrast evaluation value is obtained, for example, by differentiating the range of the wafer mark in the image from the histogram of the differential value by the P-tile method.

The above processing is repeated during the constant speed movement period of the wafer stage 5 from the position Ζc−h to the position Ζc + h in FIG. 2, and the contrast evaluation value for each wafer Ζ direction position is plotted in FIG. It is. A quadratic function approximation curve 39 is obtained by the least squares method from the data 38 at each 法 position, and this peak Ζtc is set as the focal point position. In addition to the least squares method, the peak may be obtained based on the calculated value of the center of gravity or the degree of object.

According to the present embodiment, it is not necessary to wait for the vibration convergence due to the step driving of the Ζ stage, so that the in-focus position of the alignment scope can be detected at high speed. For example, a range of ± 10 μm from the temporary focus center is 1 sec.
Even if the scanning is performed in the same way, the focus measurement is completed in one second per one shot, and even if 12 shots per wafer
It only takes seconds. In addition, the accumulation time is 33 msec.
Even so, the amount of the Z stage that moves during 33 msec is 0.66 μm, and the depth of focus of a normal off-axis alignment scope is several μm. Is obtained.

It should be noted that if the Z-direction scanning range Zscan, the detection time Tmeas, the image pickup device accumulation time Ig, and the detection Z-direction resolution Zres are set so as to satisfy the following equations, high-precision detection can be expected.

[0038]

(Equation 2) In the above, the embodiment in which the focus position of the off-axis scope 9 is detected has been described.
Alternatively, the in-focus position of the TTL alignment scope 10 when the illumination system 11 is a CW light source can be similarly obtained.

Second Embodiment In the first embodiment, the wafer stage 5 is
Although an example in which the in-focus measurement is performed while moving at a constant speed in the direction has been described, according to the present invention, even if the wafer position during the measurement period is sent in a staircase (step) shape as shown in FIG. The in-focus position can be detected. In FIG. 5, reference numeral 61 denotes a Z stage at a Δh pitch from height 0 to height Ζ.
The step pattern when sent to h, 62 is an error component. Ig is an image capture period. Conventionally, capture has started at time t1 after a certain time td has elapsed after entering a small tolerance Zt. However, if the present invention is applied, the tolerance enters the tolerance as shown in FIG. Even when the capture is started at time t2 when the image is not captured, the Z-direction position Ζk 'of the wafer stage corresponding to the image accumulated by Ig is the error at each Ζ-direction position measurement sampling position as in FIG.

[0040]

(Equation 3) Since the error can be corrected, data can be captured without waiting for the stage to settle.

As in the case of FIG. 3, the position in the wafer Ζ direction is sent stepwise within the range of Zc ± h around the temporary focus point Zc, and the image is fetched at the same fetch timing as in FIG. Then, the data of FIG. 4 is obtained as in the case of FIG. 3, and the in-focus position can be obtained from this data.

Third Embodiment FIG. 6 is a block diagram showing a control system according to a third embodiment of the present invention. In FIG. 6, the wafer stage control system 22 includes rotations α, β, and Z around axes parallel to the Ζ direction (X and Y axes).
Only the control system of the height Z) on the axis is shown. When driving in the を direction, the measurement pulse 8 from the synchronization signal generation unit 84 is used.
5, the wafer {direction measured by the position measurement unit 82}
The arithmetic unit 81 outputs the difference between the value of the direction sensor 6 and the Ζ direction drive profile calculated and calculated by the arithmetic unit 81 to the Z direction drive unit 83 to drive the Ζ direction actuator 7. The image obtained from the imaging device 13 is
Take in. At this time, a GATE signal 86 indicating the accumulation period of the image sensor 13 is sent to the wafer Z direction measurement unit 82 so that the wafer Ζ direction measurement unit 82 can know at what timing an image is accumulated. Or
The synchronizing signal 87 may be output from the synchronizing signal generator 84 to the image processor. However, the GATE signal 8 is usually used because it is easier for the image processor 20 to process with a signal generated internally.
6 to the wafer Ζ direction measuring unit 82 to send PPL or digital P
Synchronize with LL. As a result, the processing of the present embodiment becomes possible.

Fourth Embodiment The projection lens changes the lens image surface or causes a curvature of field due to the thermal effect of exposure light or light reflected from the wafer during wafer exposure. In order to prevent this, the exposure height, the reflectance of the wafer, and the reticle transmittance are used as parameters to calculate the image plane change, or the image plane of the projection lens is measured during wafer replacement, etc. There is a method to follow the image plane, but the former is difficult to follow the change in the image plane by calculation, and it actually causes an error, and the latter takes time to detect the focus of the projection lens. There's a problem.

According to the present invention, not only the change of the focal point of the alignment scope but also the change of the focal point of the projection lens 1 (image plane of the projection lens) can be detected at high speed.

A method for detecting a change in the image plane of the projection lens according to the present invention will be described with reference to FIG. TTR alignment light source 1
CW light having a wavelength equal to or near the exposure light emitted from the exposure light from the TTR alignment scope 1
The light passes through the reticle 2 and the projection lens 1 through the switching mirror 17 to enter the exposure area of the projection lens 1. At this time, a stage mark 8 having a mark in a sagittal direction with a pitch close to the resolution limit of the projection lens 1 is placed at a position where the alignment light is irradiated on the wafer stage 5. Since the portion other than the mark of the stage mark 8 is a reflection surface for the alignment light, the reflected light in the NA of the projection lens 1 passes through the projection lens 1 and the reticle 2 and passes through the switching mirror 17 to perform the TTR alignment. The image enters the scope 10 and the image of the stage mark 8 is formed on the image sensor 13.

When the contrast of the image is measured while scanning the wafer stage 5 in the Ζ direction in the same manner as in the case of the alignment scope 9, a measurement result as shown in FIG. 4 is obtained. Find the focal position. Normally, when the image plane position is obtained, the curvature of the field often occurs.
Is moved, the in-focus positions at a plurality of points having different image heights are obtained, and the image plane is obtained from these data. When the curvature of field is small, the image plane may be obtained from data of one image height. This image plane is stored in a storage device (not shown) connected to the control unit 24 and managed as a device offset. The image plane change can be detected by comparing the recorded image plane with the newly measured image plane. When aligning the Z direction of the wafer stage 5 with this image plane, the least square plane of the image plane is determined, and the wafer plane is aligned with this plane. In FIG. 1, only one set of the TTR alignment scope 10, the image pickup device 13, and the TTR alignment light source 12 is formed, but the TT is similarly placed at a symmetric position about the projection lens optical axis AX.
By providing an R observation system, a plurality of image pickup devices can simultaneously obtain a plurality of image focus in-focus positions. In this case, the synchronization signal applied to the plurality of image sensors is the same or the other is P
Synchronization is performed by LL or the like, and measurement is performed simultaneously by a plurality of image sensors.

Fifth Embodiment The present invention can be applied even when the exposure light source is pulse light. Also in this case, the sequence is the same as that of the above-described CW light, but the image pickup element captures the image when the pulse is emitted. Therefore, the Zk position at the time of image capture is based on FIG.

[0048]

(Equation 4) Here, δj is given by sampling data at (or before) the pulse emission. As a result, it is possible to eliminate an error when no pulse is output.

The configuration of the control system in this case is such that the light emission timing signal 90 output from the exposure control unit 88 in FIG. 6 is received by the wafer Ζ direction measurement system 82, and the timing at which the pulse is emitted is determined by the wafer に お い て direction measurement unit. 82 to know. 89 is a pulse light source. In this case, the light emission timing signal 90 is transmitted to the wafer
And synchronize with a PLL or digital PLL. Alternatively, the synchronizing signal 91 is sent from the synchronizing signal generator 84 to the exposure controller.
May be issued.

Sixth Embodiment In the above description, the timing of the image sensor is set to, for example, NTS.
Although a CCD camera or the like compliant with C was fixed, if the storage time of an image pickup device such as a CCD line sensor or a CCD camera with an electronic shutter can be changed, the storage time is set to the maximum of the vibration components of the control system of the wafer stage. Can be detected with high precision by making the frequency component an integral multiple of the period of the frequency component having the power.

FIG. 8 shows this state. The error component 71 of the position of the stage in the Z direction oscillates at the natural frequency of the wafer stage in the Z direction, which is a natural frequency of the apparatus. Reference numeral 72 denotes a power spectrum of the error component 71, which has the maximum power at the frequency fc. The frequency component having the maximum power of the vibration component of the control system can be obtained by measuring the actual position of the wafer stage when the stage is stepped, for example. Is set to an integral multiple of the cycle of this frequency component as shown in the following equation.

[0052]

(Equation 5) In this case, an image having an average value of n periods can be obtained regardless of the phase of the vibration, and the position accuracy is improved. In this case, it is not necessary to add the error component δi in the equation (1).

[0053]

As described above, according to the first aspect of the present invention, in the method of determining the in-focus position of the optical system, the object is moved by the stage movable in the optical axis direction of the optical system. Moving from one side of the predetermined range including the imaging plane of the system to the other, and taking an image of the object observed through the optical system a plurality of times by an image sensor during the movement period, and obtaining the obtained stage position. By obtaining the in-focus position of the optical system from a plurality of images different from each other, the in-focus position of the optical system can be obtained in a short measurement time without being affected by the vibration of the stage accompanying the step driving of the stage.

[0054] In the first aspect, further,
A measurement timing signal is generated during the movement period, the position of the stage is measured in synchronization with the measurement timing signal, and an accumulation period of the image sensor is monitored to determine a position error of the stage during the accumulation period. By correcting the position of the stage corresponding to the image obtained by the imaging device based on the position error, the focal point position of the optical system can be obtained with high accuracy.

Further, in the first aspect, the accumulation period of the image sensor is made substantially coincident with an integral multiple of a cycle of a frequency component having a maximum power among vibration components of a control system for moving the stage. By obtaining the in-focus position of the optical system from a plurality of images obtained by observation by the imaging device, the optical system can be measured in a short time with a simple configuration without being affected by the vibration of the stage accompanying the step driving of the stage. The in-focus position can be obtained.

According to the second aspect of the present invention, in the direction of the optical axis of the optical system, or in the direction of rotation about an axis parallel to the axis perpendicular to the direction of the optical axis and a plane normal to the optical axis. An object is moved by a movable stage from one side of the predetermined range including the imaging plane of the optical system to the other, and one or more images of the object observed through the optical system during the movement period are displayed. By measuring the image plane of the optical system from a plurality of images with different stage positions or postures and image heights obtained by imaging with an image sensor, short measurement without being affected by the vibration of the stage accompanying the step driving of the stage The focal point position of the optical system can be obtained in time.

Further, in the second aspect, further,
A measurement timing signal is generated during the movement period, and the position and orientation of the stage are measured in synchronization with the measurement timing signal and the accumulation period of the imaging device is monitored to monitor the position and the position of the stage during the accumulation period. An image plane of the optical system can be obtained with high accuracy by obtaining a posture error and correcting the position and posture of the stage corresponding to the image obtained by the image sensor based on the position and posture errors.

In the second aspect, when the observation light is pulse light, a measurement timing signal is generated during the movement period, and the position of the stage is synchronized with the measurement timing signal. Monitoring the accumulation period of the imaging device and the emission timing of the pulsed light to determine the position and orientation error of the stage during, before, or after the light emission during the accumulation period. By correcting the position and posture of the stage corresponding to the image obtained by the element based on the position and posture errors, the image plane of the optical system can be obtained with high accuracy.

Further, in the second aspect, one or a plurality of imagings whose accumulation period substantially coincides with an integral multiple of the cycle of the frequency component having the maximum power among the vibration components of the control system in the moving direction of the stage. By obtaining the image plane of the optical system from a plurality of images obtained by observing with the element, the focusing of the optical system can be performed in a short time with a simple configuration without being affected by the vibration of the stage accompanying the step driving of the stage The position can be determined.

[Brief description of the drawings]

FIG. 1 is a partial schematic view of a projection exposure apparatus using a focus position detection method according to a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a relationship between a wafer height, an acceleration, and an error component when the in-focus position detecting method according to the first embodiment of the present invention is used.

FIG. 3 is an explanatory diagram showing a relationship among a wafer height, an image pickup device accumulation time, and a height control system sampling timing when the in-focus position detecting method according to the first embodiment of the present invention is used.

FIG. 4 is an explanatory diagram showing a relationship between a wafer Z direction position and a contrast evaluation value in the first embodiment of the present invention.

FIG. 5 is an explanatory diagram showing a relationship among a wafer height, an error component, and a sampling timing when the wafer height is step-driven in the second embodiment of the present invention.

FIG. 6 is a schematic diagram of a control system for implementing a focus position detection method according to a third embodiment of the present invention.

FIG. 7 is an explanatory diagram showing a relationship among a wafer height, an image pickup device accumulation time, a height control system sampling timing, and a pulse emission timing when the in-focus position detection method according to the third embodiment of the present invention is used. .

FIG. 8 is an explanatory diagram of an error component of a wafer height and a frequency component thereof when a focus position detection method according to a sixth embodiment of the present invention is used.

[Explanation of symbols]

1: Reduction projection lens, 2: Reticle, 3: Reticle stage, 4: Wafer, 5: Wafer stage, 8: Stage mark, 9: Off-axis alignment scope, 1
0: TTL alignment scope, 11: illumination system, 1
3, 14, 16: imaging device, 15: TTR alignment scope, 20: image processing unit, 22: wafer position control system, 23: reticle position control system, 24: main control unit.

Claims (11)

[Claims] An object is moved from one side to another of a predetermined range including an image forming plane of the optical system by a stage movable in an optical axis direction of the optical system, and is moved through the optical system during the moving period. The image of the object to be observed is imaged a plurality of times by an image sensor,
A focus position detection method, wherein a focus position of the optical system is obtained from a plurality of images obtained at different stage positions. 2. A stage for generating a measurement timing signal during the movement period, measuring a position of the stage in synchronization with the measurement timing signal, and monitoring an accumulation period of the image pickup device. Find the position error of
The in-focus position detecting method according to claim 1, wherein a position of the stage corresponding to an image obtained by the imaging device is corrected based on the position error. 3. The observation light is pulsed light, a measurement timing signal is generated during the movement period, the position of the stage is measured in synchronization with the measurement timing signal, and the accumulation period of the imaging element is measured. And monitoring the light emission timing of the pulse light to determine the position error of the stage before or after light emission during the light emission during the accumulation period, and determine the position of the stage corresponding to the image obtained by the imaging device. 2. The in-focus position detecting method according to claim 1, wherein the correction is performed based on the position error. 4. The apparatus according to claim 1, wherein the accumulation period of the image sensor is made substantially equal to an integral multiple of a cycle of a frequency component having a maximum power among vibration components of a control system in a moving direction of the stage. The focus position detection method described in the above. 5. The movement according to claim 1, wherein the movement is a uniform movement.
The focus position detection method according to any one of the above. 6. The in-focus position detecting method according to claim 1, wherein the movement is a fine pitch step movement. 7. The optical system according to claim 1, wherein the contrast of each of the plurality of images obtained by the image sensor is evaluated, and a position where the evaluation value is maximum is set as a focal point position of the optical system. In-focus position detection method. 8. An optical system comprising: a stage movable in an optical axis direction of an optical system or a rotation direction about an axis parallel to a direction perpendicular to the optical axis direction and a plane normal to the optical axis; Moving from one of the predetermined ranges including the imaging surface of the system to the other, and capturing an image of the object observed through the optical system by one or more imaging elements during the movement period, and obtained. An in-focus position detecting method, wherein an image plane of the optical system is obtained from a plurality of images having different stage positions or postures and image heights. 9. A measurement timing signal is generated during the movement period, and a position and an orientation of the stage are measured in synchronization with the measurement timing signal, and an accumulation period of the image sensor is monitored to monitor the stage. The position and orientation error of the stage is obtained, and the position and orientation of the stage corresponding to an image obtained by the imaging device are corrected based on the position and orientation error. Focus position detection method. 10. The observation light is pulsed light, a measurement timing signal is generated during the movement period, and the position and orientation of the stage are measured in synchronization with the measurement timing signal. The accumulation period and the light emission timing of the pulse light are monitored to determine the position and orientation errors of the stage before and after the light emission during the accumulation period and before and after the light emission. 9. The method according to claim 8, wherein the position and orientation of the stage are corrected based on the position and orientation errors. 11. The apparatus according to claim 8, wherein the accumulation period of the image sensor is made substantially equal to an integral multiple of a cycle of a frequency component having a maximum power among vibration components of a control system in a movement direction of the stage. The focus position detection method described in the above.