JP2007281126A - Method and device for measuring position, and exposure device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To discriminate correctly between an arcuate contour and a non-arcuate contour so as to obtain accurate positional information as to a measurement object, when positional information as to the measurement object having both arcuate contours and non-arcuate contours is obtained. <P>SOLUTION: The position measuring method comprises a first step to photo a part of the contour of the measurement object present in a photographing field provided at two or more points, a second step to rotate the measurement object very little, a third step to photo a part of the contour of the measurement object present in the photographing fields after very little rotation is performed, a fourth step to judge whether a part of the contour contained in the photographing fields is arcuate or non-arcuate on the basis of a photographing results obtained in the first and third step, and a fifth step to calculate the circular center and radius of the measurement object subjected to circular approximation as the positional information by subjecting the measurement object to circular approximation. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

 The present invention relates to a position measurement method and a position measurement apparatus for measuring position information of a measurement object having an arcuate contour and a non-arc-shaped outline, and in particular, measurement of position information of a substrate such as a semiconductor wafer as the measurement object. The present invention relates to an exposure apparatus provided with a position measuring apparatus that performs the above.

  Conventionally, in a photolithography process which is one of manufacturing processes of a semiconductor element, a liquid crystal display element, a thin film magnetic head, and other micro devices, a mask or a reticle (hereinafter, these are collectively referred to as a “mask”). An exposure apparatus is used that transfers a formed pattern onto a substrate such as a semiconductor wafer (hereinafter abbreviated as a wafer) or a glass plate coated with a photosensitive agent such as a photoresist via a projection optical system. As one of the exposure methods used in such an exposure apparatus, a step-and-repeat method is known. In this step-and-repeat method, after the pattern formed on the reticle is exposed to a predetermined shot area set on the wafer, the wafer stage is stepped by a certain distance to make another shot on the wafer. By exposing the area and repeating this operation for all shot areas set on the wafer, the image of the pattern formed on the reticle is transferred to the entire wafer. An exposure apparatus that employs this step-and-repeat method is called a stepper and is widely used in the manufacturing process of semiconductor elements and the like.

  In such an exposure apparatus, an alignment technique called enhanced global alignment (EGA) is used in order to align the reticle and the wafer with high accuracy. This EGA images fine alignment marks formed in association with each of several representative (3 to 9) shot areas provided on a wafer, and performs statistical calculations based on the imaging results. Thus, the arrangement coordinates of all shot areas set on the wafer are obtained with high accuracy, and the reticle and wafer are aligned based on the arrangement coordinates of each shot area. Hereinafter, alignment using EGA as described above is referred to as fine alignment.

  In the fine alignment, it is necessary to image the fine alignment mark formed on the wafer at a high magnification, and the imaging field of view (imaging range) is inevitably narrowed. Therefore, when the wafer is placed in a state of being largely displaced with respect to the wafer stage of the exposure apparatus, there is a possibility that the fine alignment mark does not enter the imaging field. In such a case, it is necessary to rotate or move the wafer stage and perform a search for the fine alignment mark so as to be within the imaging field of view, and there is a problem that a great deal of time is wasted.

  Therefore, when the wafer is placed on the wafer stage, pre-alignment for aligning the wafer is performed prior to fine alignment so that the fine alignment mark surely enters the imaging field. Such pre-alignment is further divided into a first pre-alignment and a second pre-alignment. In the first pre-alignment, the wafer is placed on a rotary table provided in the wafer transfer path and rotated, and the eccentricity of the wafer and the notch or orientation flat (hereinafter referred to as orientation flat) formed on the wafer are detected by the line sensor. The rotation of the wafer is controlled so that the notch or orientation flat is positioned in a predetermined direction. The wafer on which the notch or orientation flat is aligned by such first pre-alignment is transferred from the rotary table onto the second pre-alignment stage by the transfer arm. At this time, the stage position is controlled so that the center position of the second pre-alignment stage and the wafer center position coincide with each other based on the amount of eccentricity of the wafer obtained by the first pre-alignment.

  In the second pre-alignment, first, with respect to the contour (edge) of the wafer placed on the stage, for example, one contour including a notch or orientation flat (non-arc-shaped contour), an arc-shaped edge (arc-shaped contour) ) Including a plurality of contours. That is, in the first pre-alignment, the wafer is aligned so that the notch or orientation flat is included in the pre-defined imaging field of view, and therefore the notch or orientation flat or arcuate edge is included in which imaging field of view. Is known. Then, by performing predetermined image processing based on the imaging result of the wafer edge, the wafer position information (the center position and radius of the wafer, the rotational deviation amount around the center axis) is measured. Then, after the wafer is aligned based on the position information thus obtained, the wafer is transferred to the wafer stage of the exposure apparatus by the transfer arm. As described above, it is not always necessary to perform the second pre-alignment in the transfer path. After the first pre-alignment is completed, the wafer is directly transferred to the wafer stage of the exposure apparatus, and the second pre-alignment is performed on the wafer stage. May be performed.

   By the way, in recent years, it is extremely necessary to increase the throughput, that is, to increase the number of substrates processed within a unit time. As a method for realizing such a high throughput, a method in which the first pre-alignment is omitted and only the second pre-alignment is performed is considered. However, according to this method, since the notch or orientation flat is not aligned by the first pre-alignment, it is uncertain which imaging field of view contains the notch or orientation flat. Therefore, it is necessary to geometrically approximate the wafer edge for each edge image in each imaging field, and determine whether the wafer edge included in the imaging field is an arc edge or a non-arc edge (notch or orientation flat). There is.

 However, as described above, when determining the shape of the wafer edge included in each imaging field by geometric approximation, the shape of the notch or orientation flat may be different depending on the wafer. It was difficult. Also, since the edge shape is ambiguous near the boundary between the notch or orientation flat and the arcuate edge, the shape of the wafer edge should be determined by geometric approximation when such a boundary is included in the imaging field of view. Was difficult. As a result, even though notches or orientation flats are actually included in the imaging field of view, it is determined that arc-shaped edges are included, and accurate wafer position information cannot be obtained. there were.

  The present invention has been made in view of such circumstances, and when measuring position information of a measurement object having an arcuate contour and a non-arcuform contour, the arcuate contour and the non-arcuform contour are accurately measured. The purpose is to obtain accurate position information.

The present invention adopts the following configuration corresponding to each diagram shown in the embodiment. However, the reference numerals with parentheses attached to each element are merely examples of the element and do not limit each element.
In order to solve the above problems, a position measuring method according to the present invention is a position measuring method for measuring position information of a measurement object (W) having an arcuate contour and a non-arcuform contour, and is provided at a plurality of locations. A first step (step S1) for imaging a part of the outline of the measurement object that exists in each of the provided imaging fields (2a to 4a), and a second step (step) for slightly rotating the measurement object S2), a third step (step S3) for imaging a part of the contour existing in the imaging field after the micro rotation, an imaging result by the first step, and an imaging result by the third step. Based on the fourth step (step S5) for determining whether a part of the contour included in each imaging field of view is an arc-shaped contour or a non-arc-shaped contour, and the arc-shaped contour is determined in the fourth step. A circle approximation of the measurement object is performed based on an image in the imaging field determined to be included as a part of the outline, and a circle center and a radius of the measurement object approximated by the circle are calculated as the position information. And 5 steps (step S6).
According to the present invention, after imaging a part of the outline of the measurement object respectively present in the imaging visual field provided at a plurality of locations, the measurement object is slightly rotated, and after the minute rotation, the imaging A part of the contour existing in the field of view is imaged, and it is determined whether a part of the contour included in each field of view is an arc-shaped contour or a non-arc-shaped contour based on the imaging results before and after the minute rotation. Therefore, it is possible to accurately determine whether the contour is an arc-shaped contour or a non-arc-shaped contour. As a result, it is possible to prevent erroneous determination and obtain accurate position information of the measurement object.

A position measuring device (LM) according to the present invention is a position measuring device for measuring position information of a measuring object having an arcuate contour and a non-arc-shaped contour, and is a measurement object provided rotatably. And a rotation control device (5a) for controlling the rotation of the measurement object stage, and different contours of the measurement object held on the measurement object stage. A plurality of imaging devices (2, 3, 4) for imaging, an imaging result of each imaging device before micro-rotation of the measurement object stage, and an imaging of each imaging device after micro-rotation of the measurement object stage Based on the result, a determination device (5d) for determining whether a part of the contour imaged by each imaging device is an arc-shaped contour or a non-arc-shaped contour, and the determination device contours the arc-shaped contour. Included as part of A position information calculation device (5e) that performs a circle approximation of the measurement object based on the image of the image pickup device and calculates a circle center and a radius of the measurement object approximated by the circle as the position information. It is characterized by that.
According to the present invention, since it is possible to accurately determine whether a part of the contour imaged by each imaging device is an arc-shaped contour or a non-arc-shaped contour, the position information of the measurement object can be obtained accurately. It is possible to provide a position measurement device capable of

An exposure apparatus (ST) according to the present invention is an exposure apparatus that transfers a pattern formed on a mask (R) onto a substrate (W), and measures position information of at least one of the mask and the substrate. The position measuring device is provided.
According to the present invention, since the position measuring apparatus having the above-described features is provided, an exposure apparatus capable of accurately obtaining the position information of the substrate or the mask can be provided.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1 is a schematic view showing the arrangement of an exposure apparatus provided with a position measurement apparatus according to the first embodiment of the present invention. Further, as an exposure apparatus in the present embodiment, a stepper that transfers a pattern of a semiconductor element formed on a reticle (mask) to a wafer (substrate) by a step-and-repeat method will be described as an example. Furthermore, the wafer as the measurement object has an arcuate contour and a non-arcuform contour (notch or orientation flat) as its external features. In the first embodiment, the notch is formed as a non-arc contour. A wafer having the above will be described as an example.

  In the following description, the XYZ orthogonal coordinate system shown in FIG. 1 is set, and the positional relationship of each member will be described with reference to this XYZ orthogonal coordinate system. The XYZ orthogonal coordinate system is set so that the X axis and the Y axis are parallel to the wafer stage, and the Z axis is set in a direction orthogonal to the wafer stage. In the XYZ coordinate system in the figure, the XY plane is actually set to a plane parallel to the horizontal plane, and the Z-axis is set vertically upward.

 As shown in FIG. 1, the exposure apparatus ST in the first embodiment includes a position measurement apparatus LM, a wafer transfer apparatus ARM, an illumination optical system 6, a reticle stage RST, a projection optical system PL, a wafer stage WST, and a stage control system 13. The image forming apparatus 14 for fine alignment, a fine alignment control system 15 and a main control system 16 are included.

  The position measuring device LM includes a rotary table (measurement object stage) 1, a first imaging device 2, a second imaging device 3, a third imaging device 4, and a pre-alignment control system 5. The position information of the wafer W placed on the turntable 1 (the center position and radius of the wafer W, the amount of rotational deviation around the center axis) is measured, and the wafer W is aligned based on the position information, that is, Pre-alignment is performed.

 The rotary table 1 is a table that can be rotated by a driving mechanism such as a stepping motor (not shown), and holds a wafer W transferred from an upstream transfer device (not shown) on an XY plane by a vacuum suction mechanism. Under the control of the pre-alignment control system 5, the wafer W is rotated in a predetermined direction. The first imaging device 2, the second imaging device 3, and the third imaging device 4 are, for example, CCD cameras, which are arranged at predetermined positions above the rotary table 1, respectively, and the outline (edge) of the wafer W, respectively. The imaging region including a part of the imaging region is imaged, and the image data of each imaging region is output to the pre-alignment control system 5. FIG. 2 is a plan view showing an imaging region (imaging field of view, imaging range) of each of the imaging devices 2 to 4. As shown in FIG. 2, the imaging area of the first imaging device 2 is 2a, the imaging area of the second imaging device 3 is 3a, and the imaging area of the third imaging device 4 is 4a.

 In the present embodiment, the amount of deviation between the center of the wafer W and the rotation center of the turntable 1 depends on the mechanical accuracy of the upstream transfer device, and the wafer W is placed on the turntable 1. In this case, each imaging region (imaging field of view) 2a to 4a is only guaranteed to include a part of the edge of the wafer W, and it is undefined which imaging region includes the notch N or the arc-shaped edge. In the present embodiment, as shown in FIG. 2, the position where the notch N is parallel to the positive direction of the Y axis is set as the reference position of the wafer W. As described above, since it is indefinite which imaging region includes the notch N or the arc-shaped edge, after measuring the position information of the wafer W, the wafer W is aligned (prealigned) with the reference position. There is a need. Accordingly, since it is necessary to check whether the notch N is present at the reference position, it is desirable to set at least one of the imaging regions in an area near the reference position of the notch N. In the present embodiment, the first imaging region 2a is set as such. The arrangement of the second imaging area 3a and the third imaging area 4a is not limited to the arrangement shown in FIG.

  As shown in FIG. 3, the pre-alignment control system 5 includes a pre-alignment control device 5a, a storage device 5b, a binarization processing device 5c, an edge determination device 5d, and a position information calculation device 5e. The pre-alignment control device 5a controls the overall operation of the position measuring device LM under the control of the main control system 16. Specifically, the pre-alignment control device 5a controls the rotation of the turntable 1, while the image pickup regions 2a to 4a input from the image pickup devices 2 to 4 before the turntable 1 is slightly rotated. The image data is stored in the storage device 5b, and the image data of the imaging regions 2a to 4a after the minute rotation of the turntable 1 is stored in the storage device 5b. The storage device 5b stores the image data of the imaging regions 2a to 4a before and after the minute rotation of the turntable 1 according to the request of the pre-alignment control device 5a, while the request of the binarization processing device 5c. Accordingly, the image data of the imaging regions 2a to 4a before and after the minute rotation of the turntable 1 is output to the binarization processing device 5c. Further, the storage device 5b outputs the image data of the imaging regions 2a to 4a after the minute rotation of the turntable 1 to the position information calculation device 5e in response to a request from the position information calculation device 5e.

 Under the control of the pre-alignment control device 5a, the binarization processing device 5c acquires the image data of the imaging regions 2a to 4a before and after the micro-rotation of the turntable 1 from the storage device 5b. Data binarization processing is performed, and each image data (binarized image data) after the binarization processing is output to the edge determination device 5d. The edge determination device 5d determines whether the wafer edge included in each of the imaging regions 2a to 4a is an arc-shaped edge or a notch (non-arc-shaped edge) based on the binarized image data, and indicates the determination result. The edge determination signal is output to the pre-alignment control device 5a and the position information calculation device 5e.

 The position information calculation device 5e acquires image data of the imaging area including the arcuate edge after the minute rotation from the storage device 5b based on the edge determination signal, and based on the image data of the imaging area including the arcuate edge. The center position and radius of the wafer W are calculated, and the image data of the imaging region including the notch N after micro rotation is obtained from the storage device 5b, and the wafer is calculated based on the image data of the imaging region including the notch N. The rotational deviation amount of W is calculated. Further, the position information calculation device 5e outputs the center position, radius, and rotational deviation amount of the wafer W as position information to the pre-alignment control device 5a.

Further, the pre-alignment control device 5 a performs rotation control of the rotary table 1 based on the position information of the wafer W to perform pre-alignment of the wafer W, and outputs the position information of the wafer W to the main control system 16. .
Details of the operation of the position measuring device LM configured as described above will be described later.

Hereinafter, the description will be returned to FIG.
Wafer transfer device ARM is, for example, a robot arm having a vacuum suction mechanism, and grips wafer W by the vacuum suction mechanism under the control of main control system 16 and transfers wafer W from rotary table 1 to wafer stage WST. At this time, the wafer W is transported while maintaining the state aligned with the reference position.

The illumination optical system 6 includes a light source unit, a shutter, an optical integrator (for example, a fly-eye lens), a beam splitter, a condenser lens system, a reticle blind, an imaging lens system, and the like (all not shown). Under the control of the main control system 16, the illumination light IL is emitted toward the reticle R held on the reticle stage RST. Here, as the light source unit, an excimer laser light source such as a KrF excimer laser light source (oscillation wavelength 248 nm) or an ArF excimer laser light source (oscillation wavelength 193 nm), an F ₂ laser light source (oscillation wavelength 157 nm), an Ar ₂ laser light source ( An oscillation wavelength of 126 nm), a copper vapor laser light source, a harmonic generator of a YAG laser, or an ultrahigh pressure mercury lamp (g-line, i-line, etc.) can be used. In this embodiment, a case where a fly-eye lens is provided as an optical integrator will be described as an example. However, the present invention is not limited to this, and a rod integrator (an internal reflection type integrator), a diffractive optical element, or the like can be used.

    The illumination optical system 6 configured in this manner will be described in detail. The illumination light IL emitted from the light source unit enters a fly-eye lens as an optical integrator when the shutter is open. When the illumination light IL enters the fly-eye lens, a surface light source consisting of a large number of light source images, that is, a secondary light source is formed on the exit-side focal plane. The illumination light IL emitted from the fly-eye lens reaches the reticle blind via the beam splitter and the condenser lens system. The illumination light IL that has passed through the reticle blind is emitted onto the reticle R held on the reticle stage RST via the imaging lens system.

  The reticle stage RST includes a reticle mount 7 and a reticle table 8. The reticle mount 7 is a support for the reticle table 8. The reticle table 8 is installed on the reticle mount 7 and can be moved and rotated in the XY plane by a driving mechanism such as a stepping motor (not shown). The reticle table 8 holds the reticle R, which is transported from a reticle transport device (not shown), on the XY plane by a vacuum suction mechanism, while holding the reticle R under a control of the stage control system 13. Align to position.

  Projection optical system PL is composed of a refractive optical system having a predetermined reduction magnification (for example, 1/5, 1/4, or 1/6), and its output optical axis is below the reticle stage RST and the output optical axis thereof is the output of the illumination light IL. It arrange | positions so that it may correspond with the light emission axis IX. For this reason, the illumination light IL that has passed through the reticle R enters the surface of the wafer W on the wafer stage WST via the projection optical system PL. That is, the pattern formed on the reticle R as a mask is reduced to, for example, ¼ or ５ through the projection optical system PL, and is projected and exposed to each shot area on the surface of the wafer W coated with the photoresist. Is done.

  Wafer stage WST includes a wafer gantry 9, an XY stage 10, a substrate table 11, and a wafer holder 12. The wafer mount 9 is a support for the XY stage 10, the substrate table 11, and the wafer holder 12. The XY stage 10 is installed on the wafer gantry 9 and can be moved in the XY plane by a driving mechanism (not shown) such as a two-dimensional linear actuator. The substrate table 11 is supported by three shafts (not shown) at three different support points on the XY stage 10, and can be moved in the Z direction by a lifting / lowering drive mechanism of these three shafts. At the same time, tilting with respect to the XY plane is possible. The wafer holder 12 is installed on the substrate table 11 and holds the wafer W transferred from the wafer transfer device ARM on the XY plane by a vacuum suction mechanism. The wafer holder 12 can be rotated around the Z axis by a driving mechanism such as a stepping motor (not shown). The XY stage 10, the substrate table 11, and the wafer holder 12 define the XYZ coordinates of the wafer W, the amount of rotation about the Z axis, and the tilt angle with respect to the XY plane under the control of the stage control system 13.

  A center table (not shown) for transferring the wafer W to and from the wafer transfer device ARM is provided at a substantially central position of the substrate table 11 and the wafer holder 12. The center table has a vacuum suction mechanism for holding the wafer W, a moving mechanism in the Z-axis direction, and a rotating mechanism around the Z-axis, and is lifted in the Z direction under the control of the stage control system 13. Then, while holding the wafer W transferred from the wafer transfer device ARM, the wafer W is lowered and placed on the wafer holder 12.

  The stage control system 13 controls the reticle stage RST (specifically, the reticle table 8) and the wafer stage WST (specifically, the XY stage 10, the substrate table 11, the wafer holder 12, and the center table) under the control of the main control system 16. To do. The fine alignment imaging device 14 is, for example, an off-axis type alignment sensor, which is arranged on the side surface of the projection optical system PL, and includes several representative (3 to 9) shot regions provided on the wafer W. The fine alignment marks formed along with the respective images are imaged, and image data as the imaging results are output to the fine alignment control system 15. Under the control of the main control system 16, the fine alignment control system 15 performs EGA processing based on the image data of the fine alignment mark, calculates the array coordinates of each shot area, and calculates the array coordinates of each shot area. The shot area arrangement information shown is output to the main control system 16.

  The main control system 16 controls the overall operation of the exposure apparatus ST based on a predetermined control program. Specifically, the main control system 16 controls the stage control system 13 based on shot area arrangement information (that is, reticle stage). By aligning the RST and the wafer stage WST in synchronization, the reticle R and the wafer W are aligned (fine alignment). The main control system 16 also controls the center of the center table based on the position information of the wafer W acquired from the position measuring device LM when the wafer W is transferred to the wafer stage WST (specifically, the center table). The position of the XY stage 10 is controlled via the stage control system 13 so that the position matches the center position of the wafer W.

  Next, the operation of the exposure apparatus ST in the first embodiment configured as described above, in particular, the operation of the position measurement apparatus LM provided in the exposure apparatus ST will be described in detail.

  FIG. 4 is an operation flowchart when the position of the wafer W is measured by the position measuring apparatus LM. It is assumed that the wafer W is transferred from the upstream transfer device onto the rotary table 1 of the position measuring device LM in advance. Further, as described above, when the wafer W is placed on the turntable 1, it is only guaranteed that each of the imaging regions 2a to 4a includes a part of the edge of the wafer W, and the notch N or the arc-shaped edge. It is indefinite which imaging region is included. Hereinafter, as illustrated in FIG. 5, the description will be given assuming that the wafer W is placed in a state where the notch N is included in the first imaging region 2a at a position slightly shifted from the reference position. . The second imaging area 3a and the third imaging area 4a include arcuate edges.

  First, each of the imaging devices 2 to 4 of the position measuring device LM images the corresponding imaging regions 2a to 4a, and outputs the image data as the imaging result to the pre-alignment control device 5a (step S1). This image data is image data (image data before rotation) of the imaging regions 2a to 4a before the micro rotation of the turntable 1. The pre-alignment control device 5a stores the pre-rotation image data of each of the imaging regions 2a to 4a in the storage device 5b.

  Subsequently, the pre-alignment control device 5a performs control so that the turntable 1 is slightly rotated, that is, the wafer W is slightly rotated (step S2). The notch after such a slight rotation is referred to as a notch N ′. Although the rotation direction of the wafer W may be clockwise or counterclockwise, it is assumed that the wafer W is rotated clockwise as shown in FIG. If the minute rotation amount is θ, it is desirable that the minute rotation amount θ is about half of the size of the imaging region. Specifically, when the length of the long side of the first imaging region 2a is L and the radius of the wafer W is r, the minute rotation amount θ is expressed by the following relational expression (1).

  Here, the reason why the rotation amount of the wafer W is minute is that the center position of the wafer W and the rotation center of the turntable 1 are shifted when the wafer W is transferred to the turntable 1, that is, eccentricity. This is for minimizing the wafer edge change caused by the eccentricity, which may occur in the image after the micro-rotation described below, even if this occurs.

  And each imaging device 2-4 images each imaging area 2a-4a after rotating the rotation table 1 minutely, and outputs the image data (post-rotation image data) which is the said imaging result to the pre-alignment control apparatus 5a. (Step S3). The pre-alignment control device 5a stores the post-rotation image data of each of the imaging regions 2a to 4a in the storage device 5b.

  Next, the pre-alignment control device 5a instructs the binarization processing device 5c to perform binarization processing on the pre-rotation image data and post-rotation image data. The binarization processing device 5c acquires pre-rotation image data and post-rotation image data of the imaging regions 2a to 4a from the storage device 5b, and performs binarization processing on these image data (step S4). As is well known, binarization processing compares luminance information for each pixel included in image data with a threshold value, and converts all pixels having luminance values smaller than the threshold value to black luminance, while exceeding the threshold value. All pixels having luminance are converted to white luminance. In this embodiment, for example, the binarization process is performed so that the brightness of the wafer edge is black and the brightness of other backgrounds is white. FIG. 6A shows pre-rotation image data and post-rotation image data of the first imaging region 2a after binarization processing. FIG. 6B shows pre-rotation image data and post-rotation image data of the second imaging region 3a after the binarization process. FIG. 6C shows pre-rotation image data and post-rotation image data of the third imaging region 4a after the binarization process. In these figures, shaded portions indicate black luminance.

  Here, FIG. 7 shows the difference between the pre-rotation image data and the post-rotation image data for each imaging region. FIG. 7A shows difference image data in the first imaging region 2a. FIG. 7B shows difference image data in the second imaging region 3a. FIG. 7C shows difference image data in the third imaging region 4a. As can be seen from these drawings, the difference image data of the second imaging region 3a and the third imaging region 4a including the arc-shaped edge is almost all black. That is, in the case of an arcuate edge, since the edge shape does not change even if the wafer W is rotated slightly, the pre-rotation image data and the post-rotation image data are substantially the same. The brightness is zero, that is, all black. On the other hand, as shown in FIG. 7A, when the notch N (N ′) is included, the pixel areas corresponding to the notch N and the notch N ′ are white, but the other pixel areas are black. That is, when the wafer edge is the notch N, the pre-rotation image data and the post-rotation image data are different. Therefore, when the difference between them is taken, only the pixel area corresponding to the notch N and the notch N ′ is white.

  Thus, when the wafer edge is notch N, the total difference value between the pre-rotation image data and the post-rotation image data (the sum of the luminance difference values calculated for each pixel) has a certain value, and the wafer edge has an arc shape. In the case of an edge, the total difference value is almost zero. Therefore, the total difference value between the pre-rotation image data and the post-rotation image data is calculated for each imaging region, and is compared with a predetermined threshold value (first threshold value) to be included in each imaging region 2a to 4a. It can be determined whether the wafer edge is an arcuate edge or notch N.

  FIG. 6D shows pre-rotation image data and post-rotation image data when, for example, the vicinity of the boundary between the notch N and the arcuate edge is included in the imaging region, and FIG. 6 (d) is differential image data. As can be seen from these figures, even if the vicinity of the boundary between the notch N and the arcuate edge is included in the imaging region, the total difference value between the pre-rotation image data and the post-rotation image data has a certain value. Yes. That is, even when the vicinity of the boundary between the notch N and the arcuate edge, which is difficult to discriminate with the conventional method, is included in the imaging region, the wafer edge can be discriminated accurately by the method described above. it can.

 Based on the principle as described above, the edge discriminating device 5d receives the pre-rotation image data and the post-rotation image data (binarized image data) after the binarization processing of the imaging regions 2a to 4a from the binarization processing device 5c. Is obtained, the total difference value is calculated on the basis of the binarized image data before and after the rotation for each imaging region, the total difference value is compared with the first threshold value, and the total difference value is calculated from the first threshold value. When it is small, it is determined that the arcuate edge is included in the imaging region. On the other hand, when the total difference value is greater than or equal to the first threshold value, it is determined that the notch N is included in the imaging region. (Step S5). In the present embodiment, the edge determination device 5d determines that the first imaging region 2a includes the notch N, and the second imaging region 3a and the third imaging region 4a include arcuate edges. Then, the edge determination device 5d outputs an edge determination signal indicating the determination result of the wafer edge to the pre-alignment control device 5a and the position information calculation device 5e.

  The position information calculation device 5e acquires post-rotation image data of the imaging region including the arc-shaped edge from the storage device 5b based on the edge determination signal, and the wafer based on the post-rotation image data including the arc-shaped edge. The center position and radius of W are calculated, and the rotated image data of the imaging region including the notch N (N ′) is acquired from the storage device 5b, and the wafer W is based on the rotated image data including the notch N ′. Is calculated (step S6). In the present embodiment, the center position and radius of the wafer W are calculated based on the rotated image data of the second imaging region 3a and the third imaging region 4a. Hereinafter, a specific example of a method for calculating the center position and radius of the wafer W will be described.

  First, the position information calculation device 5e performs image processing based on the rotated image data of the second imaging region 3a and the third imaging region 4a, and generates a point group including a plurality of points along the arcuate edge. Then, circular approximation of the arc-shaped edge is performed by applying the least square method to the point group. Specifically, when there are n points having coordinates (Xi, Yi); (i = 1, 2,..., N) in the point group, the coordinates of the center position of the wafer W to be obtained are (a, b ), Where r is the radius, the equation of the circle is expressed by the following equation (2). When the expression (2) is expanded, the following expression (3) is obtained, and when the expression (3) is further modified, it is expressed by the following expression (4).

  Using the above equation (4), the coordinates of each of the n points are represented simultaneously by the following equation (5). When equation (5) is placed as in equation (6), the solution to be obtained (matrix X ) Is expressed by the following equation (7) by the least square method. Therefore, the components a and b of the matrix X are the coordinates of the center position of the circle to be obtained. The radius r can be obtained by the following equation (8).

 The position information calculation device 5e calculates the center position and radius of the circle by the geometric circle approximation as described above. Note that the image data used when performing the circular approximation may be image data before the minute rotation. As shown in FIG. 5, the position information calculation device 5e calculates the rotational deviation amount φ of the wafer W by performing image processing based on the rotated image data in the first imaging region 2a. Thus, the rotational deviation amount φ indicates the deviation amount of the notch N ′ with respect to the reference position. The position information calculation device 5e outputs the center position, radius, and rotation deviation amount calculated as described above to the pre-alignment control device 5a as the position information of the wafer W. The rotational deviation amount φ can be calculated from the image data before the minute rotation. In this case, the minute rotation amount θ of the rotary table 1 needs to be added to the rotation deviation amount φ calculated as described above. There is.

 Further, for example, as shown in FIG. 8, when the notch N is included in the third imaging region 4a, in step S6, the first imaging region 2a and the second imaging region including arcuate edges are included. Based on the image data 3a, the center position and radius of the wafer W are calculated. Note that the rotational deviation amount φ of the wafer W can also be calculated based on the image data of the third imaging region 4a. In this case, for example, as shown in FIG. 9, there may be a case where the notch N is not included in any imaging region, or a case where only a part of the notch N is included. In this case, since it is determined in step S5 that all the imaging areas include arc-shaped edges, in step S6, the center position and radius of the wafer W are determined based on the rotated image data of all the imaging areas. While calculating, the amount of rotational deviation is not calculated. As described above, when it is determined that the notch N is not included in any imaging region, the pre-alignment control device 5a proceeds to the process of step S2 and rotates the turntable 1 slightly. That is, when it is determined that the notch N is not included in any imaging region, even if the center position and radius of the wafer W can be calculated from the image data including the arc-shaped edge, the rotational deviation amount of the wafer W Since φ cannot be calculated, the processes in steps S2 to S5 are repeated until the notch N is included in any imaging region.

 Then, when the pre-alignment control device 5a acquires the position information of the wafer W by the above processing, the pre-alignment control apparatus 5a performs pre-alignment of the wafer W based on the position information (step S7). Specifically, the turntable 1 is rotated by the rotation deviation amount φ of the wafer W, and the notch N is aligned with the reference position. The pre-alignment control device 5a outputs the position information of the wafer W to the main control system 16 after the completion of the pre-alignment (step S8).

  On the other hand, the main control system 16 controls the wafer transfer device ARM to transfer the wafer W after pre-alignment from the rotary table 1 to the wafer stage WST (specifically, the center table). At this time, the main control system 16 makes the center position of the center table coincide with the center position of the wafer W based on the position information (particularly the center position and radius) of the wafer W acquired from the pre-alignment control device 5a. The position of the XY stage 10 is controlled. The center table rises to a predetermined height, receives the wafer W from the wafer transfer device ARM, then descends, and places the wafer W on the wafer holder 12.

  The main control system 16 controls the illumination optical system 6, the stage control system 13, and the fine alignment control system 15 to perform the wafer W exposure process. Since this exposure process is the same as in the prior art, a detailed description thereof is omitted, but first, representative several (3 to 9) shots provided on the wafer W by the fine alignment imaging device 14. A fine alignment mark formed in association with each region is imaged. Then, the fine alignment control system 15 performs EGA processing based on the image data of the fine alignment mark, calculates the array coordinates of each shot area, and mainly uses shot area array information indicating the array coordinates of each shot area. Output to the control system 16. The main control system 16 aligns the shot areas set on the wafer W based on the shot area arrangement information, and sequentially transfers the pattern of the reticle R onto the wafer W via the projection optical system PL. . Further, the position information (particularly the center position and radius) of the wafer W obtained by the position measuring device LM is used as an offset amount when aligning each shot area.

  As described above, according to the first embodiment, in the pre-alignment of the wafer W, when the first pre-alignment as in the related art is omitted, that is, in which imaging region the notch N or the arc-shaped edge is included is undefined. Even in this case, it is possible to accurately determine whether the wafer edge included in each imaging region is a notch N or an arcuate edge. As a result, only the image data of the arc-shaped edge is accurately extracted, and the center position and radius of the wafer W are calculated based on the arc-shaped image data, so that accurate position information can be obtained.

[Second Embodiment]
Next, a second embodiment of the present invention will be described. The second embodiment is an example in which the wafer W has an orientation flat that is a straight edge instead of the notch N as a non-arc-shaped edge. Accordingly, the apparatus configurations of the position measurement apparatus LM and the exposure apparatus ST are the same as those in the first embodiment, and hence the description similar to that in the first embodiment is omitted below, and only the characteristic parts in the second embodiment are described. explain.

  FIG. 10 is a plan view of the wafer W in the second embodiment. As shown in this figure, it is assumed that the first imaging region 2a and the second imaging region 3a include an arcuate edge and the third imaging region 4a includes an orientation flat F. Note that the orientation flat F after the slight rotation is denoted by F ′. Further, the reference position of the wafer W is set when the orientation flat F is parallel to the Y axis. FIG. 11A shows pre-rotation image data and post-rotation image data of the third imaging region 4a after the binarization processing. FIG. 11B shows difference image data in the third imaging region 4a. Note that an imaging region including an arcuate edge is the same as that in the first embodiment, and a description thereof will be omitted.

  As can be seen from FIG. 11B, even when the wafer edge is orientation flat F, the total difference value between the pre-rotation image data and the post-rotation image data has a certain value. Therefore, by calculating the total difference value between the pre-rotation image data and the post-rotation image data for each imaging region and comparing it with a predetermined threshold, it is possible to determine whether the wafer edge included in each imaging region 2a to 4a is an arcuate edge. Or orientation flat F can be discriminated. Further, even when the vicinity of the boundary between the orientation flat F and the arcuate edge, which is difficult to discriminate with the conventional method, is included in the imaging region, the wafer edge can be discriminated accurately.

 Therefore, the operation of the position measurement apparatus LM in the second embodiment differs from the operation in the first embodiment in a method of calculating the rotation deviation amount φ of the wafer W, and other wafer edge discrimination methods and wafer W The calculation method of the center position and the radius is the same. Hereinafter, a method for calculating the rotational deviation amount φ of the wafer W in the second embodiment will be specifically described.

 The rotation deviation amount φ of the wafer W having the orientation flat F is an inclination of the orientation flat F with respect to the Y axis, as shown in FIG. Therefore, first, image processing is performed based on post-rotation image data including the orientation flat F, a point group including a plurality of points along the orientation flat F is generated, and the orientation square F is applied to the point group by applying the least square method. The linear approximation of is performed. Then, the inclination of the orientation flat F with respect to the Y axis, that is, the rotational deviation amount φ of the wafer W can be obtained based on the straight line obtained from the geometric approximation as described above. On the other hand, in the pre-alignment of the wafer W in the second embodiment, the rotary table 1 is rotated by the rotational displacement amount φ of the wafer W obtained as described above, and the orientation flat F is parallel to the Y axis. W will be aligned.

 As described above, according to the second embodiment, when pre-alignment of the wafer W is omitted, the conventional pre-alignment is omitted, that is, in which imaging region the orientation flat F or the arc-shaped edge is included. Even if it is indefinite, it is possible to accurately determine whether the wafer edge included in each imaging region is orientation flat F or an arcuate edge. As a result, only the image data of the arc-shaped edge is accurately extracted, and the center position and radius of the wafer W are calculated based on the arc-shaped image data, so that accurate position information can be obtained.

 In the second embodiment, before the turntable 1 is slightly rotated, a point group including a plurality of points along the wafer edge is generated for each pre-rotation image data of the imaging regions 2a to 4a. By applying the least square method to the group, the wafer edge is linearly approximated, the residual between the straight line obtained by the linear approximation and each point is calculated, and the wafer edge included in the imaging region is arc-shaped based on the residual It may be determined whether it is an edge or orientation flat F. In the case of an arcuate edge, the variation in the residual is large, whereas in the case of the orientation flat F, the variation in the residual is small. Therefore, for example, by comparing the maximum value of the residual with a predetermined threshold value, it is possible to determine the wafer edge included in the imaging region. Further, the determination of the wafer edge is not limited to the determination of the wafer edge based on the maximum residual value. For example, the determination of the wafer edge may be performed based on the average value of a plurality of residual data. However, this method can be applied only when the non-arc-shaped edge is a straight line shape, and when the vicinity of the boundary between the orientation flat F and the arc-shaped edge is included in the imaging region, or in the first embodiment. Thus, this is not applicable when the non-arc-shaped edge is a notch N.

 In the first and second embodiments, the wafer W having the notch N or the orientation flat F as an example of the non-arc-like edge has been described. However, the present invention is not limited to this, and the non-arc shape having a shape other than the notch or orientation flat. The present invention can be applied even to an edge. In addition, for example, even when a foreign object or the like adheres to an arcuate edge, as a result, it can be regarded as a non-arced edge as the shape of the edge. The center position and radius of the wafer W can be obtained by excluding the image data, and the accuracy of the position information can be improved.

 In the first and second embodiments, the wafer edge is determined based on the total difference value between the image data before and after the minute rotation. However, the present invention is not limited to this, and shows the degree of coincidence between the image data before and after the minute rotation. A correlation value is obtained, the correlation value is compared with a predetermined threshold (second threshold), and if the correlation value is smaller than the second threshold, it is determined that a non-arc-shaped edge is included in the imaging region. Further, when the correlation value is equal to or larger than the second threshold value, the wafer edge may be determined by determining that the arc-shaped edge is included in the imaging region.

 Further, the measurement object is not limited to the wafer W, and may be any other object as long as it has an arcuate edge and a non-arced edge. For example, in the exposure apparatus, when a mask or reticle having an arc-shaped edge and a non-arc-shaped edge is adopted, position information of the mask or reticle can be measured according to the present invention.

 Moreover, in the said 1st and 2nd embodiment, although the wafer edge was imaged with the three imaging devices 2-4, it is not limited to this, Furthermore, you may provide a some imaging device. The more the image data of the arc-shaped edge, the higher the accuracy of calculating the center position and radius of the wafer W. Therefore, it is desirable to provide as many imaging devices as possible within the allowable range of the apparatus cost.

 In the first and second embodiments, the position information of the wafer W is measured and the pre-alignment is performed on the turntable 1. However, the present invention is not limited to this, and an imaging apparatus that images the wafer edge is included in the projection optical system PL. It may be arranged on the side surface, and measurement of position information of wafer W and pre-alignment may be performed on wafer stage WST.

 The position measuring apparatus LM in the first and second embodiments is not only an exposure apparatus, but also an inspection apparatus that inspects the overlay accuracy of the pattern formed on the wafer, and the line width of the pattern formed on the wafer. It can also be used for aligning a wafer to be inspected with a predetermined accuracy in an inspection apparatus for inspecting, an inspection apparatus for inspecting a macro defect of a pattern formed on a wafer, and other inspection apparatuses.

1 is a schematic configuration diagram of an exposure apparatus ST provided with a position measurement apparatus LM in a first embodiment of the present invention. It is explanatory drawing which shows each imaging area in 1st Embodiment of this invention. It is a block diagram of the pre-alignment control system 5 in the first embodiment of the present invention. It is an operation | movement flowchart of the position measuring device LM in 1st Embodiment of this invention. It is the 1st explanatory view showing operation of position measuring device LM in a 1st embodiment of the present invention. It is the 2nd explanatory view showing operation of position measuring device LM in a 1st embodiment of the present invention. It is the 3rd explanatory view showing operation of position measuring device LM in a 1st embodiment of the present invention. It is a 4th explanatory view showing operation of position measuring device LM in a 1st embodiment of the present invention. It is a 5th explanatory view showing operation of position measuring device LM in a 1st embodiment of the present invention. It is the 1st explanatory view showing operation of position measuring device LM in a 2nd embodiment of the present invention. It is the 2nd explanatory view showing operation of position measuring device LM in a 2nd embodiment of the present invention.

Explanation of symbols

 LM ... position measuring device, ST ... exposure device, ARM ... wafer transfer device, 6 ... illumination optical system, RST ... reticle stage, PL ... projection optical system, WST ... wafer stage, 13 ... stage control system, 14 ... for fine alignment Image pickup device, 15 ... fine alignment control system, 16 ... main control system, 1 ... rotary table (stage for measurement object), 2 ... first image pickup device, 3 ... second image pickup device, 4 ... third image pickup Devices, 5 ... pre-alignment control system, 5a ... pre-alignment control device (rotation control device), 5b ... storage device, 5c ... binarization processing device, 5d ... edge discrimination device (determination device), 5e ... position information calculation device (Position information calculation device)

Claims (13)

A position measurement method for measuring position information of a measurement object having an arcuate contour and a non-arcuform contour,
A first step of imaging a part of the contour of the measurement object, each present in an imaging field of view provided at a plurality of locations;
A second step of micro-rotating the measurement object;
A third step of imaging a part of the contour respectively present in the imaging field after the minute rotation;
A fourth step of determining whether a part of the contour included in each imaging visual field is an arc-shaped contour or a non-arc-shaped contour based on the imaging result of the first step and the imaging result of the third step;
Based on the image in the imaging field determined to include the arc-shaped contour as a part of the contour in the fourth step, circle approximation of the measurement object is performed, and the circle of the measurement object approximated to the circle A fifth step of calculating a center and a radius as the position information;
A position measurement method characterized by comprising: The fourth step includes
Obtaining a difference value between luminance information in the image captured in the first step and luminance information in the image captured in the third step for each imaging visual field;
When the difference value is smaller than the first threshold value, it is determined that an arcuate contour is included in the imaging field as part of the contour, while when the difference value is equal to or greater than the first threshold value, Determining that a non-arc-shaped contour is included in the imaging field as part of the contour;
The position measuring method according to claim 1, further comprising: The fourth step includes
Obtaining a correlation value between the luminance information in the image captured in the first step and the luminance information in the image captured in the third step for each imaging field;
When the correlation value is smaller than the second threshold value, it is determined that a non-arc-shaped contour is included in the imaging field as a part of the contour, while when the correlation value is equal to or larger than the second threshold value. Determining that an arcuate contour is included in the imaging field as part of the contour;
The position measuring method according to claim 1, further comprising: Between the first step and the second step,
Generating a point group consisting of a plurality of points along a part of the contour based on the imaging result of the first step for each imaging field;
Linearly approximating the point cloud;
Calculating a residual between a straight line obtained by the linear approximation and each point;
Determining whether a linear contour is included in the imaging field as the non-arc-shaped contour based on the residual; and
The position measurement method according to claim 1, wherein the position measurement method includes:  In the fourth step, when it is determined that the non-arc-shaped contour is not included in all the imaging fields, the measurement object is set so that the non-arc-shaped contour is included in any imaging field. The position measuring method according to any one of claims 1 to 4, further comprising a step of rotating.  6. A step of calculating a rotational deviation amount around the central axis of the measurement object as position information based on an image within an imaging field determined to include a non-arc-shaped contour. The position measurement method according to any one of the above. A position measuring device for measuring position information of a measurement object having an arcuate contour and a non-arcuform contour,
A stage for a measurement object provided rotatably,
A rotation control device for controlling the rotation of the measurement object stage;
A plurality of imaging devices that respectively image different portions of the contour of the measurement object held on the measurement object stage;
Based on the imaging result of each imaging device before the micro-rotation of the measurement object stage and the imaging result of each imaging device after the micro-rotation of the measurement object stage, the contour imaged by each imaging device A determination device for determining whether a part is an arc-shaped contour or a non-arc-shaped contour;
Based on the image of the imaging device determined to include the arc-shaped contour as a part of the contour by the determination device, a circle approximation of the measurement target is performed, and the circle center of the measurement target approximated by the circle and A position information calculation device that calculates a radius as the position information;
A position measuring device comprising:   The determination device includes, for each imaging device, luminance information in an image captured before the measurement object stage is rotated slightly and luminance information in an image captured after the measurement object stage is rotated slightly. When a difference value is obtained and the difference value is smaller than a first threshold value, it is determined that an arcuate contour is included in the imaging range of the imaging device as a part of the contour, while the difference value is the first value. The position measuring device according to claim 7, wherein a non-arc-shaped contour as a part of the contour is determined to be included in an imaging range of the imaging device when the threshold is equal to or greater than the threshold value.   The determination device includes, for each imaging device, luminance information in an image captured before the measurement object stage is rotated slightly and luminance information in an image captured after the measurement object stage is rotated slightly. When a correlation value is obtained and the correlation value is smaller than a second threshold value, it is determined that a non-arc-shaped contour is included in the imaging range of the imaging device as a part of the contour, while the correlation value is The position measuring device according to claim 7, wherein if it is equal to or greater than a threshold value of 2, it is determined that an arcuate contour is included in an imaging range of the imaging device as a part of the contour.   The determination device generates, for each imaging device, a point group including a plurality of points along a part of the contour based on an imaging result before the measurement object stage is slightly rotated. 8. It is determined whether or not a linear contour is included in each imaging range as the non-arc-shaped contour based on a residual between a straight line obtained by linear approximation and each point. The position measuring device according to any one of?  When the rotation control device determines that the non-arc-shaped contour is not included in the imaging range of all the imaging devices in the determination device, the non-arc-shaped contour is in the imaging range of any imaging device. The position measurement apparatus according to claim 7, wherein the stage for measurement object is rotated so as to be included.   The position information calculation device calculates a rotational deviation amount around the central axis of the measurement object as position information based on an image of an imaging device determined to include a non-arc-shaped contour. The position measuring device according to any one of to 11. An exposure apparatus for transferring a pattern formed on a mask onto a substrate,
An exposure apparatus comprising: a position measuring device according to claim 12 for measuring position information of at least one of the mask and the substrate.

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