JP2009168634A - Shape measuring method, and shape measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To perform correct shape measurement by removing the influence of a foreign substance adhering to its end surface when the shape of the end surface of a disk-like measuring object such as a semiconductor wafer is measured based on its projected image. <P>SOLUTION: Distribution information (original contour shape information) on a contour position of the measuring section is derived by image processing of a pick-up image with a camera (S4), an approximate curve to the contour shape information is calculated (S5), and the information whose residual is within a predetermined tolerance is extracted as true contour shape information from the original contour shape information (S6). <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a shape measuring method for measuring the shape of a chamfered end of a disk-shaped measuring object (mainly a semiconductor wafer, other hard disk aluminum substrate, glass substrate, etc.) based on the projected image. And a shape measuring apparatus.

When manufacturing a semiconductor wafer (hereinafter referred to as a wafer) or manufacturing a device using a wafer, the edge (edge) of the wafer may be damaged or chipped due to contact with other components or a wafer holding member. There is a case. In addition, the wafer may break due to the scratches and chips. It is considered that the ease of occurrence of scratches and chips at the edge of the wafer is related to the shape of the wafer end face (so-called edge profile portion). For this reason, it is important to correctly measure the edge profile of a disk-shaped measuring object represented by a wafer. The shape of the end face here is a profile in the thickness direction (one-dimensional direction) of the wafer, that is, the shape of the cross section in the thickness direction, and is hereinafter referred to as an edge profile.
A typical example of the edge profile measurement method is the nondestructive inspection method (SEMI-MF-) specified in the Semi Standard, which is a standard established by the Semiconductor Equipment and Materials International (SEMI). 928-0305 Standard Method B). In this non-destructive inspection method, light is projected from the direction almost parallel to the front and back surfaces of the wafer on the chamfered edge of the disk-shaped wafer, and the camera is viewed from the direction opposite to the projection direction. In this method, a projected image of the end face of the wafer is picked up and the shape of the end face of the wafer is measured based on the projected image (hereinafter referred to as an optical projection measurement method). The contour of the projected image obtained by this optical projection measurement method represents the cross-sectional shape of the end face of the wafer (the cross-sectional shape cut in the thickness direction).
The optical projection measurement method is shown, for example, in Patent Document 1 as a shape detection method using a shape detector that detects the cross-sectional shape of a wafer. Patent Document 2 proposes an optical system for preventing the occurrence of blurring of edges and diffraction fringes in a projected image in the optical projection measurement method.
FIG. 3A is a diagram illustrating an example of a projection image (black shadow portion) obtained by imaging the end face of the wafer 1 by the optical projection measurement method.

The main purpose of the edge profile measurement is to evaluate whether the end face shape is within an allowable range with respect to a predetermined design shape (appropriateness). For this reason, in the measurement of the edge profile, usually, an index value of the end face shape is calculated by executing predetermined image processing on the projected image of the wafer end face, and whether the calculated index value is within an allowable range. The suitability is determined depending on whether or not. The index values are, for example, a chamfering width k, a chamfering angle θ, a chamfering radius rm (also referred to as a tip R) of the wafer end surface, and the like.
FIG. 4 is a diagram for explaining an example of the index value of the edge profile of the wafer. As shown in FIG. 4, the chamfer width k is determined from the boundary position Q1 (or Q2) between the front and back surfaces of the wafer (surfaces substantially parallel to each other) and the chamfered portion E (end surface) at the end in the projected image. , The width to the apex of the chamfered portion (end surface) (the length in the direction parallel to the front and back surfaces (radial direction of the wafer 1)). Further, the chamfering angle θ is an angle formed by an extension line of the front and back surfaces of the wafer 1 and a tangent to the surface of the chamfered portion E (end surface) near the boundary position Q1 (or Q2) in the projection image. The chamfer radius rm is the radius of the arc when the chamfered portion E (end surface) is approximated by an arc.
JP 7-218228 A JP 2006-145487 A

By the way, a measurement environment of a measurement object that is a precision part such as a wafer (semiconductor wafer) is usually maintained in a clean environment, but rarely foreign matter such as dust is attached to the measurement object. If foreign matter such as dust adheres to the measurement site (end surface) of the wafer (measurement object) in the optical projection measurement method, depending on the position of the adhering material, the attached image may be added to the projected image of the wafer edge. The projected image of the kimono may appear as a protrusion. FIG. 3B schematically shows a state in which a projection image of an adhering substance (foreign matter) is reflected in a projection image (black shaded portion) obtained by imaging the end face of the wafer 1 by the optical projection measurement method. FIG. Note that the size of the projection image of the deposit in FIG. 3B does not necessarily represent the size of the deposit on the actual wafer 1.
As shown in FIG. 3B, when an image of an adhering substance such as dust is reflected in the projection image obtained by the optical projection measurement method, the end surface shape (the index value) of the measurement object is accurately measured. However, there is a problem that a wafer that should be identified as a conforming product is erroneously identified as a nonconforming product.
Therefore, the present invention has been made in view of the above circumstances, and the object of the present invention is to measure the shape of the end face of a disk-shaped measuring object such as a semiconductor wafer based on the projected image. An object of the present invention is to provide a shape measuring method and a shape measuring device capable of removing the influence of a foreign substance adhering to an end face and performing correct shape measurement.

In order to achieve the above object, the shape measuring method according to the present invention is applied to a measuring portion including a chamfered end portion of a disk-shaped measuring object such as a semiconductor wafer on each side of the measuring object. Light is projected by the light projecting means from a parallel direction, and a projected image of the end surface of the measurement object is captured by the image capturing means from a direction opposite to the light projecting direction, and the measurement object is based on the projected image. This is a method of measuring the shape of the end face of the above, and is a method of executing the following steps (1-1) to (1-3) by a predetermined processor.
(1-1) An image processing procedure for deriving distribution information of the contour position of the measurement unit by image processing on a captured image by the imaging unit.
(1-2) An approximate curve calculation procedure for calculating an approximate curve for the distribution information of the contour position obtained by the image processing procedure.
(1-3) The measurement in which the residual with respect to the approximate curve calculated by the approximate curve calculation procedure is within a predetermined allowable range from the distribution information of the contour position obtained by the image processing procedure True contour information extraction procedure for extracting as distribution information of the true contour position of the part.
For example, the approximate curve calculation procedure includes an Nth order expression where N is an integer equal to or greater than 2, an arc or elliptic arc expression, a combination of the Nth order expression and an arc or elliptic arc expression, the Nth order expression and a first order Least squares of a curve expression represented by one of a combination of an expression, a combination of an arc or elliptical arc expression and a linear expression, or a combination of the Nth order expression and an arc or elliptical arc expression and a primary expression It is conceivable that this is a procedure for calculating an approximate curve by approximation.
Note that the true contour information extraction procedure is a tolerance in which a residual for the approximate curve calculated by the approximate curve calculation procedure is determined in advance from the distribution information of the contour position obtained by the image processing procedure. It can also be said that it is a procedure for removing the thing exceeding.

In general, the end of a measurement object such as a wafer is chamfered with a relatively smooth curve shape that can be approximated by a curve equation such as an Nth order equation (2 ≦ N) or an arc equation as a target shape. Therefore, if no foreign matter is attached to the end of the measurement object, the distribution information (the set of coordinates representing the contour position) of the contour position of the measurement unit obtained by image processing on the captured image by the imaging unit is It can be approximated with high accuracy (with a small residual) by the equation of the curve according to the target shape.
In addition, the measurement site of measurement objects that are precision parts such as wafers (semiconductor wafers) is usually maintained in a clean environment, so even if foreign matter adheres to the edges of the measurement object, The adhesion location is a small part of the end of the measurement object.
Therefore, by calculating an approximate curve by a curve formula corresponding to the target shape for the distribution information (contour shape information) of the contour position obtained by image processing on the image of the projection image of the measurement unit, the projected image of the foreign object Only the information on the contour position of the part of FIG. Therefore, it is possible to extract the distribution information of the true contour position of the measurement unit from which the information of the contour position of the adhered part of the foreign substance has been removed by the true contour information extraction procedure.

Moreover, this invention can also be grasped | ascertained as a shape measuring apparatus which performs the shape measuring method which concerns on this invention shown above.
That is, the shape measuring apparatus according to the present invention is characterized by including each of the components shown in the following (2-1) to (2-5).
(2-1) A light projecting means for projecting light from a direction parallel to the front and back surfaces of the measurement object to a measurement part including a chamfered end portion of the disk-shaped measurement object.
(2-2) Imaging means for capturing a projection image of the measuring unit from a direction opposite to the light projecting direction by the light projecting means.
(2-3) Image processing means for deriving distribution information of the contour position of the measurement unit by image processing on a captured image by the imaging means.
(2-4) Approximate curve calculating means for calculating an approximate curve for the distribution information of the contour position obtained by the image processing means.
(2-5) The measurement in which the residual with respect to the approximate curve calculated by the approximate curve calculation unit is within a predetermined allowable range from the distribution information of the contour position obtained by the image processing unit True contour information extracting means for extracting as distribution information of the true contour position of the part.
The shape measuring apparatus according to the present invention also has the same effects as the shape measuring method according to the present invention described above.

  According to the present invention, when measuring the contour shape of the end face of a disk-shaped measurement object such as a semiconductor wafer based on the projected image, the true contour position from which the information on the contour position of the adhered part of the foreign matter has been removed. Distribution information can be extracted. As a result, the correct shape measurement can be performed by removing the influence of the foreign matter adhering to the end face.

Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings so that the present invention can be understood. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention.
1 is a schematic plan view of a shape measuring apparatus W according to an embodiment of the present invention, FIG. 2 is a schematic side view of the shape measuring apparatus W, and FIG. 3 is a diagram showing an example of a projected image of an end face of a semiconductor wafer, 4 is a diagram for explaining an example of an index value of an edge profile (end surface shape) of a semiconductor wafer, FIG. 5 is a flowchart showing a procedure of a shape measurement process executed by the shape measuring apparatus W, and FIG. 6 is a shape measuring apparatus. FIG. 7 is a diagram illustrating an example of distribution information of an outline position obtained by W and an approximate curve thereof, and FIG. 7 is an approximate curve when an end shape of a semiconductor wafer is approximated by a curve equation represented by a combination of a plurality of equations FIG.

The shape measuring apparatus W according to the present invention uses a light projecting unit from a direction parallel to the front and back surfaces of a wafer 1 to a chamfered end of a wafer 1 (semiconductor wafer) that is a disk-shaped measurement object. While projecting light, a projected image of a predetermined range (hereinafter referred to as a measurement unit) including an end portion (chamfered portion) of the wafer 1 is captured by a camera 7a from a direction opposite to the projecting direction, This is an apparatus for measuring the shape (contour position distribution) and thickness of the edge of the wafer 1 based on the projected image.
The wafer 1 is made of, for example, a semiconductor having a radius of about 150 [mm] and a thickness of about 0.8 [mm], and its outer peripheral end (peripheral surface) is chamfered.
The configuration of the shape measuring apparatus W will be described below with reference to the plan view shown in FIG. 1 and the side view shown in FIG. In FIG. 2, some of the components shown in FIG. 1 are omitted.
As shown in FIGS. 1 and 2, the shape measuring device W includes a point light source 2 as a light projecting unit that is a light projecting optical system (an example of a light projecting unit), and the light from the point light source 2 is converted into parallel light. A collimator lens 3 and a mask unit 8 are provided.
The point light source 2 is, for example, a light source that emits white LED light through a pinhole having a diameter of about 300 μm to 400 μm. The light emitting portion (pinhole) of the point light source 2 is disposed at the focal position of the collimator lens 3.
The collimator lens 3 is collimated (parallel) in a direction (light projecting direction) parallel to both the front and back surfaces of the measurement unit while passing the light emitted from the point light source 2 and traveling toward the measurement unit. It is a lens to be lightened.
The mask portion 8 is a plate-like member in which an opening portion 8o is formed. By restricting the passage of the light beam in the range outside the opening portion 8o, the light beam traveling from the collimator lens 3 toward the wafer 1 side. Among them, the passage of light outside the imaging range of the camera 7a viewed from the light projecting direction R1 is blocked. The mask unit 8 blocks light from passing through the collimator lens 3 to the wafer 1 at a position that is relatively far from the range of the projected image of the wafer 1. It is possible to prevent the non-parallel light component from being included in the luminous flux as much as possible. 1 and 2 show an example in which two mask portions 8 are provided, but an embodiment in which one or three or more mask portions 8 are provided, or the mask portion 8 is provided. Examples that are not possible are also conceivable.
The interval (distance) between the mask portion 8 (closest to the wafer 1) and the first lens 4 is set to about 200 [mm], for example, and the edge portion of the wafer 1 has a light flux (between them) ( (Parallel light) in the optical path.
Then, the parallel light beam Lp after passing through the mask portion 8 is projected from the direction R1 parallel to the front and back surfaces of the wafer 1 to the measurement portion (edge portion) including the end portion of the wafer 1.

Further, the shape measuring apparatus W is a first camera 7a (corresponding to an imaging unit) that captures a projected image of a measurement unit (edge) including an end face of the wafer 1 from a direction R2 facing the light projection direction R1 with respect to the wafer 1. 1 lens 4, aperture 5, second lens 6, and image sensor 7 (CCD or the like).
The first lens 4, the diaphragm 5 and the second lens 6 constitute a telecentric lens, and light passing through the first lens 4 is input to the image sensor 7. A projected image of (edge) is captured.
As described above, the shape measuring apparatus W projects parallel light onto the wafer 1, so that the wafer 1 has a long depth length in the optical axis direction (projection direction R 1) of the parallel light. In the image sensor 7, it is possible to obtain a projection image with a relatively small degree of contour blur. Further, by adopting a point light source 2 using a white LED having a multi-wavelength component instead of a strong single-wavelength light, even if the wafer 1 has a long depth in the light projecting direction R1, In the image sensor 7, a good captured image with few diffraction fringes generated in the vicinity of the contour of the projected image can be obtained.

The shape measuring device W further includes a central suction support mechanism 9, an image processing device 10, and a control device 11.
The image processing apparatus 10 is an arithmetic unit that executes image processing based on an image captured by the image sensor 7 (an image including a projection image of the wafer 1). For example, the image processing apparatus 10 executes a predetermined program stored in the storage unit in advance. A DSP (Digital Signal Processor) provided with a processor for processing, a personal computer, and the like. The image processing apparatus 10 calculates an index value of the end face shape of the wafer 1 by executing predetermined image processing on a captured image (projected image) by the image sensor 7. The image processing apparatus 10 executes input of a captured image (image data) by the image sensor 7 and image processing based on the captured image in accordance with a control command from the control device 11.
The central suction support mechanism 9 supports the disk-shaped wafer 1 by vacuum suction of the central portion of one surface (for example, the lower surface). Further, the central suction support mechanism 9 rotates and stops the wafer 1 in the circumferential direction around the central portion (center point Ow) of the wafer 1 as a rotation axis, thereby allowing the end portion at any position in the circumferential direction of the wafer 1 to move. It is also a device that adjusts whether the measuring unit is positioned in the optical path of the light beam. The central suction support mechanism 9 includes a rotation encoder (not shown) as an angle detection sensor for detecting the support angle (rotation angle) of the wafer 1, and positions the support position (support angle) of the wafer 1 based on the detection angle. Do. The central suction support mechanism 9 positions the support position of the wafer 1 in accordance with a control command from the control device 11.
The control device 11 is a computer including a CPU and its peripheral devices, and the CPU executes the control program stored in advance in the storage unit, whereby the image processing device 10 and the central suction support mechanism 9 are controlled. It is a device that controls (outputs a control command).

Next, the procedure of the shape measurement process (shape measurement method) by the shape measurement apparatus W will be described with reference to the flowchart shown in FIG.
In the shape measurement process described below, notches and the like among the eight positions which are the end portions (edge portions) of the wafer 1 and whose center angles with respect to the center point Ow are shifted by 45 degrees are defined as the measurement positions. An example in which shape measurement is performed on seven measurement units (first to seventh measurement units) excluding the case will be described. The angle of the rotation axis of the central suction support mechanism 9 when the i-th measurement unit (i = 1 to 7) is located at the imaging position of the projected image is referred to as i-th support angle ψ (i). S1, S2,... Shown below represent identification codes of processing procedures (steps). Further, the processing of the image processing apparatus 10 and the operation of the central suction support mechanism 9 described below are executed in accordance with a control command of the control apparatus 11. The processing executed by the image processing device 10 and the control device 11 is realized by a processor provided therein executing a predetermined program.

First, the control device 11 executes an initial setting process such as initialization of a predetermined counter variable i (i = 1) (S1). At this time, the point light source 2 is turned on and light projection to the wafer 1 is started.
Further, the central suction support mechanism 9 supports the wafer 1 at a support position where the i-th support angle ψ (i) is reached (S2). As a result, the i-th measurement unit is positioned at the imaging position.
Subsequently, in a state where the wafer 1 is supported at the position of the i-th reference support angle ψ (i), a projection image of the i-th measurement unit on the wafer 1 is captured by the image sensor 7 (S3). Further, the image processing apparatus 10 captures the captured image (image data) and stores the captured image (image data) in a predetermined storage unit (such as a memory provided in the image processing apparatus 10) (S3). FIG. 3 schematically shows an example of the captured image obtained in step S7.

Subsequently, the image processing apparatus 10 executes predetermined image processing based on the captured image (image of the projected image of the end portion of the wafer 1) captured in step S3, so that the contour of the i-th measurement unit is obtained. Position distribution information, that is, information on the boundary position between a dark part (shadow part) that is a portion of the projected image of the wafer 1 and the other bright part (hereinafter referred to as original contour shape information) is derived (calculated) ( S4). Further, the image processing apparatus 10 stores the derived original contour shape information in a predetermined storage unit (such as a memory provided in the control device 11) (S4).
For example, the image processing apparatus 10 has a positive luminance change rate in the Y-axis direction (the thickness direction of the wafer 1) at each position in the X-axis direction (the direction orthogonal to the thickness direction of the wafer 1) of the projected image. A position (coordinates) having a maximum value and a negative minimum value is detected, and a set of the detected positions (coordinates) is used as the original contour shape information.
Further, the image processing apparatus 10 calculates an approximate curve for the original contour shape information obtained by the process of step S4, and stores the calculation result in a predetermined storage unit (a memory or the like provided in the image processing apparatus 10). (S5).
For example, the image processing apparatus 10 calculates an approximate curve by least square approximation based on an equation of a curve represented by an Nth order equation (N is an integer of 2 or more).

6A and 6B show an example of the original contour shape information (contour position distribution information) obtained in step S4 and the approximate curve obtained in step S5 in the XY coordinate system. FIG. In FIG. 6, the original contour shape information is represented by diamond-shaped drawing points. The approximate curve shown in FIG. 6 is an approximate curve in which the original contour shape information is calculated by least square approximation using a quartic equation.
In general, the end of a measurement object such as a wafer is chamfered with a relatively smooth curve shape that can be approximated by a curve equation such as an Nth order equation (2 ≦ N) or an arc equation as a target shape. Therefore, in the original contour shape information obtained by image processing on the captured image by the camera 7a, the portion where the foreign matter is not attached in the measurement unit is approximated with high accuracy (with a small residual) by a curve equation. it can.
On the other hand, in the original contour shape information, the approximate curve obtained by the process of step S5 is applied to the portion where the foreign matter adheres in the measurement unit, as in the portion surrounded by a wavy circle in FIG. The residual for becomes larger.

Therefore, the image processing apparatus 10 has a residual with respect to the approximate curve calculated by the process of step S5 within the predetermined allowable range from the original contour shape information obtained by the process of step S4. Only the object is extracted as the true contour shape information (true contour position distribution information) of the measurement unit from which the information on the contour position of the adhered part of foreign matter is removed, and the extracted information is stored in a predetermined storage unit (S6).
For example, the image processing apparatus 10 extracts, as the true contour shape information, a residual (distance) within 3 [μm] from the original contour shape information.
The process of step S6 is performed when the residual for the approximate curve calculated by the process of step S5 exceeds the predetermined allowable range from the original contour shape information obtained by the process of step S4. It can also be said to be processing for removing (data surrounded by a wavy circle in FIG. 6).
Next, the control device 11 calculates an index value of the end face shape of the wafer 1 based on the true contour shape information obtained by the process of step S7, and stores the calculation result in a predetermined storage unit ( S7). The index value of the end face shape obtained in this way is a measurement value that is not affected by the foreign matter adhering to the end face.
Here, as the index value, any one of the chamfering width k and the chamfering radius rm of the end surface of the wafer 1 can be considered. The contents of each index value are as already described based on FIG.

Next, the control device 11 counts up the counter variable i (i = i + 1) (S8), and determines whether the numerical value exceeds a set value M (here, M = 7). To determine whether or not the measurement (S2 to S7) for all the measurement units has been completed (S9).
And the shape measuring apparatus W complete | finishes a shape measurement process, after performing the process of step S2-S7 about all the said measurement parts.
As described above, according to the shape measuring apparatus W, it is possible to remove the influence of the foreign matter adhering to the end face of the wafer 1 and perform correct shape measurement.

In the embodiment described above, an example in which the image processing apparatus 10 calculates an approximate curve by least square approximation using an equation of a curve represented by an Nth order equation (N ≧ 2: for example, N = 4) has been described. .
In addition, in step S5 (approximate curve calculation procedure), the image processing apparatus 10 performs a circular arc or elliptical arc expression, a combination of an Nth order expression and an arc or elliptical arc expression, a combination of an Nth order expression and a primary expression, an arc Alternatively, an approximate curve is calculated by least square approximation using a curve expression represented by one of a combination of an elliptic arc expression and a linear expression, or an N-order expression and an arc or elliptic arc expression and a linear expression. It is also possible.
FIG. 7 shows an approximate curve Lw when the edge shape of the wafer 1 is approximated by a curve equation represented by a combination (connection) of a plurality of equations (quaternary equation, linear equation and arc equation). It is the figure represented typically. That is, the approximate curve Lw shown in FIG. 7 is approximated by a quartic equation for the range from the end x0 in the direction orthogonal to the thickness direction of the wafer 1 to the position x1 away from the center 1 of the wafer 1 by a predetermined distance. The range from the position x1 to the position x2 further away from the center of the wafer 1 by a predetermined distance is approximated by a linear expression (straight line), and from the position x2 to the position x3 further away from the wafer 1 by a predetermined distance in the center direction. Is approximated by an arc equation, and the range from the position x3 to a position x4 further away from the center of the wafer 1 by a predetermined distance is approximated by a linear expression (straight line). It should be noted that what kind of curve equation is used to approximate the approximate curve Lw is set in advance according to the target shape at the time of chamfering the end of the measurement object.

  The present invention can be used mainly for measuring the shape of an end face of a disk-shaped measuring object such as an aluminum substrate or a glass substrate for a semiconductor wafer or other hard disk.

1 is a schematic plan view of a shape measuring apparatus W according to an embodiment of the present invention. The schematic side view of the shape measuring apparatus W. FIG. The figure showing an example of the projection image of the end surface of a semiconductor wafer. The figure for demonstrating an example of the index value of the edge profile (end surface shape) of a semiconductor wafer. The flowchart showing the procedure of the shape measurement process performed by the shape measuring apparatus W. The figure showing an example of the distribution information of the outline position obtained by the shape measuring apparatus W, and its approximate curve. The figure which represented typically the approximation curve in case the edge part shape of a semiconductor wafer is approximated by the formula of the curve represented by the combination of a some type | formula.

Explanation of symbols

W: Shape measuring apparatus 1: Wafer 2: Point light source 3: Collimator lens 4: First lens 5: Aperture 6: Second lens 7: Image sensor 7a: Camera 8: Mask unit 9: Central suction support mechanism 10: Image processing device 11: Control devices S1, S2,...: Processing procedure (step)

Claims (4)

A direction opposite to the light projecting direction when light is projected from a direction parallel to the front and back surfaces of the measuring object to the measuring part including the chamfered end of the disk-shaped measuring object. A shape measuring method for deriving information on the contour shape of the measurement unit based on a projection image of the measurement unit obtained by the imaging,
With a given processor
An image processing procedure for deriving distribution information of the contour position of the measurement unit by image processing on a captured image by the imaging means;
An approximate curve calculation procedure for calculating an approximate curve for the distribution information of the contour position obtained by the image processing procedure;
The true contour of the measurement unit is determined so that the residual with respect to the approximate curve calculated by the approximate curve calculation procedure from the distribution information of the contour position obtained by the image processing procedure is within a predetermined allowable range. True contour information extraction procedure to extract as position distribution information,
The shape measuring method characterized by performing.   The approximate curve calculation procedure is an N-order expression where N is an integer of 2 or more, an arc or elliptic arc expression, a combination of the N-order expression and an arc or elliptic arc expression, the N-order expression and the linear expression, A least square approximation by a curve equation represented by any one of the following combinations: an arc or elliptic arc equation and a linear equation, or a combination of the N th equation and an arc or elliptic arc equation and a linear equation. The shape measuring method according to claim 1, which is a procedure for calculating an approximate curve. A light projecting means for projecting light from a direction parallel to the front and back surfaces of the measurement object to a measurement part including a chamfered end in the disk-shaped measurement object;
An imaging unit that captures a projection image of the measurement unit from a direction opposite to a light projecting direction by the light projecting unit;
Image processing means for deriving distribution information of the contour position of the measurement unit by image processing on a captured image by the imaging means;
An approximate curve calculating means for calculating an approximate curve for the distribution information of the contour position obtained by the image processing means;
The true contour of the measurement unit is determined so that the residual with respect to the approximate curve calculated by the approximate curve calculation unit from the distribution information of the contour position obtained by the image processing unit is within a predetermined allowable range. True contour information extraction means for extracting as position distribution information;
A shape measuring apparatus comprising:   The approximate curve calculation means is an N-order equation where N is an integer of 2 or more, an arc or elliptic arc equation, a combination of the N-order equation and an arc or elliptic arc equation, the N-order equation and the linear equation, A least square approximation by a curve equation represented by any one of the following combinations: an arc or elliptic arc equation and a linear equation, or a combination of the N th equation and an arc or elliptic arc equation and a linear equation. The shape measuring apparatus according to claim 3, wherein an approximate curve is calculated.

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