JP2007327892A - Interference measuring apparatus and interference measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coordinate calibration method capable of efficiently calibrating the abscissas of measurement data of a surface shape measured with an interferometer, and that is easily applicable to various kinds of objects to be inspected. <P>SOLUTION: Surface shape measurement by the use of the interferometer is performed, after integrating a light-shielding plate 2 and an object to be inspected 1 into a body, and restricting the measuring area by an edge 2a of the shielding plate 2. Moreover, the positional relation between the measuring area restricted by the shielding plate 2 and reference coordinates of a surface to be inspected 1a are specified by respective reference surfaces 1b, 1c, 2b, 2c, and relative position information of the measuring area is found separately, beforehand. The measuring area restricted by the shielding plate 2 is extracted from measurement results of the interferometer, and the abscissas of the surface shape measurement data are calibrated by the interferometer, based on the relative positional information, with respect to a reference coordinate system on the object 1. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an interference measuring apparatus and an interference measuring method for measuring a highly accurate surface shape of an optical element such as a lens or a mirror.

  In recent years, with the increase in accuracy of optical devices, it is required to process the surface shape of optical elements such as lenses and mirrors constituting the device with high accuracy. As a method of processing optical elements, etc. with high accuracy, the surface shape of the optical element is measured to obtain the difference from the desired shape, and the correction shape is partially processed by the processing machine based on the information, and the desired shape is obtained. The method of approaching is generally adopted.

  As a surface shape measuring device for performing correction processing, there is an interference measuring device using an interferometer having excellent measurement accuracy. With this device, the abscissa of each point on the surface to be measured, that is, the positional information in the plane perpendicular to the optical axis of the interferometer, and the area sensor that captures the interference fringes are taken with high precision, The surface shape measurement data represented in the coordinate system is calibrated so as to be represented by the abscissa on the test object. The coordinate system used as a reference at this time must be a reference coordinate system that can be used in a processing machine. For example, a coordinate system defined by a reference surface formed on an optical element can be used. Thus, based on the surface shape measurement data expressed in the reference coordinate system defined by the reference surface, the correction processing position and the correction processing amount are determined, and the processing is performed with reference to the reference surface, thereby interfering. Correction processing using the measurement result by the meter becomes possible.

As a conventional method for calibrating the absolute position of the abscissa in the surface shape measurement by the interferometer, there is one disclosed in Patent Document 1. This utilizes a calibration optical member in which a pattern such as a light scattering region is formed on the surface to be examined. By forming the pattern with reference to the reference surface of the calibration optical member, the relationship with the reference surface becomes known. A calibration value that calibrates the absolute position of the abscissa if the pattern portion is specified from the result of measuring the optical member for calibration with the interferometer, the center of gravity is calculated, and the relationship between the known pattern and the reference plane is used. (Coordinate calibration value) can be obtained. After that, the surface shape of the test object is measured with an interferometer instead of the calibration optical member, and the absolute value of the abscissa of the measured surface shape is obtained by applying the calibration value to the obtained surface shape measurement data. Can be calculated.
JP 2002-333305 A

  However, the calibration value obtained by the method disclosed in Patent Document 1 is used to convert the abscissa of the surface shape measurement data into a coordinate system defined by the reference surface of the calibration optical member. Therefore, when the calibration optical member is replaced with the test object, an error occurs in the abscissa calibration value if the reference surface position of the test object does not match the reference surface position of the calibration optical member.

  However, when the state of the interference fringes changes and the fringes become dense when the calibration optical member is replaced with the test object, it is necessary to adjust the position and orientation of the test object so that the interference fringes become sparse. Therefore, it easily occurs when the reference surface position of the test object is different from the reference surface position of the calibration optical member.

  Also, if the design value of the test object is different, the relationship between the test surface and the reference surface is also different, so calibration optical members and calibration values cannot be used as they are, and calibration optical members are prepared for each design value. Therefore, when measuring various optical elements, a large cost is required.

  The present invention has been made in view of the above problems, and can easily calibrate the abscissa of surface shape measurement data measured by an interferometer and can be easily applied to a wide variety of specimens. An object of the present invention is to provide a measuring device and an interference measuring method.

  In order to achieve the above object, the interference measuring apparatus of the present invention detects interference fringes obtained by causing the test light reflected by the test object and the reference light to interfere with each other, and detects the detected interference. An interferometer that measures the surface shape of the test object based on fringe information, a measurement area limiting means for limiting the measurement area of the test object, and the measurement area limited by the measurement area limiting means And position reference means for obtaining relative position information of the measurement area, and extracting surface shape measurement data of the measurement area from the measurement result of the interferometer And calculating means for calibrating the surface shape measurement data based on the relative position information of the measurement area with respect to the reference coordinates.

  According to the interference measurement method of the present invention, an interference fringe obtained by causing the test light reflected by the test object and the reference light to interfere with each other is detected by a detector, and the interference fringe is based on the detected interference fringe information. In the interferometry method for measuring the surface shape of the test object, a measurement area limiting step for limiting the measurement area of the test object by a measurement area limiting means, and the positions of the measurement area and the reference coordinates on the test object A position identifying step for identifying a relationship and obtaining relative position information of the measurement region; a measurement region extracting step for extracting surface shape measurement data of the measurement region from a measurement result based on the interference fringes; and Calibrating the surface shape measurement data based on the relative position information of the measurement region.

  Coordinate calibration for representing the surface shape measurement data measured by the interferometer with the reference coordinates on the object can be easily performed. In addition, it can easily handle a wide variety of specimens with a light-shielding plate that can be manufactured at low cost, and does not require a special stage or measuring instrument on the device side. Therefore, the apparatus cost can be greatly reduced.

  The surface shape measurement accuracy of the interferometer is extremely superior to that of a three-dimensional coordinate measuring instrument, etc., so that the amount of correction machining and the correction processing position are obtained from the difference from the desired shape using the surface shape measurement data obtained by the interferometer. By processing, a highly accurate optical element can be produced.

  The best mode for carrying out the present invention will be described with reference to the drawings.

  As shown in FIG. 1, a light shielding plate 2 shown in FIG. 2 is used for a test object 1 having a test surface 1a and two reference surfaces (outer shape references) 1c and 1b, which are measurement areas. The light shielding plate 2 includes an edge 2a that forms an opening that is a measurement area limiting unit, and reference surfaces (outer shape references) 2b and 2c that are alignment units corresponding to the reference surfaces 1b and 1c of the test object 1.

  That is, the light-shielding plate 2 having an opening for limiting the measurement region by the interferometer is installed in the optical path of the interferometer to limit the light beam of the test light. The shape of the opening of the light-shielding plate 2 is designed so that the lengths of the perpendiculars drawn from the edge 2a of the opening to the test surface 1a are equal over the entire circumference when installed in the light beam of the test light. Is done.

  Position specifying means for specifying the positional relationship between the opening of the light shielding plate 2 and the reference coordinates (x, y coordinates) on the test object 1 is based on position measurement, and uses positioning means such as an external reference. There are two ways.

  In the case of the position measurement, the positional relationship between the measurement region and the reference coordinate system on the test object is specified by measuring the positional relationship with the test object after fixing the light shielding plate to the test object. When it is difficult to fix the light shielding plate to the test object, the light shielding plate may be fixed to the holding jig for the test object. The measurement of the positional relationship between the test object and the light shielding plate can be performed by using a coordinate measuring device.

  When using alignment means for specifying the positional relationship, as shown in FIGS. 1 and 2, reference surfaces 1b, 1c, 2b, which are external reference for alignment of the object 1 and the light shielding plate 2, It is desirable to integrate by fixing means after positioning by 2c. Thereby, the positional relationship between the reference coordinates on the test object 1 and the opening of the light shielding plate 2 can be specified, and the relative position information of the measurement region limited by the opening of the light shielding plate 2 can be obtained. When it is difficult to fix the light shielding plate 2 to the test object 1, the test object 1 and the light shielding plate 2 are respectively aligned with the holding jig 4 of the test object 1, as shown in FIG. May be integrated.

  In any case, it is desirable that the test object 1 and the light shielding plate 2 are abutted against the abutting member 3 and positioned on the basis of the outer shape.

  Then, a measurement area limited by the light shielding plate is extracted from the measurement result obtained by the interferometer by the calculation means, and the abscissa of the surface shape measurement data is calibrated. It is desirable that the measurement region is extracted by obtaining an interference fringe intensity distribution after making the interference fringes in a single-color state and extracting a region having a high interference fringe intensity value. Alternatively, the interference fringe intensity change rate is obtained when the test object or reference prototype is moved in the optical axis direction by a minute amount or the wavelength of the test light is changed by a minute amount. An area may be extracted. Here, the minute amount means a range in which interference fringes can be recognized.

  Subsequently, coordinate calibration is performed to represent the surface shape measurement data of the measurement region by the interferometer with the reference coordinates on the test object. This is based on the abscissa calibration value (coordinate calibration value) for representing the position of the measurement area by the interferometer in reference coordinates using the relative position information of the measurement area by the opening of the light shielding plate and the reference coordinates on the test object. ) And is applied to the surface shape measurement data by the interferometer.

  Further, the abscissa correction value may be corrected by obtaining an error amount of the abscissa calibration value generated with the distortion of the measurement region extracted from the measurement result by the interferometer. First, using the shape information of the test object and the shape information of the opening of the light shielding plate, the relationship between the distortion of the measurement region extracted from the measurement result by the interferometer and the error amount of the abscissa calibration value is obtained in advance. deep. Each time measurement is performed on each test object, an error amount (coordinate error) of the abscissa calibration value is obtained and corrected from the distortion of the extracted measurement region.

  1 to 3 are diagrams for explaining the first embodiment. A light shielding plate 2 shown in FIG. 2 is brought into close contact with the test object 1 shown in FIG. The test object 1 includes reference planes 1b and 1c that are external reference in the x and y directions, thereby defining the abscissa. The light-shielding plate 2 is a thin plate that has been roughened to suppress light reflection, and includes two reference surfaces 2b and 2c that are orthogonal to each other for alignment with the test object 1. Yes.

  The central portion of the light shielding plate 2 has an opening that allows test light to pass through during interferometer measurement, and the positional relationship between the shape of the edge 2a that forms the periphery of the opening and the two reference surfaces 2b and 2c is known. It shall be. As will be described later, the shape of the edge 2a depends on the design shape of the test surface 1a of the test object 1, but when the edge 2a has a point-symmetric shape, notches (shape portions) 2d, 2e For example, the rotation angle (direction) can be identified.

  The abscissa calibration method using the light shielding plate 2 will be described with reference to FIGS.

  Before the surface shape measurement by the interferometer, as shown in FIG. 3, the reference surfaces 1 b and 1 c of the test object 1 are matched with the reference surfaces 2 b and 2 c of the light shielding plate 2 using the abutting member 3. The test object 1 and the light shielding plate 2 are integrated by a fixing means (not shown). At this time, the opening shape of the light shielding plate 2 is designed so that the opening of the light shielding plate 2 coincides with the test surface 1a which is the measurement region. More specifically, when the test object 1 and the light shielding plate 2 are integrated, the lengths of the perpendiculars drawn from the edge 2a of the light shielding plate 2 to the test surface 1a of the test object 1 become equal over the entire circumference of the opening. To design. The shape of the opening of the light shielding plate 2 can be arbitrarily designed when the test surface 1a is a flat surface, and becomes a circular opening when the test surface 1a is a spherical surface.

  In this way, the test object 1 and the light shielding plate 2 are integrated and mounted on the interferometer, and the surface shape of the test surface 1a is measured. As a result of the measurement, as shown in FIG. 4, only the region limited by the edge 2a of the opening of the light shielding plate 2 is measured, and the position information of the reference surfaces 1b and 1c of the test object 1 on the outside is obtained. I can't. That is, position information (relative position information) with respect to the reference coordinates of the test surface 1a cannot be obtained directly from the measurement result of the interferometer. The abscissa of the measurement result of the interferometer is expressed in pixel units of the area sensor, and the length per pixel varies depending on the radius of curvature of the test surface 1a.

  However, the shape of the edge 2a of the light shielding plate 2 and the positional relationship with the reference surfaces 2b and 2c are known, and the reference surfaces 1b and 1c of the test object 1 and the reference surfaces 2b and 2c of the light shielding plate 2 are made to coincide. Therefore, the position of the reference coordinate can be obtained from the position information of the edge 2a. However, since it is necessary to measure the entire circumference of the edge 2a at the same time when measuring the surface shape, the light shielding plate is arranged so that the entire circumference of the edge 2a is located outside the measurement region and within the light flux range of the test light of the interferometer. 2 must be designed.

  A procedure for obtaining the position of the reference coordinate on the test object 1 from the position information of the edge 2a will be described below.

  First, position information of the edge 2a of the opening is extracted from the measurement result of the interferometer. This can be done by measuring the interference fringe intensity after making the interference fringe so-called one-color, and extracting the place where the measured interference fringe intensity changes sharply as the edge 2a of the opening. The spatial variation of the interference fringe intensity can be quantified by a general image processing technique. For example, by applying a differential filter such as a Sobel filter or a Laplacian filter, the pixel of the area sensor corresponding to the edge 2a is emphasized as an edge.

  As another extraction method, the interference fringe intensity change rate is obtained by moving the test object or reference prototype in the direction of the optical axis or changing the wavelength of the test light by a minute amount. A region having a large intensity change rate may be extracted. Further, when the interference fringe intensity is modulated by the so-called phase shift method, the place where the interference fringe modulation occurs is regarded as the inside of the edge 2a of the opening, and the place where the interference fringe modulation does not occur is regarded as the outside of the edge 2a of the opening. The edge 2a may be extracted.

  Next, by fitting the extracted edge 2a with a known actual shape, the length per pixel of the measurement result and the positions of the reference planes 1b and 1c are obtained. However, since the abscissa of the point group obtained as a measurement result represents the coordinates on the test surface 1a, if the test surface 1a is a spherical surface, using the actual shape data of the edge 2a as it is causes an error in the magnification. . Therefore, the actual shape data of the edge 2a is enlarged using the radius of curvature of the test surface 1a and the length of the perpendicular line dropped from the edge 2a of the opening to the test surface 1a. For example, when the test surface 1a is a concave surface having a radius of curvature R and the length of the perpendicular line extending from the edge 2a to the test surface 1a is h, the actual shape data of the edge 2a is enlarged by R / (R−h) times. And fitting.

  The fitting is preferably performed using information about the entire circumference of the edge 2a, but may be performed using a parameter representative of the shape of the edge 2a. For example, if the edge 2a is circular, the edge 2a extracted from the measurement result is circularly approximated to obtain the center position and radius, and further, one side forming a notch is obtained to determine the length per pixel and the reference plane 1b. The position of 1c can be obtained.

  Finally, using the obtained length per pixel and the positions of the reference surfaces 1b and 1c, the position of the reference coordinates is determined, and calibration is performed so that the abscissa of the surface shape measurement data represents the reference coordinates. If the surface shape measurement data is expressed in reference coordinates, the correction processing position based on the surface shape measurement data by the interferometer can be obtained by determining the correction processing position with reference to the reference surfaces 1b and 1c in the processing machine. .

  In addition, when the edge 2a of the light-shielding plate 2 has a point-symmetric shape, the cutouts 1d and 1e are used as the characteristic shapes. However, the present invention is not limited to this. For example, a small circle is formed outside the edge 2a. And the position of the center of gravity may be used as a reference.

  Further, the light shielding plate 2 is provided with reference surfaces 2b and 2c, and the abutting member 3 is used to make the reference surfaces 1b and 1c of the test object 1 coincide with the reference surfaces 2b and 2c of the light shielding plate 2. It is not limited to the system using such alignment means. The test object 1 and the light shielding plate 2 may be integrated so that the relationship between the edge 2a of the light shielding plate 2 and the reference coordinate system of the test object 1 is known. For example, the light shielding plate 2 having no reference surface is integrated with the test object 1, and the shapes of the reference surfaces 1b and 1c of the test object 1 and the edge 2a of the light shielding plate 2 are measured by a three-dimensional coordinate measuring device. Also good.

  FIG. 5 illustrates the second embodiment. In the present embodiment, the light shielding plate 2 is fixed to the holding jig 4 for interference measurement. The holding jig 4 includes an abutting member 3 for positioning the test object 1 and the light shielding plate 2 (see FIG. 5B), and the reference surface of the light shielding plate 2 is abutted against the abutting member 3. After positioning the light shielding plate 2, the light shielding plate 2 is fixed to the holding jig 4. Furthermore, by positioning the test object 1 by abutting the reference surface of the test object 1 against the abutting member 3 of the holding jig 4, the relationship with the edge 2a of the opening of the light shielding plate 2 may be known. it can.

  As in the first embodiment, the edge 2a of the opening of the light shielding plate 2 is extracted from the measurement result by the interferometer, the position of the reference coordinate on the test object 1 is obtained, and the abscissa of the surface shape measurement data is detected. Calibrate to represent reference coordinates on object 1.

  In this embodiment, the holding jig 4 for interference measurement is provided with the light shielding plate 2, and preparation for abscissa calibration is completed at the stage when the test object 1 is mounted on the holding jig 4 in order to perform surface shape measurement. To do. Therefore, there is an advantage that the measurement tact can be suppressed to the same level as that of the normal surface shape measurement.

  In addition, a present Example is not limited to utilization of the reference plane of the light-shielding plate 2, and the butting member 3 of the holding jig 4. FIG. A function capable of positioning with high accuracy when the test object 1 is attached to and detached from the holding jig 4, and the edge 2 a of the light shielding plate 2 and the test object in a state where the test object 1 is mounted on the holding jig 4. It is only necessary that the positional relationship with one reference coordinate is known.

  In this way, the abscissa of the surface shape measurement data by the interferometer can be calibrated, but depending on the positional relationship between the light shielding plate 2 and the interferometer body, the shape of the edge 2a of the light shielding plate 2 extracted from the measurement result of the interferometer May be distorted, causing an error in the abscissa calibration value based on the relative position information by the edge 2a. Hereinafter, a method for correcting the coordinate error accompanying the distortion of the edge shape of the opening extracted from the measurement result of the interferometer will be described.

  FIG. 6 shows a case where the interferometer 5 measures the planar shape of the test surface 1a of the test object 1 using the reference prototype 6 having the reference surface 6a. In FIG. 6, the test object 1 and the light shielding plate 2 are positioned via the abutting member 3. However, since the light shielding plate 2 is attached to be inclined with respect to the optical axis 7 of the interferometer 5, the light shielding plate 2. The test light passing through the opening changes in accordance with the amount of inclination of the light shielding plate 2. As a result, even if the edge 2a of the light shielding plate 2 is a perfect circle, the edge shape extracted from the measurement result of the interferometer 5 is distorted into an ellipse as shown in FIG. When the ellipse is distorted and fitted as a circle, the position of the reference coordinate with respect to the measurement result of the surface shape is obtained, and the x and y axes, which are the abscissas of the reference coordinate system of the test object 1, are calculated. , X and Y axes. As described above, an abscissa error actually occurs with respect to the reference coordinate system having the x and y coordinates in FIG.

  Therefore, the error of the abscissa accompanying the distortion of the edge shape of the light shielding plate 2 extracted from the measurement result of the interferometer 5 is corrected as follows.

  First, the relationship between the amount of inclination of the light shielding plate 2 with respect to the optical axis 7 and the distortion of the measurement result of the interferometer 5 is obtained using the shape information of the test surface 1 a and the shape information of the edge 2 a of the light shielding plate 2. Then, when fitting the edge shape extracted from the measurement result to the actual shape of the edge 2a, the amount of inclination is also included in the parameters. Finally, the error due to the distortion of the edge shape is also corrected by obtaining the relationship between the measurement result of the interferometer and the reference coordinate system on the test object 1 in consideration of the tilt amount of the light shielding plate 2.

  Also in the case of spherical measurement, since an abscissa error accompanying distortion of the edge shape occurs, correction is performed in the same manner as in the case of a plane. The difference between the spherical surface and the plane is not only the inclination of the light shielding plate 2 with respect to the optical axis 7 of the interferometer 5, but also extracted from the measurement result of the interferometer 5 even if the light shielding plate 2 is laterally displaced in a plane perpendicular to the optical axis 7. The edge shape is distorted. Therefore, when fitting the edge shape extracted from the measurement result to the actual shape of the edge 2a, in addition to the inclination amount of the light shielding plate 2, the lateral displacement amount in the plane perpendicular to the optical axis 7 of the interferometer 5 is also included in the parameters. To fit. Although the edge shape extracted from the measurement result of the interferometer 5 is distorted to a shape close to an ellipse even if the light shielding plate 2 is tilted or laterally shifted with respect to the optical axis 7, neither is a true ellipse but different distortion methods. To do. Therefore, the tilt amount and the lateral shift amount of the light shielding plate 2 are independent parameters and can be fitted simultaneously.

  Further, when the surface shape is measured by the interferometer 5, the interference fringes are measured in a so-called fringe one-color state, and therefore the positional relationship between the test object 1 and the optical axis 7 of the interferometer 5 is not arbitrary and is limited. Furthermore, since the test object 1 and the light shielding plate 2 are positioned via the abutting member 3, the positional relationship between the optical axis 7 and the light shielding plate 2 is also limited. Therefore, when the positional relationship between the optical axis 7 of the interferometer 5 and the light shielding plate 2 is included in the fitting as a constraint, the abscissa calibration can be performed with higher accuracy. However, the shape accuracy of the test object 1 and the light shielding plate 2 needs to be good.

FIG. 3 is an elevation view showing only a test object according to Example 1. FIG. 3 is an elevation view showing only a light shielding plate according to Example 1. The test object and light-shielding plate by Example 1 are shown in the state integrated, (a) is the elevation, (b) is sectional drawing taken along the AA line of (a). . It is a figure which shows the relationship between the to-be-tested surface and the edge of a light-shielding plate in surface shape measurement data. FIG. 7 shows Example 2, in which (a) is an elevational view showing a holding jig integrated with a light shielding plate, and (b) is a cross-sectional view showing the holding jig and a test object. It is a figure explaining the fall of a test object. It is a figure which shows the distortion of a measurement area | region.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Test object 1a Test surface 1b, 1c, 2b, 2c Reference surface 2 Light-shielding plate 2a Edge 3 Abutting member 4 Holding jig 5 Interferometer 6 Reference master 6a Reference surface 7 Optical axis

Claims (12)

  The detector detects the interference fringes obtained by causing the test light reflected by the test object and the reference light to interfere with each other, and measures the surface shape of the test object based on the information of the detected interference fringes An interferometer, a measurement area limiting means for limiting the measurement area of the test object, and a positional relationship between the measurement area limited by the measurement area limiting means and reference coordinates on the test object And a position specifying means for obtaining relative position information of the measurement area, and surface shape measurement data of the measurement area is extracted from the measurement result of the interferometer, And an arithmetic means for calibrating the surface shape measurement data based thereon.   The interference measurement apparatus according to claim 1, wherein the measurement region limiting unit includes a light shielding plate having an opening provided in a light beam of the test light.   The interference measurement apparatus according to claim 2, wherein the light shielding plate has a shape portion indicating the directionality of the opening.   The interference measurement apparatus according to claim 2, wherein the position specifying unit includes an alignment unit that aligns the test object and the light shielding plate.   The interference measurement apparatus according to claim 4, wherein the position specifying unit includes a fixing unit that fixes the test object or a holding jig for the test object and the light shielding plate.   The interference measurement apparatus according to claim 4, wherein the test object and the light shielding plate have an outer shape reference for alignment with each other. The detector detects the interference fringes obtained by causing the test light reflected by the test object and the reference light to interfere with each other, and measures the surface shape of the test object based on the information of the detected interference fringes In the interference measurement method to
A measurement region limiting step of limiting the measurement region of the test object by a measurement region limiting means;
Identifying the positional relationship between the measurement area and the reference coordinates on the test object, a position specifying step for obtaining relative position information of the measurement area,
A measurement region extraction step for extracting surface shape measurement data of the measurement region from the measurement result based on the interference fringes;
A step of calibrating the surface shape measurement data based on the relative position information of the measurement area with respect to the reference coordinates.   The interference measurement method according to claim 7, wherein, in the measurement region limiting step, a light shielding plate is installed in a light beam of the test light to limit the light beam.   9. The positional relationship between the test object and the light shielding plate is specified by aligning and integrating the test object and the light shielding plate in the position specifying step. Interference measurement method.   10. The method according to claim 7, wherein, in the measurement region extraction step, the interference fringe intensity distribution is acquired after the interference fringes are in a single-colored state, and a region where the interference fringe intensity value increases is extracted. The interference measurement method described.   In the measurement region extraction step, the interference fringe intensity change rate is obtained by moving the test object in the optical axis direction of the test light or changing the wavelength of the test light, and the interference fringe The interference measurement method according to claim 7, wherein a region where the intensity change rate increases is extracted.   The interference measurement method according to claim 7, further comprising a step of correcting a coordinate error caused by the distortion of the extracted measurement region in the measurement region extraction step.

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