JP2011117766A - Interference measuring method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To determine the coordinates of the shape measurement data of a surface under measurement with respect to an object under measurement with high precision. <P>SOLUTION: The interference measuring method includes: a mark formation process (S1); a shape measuring process (S2); a mark detection process (S3); and a coordinates calculation process (S4). In the S1 mark formation process, a reference mark is formed on the surface under measurement of the object under measurement. In the mark detection process, the position of the standard mark with the coordinate system of an area sensor as a reference is detected from the shape measurement data obtained in the shape measuring process. In the coordinates calculation process, the correspondence between the position information of the reference mark with the coordinate system of the object under measurement formed in the mark formation process as a reference and the position information of the reference mark with the coordinate system of the area sensor detected in the mark detection process as the reference is determined. On the basis of the correspondence, calculation for converting the shape measurement data obtained in the shape measuring process into the coordinate system of the object under measurement is performed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an interference measurement method for obtaining shape measurement data of a test surface with reference to a coordinate system of a test object.

  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 position 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 accuracy, and the shape measurement data expressed in the area sensor coordinate system is taken as the object to be tested. Calibrate to represent in the coordinate system. 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. As described above, the correction processing position and the correction processing amount are determined based on the shape measurement data represented by the reference coordinate system defined by the reference plane, and the interferometer is executed by referring to the reference plane. It is possible to perform correction processing using the measurement result of

  As a method of converting the shape measurement data based on the coordinate system of such an area sensor into the coordinate system of the test object, there is one disclosed in Patent Document 1. This uses a measurement optical member for calibration in which a light shielding pattern such as a light scattering region is formed on the surface to be examined. By forming the light shielding pattern with reference to the reference surface of the measurement optical member, the relationship with the reference surface becomes known. From the result of measuring the measurement optical member with an interferometer, the position of the center of gravity is calculated by identifying the light-shielding pattern portion, and if the relationship between the known light-shielding pattern and the reference plane is used, the shape measurement data can be converted to the coordinates of the measurement optical member A calibration value for calibrating the system can be obtained. After that, instead of the measurement optical member, the surface shape of the test object is measured with an interferometer, and the calibration value is applied to the obtained shape measurement data, thereby obtaining the shape measurement data based on the coordinate system of the measurement optical member. Can be calculated.

JP 2002-333305 A

  However, in the conventional interference measurement method, the shape measurement data based on the coordinate system of the area sensor is converted into a coordinate system based on the reference surface of the measurement optical member. Therefore, when the measurement optical member is replaced with the test object, if the reference surface position of the test object does not match the reference surface position of the measurement optical member, the shape measurement data converted to the coordinate system of the reference surface is used. An error is included. For this reason, in the shape correction processing that partially corrects the shape of the test surface based on the shape measurement data, the shape measurement data based on the coordinate system of the test object is not accurate. Processing could not be performed.

  Therefore, an object of the present invention is to provide an interference measurement method capable of obtaining shape measurement data of a test surface with reference to the coordinate system of the test object with high accuracy.

  The present invention provides a mark forming step for forming a reference mark on a test surface of a test object, and interference fringes obtained by causing interference between measurement light reflected on the test surface and reference light by an area sensor. A shape measuring step of imaging and measuring the shape of the test surface including the reference mark based on the captured interference fringe data to obtain the shape measurement data of the test surface; and A mark detection step for detecting the position of the reference mark with reference to the coordinate system of the area sensor; and the position information of the reference mark with reference to the coordinate system of the test object formed in the mark formation step; Based on the correspondence with the position information of the reference mark based on the coordinate system of the area sensor detected in the mark detection step, the shape measurement data obtained in the shape measurement step Is characterized in that and a coordinate calculating step for performing an operation of converting the coordinate system of the object.

  According to the present invention, since the reference mark is formed on the test surface of the test object, the work of replacing the conventional measurement optical member with the test object can be omitted, and the test is performed based on the coordinate system of the test object. It is possible to suppress an error from being added to the surface shape measurement data. Therefore, the shape measurement data of the test surface based on the coordinate system of the test object can be obtained with high accuracy. As a result, it is possible to carry out the shape correction processing for processing the target surface into the target shape with high accuracy.

It is a figure which shows the processing apparatus of the reference mark in 1st Embodiment. It is a figure which shows the interference measuring device which measures the shape of the to-be-tested surface in 1st Embodiment. It is a figure which shows the flowchart of an interference measuring method. It is a figure which shows the shape of a test object roughly. It is a figure which shows the cross-sectional shape of the reference mark on a to-be-tested surface. It is a figure which shows the processing apparatus of the reference mark in 2nd Embodiment. It is a figure which shows the interference measuring device which measures the shape of the to-be-tested surface in 2nd Embodiment. It is a figure which shows the shape of a test object roughly. It is a figure which shows the cross-sectional shape of the reference mark on a to-be-tested surface.

  Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings.

[First Embodiment]
In the first embodiment, the polishing apparatus 8 as the processing apparatus shown in FIG. 1 is provided with an interference measuring apparatus 10 such as a Twiman Green interferometer shown in FIG. In FIG. 1, a polishing apparatus 8 performs polishing on a test object 1 that is an optical element such as a mirror or a lens. A polishing tool 4 as a processing tool, a processing head 5 that holds the polishing tool 4, and An XY stage 6 facing the polishing tool 4 is provided. The polishing apparatus 8 includes a controller 100 that controls the entire apparatus, such as the processing head 5 and the XY stage 6. A test object 1 is fixed on the XY stage 6. In the first embodiment, the test surface 1a of the test object 1 is a flat surface. The processing head 5 holds and rotates the polishing tool 4 to rotate the polishing tool 4. By polishing the rotating polishing tool 4 against the test surface 1a of the test object 1, the test surface 1a is polished. At this time, by moving the XY stage 6, the polishing tool 4 is relatively scanned on the test surface 1 a of the test object 1. Here, an abrasive is intermittently supplied between the test object 1 and the polishing tool 4.

  The interference measurement apparatus 10 shown in FIG. 2 measures the shape of the test surface 1a. The laser light emitted from the laser light source 11 is shaped into a light beam having a predetermined cross section via the beam expander 12 and then enters the half mirror 13. A part of the light beam is transmitted through the half mirror 13 and is incident on the reference mirror 14. The light beam incident on the reference mirror 14 is reflected as reference light on the reference surface 14 a of the reference mirror 14 and returns to the half mirror 13. On the other hand, the light beam reflected by the half mirror 13 enters the test object 1, is reflected as measurement light on the test surface 1 a, and returns to the half mirror 13. The reference light reflected by the half mirror 13 and the measurement light transmitted through the half mirror 13 interfere with each other and are projected onto the area sensor 16 via the imaging lens 15, and interference fringes are formed on the area sensor 16. The image is formed and imaged by the area sensor 16. At this time, the reference mirror 14 is moved by a predetermined amount in the optical axis direction to obtain data of a plurality of different interference fringes. By analyzing the data of these interference fringes, the shape measurement data of the test surface 1a is obtained. Here, the shape measurement data of the test surface 1 a is expressed as a coordinate system of the area sensor 16.

  Next, referring to the flowchart shown in FIG. 3, the operation of measuring the test surface 1a of the test object 1 using the interference measurement device 10 before the polishing process device 8 corrects the test object 1 is performed. While explaining.

  First, two reference marks 3a and 3b are formed on the test surface 1a of the test object 1 by the polishing apparatus 8 (S1: mark forming process). Here, as shown in FIGS. 4A and 4B, the reference marks 3a and 3b are formed in a concave shape in cross section in a plan view by the polishing tool 4 in FIG. Specifically, the reference marks 3a and 3b are formed in a concave spherical shape. For example, each fiducial mark 3a, 3b has a cross section in the x direction in FIG. 5 (a) and a cross section in the y direction in FIG. 5 (b). did. At this time, the controller 100 of the polishing apparatus 8 acquires position information of the reference marks 3a and 3b with reference to the coordinate system of the test object 1. In the first embodiment, the controller 100 uses the coordinate system of the test object 1 as an xy orthogonal coordinate system, and positions of the reference marks 3a and 3b with reference to the xy orthogonal coordinate system of the test object 1. As information, coordinates (Xa, Ya), (Xb, Yb) are acquired. As shown in FIG. 4, the test object 1 is formed in a circular shape in plan view, and the two reference marks 3 a and 3 b are arranged 180 degrees rotationally symmetrical with respect to the center of the test object 1. . Here, the controller 100 calculates the dwell time of the polishing tool 4 in advance based on the design shape of the reference marks 3a and 3b, and forms the reference marks 3a and 3b. Thus, the reference marks 3a and 3b can be formed by averaging errors caused by the polishing apparatus 8 such as the shape of the polishing tool 4 and positioning errors of the polishing apparatus 8, and the reference marks for the surface 1a to be measured. 3a and 3b can be positioned and formed with high accuracy.

  Next, shape measurement data of the test surface 1a including the reference marks 3a and 3b formed in the mark forming step S1 is acquired by the interference measuring apparatus 10 (S2: shape measuring step). In this shape measurement step, shape measurement data is acquired with reference to the coordinate system of the area sensor 16. The shape measurement data obtained in this shape measurement step is acquired by the controller 100 of the polishing apparatus 8.

  Next, the controller 100 detects the positions of the reference marks 3a ′ and 3b ′ with reference to the coordinate system of the area sensor 16 from the shape measurement data of the surface 1a to be measured in the shape measurement step of S2 (S3: mark detection step). ). The symbol “′” is used below to indicate the position of the imaging target on the sensor surface of the area sensor 16. In the first embodiment, the controller 100 uses the coordinate system of the area sensor 16 as the x′-y ′ orthogonal coordinate system, and the reference marks 3a ′ and 3b with the x′-y ′ orthogonal coordinate system of the area sensor 16 as a reference. Detect the position of '. Here, the controller 100 stores the design formulas of the reference marks 3a and 3b, and the shape measurement of the reference marks 3a ′ and 3b ′ in the shape measurement data of the test surface 1a obtained in the shape measurement step of S2. Curve fitting is applied to the data, which is a spherical expression. As a result, the controller 100 detects the positions of the reference marks 3a ′ and 3b ′ as coordinates on the area sensor 16 with the coordinates (Xa ′, Ya ′) and (Xb ′, Yb ′) with high accuracy. .

  Next, the controller 100 detects the position information of the reference marks 3a and 3b with reference to the xy orthogonal coordinate system of the test object 1 and the reference mark 3a with reference to the x′-y ′ orthogonal coordinate system of the area sensor 16. The correspondence with the position information of “3b” is obtained. That is, the controller 100 obtains a coordinate transformation matrix from the x′-y ′ orthogonal coordinate system of the area sensor 16 to the xy orthogonal coordinate system of the test object 1. More specifically, the positional information of the reference marks 3a and 3b based on the xy orthogonal coordinate system of the test object 1 formed in the mark forming process is expressed by coordinates (Xa, Ya), (Xb, Yb). Further, the position information of the reference marks 3a ′ and 3b ′ with reference to the x′-y ′ orthogonal coordinate system of the area sensor 16 detected in the mark detection step is the coordinates (Xa ′, Ya ′), (Xb ′). , Yb ′). Therefore, simultaneous equations showing the relationship between the coordinates (Xa, Ya) and (Xb, Yb) and the coordinates (Xa ′, Ya ′) and (Xb ′, Yb ′) can be obtained. The controller 100 is controlled from the coordinate system of the area sensor 16 by simultaneous equations obtained from the coordinates (Xa, Ya) and (Xb, Yb) and the coordinates (Xa ′, Ya ′) and (Xb ′, Yb ′). A coordinate transformation matrix to the coordinate system of the specimen 1 is obtained. And the controller 100 performs the calculation which converts the shape measurement data obtained by the shape measurement process of S2 into the coordinate system of the test object 1 by this coordinate conversion matrix (S4: coordinate calculation process). Thereby, the shape measurement data measured on the basis of the coordinate system of the area sensor 16 is converted into the coordinate system of the test object 1 which is a coordinate system defined by the polishing apparatus 8 as a processing apparatus.

  As described above, according to the first embodiment, since the reference marks 3a and 3b are formed on the test surface 1a of the test object 1, the work of replacing the conventional measurement optical member with the test object can be omitted. It is possible to suppress an error from being added to the shape measurement data of the surface 1a to be measured with reference to the coordinate system of 1. Therefore, the shape measurement data of the test surface 1a based on the coordinate system of the test object 1 can be obtained with high accuracy. Thereby, it becomes possible to perform the shape correction process which processes the to-be-tested surface 1a in the target shape with high precision.

  The positions where the reference marks 3a and 3b are formed are not necessarily arranged 180 degrees rotationally symmetrical with respect to the center of the test object 1, and the position of the test object is determined based on the coordinate system of the test object 1. What is necessary is just to set two different points in order to specify. Further, when the shape of the test surface 1a is an aspherical surface and the optical axis position of the test surface 1a is determined, the test object is based on the coordinate system of the test object 1 even if there is only one reference mark. In this case, one may be used.

[Second Embodiment]
In the second embodiment, the ion beam processing apparatus 21 as the processing apparatus shown in FIG. 6 is provided with an interference measurement apparatus 10A such as a Fizeau interferometer shown in FIG. Note that in the second embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and description thereof is omitted. An ion beam processing apparatus 21 shown in FIG. 6 performs ion beam processing on a test object 1 that is an optical element such as a mirror or a lens, and includes an ion beam gun 23 as a processing tool having a pair of electrodes 27, And a gas source 28 for supplying gas to the beam gun 23. The ion beam processing apparatus 21 includes a work stage 22 on which the test object 1 is placed, a vacuum container 26 that covers the test object 1 and the work stage 22, and a vacuum pump 25 connected to the vacuum container 26. I have. The ion beam processing apparatus 21 includes a controller 100A that controls the entire apparatus such as the ion beam gun 23 and the work stage 22.

  A test object 1 is fixed on the work stage 22. In the second embodiment, the test surface 1a of the test object 1 is a spherical surface. The work stage 22 is configured to be able to scan in directions of six degrees of freedom (x, y, z, θx, θy, θz). The ion beam gun 23 irradiates the test surface 1a of the test object 1 with the ion beam accelerated by the electrode 27 to process the test surface 1a. At this time, by moving the work stage 22, the ion beam gun 23 is relatively scanned on the test surface 1a of the test object 1.

  The interference measuring apparatus 10A shown in FIG. 7 measures the shape of the test surface 1a. The laser light emitted from the laser light source 11 is shaped into a light beam having a predetermined cross section via the beam expander 12 and then enters the half mirror 13. The light beam is reflected by the half mirror 13 and is incident on the reference lens 17. A part of the light beam incident on the reference lens 17 is reflected as reference light on the reference surface 17 a of the reference lens 17 and returns to the half mirror 13. On the other hand, the light beam transmitted through the reference lens 17 is incident on the test object 1, reflected as measurement light on the test surface 1 a, and returns to the half mirror 13. The reference light reflected by the reference lens 17 and the measurement light transmitted through the reference lens 17 and reflected by the test surface 1a interfere with each other, and are projected onto the area sensor 16 via the imaging lens 15, so that the area An interference fringe is formed on the sensor 16 and is imaged by the area sensor 16. At this time, the reference lens 17 is moved by a predetermined amount in the optical axis direction to obtain data of a plurality of different interference fringes. By analyzing the data of these interference fringes, the shape measurement data of the test surface 1a is obtained. Here, the shape measurement data of the test surface 1 a is expressed as a coordinate system of the area sensor 16.

  Next, an operation for measuring the test surface 1a of the test object 1 using the interference measuring apparatus 10A before the correction process is performed on the test object 1 by the ion beam processing apparatus 21 will be described. Each process is substantially the same as the flowchart shown in FIG. 3, and will be described with reference to FIG. First, three reference marks 3a, 3b, 3c are formed on the test surface 1a of the test object 1 by the ion beam processing apparatus 21 (S1: mark forming process). Here, as shown in FIGS. 8A and 8B, the reference marks 3a and 3c are arranged at opposing positions, and the reference mark 3b is arranged in a direction of 90 degrees with respect to the reference marks 3a and 3b. . As shown in FIG. 9A, the reference marks 3a and 3c have a sine wave cross section in the x direction, and the reference mark 3b has a sine wave cross section in the y direction as shown in FIG. 9B. It is formed into a shape. That is, each of the reference marks 3a, 3b, 3c is formed in a sine wave shape in cross section in a direction (circumferential direction) orthogonal to a direction (radial direction) from the center to the outward direction. For example, each of the reference marks 3a, 3b, and 3c has a shape with a period of 2 mm and PV of 200 nm. At this time, the controller 100 </ b> A of the ion beam processing apparatus 21 acquires position information of the reference marks 3 a, 3 b, 3 c with reference to the coordinate system of the test object 1. Here, the controller 100A calculates the residence time of the ion beam gun 23 in advance based on the design shape of the reference marks 3a, 3b, 3c, and forms the reference marks 3a, 3b, 3c. Thereby, the reference marks 3a, 3b, 3c can be formed by averaging errors caused by the ion beam processing apparatus 21 such as the shape of the ion beam gun 23 and positioning errors of the ion beam processing apparatus 21. Therefore, it becomes possible to position and form the reference marks 3a, 3b, 3c with respect to the test surface 1a with high accuracy.

  Next, shape measurement data of the test surface 1a including the reference marks 3a, 3b, 3c formed in the mark forming step S1 is acquired by the interference measuring apparatus 10A (S2: shape measuring step). In this shape measurement step, shape measurement data is acquired with reference to the coordinate system of the area sensor 16. The shape measurement data obtained in this shape measurement step is acquired by the controller 100A of the ion beam processing apparatus 21.

  As in the first embodiment, the symbol “′” is used below to indicate the position of the imaging target on the sensor surface of the area sensor 16. Next, the controller 100A detects the positions of the reference marks 3a ′, 3b ′, 3c ′ with reference to the coordinate system of the area sensor 16 from the shape measurement data of the surface 1a to be measured in the shape measurement process of S2 (S3: Mark detection process). Here, the controller 100A stores design formulas for the reference marks 3a, 3b, and 3c. The controller 100A is a sine that is a design equation for the shape measurement data of the three reference marks 3a ′, 3b ′, 3c ′ in the shape measurement data of the surface 1a to be measured obtained in the shape measurement step of S2. Curve fitting the wave equation. As a result, the positions of the reference marks 3a ', 3b', 3c 'in the circumferential direction can be obtained. Here, when the sine wave equation is curve-fitted with respect to the reference marks 3a ′ to 3c ′, the curve can be fitted with a plurality of cross sections, and the average value thereof can be obtained to obtain the position with higher accuracy. it can. Next, an intersection position (X1 ', Y1') between a straight line connecting two points from the positions of the reference marks 3a and 3c and a straight line extending from the reference mark 3b can be obtained. Further, the reference mark 3b 'rotation direction Rz' with respect to a straight line connecting two points from the positions of the reference marks 3a 'and 3c' can be obtained. That is, the controller 100A can detect the coordinate system of the area sensor 16 with high accuracy as the coordinates on the area sensor 16 from the circumferential positions of the reference marks 3a ', 3b', 3c '.

  Next, the controller 100A similarly obtains (X1, Y1) and Rz from the position information of the reference marks 3a to 3c of the test object 1 formed in the mark forming process. Here, the coordinate system of the test object 1 formed in the mark formation process is used as a reference (X1, Y1), and the coordinate system of Rz and the area sensor 16 detected in the mark detection process is used as a reference. Simultaneous equations can be obtained from (X1 ′, Y1 ′) and Rz ′. The controller 100A obtains a coordinate transformation matrix from the coordinate system of the area sensor 16 to the coordinate system of the test object 1 based on the simultaneous equations. Then, the controller 100A performs an operation of converting the shape measurement data obtained in the shape measurement process of S2 into the coordinate system of the test object 1 using this coordinate conversion matrix (S4: coordinate calculation process). Thereby, the shape measurement data measured on the basis of the coordinate system of the area sensor 16 is converted into the coordinate system of the test object 1 which is a coordinate system defined by the ion beam processing apparatus 21 as the processing apparatus.

  As described above, according to the second embodiment, since the reference marks 3a, 3b, and 3c are formed on the test surface 1a of the test object 1, the work of replacing the conventional measurement optical member with the test object can be omitted. It is possible to suppress an error from being added to the shape measurement data of the test surface 1a based on the coordinate system of the test object 1. Therefore, the shape measurement data of the test surface 1a based on the coordinate system of the test object 1 can be obtained with high accuracy. Thereby, it becomes possible to perform the shape correction process which processes the to-be-tested surface 1a in the target shape with high precision.

  The reference marks 3a and 3c need to be formed at opposing positions, but the reference mark 3b may be formed at an arbitrary position. In order to specify the position of the test object based on the coordinate system of the test object 1, two points may be set. However, in calculating the above-described coordinate transformation matrix, the larger the number of marks, the smaller the error. Further, when the shape of the test surface 1a is an aspherical surface and the optical axis position of the test surface 1a is determined, the number of reference marks may be one.

  In addition, although this invention was demonstrated based on the said embodiment, this invention is not limited to this. In the first embodiment, the case where there are two reference marks has been described. However, the present invention is not limited to this, and the number of reference marks may be one, or may be three or more. In order to obtain the shape measurement data with high accuracy, it is preferable that there are two or more reference marks.

  In the second embodiment, the case where there are three reference marks has been described. However, the present invention is not limited to this. The number of reference marks may be one or two, and may be four or more. In order to obtain the shape measurement data with high accuracy, it is preferable that there are two or more reference marks. Here, if necessary, the reference mark formed on the test surface has a shape obtained by reversing the reference marks 3a and 3b in the mark forming process of S1 when the processing surface is corrected by the processing apparatus. By adding to the measurement data, it can be removed at the same time. For example, if the reference mark formed on the test surface is outside the optical effective surface, the reference mark does not need to be removed. Simultaneously with the correction processing, processing for removing the reference mark may be performed.

1 Test object 1a Test surface 3a Reference mark 3b Reference mark 3c Reference mark 16 Area sensor

Claims (4)

A mark forming step of forming a reference mark on the test surface of the test object;
An interference fringe obtained by causing the measurement light reflected on the test surface and the reference light to interfere with each other is imaged by an area sensor, and the test mark including the reference mark based on the captured data of the interference fringe A shape measuring step of measuring the shape of the surface to obtain the shape measurement data of the test surface;
A mark detection step of detecting the position of the reference mark with reference to the coordinate system of the area sensor from the shape measurement data;
Position information of the reference mark based on the coordinate system of the test object formed in the mark forming step, and the reference mark based on the coordinate system of the area sensor detected in the mark detection step A coordinate calculation step of performing an operation of converting the shape measurement data obtained by the shape measurement step into a coordinate system of the test object based on a correspondence relationship with the position information of Measurement method.   In the mark detection step, the position of the reference mark relative to the coordinate system of the area sensor is obtained by curve fitting a design formula of the reference mark with respect to the shape measurement data obtained in the shape measurement step. The interference measurement method according to claim 1, wherein:   The interference measurement method according to claim 1, wherein in the mark formation step, the reference mark is formed in a concave cross section.   The interference measurement method according to claim 1, wherein, in the mark formation step, the reference mark is formed in a sine wave shape in cross section.

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