JP2010008345A - Shape measurement apparatus and shape measurement method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a shape measurement apparatus capable of measuring the surface shape of an objected to be detected. <P>SOLUTION: The shape measurement apparatus 1 for separating light from a light source into object light with which an object to be detected is irradiated and reference light that serves as a benchmark, and for measuring the surface shape of the object by analyzing an interference pattern obtained by an optical path difference between the object light reflected by the surface of the object and the reference light includes: a CCD element 8 for acquiring a plurality of surface images of a part of the object, including the interference pattern; a computing section 11 for performing a phase analysis of the interference pattern with use of the surface images, and for acquiring partial surface shape data indicative of the surface shape of the part of the object; and a data integration section 12 for stitching one piece of partial surface shape data to another, and for integrating them into surface shape data on either an annular zone that is a part of the surface shape of the object or the whole object. The CCD element 8 moves a plane of reference to a plurality of different locations on the optical axis of the reference light, and continuously acquires surface images at predetermined intervals while rotating the object at a certain speed. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a shape measuring apparatus and a shape measuring method for measuring a surface shape of a test object by analyzing interference fringes generated by light reflected on the surface of the test object.

Conventionally, when measuring the surface shape of a large-area, high-inclined specimen using an interferometer, the surface of the specimen is divided into a plurality of measurement areas that can be measured by the interferometer, and measurement of each area is performed. A method for measuring the shape of the entire surface by connecting the results has been proposed (see, for example, Patent Document 1).
As a method of connecting the measurement results, a plurality of measurement areas are set in advance so as to overlap each other, and all the other measurement data are set so that the correlation function between one measurement data and the other measurement data in the overlapping portion takes a maximum value. There is known a method of performing coordinate fitting on the fitting (see, for example, Patent Document 2).

In the above-described method, in order to measure the shape of each divided measurement region with high accuracy, it is necessary to perform a phase analysis by fringe scanning of the interference fringes on the surface of the test object. Therefore, normally, the test object is stopped for each measurement region, the reference surface of the interferometer is moved to a plurality of positions on the optical axis, and the measurement region is subjected to fringe scanning. The procedure of performing fringe scanning is taken.
JP 2003-57016 A Japanese Patent No. 3162355

  However, when the surface shape is measured by the procedure as described above, a measurement error may occur due to a slight movement of the test object in a stationary state. In addition, rotation and stop of the test object and movement of the interferometer for fringe scanning (minimum 3 positions, usually 4 positions or more) are performed for each measurement area, which requires a long time for measurement. It becomes more prominent as the number of area divisions increases.

  In addition, when the method described in Patent Document 2 is used to connect a plurality of measurement regions, it takes a processing time and is not suitable for high-speed measurement. Furthermore, there is a problem that it is easily affected by measurement errors due to noise.

  The present invention has been made in view of the above circumstances, and an object thereof is to provide a shape measuring apparatus and a shape measuring method capable of measuring the surface shape of a test object in a short time.

  In the first aspect of the present invention, the light emitted from the light source is separated into object light irradiated on the test object and reference light reflected on the reference surface, and the object light reflected on the surface of the test object And a shape measuring device for measuring a surface shape of the test object by analyzing an interference fringe obtained by an optical path difference between the reference light and a reference image, wherein a surface image of a part of the test object including the interference fringe is obtained. A plurality of imaging units, a phase analysis unit that performs phase analysis of the interference fringes using the surface image and acquires partial surface shape data indicating a partial surface shape of the test object, and each of the portions A data integration unit that combines surface shape data and integrates the surface shape data of a ring-shaped region that is a part of the surface shape of the test object or the entire test object, and the imaging unit includes the reference Moving the surface to a plurality of different positions on the optical axis of the reference light, While the specimen is rotated at a constant speed and wherein the intermittently obtaining the surface images at predetermined intervals.

  According to the shape measuring apparatus of the present invention, since the surface image including the interference fringes in each region of the test object is acquired intermittently while the test object is rotating, the reference surface is moved many times. There is no need to let them.

  The data integration unit obtains an approximate curve of the one partial surface shape data by performing fitting with an approximate function on one of the partial surface shape data having overlapping regions with each other, The other partial surface shape data may be coordinate-transformed and joined so that the sum of squares of the difference from the partial surface shape data is minimized. In this case, the processing can be further speeded up.

  The approximate function may be a NURBS function. Further, when the data integration unit acquires the approximate curve using the NURBS function, the difference between two adjacent point sequence data among the point sequence data of the partial surface shape data is a predetermined value or more. In addition, the weight of the NURBS function for one of the two point sequence data may be reduced, and among the point sequence data of the partial surface shape data, the weight of the point sequence data having a period corresponding to a predetermined frequency is increased. May be. If it does in this way, the measurement noise by the impurity etc. of the to-be-tested object surface can be excluded suitably, and a more exact surface shape measurement can be performed.

  According to a second aspect of the present invention, the light emitted from the light source is separated into object light irradiated on the test object and reference light serving as a reference, and the object light reflected on the surface of the test object and the reference A shape measuring method for measuring a surface shape of the test object using an interferometer that analyzes an interference fringe obtained by an optical path difference with light, wherein the reference surface is a first position on an optical axis of the reference light. A first step of acquiring the interference fringes as a plurality of first interference fringes by irradiating the object light from a direction that forms a predetermined angle with the optical axis of the test object, and the reference surface, A plurality of interference fringes are formed by fixing the object light to a second position on the optical axis of the reference light different from the first position, irradiating the object light from a direction that forms the predetermined angle with the optical axis of the test object. The second step of acquiring as the second interference fringes, and the reference surface before the first position and the second position are different The interference fringes are obtained as a plurality of third interference fringes by fixing the object light to a third position on the optical axis of the reference light and irradiating the object light from a direction that forms the predetermined angle with the optical axis of the test object. And performing phase analysis using the first interference fringe, the second interference fringe, and the third interference fringe to obtain partial surface shape data indicating a partial surface shape of the test object A phase analysis step, and an integration step of connecting the partial surface shape data to obtain a ring-shaped region that is a part of the surface shape of the test object or the entire surface shape data, the first step, In at least one of the second step and the third step, the plurality of interference fringes are acquired intermittently every predetermined time while rotating the test object at a constant speed around the optical axis. It is characterized by that.

  According to the shape measuring method of the present invention, since interference fringes can be acquired while rotating the test object, the time required for acquiring the interference fringes is shortened and surface shape measurement can be performed in a shorter time. .

  According to the shape measuring apparatus and the shape measuring method of the present invention, the surface shape of the test object can be measured in a short time.

  A first embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a diagram showing a shape measuring apparatus 1 according to the present invention. The shape measuring apparatus 1 includes an interferometer 2 and an image processing unit 3 that processes an acquired image of the interferometer 2. The interferometer 2 is a known Fizeau type interferometer. The principle is briefly described as follows.

The light L emitted from the light source 4 is reflected by the object light L1 irradiated on the surface of the test object S and the reference spherical surface (reference surface) 5, and is separated into the reference light L2 serving as a reference. The object light L1 reflected from the surface of the test object S interferes with the reference light L2, and becomes interference light L3. The interference light L3 that has passed through the beam splitter 6 is imaged on a CCD element (image conversion photoelectric element, image pickup unit) 8 by the imaging lens 7, and interference fringes caused by the optical path difference between the object light L1 and the reference light L2 are obtained. It is done. A moving mechanism 5A for moving the reference spherical surface 5 along the optical axis of the reference light L2 is attached to the reference spherical surface 5. A piezo element or the like can be used as the moving mechanism 5A.
The surface image of the test object S including the interference fringes acquired by the CCD element 8 is sent to the image processing unit 3 and processed for measuring the shape of the test object S. The detailed configuration of the image processing unit 3 will be described later.

  FIG. 2 is a diagram showing a polishing machine (processing machine) 20 of the optical element SB to which the shape measuring device 1 is attached. The interferometer 2 of the shape measuring apparatus 1 is mounted to measure the surface shape of the optical element SB after polishing using the optical element SB as a test object, and feed back the measurement result to the polishing machine 20 for reprocessing. It has been.

  The polishing machine 20 includes a spindle 21 and a polishing unit (processing unit) 22. An optical element SB, which is a test object, is attached to one end of the spindle 21 in the axial direction. A rotation shaft 23 passing through the axis of the spindle 21 is connected to a rotation mechanism 24 such as a motor, and the spindle 21 and the optical element SB attached to the spindle can be rotated around the axis of the spindle 21.

  The polishing unit 22 is provided with a grindstone 25 on the surface facing the optical element SB, and is configured to advance and retract to a position in contact with the optical element SB. By rotating the spindle 21 with the grindstone 25 of the polishing unit 22 in contact with the optical element SB, the optical element SB fixed to the spindle 21 is polished.

  The interferometer 2 forms a predetermined angle (for example, δ) with respect to the axis of the spindle 21 and is disposed so that its optical axis is directed toward the center of curvature of the optical element SB. A moving mechanism 9 is attached to the interferometer 2, and the interferometer 2 is moved forward and backward in its own axis (same as the optical axis X1 of the object light L1), and the angle δ is changed. 2 can be rotated.

  FIG. 3 is a block diagram showing the connection of each part of the shape measuring apparatus 1 and the polishing machine 20. As shown in FIG. 3, the image processing unit 3 performs an interference fringe phase analysis, and an index shape extraction unit 10 that recognizes and extracts a shape as an index of an integration process described later from the surface shape data of the optical element SB. A data integration unit that obtains surface shape data of the entire optical element SB by connecting the surface shape data of each part of the optical element SB together with a calculation unit (phase analysis unit) 11 that acquires part of the surface shape data of the optical element SB 12.

The calculation unit 11 is connected to the CCD element 8, the index shape extraction unit 10, and the data integration unit 12. Moreover, each moving mechanism 5A, 9 and the calculating part 11 are connected to the control part 13 which controls the shape measuring apparatus 1 whole.
The image processing unit 3 and the control unit 13 may be provided inside the shape measuring apparatus 1 or may be provided in an external device such as a personal computer connected to the interferometer 2.

  The polishing unit 22 and the rotation mechanism 24 of the polishing machine 20 are connected to a polishing machine control unit 26 that controls the operation of the polishing machine 20. The polishing machine control unit 26 is connected to the control unit 13 of the shape measuring apparatus 1 and is configured to be able to feed back the measurement result of the shape measuring apparatus 1 to the polishing machine 20.

  A procedure for measuring and processing the surface shape of the optical element SB by the shape measuring apparatus 1 and the polishing machine 20 configured as described above will be described below with reference to FIGS. 4 to 8C.

FIG. 4 is a flowchart showing a processing procedure of the optical element SB by the polishing machine 20.
First, in step S1, the grindstone 25 of the polishing unit 22 is brought into contact with the optical element SB fixed to the spindle 21 via the polishing machine control unit 26, and the spindle 21 is rotated by the rotation mechanism 24 to rotate the optical element SB. Surface processing is performed. After the processing is completed, the surface of the optical element SB is cleaned and the polishing unit 22 is retracted by the polishing machine control unit 26 in order to perform surface shape measurement by the shape measuring apparatus 1. Then, in the subsequent step S2, the surface shape of the optical element SB is measured using the shape measuring apparatus 1.

  FIG. 5 is a flowchart showing each step of the surface shape measurement in step S2. The shape measurement method performed in this step includes an interference fringe acquisition step S11 for acquiring a partial surface image of the optical element SB including the interference fringes (hereinafter simply referred to as “surface image”), and a plurality of surface images. And a phase analysis step S12 for performing phase analysis of interference fringes, and an integration step S13 for integrating all images and acquiring surface shape data of the entire optical element SB. Hereinafter, each step will be described with reference to the drawings.

First, as a measurement preparation, the control unit 13 fixes the reference spherical surface 5 to the first position P1, which is one of the positions of the reference spherical surface 5 from which interference fringes are acquired, by the moving mechanism 5A. Then, the interferometer 2 is rotated so that its optical axis forms a predetermined angle δ with respect to the axis of the spindle 21. Next, the user moves and fixes the interferometer 2 via the moving mechanism 9 so that the distance between the optical element SB and the interferometer 2 becomes a predetermined position.
Here, it is desirable that the predetermined position is a position where the curvature radius of the wavefront of the object light L1 coincides with the approximate curvature radius of the optical element SB within the region irradiated with the object light L1. In this state, an arbitrary position on the outer periphery of the optical element SB is set as the reference position PS, and the acquisition of the surface image is started from a state (start position) where the reference position PS is positioned at the top in FIG.

  FIG. 6 is a diagram illustrating the surface of the optical element SB on which the reference position PS is set. In the measurement method of the present embodiment, the surface image of the optical element SB is acquired by being divided into four overlapping regions R1, R2, R3, and R4, and surface shape data (partial surface shape data) of each region is obtained by phase analysis. ) And then connecting (fitting) in an integration step to be described later to obtain surface shape data (total surface shape data) of the entire optical element SB.

Next, in the interference fringe acquisition process of step S11, the control unit 13 drives the rotation mechanism 24 via the polishing machine control unit 26 to rotate the spindle 21 at a constant speed, for example, 20 rotations per minute. Then, as shown in FIG. 6, from the time when the reference position PS moves to the start position, surface images in the respective regions R1 to R4 are acquired using the interferometer 2 at a predetermined sampling period based on the rotation speed of the spindle 21. To do. At this time, the position of the reference spherical surface 5 is fixed at the first position P1.
For example, in the present embodiment, each of the regions R1 to R4 differs by 90 degrees in terms of the rotation angle of the optical element SB, so that the interference fringes are generated at a sampling period of 750 milliseconds (ms) in which the optical element rotates 90 degrees. Get it. As described above, the calculation unit 11 calculates a necessary sampling period from the rotation speed of the optical element SB and the set position of the acquired surface image.

  Specifically, the control unit 13 starts acquiring the surface image 3 seconds after the rotation start of the rotation of the optical element SB once. First, in a state where the position of the reference spherical surface 5 of the interferometer 2 is fixed at the first position P1, a surface image of the region R1 shown in FIG. Each time 750 ms (predetermined time) that rotates 90 degrees passes, surface images of regions R2, R3, and R4 shown in FIGS. 7B, 7C, and 7D, respectively, are acquired. At this time, if all pixels of the CCD element 8 are set to perform synchronous reading, an image can be acquired at a higher speed. In this way, surface images (first interference fringes) in the regions R1 to R4 of the optical element SB when the reference spherical surface 5 is located at the first position P1 are continuously acquired (first step).

  Here, the acquisition of interference fringes is temporarily stopped, the spindle 21 idles, and the optical element SB also idles accordingly. In the meantime, the controller 13 applies a voltage to the piezo element of the moving mechanism 5A to retract the reference spherical surface 5 by a predetermined distance along the optical axis X1 shown in FIG. 1, and a second position P2 different from the first position. Move to and fix. The idle rotation of the spindle 21 may be performed a plurality of times in consideration of the time required for the movement of the reference spherical surface 5 by the moving mechanism 5A and the time required for fine adjustment after the movement.

  After the reference spherical surface 5 is fixed at the second position P2, the acquisition of the surface image is started again at an arbitrary timing at which the reference position PS moves to the start position. Then, in the same manner as in the first step described above, surface images (second interference fringes) in the regions R1 to R4 when the reference spherical surface 5 is located at the second position P2 are continuously acquired (second step). .

  Thereafter, in the same procedure, the reference spherical surface 5 is moved along the optical axis X1, moved to the third position P3 and the fourth position P4 different from the second position P2, and the third interference pattern and the fourth interference pattern are Each is acquired continuously. That is, four types of first to fourth interference fringes are acquired in the regions R1 to R4, respectively, as the surface image of the surface of the optical element SB. All the acquired surface image data are sequentially sent from the CCD element 8 to the calculation unit 11. Here, the interference fringe acquisition process ends, and the process proceeds to step S12.

  In the phase analysis step of step S12, the calculation unit 11 extracts four corrected surface images obtained by fixing the reference spherical surface 5 to the first position P1 to the fourth position P4 for a specific region (for example, the region R1). Then, these phase changes are analyzed to obtain partial surface shape data in the region of the optical element SB. The calculation unit 11 performs the same operation in all regions R1 to R4 to obtain partial surface shape data of each region.

  In the integration step of step S13, the data integration unit 12 connects the surface shape data of each region acquired in step S12 using a common index shape M and integrates it into one data, and the surface of the optical element SB. Get the whole shape data.

  First, the index shape extraction unit 10 selects an arbitrary region as a reference region (fitting region) from the surface shape data of the regions R1 to R4, and a region where all the four regions R1 to R4 shown in FIG. 6 overlap. An index shape M serving as a fitting index is extracted from SR1 by a known shape extraction method or the like. Therefore, as shown in FIGS. 7A to 7D, the index shape M is included in the surface shape data of all the regions R1 to R4 in a state where the position and orientation are different. The extracted index shape M information is transmitted to the data integration unit 12.

  As the index shape M, for example, a fine scratch on the surface of the optical element SB can be used. There is no particular limitation on the shape, but if the same shape is accidentally present in the region SR1, fitting cannot be performed satisfactorily, and therefore a specific shape is preferable. In addition, it is preferable to set a shape that is asymmetric with respect to rotation because correction can be performed using both the position and orientation parameters. The user sets a desired condition in the data integration unit 12 in advance for the index shape to be extracted.

  Next, the data integration unit 12 extracts the surface shape data of the index shape M portion from the surface shape data of the reference region, performs fitting using the NURBS function shown in Equation 1, and approximates the curved surface of the surface shape data of the index shape M A curve (approximate curve) is obtained.

  In the NURBS function, weighting can be performed for each coordinate by changing the value of ω. Therefore, when it can be determined that the value of a certain coordinate is clearly an incorrect value due to a measurement error or dust adhering to the surface of the optical element SB, no weight is given to the coordinate or the weight is smaller than other coordinates. By doing so, a more accurate approximate curve can be obtained.

For example, in the surface shape data DM of the index shape M shown in FIG. 8A, when the point sequence data C1 is an illegal value due to dust or the like, the fitting using a normal polynomial or the like is shown in FIG. 8B. As shown, an approximate curve A1 including noise of the point sequence data C1 is acquired. However, when the NURBS function is used, the influence of the point sequence data C1 is eliminated or corrected as shown in FIG. 8C. In addition, a more accurate approximate curve A2 can be obtained.
The determination as to whether or not the value is an illegal value may be made sequentially by the user looking at the surface shape data, or may be automatically determined by giving a condition for the determination to the data integration unit 12. For example, it is determined that an outlier that falls outside a predetermined range is an incorrect value, or when the difference between adjacent point sequence data is greater than or equal to a predetermined value, the point sequence data that is further away from the average value of the point sequence data Conditions such as judging an illegal value.

  After obtaining the approximate curve of the index shape M, the surface shape data of the index shape M in the surface shape data of the remaining region (fitting region) is extracted, and the sum of squares of the difference between the approximate curve and the surface shape data is minimized. Thus, the correction amount of the fitting area is calculated by the least square method. The correction amount is associated with, for example, translation amounts dx, dy, dz along the x-axis, y-axis, and z-axis, and tilt amounts da, db, dc around the respective axes, and a shift in the optical axis direction. There are seven types of similar magnification P for enlargement / reduction deformation. The calculation unit 11 performs the above calculation for all the fitting regions, and calculates the correction amount of each fitting region.

  After calculating the correction amount, the data integration unit 12 converts all coordinate values of the surface shape data of each fitting region based on the correction amount, and fits the surface shape of the region selected as the reference. Then, the entire surface shape data of the optical element SB is obtained by connecting the surface shape data of all the regions. Thus, the surface shape measurement in step S2 is completed. The acquired entire surface shape data is sent to the polishing machine controller 26.

  In step S3, the polishing machine control unit 26 determines whether or not the surface of the optical element SB has been processed within the target accuracy range based on the entire surface shape data sent from the control unit 13 of the shape measuring apparatus 1. To do. If the determination result is YES, the surface processing ends. If the determination result is NO, the process proceeds to step S4, and the corrected machining locus of the polishing unit 22 is set by the polishing machine control unit 26 based on the entire surface shape data.

  Then, the process returns to step S <b> 1, and the polishing machine control unit 26 performs the second processing based on the corrected processing locus via the polishing unit 22. After the processing, the shape measurement of the surface of the optical element SB is performed again by the shape measuring apparatus 1. This series of operations is repeated until “YES” is determined in step S3.

According to the shape measuring apparatus 1 of the present embodiment, a mechanism such as a rotary encoder is used by the CCD element 8 intermittently acquiring surface images at predetermined intervals while the optical element SB is rotated at a constant rotational speed. A surface image at a desired position of the optical element SB is acquired without any problem. And the phase analysis using the surface image which the calculating part 11 acquired is performed, and the partial surface shape data of optical element SB are acquired. Further, the surface integration data of the optical element SB is acquired by connecting the measurement results of the respective regions in the data integration unit 12.
Therefore, it is not necessary to move the reference spherical surface 5 to each position of the first position P1 to the fourth position P4 every time a surface image of each area is acquired, and thus surface shape measurement having the same degree of accuracy as the conventional method. Can be completed in a much shorter time.

  In addition, since a rotation amount detection mechanism such as a rotary encoder for detecting the rotation angle amount of the optical element SB that is the test object is not required, when mounting to a processing machine such as the polishing machine 20 as in the present embodiment. However, it is not necessary to install the mechanism separately, and it is possible to configure a shape measuring apparatus that has a very high versatility for incorporation into a processing machine.

  Further, the optical element SB is rotated by one rotation and one or several rotations for moving the reference spherical surface 5 in a state where the reference spherical surface 5 is fixed from the first position P1 to the fourth position P4. As a result, all the surface images including the interference fringes necessary for the shape measurement can be acquired, so that the shape measurement can be performed in a shorter time.

  In addition, since it is not necessary to stop the optical element SB when acquiring the interference fringes, it is possible to prevent the occurrence of a shape measurement error due to blurring when the optical element SB is stationary. Further, since it is not necessary to make the optical element SB stationary, it is not necessary to provide a servo mechanism on the spindle 21. Therefore, it can be applied to a wider range of processing machines.

  Furthermore, when it is desired to increase the measurement accuracy, it is only necessary to adjust so that the sampling period of the surface image by the CCD element 8 is shortened to acquire a larger number of surface images, so that the shape can be easily formed without increasing the measurement time. Measurement accuracy can be increased. At this time, if the time required for acquiring the interference fringes of the CCD element 8 becomes longer than the above-described interference fringe acquisition interval, it can be adjusted by slowing the rotation speed of the optical element SB.

  Further, in the integration step of step S13, the data integration unit 12 acquires an approximate curve of the surface shape data of the index shape M using the NURBS function, and performs fitting of the surface shape data of each region based on the approximate curve. . Therefore, impurities such as dust and incorrect values due to measurement errors can be eliminated, fitting based on a more accurate approximate curve can be performed, and highly accurate surface shape data can be obtained.

In the present embodiment, an example has been described in which an approximate curve of the surface shape data of the index shape M of the region selected as the reference is acquired, and fitting is performed by the point square data of the surface shape of the fitting region and the least square method. Instead of this, an approximation curve may be acquired by the same method for the surface shape data of the index shape M in the fitting region, and the fitting of both may be performed using the correlation coefficient.
Further, the weighting of the coordinates when obtaining the approximate curve may be performed using a so-called frequency filter that changes the weights of the coordinates corresponding to a specific frequency by increasing or decreasing the weight.
In addition, although the above-described NURBS function does not have the merit, fitting may be performed by obtaining an approximate curve using a general polynomial or the like.

  Further, in the present embodiment, the example in which the fitting is performed using the common index shape M for the surface shape data of all the regions has been described, but instead, each region is superimposed on the adjacent region. Fitting may be performed using different index shapes for each region by extracting arbitrary index shapes that differ from one part to another.

  At this time, when fitting the adjacent areas sequentially clockwise or counterclockwise and fitting the last area, the correction amount is also calculated for the first reference area and the detected correction is performed. The calculation unit and the data integration unit may be set so as to correct all fittings based on the amount error.

  In addition, according to the shape measuring method of the said embodiment, although the shape data of a part of ring-shaped area | region can be acquired among the surfaces of optical element SB, the area | region of optical element SB irradiated with object light L1 Is generally narrower than the entire surface of the optical element SB, it is difficult to obtain surface shape data of the entire optical element SB.

  In this case, after the step S2 is completed, the interferometer 1 is rotated by, for example, 15 degrees through the moving mechanism 9 to change the angle δ. And the process similar to said step S2 is continued. In this manner, surface shape data of the interference fringe acquisition region that covers the entire optical element SB is obtained by acquiring the surface shape data of the plurality of annular regions. Thereafter, the surface shape data of the entire optical element SB is acquired by integrating the surface shape data of all the zonal regions into one data by the same process as the integration step of step S15.

  As mentioned above, although one Embodiment of this invention was described, the technical scope of this invention is not limited to the said embodiment, A various change can be added in the range which does not deviate from the meaning of this invention.

  For example, in the above-described embodiment, an example in which a Fizeau interferometer is used has been described. However, the present invention is not limited to any one that performs a fringe scan by advancing or retracting either the reference surface or the test object. The present invention can also be applied to a shape measuring apparatus using another type of interferometer such as a Wyman Green type.

  Furthermore, in the above-described embodiment, an example has been described in which the calculation unit 11 calculates a sampling period for acquiring a surface image and also functions as a phase analysis unit that performs phase analysis, but these processes are different. The shape measuring apparatus of the present invention may be configured so that it can be shared by the mechanism to enable faster processing.

It is a figure which shows the structure of the shape measuring apparatus of one Embodiment of this invention. It is a figure which shows the polisher with which the interferometer of the same shape measuring apparatus was attached. It is a block diagram which shows the connection of each part of the same shape measuring apparatus and the polisher. It is a flowchart which shows the process sequence of the optical element by the polisher. It is a flowchart which shows the procedure of the surface shape measurement in FIG. It is a figure which shows the area | region which acquires each surface image of an optical element. (A)-(d) is a figure which shows the surface image and index shape in the same area | region, respectively. (A) is a figure which shows an example of partial surface shape data, (b) and (c) are figures which show an example of fitting of the approximate function with respect to the partial surface shape data, respectively.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Shape measuring device 2 Interferometer 4 Light source 5 Reference spherical surface (reference surface)
8 CCD element (imaging part)
11 Calculation unit (phase analysis unit)
12 data integration unit L1 object light L2 reference light M index shape P1 first position P2 second position P3 third position S12 phase analysis step S13 integration step SB optical element (test object)

Claims (6)

The light emitted from the light source is separated into the object light irradiated on the test object and the reference light reflected on the reference surface, and the optical path difference between the object light reflected on the surface of the test object and the reference light A shape measuring device for analyzing the obtained interference fringes and measuring the surface shape of the test object,
An imaging unit that acquires a plurality of surface images of a part of the test object including the interference fringes;
A phase analysis unit that performs phase analysis of the interference fringes using the surface image and acquires partial surface shape data indicating a partial surface shape of the test object;
A data integration unit that joins each partial surface shape data and integrates it into a ring-shaped region that is a part of the surface shape of the test object or the surface shape data of the entire test object,
With
The imaging unit moves the reference surface to a plurality of different positions on the optical axis of the reference light, and intermittently acquires the surface image at predetermined intervals while rotating the test object at a constant speed. A feature measuring device.   The data integration unit obtains an approximate curve of the one partial surface shape data by performing fitting with an approximate function on one of the partial surface shape data having overlapping regions with each other, 2. The shape measuring apparatus according to claim 1, wherein the other partial surface shape data is coordinate-transformed and joined so that the sum of squares of the difference from the partial surface shape data is minimized.   The shape measuring apparatus according to claim 2, wherein the approximate function is a NURBS function.   The data integration unit, when acquiring the approximate curve using the NURBS function, among the point sequence data of the partial surface shape data, when the difference between two adjacent point sequence data is a predetermined value or more, The shape measuring apparatus according to claim 3, wherein a weight of the NURBS function for one of the two point sequence data is reduced.   The data integration unit, when acquiring the approximate curve using the NURBS function, increases the weight of the point sequence data having a period corresponding to a predetermined frequency among the point sequence data of the partial surface shape data. The shape measuring apparatus according to claim 3. Interference obtained by separating the light emitted from the light source into object light irradiated on the test object and reference reference light, and an optical path difference between the object light reflected on the surface of the test object and the reference light A shape measuring method for measuring the surface shape of the test object using an interferometer for analyzing fringes,
The reference plane is fixed at a first position on the optical axis of the reference light, the object light is irradiated from a direction that forms a predetermined angle with the optical axis of the test object, and the interference fringes are formed in a plurality of first directions. A first step of acquiring as interference fringes;
Fixing the reference surface at a second position on the optical axis of the reference light different from the first position, irradiating the object light from a direction that forms the predetermined angle with the optical axis of the test object; A second step of acquiring the interference fringes as a plurality of second interference fringes;
A direction in which the reference surface is fixed at a third position on the optical axis of the reference light different from the first position and the second position, and the object light is at a predetermined angle with the optical axis of the test object A third step of acquiring the interference fringes as a plurality of third interference fringes,
A phase analysis step of performing phase analysis using the first interference fringe, the second interference fringe, and the third interference fringe, and obtaining partial surface shape data indicating a partial surface shape of the test object;
An integration step of connecting the partial surface shape data to obtain a ring-shaped region that is part of the surface shape of the test object or the entire surface shape data;
With
In at least one of the first step, the second step, and the third step, while rotating the test object at a constant speed around the optical axis, a plurality of the intermittently a plurality of the time A shape measuring method, wherein interference fringes are acquired.

Images