JP5558139B2 - Shape measuring method and shape measuring apparatus - Google Patents

Description

  The present invention relates to a shape measuring method, more specifically, a shape measuring method for measuring the surface shape of a test object using interference fringes generated by light reflected on the reference surface and the surface of the test object, and the same shape measurement The present invention relates to a shape measuring apparatus for executing a method.

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 entire surface by connecting the results has been proposed.
In this shape measurement method, in order to perform shape measurement of each divided measurement region with high accuracy, phase analysis by fringe scanning of interference fringes including shape information of the surface of the test object is required. 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.

  However, when the surface shape is measured in the above procedure, the rotation and stop of the test object and the movement of the reference surface for the fringe scanning (usually 4 positions or more) are performed for each measurement region. It takes a long time. This becomes more prominent as the number of measurement area divisions increases.

  In order to solve this problem and improve the measurement efficiency, the inventor of the present invention (the present inventor) has proposed a shape measuring method described in Patent Document 1. In this shape measurement method, the test object is rotated instead of being stationary, and the test object is imaged intermittently every time the test object rotates by a predetermined angular amount, and the surface image of the test object including interference fringes is obtained. Get more than one. By repeating this by changing the position of the reference plane, a necessary number of interference fringes are acquired and phase analysis is performed. In this shape measurement method, it is not necessary to frequently rotate and stop the test object, and the measurement efficiency can be remarkably improved.

JP 2009-192369 A

However, the present inventors have found that further improvement of the shape measuring method described in Patent Document 1 can be expected by solving the following problems.
In the shape measurement method described in Patent Document 1, the acquired interference fringes may include noise due to disturbances during imaging and various other causes. When the degree of noise is significant, the interference fringes cannot be used for phase analysis, and the interference fringes at a certain angle amount are lost. As a result, there is a problem that the shape measurement itself cannot be performed.
Furthermore, even when the interference fringes do not contain noise, there is a possibility that the timing for sampling the interference fringes may be shifted under the condition that the test object is in a dynamic state. There is also a problem.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a shape measuring method and a shape measuring apparatus capable of efficiently performing surface shape measurement while suppressing loss of interference fringes.

  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 method for measuring the surface shape of the test object using a shape measuring device for analyzing interference fringes obtained by an optical path difference between the reference light and the reference light, wherein the reference surface is fixed at a first position. Irradiating the object with the object light to obtain first interference fringes at a plurality of positions of the object, and the reference surface is different from the first position with the light of the reference light A second step of fixing the second position on the axis, irradiating the test object with the object light, and obtaining second interference fringes at the plurality of positions; and the reference surface, the first position and The object light is fixed to a third position on the optical axis of the reference light different from the second position, and the object light is applied to the test object. Irradiating and acquiring the third interference fringes at the plurality of positions, using the first interference fringes, the second interference fringes, and the third interference fringes, the interference at the plurality of positions. A phase analysis step of performing phase analysis of fringes, wherein at least one of the first interference fringes, the second interference fringes, and the third interference fringes is relative to the shape measuring device. It is acquired based on a plurality of interference fringes intermittently acquired in the vicinity of the plurality of positions while being moved.

At least one of the first interference fringe, the second interference fringe, and the third interference fringe intermittently near the plurality of positions while moving the object relative to the shape measuring device . You may acquire by the interpolation process using the acquired some interference fringe.

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 reflected on the reference surface, and the object light reflected on the surface of the test object A shape measuring device for measuring a surface shape of the test object by analyzing an interference pattern obtained by an optical path difference between the reference beam and the reference light, and acquiring a surface image of the test object including the interference pattern And a control unit that controls the timing at which the imaging unit acquires the surface image, and the control unit moves the test object relative to the test object that moves relative to the shape measuring device. In the vicinity of the timing at which the shape measuring device and the shape measuring device are in a predetermined positional relationship, the imaging means is intermittently acquired the surface image a plurality of times , and the test object and the shape measuring device are in a predetermined positional relationship. A plurality of the surface images acquired in the vicinity of the timing when By an interpolation processing using the, and further comprising a calculation unit for generating an interpolated surface image.

  According to the shape measuring method and the shape measuring device of the present invention, it is possible to efficiently measure the surface shape while suppressing the loss of interference fringes.

It is a figure which shows the shape measuring apparatus used for the shape measuring method of 1st Embodiment of this invention. It is a functional block diagram of the same shape measuring apparatus. It is a flowchart which shows the flow of the same shape measuring method. It is a figure which shows an example of the relationship between the rotation angle of an optical element, and the timing of interference fringe acquisition. It is a figure which shows the example of the acquired interference fringe and the selected 1st interference fringe. (A) And (b) is a figure which shows the example of both the acquired interference fringe and the selected 1st interference fringe. It is a flowchart which shows the flow of the interference fringe acquisition process in the shape measuring method of 1st Embodiment of this invention. It is a flowchart which shows the flow of the 1st selection process in the interference fringe acquisition process.

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 used in the shape measuring method of the present embodiment. The shape measuring apparatus 1 includes a known Twiman Green type interferometer. The principle of the interferometer will be briefly described as follows.
The light L emitted from the light source 2 is reflected by the object light L1 irradiated on the surface of the test object S and the reference plane (reference surface) 3 and separated into the reference light L2 serving as a reference. The object light L1 reflected by the surface of the optical element S, which is the test object in the present embodiment, interferes with the reference light L2 and becomes interference light L3. The interference light L3 is imaged on the CCD element (imaging means) 6 by the imaging lens 5, and interference fringes caused by the optical path difference between the object light L1 and the reference light L2 are obtained. A moving mechanism 3A for moving the reference plane 3 along the optical axis of the reference light L2 is attached to the reference plane 3. A piezo element or the like can be employed as the moving mechanism 3A.

The optical element S is attached to one end of the spindle 12 in the axial direction. A rotating shaft 14 passing through the axis of the spindle 12 is connected to a rotating mechanism 15 such as a motor, and the spindle 12 and the optical element S attached to the spindle are rotated around the axis of the spindle 12 (direction indicated by an arrow θ in FIG. 1). Can be rotated. A rotary encoder 16 is installed on the rotating shaft 14, and the rotation angle of the rotating shaft 14 (the amount of relative movement of the optical element S with respect to the shape measuring device 1) can be detected.
The shape measuring apparatus 1 is arranged so that the optical axes X1 of the object light L1 and the reference light L2 are opposed to the optical element S at a predetermined angle with respect to the axis of the spindle 12.

FIG. 2 is a functional block diagram of the shape measuring apparatus 1. As shown in FIG. 2, the CCD element 6 is connected to a calculation unit 8 that performs selection of interference fringes, which will be described later, and phase analysis based on the selected interference fringes. The CCD element 6, the moving mechanism 3 </ b> A, and the calculation unit 8 are connected to a control unit 9 that controls the entire shape measuring apparatus 1. Further, a rotary encoder 16 attached to the spindle 12 is also connected to the control unit 9 so that the control unit 9 can detect the rotation angle of the rotary shaft 14.
The calculation unit 8 and the control unit 9 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 CCD element 6 and the moving mechanism 3A.

  A procedure for measuring the surface shape of the optical element S by the shape measuring method of the present embodiment using the shape measuring apparatus 1 configured as described above will be described below with reference to FIGS.

FIG. 3 is a flowchart showing the flow of the shape measuring method of the present embodiment. The shape measuring method of the present embodiment includes an interference fringe acquisition step S10 for acquiring an interference fringe used for phase analysis, and a phase analysis step S20 for performing phase analysis using the acquired interference fringe and acquiring a partial shape of the optical element S. And an integration step S30 for acquiring the surface shape of the entire optical surface of the optical element S by connecting the acquired partial shapes.
First, as preparation for shape measurement, the user fixes the optical element S to the spindle 12 so that the optical axis thereof coincides with the axis of the rotating shaft 14.

Next, in the interference fringe acquisition step of step S10, the interference fringes on the surface of the optical element S used in the phase analysis step S20 are acquired.
The user uses the moving mechanism 3A to fix the shape measuring device 1 in a state where the reference plane 3 is fixed to a first position P1 that is one of the positions (reference positions) of the reference plane 3 from which interference fringes are obtained. The axis X1 is moved so as to form a predetermined angle with respect to the axis of the spindle 12 (coincident with the axis of the rotary shaft 14). Then, the shape measuring device 1 is fixed so that the distance between the optical element S and the shape measuring device 1 is 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 S in the region irradiated with the object light L1.

The user sets an arbitrary position on the outer periphery of the optical element S as the reference position PS, and defines a state in which the reference position PS is located immediately above the optical axis of the optical element S as a rotation angle of 0 degrees. To do.
In the following description, it is assumed that the rotation angle increases clockwise, and the region on the surface of the optical element S irradiated with the object light L1 when the optical element S reaches a certain rotation angle is defined as the rotation angle. This is called the “rotation position” of the corner.

  Next, the user drives the rotation mechanism 15 to rotate the spindle 12 at a constant speed, for example, 20 rotations per minute. The rotation amount of the spindle 12 is transmitted to the control unit 9 by the rotary encoder 16. Based on the signal from the rotary encoder 16, the control unit 9 starts acquiring interference fringes from a state where the rotation angle of the optical element S becomes 0 degrees.

  FIG. 4 is a diagram illustrating an example of the relationship between the rotation angle of the optical element S and the interference fringe acquisition timing (sample timing). While detecting the signal of the rotary encoder 16, the control unit 9 detects a surface image of a part of the optical element S including the interference fringes (hereinafter simply referred to as “interference”) at a plurality of rotation positions corresponding to a plurality of rotation angles set in advance. The CCD element 6 is intermittently acquired. At this time, if all pixels of the CCD element 6 are set to perform synchronous readout, interference fringes can be acquired at high speed.

  In the present embodiment, the interference fringes are acquired at each rotation position when the optical element S rotates relative to the shape measuring apparatus 1 and the rotation angles become 0 degrees, 90 degrees, 180 degrees, and 270 degrees. However, the control unit 9 controls the sample timing of the CCD element 6 so that a plurality of interference fringes are intermittently acquired in the vicinity of each rotational position.

  Specifically, the control unit 9 detects the signal of the rotary encoder 16 and acquires the interference fringes when the rotation angle of the optical element S becomes 0.1 degrees less than the above position. 6 is operated, and then interference fringes are acquired twice more each time the rotation angle increases by 0.1 degree. That is, for example, the control unit 9 acquires interference fringes at the rotation positions at three points of rotation angles of 89.9 degrees, 90.0 degrees, and 90.1 degrees at and near the rotation position of the rotation angle of 90 degrees. The CCD element 6 is operated as follows. The acquired interference fringes are sent from the CCD element 6 to the control unit 9.

  If there is no time lag in the exchange of information between the control unit 9 and the rotary encoder 16 and the exchange between the control unit 9 and the CCD element 6, as shown in FIG. 5, the rotation position is 90.0 degrees. Since the interference fringes are acquired, the control unit 9 selects the interference fringes as the interference fringes used in the phase analysis step S20.

  On the other hand, when a time lag occurs in the exchange of information between the control unit 9 and the rotary encoder 16 or in the exchange between the control unit 9 and the CCD element 6, the timing at which the control unit 9 instructs the CCD element 6 and the actual interference fringes. There is a deviation from the timing at which is acquired. In the example shown in FIG. 4, the timing instructed by the control unit 9 substantially coincides with the timing at which the interference fringes are actually acquired at the rotational position of the rotational angle of 270 degrees, but a deviation occurs at other rotational positions. ing. At this time, there may be a case where a gap also occurs between the three points at which the interference fringes are acquired, and the three points are not evenly spaced.

As in the example illustrated in FIG. 6A, when the acquired interference fringes do not exist at the set rotation position (for example, 90.0 degrees), the control unit 9 The interference fringe acquired at the point closest to (in this case, 90.004 degrees) is selected as the interference fringe used in the phase analysis step S20.
In addition, as shown in FIG. 6B, there is an interference fringe acquired at the set rotational position in the acquired interference fringe, but it contains noise N and cannot be suitably used for phase analysis. The control unit 9 selects the interference fringes acquired at the point closest to the rotation position (in this case, 89.992 degrees) other than the interference fringes including the noise N as the interference fringes used in the phase analysis step S20.
In this way, the interference fringes (first interference fringes) at the respective rotational positions described above when the reference plane 3 is present at the first position P1 are obtained one by one (first step).

  After completion of the first step, the acquisition of interference fringes is paused, the spindle 12 idles, and the optical element S also idles accordingly. Meanwhile, the control unit 9 operates the moving mechanism 3A to retract the reference plane 3 by a predetermined distance along the optical axis of the reference light L2, and is different from the first position P1 and on the optical axis of the reference light L2. Move to the second position P2 (see FIG. 1) and fix. The idle rotation of the spindle 12 may be performed a plurality of times in consideration of the time required for movement by the moving mechanism 3A and the time required for fine adjustment after movement.

  After the reference plane 3 is fixed at the second position P2, acquisition of interference fringes at the second position P2 is started from a position where the rotation angle of the optical element S becomes 0 degrees. Then, in the same manner as in the first step described above, a plurality of interference fringes in the vicinity of each rotation position when the reference plane 3 is located at the second position P2 are intermittently acquired, and interference fringes (second interference) at each rotation position are obtained. Stripes) are selected and acquired one by one (second step).

  Thereafter, in the same procedure, the reference plane 3 is moved to the third position P3 and the fourth position P4 on the optical axis of the reference light L2 behind the second position P2, and the third interference fringe and the fourth interference fringe are obtained. (3rd process, 4th process). That is, four types of interference fringes of the first to fourth interference fringes are acquired at each rotation position at intervals of 90 degrees as the rotation angle. All the acquired first to fourth interference fringe data is sent from the control unit 9 to the calculation unit 8, and the interference fringe obtaining step S10 is completed.

  In the subsequent phase analysis step of step S20, the calculation unit 8 extracts the first to fourth interference fringes at a certain rotational position from the interference fringes sent from the control unit 9, and analyzes these phase changes. The surface shape data of the rotational position is obtained. The calculation unit 8 performs the same operation at all the rotational positions where the interference fringes are acquired, and obtains surface shape data at all the rotational positions. That is, in the case of this embodiment, four surface shape data are obtained.

  In the integration step of step S30, the calculation unit 8 integrates each surface shape data into one data by using the overlapping portion of the surface shape data at each rotation position, and is a part of the surface of the optical element S. The surface shape data of the annular zone area is acquired. As the integration method, various known methods can be appropriately selected and used. Thus, the surface shape measurement of the optical element S is completed.

When the ratio of the area irradiated with the object light L1 to the surface of the optical element S is sufficiently wide, the shape data of the entire surface of the optical element S is acquired in the integration step S30, but the irradiation of the object light L1 is performed. Since the area of the optical element S to be applied is generally narrower than the entire surface of the optical element S, the shape data obtained by one-time shape measurement is that of a part of the ring-shaped area on the surface of the optical element S. Become. Therefore, it is usually difficult to obtain the shape data of the entire optical element S by a single shape measurement.
In such a case, after the shape measurement is completed, the shape measuring apparatus 1 is moved to change the region of the optical element S irradiated with the object light L1. Then, the shape measurement method of the present embodiment is executed again, and surface shape data of different annular zones in the optical element S is acquired. This is repeated as many times as necessary to obtain surface shape data sufficient to cover the entire optical element S. Thereafter, the surface shape data of the entire optical element S may be acquired by integrating the surface shape data of each annular zone region by the same procedure as in the integration step S30.

According to the shape measurement method of this embodiment and the shape measurement device 1 that executes the shape measurement method, in the interference fringe acquisition step S10, a plurality of rotations corresponding to a predetermined relative movement amount of the optical element S with respect to the shape measurement device 1. In the vicinity of the position, the control unit 9 operates the CCD element 6 to intermittently obtain a plurality of interference fringes, from which the first to fourth interference fringes used in the phase analysis step S20 are selected. Is obtained.
Therefore, even when interference fringes acquired at each rotational position include those that cannot withstand phase analysis, other interference fringes are selected as the first to fourth interference fringes, and the phase analysis step S20 is performed. Therefore, it is possible to suitably prevent the situation in which the shape measurement becomes impossible due to the loss of the interference fringe data.

  Moreover, in the shape measuring apparatus 1 of this embodiment, when the control part 9 selects the interference fringe used in phase analysis process S20, the interference fringe acquired in the rotation position nearest to the set rotation position is shown. Therefore, the error in the phase analysis process can be minimized.

  In the shape measurement method of the present invention, the number of interference fringes intermittently acquired in the vicinity of each rotational position of the test object and the acquisition interval may be appropriately set based on the required accuracy of shape measurement. In general, as the interference fringe acquisition interval is narrowed, the phase analysis step can be performed using the interference fringe acquired at a rotation position closer to the set rotation position, and thus the accuracy of shape measurement is improved. When the performance of the imaging means such as the CCD element 6 becomes a bottleneck for reducing the interference fringe acquisition interval, the acquisition interval can be further reduced by reducing the rotation speed of the spindle 12.

Next, a second embodiment of the present invention will be described with reference to FIGS. The difference between the shape measurement method of the present embodiment and the first embodiment described above is that, in the process of acquiring the first to fourth interference fringes, interpolation processing based on the obtained interference fringes is performed as necessary. Is a point. In the following description, the same components as those already described are denoted by the same reference numerals and redundant description is omitted.
The shape measurement method of this embodiment is different from the first embodiment only in that an interference fringe acquisition step S40 is provided instead of the interference fringe acquisition step S10, and the operation modes of the control unit 9 and the calculation unit 8 are changed. Only by the shape measuring apparatus 1 described above can be executed.

  7 and 8 are flowcharts showing the flow of the interference fringe acquisition step S40 in the shape measurement method of the present embodiment. As shown in FIG. 7, the interference fringe acquisition step S40 includes a first selection step S42 for selecting the first to fourth interference fringes at the first rotation position, and the first to fourth interference fringes at the second rotation position. A second selection step S43 for selecting the first, a fourth selection step S44 for selecting the first to fourth interference fringes at the third rotational position, and a first selection step for selecting the first to fourth interference fringes at the fourth rotational position. 4 selection process S45. In the present embodiment, the rotation angles of the first to fourth rotation positions are set to 0 degrees, 90 degrees, 180 degrees, and 270 degrees, respectively, as in the first embodiment.

First, in step S41, three interference fringes are intermittently acquired in the vicinity of each rotational position at each reference position in the same procedure as in the first embodiment. That is, in this embodiment, in step S41, a total of 48 interference fringes, which are the product of these four reference positions, four rotation positions, and three interference fringes, are acquired by the CCD element 6 and sent to the control unit 9. In step S41, the first through fourth interference fringes are not yet selected.
After step S41 ends, the process proceeds to a first selection step in step S42.

  FIG. 8 is a flowchart showing a detailed flow of the first selection step S42 shown in FIG. Since the second selection process S42 to the fourth selection process S45 are also performed in the same flow, the detailed flow of the first to fourth selection processes will be described here by taking the first selection process S42 as an example.

First, in step S51, the control unit 9 reads all the interference fringes acquired in the vicinity of the first rotation position, and determines whether there is a rotation position where the interference fringes are acquired at all reference positions. If the determination is yes, the process proceeds to step S52. In step S52, the control unit 9 adopts the interference fringes at the rotation position and selects them as the first to fourth interference fringes at the first rotation position, and sets the rotation angle of the first rotation position in the integration step S30. The first selection step S42 is completed after correcting the rotation angle at the rotation position where the interference fringes have been acquired.
If the determination in step S51 is no, the process proceeds to step S53.

  In step S53, the control unit 9 compares the interference fringes acquired in the vicinity of the first rotation position, and determines whether there is a rotation position where the interference fringes are acquired at two or three reference positions. If the determination is yes, the process proceeds to step S54. In step S54, the control unit 9 adopts the interference fringes at the rotation position and selects the interference fringes at the corresponding reference position from the first to fourth interference fringes at the first rotation position. Then, at the reference position where no interference fringe is acquired at the rotational position, two or more actually obtained interference fringes are used to generate an interference fringe (interpolated surface image) at the rotational position by interpolation processing. One of the first to fourth interference fringes is selected as an insufficient interference fringe.

As a method of the interpolation process, various known methods can be appropriately selected and used, and the rotation angle of the interference fringe to be used may or may not sandwich the rotation angle of the rotation position. In addition, since the accuracy of interference fringes generated by interpolation processing increases as the number of interference fringes used increases, in this embodiment, all three interference fringes are interpolated unless there are interference fringes that cannot be used due to noise or the like. It is preferable to be used for.
After all the first to fourth interference fringes have been acquired, the control unit 9 corrects the rotation angle of the first rotation position in the integration step S30 to the rotation angle of the rotation position, and the first selection step S42 ends.
If the determination in step S51 is no, the process proceeds to step S55.

  In step S55, the control unit 9 generates an interference pattern (interpolated surface image) at the first rotation position based on the acquired interference pattern at each reference position by interpolation processing. The flow of the interpolation process is the same as that in step S54. And the interference fringe in each reference position produced | generated by the interpolation process is selected as a 1st thru | or 4th interference fringe, and 1st selection process S42 is complete | finished. Since interference fringes corresponding to the first rotation position are generated in step S55, the rotation angle of the first rotation position in the integration step S30 is not corrected as in steps S52 and S54.

Through the first selection step S42 described above, the first to fourth interference fringes at the first rotational position are acquired and sent from the control unit 9 to the calculation unit 8.
Thereafter, the second selection step S43 to the fourth selection step S45 are executed by the control unit 9 in the same flow, and the first to fourth interference fringes at the second to fourth rotation positions are acquired and sent to the calculation unit 9. This completes the interference fringe acquisition step S40 of the present embodiment. In other words, in the present embodiment, the first to fourth steps are not performed in order but are performed in parallel, and all are completed simultaneously when the fourth selection step S45 is completed.
Thereafter, similarly to the first embodiment, the phase analysis step S20 and the integration step S30 are performed, and the shape measurement is completed.

  In the shape measuring method of the present embodiment, the interference fringes corresponding to the respective rotational positions are generated by interpolation processing in the selection steps S42 to S45 in the interference fringe acquisition step S40, and the first to fourth interference fringes are generated. Therefore, as in the first embodiment, it is possible to suitably prevent the occurrence of a situation in which shape measurement becomes impossible due to loss of interference fringe data. Furthermore, since the rotation position of the generated interference fringes is completely coincident with the corresponding first to fourth rotation positions, the error can be reduced and surface shape measurement with higher accuracy can be performed.

Moreover, since each selection process S42 thru | or S45 is equipped with step S51 thru | or S54, when the interference fringe acquired at the common timing exists, the said interference fringe is utilized as a part of 1st thru | or 4th interference fringe. However, an insufficient interference fringe is generated by interpolation processing. Interference fringes generated by the interpolation process include a small amount of error, but minimizing the use of the interference fringes generated by the interpolation process can further improve the accuracy of surface shape measurement. it can.
In the present embodiment, the example in which the interference fringe acquisition step S40 includes steps S51 to S54 for minimizing the interpolation processing has been described. However, the first to fourth steps are not necessarily provided without including the steps S51 to S54. You may make it produce | generate the interference fringe of a rotation position by an interpolation process. In this case, when the interference fringes at the first to fourth rotation positions have already been acquired, the interpolation process may be canceled.

The embodiments of the present invention have been described above. However, the technical scope of the present invention is not limited to the above-described embodiments, and combinations of components in the embodiments may be changed without departing from the spirit of the present invention. Various changes can be added to or deleted from each component.
For example, in each of the above-described embodiments, after the acquisition of the interference fringes at the first position P1 is completed, the optical element S is in a state where the rotation angle is 0 degree even after the reference plane 3 is moved to the second position P2. Although the example in which the optical element S performs idling has been described so far, the present invention is not limited to this. For example, the rotation angle of the optical element S at the time when the reference plane 3 is completely moved to the second position P2 without rotating the optical element S is set to 0 degree, and the interference fringes at the second position P2 from the position of the rotation angle. Acquisition may be started. In this case, in the phase analysis step, the calculation unit 8 may be set so as to perform processing based on the rotational angle difference between the first interference fringe acquisition and the second interference fringe acquisition.

  In the above embodiment, an example in which interference fringes are acquired while rotating the optical element S at all the reference positions P1 to P4 has been described. However, the present invention is not limited to this, and some references are made. Only at the position (for example, P1), the interference fringes are acquired while rotating the optical element S, and at the remaining reference positions, the optical element S is rotated by a predetermined rotation angle and kept stationary as in the prior art. Interference fringes may be acquired. Even in this case, the time required for obtaining interference fringes can be considerably reduced.

Furthermore, there may be at least three reference positions from which interference fringes are acquired, and there may be five or more reference positions. In this case, the phase analysis process may be performed using a known phase analysis method that differs depending on the number of steps.
In addition, the number of rotation positions from which interference fringes are acquired is not limited to the four positions described above, and may be set as appropriate. The interval between the rotation positions is also determined so that the acquired interference fringes are at least one other interference fringe. As long as it has an overlap area and can be integrated by the integration process, it does not necessarily have to be equidistant (angle amount).

  Furthermore, the surface shape measuring method of the present invention is not limited to an object having an axially symmetric shape such as the optical element S described above, but can be applied to an object that is not axially symmetric and has a free-form surface. Can do. In this case, a plurality of interference fringe acquisition positions indicating the relative movement amount between the test object and the shape measurement device are set on the scanning locus of the shape measurement device with respect to the test object, and the vicinity of each of the interference fringe acquisition positions is set. Thus, a plurality of interference fringes may be obtained intermittently. The flow after obtaining the interference fringes is substantially the same as in the above-described embodiments.

  In addition, in the above-described embodiment, an example in which a Twiman Green type interferometer is used for the shape measuring apparatus has been described. However, the present invention performs a fringe scan by advancing or retracting either the reference surface or the test object. Other types of interferometers such as a Fizeau type can be used as long as they do.

DESCRIPTION OF SYMBOLS 1 Shape measuring apparatus 2 Light source 3 Reference plane (reference surface)
6 CCD element (imaging means)
8 arithmetic unit 9 control unit L1 object light L2 reference light P1 first position P2 second position P3 third position S optical element (test object)
S20 Phase analysis process

Claims (3)

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 method for measuring the surface shape of the test object using a shape measuring device for analyzing the obtained interference fringes,
A first step of fixing the reference surface at a first position, irradiating the object with the object light, and acquiring first interference fringes at a plurality of positions of the object;
The reference plane is fixed at a second position on the optical axis of the reference light different from the first position, the object light is irradiated onto the test object, and second interference fringes at the plurality of positions are obtained. A second step of
The reference surface is fixed to a third position on the optical axis of the reference light different from the first position and the second position, the object light is irradiated to the object to be examined, and the plurality of positions at the plurality of positions are irradiated. A third step of obtaining three interference fringes;
A phase analysis step of performing phase analysis of the interference fringes at the plurality of positions using the first interference fringes, the second interference fringes, and the third interference fringes;
With
At least one of the first interference fringe, the second interference fringe, and the third interference fringe intermittently near the plurality of positions while moving the object relative to the shape measuring device. A shape measuring method, which is acquired based on a plurality of acquired interference fringes. At least one of the first interference fringe, the second interference fringe, and the third interference fringe intermittently near the plurality of positions while moving the object relative to the shape measuring device . The shape measuring method according to claim 1, wherein the shape measuring method is acquired by an interpolation process using a plurality of acquired interference fringes. 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,
Imaging means for acquiring a surface image of the test object including the interference fringes;
A control unit that controls the timing at which the imaging unit acquires the surface image;
With
The controller is intermittently connected to the imaging unit in the vicinity of a timing at which the test object and the shape measuring device have a predetermined positional relationship with respect to the test object that moves relative to the shape measuring device. To obtain the surface image multiple times ,
The image processing apparatus further includes a calculation unit that generates an interpolated surface image by interpolation processing using a plurality of the surface images acquired in the vicinity of a timing at which the test object and the shape measuring device have a predetermined positional relationship. A shape measuring device.

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