JP2008089356A - Aspheric surface measuring element, lightwave interference measuring device and method using the aspheric surface measuring element, aspheric surface shape correction method, and system error correction method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an aspheric surface measuring element capable of performing correction processing after the production as well as obtaining a stable measurement result having little adverse effect of unnecessary light or fluctuation of air on an optical path, and superior in working efficiency of alignment adjustment or the like; an lightwave interference measuring device and method using the aspheric surface measuring element; an aspheric surface correction processing method; and a system error correction method. <P>SOLUTION: An aspheric surface measuring element 6A comprising a single lens member is disposed between an optical measuring system and a measured aspheric surface 71A of a measured object 7A. The reference spherical surface 61A transmits a portion of measuring light entering almost vertically to the spherical surface and makes a reference light by reflecting the residue of the measuring light, while an aspheric surface 62A on the other side is shaped so that each ray of the measuring light passing from the reference spherical surface 61A to the measured aspheric surface 71A enters almost vertically to the measured aspheric surface 71A and the optical path length of each ray becomes almost constant. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an aspherical measurement element used for measuring an aspherical shape such as an aspherical lens or a mold for molding an aspherical lens, a light wave interference measuring apparatus and method using the aspherical measuring element, The present invention relates to an aspherical shape correction method using a measurement result obtained using a spherical measuring element, and a system error correction method of a lightwave interference measuring apparatus.

  Conventionally, an aspherical measuring element having a reference aspherical surface formed in a shape similar to the design shape of the aspherical surface to be measured is disposed close to the reference aspherical surface and the aspherical surface to be measured so as to face each other. There is a method for measuring the shape of a measured aspheric surface based on interference fringes obtained by optical interference between reflected light of a light beam irradiated on the measured aspheric surface via a measuring element and reflected light from a reference aspheric surface. It is known (see Patent Document 1 below).

  The aspherical measuring element used here is constituted by a lens member, but a zone plate is also used as the aspherical measuring element. For example, in Patent Document 2 below, a transmission type diffraction grating composed of a concentric ring pattern is provided in a region corresponding to measurement of an aspheric surface to be measured, and a reflection type for alignment is provided in a region not corresponding to measurement. A measuring method using an aspherical measuring element having a diffraction grating is disclosed. In this measurement method, a spherical wave output from the measurement optical system is irradiated onto the measured aspheric surface via the aspherical measurement element, and the reflected light from the measured aspheric surface and the measurement optical system are arranged. The shape of the aspheric surface to be measured is measured on the basis of interference fringes obtained by optical interference with reference light from the reference standard surface.

JP-A-6-241743 JP-A-8-21712

  However, in the method described in Patent Document 1, it is necessary to dispose the reference aspheric surface of the aspherical measurement element and the measured aspherical surface very close to each other. Great care must be taken to avoid contact of the aspheric surfaces. When measuring other aspheric surfaces to be measured, a predetermined work space must be secured between the aspheric surface to be measured and the aspheric measuring element, and the aspheric surface to be measured must be placed and aligned again. There is also a problem that workability is poor because it must be done.

  On the other hand, in the method described in Patent Document 2, it is easy to secure a necessary work space between the aspherical surface measuring element and the measured aspherical surface, but the optical distance between the measured aspherical surface and the reference reference surface is small. Since it becomes long, there is a possibility that a measurement error may occur due to fluctuation of air on the optical path. In addition, in an aspherical measuring element constituted by this type of zone plate, unnecessary diffracted light may cause measurement errors, and it is difficult to ensure the reliability of measurement accuracy. Furthermore, there is also a problem that it is difficult to perform correction processing according to the measurement system actually used after being manufactured.

  The present invention has been made in view of such circumstances, and is capable of obtaining a stable measurement result that is hardly affected by air fluctuations and unnecessary light on the optical path, and is excellent in workability such as alignment adjustment, An aspherical measuring element capable of performing correction processing after manufacture, a light wave interference measuring apparatus and method using such an aspherical measuring element, an aspherical correction processing method, and a system error correction method The purpose is to provide.

  An aspherical measuring element according to the present invention is disposed between a measuring optical system that outputs measuring light composed of spherical waves and a measured aspherical surface, and has the following features. .

  That is, the lens surface is configured as a single lens member, and the lens surface facing the measurement optical system transmits part of the measurement light incident substantially perpendicular to the lens surface, and the measurement light. A reference reference spherical surface (reference reference surface formed by a spherical surface) is reflected to reflect the remainder of the lens, and the lens surface facing the measured aspheric surface is separated from the reference standard spherical surface by the measured non-measured surface. Each light beam of the measurement light reaching the spherical surface is incident on the aspheric surface to be measured substantially perpendicularly, and the optical path length of each light beam is formed to be substantially constant.

  In the aspherical surface measuring element according to the present invention, it is preferable to provide a plane reflecting portion for adjusting the tilt posture with respect to the measuring optical system.

  The light wave interference measuring apparatus according to the present invention includes a light source unit, a measurement optical system that converts a light beam emitted from the light source unit into a spherical wave and outputs the spherical wave, and a space between the measurement optical system and the measured aspheric surface. The interference fringe obtained by optical interference between the aspherical measurement element according to the present invention and the reference light from the reference standard spherical surface of the aspherical measurement element and the return light from the measured aspherical surface. And imaging means for imaging.

  In the light wave interference measuring apparatus according to the present invention, the measurement optical system includes a reference lens unit at a position facing the aspherical surface measuring element, and the reference lens unit includes one optical axis adjusting spherical surface. And a lens group that allows the light beam from the light source unit to enter the optical axis adjusting spherical surface substantially perpendicularly.

  Further, the light source unit is a low coherence light source unit that has a short coherence distance of the emitted light beam, and the measurement optical system branches the light beam emitted from the low coherence light source unit into two light beams, A detour unit that adjusts the difference between the optical path lengths of the two light beams after the one light beam is detoured with respect to the other light beam and then the two light beams are recombined and recombined It may be made up of.

  Further, the detour unit substantially matches the difference between the optical path lengths of the two light beams from the branching to the recombining with the round-trip optical path length from the reference standard spherical surface to the measured aspherical surface. It is preferable that the switch is configured to be switchable to a state that substantially matches the reciprocal optical path length from the reference spherical surface to the reference standard spherical surface.

  Further, the detour unit may be configured to perform fringe scan measurement by minutely changing the difference between the optical path lengths of the two light beams.

  Alternatively, as the light source unit, a wavelength scanning light source unit capable of scanning the wavelength of the emitted light beam is used, and the fringe scan measurement is performed by scanning the wavelength of the light beam from the wavelength scanning light source unit. It may be.

  The reference standard spherical surface is provided with a light amount ratio adjustment film having a multilayer structure in which at least one light reflection / absorption layer and at least one dielectric antireflection layer are laminated, and the light amount The ratio adjusting film has a function of reflecting a part of incident light from the measurement optical system side and absorbing the remaining part and then emitting the remaining part toward the aspheric surface to be measured. The return light incident from the aspherical surface to be measured may have a function of absorbing a part of the return light and suppressing the reflection and emitting the remainder.

  In the light wave interference measuring method according to the present invention, the aspherical surface measuring element according to the present invention is disposed between the measuring optical system that converts the light beam emitted from the light source unit into a spherical wave and outputs it, and the measured aspherical surface. The phase information of the measured aspheric surface is obtained by analyzing interference fringes obtained by optical interference between the reference light from the reference standard sphere of the aspherical measurement element and the return light from the measured aspheric surface. It is characterized by seeking.

  In the light wave interference measuring method according to the present invention, when the interference fringes are analyzed, a coordinate conversion process for correcting distortion can be performed.

  Further, the aspheric surface to be measured may be divided into a plurality of measurement regions, the measurement is performed for each of the divided measurement regions, and the measurement results for the measurement regions may be connected.

  The aspherical shape correction method according to the present invention includes an aspherical surface measuring element according to the present invention between a measuring optical system that converts a light beam emitted from a light source unit into a spherical wave and outputs the spherical wave. And analyzing interference fringes obtained by optical interference between the reference light from the reference standard sphere of the aspherical measurement element and the return light from the measured aspherical surface, and based on the analysis result, measure the aspherical surface. The aspherical shape of the working element is corrected.

  In another aspherical shape correction method according to the present invention, an aspherical measurement according to the present invention is provided between a measuring optical system that converts a luminous flux emitted from a light source unit into a spherical wave and outputs the spherical wave, and a measured aspherical surface. And an interference fringe obtained by optical interference between the reference light from the reference standard spherical surface of the aspherical surface measuring element and the return light from the measured aspherical surface, and analyzing the interference target based on the analysis result. The shape of the measurement aspheric surface is corrected and processed.

  In the system error correction method according to the present invention, the aspherical surface measuring element according to the present invention is disposed between the measuring optical system that converts the light beam emitted from the light source unit into a spherical wave and outputs the spherical wave, and the measured aspherical surface. Then, an interference fringe obtained by optical interference between the reference light from the reference standard sphere of the aspherical surface measuring element and the return light from the measured aspherical surface is analyzed, and the system of the lightwave interference measuring device is based on the analysis result It is characterized by correcting an error.

  The above "single lens member" means a lens member having a structure that can be handled as a single member, a so-called cemented lens formed by bonding a plurality of lenses, or a GRIN in which the refractive index distribution changes. It is a concept including a lens such as a lens.

The aspherical surface measuring element according to the present invention has the following effects due to the above configuration.
In other words, since the aspherical measurement element itself has a reference standard surface (reference standard spherical surface) in the light wave interference measurement, it is assumed that the reference standard surface is set at a position apart from the element. Compared to the influence of air fluctuations on the optical path, the measurement results are highly reliable. In addition, since it is configured as a single lens member, there is no problem that unnecessary diffracted light is generated, as in the prior art using a zone plate. Stable measurement results can be obtained. Furthermore, it is also possible to perform post-manufacture correction processing, which is difficult with a zone plate.

  In addition, the lens surface facing the measurement optical system transmits a part of the measurement light incident substantially perpendicular to the lens surface, and reflects the remainder of the measurement light to serve as reference light. Since it is a reference spherical surface, it can be easily incorporated into an interferometer device configured to output a spherical wave (for example, an interferometer device for measuring a spherical shape), and by incorporating it, an aspherical surface is obtained. Can be measured. Furthermore, alignment adjustment of the element with respect to the measurement optical system is performed based on interference fringes obtained by optical interference between the light beam from the reference spherical surface arranged in the measurement optical system on the interferometer device side and the light beam from the reference standard spherical surface on the element side. Can also be easily performed. In particular, according to the apparatus provided with the plane reflection unit for adjusting the tilt posture with respect to the measurement optical system, the tilt adjustment of the optical axis can be easily performed, so that the alignment adjustment can be performed more quickly.

  In the aspherical measuring element of the present invention, the aspherical shape of the lens surface facing the measured aspherical surface is such that each light beam of the measuring light from the reference standard spherical surface to the measured aspherical surface is the measured aspherical surface. Are formed so that the optical path lengths of the respective light beams are substantially constant with each other, and an aspheric shape is formed so that a predetermined work space can be set between the measured aspheric surfaces. It is possible to determine this, and it is not necessary to have a shape similar to the measured aspherical surface and to place it close to the measured aspherical surface as in the prior art. Therefore, it is easy to handle and the workability such as alignment is remarkably improved as compared with the prior art.

  On the other hand, according to the light wave interference measuring apparatus and method according to the present invention, since the aspherical measuring element of the present invention as described above is used, alignment adjustment work at the time of installation of the test aspherical surface is easy, In addition, the measurement of the test aspheric surface can be performed stably with high accuracy.

  Further, according to the aspherical shape correction method of the present invention, correction processing is performed based on interference fringe information obtained using the aspherical measurement element of the present invention. It becomes possible to correct and process the shape of the aspheric surface to be detected with high accuracy.

  Furthermore, according to the system error correction method of the present invention, the system error correction is performed based on the interference fringe information obtained by using the aspherical surface measuring element of the present invention, so that the system error of the optical interference measuring apparatus is highly accurate. It becomes possible to correct to.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a cross-sectional view showing the shape and action of an aspherical surface measuring element according to an embodiment of the present invention, and FIG. 2 is a diagram schematically showing the configuration of a lightwave interference measuring apparatus according to an embodiment of the present invention. It is.

  The aspherical measuring element 6A shown in FIG. 1 is disposed between a measuring optical system (not shown) that outputs measuring light composed of spherical waves and a measured aspherical surface 71A of the measured body 7A. It is configured as a single lens member. The lens surface facing the measurement optical system (the lens surface on the left side in the figure) transmits part of the measurement light incident substantially perpendicular to the lens surface and reflects the remainder of the measurement light. A reference standard spherical surface 61A serving as a reference light is provided, and the lens surface (the lens surface on the right side in the drawing) facing the measured aspheric surface 71A is measured from the reference standard spherical surface 61A to the measured aspheric surface 71A (strictly, Is an ideal surface formed as designed) and each light ray of the measurement light (ray locus is shown) is substantially perpendicularly incident on the aspheric surface 71A to be measured, and the optical path lengths of the respective light rays are substantially equal to each other. The aspherical surface 62A is shaped so as to be constant. Further, the aspherical surface measuring element 6A includes a plane reflecting portion 63A for adjusting the tilt posture with respect to the measuring optical system (a surface perpendicular to the optical axis indicated by a one-dot chain line in the figure and viewed from the right side in the figure as an annular shape ). The point P in the figure is the center of curvature of the reference standard spherical surface 61A.

  On the other hand, the light wave interference measuring apparatus shown in FIG. 2 measures the shape of the measured aspheric surface 71 of the measured object 7 using the aspherical surface measuring element 6 and adjusts the positioning with the interferometer body 1. Unit 3 and image analysis processing unit 5. The aspherical measuring element 6 shown in FIG. 2 is different in shape from that shown in FIG. 1, but has a basic configuration (reference reference surface 61, aspherical surface 62, and planar reflecting portion 63). ) And the operation are the same as those of the aspherical surface measuring element 6A shown in FIG. The measured object 7 shown in FIG. 2 is different from the measured object 7A shown in FIG. 1. In addition to the measured aspherical surface 71, a plane reflecting portion 72 for adjusting the tilt posture with respect to the measuring optical system is provided. I have. The object to be measured 7 is assumed to be a mold for molding an aspheric lens, but the object to be measured is not limited to this, and the aspheric lens itself is the object to be measured. Is also possible.

  The interferometer body 1 includes a low coherence light source 11L (mainly used for measurement) composed of a light emitting diode (LED), a super luminescent diode (SLD), a halogen lamp, etc., and helium. A high coherence light source unit 11H (mainly used for adjusting the optical axis) constituted by a neon laser, a semiconductor laser (LD), or the like is arranged to be selectively switchable. In addition, the interferometer main body 1 branches the low coherent light beam that has been emitted from the low coherent light source unit 11L and then made parallel light by the collimator lens 12L for the low coherent light beam into two light beams, A bypass unit 10 is provided that adjusts the difference in optical path length of the two light beams after the one light beam is detoured with respect to the other light beam and then the two light beams are recombined. Do it.

  In the present embodiment, the detour unit 10 transmits the light beam emitted from the low coherence light source unit 11L via the collimator lens 12L and the first light beam reflected leftward in the drawing and the upper side in the drawing. A half mirror 13 that branches into a second light beam, a first reflection mirror 14 that retroreflects the first light beam, and an optical path length compensation compensator arranged on the optical path of the second light beam. 15, a second reflecting mirror 16 that retroreflects the second light flux that has passed through the compensation plate 15, and a position adjusting means 20 that holds the first reflecting mirror 14. The position adjusting means 20 is constituted by a pulse stage or the like, and by changing the distance from the first reflecting mirror 14 to the half mirror 13, optical interference measurement or light using the low coherent light beam can be performed. Until the interference fringe information necessary for the axis adjustment is obtained, it is branched by the half mirror 13, reflected by the first and second reflecting mirrors 14 and 16, respectively, and recombined in the half mirror 13 again. The difference between the optical path lengths of the first and second light beams is adjustable. The position adjusting means 20 is configured to be able to finely move the first reflecting mirror 14 in the optical axis direction when performing fringe scan measurement.

  The interferometer body 1 includes a third reflection mirror 18 and a light shielding plate 19 that are detachably arranged on the optical path of the bypass unit 10. The third reflection mirror 18 and the light shielding plate 19 are disposed outside the optical path when the low coherence light source unit 11L is used, and are disposed on the optical path when the high coherence light source unit 11H is used. It has come to be. The third reflecting mirror 18 receives the high coherent light beam output from the high coherent light source unit 11H to the left in the drawing through the collimator lens 12H for high coherent light beam and the isolator 17 for preventing return light. The light is reflected upward in the figure and guided onto the same optical path as the low coherent light beam. The light shielding plate 19 has the high coherent light beam transmitted through the half mirror 13 and the compensation plate 15 as the second coherent light beam. This prevents the light from entering the reflection mirror 16.

  Further, the interferometer main body 1 is provided with a beam diameter enlarging lens 21, a beam splitter 22, a collimator lens 23, a reference plate 24, an imaging lens 25, and an imaging means 26 having a light detection surface. The reference plate 24 is a parallel plate provided with a reference plane 24a smoothed with high accuracy and a back surface 24b arranged in parallel with the reference plane 24a, and an antireflection film is attached to the back surface 24b. It is installed. Further, the reference plate 24 is held by a biaxial tilt adjusting means (not shown), and is configured such that tilt adjustment with respect to the optical axis of the collimator lens 23 is performed in an alignment adjusting step described later. Further, the reference plate 24 is configured to be able to exit out of the optical path in an alignment adjustment stage described later.

  On the other hand, the positioning adjusting unit 3 includes a reference lens unit 30 that converts the parallel light beam output from the interferometer body unit 1 upward in the drawing into a spherical wave, and an optical path of the spherical wave emitted from the reference lens unit 30. A shutter 34 configured to be openable and closable, a first mounting table 35 on which the aspherical measuring element 6 is mounted and held, and a second mounting table 36 on which the measured object 7 is mounted and held. It is equipped with.

  The reference lens unit 30 constitutes a measurement optical system together with each optical member arranged in the interferometer body unit 1, and an optical axis adjusting spherical surface 32 a is provided on the side facing the aspherical surface measuring element 6. An objective lens 32 and a lens group 31 (shown as one lens in the drawing) that allows the parallel light beam from the interferometer main body 1 to enter the optical axis adjusting spherical surface 32a substantially perpendicularly. 33, and is configured to be inserted into and removed from the optical path between the interferometer main body 1 and the aspherical surface measuring element 6. Further, the reference lens unit 30 is held via a biaxial tilt adjusting unit and a triaxial position adjusting unit (both not shown), and the optical axis with respect to the interferometer body unit 1 in the alignment adjustment stage described later. Tilt adjustment and position adjustment with respect to the aspherical surface measuring element 6 are performed.

  The first mounting table 35 is configured as shown in FIG. 3 (plan view of the first mounting table 35), for example. As shown in FIG. 2, the first mounting table 35 includes the aspherical surface measuring element 6 so that the reference standard spherical surface 61 of the aspherical surface measuring element 6 faces the optical axis adjusting spherical surface 32a of the standard lens unit 30. 6 so that the reference reference spherical surface 61 can be faced in a state where the aspherical measurement element 6 is held, and a support part 35a that supports the plane reflecting part 63 of the aspherical measurement element 6 at three points. The center window portion 35b is opened, and three peripheral window portions 35c are opened so that the planar reflection portion 63 can face the same in the holding state (see FIG. 3). The first mounting table 35 is held by a biaxial inclination adjusting means (not shown) so that the inclination posture of the held aspherical measuring element 6 can be adjusted in the alignment adjustment stage described later. It is configured.

  As shown in FIG. 2, the second mounting table 36 holds the measured object 7 so that the measured aspheric surface 71 of the measured object 7 faces the aspherical surface 62 of the element 6 for measuring the aspheric surface. In the state where the measured object 7 is held, the measured aspherical surface 71 and the planar reflecting portion 72 of the measured object 7 can be viewed from below in the figure. Further, the second mounting table 36 is held via a triaxial position adjusting means (not shown), and is configured so that the position of the held measured aspheric surface 71 can be adjusted in the alignment adjustment stage described later. Has been.

  The first and second mounting tables 35 and 36 may be configured to suck and hold the aspherical surface measuring element 6 and the measured object 7 respectively.

  The image analysis processing unit 5 includes a computer 51 that performs image processing on the image captured by the imaging unit 26, various arithmetic processes, and drive control of various adjustment units, and a monitor device 52 that displays an interference fringe image and the like. And an input device 53 for making various inputs to the computer 27.

  Next, alignment adjustment performed prior to measurement in the optical interference measuring apparatus shown in FIG. 2 will be described. FIG. 4 is a diagram showing the alignment adjustment procedure step by step in the order of (a) to (f). In the following alignment adjustment, the high coherence light beam emitted from the high coherence light source unit 11H is used (in FIG. 2, the reflection mirror 18 and the light shielding plate 19 are arranged on the optical path of the detour unit 10). )

  (1) First, as shown in FIG. 4A, the optical axes of the collimator lens 23 and the reference plate 24 are adjusted using a corner cube 81. This optical axis adjustment is performed by changing the inclination of the reference plate 24 with respect to the collimator lens 23 using biaxial inclination adjusting means (not shown) that holds the reference plate 24.

  (2) Next, as shown in FIG. 4 (b), the measurement object 7 for measurement (measured aspheric surface 71 is formed with high accuracy on the second mounting table 36, and the shape measurement is performed. And the optical axis of the measured aspherical surface 71 of the measured object 7 and the interferometer main body 1 are adjusted. This optical axis adjustment is obtained by optical interference between the return light reflected from the reference plane 24a of the reference plate 24 and the return light reflected from the plane reflecting portion 72 of the measured object 7 after passing through the reference plate 24. This is performed by changing the tilt of the interferometer body 1 with respect to the measured object 7 using the biaxial tilt adjusting means 82 installed in the interferometer body 1 so that the interference fringes are in a null fringe state.

  (3) Next, as shown in FIG. 4C, the aspherical surface measuring element 6 is placed on the first mounting table 35, and the optical axis between the aspherical surface measuring element 6 and the interferometer body 1. Make adjustments. This optical axis adjustment is based on optical interference between the return light reflected from the reference plane 24 a of the reference plate 24 and the return light reflected from the plane reflection portion 63 of the aspherical surface measuring element 6 after passing through the reference plate 24. The biaxial inclination adjusting means (not shown) that holds the first mounting table 35 is used to adjust the inclination of the aspherical surface measuring element 6 with respect to the interferometer body 1 so that the obtained interference fringes are in a null fringe state. This is done by changing.

  (4) Next, as shown in FIG. 4 (d), a reference lens unit 30 is arranged on the optical path between the first mounting table 35 and the interferometer body 1, and interferes with the reference lens unit 30. Optical axis adjustment with the meter body 1 is performed. In this optical axis adjustment, in the state where the optical path between the reference lens unit 30 and the aspherical surface measuring element 6 is closed by the shutter 34, the return light reflected from the reference plane 24a of the reference plate 24 and the reference plate 24 are adjusted. The reference lens unit so that the interference fringes obtained by light interference with the return light that is transmitted and incident on the reference lens unit 30 and reflected from the optical axis adjusting spherical surface 32a of the reference lens unit 30 are in a null-striped state. This is performed by changing the inclination of the reference lens unit 30 with respect to the interferometer body 1 using a biaxial inclination adjusting means (not shown) that holds the reference numeral 30.

  (5) Next, as shown in FIG. 4E, the optical axes of the reference lens unit 30 and the aspherical surface measuring element 6 are adjusted. In this optical axis adjustment, the shutter 34 shown in FIG. 4D is opened (not shown in FIGS. 4E and 4F), and the reference plate 24 is moved out of the optical path (FIG. 4). In (e) and (f), this state is indicated by a two-dot chain line) and the return light incident on the reference lens unit 30 and reflected from the optical axis adjusting spherical surface 32a of the reference lens unit 30 and the reference lens unit A triaxial position for holding the reference lens unit 30 so that the interference fringes obtained by optical interference with the return light transmitted through 30 and reflected from the reference standard spherical surface 61 of the aspherical surface measuring element 6 are in a null fringe state. This is done by changing the position of the reference lens unit 30 with respect to the aspherical surface measuring element 6 using an adjusting means (not shown). By this optical axis adjustment, each light beam of the spherical wave transmitted through the reference lens unit 30 enters the reference standard spherical surface 61 of the aspherical surface measuring element 6 substantially perpendicularly.

  (6) Next, as shown in FIG. 4 (f), optical axis adjustment of the aspherical surface measuring element 6 and the measured aspherical surface 71 of the measured object 7 is performed. This optical axis adjustment is performed on the aspherical surface measuring element 6 via the reference lens unit 30 in a state where the shutter 34 shown in FIG. 4D is opened and the reference plate 24 is retracted out of the optical path. Further, the reference light reflected from the reference standard spherical surface 61 of the aspherical surface measuring element 6 is incident on the measured aspherical surface 71 of the measured body 7 via the standard lens unit 30 and the aspherical surface measuring element 6. Triaxial position adjusting means (not shown) that holds the second mounting table 36 is used so that interference fringes obtained by optical interference with the return light reflected from the measured aspheric surface 71 are in a null fringe state. Thus, the measurement is performed by changing the position of the aspheric surface 71 to be measured with respect to the reference lens unit 30. By this optical axis adjustment, each light beam of the aspherical wave transmitted through the aspherical surface measuring element 6 enters the measured aspherical surface 71 substantially perpendicularly.

  In the above procedure, the measured object 7 is used for the master, but it is also possible to perform alignment adjustment using the measured object 7 of the sample to be measured. In addition, the alignment adjustment is performed using the master, and the measurement can be performed by replacing the master and the sample.

  The alignment adjustment is completed by the above procedures (1) to (6), and preparations for measurement by the light wave interference measuring apparatus of this embodiment are completed. Hereinafter, a light wave interference measurement method, an aspherical shape correction method, and a system error correction method using the light wave interference measurement apparatus of the present embodiment will be described.

  These methods are different from each other in how the obtained interference fringe information is used, and the procedure until obtaining the interference fringe information is common. The procedure will be described, and an aspheric shape correction method and a system error correction method will be supplementarily described.

  (A) First, in FIG. 2, the reflection mirror 18 and the light shielding plate 19 are retracted from the optical path of the detour unit 10, and the light source unit to be used is switched from the high coherence light source unit 11H to the low coherence light source unit 11L.

  (B) Next, the optical path length difference is adjusted in the detour unit 10. This adjustment is performed by the half mirror 13 and the first light flux that is emitted from the low coherence light source 11L, branched by the half mirror 13, and then retroreflected from the first reflecting mirror 14 and returned to the half mirror 13. After branching, the difference in optical path length from the second light beam retroreflected from the second reflecting mirror 16 and returning to the half mirror 13 is determined from the reference standard spherical surface 61 of the aspherical surface measuring element 6 to the measured object 7. This is performed by changing the position of the first reflecting mirror 14 using the position adjusting means 20 so as to be in a state that substantially matches the reciprocating optical path length to the measured aspheric surface 71.

  By adjusting the optical path length difference, the low pass rate output from the detour unit 10 and incident on the aspherical surface measuring element 6 through the beam diameter expanding lens 21, the beam splitter 22, the collimator lens 23, and the reference lens unit 30. Of the interference light beam, a part of the light beam reflected from the reference standard spherical surface 61 and a part of the light beam transmitted through the aspherical surface measuring element 6 and reflected from the measured aspherical surface 71 of the measured object 7. The optical path lengths substantially coincide with each other (for example, when the optical path length of the first light beam is longer than the optical path length of the second light beam, reference is made to the first light beam reaching the aspherical surface measuring element 6. Of the luminous flux reflected from the reference spherical surface 61 and the second luminous flux reaching the aspherical surface measuring element 6, the luminous flux transmitted through the aspherical surface measuring element 6 and reflected from the measured aspherical surface 71 of the measured object 7. Between these luminous fluxes) Wavefront carrying interference fringes information by Hikari Jiru interference is formed.

  (C) Next, the wavefront carrying the interference fringe information is captured by the imaging means 26 and an interference fringe image is captured. It is to be noted that, when the interference fringe image is picked up, it is preferable to use a fringe scan measurement method for obtaining a plurality of interference fringe images by finely moving the position of the first reflecting mirror 14 by a predetermined distance using the position adjusting means 20. .

  (D) Next, the interference fringe image picked up by the image pickup means 26 is analyzed by the computer 51 to obtain the shape information of the aspheric surface 71 to be measured, and this numerical data, image data, etc. are displayed on the monitor device 52. In the analysis, a coordinate conversion process for correcting the distortion (distortion) of the correspondence between the coordinate system on the measured aspherical surface 71 and the coordinate system on the light detection surface (imaging device) of the imaging unit 26 is performed. .

  It is possible to obtain shape error information from the design value of the measured aspheric surface 71 based on the analysis result of the interference fringe image and correct the shape of the measured aspheric surface 71 based on the shape error information. (One Embodiment of the shape correction method of the aspherical surface which concerns on this invention).

  Further, the measurement analysis similar to the above is performed using the measurement object 7 for master, and based on the analysis result, the shape error information of the aspheric surface 62 of the aspheric surface measuring element 6 is obtained, and based on this shape error information. It is also possible to correct the shape of the aspherical surface 62 of the aspherical surface measuring element 6 (another embodiment of the aspherical shape correcting method according to the present invention).

  Further, the same measurement analysis as described above is performed using the measurement object 7 for master, and system error information of the optical interference measurement apparatus is obtained based on the analysis result. Based on the system error information, the optical interference measurement apparatus It is also possible to correct the system error (one embodiment of the system error correction method according to the present invention). For example, it is possible to store system error information and correct the measurement result of the sample based on the system error information.

  In the above description, it is assumed that the entire area of the measured aspheric surface can be measured at one time using one aspheric measuring element, but depending on the shape of the measured aspheric surface, Since the light rays returning from the spherical surface to the aspherical surface measuring element intersect, there may be a case where such a measurement cannot be performed.

Below, the measurement method at the time of assuming such a case is demonstrated. FIG. 5 shows a mode in which two aspherical measuring elements are used and measurement is performed in two steps.
In the embodiment shown in FIG. 5, the measured aspheric surface 71B (combined with a concave surface and a convex surface) of the measured object 7B is shown in FIG. 5A as a region (peripheral region) indicated by a solid line, and FIG. ) Are divided into regions (center regions) indicated by solid lines, and each region is measured separately using two aspherical surface measuring elements 6B and 6C.

  That is, in the first measurement, the peripheral region of the measured aspheric surface 71B using the aspherical surface measuring element 6B (having the reference standard spherical surface 61B, the aspherical surface 62B, and the planar reflecting portion 63B) shown in FIG. Measure. This aspherical surface measuring element 6B uses only the region indicated by the solid line in the drawing in the reference standard spherical surface 61B and the aspherical surface 62B, and the shape of the region indicated by the dotted line in the drawing does not matter. In this first measurement, in order to prevent the measurement light from entering the central region of the measured aspheric surface 71B via the aspheric measurement element 6B and the reflected light from becoming stray light, the aspheric surface is used. A mask is set on the left side of the measuring element 6B in the drawing or at a predetermined position between the aspherical measuring element 6B and the measured object 7B.

Next, using the aspherical surface measuring element 6C (having the reference standard spherical surface 61C, the aspherical surface 62C, and the planar reflecting portion 63C) shown in FIG. 5B, the second time relating to the central region of the measured aspherical surface 71B. Measure. In the second measurement, alignment adjustment of the aspherical surface measuring element 6C is performed. In addition, in order to prevent measurement light from entering the peripheral region of the measured aspheric surface 71B via the aspheric measurement element 6C and the reflected light from becoming stray light, FIG. A mask is set at a predetermined position between the left side or the aspherical surface measuring element 6C and the measured object 7B.
Next, the shape information of the entire area of the aspheric surface 71 to be measured is obtained by connecting the data obtained by the first measurement and the second measurement.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to this embodiment, A mode can be variously changed.

  For example, in the above aspect, the alignment adjustment is performed using the high coherent light beam, but a part of the alignment adjustment may be performed using the low coherent light beam. For example, the optical axis adjustment between the reference lens unit 30 and the aspherical surface measuring element 6 described in the alignment adjustment procedure (5) can be performed using a low coherent light beam. However, in this case, it is necessary to adjust the optical path length difference in the detour unit 10. That is, the difference between the optical path lengths of the first and second light beams in the detour unit 10 is determined as the reciprocating optical path from the optical axis adjusting spherical surface 32 a of the reference lens unit 30 to the reference standard spherical surface 61 of the aspherical surface measuring element 6. It is necessary to set in advance a state that substantially matches the length. On the other hand, it is not necessary to move the reference plate 24 out of the optical path, which is necessary when using a high coherence beam.

  In the above aspect, the fringe scan measurement is performed by minutely changing the difference between the optical path lengths of the first and second light beams branched in the detour unit 10. It is also possible to perform a fringe scan measurement by scanning a wavelength of a light beam from the wavelength scanning light source unit by using a wavelength scanning light source unit capable of scanning the wavelength of. A technique using such a wavelength scanning light source unit is described in, for example, Japanese Translation of PCT International Publication No. 2005-512075.

  Further, when the measured aspheric surface 71 is a highly reflective surface and the contrast of interference fringes obtained by the optical interference between the return light from the measured aspheric surface 71 and the reference light from the reference standard spherical surface 61 decreases. It is preferable to improve the contrast by attaching a light amount ratio adjusting film to the reference standard spherical surface 61. This light quantity ratio adjusting film is a film having a multilayer structure in which at least one light reflection / absorption layer and at least one dielectric antireflection layer are laminated, and is used for incident light from the reference lens unit 30 side. On the other hand, it has a function of reflecting a part thereof, absorbing a part of the remainder and then emitting the remainder toward the measured aspheric surface 71, and for returning light incident from the measured aspheric surface 71 side. Has a function of absorbing part of the light and suppressing reflection and emitting the remainder. For example, Japanese Patent Application Laid-Open No. 2006-90829 discloses a technique using such a light amount ratio adjusting film.

  In the above aspect, the measurement is performed using the low coherent light beam, and it is possible to obtain a highly accurate measurement result. However, the measurement is performed using the high coherent light beam. May be performed. In this case, only one light source unit is required and no detour unit is required, so that the apparatus configuration can be simplified and the cost can be reduced.

Sectional drawing which shows the shape and effect | action of the element for aspherical surface which concerns on one Embodiment of this invention 1 is a schematic configuration diagram showing an optical interference measuring apparatus according to an embodiment of the present invention. The top view of the 1st mounting base shown in FIG. The figure which shows the procedure of alignment adjustment in steps of (a)-(f) The figure which shows the aspect which uses two aspherical surface measurement elements and performs measurement twice.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Interferometer main-body part 3 Positioning adjustment part 5 Image analysis process part 6, 6A-6C Aspherical surface measurement element 7, 7A, 7B Measured object 10 Detour part 11L Low coherence light source part 11H High coherence light source part 12L, 12H, 23 Collimator lens 13 Half mirror 14 First reflection mirror 15 Compensation plate 16 Second reflection mirror 17 Isolator 18 Third reflection mirror 19 Shading plate 20 Position adjusting means 21 Beam diameter expanding lens 22 Beam splitter 25 Imaging Lens 24 Reference plate 24a Reference plane 24b Back surface 25 Imaging lens 26 Imaging means 30 Subject positioning unit 31 Lens group 32 Objective lens 32a Optical axis adjusting spherical surface 33 Lens barrel 34 Shutter 35 First mounting table 35a Support unit 35b Central window Part 35c peripheral window part 36 second mounting table 51 computer 52 Monitor device 53 Input device 61, 61A, 61B, 61C Reference reference spherical surface 62, 62A, 62B, 62C Aspherical surface 63, 63A, 63B, 63C Planar reflection portion 71, 71A, 71B Aspheric surface to be measured 72 Planar reflection portion 81 Corner cube 82 Biaxial tilt adjustment means P Center of curvature (of the reference spherical surface)

Claims (16)

An aspherical measuring element disposed between a measuring optical system that outputs measuring light composed of spherical waves and a measured aspherical surface,
It is configured as a single lens member,
The lens surface facing the measurement optical system transmits a part of the measurement light incident substantially perpendicular to the lens surface, and reflects the remainder of the measurement light to serve as reference light. A reference spherical surface,
The lens surface on the side facing the measured aspheric surface has each light beam of the measurement light from the reference standard spherical surface to the measured aspheric surface incident on the measured aspheric surface substantially perpendicularly, and An aspherical surface measuring element having an aspherical shape formed such that optical path lengths are substantially constant.   The aspherical surface measuring element according to claim 1, further comprising a plane reflecting portion for adjusting an inclination posture with respect to the measuring optical system. A light source unit;
A measuring optical system that converts the luminous flux emitted from the light source unit into a spherical wave and outputs the spherical wave;
The aspherical measuring element according to claim 1, which is disposed between the measuring optical system and the measured aspherical surface,
An optical device comprising: imaging means for imaging interference fringes obtained by optical interference between reference light from the reference standard spherical surface of the aspherical measuring element and return light from the measured aspherical surface; Interference measurement device. The measurement optical system has a reference lens portion at a position facing the aspherical measurement element,
The reference lens unit includes one optical axis adjusting spherical surface and a lens group that allows the light beam from the light source unit to enter the optical axis adjusting spherical surface substantially perpendicularly. Item 4. The optical interference measuring apparatus according to Item 3. The light source unit is a low coherence light source unit having a short coherence distance of the emitted light beam,
The measurement optical system splits the light beam emitted from the low coherence light source unit into two light beams, re-synthesizes the two light beams after diverting one light beam with respect to the other light beam, 5. The optical interference measuring apparatus according to claim 3, further comprising a detour unit that adjusts a difference between the optical path lengths of the two light beams from when the light beam is recombined. Equipped with a high coherence light source that has a long coherence distance of the emitted light beam,
The low coherent light beam emitted from the low coherent light source unit and the high coherent light beam emitted from the high coherent light source unit can be alternatively output on the same optical path. 6. The light wave interference measuring apparatus according to claim 5, wherein:   The detour unit has a state in which the difference between the optical path lengths of the two light beams from the branching to the recombination substantially coincides with the round-trip optical path length from the reference standard spherical surface to the measured aspheric surface, 7. The light wave interference measuring apparatus according to claim 5, wherein the optical wave interference measuring apparatus is configured to be switchable between a state where the reciprocal optical path length from the optical axis adjusting spherical surface to the reference standard spherical surface is substantially the same.   8. The fringe scan measurement is performed by minutely changing a difference between the optical path lengths of the two light beams in the detour unit, wherein the detour unit is any one of claims 5 to 7. The light wave interference measuring apparatus described. The light source unit is a wavelength scanning light source unit capable of scanning the wavelength of the emitted light beam,
5. The light wave interference measuring apparatus according to claim 3, wherein fringe scanning measurement is performed by scanning the wavelength of the light beam from the wavelength scanning light source unit. The reference standard spherical surface is provided with a light quantity ratio adjustment film having a multilayer structure in which at least one light reflection / absorption layer and at least one dielectric antireflection layer are laminated,
The light quantity ratio adjusting film has a function of reflecting a part of incident light from the measurement optical system side and absorbing the remaining part and then emitting the remaining part toward the aspheric surface to be measured. And a film structure having a function of absorbing a part of the return light incident from the measured aspheric surface side while suppressing reflection and emitting the remainder. The light wave interference measuring apparatus according to any one of claims 3 to 9. The aspherical measuring element according to claim 1 or 2 is disposed between a measuring optical system that converts a luminous flux emitted from the light source unit into a spherical wave and outputs the spherical wave, and the measured aspherical surface.
The phase information of the aspheric surface to be measured is obtained by analyzing interference fringes obtained by the optical interference between the reference light from the reference standard spherical surface of the aspherical surface measuring element and the return light from the measured aspheric surface. A light wave interference measuring method characterized by the above.   12. The light wave interference measuring method according to claim 11, wherein a coordinate transformation process for correcting distortion is performed when analyzing the interference fringes.   13. The measurement aspheric surface is divided into a plurality of measurement areas, the measurement is performed for each of the divided measurement areas, and the measurement results of the measurement areas are joined together. Lightwave interference measurement method. The aspherical measuring element according to claim 1 or 2 is disposed between a measuring optical system that converts a luminous flux emitted from the light source unit into a spherical wave and outputs the spherical wave, and the measured aspherical surface.
Interference fringes obtained by optical interference between the reference light from the reference standard spherical surface of the aspherical surface measuring element and the return light from the measured aspherical surface are analyzed, and the nonspherical surface of the aspherical surface measuring element is analyzed based on the analysis result. A method for correcting the shape of an aspherical surface, comprising correcting the shape of a spherical surface. The aspherical measuring element according to claim 1 or 2 is disposed between a measuring optical system that converts a luminous flux emitted from the light source unit into a spherical wave and outputs the spherical wave, and the measured aspherical surface.
An interference fringe obtained by optical interference between the reference light from the reference standard sphere of the aspherical surface measuring element and the return light from the measured aspherical surface is analyzed, and the shape of the measured aspherical surface is determined based on the analysis result. A method for correcting the shape of an aspherical surface, wherein correction processing is performed. The aspherical measuring element according to claim 1 or 2 is disposed between a measuring optical system that converts a luminous flux emitted from the light source unit into a spherical wave and outputs the spherical wave, and the measured aspherical surface.
An interference fringe obtained by optical interference between the reference light from the reference standard sphere of the aspherical measuring element and the return light from the measured aspherical surface is analyzed, and the system error of the lightwave interference measuring apparatus is calculated based on the analysis result. A system error correction method characterized by correcting.

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