JP2010085336A - Lightwave interference measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To enable lightwave-interference measurement of the shape of an inspected surface comprising a concave surface and a convex surface. <P>SOLUTION: The position of the inspected surface 80 in the measurement light axis L direction relative to an interference optical system 2 is changed by using a sample stage 6, so that measurement light once converges and then is divergingly applied to a concave surface 81 in the case where the concave surface 81 of the inspected surface 80 is measured while the measurement light is convergingly applied to a convex surface 82 in the case where the convex surface 82 is measured. Further, an interference fringe forming optical system 70 projecting a prescribed interference fringe pattern onto the inspected surface 80 is disposed on an optical path between a light source 20 and a branching optical element 3 in order to prevent unnecessary light from being reflected from a partial area of the inspected surface 80 and entering an imaging system 4 when the measurement light is applied to the inspected surface 80. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a light wave interference measuring apparatus that irradiates a test surface with measurement light and measures the shape of the test surface based on interference fringes obtained by interference between return light from the test surface and reference light. The present invention relates to a light wave interference measuring apparatus suitable for shape measurement when a test surface has a concave surface portion and a convex surface portion.

  Conventionally, there has been known a method for identifying the shape of a test surface based on interference fringes formed by irradiating a spherical surface on a test surface with an aspherical shape and interference between return light from the test surface and reference light. However, it is difficult to obtain interference fringes corresponding to the entire test surface by such a method.

  Therefore, by sequentially moving the interferometer or the test surface in the direction of the measurement optical axis, interference fringes corresponding to each partial region in the radial direction of the test surface are sequentially generated, and each interference fringe is analyzed and analyzed. A technique is known in which the shape of each partial region in the radial direction of the inspection surface is obtained and the shape of the entire inspection surface is specified by connecting them (see Patent Document 1 below).

  On the other hand, the interferometer or the test surface is sequentially moved in a plane perpendicular to the measurement optical axis, and the interference fringes corresponding to the respective partial areas of the test surface are enlarged and imaged so that the fringe analysis can be performed for each movement. A technique is also known in which each interference fringe is analyzed to determine the shape of each partial region of the test surface, and the shape of the entire test surface is specified by connecting them (see Patent Document 2 below).

JP-A-62-126305 USP 6,956,657

  In recent years, the shape of an aspheric lens has become complicated, and in one lens surface, a concave portion (concave surface portion) and a convex shape are formed around the optical axis (center axis) of the lens surface. The thing of a shape which has the part (convex surface part) which has it is used now. It is said that it is difficult to measure the shape of the test surface having such a concave portion and a convex portion by optical interference measurement, and until now, shape measurement has been performed by three-dimensional shape measurement using an optical stylus. It was.

  The reason why the shape measurement by the optical interference measurement is difficult is that, in the concave surface portion and the convex surface portion, the gradient of the surface with respect to the optical axis of the test surface is opposite to each other (when the test surface is directed upward, The concave surface portion has a downward gradient toward the optical axis, whereas the convex surface portion has an upward gradient toward the optical axis). That is, in a general optical interference measurement method, an appropriate interference fringe can be obtained only in the region where the measurement light irradiated on the test surface is retroreflected from the test surface (the return light travels backward in the original optical path). However, the measurement light applied to the surface to be measured is fixed to either a spherical wave that travels while diverging along the measurement optical axis, a spherical wave that travels while converging along the measurement optical axis, or a plane wave In the conventional interferometer, the traveling direction of the return light from the test surface is completely different between the concave surface portion and the convex surface portion, so that it is possible to obtain appropriate interference fringes in both the concave surface portion and the convex surface region. It is not possible.

  Another reason is that the shape of the test surface is complicated, and unnecessary light that hinders the formation of interference fringes is likely to be generated. That is, each return light from a plurality of different areas on the test surface may reach the same position on the imaging surface, and at this time, the return light from a certain area of the plurality of areas is not properly interfered. When it contributes to the formation of stripes, the return light from other regions becomes unnecessary light.

  This invention is made in view of such a situation, and it aims at providing the optical interference measuring apparatus which can measure the shape of the to-be-tested surface which has a concave part and a convex part. .

  In order to achieve the above object, the optical interference measuring apparatus of the present invention is configured as follows.

That is, the optical interference measuring apparatus according to the present invention converts the output light from the light source unit into measurement light, holding means for holding the test surface so that the optical axis of the test surface coincides with the measurement optical axis. An interference optical system that irradiates the test surface and combines the return light from the test surface with reference light to obtain interference light, and branching optics that branches the obtained interference light from the optical path of the interference optical system A light wave interference measuring apparatus comprising: an element; an imaging system that captures an interference fringe formed by the branched interference light; and a measurement analysis system that analyzes the captured interference fringe to obtain the shape of the test surface Because
The test surface has a concave surface portion that is concave toward the interference optical system side around the optical axis, and a convex surface portion that is convex toward the interference optical system side around the optical axis,
The interference optical system outputs a spherical wave or a cylindrical wave that travels while converging along the measurement optical axis as the measurement light,
When measuring the concave surface portion, when measuring the convex surface portion so that the concave portion is irradiated while diverging after the measurement light once converges, the convex surface while converging the measurement light. An irradiation position variable means for changing the relative position of the test surface relative to the interference optical system in the measurement optical axis direction so as to be irradiated to a part;
In order to prevent generation of unnecessary light that is reflected from a partial region of the test surface and is incident on the imaging system when the measurement light is irradiated on the test surface, the light is incident on the partial region. A light amount distribution adjusting means for adjusting a light amount distribution on the test surface of the measurement light so that the light amount of the measurement light is reduced,
The light amount distribution adjusting unit includes an interference fringe forming optical system disposed on an optical path between the light source unit and the branch optical element, and in the interference fringe forming optical system, the light source unit from the light source unit The light quantity distribution is adjusted by an interference fringe pattern obtained by branching output light into two light beams, and combining the two light beams after passing through different paths. .

In the present invention, a plurality of inter-region interference fringes corresponding to each of the concave surface portion or the plurality of partial regions of the convex surface portion are sequentially changed in the imaging system while the relative position is sequentially changed using the irradiation position varying means. Image
In the measurement analysis system, shape information for each of the plurality of partial regions is obtained based on the plurality of region-specific interference fringes, and the plurality of partial regions are merged by connecting the shape information for each of the plurality of partial regions. The shape information of the entire area can be obtained.

  In the present invention, the test surface includes a columnar shape in addition to a rotationally symmetric shape around the optical axis (center axis) of the test surface.

  In addition, the concave surface portion is a region that is inclined downward toward the optical axis of the test surface when the test surface is directed upward, that is, when a normal line is set on the concave surface portion, the normal line is , Means a region that will extend so as to approach the optical axis of the test surface as it moves away from the concave portion along the normal line, and the convex surface portion when the test surface is directed upward, A region that is inclined upward toward the optical axis of the test surface, that is, when a normal line is set on the convex surface part, the test surface starts from the beginning as the normal line moves away from the convex surface part along the normal line. It means a region that extends away from the optical axis.

  The lightwave interference measuring apparatus according to the present invention has the following configuration and effects as described above.

  That is, in the light wave interference measuring apparatus of the present invention, when measuring the concave surface by changing the relative position of the surface to be measured in the measurement optical axis direction using the irradiation position varying means, the measurement light is temporarily transmitted. When the convex surface portion is irradiated while diverging after convergence, and the convex surface portion is measured, the measurement light is irradiated to the convex surface portion while converging.

  As a result, the return light of the measurement light retroreflected by the test surface can be generated in both the concave surface portion and the convex surface region, so that the appropriate interference fringes in both the concave surface portion and the convex surface region. Can be obtained.

  Further, by adjusting the light amount distribution on the test surface of the measurement light so that the light amount of the measurement light incident on a partial region of the test surface is reduced by the light amount distribution adjusting means at the time of irradiation of the measurement light, Since it is possible to prevent the generation of unnecessary light that is reflected from the partial area and incident on the imaging system when the measurement surface is irradiated with measurement light, appropriate interference fringes carrying shape information of the measurement area Can be obtained.

  Therefore, according to the light wave interference measuring apparatus according to the present invention, it is possible to measure the shape of the test surface having the concave portion and the convex portion with high accuracy.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a schematic configuration diagram of a lightwave interference measuring apparatus according to an embodiment of the present invention.

  The light wave interference measuring apparatus 1 of the present embodiment shown in FIG. 1 measures and analyzes the shape of a test surface 80 (the lens surface on the upper side of the test lens 8 in the drawing) of the test lens 8. The interference optical system 2 that irradiates the surface 80 with measurement light and combines the return light from the test surface 80 with the reference light to obtain interference light, and a half that branches the obtained interference light from the optical path of the interference optical system 2 A branching optical element 3 such as a mirror, an image pickup system 4 for picking up an interference fringe formed by the branched interference light, a measurement analysis system 5 for analyzing the picked-up interference fringe to obtain the shape of the test surface 80, and The sample stage 6 on which the test lens 8 is placed and held, and the light amount distribution adjusting means 7 are provided.

  The interference optical system 2 has a Fizeau type optical system arrangement, and includes a light source unit 20 that outputs a highly coherent light beam and a first collimator that converts output light from the light source unit 21 into a parallel light beam. A lens 21, a converging lens 22 that temporarily converges the parallel light flux from the first collimator lens 21, and a pinhole plate 23 having a pinhole 23a disposed at a converging point of the converging light flux from the converging lens 22, A second collimator lens 24 that converts the divergent light beam that has passed through the pinhole 23a into a parallel light beam, and a parallel light beam from the second collimator lens 24 is converted into a spherical wave that travels while converging along the measurement optical axis L. And a spherical reference lens 25.

  The spherical standard lens 25 has a reference standard spherical surface 25a having a spherical shape, and a part of the light beam from the second collimator lens 24 incident on the spherical standard lens 25 is reflected on the reference standard spherical surface 25a. The light beam is retroreflected to become reference light, and another part of the light flux is made to be measurement light composed of spherical waves and output toward the test surface 80. Then, a part of the measurement light reflected from the test surface 80 is combined with the reference light reflected by the reference standard spherical surface 25a, whereby interference light is obtained.

  In the present embodiment, the spherical reference lens 25 is configured to be replaceable with a flat reference plate 26 or a cylindrical reference lens 27. The plane reference plate 26 has a reference reference plane 26a, and a predetermined area (an off-axis stop point section described later) on the test surface 80 or another test surface (a test surface 90 described later) having a columnar shape. 83, 93). The cylindrical reference lens 27 has a reference standard cylindrical surface 27a having a cylindrical surface (cylindrical surface) extending in a direction perpendicular to the paper surface of FIG. 1 and is used when measuring a test surface 90 described later. In FIG. 1, the spherical reference lens 25 and the cylindrical reference lens 27 are shown as being composed of a single lens, but in reality, the spherical reference lens 25 and the cylindrical reference lens 27 may be composed of a plurality of lenses. Further, the spherical reference lens 25, the flat reference plate 26, and the cylindrical reference lens 27 are held on a measurement optical axis L by a fringe scan adapter (not shown), and in the measurement optical axis L direction when performing fringe scan measurement or the like. It is configured so that it can be moved slightly.

  The imaging system 4 includes an imaging lens 40 and an imaging camera 41 having a two-dimensional image sensor 42 made of a CCD, a CMOS, or the like, and is formed on the two-dimensional image sensor 42 by the imaging lens 40. The image data of the interference fringes is obtained.

  The measurement analysis system 5 includes a shape analysis unit 50 including a computer for obtaining shape data of the test surface 80 based on image data of interference fringes acquired by the two-dimensional image sensor 42, and the shape analysis unit 50. The display device 51 includes an analysis result and an image, and an input device 52 including a keyboard and a mouse. In the present embodiment, the shape analyzing unit 50 is configured to control the driving of the sample stage 6 and the light amount distribution adjusting unit 7 (more specifically, a moving mechanism 74 described later).

The sample stage 6 constitutes a holding means and an irradiation position variable means in the present embodiment, and the position of the lens 8 to be adjusted is adjusted so that the optical axis C ₁ of the test surface 80 coincides with the measurement optical axis L. In addition, the irradiation position of the measurement light on the test surface 80 is changed by moving the test lens 8 in the direction of the measurement optical axis L.

  The light amount distribution adjusting means 7 prevents the generation of unnecessary light that is reflected from a partial region of the test surface 80 and incident on the imaging system 4 when the test surface 80 is irradiated with measurement light. The light quantity distribution on the test surface 80 of the measurement light is adjusted so that the light quantity of the measurement light incident on the partial area is reduced. The measurement light between the first collimator lens 21 and the converging lens 22 is adjusted. An interference fringe forming optical system 70 is provided on the optical path of the parallel light flux. This interference fringe forming optical system 70 has a Fabry-Perot type optical system arrangement, and a flat substrate 71 having a semi-transmissive reflective plane 71a and a spherical substrate 72 having a semi-transmissive reflective spherical surface 72a are formed by a semi-transmissive reflective plane. 71a and transflective spherical surface 72a are arranged on the optical path so as to face each other. In the interference fringe forming optical system 70, the first light flux that transmits the output light from the light source unit 20 that has passed through the first collimator lens 21 and the flat substrate 71 is transmitted through the semi-transmissive reflective spherical surface 72 a in the semi-transmissive reflective spherical surface 72 a. And the second light beam reflected by the transflective spherical surface 72a. A part of the second light flux is retroreflected on the transflective flat surface 71a and interferes with the first light flux. Due to this interference, an interference fringe pattern for adjusting the light quantity distribution of the measurement light (details will be described later). To be formed).

  The spherical substrate 72 is configured to be replaceable with an inclined surface substrate 73 having a transflective inclined surface 73a. The inclined surface substrate 73 is used when measuring another test surface (a test surface 90 described later) having a columnar shape. Further, the planar substrate 71 is held by a moving mechanism 74 and is configured to be finely moved in the measurement optical axis L direction when changing the interference fringe pattern.

Next, the test lens 8 will be described. FIGS. 2A and 2B are diagrams (A is a cross-sectional view and FIG. 2B is a plan view) showing a configuration of the lens 8 to be examined.
Subject lens 8 as shown in FIG. 2 has a test surface 80 of the rotationally symmetric around the optical axis C _1,該被interfering optical system 80, the interference optical around the optical axis C ₁ system 2 side concave portion 81 which is concave (upper side in FIG. 2 (a)), a convex portion 82 which is convex to the optical axis C ₁ in the interference optical system 2 side to the center, the concave portion 81 and convex portion 82 and an off-axis stop point portion 83 located at a boundary portion with 82.

Concave portion 81, when directed to the test surface 80 upwardly, the area comprising a down slope toward the optical axis C _1, namely, the normal line N ₁ stood the concave surface portion 81, normal line N ₁ along a once approached (cross) as to extend region to the optical axis C ₁ in accordance with the distance from the concave portion 81, the convex portion 82, when directed to the test surface 80 upwards, towards the optical axis C ₁ Te region to be a rising gradient, i.e., the normal N ₂ stood on the convex surface portion 82 is, in a region extending away from the optical axis C ₁ from the beginning in accordance with the distance from the convex portion 82 along the normal line N ₂ is there. In addition, strictly speaking, the off-axis stop point portion 83 is a linear region in which the direction of the normal line N ₃ standing on the off-axis stop point portion 83 coincides with (is parallel to) the direction of the optical axis C _1. although, it is taken a little wider in the present embodiment, the annular region of the drawing width d ₂ and the off-axis stationary point portion 83. Then, a concave region having a width (diameter) d ₁ positioned on the inner peripheral side of the off-axis stop point portion 83 is defined as a concave surface portion 81, and an annular shape having a width d ₃ positioned on the outer peripheral side of the off-axis stop point portion 83. The convex region is a convex surface portion 82.

  Hereinafter, the operation and measurement procedure of the optical interference measuring apparatus 1 will be described. FIG. 3 is a diagram showing an irradiation pattern of the measurement light to the test surface 80 ((A) is the concave surface portion 81, (B) is the convex surface portion 82, and (C) is each measurement of the off-axis stop point portion 83). FIG. 4 is a diagram illustrating an example of an interference fringe pattern when measuring the test surface 80 ((A) is a concave surface portion 81, (B) is a measurement time of each of the convex surface portion 82 and the off-axis stop point portion 83). It is. In the following description, a case where measurement is performed in the order of the concave surface portion 81, the convex surface portion 82, and the off-axis stop point portion 83 of the test surface 80 is taken as an example, but the measurement order can be changed as appropriate.

(1) First, using the sample stage 6, the position of the test lens 80 is adjusted so that the optical axis C ₁ of the test surface 80 coincides with the measurement optical axis L. It is assumed that the alignment adjustment of the interference optical system 2, the branch optical element 3, and the imaging system 4 has been completed.

  (2) Next, in order to measure the concave surface portion 81 of the test surface 80, the sample stage 6 is used to adjust the position of the test surface 80 in the measurement optical axis L direction. In this position adjustment, the measurement light composed of the spherical wave output from the interference optical system 2 once converges on the measurement optical axis L as shown in FIG. 3A, and then enters the concave portion 81 while diverging. It is performed so that it will be in the state to do.

(3) Next, by using the interference fringe forming optical system 70, an interference fringe pattern P ₁ (see FIG. 4A) for adjusting the light quantity distribution of the measurement light at the time of measurement of the concave surface portion 81 is formed. This interference fringe pattern P ₁ is such that a light stripe area S ₁ with a large amount of light (bright) is formed at the center, and a dark stripe area S ₂ with a small amount of light (dark) is formed at the periphery thereof. when measuring a concave portion 81, Akirashima area S ₁ is projected onto the concave portion 81, Classima area S ₂ is set to be projected on the convex portion 82 and the off-axis stationary point portion 83. By projecting the interference fringe pattern P ₁ , generation of unnecessary light from the convex surface portion 82 and the off-axis stop point portion 83 during measurement of the concave surface portion 81 is prevented.

(4) Next, the concave surface portion 81 is irradiated with the measurement light, and formed by interference between the return light reflected from the measured region of the concave surface portion 81 and the reference light from the reference standard spherical surface 25a of the spherical standard lens 25. The interference fringes to be picked up are picked up by the image pickup system 4, and the image data is input to the shape analysis means 50. The concave surface portion 81 has an aspherical shape, and the curvature changes from place to place, so it is difficult to obtain an interference fringe image corresponding to the entire concave surface portion 81 at a time. Therefore, while the sample stage 6 is sequentially changed the position of the measuring optical axis L direction of the test surface 80 with a plurality of each partial area (each partial area of the concave portion 81 around the optical axis C ₁ circle A plurality of area-specific interference fringes corresponding to a plate shape or an annular shape are sequentially imaged in the imaging system 4 to acquire each image data.

  (5) Next, in order to measure the convex portion 82 of the test surface 80, the position of the test surface 80 in the measurement optical axis L direction is adjusted using the sample stage 6. This position adjustment is performed so that the measurement light composed of the spherical wave output from the interference optical system 2 enters the convex portion 82 while converging as shown in FIG.

(6) Next, using the interference fringe forming optical system 70, an interference fringe pattern P ₂ (see FIG. 4B) for adjusting the light quantity distribution of the measurement light at the time of measuring the convex surface portion 82 is formed. This interference fringe pattern P ₂ is a dark stripe area S ₂ with a small amount of light (dark) formed in the center, and a bright stripe area S ₁ with a large amount of light (bright) formed in the periphery thereof. when measuring a convex surface portion 82, Akirashima area S ₁ is projected onto the convex portion 82 and the off-axis stationary point portion 83 is set so as Classima area S ₂ is projected to the concave portion 81. The projection of the interference fringe pattern P _2, so as to prevent the occurrence of unnecessary light from the concave portion 81 at the time of measurement of the convex portion 82. In the measurement of the convex surface portion 82, the measurement light is also applied to the off-axis stop point portion 83. The reflected light from the off-axis stop point portion 83 is obtained by ray tracing by computer simulation or the like. , after confirming that not unnecessary light which will be described later, so that projecting the light shielding pattern P _2.

(7) Subsequently, the convex surface portion 82 is irradiated with the measurement light, and formed by interference between the return light reflected from the measurement region of the convex surface portion 82 and the reference light from the reference standard spherical surface 25a of the spherical standard lens 25. The interference fringes to be picked up are picked up by the image pickup system 4, and the image data is input to the shape analysis means 50. Note that the convex surface portion 82 has an aspherical shape, and the curvature varies from place to location, so that it is difficult to obtain an interference fringe image corresponding to the entire convex surface portion 82. Therefore, as in the measurement of the concave surface portion 81, the sample surface 6 is used to sequentially change the position of the surface 80 to be measured in the measurement optical axis L direction for each of the plurality of partial regions (each partial region). the multiple regions specific interference fringes corresponding to the annular shape around the optical axis C ₁₎ sequentially captured by the image capturing system 4, so as to obtain the respective image data.

(8) Next, in order to measure the off-axis stationary point 83 of the test surface 80, the flat reference plate 26 is arranged on the measurement optical axis L instead of the spherical reference lens 25, and the sample stage 6 is used. Then, the position of the test surface 80 in the measurement optical axis L direction is adjusted. In this position adjustment, as shown in FIG. 3C, the measurement light composed of a plane wave output from the interference optical system 2 is incident on the off-axis stop point portion 83, and the shape information of the off-axis stop point portion 83 is obtained. Is performed so that the imaging system 4 can capture an image of the interference fringes carrying the. At the time of measurement of the off-axis stationary point portion 83, by using the interference fringes forming optical system 70 to form an interference fringe pattern P ₂ described above, this is to be projected onto the test surface 80 (the translucent areas S ₁ There is projected on the convex portion 82 and the off-axis stationary point portion 83, the light shielding area S ₂ is to be projected to the concave portion 81).

(9) Subsequently, the measurement light is irradiated to the off-axis stop point 83, and interference between the return light reflected from the off-axis stop point 83 and the reference light from the reference reference plane 26a of the flat reference plate 26 is achieved. The imaging system 4 captures the interference fringes formed by the above and inputs the image data to the shape analysis means 50. In the measurement of the off-axis stop point 83, the convex surface 82 is also irradiated with measurement light. However, the reflected light from the convex surface 82 is reflected by the ray tracing by computer simulation or the like as described later. after confirming that not unnecessary light, so that projecting the light shielding pattern P _2.

  (10) Next, the shape analysis means 50 obtains the shape information of the concave surface portion 81, the convex surface portion 82, and the off-axis stop point portion 83 based on the image data of each interference fringe, and connects the shape information to each other. Thus, the shape information of the entire test surface 80 is obtained. Specifically, shape information for each of the plurality of partial regions is obtained based on the image data of the plurality of region-specific interference fringes corresponding to the plurality of partial regions of the concave surface portion 81, and the shape information for each of the plurality of partial regions is obtained. By connecting them together, the shape information of the entire concave surface portion 81 obtained by merging the plurality of partial regions is obtained. Similarly, shape information for each of the plurality of partial areas is obtained based on the image data of the plurality of area-specific interference fringes corresponding to the plurality of partial areas of the convex portion 82, and the shape information for each of the plurality of partial areas is connected to each other. By combining them, shape information of the entire convex surface portion 82 obtained by merging the plurality of partial regions is obtained. Further, the shape information of the off-axis stop point 83 is obtained based on the image data of the interference fringes corresponding to the off-axis stop point 83. Then, the shape information of the entire test surface 80 is obtained by connecting the shape information of the entire concave surface portion 81, the entire convex surface portion 82, and the off-axis stop point portion 83.

As described above, the interference fringe patterns P ₁ and P ₂ are unnecessary light that is reflected from a partial region of the test surface 80 and incident on the imaging system 4 when the test surface 80 is irradiated with measurement light. In order to prevent the occurrence of this, the amount of measurement light incident on this partial region is reduced. Here, this unnecessary light will be described with reference to FIG. FIG. 5 is a schematic diagram showing unnecessary light generated at the time of measurement. A front view of the two-dimensional image sensor 42 is schematically shown in the upper part of FIG. 5 together with a cross-sectional view thereof. To position). In FIG. 5, the optical system including the branch optical element 3, the second collimator lens 24, the spherical reference lens 25, and the imaging lens 40 is shown in a simplified manner.

As shown in FIG. 5, in order to measure the convex surface portion 82 of the test surface 80, the case where the test surface 80 is irradiated with measurement light composed of converging spherical waves will be considered. At this time, there is light that is retroreflected from the convex surface portion 82 and enters the imaging point F on the two-dimensional image sensor 42 through the spherical reference lens 25, the second collimator lens 24, the branching optical element 3, and the imaging lens 40. And On the other hand, when there is a large amount of light that is reflected from the concave surface portion 81 and is incident on the imaging point F, this light becomes unnecessary light. In addition, since the test surface 80 has a rotationally symmetric shape, the position where such unnecessary light is incident is generated on the two-dimensional image sensor 42 so as to draw a circle. In the present embodiment, when measuring the convex portion 82, by projecting said interference fringe pattern P ₂ on the test surface 80, it is possible to reduce the power of the measuring beam incident on the concave portion 81, the Such unnecessary light can be prevented from being generated. The same applies to the development and operation of the interference fringe pattern P ₁ of the unwanted light when measuring the concave portion 81.

  Further, it is possible to know in advance by ray tracing by computer simulation or the like from which position of the test surface 80 the unnecessary light is generated when the measurement light is irradiated. Therefore, an interference fringe pattern (not shown) that is grasped by such ray tracing and that reduces the amount of measurement light only in an area where unnecessary light is generated may be projected onto the test surface 80.

  Next, the case of measuring another test lens (the test lens 9 shown in FIG. 6) will be described. 6A and 6B are diagrams (a cross-sectional view and FIG. 7B a plan view) showing the configuration of another lens 9 to be tested. FIG. 7 shows interference fringes when measuring the test surface 90 of the lens 9 to be tested. It is a figure which shows an example (at the time of each measurement of a convex surface part and an off-axis stop point part) of an example ((A) is a concave surface part and (B)).

As shown in FIG. 6, the test lens 9 has a test surface 90 having a columnar shape which is symmetrical in the drawing with the optical axis C ₂ in between, and the test surface 90 has an optical axis C _2. a concave portion 91 which is concave, a convex portion 92 that protrudes in the interference optical system 2 side around the optical axis C ₂ of the above about the interference optical system 2 side (upper side in FIG. 6 (a)), It has an off-axis stop point portion 93 located at the boundary portion between the concave surface portion 91 and the convex surface portion 92.

The features of the shapes of the concave surface portion 91, the convex surface portion 92, and the off-axis stop point portion 93 are the same as those of the test surface 80 except that they constitute a part of the column surface shape. _Two straight belt-shaped regions having a width d ₂ ′ are defined as off-axis stationary point portions 93, and a concave region having a width (diameter) d ₁ ′ located inside the two off-axis stationary point portions 93 is defined as a concave surface portion 91. Two straight belt-like regions having a width d ₃ ′ located outside each off-axis stop point portion 93 are defined as a convex surface portion 92.

  When measuring the test surface 90 of the test lens 9, the cylindrical reference lens 27 shown in FIG. 1 is arranged on the measurement optical axis L. The measurement procedure is the same as that for measuring the test surface 80, and a detailed description thereof will be omitted.

On the other hand, the light-shielding pattern P ₃ shown in FIG. 7A is formed using the interference fringe forming optical system 70 when measuring the concave surface portion 91. The light shielding pattern P ₃ is the light intensity larger (brighter) Akirashima area S ₁ of the straight strip is formed in the center portion, the peripheral portion, the light amount small (dark) of the two dark stripes area S ₂ is formed are those, when measuring the concave portion 91, Akirashima area S ₁ is projected onto the concave portion 91 is set so as Classima area S ₂ is projected on the convex portion 92 and the off-axis stationary point portion 93 ing. By projecting the light shielding pattern P ₃ , unnecessary light from the convex surface portion 92 and the off-axis stop point portion 93 at the time of measuring the concave surface portion 91 is prevented.

The light shielding pattern P ₄ shown in FIG. 7 (B), when measuring the convex portion 92, and is formed by using the interference fringes forming optical system 70. The light-shielding pattern P ₄ is the light amount small (dark) dark fringe area S ₂ of the straight strip is formed in the center portion, in the left and right sides, the light amount larger (brighter) of the two Akirashima area S ₁ is formed are those, when measuring the convex surface portions 92, Akirashima area S ₁ is projected onto the convex portion 92 and the off-axis stationary point portion 93 is set so as Classima area S ₂ is projected to the concave portion 91 ing. The projection of the light-shielding pattern P _4, so as to prevent the occurrence of unnecessary light from the concave portion 91 at the time of measurement of the convex portion 92. When measuring the convex surface portion 92, the off-axis stationary point portion 93 is also irradiated with the measuring light. However, the reflected light from the off-axis stationary point portion 93 is reflected by ray tracing by computer simulation or the like. , so that after confirming that not unnecessary light of the foregoing, projecting the light shielding pattern P _4.

Further, the light-shielding pattern P ₄ is also used when measuring the off-axis stationary point portion 93. That is, when measuring the off-axis stop point portion 93, the flat reference plate 26 is disposed on the measurement optical axis L instead of the cylindrical reference lens 27, and the light shielding pattern P is used using the interference fringe forming optical system 70. ₄ is projected onto the test surface 90 (the translucent area S ₁ is projected onto the convex surface portion 92 and the off-axis stop point portion 93, and the light shielding area S ₂ is projected onto the concave surface portion 91. ). In measuring the off-axis stop point 93, the convex surface 92 is also irradiated with measurement light. However, the reflected light from the convex surface 92 is reflected by the ray tracing by computer simulation or the like as described above. after confirming that not unnecessary light, so that projecting the light shielding pattern P _4.

  As mentioned above, although embodiment of this invention was described in detail, this invention is not limited to the above-mentioned embodiment, A various aspect can be changed.

  For example, in the above-described embodiment, in order to measure both the rotationally symmetric test surface 80 and the columnar test surface 90, the spherical reference lens 25 that outputs spherical waves and the cylindrical reference that outputs cylindrical waves. Although the lens 27 is interchangeably provided, it is not necessary to provide two types of reference lenses when the shape of the surface to be measured is limited.

  In the above-described embodiment, when measuring the off-axis stop points 83 and 93 of the test surfaces 80 and 90, the plane reference plate 26 that outputs a plane wave is replaceably provided. When the outer stationary point is not a measurement target or when measurement is possible with the spherical reference lens 25 or the cylindrical reference lens 27 even when the measurement is symmetrical, the flat reference plate 26 is not necessary.

  Further, in the above-described embodiment, the interference fringe forming optical system 70 of the light amount distribution adjusting means 7 has a Fabry-Perot type optical system arrangement, but has another optical system arrangement such as a Michelson type. It is also possible to use an interference fringe forming optical system.

  FIG. 8 shows a configuration example including another interference fringe forming optical system 70A. 8 that are conceptually similar to the constituent elements in the above embodiment are the same or similar numbers as those used in FIGS. 1 to 7 (the letter A is appended after the number). The detailed description is omitted. Further, since the interference optical system 2A shown in FIG. 8 includes the interference fringe forming optical system 70A, the positions of the light source unit 20 and the first collimator lens 21 are different from those of the interference optical system 2 of the above embodiment. The other parts are the same in configuration and are not shown.

  The interference fringe forming optical system 70A shown in FIG. 8 has a Michelson type optical system arrangement, and is a transflective reflector 75, a reflective planar substrate 76 having a reflective plane 76a, and a reflective spherical substrate having a reflective spherical surface 77a. 77. This interference fringe forming optical system 70A transmits the output light from the light source unit 20 that has passed through the first collimator lens 21 through the transflective reflector 75 to the right in the figure and travels, It is configured to branch into a second light beam that travels while being reflected upward in the middle. The first light flux is retroreflected at the reflection plane 76a, and the second light flux is retroreflected at the reflection spherical surface 77a, and is combined with each other by the transflective plate 75 to interfere. Due to this interference, an interference fringe pattern for adjusting the light quantity distribution of the measurement light is formed.

  The reflective spherical substrate 77 is configured to be exchangeable with a reflective inclined surface substrate 78 having a reflective inclined surface 78a. The reflective inclined surface substrate 78 is used when measuring the test surface 90 having a columnar shape. Further, the reflection flat substrate 71 is held by a moving mechanism 74A, and is configured to be finely moved in the left-right direction in the figure when changing the interference fringe pattern.

  The interference fringe pattern formed by the interference fringe forming optical systems 70 and 70A is once imaged on the screen, and the imaged interference fringe pattern is projected onto the test surfaces 80 and 90 via the interference optical system. You may do it.

  In the above-described embodiment, the interference optical system has a Fizeau type optical system arrangement. However, an interference optical system having another optical system arrangement such as a Michelson type may be used.

1 is a schematic configuration diagram of a lightwave interference measurement apparatus according to an embodiment. The figure which shows the structure of a to-be-tested lens ((A) sectional drawing, (B) top view) The figure which shows the irradiation pattern (at the time of each measurement of (A) concave surface part, (B) convex surface part, (C) off-axis stop point part) of measurement light The figure which shows an example of an interference fringe pattern ((A) is a concave surface part, (B) is at the time of each measurement of a convex surface part and an off-axis stop point part). A diagram schematically showing the unnecessary light generated The figure which shows the structure of another test lens ((A) sectional drawing, (B) top view) The figure which shows an example of the interference fringe pattern at the time of other test surface measurement ((A) is a concave surface part, (B) is at the time of each measurement of a convex surface part and an off-axis stop point part). The figure which shows the structural example provided with another interference fringe formation optical system

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light wave interference measuring device 2,2A Interference optical system 3 Branching optical element 4 Imaging system 5 Measurement analysis system 6 Sample stage 7 Light quantity distribution adjustment means 8,9 Test lens 20 Light source part 21 First collimator lens 22 Converging lens 23 Pinhole Plate 23a Pinhole 24 Second collimator lens 25 Spherical reference lens 25a Reference reference sphere 26 Plane reference plate 26a Reference reference plane 27 Cylindrical reference lens 27a Reference reference cylindrical surface 40 Imaging lens 41 Imaging camera 42 Two-dimensional image sensor 50 Shape analysis means DESCRIPTION OF SYMBOLS 51 Display apparatus 52 Input apparatus 70,70A Interference fringe formation optical system 71 Planar substrate 71a Semi-transmission reflection plane 72 Spherical substrate 72a Semi-transmission reflection spherical surface 73 Inclined surface substrate 73a Semi-transmission reflection inclination surface 74, 74A Movement mechanism 75 Semi-transmission reflection plate 76 reflection plane substrate 76a reflection plane 77 Reflective spherical substrate 77a Reflective spherical surface 78 Reflective inclined surface substrate 78a Reflective inclined surface 80, 90 Test surface 81, 91 Concave surface portion 82, 92 Convex surface portion 83, 93 Off-axis stop points C ₁ , C ₂ ) optical axis L measurement optical axis N ₁ to N ₃ normal P ₁ to P ₄ fringe pattern S ₁ (interference fringe pattern) of Akirashima area S ₂ (interference fringe pattern) Classima area

Claims (2)

Holding means for holding the test surface so that the optical axis of the test surface coincides with the measurement optical axis, and the test surface by converting the output light from the light source unit into measurement light and irradiating the test surface An interference optical system that combines return light from the reference light with reference light to obtain interference light, a branch optical element that branches the obtained interference light from the optical path of the interference optical system, and a branched interference light An optical interference measuring apparatus comprising: an imaging system that images an interference fringe; and a measurement analysis system that analyzes the captured interference fringe to obtain the shape of the test surface;
The test surface has a concave surface portion that is concave toward the interference optical system side around the optical axis, and a convex surface portion that is convex toward the interference optical system side around the optical axis,
The interference optical system outputs a spherical wave or a cylindrical wave that travels while converging along the measurement optical axis as the measurement light,
When measuring the concave surface portion, when measuring the convex surface portion so that the concave portion is irradiated while diverging after the measurement light once converges, the convex surface while converging the measurement light. An irradiation position variable means for changing the relative position of the test surface relative to the interference optical system in the measurement optical axis direction so as to be irradiated to a part;
In order to prevent generation of unnecessary light that is reflected from a partial region of the test surface and is incident on the imaging system when the measurement light is irradiated on the test surface, the light is incident on the partial region. A light amount distribution adjusting means for adjusting a light amount distribution on the test surface of the measurement light so that the light amount of the measurement light is reduced,
The light amount distribution adjusting unit includes an interference fringe forming optical system disposed on an optical path between the light source unit and the branch optical element, and in the interference fringe forming optical system, the light source unit from the light source unit The light quantity distribution is adjusted by an interference fringe pattern obtained by branching output light into two light beams, and combining the two light beams after passing through different paths. Lightwave interference measurement device. While sequentially changing the relative position using the irradiation position variable means, a plurality of inter-region interference fringes corresponding to each of the concave surface portion or a plurality of partial regions of the convex surface portion is sequentially imaged in the imaging system,
In the measurement analysis system, shape information for each of the plurality of partial regions is obtained based on the plurality of region-specific interference fringes, and the plurality of partial regions are merged by connecting the shape information for each of the plurality of partial regions. 2. The optical interference measuring apparatus according to claim 1, wherein shape information of the entire area is obtained.

Images