JP2003322587A - Surface shape measuring instrument - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a measuring instrument capable of highly efficiently measuring a surface shape during working even at a middle working stage before the stage where the surface shape measuring becomes possible with an interferometer, in a aspherical working. <P>SOLUTION: In the surface shape measurement by a Shack-Hartman method, a light beam incident on a microlens array is divided in two or more, and a microlens array and a sensor (CCD: charge coupled device) are disposed for each of the light beams. A microlens array/sensor set for receiving at least one light beam among the light beams has a scanning mechanism in a plane vertical to a measurement optical axis. <P>COPYRIGHT: (C)2004,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for measuring a wavefront aberration of an optical system by a Shack-Hartmann method, and a measuring device for measuring a surface shape.

[0002]

2. Description of the Related Art Conventionally, a Shack-Hartmann method wavefront aberration measuring method has been known as an apparatus for measuring the wavefront aberration of an optical system.

For example, USP 4141652, USP 5
629765, USP4490039, Patent Publication 253.
4170 is raised.

These wavefront aberration measuring methods can be applied to the measurement of an aspherical surface or a spherical shape. The configuration of the application example is shown in FIG.

In FIG. 4, 101 is a reflecting mirror having a surface 101a to be inspected, 102 is a null lens arranged when the surface to be inspected is aspherical, and 103 is a half mirror prism, which is composed of a light source 108, a pinhole 109 and a lens 110. Illumination light of the created test surface is reflected to the test surface side. The pinhole image is formed at the intersection of the illumination optical axis 122 and the measurement system optical axis 120. Further, the intersection is the paraxial curvature center of the surface to be inspected.

Reference numeral 104 denotes a collimator lens which converts the light beam reflected from the surface to be inspected into a substantially plane wave. Reference numeral 105 denotes a microlens array, which divides the light flux from the collimator 104 for each lens element and forms an image on the surface of the sensor 106 (for example, CCD). If the incident light beam to the microlens array is a plane wave, the image forming point is on the optical axis 121-i of the microlens array (i is the sequential number of the microlens).

The surface 101a to be inspected and the microlens array are conjugated.

Since the test surface 101a and the microlens array are conjugate, one lens element of the microlens array corresponds to one region of the test surface, and there is a slope error in one region of the test surface. Then, depending on the average value of the slope error of the one area, the image forming point of the lens element corresponding to the one area is deviated from the reference image forming point.

An optical system for obtaining the reference image formation point is composed of a light source 111, a pinhole 112 and a lens 113, and has an optical axis 123. The reference light is guided to the measurement optical path by the half mirror prism 103.

[0010]

In the above conventional example, the surface to be inspected is divided by the number of elements of the microlens array. Since the number of sensor elements is limited, increasing the number of elements will reduce the number of sensor elements per element, and the dynamic range of measurement (the maximum detection slope error will be many times the minimum detection slope error) will be significantly reduced. . Conversely, if the number of sensor elements per element is increased in order to increase the measurement dynamic range, the number of elements in the microlens array will decrease, the disassembled area of the test surface will increase, and fine slope error changes will occur. It becomes impossible to capture.

The present invention solves the above problems, reduces the decomposition area of the surface to be inspected, and obtains a sufficient measurement dynamic range.

[0012]

A surface shape measuring apparatus having a measuring means according to claim 1 of the present application uses an illumination optical system for illuminating a surface to be inspected and light reflected from the surface to be inspected into a substantially plane wave. A collimator lens, a beam splitter that splits the optical path from the collimator lens into a plurality of optical paths, a microlens array that forms a multipoint image corresponding to each of the plurality of optical paths split by the beam splitter, and a microlens array. Of the sensor (light receiving element array) placed at the image forming position, a holding member for holding the microlens array and the sensor, and one or more pairs of the microlens array, the sensor and the holding member are perpendicular to the optical axis. A reference pinhole image that has a mechanism for moving in a plane, forms a reference pinhole image at a position corresponding to the focal point of the collimator, and guides it to the sensor side in the measurement optical path. System, and an arithmetic unit for calculating the slope error of the surface to be inspected from the difference between the image formation position of the microlens array due to the light flux from the reference optical system and the image formation position of the microlens array due to the light flux reflected from the surface to be inspected. Is characterized by.

Further, the surface shape measuring apparatus provided with the measuring means described in claim 2 of the present application is characterized in that the illumination optical system and the reference optical system have a common optical portion.

Further, the surface shape measuring apparatus provided with the measuring means according to claim 3 of the present application is for correcting the aberration of the measuring system between the surface to be inspected and the light guide point to the measuring optical path of the reference optical system. It is characterized by having a null lens.

Further, in the surface shape measuring apparatus provided with the measuring means described in claim 4 of the present application, the set of the microlens array, the sensor and the holding body are respectively shifted with respect to the divided optical axis of the collimator. It is characterized by being arranged.

Further, in the surface shape measuring device provided with the measuring means according to claim 5 of the present application, a surface perpendicular to the collimator optical axis is formed by dividing one or more sets of the microlens array, the sensor and the holder. It is characterized by having a mechanism for moving in.

[0017]

1 is a block diagram of an optical system of a surface shape measuring apparatus according to the present invention. In FIG. 1, 1 is a reflecting mirror having a surface 1a to be inspected, and 2 is an aspherical surface to be inspected. It is not necessary when the surface to be inspected is a spherical surface with a null lens that is sometimes arranged. 3 is a half mirror prism, which includes a light source 16, a pinhole 17,
The function of reflecting the illumination light of the surface to be inspected, which is formed by the lens 18, to the surface of the surface to be inspected, and the light source 16 and the pinhole 1
7. A mechanism for switching the reference light, which is made up of the lens 18 and produces a standard image formation point by the microlens array described later, to the function of reflecting it to the sensor described later.

The illumination / reference optical system is arranged so that a pinhole image is formed at the intersection of the optical axis 27 of the illumination / reference optical system and the optical axis 20 of the measuring system. Further, the intersection is the paraxial curvature center of the surface to be inspected.

Numeral 4 is a collimator lens which makes the light beam reflected from the surface to be inspected into a substantially plane wave. A beam splitter 5 divides the optical axis of the collimator into a plurality of optical axes 21 and 22. 6
Is a first microlens array placed in the optical path of the divided first optical axis 21, 7 is a first sensor, 8 is a second microlens array placed in the optical path, and 9 is a second Sensor of. Reference numeral 10 is a holder for holding the microlens arrays 6 and 8 and the sensors 7 and 9.

11 is a third microlens array placed in the optical path of the divided second optical axis 22, 12 is a third sensor, and 13 is a fourth microlens array placed in the optical axis. , 14 is a fourth sensor. Reference numeral 15 is a holder for holding the microlens arrays 11 and 13 and the sensors 12 and 14.

If the incident light flux on the microlens array is a plane wave, the image forming points are the optical axes 23-i (i is the sequential number of the microlens) of the respective microlens arrays and the optical axis 2.
4-i, optical axis 25-i, optical axis 26-i, above.

The surface 1a to be inspected and the microlens array are conjugated.

Since the surface 1a to be inspected and the microlens array are conjugate, one lens element of the microlens array corresponds to one region of the surface to be inspected, and there is a slope error in one region of the surface to be inspected. And the image forming point of the lens element corresponding to the one area deviates from the reference image forming point depending on the average value of the slope error of the one area.

The output signals from the sensors 7, 9, 12, 14 are given to the arithmetic unit 19, and the reference image forming point by the reference system and the image forming point by the reflected light on the surface to be inspected are compared, and their deviations are compared. From this, the slope error of the surface to be inspected is calculated with a predetermined algorithm.

In FIG. 1, r is the paraxial radius of curvature of the surface to be inspected, d is the diameter of the surface to be inspected, fc is the focal length of the collimator lens, e is the distance between the collimator lens and the microlens array, and fm is the microlens array. Focal length S of the lens element of S: the diameter of the measurement light beam emitted from the collimator, S ₀ :
The size of one microlens array (assuming that it is equal to the size of one sensor), the power of the null lens is 0, S / S ₀ = β, and the size of the non-light-receiving part between the sensors = 0
Then, various values necessary for the configuration of the measurement optical system are calculated as follows: fc = (β × S ₀ × r) / de = (− 1 / (r + fc) + 1 / fc) ⁻¹ where k: sensor 1 The minimum value of the detectable image shift in units of pitch, p: sensor pitch (size of one sensor element), ε: minimum detection slope error, fm = (k × p × fc) / (2 × ε × r) When the number of microlens arrays is N, the maximum detection slope error εmax is εmax = (fc × S ₀ ) / (4 × fm × r × N).

Further, letting α ′ be the image-side aperture angle of the lens elements of the microlens array, and δ = 1.22 × λ / sin α ′, the spread δ of the image formation of the lens elements of the microlens array being the diameter of the Airy disk. Becomes

FIG. 2 shows a light receiving surface when a set of microlens arrays of 3 rows and 3 columns and sensors is arranged in the optical path of one optical axis 21 divided by the beam splitter. Two
01, 202, 203, 204, 205, 206, 20
Reference numerals 7, 208, and 209 denote light receiving surfaces of one sensor (for example, one CCD), and have light receiving areas of x ₀ and y _{0 in} total. Reference numeral 210 denotes a non-light-receiving portion which exists between the sensors due to a sensor package or the like and has widths x _b and y _b.
Is hatched.

The test surface corresponding to the non-light-receiving part is not measured.

In FIG. 3, a set of microlens arrays of 3 rows and 3 columns and sensors are arranged in the optical path of one optical axis 21 divided by a beam splitter, and a microarray of 3 rows and 3 columns is arranged in the optical path of another optical axis 22. the lens array and the sensor pairs, the width x _b of the non-light-receiving section 210 _shows the light receiving surface of the case of arranging shifted by y _b. 201, 202, 203, 20
4, 205, 206, 207, 208, 209 are optical axes 2
In the optical path of 1, 211, 212, 213, 214, 21
Reference numerals 5, 216, 217, 218, and 219 denote light receiving surfaces of one sensor arranged in the optical path of the optical axis 22. 220
Is a non-light-receiving part in the light-receiving region of x ₀ , y ₀ , and x _b ×
There are 12 y _b .

Here, the microlens array arranged in the optical path of the optical axis 22 and the holder of the sensor have a mechanism capable of moving in a plane perpendicular to the optical axis 22, and the micro array arranged in the optical path of the optical axis 21. Four shifts for the lens array and sensor pair, namely (0,0), ( _xb , 0),
If (0, y _b ) and (x _b , y _b ) are measured, the non-light-receiving part is eliminated.

(Examples) Examples of the arrangement of the optical system of the surface shape measuring apparatus according to the present invention are shown in Tables 1 and 2.

[0032]

[Table 1]

[0033]

[Table 2]

However, although the calculation is performed in the one-dimensional direction, the extension to the two-dimensional direction is possible with the same value.

In the sensor array, the size of the non-light-receiving portion is sufficiently smaller than the size of the light-receiving portion.

(Examples shown in Table 1) Paraxial radius of curvature of test surface = 2000 mm, effective aperture of test surface = 800 mm, size of one pitch of sensor 0.0135 mm, number of elements in one-dimensional direction of sensor = 2048 When the minimum value of the movement of the image formation point that can be detected by the arithmetic unit is 1 pitch with the sensor 1 pitch as a unit, the minimum detection slope error = 2 sec, 4 s
For ec, various values necessary for the configuration of the measurement system are shown for the collimator emission light flux / microlens array size β = 1, 2, 3 and the number of microlens elements = 20, 30.

In the table, the minimum detection slope error 2
sec, the number of microlens elements is 20, and β = 1
Then, although the disassembled length of the surface to be inspected is 40 mm, when β = 3, that is, three sensors in the one-dimensional direction are arranged, 13.
It is greatly improved to 33 mm, and the maximum detection slope error is the same. Further, the spread of the microlens image is expanded from 0.027 mm to 0.081 mm in diameter, but it is equivalent to 6 pitches of the sensor, and the movement of the imaging point by 1 pitch can be detected by the arithmetic unit.

(Examples shown in Table 2) Paraxial radius of curvature of test surface = 9000 mm, effective aperture of test surface = 3500 mm 1 pitch size of sensor 0.0135 mm, number of elements in one-dimensional direction of sensor = 2048 When the minimum value of the movement of the image formation point that can be detected by the arithmetic unit is 1 pitch with the sensor 1 pitch as a unit, the minimum detection slope error = 2 sec, 4 s
For ec, various values necessary for the configuration of the measurement system are shown for the collimator emission light flux / microlens array size β = 1, 2, 3, and for the number of microlens elements = 20, 30.

In the table, the minimum detection slope error 2
sec, the number of microlens elements is 20, and β = 1
Then, the disassembled length of the surface to be inspected is 175 mm, but β = 3
In the above case, that is, when three sensors are arranged in the one-dimensional direction, the maximum detection slope error is the same, which is significantly improved to 58.33 mm. Further, the spread of the microlens image is expanded from 0.006 mm to 0.018 mm in diameter, but the sensor is 1.33 pitches, and the movement of the imaging point by one pitch can be sufficiently detected by the arithmetic unit.

[0040]

According to the invention described in claim 1 of the present application, the surface shape measurement in which the decomposition area of the surface to be inspected is small, that is, the number of measurement divisions of the surface to be inspected is large, and the maximum slope error that can be detected is secured. You can get the device.

According to the invention described in claim 2 of the present application,
Decrease the decomposition area, that is, increase the number of measurement divisions of the surface to be inspected,
In addition, in the surface shape measuring device that secures the maximum slope error that can be detected, the illumination system of the surface to be inspected and the reference system for obtaining the standard image formation point can be simplified.

According to the invention described in claim 3 of the present application,
Even if the surface to be inspected is an aspherical surface such as a paraboloid or a hyperboloid, a surface shape measuring device with a small decomposition area, that is, a large number of measurement divisions of the surface to be inspected, and a maximum slope error that can be detected is provided. You can get it.

According to the invention described in claim 4 of the present application,
Decrease the decomposition area, that is, increase the number of measurement divisions of the surface to be inspected,
In addition, it is possible to obtain a surface profile measuring device in which the non-measurement portion of the surface to be tested is made small in the surface profile measuring device that secures the maximum slope error that can be detected.

According to the invention described in claim 4 of the present application,
Decrease the decomposition area, that is, increase the number of measurement divisions of the surface to be inspected,
In addition, it is possible to obtain a surface profile measuring apparatus in which the non-measurement portion of the surface to be tested is eliminated in the surface profile measuring apparatus that secures the maximum slope error that can be detected.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a surface shape measuring apparatus according to the present invention.

FIG. 2 is a diagram showing a light receiving surface of one sensor array of the surface profile measuring apparatus according to the present invention.

FIG. 3 is a diagram showing the light receiving surfaces of two sensor arrays of the surface shape measuring device according to the present invention in an overlapping manner.

FIG. 4 is a diagram showing a configuration of a surface profile measuring apparatus according to a conventional example.

[Explanation of symbols]

1 Reflector 1a Surface to be inspected 2 Null lens 3 Half mirror prism 4 Collimator lens 5 Beam splitter 6 Microlens array 7 Sensor (eg CCD) 8 Microlens array 9 Sensor (eg CCD) 10 Holder holding microlens array and sensor 11 microlens array 12 sensor (eg CCD) 13 microlens array 14 sensor (eg CCD) 15 holder for holding microlens array and sensor 16 light source 17 pinhole 18 lens 19 arithmetic unit 20 optical axes 21, 22 of measurement system Optical axes 23-i, 24-i, 25-i, 25-i, 26-i of the collimator 4 divided by the beam splitter
(I is the sequential number of the microlens) is the optical axis 27 of the microlens array 6, 8, 11, 13 r The illumination / reference system r The paraxial radius of curvature d of the surface to be inspected d The diameter fc of the surface to be inspected the focal length e of the collimator lens Distance between collimator lens and microlens array fm Focal length of lens element of microlens array S Diameter of measurement light beam emitted from collimator S ₀ Size of one microlens array (assuming sensor size) 201, 202 , 203, 204, 205, 206, 2
07, 208, 209 One light receiving surface of one sensor (for example, one CCD) 210 Non-light receiving parts 201, 202, 203, 204, 205, 206 that are present between the sensors due to sensor packages, etc. , 2
07, 208, 209 Optical axes 21 211, 212, 213, 214, 215, 216, 2 of FIG.
17, 218, 219 Light receiving surface 220 of each one sensor arranged on the optical axis 22 of FIG. Sensor (for example, CCD) 107 Microlens array and holder 108 that holds the sensor Light source 109 Pinhole 110 Lens 111 Lens 112 Pinhole 113 Lens 120 Optical axis 121 of measurement system 121-i Optical axis 122 of microlens array Light of illumination system Axis 123 Reference system optical axis

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Shoji Suzuki             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Makoto Taniguchi             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation (72) Inventor Toru Matsuda             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation F term (reference) 2F065 AA46 AA53 CC21 FF10 HH13                       JJ03 JJ05 JJ09 JJ26 LL00                       LL04 LL10 LL30 LL46                 2G086 GG04

Claims (5)

[Claims] 1. An illumination optical system for illuminating a surface to be inspected, a collimator lens for making reflected light from the surface to be inspected into a substantially plane wave, a beam splitter for dividing an optical path from the collimator lens into a plurality of optical paths, Corresponding to each of the plurality of optical paths divided by the beam splitter, a microlens array for forming a multipoint image, a sensor (light receiving element array) placed at the imaging position of the microlens array, the microlens array and the A holder that holds the sensor, a reference optical system that forms a reference pinhole image at a position corresponding to the focal point of the collimator, and guides it to the sensor side in the measurement optical path, and a microlens based on the light flux from the reference optical system. Arithmetic device that calculates the slope error of the surface to be measured from the difference between the image forming position of the array and the image forming position of the microlens array due to the light flux reflected from the surface Surface shape measuring apparatus characterized by having. 2. The surface shape measuring apparatus according to claim 1, wherein the illumination optical system and the reference optical system have a common optical portion. 3. The surface shape measurement according to claim 1, further comprising a null lens for correcting aberration of the measurement system between the test surface and a light guide point of the reference optical system to the measurement optical path. apparatus. 4. The surface shape according to claim 1, wherein the set of the microlens array, the sensor, and the holder are arranged so as to be shifted with respect to the optical axes of the divided collimators. measuring device. 5. A mechanism for moving one or more sets of the microlens array, the sensor, and the holder into a plane perpendicular to the optical axis of the divided collimator. The surface shape measuring device described.