JP2003322590A - 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 of a Shack-Hartman method, measurement is performed by sweeping a microlens array and a sensor (CCD: charge coupled device) in a surface normal to a measurement optical axis. The number of divisions of an inspected surface, a weak point of the Shack- Hartman method, is improved, and a dynamic range can be ensured for measurement. <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. 2, 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 an aspherical surface, and 103 is a half mirror prism, which comprises 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 a 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 surface 101a to be inspected and the microlens array are conjugate, one lens element of the microlens array corresponds to one area of the surface to be inspected, and there is a slope error in one area of the surface to be inspected. 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 forming 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.

[0009]

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.

[0011]

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 microlens array for forming an image of a large number of substantially plane waves, a sensor (light receiving element array) placed at an imaging position of the microlens array, a holding member for holding the microlens array and the sensor. A mechanism for moving the microlens array, the sensor, and the holder within a plane perpendicular to the optical axis of the collimator lens,
The reference pinhole image is formed at a position corresponding to the focal point of the collimator, and the reference optical system that guides the light to the sensor side in the measurement optical path and the image formation position of the microlens array by the light flux from the reference optical system and the inspection target. It is characterized in that it has an arithmetic unit for calculating the slope error of the surface to be inspected from the difference in the image forming position of the microlens array due to the light flux reflected from the surface.

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 part.

Further, the surface shape measuring device provided with the measuring means according to claim 3 of the present application is for correcting 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, the surface shape measuring device provided with the measuring means described in claim 4 of the present application is characterized in that the microlens array, the sensor, and the holder can be exchanged.

[0015]

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. Reference numeral 3 denotes a half mirror prism, which has a function of reflecting the illumination light of the surface to be inspected, which is formed by the light source 8, the pinhole 9 and the lens 10, to the surface to be inspected, and is also formed by the light source 8, the pinhole 9 and the lens 10. The reference light for generating the standard image formation point by the microlens array described later is switched to the function of reflecting the reference light to the sensor side described later.

The illumination / reference optical system is arranged so that an image of a pinhole is formed at the intersection of its optical axis 22 and the measuring system optical axis 20. Further, the intersection is the paraxial curvature center of the surface to be inspected.

Numeral 4 is a collimator lens which transforms the light beam reflected from the surface to be inspected into a substantially plane wave. 5 is a microlens array,
The light flux from the collimator 4 is divided for each lens element, and an image is formed on the surface of the sensor 6 (for example, CCD).

If the incident light beam on the microlens array is a plane wave, the image forming point is the optical axis 2 of the microlens array.
1-i (i is the sequential number of the microlens).

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

Since the test surface 1a 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. 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.

That is, the slope error of the surface to be inspected can be calculated from the difference between the reference image point and the image point due to the reflected light on the surface to be inspected.

The microlens array 5 is held by a holder 7 integrally with the sensor, and the holder is the measuring optical axis 2.
Two-dimensional step scanning is carried out with a mechanism for moving in a plane perpendicular to 0.

The output signal from the sensor 5 is used as the arithmetic unit 1
1, the reference image forming point by the reference system is compared with the image forming point by the reflected light on the surface to be inspected, and the slope error of the surface to be inspected is calculated by a predetermined algorithm from the deviation.

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 :
S / S ₀ with the size of the microlens array (assuming that it is equal to the size of the sensor) and the power of the null lens set to ₀
= Β, fc = (β × S ₀ × r) / d e = (− 1 / (r + fc) + 1 / fc) ⁻¹ where k: detectable image shift in units of one sensor pitch , P: sensor pitch (size of one sensor element), ε: minimum detection slope error, fm = (k × p × fc) / (2 × ε × r) Number of microlens arrays: N Then, 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

(Examples) Tables 1, 2 and 3 show examples of the arrangement of the optical system of the surface profile measuring apparatus according to the present invention.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

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

(Examples shown in Table 1) Paraxial radius of curvature of test surface = 2000 mm, effective aperture of test surface = 800 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, 3, 4 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, the disassembled length of the surface to be inspected is 40 mm, but when β = 3, it is greatly improved to 13.33 mm, and the maximum detected slope error is the same. Also, the spread of the microlens image is 0.027 mm to 0.081 m in diameter.
Although it spreads by m, it is the sensor 6 pitches, and the movement of the imaging point by 1 pitch can be detected by the arithmetic unit.

Further, in the table, the minimum detection slope error is 4 sec when the number of microlens elements is 20 and β = 3.
If the various values that can be obtained are adopted, the maximum detection slope error will be 204.8 sec, but the minimum detection slope error 2
If a microlens array with a different focal length is used to obtain sec, the maximum detection slope error will be 10
It will be 2.4 seconds. That is, this indicates that appropriate measurement accuracy and measurement dynamic range can be obtained by exchanging the microlens array in accordance with the progress of processing of the reflecting surface. In order to maintain the stability of the measuring device due to the replacement, it is preferable to replace the microlens array and the sensor as a unit.

(Examples shown in Table 2) Paraxial radius of curvature of test surface = 9000 mm, effective diameter 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, 3, 4 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, the disassembled length of the surface to be inspected is 175 mm, but β = 4
In this case, the maximum detection slope error is the same, which is greatly improved to 43.75 mm. The spread of the microlens image is 0.006 mm to 0.025 in diameter.
Although it spreads to mm, the sensor is 1.85 pitches, and the movement of the imaging point by one pitch can be detected by the arithmetic unit.

(Examples shown in Table 3) Paraxial radius of curvature of the surface to be inspected = 800 mm, effective aperture of the surface to be inspected = 300 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, 3, 4 and the number of microlens elements = 20, 30.

In the table, the minimum detection slope error 4
sec, the number of microlens elements is 20, and β = 1
Then, the disassembled length of the surface to be inspected is 15 mm, but when β = 3, it is greatly improved to 5 mm, and the maximum detected slope error is the same. Further, the spread of the microlens image is expanded from 0.036 mm to 0.107 mm in diameter, but it is equivalent to 7.9 pitches of the sensor, and the movement of the imaging point by one pitch can be detected by the arithmetic unit.

[0038]

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,
It is possible to obtain a surface shape measuring apparatus capable of selecting appropriate detection accuracy and maximum detection slope error according to the processing stage.

[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 configuration of a surface shape 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 Microlens array 6 Sensor (for example CCD) 7 Holder 8 holding microlens array and sensor 8 Light source 9 Pinhole 10 Lens 11 Arithmetic device 20 Measurement system Optical axis 21-i is the optical axis 22 of the illumination / reference system r is the paraxial radius of curvature d of the surface to be measured d is the diameter fc of the surface to be measured focal length e of the collimator lens e is the diameter of the collimator lens and the microlens array Distance fm Focal length of lens element of microlens array S Diameter of measurement light beam emitted from collimator S ₀ Size of microlens array (assuming equal to sensor size) 101 Reflector 101a Test surface, 102 Null lens 103 Half Mirror prism 104 Collimator lens 105 My Lolens array 106 Sensor (for example, CCD) 107 Microlens array and holder for holding the sensor 108 Light source 109 Pinhole 110 Lens 111 Lens 112 Pinhole 113 Lens 120 Measurement system optical axis 121-i Microlens array optical axis 122 Illumination system Optical axis 123 Reference 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 AA36 AA53 BB05 CC21 FF01                       JJ02 JJ03 JJ25 JJ26 LL00                       LL10 LL30                 2G086 HH06

Claims (4)

[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 microlens array for forming multiple points of the substantially plane wave, and a microlens array. A sensor (light receiving element array) placed at an imaging position, a holding body for holding the microlens array and the sensor, a microlens array, the sensor and the holding body are perpendicular to the optical axis of the collimator lens. A mechanism for moving it in a plane, 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 microscopic light beam from the reference optical system. It has a computing device for calculating the slope error of the surface to be inspected from the difference between the image forming position of the lens array and the image forming position of the microlens array due to the reflected light beam from the surface to be inspected. Surface shape measurement device according to symptoms. 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 measuring apparatus according to claim 1, wherein the microlens array, the sensor, and the holder are replaceable.