JP2016024059A - Surface shape measurement method and surface shape measurement device and optical element using surface shape measurement method and surface shape measurement device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve the problem in which in a method of projecting a light flux to a measured surface via an optical system and measuring a measured surface shape by detecting a wavefront of a reflection light flux, an error of the optical system makes a highly accurate measurement of the measured surface shape difficult.SOLUTION: In a surface shape measurement method configured to: project light from a light source to a known reference surface via an optical system; measure, by a detection unit, a light lay angle distribution of a reflection light flux; similarly, measure a measured surface; and measure a measured surface shape from a difference between the measurement light ray angle distributions and a magnification distribution, the surface shape measurement method is configured to calibrate the magnification distribution on the basis of calculation of calculating a wavefront change before and after the reference surface is driven at a known amount, a result of measuring the wavefront change before and after the reference surface is driven by driving the reference surface at the known amount, and the magnification distribution.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a surface shape measuring method, a surface shape measuring device, and an optical element using them.

  As a method to measure the lens surface shape in a non-contact and high-speed manner, the surface to be measured is irradiated with spherical wave light via an optical system, and the reflected light from the surface to be measured is measured using the Shack-Hartmann sensor of the light receiving unit Non-patent document 1 discloses a method of doing this.

  This method has an advantage that the shape of the test surface with various design values can be measured as compared with an interferometer using a null lens as disclosed in Patent Document 1. In addition, compared to a stitching interferometer as disclosed in Patent Document 2 and a scanning interferometer as disclosed in Patent Document 3 that drives a sample at the time of measurement, a stage or length measuring device that is driven with high accuracy, There is an advantage that a complicated analysis program is unnecessary.

  In order to calculate the shape with high accuracy, it is known to calibrate the position error in consideration of the actual device error.The measured surface is driven by a known amount and the measured value change amount of the light receiving unit at that time is calculated. It is known that the position error is calibrated by measuring (Patent Documents 4, 5, 6, and 7).

JP 09-329427 A JP 2004-125768 A Japanese Patent Registration No. 0371747 JP 2000-97663 A Japanese Patent Laid-Open No. 10-281736 JP 2006-133059 A Japanese Patent Laid-Open No. 04-048201

Johannes Pfund, Norbert Lindlein, and Johannes Schwider, “Nonull testing of rotationally symmetrical assets: a systematic error assessment,“ Ap. Opt. 40 (2001) p. 439

  When measuring an aspherical shape as a test surface, the method using the Shack-Hartmann sensor described in Non-Patent Document 1 does not irradiate measurement light perpendicularly to the test surface. Since the test surface is reflected at an angle different from the incident light, the reflected light does not become substantially parallel light at the light receiving unit, and the reflected wavefront from the test surface is detected as a wavefront greatly deviated from the plane wavefront. Further, the amount of deviation of the reflected wavefront from the test surface from the plane wavefront is not always constant, and varies depending on the measured aspheric shape.

  Therefore, even if the reflected wavefront from the test surface is measured by the light receiving unit, the shape of the test surface cannot be obtained as it is. In order to calculate the shape of the test surface from the reflected wavefront from the test surface, two pieces of information on the reflection on the test surface and the position and angle regarding the light reception are necessary.

  If the optical system of the measuring device and its arrangement are made as designed, it may be calculated in advance for each surface to be tested, but in reality, lens processing errors (curvature radius error, polishing residue, homogeneity, There are various error factors such as thickness error, lens assembly error (positioning error in the optical axis direction, aberration, etc.), alignment error between the lens and the test surface / light receiving surface, etc. In order to calculate the shape with high accuracy, it is necessary to calibrate the position magnification and the angle magnification in consideration of an actual apparatus error.

  However, Patent Documents 4 to 7 disclose that the position magnification can be used for calibration, but do not disclose a method for calibrating the angle magnification.

  Note that the position information is the abscissa relationship between the light receiving surface and the test surface that indicates where the light beam measured by the light receiving unit is reflected on the test surface. It can be expressed as a position magnification obtained by taking Similarly, the angle information is the relationship between the light beam angle between the light receiving surface and the test surface, which indicates at which angle the light beam measured by the light receiving unit is reflected by the light receiving unit. Can be expressed as an angle magnification.

  The object of the present invention is to measure the shape of the surface to be inspected including an aspherical surface, even if the measuring device has various errors and the magnification distribution can be calibrated on the device even if it cannot be manufactured as designed. It is to provide a surface shape measuring method and a surface shape measuring apparatus capable of performing the above with high accuracy, and an optical element surface using them.

  The surface shape measurement method according to the present invention irradiates light to a surface to be measured through an optical system, and receives the light by a light receiving unit having a light receiving surface that receives reflected light from the surface to be measured. In the measuring device for measuring the surface shape of the inspection surface, a step of calculating a position magnification distribution and an angle magnification distribution on a conjugate plane with respect to the light receiving surface, and a wavefront of light reflected by a reference surface having a known surface shape are received. A step of measuring by the unit, a step of measuring the wavefront of the light reflected by the test surface by the light receiving unit, and a step of calculating the surface shape of the test surface from the difference information of the two measurement wavefronts. A surface shape measuring method including a step of calculating a wavefront on the light receiving surface of light reflected by the reference surface using a design value of the optical system, and a wavefront change before and after driving the reference surface by a known amount. Calculating the reference plane; A step of measuring a wavefront change before and after the knowledge drive, a step of calibrating the angular magnification distribution from the wavefront change before and after the known drive obtained by the calculation and measurement, the known reference surface shape, and the reference surface And a step of calculating a surface shape of the test surface using the measured value of the test surface and the calibrated angular magnification.

  According to the present invention, for example, even when there are various errors in the measuring device and it cannot be manufactured as designed, the magnification distribution can be calibrated on the device, and the surface to be tested including an aspherical surface can be calibrated. The shape can be measured with high accuracy.

1 is a schematic diagram of Example 1. FIG. It is the figure which showed the example of the light-receiving part. It is a flowchart which shows the step of a measuring method. It is a flowchart which shows the step of pre-processing. It is a flowchart which shows the step which calculates magnification distribution. It is a flowchart which shows the step of measurement. It is a flowchart which shows the step of an analysis. It is a figure for demonstrating the position and angle of a light ray. It is a figure explaining calibration of angle magnification distribution. 6 is a schematic diagram of Example 2. FIG. 10 is a flowchart illustrating steps for calculating a magnification distribution according to the second embodiment. 10 is a diagram of a magnification distribution in Example 2. FIG. It is a figure explaining the calculation method of a conjugate plane. It is the schematic of Example 3 which measures a concave surface.

Example 1
FIG. 1 shows a configuration of a measuring apparatus that measures the shape of a convex surface as an example of the present invention. This measuring device is a device for measuring the shape of the test sample 11 using information of the reference sample 10. The light from the light source 1 passes through the condenser lens 2 and the pinhole 3, is reflected by the half mirror, passes through the lens 5, becomes convergent light, and irradiates the reference surface 10a or the test surface 11a. The light reflected by the reference surface 10 a or the test surface 11 a passes through the lens 5, the half mirror 4, and the lens 7 and is received by the light receiving unit 8. The reference sample 10 and the test sample 11 are arranged on a stage 6 that can control at least one of XYZθxθyθz.

  As the light source 1, for example, a monochromatic laser, a laser diode, a light emitting diode, or the like is used. The lens 5 is used to irradiate the test surface 11a with light with convergent light, and the center of curvature near the paraxial axis of the test surface 11a and the center of curvature of the spherical wave of the convergent light are preferably substantially equal. The lens 7 is used to receive the reflected light of the test surface by the light receiving surface 8a. The design conditions of the lenses 5 and 7 include information on the object 11 to be measured, such as effective diameter, radius of curvature, and aspheric amount, and information on the light receiving unit 8, such as sensor size, configuration of the light receiving unit, and input allowable angle. Determine from

  In the measurement apparatus according to the present embodiment, it is possible to measure a plurality of aspheric shapes by combining the lens 5 and the lens 7. However, the range of shapes that can be measured with one set of lenses is limited. Therefore, the range of the aspheric shape that can be measured can be expanded by exchanging either one of the lens 5 and the lens 7 or two according to the aspheric shape to be measured.

  As the light receiving unit 8, the Shack-Hartmann sensor shown in FIG. The Shack-Hartmann sensor includes a microlens array 21 and a light receiving sensor 22 in which a large number of minute condensing lenses are arranged in a lattice pattern. An example of the light receiving sensor is a CCD. In the microlens array, the light is condensed for each minute region, and the light receiving sensor can measure the same condensing spot as the number of microlens arrays.

  Using the Shack-Hartmann sensor, the angle distribution φ of the light beam on the light receiving surface 8a is obtained. Specifically, the focused spot position is measured in advance when a plane wave is incident, and a reference for the focused spot position is obtained. Next, by arranging the test surface and measuring the condensing spot position corresponding to the reflected wavefront from the test surface, the amount of change Δp from the reference condensing spot position in the plane wave can be obtained. The ray angle distribution φ on the detection surface 8a can be obtained from the Δp and the focal length f of the microlens array by the following equation.

(Formula 1)
φ = atan (Δp / f)
The light receiving unit 8 may be anything other than the Shack-Hartmann sensor as long as it can measure the wavefront and the angular distribution. For example, as shown in FIG. 2B, a shearing interferometer or a Talbot interferometer may be configured by combining a diffraction grating and a CCD sensor. In addition, the Hartmann method using a Hartmann plate and a CCD sensor may be used.

  Further, when the reflected wavefront from the test surface is larger than the light receiving surface 8a, only a part of the reflected wavefront is measured, the light receiving unit 8 is moved, the measurement is repeated a plurality of times, and the entire wavefront and angular distribution are joined together. May be received.

  The processing unit 9 performs processing for obtaining the surface shape of the test surface 11a based on the measurement result of the light receiving unit 8. Further, it also has a function as a control unit for controlling the entire measuring apparatus.

  FIG. 3 is a flowchart of processing in the measurement apparatus of this embodiment. A: preprocessing, B: magnification distribution calibration, C: shape measurement, D: analysis, and finally the shape of the test surface is obtained. Each processing procedure will be described below in further detail in a flowchart.

  FIG. 4 summarizes the preprocessing procedure for obtaining the shape of the test surface as a flowchart. As described above, this measuring apparatus is an apparatus for measuring the shape of the sample 11 to be examined using the information of the reference sample 10. Since the reference sample 10 and the test sample 11 are lenses produced based on the same design value, the difference between the reference sample 10 and the test sample 11 is approximately similar to a few microns.

  (A-1) The shape 10a of the reference surface of the reference sample 10 is measured in advance with another high-precision measuring machine. This measuring apparatus is a system for obtaining difference information between the reference sample 10 and the test sample 11 by measuring the shapes of the reference sample 10 and the test sample 11.

  (A-2) Next, when the optical system information of the measuring device and the measurement result of the reference surface 10a obtained by the measurement of (A-1) or the design data of the reference surface are used, the light receiving surface 8a is used. An expected wavefront W is obtained by calculation using, for example, a ray tracing software. If the aberration information of the optical system, the assembly error of the optical system, the detailed error of the optical system, etc. are known in advance, the wavefront at the light receiving surface can be more accurately calculated by including it in the ray tracing. Can be estimated. The wavefront is expressed by, for example, a Zernike coefficient that is an orthogonal function.

  (A-3) Similarly, using the information of the optical system of the measuring device and the measurement result of the reference surface 10a obtained by the measurement of (A-1) or the design data of the reference surface, the reference surface 10a is made with a minute amount of light. A wavefront that is expected to be obtained at the light receiving surface 8a when tilted about the axis is obtained by calculation using, for example, a ray tracing software. The wavefront difference before and after driving is calculated from the wavefront information (A-2) of the reference plane and the wavefront information after driving the reference plane.

  Since this measuring apparatus is configured so as not to irradiate perpendicularly to the test surface, it is reflected at an angle different from the incident light on the test surface. The reflected light does not become substantially parallel light at the light receiving unit, and the reflected wavefront from the surface to be detected is detected as a wavefront greatly deviated from the plane wavefront. Further, the amount of deviation of the reflected wavefront from the test surface from the plane wavefront is not always constant, and varies depending on the measured aspheric shape.

Therefore, even if the reflected wavefront from the test surface is measured by the light receiving unit, the shape of the test surface cannot be obtained as it is. In order to calculate the shape of the test surface from the reflected wavefront from the test surface, two pieces of information on the reflection on the test surface and the position and angle regarding the light reception are necessary.

  FIG. 8 is a diagram for explaining the position and angle of a light beam, and shows the relationship between light beams on a conjugate surface of the light receiving surface and the light receiving surface of a certain light beam. The conjugate surface of the light receiving surface (hereinafter referred to as the sensor conjugate surface) is designed to be close to the reference surface and the test surface.

  The position information is the abscissa relationship between the light receiving surface and the sensor conjugate surface. FIG. 8 shows that the light beam received at the position r from the optical axis is the light beam reflected at the position R from the optical axis by the sensor conjugate plane. The position magnification distribution α is obtained by taking the ratio of the abscissa of the light receiving surface and the sensor conjugate surface (the test surface) and can be expressed as R / r. This position magnification is not constant and has a distribution corresponding to the distance from the optical axis, for example.

(Formula 2)
α = R / r
α: Position magnification distribution R: Ray position on the sensor conjugate surface r: Ray position on the light receiving surface The angle information is the relationship between the light ray angle between the light receiving surface and the sensor conjugate surface. FIG. 8 shows that when the reference surface 10a is tilted by a minute angle, the light ray angle change on the sensor conjugate surface is ΔV, and the light ray angle change on the light receiving surface is Δv. The angle magnification distribution β is obtained by taking the ratio of the light beam angle changes and can be expressed as Δv / ΔV. This angular magnification is not constant and has a distribution corresponding to the distance from the optical axis, for example.

(Formula 3)
β = Δv / ΔV
β: Angular magnification distribution ΔV: Ray angle change on sensor conjugate plane Δv: Ray angle change on light receiving surface (A-4) Coordinate magnification distribution α and angle magnification distribution β are design data of optical system and reference surface Based on the above, it is calculated using ray tracing software. If the aberration information of the optical system, the assembly error of the optical system, the surface shape of the optical system, the transmitted wavefront, etc. are known in advance, calculating with this ray tracing will give a more accurate position magnification distribution. An angular magnification distribution can be calculated.

As described above, the following three are performed as preprocessing.
A-1: Shape measurement result obtained by measuring the reference surface with another measuring device A-2: Calculate the wavefront obtained on the light receiving surface based on the information of the optical system of the measuring device and the reference surface A-3: Of the measuring device Calculate wavefront difference before and after driving a small amount of reference surface based on information on optical system and reference surface A-4: Position magnification distribution and angular magnification distribution based on information on optical system and reference surface of measuring device FIG. 5 is a flowchart showing a procedure for calibrating the magnification distribution necessary for calculating the shape of the test surface on an actual machine.

  If the optical system of the measuring device and its arrangement are as designed, the shape of the surface to be measured can be accurately obtained from the position magnification distribution and angle magnification distribution obtained in A-4. Various errors such as processing error (curvature radius error, polishing residue, homogeneity, thickness error, etc.), lens assembly error (positioning error in the optical axis direction, aberration, etc.), alignment error between the lens and the test surface / light receiving surface There is an error factor and it is not as designed. If these conditions are measured in advance as much as possible and the measurement results are taken into the ray tracing software and the magnification distribution is obtained, the accuracy will be much better than using the design values, but all states will be measured. Is difficult, and a difference in magnification distribution between calculation and actual measurement is inevitably generated.

  In order to calculate the shape of the test surface with high accuracy, it is necessary to calibrate the position magnification distribution and the angle magnification distribution on the actual machine in consideration of the error from the design value. It is characterized in that the distribution is calibrated. The flow of this magnification distribution calibration is different in design data when an error occurs in the optical system due to environmental fluctuations (changes in air pressure, humidity, temperature, etc.) during assembly alignment of this measuring device, resulting in deviation from the design value. It may be performed when measuring the test surface.

  (B-1) The reference lens 10 is installed on the stage 6 of the measuring device.

  (B-2) The light receiving unit 8 measures the wavefront reflected by the reference surface 10a. Since the light receiving unit 8 uses a Shack-Hartmann that combines a microlens array and a sensor, the ray angle distribution at each XY position can be measured, and the wavefront can be obtained from the ray angle distribution. Here, in order to perform alignment of the reference plane, the measured wavefront is compared with the wavefront previously obtained by the calculation of the ray tracing software in the preprocessing (A-2). The stage 6 adjusts the position and tilt of the reference plane in the xy plane perpendicular to the optical axis so that the difference between the tilt component and the coma component of the two becomes as small as possible.

  (B-3) The reference surface 10a after alignment is tilted around the optical axis by a small angle on the stage 6, and the reflected wavefront from the reference surface 10a is measured on the light receiving surface. The minute angle to be tilted here is equal to the angle obtained by the calculation of (A-3).

  (B-4) A measurement wavefront difference before and after driving is calculated from the measurement wavefront (B-2) before driving the reference plane and the measurement wavefront (B-3) after driving the reference plane.

  (B-5) The calculated wavefront difference (A-3) before and after driving and the calculated angular magnification distribution (A-4), which are calculated in the preprocessing in advance, are read.

  (B-6) Based on the measured wavefront difference before and after driving (ΔWm), the calculated wavefront difference before and after driving (ΔWc) calculated in the preprocessing, and the angular magnification calibration distribution β calculated in the preprocessing, Calculate as follows. An example of the angular magnification distribution is shown in FIG. The angle magnification distribution β obtained by calculation is represented by a dotted line, and the angle magnification distribution β ′ after calibration using Equation 4 is represented by a solid line, corresponding to the distance r from the optical axis on the light receiving surface, It shows that the following proportionality factor can be determined.

(Formula 4)
β ′ = β * ΔWm / ΔWc
β ′: Calibration angle magnification distribution β: Calculated angle magnification distribution ΔWm: Measurement wavefront difference ΔWc: Calculation wavefront difference In the present embodiment, the case where a minute amount is inclined to the optical axis center has been described. You may incline in two or more directions, such as 2 directions, and carry out parallel shift in the surface of an XY direction. It is important to obtain the difference between before and after driving. However, the calculated wavefront difference before and after driving in the preprocessing and the measured wavefront difference before and after driving during calibration need to be performed under the same driving conditions.

  In order to obtain the measurement wavefront before and after driving, the reference plane is driven by the stage. Therefore, in order to increase the calibration accuracy, the stage accuracy is not as good as possible. However, in actual calibration, even if there is a drive error, it is only necessary to be able to read the position accurately, and there is no significant problem in realization from the viewpoint of stage performance. For example, it is instructed to tilt by 0.5 degrees, and even if it is actually tilted by 0.5 + 0.001 degrees, if it is actually tilted by 0.501 degrees, it is sufficient to calculate under that condition, that is, calculation and measurement It is important to have the same conditions.

  In this way, by calibrating the angular magnification distribution obtained by calculation based on the relationship between measurement and calculation, it is possible to obtain a magnification distribution that is more optimized for the actual machine considering various errors on the actual machine. Can do.

  Next, C: shape measurement will be described with reference to FIG.

  (C-1) The reference lens 10 is installed on the stage 6, and the reflected wavefront from the reference lens 10 is measured by the light receiving unit. The light receiving unit uses a Shack-Hartmann sensor, and a light ray angle distribution of reflected light can be obtained. The wavefront distribution is obtained by integrating the ray angle distribution.

  When measuring the reference surface, as in (B-2), alignment of the reference surface is performed such that the tilt and shift of the stage 6 are adjusted so that the difference between the measured wavefront and the calculated wavefront is equal to or less than the threshold value. The wavefront is measured after the alignment of the reference plane. The measured wavefront information of the reference plane is stored in the processing unit.

(C-2)
Next, the reference lens 10 is retracted, and the test lens 11 is placed on the stage 6. Since it is necessary to match the reference surface and the test surface as much as possible, the position in the optical axis direction is measured in advance and the test surface is arranged at the same position before retracting the reference lens. The position in the optical axis direction may be measured using another sensor such as a length measuring device or a displacement sensor.

  Similarly to (C-1), tilt and shift alignment of the surface to be inspected is also performed, and the wavefront is measured after the alignment of the surface to be inspected. The measured wavefront information of the test surface is also stored in the sled portion as in (C-1).

  Next, the D analysis flow will be described with reference to FIG. In the shape measurement of FIG. 3C, the reference surface 10a and the test surface 11a are measured, and the ray angle distribution of the reflected light is obtained.

  (D-1) In the shape measurement of FIG. 3C, the light beam angle distribution of the reflected light obtained by measuring the reference surface 10a and the test surface 11a is obtained.

(D-2) With respect to the measured light angle distribution V ₁₀ · V ₁₁ of the reference surface 10a and the test surface 11a in (D-1), the light angle distribution v ₁₀ · v ₁₁ is calculated. As the angular magnification distribution used in Equation 5, the magnification distribution calibrated by the procedure described with reference to FIGS. 4B and 5 is used. In addition, the principal ray angle distribution η in Expression 5 indicates the incident ray angle to the reference plane of the light beam whose reflected light on the reference plane is parallel to the optical axis on the detection plane. This is obtained by calculation using ray tracing software or the like using the information of the optical system of the measuring apparatus and the design data of the reference surface, as in the case of the A pretreatment.

(Formula 5)
v = V / β + η
V: Measured ray angle distribution (V ₁₀ : Reference plane V ₁₁ : Test surface)
v: Ray angle distribution on the conjugate plane of the detection plane on the reference plane or the test plane
_{(V 10:} reference plane v _11: test surface)
β: Angular magnification distribution η: Angular distribution of principal ray Next, with respect to the ray coordinate distribution R of the light receiving surface 8a, the ray coordinate distribution r on the sensor conjugate plane is obtained by Equation 6. The light beam coordinate distribution on the light receiving surface is obtained by expressing individual center positions of the microlens array as CCD coordinates (x, y) when using a Shack-Hartmann sensor as the light receiving unit,

It becomes.

(Formula 6)
r = α × R
R: Ray coordinate distribution on the light receiving surface 8a r: Ray coordinate distribution on the sensor conjugate plane α: Position magnification distribution (D-3) The sensor conjugate plane is determined by the configuration of the optical system. It is a system that can measure multiple reference planes with an optical system. For this reason, the sensor conjugate plane and the reference plane do not ideally match. Therefore, corresponding points on the reference plane are obtained by ray tracing calculation with respect to the ray angle distributions v ₁₀ · v ₁₁ and the ray coordinate distribution r on the sensor conjugate plane obtained by (D-2). As shown in Equation 7, a difference Δs in the surface inclination (slope) between the light ray angle distribution v ₁₀ on the reference surface and the light ray angle distribution v ₁₁ on the test surface is calculated.

(Formula 7)
Δs = tan (v ₁₁ ) −tan (v ₁₀ )
(D-4) The difference Δs in the surface inclination is a differential value of the difference in surface shape between the reference surface 10a and the test surface 11a. Therefore, Δs needs to be integrated in order to obtain the surface shape difference. There are various integration methods such as fitting using a differential function of a basis function and a method of adding a difference in surface inclination as needed.

  By integrating, a difference in surface shape between the reference surface 10a and the test surface 11a is obtained, and finally by adding information of the reference surface measured in advance in (A-1) to this value, The shape of the test surface 11a can be obtained.

  By performing the above flow and calibrating the angle magnification distribution obtained by calculation from the relationship between measurement and calculation, the magnification distribution is optimized for the actual machine considering various errors on the actual machine. Can be requested. Even when there are various errors on the actual machine, the shape of the surface to be measured can be measured in a non-contact manner at high speed and with high accuracy.

  Finally, a lens having a desired shape close to the design value is created by measurement and processing. Therefore, the difference between the shape of the test surface measured using the method of the present embodiment and the design shape is calculated, the correction processing amount and the positional relationship (abscissa) are obtained, and the correction processing is performed using a processing machine. It is good to do. When a desired shape cannot be obtained at one time, the lens shape desired to be finally produced can be obtained by repeating measurement + correction processing a plurality of times.

  In the present embodiment, the sample to be examined is described as being a lens, but it may be other than a lens, or may be an optical element such as a mirror having the same shape as the lens, a mold, or the like.

(Example 2)
In the first embodiment, the sensor conjugate plane is assumed to be at the same position as the design value even if there is a manufacturing error in the optical system, and the angular magnification distribution is calibrated using the measured value, and the calibrated angular magnification distribution is used to increase the height. A technique for obtaining the shape of the test surface with high accuracy is disclosed.

  In the second embodiment, when an optical system has a large manufacturing error and the designed sensor conjugate surface is different from the actual sensor conjugate surface, in addition to calibrating the angular magnification distribution using the measured value. The magnification calibration method for calibrating the position magnification distribution is also disclosed.

  In a little more explanation, in order to obtain the shape of the test surface with high accuracy, it is desirable to place and measure the sample at substantially the same position as the sensor conjugate surface. Therefore, if the sensor conjugate plane in the design is different from the actual sensor conjugate plane, not only the position magnification distribution / angle magnification distribution is calibrated, but the actual sensor conjugate plane position is obtained and the sample is taken at that position. It is necessary to arrange and measure.

  The configuration of the apparatus is the same as that of FIG. 1 disclosed in the first embodiment, and refer to the first embodiment except for magnification calibration. A magnification calibration method that is a feature of the second embodiment will be described below with reference to FIGS. 10 is an overview of the second embodiment, FIG. 11 is a flowchart of the second embodiment, FIG. 12 is a magnification calibration in the second embodiment, and FIG. 13 is a diagram explaining calculation of a conjugate plane.

  In the first embodiment, in order to calibrate the angular magnification distribution, the reference plane as shown in FIG. 8 is tilted by a minute angle, and the wavefront before and after the tilt is measured.

  In the second embodiment, the sensor conjugate plane is also searched. Therefore, as shown in FIG. 10, the reference plane is driven in the optical axis direction (Z direction), and the reference plane is tilted by a small angle at a plurality of positions. The difference is that the wavefront is measured. FIG. 10 shows an example in which measurement is performed by arranging samples at four different locations in the optical axis direction.

  In addition, two samples are used for the magnification calibration in the second embodiment, and one is a reference surface 10a that is the same as that of the first embodiment and a test surface 11a that is created with the same design value as the reference surface 10a. The difference between the reference surface 10a and the test surface 11a preferably has a shape difference with a relatively high frequency of, for example, Z36 or more. In the second embodiment, since these two samples are used for magnification calibration, it is usually only necessary to obtain measurement data from another apparatus for the reference surface 10a, but both the reference surface 10a and the test surface 11a are used. It is necessary to acquire measurement data in another device.

  The procedure for calibrating the magnification using these two samples will be described with reference to the flow of FIG.

  (B-1) In order to measure the reference surface 10a, the reference sample 10 is placed on the stage 6 of the measuring device.

  (B-2) The light receiving unit 8 measures the wavefront reflected by the reference surface 10a. Since the light receiving unit 8 uses a Shack-Hartmann that combines a microlens array and a sensor, the ray angle distribution at each XY position can be measured, and the wavefront can be obtained from the ray angle distribution. Here, in order to perform alignment of the reference plane, the measured wavefront is compared with the wavefront previously obtained by the calculation of the ray tracing software in the preprocessing (A-2). Alignment for adjusting the position and tilt of the reference plane in the xy plane perpendicular to the optical axis is performed on the stage 6 so that the difference between the tilt component and the coma component of the two becomes as small as possible.

(B-3 / B-4)
First, the reference surface 10a after alignment is measured. Next, the stage 6 is tilted about the optical axis by a minute angle, and the reflected wavefront from the reference surface 10a is measured on the light receiving surface. The minute angle to be tilted here is equal to the angle obtained by the calculation of (A-3). A measurement wavefront before and after a small angle tilt at a certain position is obtained.

  Next, the reference plane 10a is moved in the optical axis direction (z direction) by the stage 6, and similarly, the reference plane is tilted about the optical axis by a minute angle, and the reflected wavefront from the reference plane before and after tilting is measured. Similarly, the reference surface is moved n times in the optical axis direction (z direction), and the operation of inclining the reference surface about the optical axis by a minute angle at each reference surface measurement position is repeated, and the minute angle tilt at the n reference surface positions is repeated. Get front and back measurement wavefronts.

  (B-5) The magnification distribution is calibrated from the measured wavefronts before and after the small angle tilt at the n reference plane positions obtained in (B-4).

  When the sample position is determined, the measurement wavefronts before and after the minute angle tilt of the reference plane are obtained, so that the angular magnification distribution can be calibrated at the respective sample positions by the same method as in the first embodiment. Specifically, based on the measured wavefront difference before and after driving (ΔWm), the calculated wavefront difference before and after driving (ΔWc) calculated in the preprocessing, and the angular magnification calibration distribution β calculated in the preprocessing, 4 is calculated. Here, regarding the “computed wavefront difference before and after driving (ΔWc) calculated in the preprocessing”, the calculated wavefront also changes depending on the sample position. Therefore, in the preprocessing, a plurality of calculated wavefronts corresponding to each sample position are calculated in advance. It is necessary to keep it.

  An example of the angular magnification distribution is shown in FIG. The angle magnification distribution β obtained by calculation is represented by a dotted line, and the angle magnification distribution β ′ after calibration using Equation 7 is represented by a solid line, corresponding to the distance r from the optical axis on the light receiving surface, It shows that the following proportionality factor can be determined.

(Formula 7)
β ′ = β * ΔWm / ΔWc
β ′: calibration angle magnification distribution at each sample position β: calculated angle magnification distribution at each sample position ΔWm: measured wavefront difference at each sample position ΔWc: computed wavefront difference at each sample position Error in the assembled optical system Therefore, if there is an actual sensor conjugate plane at a position different from the designed sensor conjugate plane, it is considered that the magnification on the paraxial axis of the optical system is also shifted. That is, the position magnification at r = 0 (on the optical axis) is also different. In the correct sensor conjugate plane, the fact that the angular magnification of r = 0 (on the optical axis) is substantially equal to the positional magnification of r = 0 (on the optical axis), and the calibration of the position magnification distribution uses the following equation (8). Do it. By the above procedure, the calibration angle magnification distribution and the calibration position magnification distribution at each sample position can be obtained.

  It is desirable to place the sample at approximately the same position as the sensor conjugate plane for measurement because the error is minimized. Therefore, if the magnification distribution is calibrated from the data measured by placing the sample at a position different from the correct sensor conjugate plane, an error is also included in the corrected magnification distribution, so an accurate shape is calculated after all. Can not. It can be said that the position of the sample from which the calibration magnification distribution capable of calculating the shape most accurately is obtained is closest to the correct sensor conjugate plane.

(Formula 8)
α ′ = α + (β ′ (r = 0) −α (r = 0))
α ′: calibration position magnification distribution α: calculated position magnification distribution β ′ (r = 0): calibration angle magnification on the optical axis α (r = 0): calculated position magnification on the optical axis (B-6) Since the measuring device is a system that measures the difference between two samples, another sample (test sample 11) is required to calculate the shape. In order to measure the test surface 11a, the test sample 11 is placed on the stage 6 of the measuring device.

  (B-7) The light receiving unit 8 measures the wavefront reflected by the test surface 11a. Since the light receiving unit 8 uses a Shack-Hartmann that combines a microlens array and a sensor, the ray angle distribution at each XY position can be measured, and the wavefront can be obtained from the ray angle distribution. Here, in order to perform alignment of the test surface, the measured wavefront is compared with the wavefront previously obtained by the calculation of the ray tracing software in the preprocessing (A-2). The position and inclination of the test surface in the xy plane perpendicular to the optical axis are adjusted by the stage 6 so that the difference between the tilt component and the coma component of the two becomes as small as possible.

  (B-8 / B-9) First, on the light receiving surface, the reflected wavefront from the test surface 11a after alignment is measured. Next, the test surface 10a is moved n times in the optical axis direction (z direction) on the stage 6, and the reflected wavefront from the test surface is measured at each sample position. The sample position here is the same position as the measurement (B-3 / B-4) of the reference plane 10a. It is desirable to measure at least three sample positions.

  (B-10) According to the above procedure, the measurement wavefront data, the calibration angle magnification distribution, and the calibration position magnification distribution of the reference surface 10a and the test surface 11a are obtained at a plurality of sample positions. Using the shape data of the reference surface being measured, the shape of the test surface at each sample position is recovered.

  The shape of the test surface 11a is measured in advance by another measuring device. A difference between the shape of the test surface calculated based on the measurement result and the test surface shape data in the preprocessing is a shape recovery error. FIG. 13 is a plot of the relationship between the shape recovery error and the position z on the optical axis of the sample. It can be confirmed that the shape recovery error changes for each sample position. From FIG. 13, the position on the optical axis of the sample with the smallest shape recovery error is obtained using fitting or the like. The position on the optical axis of the sample obtained here is closest to the sensor conjugate plane, and the calibration angle magnification and calibration position magnification obtained by placing the sample at that position and measuring are the calibration values of the magnification. It becomes.

  It is desirable to place the sample at approximately the same position as the sensor conjugate plane for measurement because the error is minimized. For this reason, if the magnification distribution is calibrated from data measured by placing a sample at a position that is not the correct sensor conjugate plane, an accurate shape cannot be calculated after all because the magnification distribution after calibration contains errors. . It can be said that the sample position on the optical axis at which the calibration magnification distribution capable of calculating the shape most accurately is obtained is close to the most correct sensor conjugate plane.

  Here, the position at which the shape recovery error, which is the difference between the shape obtained from the measurement and the actual shape, becomes the smallest, is set as the position of the sensor conjugate surface. As an example of another method, the shape difference before and after the tilt is calculated at multiple sample positions by calculation, and compared with the shape difference before and after the tilt obtained by measurement at multiple sample positions. A small position may be the position of the sensor conjugate plane.

  In this way, from the measurement results of the reference surface and the test surface at a plurality of sample positions, a plurality of calibration position magnifications and calibration angle magnifications are obtained, and a minimum value of error when calculating the shape is obtained. A surface can also be obtained. Accordingly, it is possible to calculate an optimum conjugate position in consideration of a change due to an error of the optical system, and to obtain an optimum angular magnification distribution and position magnification distribution at the optimum conjugate position.

  Since the optimum conjugate position has been obtained as described above, the stage 6 is moved to the optimum conjugate position obtained by the above-described method before the next step of shape measurement in FIG. Get the measurement data of the surface / test surface.

(Example 3)
The third embodiment is a measurement device that measures the shape of the concave surface, and is a system that can obtain the shape of the test sample 11 using the information of the reference sample 10 as in the first and second embodiments. ing. FIG. 13 is a diagram showing the configuration of a surface shape measuring apparatus that performs the method of the present invention. By using the configuration of FIG. 13 and using the methods of the first and second embodiments, the shape of the test surface 11a can be measured. Here, 10 ′ is a reference lens, one surface 10a ′ is a reference surface, 11 ′ is a test lens, one surface 11a ′ is a test surface, and the others are the same as in FIG.

  As in the first and second embodiments, the test lens 11 ′ is arranged at a position where the center of curvature of the diverging light from the lens 5 substantially matches the center of curvature of the paraxial region on the test surface 11 a ′. Further, the four flows of A preprocessing, B magnification distribution calculation, C shape measurement, and D analysis of the third embodiment are the same as those of the first and second embodiments.

1 light source, 2 condenser lens, 3 pinhole, 4 half mirror, 5 lens,
6 stage, 7 lens, 8 light receiving part, 8a light receiving surface, 9 processing part,
10 reference lens, 10a reference surface, 11 test lens, 11a test surface

Claims (12)

A measuring device for measuring the surface shape of the test surface by irradiating the test surface with light through an optical system and receiving the light by a light receiving unit having a light receiving surface that receives reflected light from the test surface. In
Calculating a position magnification distribution and an angle magnification distribution in a conjugate plane with respect to the light receiving surface;
Measuring a wavefront of light reflected by a reference surface having a known surface shape by the light receiving unit;
Measuring the wavefront of the light reflected by the test surface with the light receiving unit;
Calculating the surface shape of the test surface from the difference information of the two measurement wavefronts;
A surface shape measuring method including:
Calculating a wavefront on the light receiving surface of light reflected by the reference surface using a design value of the optical system;
Calculating a wavefront change before and after driving a known amount of the reference surface;
Measuring a wavefront change before and after driving a known amount of the reference surface;
Calibrating the angular magnification distribution from a wavefront change before and after driving a known amount determined by the calculation and measurement;
Calculating the surface shape of the test surface using the known reference surface shape, the measurement value of the reference surface, the measurement value of the test surface, and the calibrated angular magnification;
A surface shape measurement method comprising: A measuring device for measuring the surface shape of the test surface by irradiating the test surface with light through an optical system and receiving the light by a light receiving unit having a light receiving surface that receives reflected light from the test surface. In
Calculating a position magnification distribution and an angle magnification distribution in a conjugate plane with respect to the light receiving surface;
Measuring a wavefront of light reflected by a reference surface having a known surface shape by the light receiving unit;
Measuring the wavefront of light reflected by a test surface having a known surface shape by the light receiving unit;
Calculating the surface shape of the test surface from the difference information of the two measurement wavefronts;
A surface shape measuring method including:
Calculating a wavefront on the light receiving surface of light reflected by the reference surface using a design value of the optical system;
Calculating a wavefront change before and after driving a known amount of the reference surface;
Measuring a wavefront change before and after driving a known amount of the reference surface;
Calibrating the angular magnification distribution and the position magnification distribution from wavefront changes before and after driving a known amount obtained by the calculation and measurement;
Using the known reference surface shape, the measurement value of the reference surface, the measurement value of the test surface, the calibrated angle magnification, and the calibrated position magnification, the surface shape of the test surface A step of calculating
A surface shape measurement method comprising:   The surface shape measurement method according to claim 2, wherein the position magnification distribution is calibrated based on the angle magnification distribution.   The step of measuring the wavefront change before and after driving the reference surface by a known amount includes a measurement step at a plurality of positions in the optical axis direction, and calculating a conjugate position from the measurement result. Surface shape measurement method. Measuring the test surface at a plurality of positions in the optical axis direction;
The known reference surface shape, the measurement value of the reference surface at the plurality of positions, the measurement value of the test surface at the plurality of positions, the angle magnification calibrated for each of the plurality of positions, and the plurality of positions. Using the calibrated position magnification, and calculating the surface shape of the test surface,
5. The surface shape measuring method according to claim 4, wherein the conjugate position is calculated from a difference between the shape of the reference surface and the surface shape obtained by the calculation.   6. The surface shape measurement method according to claim 4, wherein the measurement step at a plurality of positions in the optical axis direction is measurement at at least three or more positions.   The surface shape measurement according to any one of claims 4 to 6, wherein in the step of measuring at a plurality of positions having different positions in the optical axis direction, the measurement positions of the reference surface and the test surface are the same. Method.   3. The surface shape measurement according to claim 1, wherein the change amount of the reference surface before and after driving is a change amount of the reference surface before and after tilting or a change amount of the reference surface before and after shifting. Method.   The surface shape measurement method according to claim 1, wherein the surface shape to be measured is a spherical surface or an aspherical surface.   The surface shape measuring method according to claim 1, wherein the detection unit is a Shack-Hartmann sensor, a Hartmann, a shearing interferometer, or a Talbot interferometer.   A surface shape measuring apparatus using the surface shape measuring method according to claim 1.   An optical element produced by using the surface shape measuring method according to claim 1 or the surface shape measuring apparatus according to claim 11.