JPH07234173A - Interference measuring instrument and method - Google Patents

Abstract

PURPOSE:To maintain a high measurement accuracy even if a setting error exists between an interferometer and an object to be measured by compensating the measurement value of the object to be measured based on the amount of compensation of aberration obtained while a setting error is given to a reference object to be measured. CONSTITUTION:While a setting error is given to the relative position of a reference object 80 to be measured for an interferometer 1a, a reference light reflected on a reference surface 71 of a primary standard lens 7 and a light to be inspected which is reflected on a reference spherical surface 810 are overlapped to obtain interference fringes. The interference fringes are subjected to fringe analysis and wave front aberration is expanded to an approximation polynomial and at the same time the amount of compensation of aberration is obtained and is stored at a memory 15 exclusively for data. Then, the wave front aberration is expanded to an approximate polynomial by analyzing interference fringes obtained by measuring the surface of an optical element such as a lens and an object to be inspected such as a mold and then aberration terms are compensated based on the amount of compensation obtained previously to obtain the shape of the surface to be inspected, thus accurately measuring the spherical surface shape of the object to be inspected without performing an accurate alignment even if there are setting errors such as defocusing and tilting.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interference measuring device and an interference measuring method.

[0002]

2. Description of the Related Art There are many known measuring methods and measuring devices for measuring surface shapes of various optical systems such as optical elements using an interferometer. For example, it is limited by the accuracy of the reference lens or reference surface installed in the interferometer.

As a method of removing the aberration of the interferometer itself, a spherical surface measuring method proposed by Browning et al.
An interferometer device and the like described in Japanese Patent No. 129707 are known.

In the measuring method proposed by Browning et al., An object to be measured (object to be measured) is moved to perform measurement under three conditions, and an inherent aberration of the interferometer is removed by arithmetic processing. Further, the above-mentioned JP-A-62-1
In the interferometer device described in Japanese Patent No. 29707, the prototype surface is rotated to perform measurement at several points, and this is subtracted from the measured value as correction data to remove the internal aberration of the interferometer.

However, in both the measuring method proposed by Browning et al. And the interferometer device described in Japanese Patent Laid-Open No. 62-129707,
Correcting aberrations newly generated due to the setting state of the test object, for example, when a condenser lens that does not satisfy the sine condition is used as a reference lens, It is difficult to correct the newly generated aberration.

For this reason, when the object to be inspected is installed on the interferometer, the object to be inspected is set at a predetermined position and at a predetermined angle so that aberration due to setting error of the object does not occur. Must be placed exactly. In particular, the surface where the test object is bright,
Or in the case of a bright lens, there is a great need.

[0007] Therefore, there is a problem in that the workability is poor and a highly accurate alignment device is required because alignment must be performed carefully when the object to be inspected is installed in the interferometer.

Moreover, even if the placement of the object to be inspected is carefully set using a high-accuracy alignment device, the setting error (eg, defocus or tilt) of the object to be inspected cannot be completely reduced to zero. Have difficulty. In this way, due to the existence of the setting error of the object to be inspected, high-order aberrations such as spherical aberration and coma are generated, which lowers the measurement accuracy.

NA ₀ of the condenser lens of the interferometer described above.
When the value of (numerical aperture) is large, that is, when a bright lens is used, there is a problem that the measurement accuracy is greatly reduced due to the setting error of the test object.

[0010]

SUMMARY OF THE INVENTION It is an object of the present invention to provide an interference measuring device and an interference measuring method which can obtain high measurement accuracy regardless of the setting error between the interferometer and the object to be measured.

[0011]

The above object is achieved by the present invention described in (1) to (24) below.

(1) The light from the light source is divided into two, one is used as the reference light from the reference surface, and the other is used as the test light from the test object, and the reference light and the test light are superposed. An interference measurement device that obtains an interference fringe in combination and detects a phase difference between the reference light and the test light based on the interference fringe, wherein the interference fringe is an approximation that specifies the phase difference. First means for developing into a polynomial and obtaining a value corresponding to the coefficient of each term of the approximate polynomial on the basis of the numerical aperture of the effective light flux that enters the test area or exits from the test area; In a state where a setting error is given to the relative position of the object with respect to the interference measuring device, the setting error amount is changed to perform the interference measurement at least twice, and the measurement of the reference object is obtained by the first means. Second means for obtaining the correction amount of aberration based on the value, and the object to be inspected In the interferometric measurement, the interferometer according to claim 3, further comprising: third means for correcting the measured value of the object obtained by the first means based on the correction amount.

(2) The interference measuring apparatus according to the above (1), wherein the approximate polynomial is the equation (1) shown in the following Expression 6.

[0014]

[Equation 6]

(3) The interference measuring apparatus according to (1) or (2), wherein the interference measuring apparatus has a condensing optical member in the optical path of the test light.

(4) The setting error is given at least in the optical axis direction of the condensing optical member, and the measured value to be corrected is a coefficient of an even-order term of 4th order or more in the approximation polynomial. The interferometer according to 3).

(5) The correction amount is 4 in the approximation polynomial using the coefficient W ₂₀ of the quadratic term of the approximation polynomial.
The interferometer according to (4) above, wherein the coefficient of an even-order term equal to or higher than the order is represented by a linear function.

(6) The third means is to correct the coefficient W _n0 'of the even-order term of the approximate polynomial in the object to be _measured by the equation (13) shown in the following equation (5). ).

[0019]

[Equation 7]

(7) The setting error is given at least in a direction perpendicular to the optical axis of the condensing optical member, and the measured value to be corrected is a coefficient of an odd-order term of third order or more in the approximate polynomial. The interference measurement device according to (3) above.

(8) The correction amount is obtained by using the coefficients W ₁₁ and W ₁₂ of the first-order term of the approximation polynomial to represent the coefficients of the third-order or higher odd-order terms in the approximation polynomial by a linear function. The interference measurement apparatus according to (7) above.

(9) The third means corrects the coefficient W _nm ′ of the odd-order term of the approximate polynomial in the object to be measured by the equation (25) shown in the following equation (8). ).

[0023]

[Equation 8]

(10) The interference measuring apparatus according to any one of (1) to (5), (7), and (8) above, wherein the reference test object is a test object.

(11) The light from the light source is divided into two, one is used as the reference light from the reference surface, and the other is used as the test light from the test object, and the reference light and the test light are overlapped. Along with obtaining interference fringes together, an interference measurement method for detecting a phase difference between the reference light and the test light based on the interference fringes, the relative position of the reference test object with respect to the interference measurement device. In the state where the setting error is given to, the setting error amount is changed and the interference measurement is performed at least twice to obtain a plurality of interference fringes, and the interference fringes are expanded into an approximate polynomial for specifying the phase difference, Based on the numerical aperture of the effective light flux incident on the inspection region or emitted from the inspection region, the value corresponding to the coefficient of each term of the approximate polynomial is obtained, based on the measured value of the reference object, the aberration Obtain the correction amount, and based on the correction amount in the interferometric measurement of the test object. And an interferometric measuring method, characterized in that the measured value of the test object is corrected.

(12) The interference measuring method according to (11), wherein the test light is passed through a condensing optical member.

(13) The setting error is given at least in the optical axis direction of the condensing optical member, and the measured value to be corrected is a coefficient of an even-order term of 4th order or more in the approximation polynomial. The interference measurement method according to 12).

(14) The correction amount is obtained by using a coefficient W ₂₀ of a quadratic term of the approximate polynomial to represent a coefficient of an even-order term of 4th order or higher in the approximate polynomial as a linear function. Interference measuring method described in ().

(15) The coefficient W _n0 'of the even-order term of the approximate polynomial in the test object is shown in the following _Expression 9 (1
The interference measurement method according to (14) above, which is corrected by the equation (3).

[0030]

[Equation 9]

(16) The setting error is given at least in the direction perpendicular to the optical axis of the condensing optical member, and the corrected measured value is a coefficient of an odd-order term of third order or more in the approximate polynomial. The interference measurement method according to (12) above.

(17) The correction amount is obtained by using the coefficients W ₁₁ and W ₁₂ of the first-order term of the approximation polynomial to represent the coefficients of odd-order terms of the third or higher order in the approximation polynomial by a linear function. The interference measurement method according to (16) above.

(18) The interference measuring method according to the above (17), wherein the coefficient W _nm 'of the odd-order term of the approximate polynomial in the test object is corrected by the equation (25) shown in the following Expression 10.

[0034]

[Equation 10]

(19) The above items (11) to (14), (16), (1) using an object as the reference object.
The interference measurement method according to any one of 7).

(20) The light from the light source is divided into two, one of which is reflected by the reference surface as a reference light, and the other of which is converged light or divergent light by an optical member and made incident on the surface to be inspected. As the test light reflected on the inspection surface, while obtaining the interference fringes by superimposing the reference light and the test light, the phase difference between the reference light and the test light based on the interference fringes. In the interference measurement device for detecting, the interference fringes, expanded into an approximate polynomial for specifying the phase difference, based on the numerical aperture of the effective light flux incident on the test area or exiting from the test area, A first means for obtaining a value corresponding to the coefficient of each term of the approximate polynomial and a setting error in the relative position of the reference surface to be measured with respect to the interference measuring device are changed at least twice by changing the setting error amount. Before performing the interferometric measurement of Second means for obtaining a correction amount of aberration based on the measured value of the reference test surface, and in the interferometric measurement of the test surface, the test value obtained by the first means based on the correction value. And a third means for correcting the measurement value of the surface.

(21) The interference measuring apparatus according to (20), wherein the optical member is a standard lens having the reference surface.

(22) The interference measuring apparatus according to the above (20), wherein the optical member is a lens having a positive power.

(23) The interference measuring apparatus according to the above (20), wherein the optical member is a lens having negative power.

(24) The light from the light source is divided into two, one of which is used as a reference light, and the other of which is transmitted as an inspection light by passing through an object having a function of converging or diverging a light beam. An interference measuring device for detecting the phase difference between the reference light and the test light based on the interference fringe, while obtaining an interference fringe by superimposing the test light and the test light on each other. A value corresponding to the coefficient of each term of the approximate polynomial is developed based on the numerical aperture of the effective light flux that enters into the test area or exits from the test area. (1) and at least two times the interference measurement is performed by changing the setting error amount in the state where the setting error is given to the relative position of the reference test object having the action of converging or diverging the light beam. , Obtained by the first means Second means for obtaining a correction amount of aberration based on the measured value of the reference test object, and interference measurement of the test object having the action of converging or diverging a light beam, the first means based on the correction amount. And a third means for correcting the measured value of the test object obtained by the means.

[0041]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The interference measuring apparatus and the interference measuring method of the present invention will be described below in detail with reference to the embodiments shown in the accompanying drawings. 1 and 2 show an example of measuring the surface shape,
FIG. 1 is a diagram schematically showing a first embodiment of an interference measuring apparatus of the present invention in which a reference object is installed for obtaining a correction amount and an interference measuring apparatus of the present invention in which an object is installed.

As shown in FIG. 1, the interference measuring device 1a is
A Fizeau interferometer (hereinafter referred to as an interferometer) 2a, an image pickup unit 11 which is an interference fringe detection unit, an image processing device 12 including an A / D converter and an image memory, and an arithmetic unit 13.
2, a monitor device 14, and a data-only memory (hereinafter referred to as a memory) 15 that is a storage unit.

The interferometer 2a in the interferometer 1a is
The light source 3, the objective lens 4, the collimator lens 5, the half mirror 6, the standard lens 7 also serving as a condensing optical member and a reference member, and the standard lens 7 are moved with respect to the optical axis 73 with high precision to cause interference fringes. Driving means 711 such as PZT for performing a phase shift method, which is a known method of quantifying the above, a reference object 80 also serving as a reflecting member, a reference object 80 and an object also serving as a reflecting member described later. It has a moving means 9 for positioning 8 in the optical axis 73 direction of the prototype lens 7 and a direction perpendicular to the optical axis 73, an adjustment amount control means 43, and an observation lens 10. In the interference measuring apparatus 1a having such a configuration, as shown in FIG.
An x-y-z coordinate system having the optical axis 73 of z as the z axis is assumed.

Here, the final surface of the prototype lens 7, that is, the surface of the prototype lens 7 facing the reference object 80 is
It constitutes the reference surface 71. The reference surface 71 is formed into a concave curved surface having a predetermined center of curvature, and is configured to reflect a part of incident light and allow a part of the incident light to pass through. Further, the center of curvature of the reference surface 71 is defined by the standard lens 7
It coincides with the condensing point 75 of the light transmitted through.

In general, an aplanatic lens that substantially satisfies the sine condition and has substantially no spherical aberration is used as the prototype lens. When the sine condition is satisfied, f · sin θ = h holds.

In this case, as shown in FIG. 1, h is an arbitrary height of incident light on the standard lens 7 (hereinafter referred to as incident height), and f is a focal length of the standard lens 7. . In addition, as shown in FIG. 1, θ is an angle (hereinafter, referred to as an angle between the light beam 16 incident from the reference surface 71 of the light ray incident on the standard lens 7 at the incident height h and the optical axis 73 of the standard lens 7). , Collection angle).

The reference object 80 is installed to create a correction amount described later, and has a predetermined curvature center 85.
A concave reference spherical surface (reference test surface) 810 having 0 is provided. The reference spherical surface 810 is configured to be able to reflect at least a part of the emitted light. As the reference object 80, the reference spherical surface 810 is the prototype lens 7
The size used is such that it can cover the entire range of the luminous flux from. The reference spherical surface is a spherical surface that has been processed to have good surface accuracy. In this case, the radius of curvature of the reference spherical surface is not particularly limited and may be different from the radius of curvature of the object 8 to be described later.

As shown in FIG. 2, the surface of the object 8 facing the prototype lens 7, that is, the surface 81 to be inspected is formed into a concave curved surface having a predetermined center of curvature 85, and the irradiated light is irradiated. Is configured to be capable of reflecting at least a part of.

The moving means 9 includes a base for fixing the reference object 80 and the object 8 and a reference spherical surface 810.
And means for moving the base in the optical axis 73 direction (z direction) of the prototype lens 7 and in the directions (x direction, y direction) perpendicular to the optical axis 73 for aligning the test surface 81, respectively. (Not shown). The adjustment amount control means 43 is used for the reference object 8 by the moving means 9.
This is for controlling the adjustment amounts of 0 and the test object 8, respectively.

The image pickup section 11 in the interference measuring apparatus 1a is
For example, the solid-state image sensor (CCD) 17 and the CCD 17
And a drive circuit (not shown) for driving the. The observation lens 10 has a reference spherical surface 81 at an appropriate magnification.
The images of 0 and the surface 81 to be inspected are respectively formed on the observation surface.

Computing means 13 in the interference measuring device 1a
Is for analyzing interference fringes described later based on digital data (digital signal) obtained by the image processing device 12, obtaining a correction amount, and performing a predetermined calculation process in aberration correction or the like. , A microcomputer.

In this case, the calculating means 13 develops the interference fringes into an approximate polynomial that specifies the phase difference (optical path difference) between the reference light and the test light, as will be described later, and places it in the test area. Numerical aperture of an effective light beam emitted from the incident or test region (in the present embodiment, in the interferometric measurement of the reference spherical surface 810, the effective light beam incident on or emitted from the test region of the reference spherical surface 810 is measured). In the interferometric measurement of the numerical aperture and the surface to be inspected 81, the coefficient of each term of this approximate polynomial is determined based on the effective numerical aperture of the light beam which is incident on or is emitted from the area to be inspected of the surface to be inspected 81. A first means for obtaining a corresponding value,
The interference measurement is performed in the state where a setting error is given to the relative position of the reference object 80 with respect to the interference measuring apparatus 1a, and the first measurement is performed.
Second means for obtaining a correction amount of aberration based on the measured value of the reference object 80 to be obtained by the means, and the first means based on the correction amount in the interference measurement of the object 8 to be measured. The third means for correcting the measured value of the test object 8 obtained by

The term "effective luminous flux" as used herein means that in the interferometric measurement of the reference object (reference object surface), it covers the entire area of the reference object object (reference object surface), and , Refers to a light beam that can interfere with the reference light, and in the interference measurement of the test object (test surface), can cover the entire test region of the test object (test surface) and can interfere with the reference light. Refers to the luminous flux. When the test object has a predetermined test surface as in the present embodiment, the phase difference between the reference light and the test light corresponds to the shape of the test surface.

Next, the interference measuring method of the present invention will be described. The interference measuring method of the present invention uses the above-described interference measuring device 1a shown in FIG. 1 to set an error in the reference object 80 (deviation from an appropriate position when the installation position of the reference object 80 is not appropriate). Is measured, the reference spherical surface 810 of the reference object 80 is measured, fringe analysis is performed on the obtained interference fringes, the wavefront aberration is expanded to an approximate polynomial (approximate polynomial of aberration), and the correction amount of the aberration is calculated. Ask for. Then, the surface to be inspected 81 of the object to be inspected 8 is measured, fringe analysis is performed on the obtained interference fringes, and the wavefront aberration is expanded into an approximate polynomial, and is expanded with the approximate polynomial based on the correction amount. The aberration terms are corrected, and the shape of the surface 81 to be inspected is obtained from the corrected aberration terms (including the case where both the corrected aberration terms and the uncorrected aberration terms are used).

First, the outline of the interference measuring method of the present invention will be described. As shown in FIG. 1, the reference light reflected by the reference surface 71 of the prototype lens 7 and the reference of the reference object 80 are subjected to a setting error in the relative position of the reference object 80 with respect to the interferometer 1a. The test light reflected by the spherical surface 810 is superposed and interfered with each other to obtain an interference fringe. The interference fringes thus obtained are subjected to fringe analysis by a known method to obtain quantified values. By the first means, the value obtained by the fringe analysis is expanded into an approximate polynomial representing the wavefront aberration by performing least square fitting, and the value (measured value) corresponding to the coefficient of each term is obtained. Such measurement is performed at two or more locations by changing the installation position of the reference test object 80.

Then, the second means obtains the correction amount of the aberration based on the value corresponding to the coefficient of each term of the approximate polynomial. This correction amount is normally obtained once in the memory 15 once the arrangement of the interferometer and the object to be inspected is decided.
It may be stored in the memory 15 and read from the memory 15 every time the interference measurement of the test object 8 is performed.

At the time of interferometric measurement of the object 8 to be inspected, as shown in FIG.
The reference light reflected at and the test light reflected at the test surface 81 of the test object 8 are caused to interfere with each other to obtain an interference fringe. The interference fringes thus obtained are subjected to fringe analysis by a known method to obtain quantified values.
By the first means, the value obtained by the fringe analysis is expanded into an approximate polynomial representing the wavefront aberration by performing least square fitting, and the value (measured value) corresponding to the coefficient of each term is obtained. The values (measured values) corresponding to the coefficients of the respective terms of the approximate polynomial in the interference measurement of the reference test object 81 and the test object 8 are respectively calculated by the first means.
It is obtained based on the numerical aperture (NA ₀ ) of the effective light beam that enters or is emitted from the test area.

In the aberration terms (axisymmetric aberrations) of fourth or higher order in this approximation polynomial, in addition to the aberration caused by the surface shape of the surface 81 to be measured, which is originally to be measured, the object 8 to be measured and the prototype are also included. An aberration caused by a position setting error (referred to as defocus) Δz between the lens 7 and the prototype lens 7 in the optical axis 73 direction is included.

When a condensing lens that does not satisfy the sine condition is used, the aberration term of the third or higher order odd number in the approximation polynomial is caused by the surface shape of the surface 81 to be measured that is originally to be measured. In addition to the aberration, a position setting error (referred to as decenter or tilt) between the object 8 and the standard lens 7 in the direction perpendicular to the optical axis 73 of the standard lens 7.
Aberrations caused by Δx and Δy are included.

Therefore, the third means obtains an even-order aberration (axisymmetric aberration) of the fourth order or more caused by the setting error Δz based on the correction amount of the aberration, and uses this aberration as a correction value (correction data). It is used to correct the value (measured value) of the fourth-order or higher even-order terms of the approximate polynomial.

Further, the third means obtains the aberrations of the third and higher odd orders caused by the setting errors Δx and Δy based on the correction amount of the aberration, and uses this aberration as the correction value (correction data). The value of the odd-order terms of the third order or higher of the approximate polynomial is corrected. Note that the correction value may include the aberration of the interferometer 2a itself, in addition to the aberration caused by the setting error.

The interference measuring method of the present invention will be specifically described below. To develop the interference fringe pattern for each aberration,
For example, the Zernike or Seidel coefficient expansion formula is used, and the aberration W (ρ, φ) of the interference fringe pattern is expanded as shown in formula (1) below. The values corresponding to the respective terms in the following formula (1) are obtained by measuring the surface 81 to be inspected of the object 8 to be subjected to fringe analysis and fitting the analysis data to least squares. Less than,
The value after the least-squares fitting is called the measured value.

[0063]

[Equation 11]

In the formula (1) (approximate polynomial of aberration) shown in the above-mentioned equation 11, each aberration is represented by a different order. For example, spherical aberration is represented by terms of even order of 4th order or higher, and coma aberration is represented by terms of odd order of 3rd order or higher.

However, in practice, the aberration terms (axisymmetric aberrations) of the fourth and higher order in the above equation (1) are not only the aberrations caused by the surface shape of the surface to be measured 81 to be originally measured, It also includes aberrations caused by defocus.

That is, although the fourth and higher even-order terms in the above equation (1) are spherical aberrations, in reality, in addition to the spherical aberrations caused by the surface 81 to be inspected, the aberrations caused by defocusing Of these, even-order components of 4th order or higher are included.

The defocus means the focal point 75 of the prototype lens 7 and the center of curvature 8 of the object 8 shown in FIG.
5 is a setting error (shift) in the z direction parallel to the optical axis 73. The magnitude of this setting error, that is, the magnitude of defocus is represented by Δz. in this case,
In reality, since it is a reflective system, twice the actual amount of deviation is
z.

When a condensing lens that does not satisfy the sine condition is used, the aberration terms of the third and higher odd orders in the above equation (1) are the surfaces of the surface 81 to be inspected that are to be measured. In addition to the aberration caused by the shape, it also includes the aberration caused by the tilt (decenter).

That is, although the third and higher order odd-numbered terms in the above equation (1) are coma aberrations, actually, in addition to the coma aberrations caused by the surface 81 to be inspected, among the aberrations caused by the tilt, The third-order or higher odd-order component is included.

The tilt is a setting error (deviation) in the x and y directions perpendicular to the optical axis 73 between the focal point 75 of the prototype lens 7 and the center of curvature 85 of the object 8 shown in FIG. )
Is meant. In this case, the magnitude of the setting error in the x-axis direction, that is, the magnitude of the tilt in the x-axis direction is represented by Δx, and the magnitude of the setting error in the y-axis direction, that is, the magnitude of the tilt in the y-axis direction is represented by Δy. Express with.

The third term of the above equation (1) is a quadratic component generated due to defocus,
It is treated as a setting error. Similarly, the first term and the second term of the equation (1) are first-order components generated by the presence of the tilt, and are processed as setting errors.

Here, the influence of the defocus and the tilt on the aberration will be specifically described. FIG. 3 and FIG. 4 are diagrams showing configuration examples of a condenser lens that substantially satisfies the sine condition and a condenser lens that does not satisfy the sine condition, respectively. Note that FIG.
The lens shown in (1) is obtained by slightly changing the design parameters of the lens shown in FIG. 3 and changing only the sine condition.

FIG. 5 is a graph (aberration diagram) showing the spherical aberration (SA) and the sine condition (SC) of the condenser lens substantially satisfying the sine condition shown in FIG.
[Fig. 4] is a graph (aberration diagram) showing spherical aberration (SA) and sine condition (SC) of a condenser lens that does not satisfy the sine condition shown in Fig. 4. The horizontal axis of each of the graphs shown in FIGS. 5 and 6 represents the amount of spherical aberration, and the vertical axis represents the incident height of the light beam.

Regarding such two types of condenser lenses,
On the surface 81 to be inspected of the object 8 having no shape error, the defocus is reciprocated by 6λ (6 lines) and 12λ, respectively.
When two types of (12 lines) are given, the relationship between the fourth-order and even-order aberrations generated by this defocus and the incident height (h) was obtained by ray tracing.

FIG. 7 is a graph showing the relationship between the incident height (h) and the aberrations of the fourth and higher even-numbered orders generated by the defocusing of the condenser lens satisfying the sine condition, and FIG. FIG. 4 is a graph showing the relationship between the fourth-order and even-order aberrations caused by defocusing of a condenser lens that does not satisfy the sine condition, and the incident height (h).

The horizontal axis of each of the graphs shown in FIGS. 7 and 8 represents the incident height (h) when the maximum incident height (h _max ) is 1, that is, ρ, and the vertical axis represents a predetermined value. The aberration amount of the even-numbered fourth or more order due to the defocus obtained by the calculation at the incident height (h) is shown.

Comparing the graph shown in FIG. 7 with the graph shown in FIG. 8, it can be seen that the condenser lens which does not satisfy the sine condition has more aberrations of the fourth and higher even orders due to defocus. I understand. Further, from the graphs shown in FIGS. 7 and 8, the amount of aberration of the fourth and higher even orders due to defocus is proportional to the size of the defocus (changes substantially linearly with respect to the size of the defocus). I understand.

Regarding the two types of condenser lenses,
Tilts are reciprocated by 10λ (10 pieces) and 50λ on the test surface 81 of the test object 8 having no shape error.
When two types (50 lines) were given, the relation between the third-order and higher odd-order aberrations caused by this tilt and the incident height (h) was obtained by ray tracing.

FIG. 9 is a graph showing the relation between the incident height (h) and the aberrations of the third and higher odd-numbered orders caused by the tilt of the condenser lens satisfying the sine condition, and FIG. 3 is a graph showing a relationship between an incident aberration (h) and an aberration of an odd-numbered order of 3 order or more caused by tilting of a condenser lens that does not satisfy the sine condition.

[0080] The horizontal axis of each graph shown in FIGS. 9 and 10, the maximum incidence height (h _{ma x)} the incidence height in the case of a 1 (h), i.e. shows a [rho, the vertical axis, a predetermined By tilt calculated from the incident height (h) of 3
The aberration amounts of odd-numbered orders and higher are shown.

Comparing the graph shown in FIG. 9 with the graph shown in FIG. 10, in the case of the condensing lens satisfying the sine condition, the aberrations of the third and higher odd orders due to tilt do not occur ( Actually, since the sine condition is not completely satisfied, an aberration of an odd-numbered third order or higher due to tilt is slightly generated.) However, in the case of a condenser lens where the sine condition is not satisfied, It can be seen that third-order and higher odd-order aberrations due to tilt, that is, coma, occur.

Further, from the graph shown in FIG. 10, it is understood that the amount of aberration of the third and higher odd orders due to the tilt is proportional to the magnitude of the tilt (it changes almost linearly with respect to the magnitude of the tilt). .

In the present invention, even-order aberrations of the fourth order or higher caused by such defocus and odd-order aberrations of the third order or higher caused by the tilt are obtained, and these aberrations are used as correction values (correction data), By subtracting the correction value from the measurement value, an accurate corrected measurement result (corrected measurement value) can be obtained regardless of the relative positional relationship between the test object and the interferometer. Hereinafter, defocus and tilt are divided into cases, and in the case of defocus, the case of correcting the 4th and 6th order coefficients is representative, and in the case of tilt, the case of the 3rd order and representative The case of correcting the fifth-order coefficient will be described.

[In case of defocus] The correction amount of the aberration is obtained in advance as described below, and this correction amount is stored in the memory 15. In order to obtain the correction amount, first, as shown in FIG. 11, the reference light reflected by the reference surface 71 of the prototype lens 7 and the reference object 80 are defocused. By interfering with the test light reflected by the reference spherical surface 810 to obtain interference fringes, fringe analysis is performed, and analysis data is subjected to least-squares fitting to develop into an approximate polynomial of the above formula (1), and A value (measured value) corresponding to the coefficient of each term is obtained based on the numerical aperture NA ₀ of the effective light flux that enters the test area (or exits from the test area of the reference spherical surface 810).

Here, the maximum incident height from the optical axis 73 when an effective light beam enters the prototype lens (optical member) 7 is h
_max , f is the focal length of the prototype lens (optical member) 7, and θ _max is the angle between the outermost ray of the effective luminous flux after passing through the prototype lens (optical member) 7 and the optical axis 73. , The numerical aperture NA ₀ is expressed by the following equation. NA ₀ = h _max / f = sin θ _max

Further, the installation position of the reference object 80 is changed, that is, the size of the defocus Δz (Δz = 0.
(Including the case of the ideal position) is changed to develop the approximation polynomial of the above equation (1) in the same manner as described above, and the numerical aperture NA ₀ of the effective light beam incident on the test region of the reference spherical surface 810 is changed.
Based on, the value corresponding to the coefficient of each term is obtained. In this way, the interference measurement for the reference object 80 is performed at two or more places. To change the installation position of the reference test object 80, for example, the deviation of the reference test object 80 from the reference position (position with zero deviation) in the optical axis 73 direction is changed. In this case, as shown in FIG. 11, for example, the deviations Δz ₁ and Δz ₂
It is assumed that the approximate polynomials are obtained by making measurements at three points, and Δz ₃ . In the measurement of the reference object 80, it is assumed that the incident height on the prototype lens 7 is h ₀ and the radius of the interference fringes 45 formed on the observation surface of the imaging unit 11 is r ₀ .

Next, based on the measured values at each set position, a coefficient of an even order of four or more (axisymmetric aberration coefficient) W _{40 with} respect to the second-order coefficient (defocus coefficient) W ₂₀ of the above equation (1). , W ₆₀ relationship is sought. W against W ₂₀
A function that best fits ₄₀ and W ₆₀ is obtained by the least squares method, and this is set as the correction amount.

12 and 13 are graphs showing the relationship between W ₂₀ and W ₄₀ and the relationship between W ₂₀ and W _60, which are obtained based on the measured values at each set position. Figure 1
As shown in FIG. 2, this correction amount is represented by a linear function of W ₂₀ and W ₄₀ as shown in the equation (2) below.

[0089]

[Equation 12]

In this case, the memory 15 has the above (2)
The coefficient (slope) a ₄ and the coefficient (intercept) b _{4 of the} equation are stored, and the coefficient a ₄ and b ₄ are read from the memory 15 each time the interference measurement of the object 8 is performed. Further, as shown in FIG. 13, this correction amount is represented by a linear function of W ₂₀ and W ₆₀ as shown in the equation (3) below.

[0091]

[Equation 13]

In this case, the memory 15 has the above (3)
The coefficient (slope) a ₆ and the coefficient (intercept) b _{6 of the} equation are stored, and the coefficient a ₆ and b ₆ are read from the memory 15 each time the interference measurement of the object 8 is performed.

Here, since the prototype lens 7 is the lens of the interferometer 2a, b ₄ and b in the above equations (2) and (3) are used.
₆ is the aberration of the interferometer 2a itself. This b
₄ , b ₆ can be removed by a known method (for example, the method of Bruning et al.). Therefore, with the correction amounts a ₄ and a ₆ kept constant, b ₄ = 0,
It is also possible to set b ₆ = 0.

When the test object 8 is used as the reference test object 80, b ₄ and b in the above equations (2) and (3) are used.
Reference numeral ₆ shows the aberration of the interferometer 2a and the aberration of the test object 8, respectively. These b ₄ and b ₆ are the known methods (for example, the method of Bruning et al.) And are expressed by the aberrations α ₄ and α ₆ of the interferometer 2a as shown in the equations (4) and (5) below. , Β ₄ and β _{6 of the} test object 8 can be separated.

[0095]

[Equation 14]

Therefore, when the test object 8 is used as the reference test object 80, from the correction amounts b ₄ and b ₆ , the above (4)
The aberrations β ₄ , β ₆ , of the test object 8 in the expressions and (5),
That is, the corrected measurement value of the fourth order and the corrected measurement value of the sixth order can be obtained.

The value obtained by subtracting b ₄ from W ₄₀ obtained by the above equation (2) is the coefficient of the 4th-order aberration caused by defocus, and subtracting b ₆ from W ₆₀ obtained by the above equation (3). Is the coefficient of the 6th-order aberration caused by defocus.

In this way, the aberration correction amount is obtained in advance, the correction amount is stored in the memory 15, and the interference measurement of the test object 8 is performed. In the interferometric measurement of the test object 8, FIG.
As shown in FIG. 7, the reference object 80 is replaced by the inspection object 8, and the reference light reflected by the reference surface 71 of the prototype lens 7 and the inspection light reflected by the inspection surface 81 of the inspection object 8 By interfering with each other to obtain interference fringes, fringe analysis is performed, and least-squares fitting of the analysis data is performed to develop into an approximate polynomial of the above equation (1) and incident (or to Numerical aperture NA of the effective light beam emitted from the inspection area of the inspection surface 81)
_The value (measured value) corresponding to the coefficient of each term is obtained based on ₀ .

Here, as in the case of the interferometric measurement of the reference object 80, the maximum incident height from the optical axis 73 when the effective light beam enters the standard lens (optical member) 7 is h _max , and the standard When the focal length of the lens (optical member) 7 is f and the angle between the outermost ray of the effective light beam after passing through the prototype lens (optical member) 7 and the optical axis 73 is θ _max , the numerical aperture is NA ₀
Is represented by the following equation. NA ₀ = h _max / f = sin θ _max

In the measurement of the test object 8, the measurement range, that is, the height of incidence h ₁ on the standard lens 7 is determined in advance. The radius of the interference fringes 47 formed on the observation surface of the imaging unit 11 at the incident height h ₁ is r ₁ and r ₁ / r
It is assumed that ₀ = h ₁ / h ₀ = s.

Here, the coefficients of the second-order, fourth-order and sixth-order aberrations when the incident height is h ₁ are C, D and E, respectively.
And each of the coefficients C, D and E has an incident height h _0.
The coefficient W ₂₀ of the second-order, fourth-order and sixth-order aberrations at
When represented by W ₄₀ and W ₆₀ and the above s, they are represented by the following equations (6), (7) and (8).

[0102]

[Equation 15]

Therefore, the above equation (2) is converted into the coefficients C and D.
When it is rewritten by using the formula (9), it is expressed as the following formula (9).

[0104]

[Equation 16]

The above equation (9) represents the coefficient of the 4th-order aberration generated by defocus and the coefficient of the 4th-order aberration of the interferometer 2a itself when the object 8 is measured at the incident height h _1. Is a formula for obtaining the correction value of the coefficient of the fourth-order aberration. Similarly, the above equation (3) is converted into the coefficient C
When rewritten by using
It is expressed as in equation (0).

[0106]

[Equation 17]

According to the above equation (10), the incident height h _{1 on the} test object 8 is
In the case of measurement by the equation (6), a formula for obtaining the coefficient of the 6th-order aberration generated by defocus and the coefficient of the 6th-order aberration of the interferometer 2a itself, that is, a formula for obtaining the correction value of the 6th-order aberration coefficient is there.

In this embodiment, a correction value is obtained by the above equations (9) and (10), and the correction value is subtracted from the measurement value of the object 8 to obtain an accurate corrected measurement result (corrected measurement value). ) Get. That is, the fourth measured value of the test object 8 is W
_{When 40} ′ and the second-order measured value are W ₂₀ ′, the fourth-order corrected measured value W ₄₀ ″ is obtained from the equation (11) shown in the following Eq.

[0109]

[Equation 18]

In addition, the sixth-order measured value of the test object 8 is W ₆₀ ',
When the second-order measurement value is W ₂₀ ′, the sixth-order corrected measurement value W ₆₀ ″ is obtained from the equation (12) shown in the following Expression 19.

[0111]

[Formula 19]

When correcting the coefficients (measurement values) of aberrations of even-numbered orders of 8th and higher, the correction amount is calculated based on the measurement value of the reference object 80 in the same manner as described above, and the correction amount is calculated. Then, the correction value of the even-order aberrations of 8th order or more is obtained, and the correction value is subtracted from the value obtained by the fringe analysis.

The correction of the fourth-order and sixth-order coefficients has been representatively described above, but the general formula of the correction formula relating to defocus including these is represented by the following formula (13).

[0114]

[Equation 20]

As described above, from the quadratic coefficient W ₂₀ and the correction amount of the aberration which is obtained by analyzing the interference fringes and developing the approximation polynomial,
A correction value for an axially symmetric aberration of the following or higher can be easily obtained. The quadratic coefficient W ₂₀ is called a defocus term in the usual fringe analysis method and is processed as a setting error as described above.

In the present invention, regarding defocus,
As described above, the aberrations of the fourth and higher even-numbered orders obtained by the fringe analysis, that is, the axisymmetric aberrations of the fourth and higher orders are corrected. In this case, the order of the aberration to be corrected is appropriately determined according to various conditions such as the value of the numerical aperture NA ₀ (sin θ _max ) of the prototype lens 7 and the target measurement accuracy.
The 4th and 6th order is sufficient.

[Case of Tilt] The correction amount of the aberration is calculated in advance as described below, and the correction amount is stored in the memory 15. To obtain the correction amount, first, as shown in FIG. 11, the reference light reflected by the reference surface 71 of the prototype lens 7 in a state where the reference object 80 is tilted (for example, tilted in the x direction). And interference with the test light reflected by the reference spherical surface 810 of the reference test object 80 to obtain interference fringes, fringe analysis is performed, and least squares fitting of the analysis data is performed to develop into an approximate polynomial of the above formula (1). And the reference spherical surface 8
A value (measured value) corresponding to the coefficient of each term is obtained based on the numerical aperture NA ₀ of the effective light flux that enters (or exits from the test area of the reference spherical surface 810) the 10 test areas.

In this case, the coefficients of the first-order aberration terms caused by the tilts in the x-direction and the y-direction are W ₁₁ and W ₁₂ , respectively, and the coefficients of the terms including the third-order aberrations caused by the tilts in the x-direction and the y-direction are included. W ₃₁ and W respectively
₃₂ , the coefficients of the terms including the fifth-order aberration caused by the tilts in the x-direction and the y-direction are W ₅₁ and W ₅₂ , respectively.

Here, the maximum incident height from the optical axis 73 when an effective light beam enters the prototype lens (optical member) 7 is h
_max , f is the focal length of the prototype lens (optical member) 7, and θ _max is the angle between the outermost ray of the effective luminous flux after passing through the prototype lens (optical member) 7 and the optical axis 73. , The numerical aperture NA ₀ is expressed by the following equation. NA ₀ = h _max / f = sin θ _max

Further, the installation position of the reference object 80 is changed, that is, the tilt size Δx (including the case of Δx = 0 (ideal position)) is changed, and the same as the above ( It is expanded to the approximate polynomial of equation (1) and the reference sphere 8
Values corresponding to the coefficients of the respective terms are obtained based on the numerical aperture NA ₀ of the effective light beam incident on the 10 test areas. In this way, the interference measurement for the reference object 80 is performed at two or more places. To change the installation position of the reference object 80,
For example, the deviation of the reference object 80 from the reference position (position with zero deviation) in the direction perpendicular to the optical axis 73 (x direction) is changed. In the measurement of the reference object 80, it is assumed that the incident height on the prototype lens 7 is h ₀ and the radius of the interference fringes 45 formed on the observation surface of the imaging unit 11 is r ₀ .

Then, based on the measured values at the respective set positions, the relationship between the coefficients W ₃₁ and W ₅₁ of odd orders higher than or equal to the third order with respect to the first order coefficient W ₁₁ of the equation (1) is obtained. A function that best fits W ₃₁ and W ₅₁ with respect to W ₁₁ is obtained by the method of least squares, and this is set as a correction amount. One of the correction amounts is expressed by the following equation (14),
It is represented by a linear function of W ₁₁ and W ₃₁ .

[0122]

[Equation 21]

In this case, the memory 15 stores the above (1
The coefficient (slope) a ₃ and the coefficient (intercept) b _{3 of the} equation 4) are stored, and the coefficient a ₃ and b ₃ are read from the memory 15 each time the interference measurement of the object 8 is performed. Further, the other of the correction amounts is W ₁₁ as expressed by the following equation (15).
And a linear function of W ₅₁ .

[0124]

[Equation 22]

In this case, the memory 15 stores the above (1
The coefficient (slope) a ₅ and the coefficient (intercept) b _{5 of the} equation 5) are stored, and the coefficient a ₅ and b ₅ are read from the memory 15 each time the interference measurement of the object 8 is performed.

Here, since the prototype lens 7 is the lens of the interferometer 2a, b in the above equations (14) and (15) is used.
₃ and b ₅ are aberrations of the interferometer 2a itself.
The b ₃ and b ₅ are obtained by known methods (for example, Brunin
g) and the like). Therefore, while keeping the correction amounts a ₃ and a ₅ constant, b ₃
It is also possible to set = 0 and b ₅ = 0.

When the test object 8 is used as the reference test object 80, b in the above equations (14) and (15) is used.
₃ and b ₅ are the aberration of the interferometer 2a and the object to be inspected 8 respectively.
And the aberration of. These b ₃ and b ₅ are known methods (for example, the method of Bruning et al.),
It is possible to separate the aberrations α ₃ and α ₅ of the interferometer 2a and the aberrations β ₃ and β _{5 of the} object 8 to be inspected from the equations (16) and (17) shown in FIG.

[0128]

[Equation 23]

Therefore, when the test object 8 is used as the reference test object 80, from the correction amounts b ₃ and b ₅ , the above (1
Aberration β _{3 of} the test object 8 in the equations (6) and (17),
β ₅ , that is, the third-order corrected measurement value and the fifth-order corrected measurement value can be obtained.

Note that W ₃₁ obtained by the above equation (14)
The value obtained by subtracting b ₃ from is the coefficient of the third-order aberration caused by the tilt, and the value obtained by subtracting b ₅ from W ₅₁ obtained by the equation (15) is the coefficient of the fifth-order aberration caused by the tilt. The tilt in the x direction has been described above as a representative, but the tilt in the y direction may be performed in the same manner as described above.

In this way, the correction amount of the aberration is obtained in advance, the correction amount is stored in the memory 15, and the interference measurement of the test object 8 is performed. In the interferometric measurement of the test object 8, FIG.
As shown in FIG. 7, the reference object 80 is replaced by the inspection object 8, and the reference light reflected by the reference surface 71 of the prototype lens 7 and the inspection light reflected by the inspection surface 81 of the inspection object 8 By interfering with each other to obtain interference fringes, fringe analysis is performed, and least-squares fitting of the analysis data is performed to develop into an approximate polynomial of the above equation (1) and incident (or to Numerical aperture NA of the effective light beam emitted from the inspection area of the inspection surface 81)
_The value (measured value) corresponding to the coefficient of each term is obtained based on ₀ .

Here, as in the case of the interference measurement of the reference object 80, the maximum incident height from the optical axis 73 when the effective light beam enters the standard lens (optical member) 7 is h _max , and the standard When the focal length of the lens (optical member) 7 is f and the angle between the outermost ray of the effective light beam after passing through the prototype lens (optical member) 7 and the optical axis 73 is θ _max , the numerical aperture is NA ₀
Is represented by the following equation. NA ₀ = h _max / f = sin θ _max

In the measurement of the object 8 to be inspected, the measurement range, that is, the height of incidence h ₁ on the prototype lens 7 is determined in advance. The radius of the interference fringes 47 formed on the observation surface of the imaging unit 11 at the incident height h ₁ is r ₁ and r ₁ / r
It is assumed that ₀ = h ₁ / h ₀ = s.

Here, the coefficients of the 1st, 3rd and 5th order aberrations when the incident height is h ₁ are G, H and I, respectively.
And each of the coefficients G, H, and I has an incident height h _0.
The coefficient W ₁₁ of the first-, third-, and fifth-order aberrations at
When represented by W ₃₁ , W ₅₁ and s, they are represented by the following equations (18), (19) and (20).

[0135]

[Equation 24]

Therefore, when the above equation (14) is rewritten using the coefficients G and H, it can be expressed as the following equation (21).

[0137]

[Equation 25]

According to the above equation (21), the incident height h _{1 on the} test object 8 is
3 caused by tilt when measured at 3
This is an expression for obtaining the coefficient of the next aberration and the coefficient of the third-order aberration of the interferometer 2a itself, that is, an expression for obtaining the correction value of the coefficient of the third-order aberration. Similarly, when the above equation (15) is rewritten using the coefficients G and I, the following equation 26 is obtained (2
It is expressed as in equation (2).

[0139]

[Equation 26]

According to the above equation (22), the incident height h _{1 on the} test object 8 is
Generated by tilt when measured at 5
This is an expression for obtaining the coefficient of the next aberration and the coefficient of the fifth-order aberration of the interferometer 2a itself, that is, an expression for obtaining the correction value of the coefficient of the fifth-order aberration.

In the present embodiment, the correction value is obtained by the equations (21) and (22), and the correction value is subtracted from the measurement value of the object 8 to obtain an accurate corrected measurement result (corrected measurement value). ) Get. That is, assuming that the third-order measured value of the test object 8 is W ₃₁ ′ and the first-order measured value is W ₁₁ ′, the third-order corrected measured value W ₃₁ ″ is shown in the following Expression 27 (23). Obtained from the formula.

[0142]

[Equation 27]

Further, the fifth measured value of the test object 8 is W ₅₁ ',
When the primary measurement value is W ₁₁ ′, the fifth-order corrected measurement value W ₅₁ ″ is obtained from the equation (24) shown in the following Expression 28.

[0144]

[Equation 28]

When correcting the coefficients (measured values) of the aberrations of the odd orders of 7th and higher, the correction amount is obtained based on the measured value of the reference object 80 in the same manner as described above. A correction value for an odd-order aberration of 7th order or more is calculated from the above, and the correction value is subtracted from the value calculated by the fringe analysis.

As described above, from the first-order coefficient W ₁₁ of the aberration and the correction amount, which are obtained by analyzing the interference fringes and developing the approximation polynomial, 3
A correction value for an odd-order aberration equal to or higher than the order can be easily obtained.

The first-order coefficient W ₁₁ is called a tilt term in the usual fringe analysis method, and is processed as a setting error in the direction (x direction) perpendicular to the optical axis as described above. Although the x direction has been representatively described above, the y direction may be similar to the above.

The correction of the third-order and fifth-order coefficients has been described above as a representative, but the general formula of the correction formula relating to the tilt including them is represented by the formula (25) shown in the following formula 29.

[0149]

[Equation 29]

In the present invention, as to the tilt, as described above, the aberrations of the third and higher order odd numbers obtained by the fringe analysis are corrected. In this case, the order of the aberration to be corrected is appropriately determined according to various conditions such as the value of the numerical aperture NA ₀ of the prototype lens 7 and the target measurement accuracy.
A third or fifth order is sufficient.

When the numerical aperture NA ₀ of the prototype lens 7 is large, the aberrations caused by the defocus and the tilt are large, so that the influence of the defocus and the tilt on the measured value is large. However, according to the present invention, even when the value of NA ₀ of the prototype lens 7 is large (when a relatively bright condenser lens is used), for example, by increasing the order of aberration to be corrected, More accurate corrected measurement values are obtained.

If a non-volatile memory is used as the memory 15, the stored correction amount or data related thereto is not erased even when the power of the interference measuring device 1a is turned off. It has the advantage that it can be used for each interferometric measurement.

Next, the operation of the interference measuring apparatus 1a when measuring the aberration (shape measurement) of the surface 81 to be inspected of the object 8 will be described. The alignment of the test object 8 is performed before the aberration measurement of the test surface 81. As shown in FIG. 2, the test object 8 is fixed to the base of the moving means 9 of the interference measuring apparatus 1a, and the moving means 9 moves the test object 8 in the optical axis 73 direction and the direction perpendicular to the optical axis 73. The object 8 to be inspected is moved and set at a predetermined position (it is not necessary to strictly set it to a position having no setting error). In this case, for example, by irradiating light from the light source 3 and confirming it with a monitor device (not shown), so that interference fringes appear, that is, the condensing point 75 of the prototype lens 7,
The test object 8 is arranged so that the center of curvature 85 of the test object 8 is substantially coincident.

The light emitted from the light source 3 in the interference measuring apparatus 1a passes through the objective lens 4 and the collimating lens 5 in order and becomes a parallel light expanded to a desired light beam diameter. The parallel light enters the half mirror 6, and a part of the parallel light passes through the half mirror 6. The light transmitted through the half mirror 6 is incident on the prototype lens 7, and when transmitted through the prototype lens 7, is vertically incident on each part of the reference surface 71, and a part of the light is transmitted through the reference surface 71. The rest is reflected by the reference surface 71.

The light reflected by the reference surface 71 passes through the prototype lens 7 to become parallel light again, and is partially reflected by the half mirror 6 toward the observation lens 10 side. This reflected light is
It reaches the CCD 17 of the image pickup section 11 through the observation lens 10 and becomes reference light.

On the other hand, the light transmitted through the reference surface 71 is once condensed on the condensing point 75, and then is irradiated on the surface 81 to be inspected of the object 8 to be inspected and reflected by the surface 81 to be inspected. The light is once focused on the center of curvature 85 of the surface 81 or in the vicinity thereof, and then is incident on the reference surface 71 again. Then, the light incident on the reference surface 71 passes through the prototype lens 7 to become parallel light again, and further enters the half mirror 6, and a part of the light is reflected by the half mirror 6 toward the observation lens 10 side. This reflected light reaches the CCD 17 of the image pickup section 11 through the observation lens 10 and becomes the test light.

In this way, the light reflected by the reference surface 71 (reference light) and the light transmitted through the reference surface 71 and reflected by the surface to be inspected 81 (light to be inspected) interfere with each other, so that an image is picked up. Interference fringes are formed on the CCD 17 of the unit 11.

The image pickup section 11 converts the interference fringe pattern into an analog electric signal. This analog electric signal is converted into a digital signal by the A / D converter of the image processing device 12, and then input to the computing means 13 and the monitor device (not shown).

A monitor device (not shown) performs a predetermined signal processing on the input digital signal to project an image corresponding to the pattern of the interference fringes, and the interference fringes can be observed through the image. When there is defocus, the interference fringes become concentric circles, and when there is tilt, the interference fringes become a group of straight lines with equal pitch (the shape changes slightly if the sine condition is not satisfied). .

As described above, the calculating means 13 drives the prototype lens 7 by the driving means 711 by means of a means (not shown) based on the digital signal input from the image processing device 12, and the well-known phase shift method or the like. The interference fringes are quantified by, that is, fringe analysis is performed. Then, the wavefront aberration of the test surface 81 (aberration due to the surface shape of the test surface 81 and aberrations caused by defocus or tilt) is calculated from the discrete wavefront aberration values obtained by the fringe analysis by calculation such as least square fitting. Is calculated, and the above-described predetermined correction is performed based on the correction amount of the aberration that is obtained in advance.

Next, regarding the method of obtaining the correction amount and the method of calculating and correcting the aberration of the surface 81 to be inspected of the object 8, in the case of defocusing, among the aberrations of even-numbered orders of 4 or more. In the case of correcting only the 4th and 6th order aberrations, in the case of tilt, of the case of correcting only the 3rd and 5th order aberrations among the 3rd and higher order odd order aberrations, Each will be explained.

FIGS. 15 and 16 show the operation of the interferometer 1a for obtaining the correction amount for the defocus and the case where the aberration of the surface 81 to be inspected of the object 8 is measured. It is a flowchart which shows operation | movement of the interference measurement apparatus 1a at the time of correct | amending only 6th-order aberration. Less than,
In the case of defocus, this flowchart will be described.

First, the operator sets the reference object 80 on the interference measuring apparatus 1a (step 101). Then
Defocus is applied to the reference object 80 (step 1
03). That is, the magnitude of defocus Δz is changed. Next, the interferometer 2a of the interferometer 1a starts measuring the shape of the reference spherical surface 810 of the reference object 80 (step 104).

The calculation means 13 performs fringe analysis based on the digital signal input from the image processing device 12, and obtains a value corresponding to the coefficient of each term in the equation (1), that is,
W ₁₁ , W ₁₂ , W ₂₀ , W ₂₂ , W ₃₁ , W ₃₂ , W ₄₀ , W ₅₁ , W
₅₂ , W ₆₀ ... Are calculated (step 10).
5). In addition, the calculated W ₁₁ , W ₁₂ , W ₂₀ ,
The measured values are W ₂₂ , W ₃₁ , W ₃₂ , W ₄₀ , W ₅₁ , W ₅₂ , W _60, ...

Then, each of the measured values is stored in a predetermined area of the memory 15 (step 106). Repeat steps 103 to 106. For example, when the number of measurement points is 3, the steps 103 to 106 are 3 times.
Executes once.

Next, the correction amount indicating the relationship between W ₂₀ and W _{40 and} the relationship between W ₂₀ and W ₆₀ for each Δz is obtained (step 108). That is, the equations (2) and (3) are obtained. Next, the coefficient a _{4 of} each correction amount,
Each of b ₄ , a ₆ and b ₆ is stored in a predetermined area of the memory 15 (step 109).

Next, the worker sets the test object 8 in place of the reference test object 80 in the interference measuring apparatus 1a (step 110). Then, the interferometer 2a of the interferometer 1a starts measuring the shape of the surface 81 to be inspected of the object 8 (step 111).

The calculation means 13 performs fringe analysis based on the digital signal input from the image processing device 12, and the value corresponding to the coefficient of each term in the above equation (1), that is,
W ₁₁ , W ₁₂ , W ₂₀ , W ₂₂ , W ₃₁ , W ₃₂ , W ₄₀ , W ₅₁ , W
₅₂ , W ₆₀ ... Coefficients W ₁₁ ', W ₁₂ ',
_{W 20 ', W 22',} W 31 ', W 32', W 40 ', W 51', W
₅₂ ', W ₆₀ ' ... are calculated (step 11)
2). In addition, the calculated W ₁₁ ′, W ₁₂ ′,
_{W 20 ', W 22',} W 31 ', W 32', W 40 ', W 51', W
₅₂ ', W ₆₀ ' ... are measured values.

Then, the calculation means 13 corrects the aberration based on the correction amount (step 113). That is,
Substituting the above W ₂₀ ′, W ₄₀ ′, a ₄ , b ₄ and s into the above equation (11), the coefficient W ₄₀ ′ of the fourth-order aberration is corrected,
A fourth-order corrected measurement value W ₄₀ ″ is obtained.

Further, in the above equation (12), W ₂₀ ′, W
By substituting ₆₀ ′, a ₆ , b ₆ and s, the coefficient W ₆₀ ′ of the 6th-order aberration is corrected, and the corrected measured value W ₆₀ ″ of the 6th-order is obtained.
In this way, corrected measurement values of the 4th and 6th orders, that is, the 4th and 6th order aberrations in the absence of defocus, are obtained. It should be noted that such correction related to defocus is performed only for axially symmetric aberrations.

Next, the amount of aberration is displayed for each order of aberration (step 114). in this case,
The aberration amount of each order is, for example, the monitor device 1
4 is displayed as an image or is output by a printer (not shown). This is the end of this program.

17 and 18 show the operation of the interferometer 1a for obtaining the correction amount for the tilt and the case where the aberration of the surface 81 to be inspected of the object 8 is measured. Interferometer 1a for correcting only the following aberrations
3 is a flowchart showing the operation of FIG. In the case of tilt, this flowchart will be described below.

First, the operator sets the reference object 80 on the interference measuring apparatus 1a (step 301). Then
Tilt the reference object 80 (step 30).
3). That is, the tilt size Δx is changed. Next, the interferometer 2a of the interferometer 1a starts measuring the shape of the reference spherical surface 810 of the reference object 80 (step 304).

The calculation means 13 performs fringe analysis based on the digital signal input from the image processing device 12, and the value corresponding to the coefficient of each term in the above equation (1), that is,
W ₁₁ , W ₁₂ , W ₂₀ , W ₂₂ , W ₃₁ , W ₃₂ , W ₄₀ , W ₅₁ , W
₅₂ , W ₆₀ ... Are calculated (step 30).
5). In addition, the calculated W ₁₁ , W ₁₂ , W ₂₀ ,
The measured values are W ₂₂ , W ₃₁ , W ₃₂ , W ₄₀ , W ₅₁ , W ₅₂ , W _60, ...

Then, the measured values are stored in predetermined areas of the memory 15 (step 306). Repeat steps 303 to 306. For example, if the number of measurement points is three, steps 303 to 306 are set to three.
Executes once.

Next, from the measured values at each tilt,
Correction amounts indicating the relationship of W ₃₁ with respect to W ₁₁ and the relationship of W ₅₁ with respect to W ₁₁ are obtained (step 308). That is, the above equations (14) and (15) are obtained. Then, the coefficients a ₃ , b ₃ , a ₅ and b _{5 of the} respective correction amounts
Are stored in predetermined areas of the memory 15 (step 309). Also in the y direction, as in the x direction,
Perform steps up to step 309.

Next, the worker sets the test object 8 in place of the reference test object 80 in the interference measuring apparatus 1a (step 310). Then, the shape measurement of the surface 81 to be inspected of the object 8 is started by the interferometer 2a of the interference measuring apparatus 1a (step 311).

The calculation means 13 performs fringe analysis based on the digital signal input from the image processing device 12, and the value corresponding to the coefficient of each term in the above equation (1), that is,
W ₁₁ , W ₁₂ , W ₂₀ , W ₂₂ , W ₃₁ , W ₃₂ , W ₄₀ , W ₅₁ , W
₅₂ , W ₆₀ ... Coefficients W ₁₁ ', W ₁₂ ',
_{W 20 ', W 22',} W 31 ', W 32', W 40 ', W 51', W
₅₂ ', W ₆₀ ' ... are calculated (step 31)
2). In addition, the calculated W ₁₁ ′, W ₁₂ ′,
_{W 20 ', W 22',} W 31 ', W 32', W 40 ', W 51', W
₅₂ ', W ₆₀ ' ... are measured values.

Then, the calculating means 13 performs aberration correction based on the correction amount (step 313). That is,
Substituting the W ₁₁ ′, W ₃₁ ′, a ₃ , b ₃ and s into the equation (23), the coefficient W ₃₁ ′ of the third-order aberration is corrected,
A third-order corrected measurement value W ₃₁ ″ is obtained.

Further, in the above equation (24), W ₁₁ ′, W
₅₁ ', by substituting a _5, b ₅ and s, the coefficient W ₅₁ of fifth order aberration' is corrected to obtain a "fifth-order corrected measured value W _51.
In this way, the corrected measurement values of the 3rd and 5th orders, that is, the 3rd and 5th order aberrations in the absence of tilt are obtained. Note that such a tilt correction is performed only for odd-order aberrations. The y direction is also corrected in the same manner as the x direction.

Next, the amount of aberration is displayed for each aberration of each order (step 314). in this case,
The aberration amount of each order is, for example, the monitor device 1
4 is displayed as an image or is output by a printer (not shown). This is the end of this program.

Next, a second embodiment of the interference measuring apparatus of the present invention will be described. FIG. 19 is a diagram schematically showing a second embodiment of the interference measuring apparatus of the present invention. The interference measuring apparatus 1b shown in the figure uses a Fizeau interferometer like the interference measuring apparatus 1a described above, and the object to be measured is a lens (lens to be measured).
23, which is a device in the case where the lens 23 to be inspected also serves as a condensing optical member. The phase difference between the reference light and the test light in this case corresponds to the wavefront aberration of the lens.

In the case of this interference measuring apparatus 1b, since the condenser lens changes every measurement (because of the object to be inspected), it is necessary to obtain the correction amount each time, but if the lens type is the same. Assuming that performances such as sine conditions are almost the same, a reference object (not shown) is installed at the position of the lens 23 to be inspected, and interference measurement is performed to obtain a correction amount.

The interference measuring device 1b includes a Fizeau interferometer (hereinafter referred to as an interferometer) 2b, an image pickup unit 28 which is an interference fringe detecting means, and an image processing device (not shown) including an A / D converter and an image memory. , A calculation device, a monitor device, and a memory that is a storage device. In this case, the image pickup unit 28, the image processing device, the calculation means, the monitor device, and the memory of the interference measuring device 1b are respectively the image pickup unit 11, the image processing device 12, and the image processing device 12 of the interference measuring device 1a.
Since it has the same configuration as the computing means 13, the monitor device 14, and the memory 15, the description thereof will be omitted.

The interferometer 2b in the interference measuring apparatus 1b is
Light source 18, objective lens 19, collimator lens 20
, Half mirror 21, and flat prototype 22 as a reference member
And a drive means 222 such as a PZT for moving the plane prototype 22 with high precision with respect to the optical axis 26 and performing the phase shift method.
A reflecting mirror 24 that is a reflecting member, and a moving unit 2 that can move the reflecting mirror 24 in the direction of the optical axis 26 and in the direction perpendicular to the optical axis 26.
5, an adjustment amount control means (not shown), and an observation lens 27.

In this case, the light source 18, the objective lens 19, the collimator lens 20, the half mirror 21, of the interferometer 2b,
Moving means 25, adjustment amount control means and observation lens 27
Have the same configurations as the light source 3, the objective lens 4, the collimator lens 5, the half mirror 6, the moving means 9, the adjustment amount control means 43, and the observation lens 10 of the interferometer 2a, respectively, and therefore description thereof will be omitted.

The flat prototype 22 in the interferometer 2b reflects a part of the incident light and transmits a part thereof. The final surface of the flat prototype 22, that is, the surface of the flat prototype 22 that faces the lens 23 under test constitutes a reference surface 221.

The reflecting mirror 24 in the interferometer 2b is formed into a concave curved surface so as to have a predetermined center of curvature, and the surface accuracy is very good. A lens having the design performance of the lens to be inspected is used as the reference object to be installed when obtaining the correction amount.

In the case of the interference measuring apparatus 1b having such a structure, the moving means 25 moves the reflecting mirror 24 in the direction of the optical axis 26 and in the direction perpendicular to the optical axis 26, and the reflecting mirror 24 is moved.
Are set in place. Alternatively, the lens 23 to be inspected and the reference object to be inspected are moved in the direction of the optical axis 26 and in the direction perpendicular to the optical axis 26 by moving means (not shown), and
3 and the reference test object are installed at predetermined positions.

The light emitted from the light source 18 in the interference measuring apparatus 1b passes through the objective lens 19 and the collimating lens 20 in order and becomes a parallel light expanded to a desired light beam diameter. The parallel light is incident on the half mirror 21, and a part of the parallel light passes through the half mirror 21.

The light transmitted through the half mirror 21 is incident on the flat prototype 22, a part of which is transmitted through the flat prototype 22 (reference surface 221), and the rest is the reference plane 2 of the flat prototype 22.
It reflects at 21. The light reflected by the reference surface 221 of the flat prototype 22 again enters the half mirror 21, and a part of the light is reflected by the half mirror 21 toward the observation lens 27 side.
The reflected light reaches the solid-state image sensor (CCD) 29 of the image pickup unit 28 through the observation lens 27 and serves as reference light.

On the other hand, the light transmitted through the reference surface 221 is
The light enters the lens 23 to be inspected, passes through the lens 23 to be inspected, and is once condensed, and then is irradiated to the reflecting mirror 24.
Reflect on. The light reflected by the reflecting mirror 24 returns to the original path, passes through the lens to be inspected 23, becomes parallel light again, and is incident on the flat plate prototype 22. The light enters the mirror 21, and a part of the light is reflected by the half mirror 21 toward the observation lens 27 side. The reflected light reaches the CCD 29 of the image pickup unit 28 through the observation lens 27 and becomes the test light.

Hereinafter, the operations of the image pickup unit 28, the image processing device, the calculation means, the monitor device, and the memory (for example, how to obtain the correction amount, the correction method, etc.) are the same as those of the interference measuring device 1a. .

In this interference measuring apparatus 1b, when performing interference measurement of the reference object, the maximum incident height from the optical axis 26 of the effective light beam incident on the reference object is h _max , and the focus of the reference object is Let f be the distance and θ _max be the angle between the outermost light beam of the focused light of the effective test light beam and the optical axis 26. When measuring the interference of the lens (test object) 23 under test, The maximum incident height from the optical axis 26 of the effective luminous flux incident on the inspection lens (inspection object) 23 is h _max , the focal length of the inspected lens (inspection object) 23 is f, and the inspected lens of the effective luminous flux ( When the angle between the outermost ray of the focused light by the object 23) and the optical axis 26 is θ _max , the numerical aperture NA ₀ is expressed by the following equations, respectively, and is based on this NA ₀ . Then, similar to the interference measuring apparatus 1a described above, a predetermined calculation is performed. NA ₀ = h _max / f = sin θ _max

The interference measuring apparatus 1b is an apparatus for measuring an object to be inspected (lens 23 to be inspected having a positive power) having a function of condensing a light beam. An apparatus for measuring an object to be inspected (a lens to be inspected having a negative power) having a function of diverging a light beam may be used. In this case, for example, in the interference measuring apparatus 1b, the curvature of the reflecting mirror 24, the reference test object, and the like may be changed appropriately. Further, the angle formed between the optical axis 26 and the outermost light beam of the divergent light from the reference test object or the test object of the effective luminous flux is θ _max .

Next, a third embodiment of the interference measuring apparatus of the present invention will be described. FIG. 20 is a diagram schematically showing a third embodiment of the interference measuring apparatus of the present invention. In the case of this interference measuring device 1c, a reference object (not shown) is installed at the position of the object 38, and interference measurement is performed to obtain a correction amount, as in the case of the interference measuring device 1a.

An interferometer 1c shown in the figure comprises a Twyman-Green interferometer (hereinafter referred to as an interferometer) 2c,
The imaging unit 41, which is an interference fringe detection unit, and an A / D (not shown)
The image processing apparatus includes a converter and an image memory, an arithmetic unit, a monitor unit, and a memory that is a storage unit.

In this case, the image pickup section 4 of the interference measuring apparatus 1c
1. The image processing device, the computing means, the monitor device, and the memory are respectively the image pickup unit 1 of the interference measurement device 1a.
1, image processing device 12, calculation means 13, monitor device 1
4 and the memory 15 have the same configuration, the description thereof will be omitted. Further, the reference object of the interference measuring apparatus 1c has the same configuration as the reference object 80 of the interference measuring apparatus 1a, and therefore its explanation is omitted.

The interferometer 2c in the interference measuring device 1c is
Light source 30, objective lens 31, collimator lens 32
A beam splitter 33, a reflecting mirror 34 as a reference member, a drive system 35 for driving the reflecting mirror 34, a condensing lens 36 as a condensing optical member, and an object 38 that also serves as a reflecting member. Optical axis 37 direction of lens 36 and optical axis 37
It has a moving unit 39 that can move in a direction perpendicular to the direction, an adjustment amount control unit (not shown), and an observation lens 40.

In this case, the light source 30, the objective lens 31, the collimator lens 32, the moving means 39, the adjustment amount control means, the observation lens 40 and the object 38 of the interferometer 2c are the light source 3, Since the objective lens 4, the collimator lens 5, the moving unit 9, the adjustment amount control unit 43, the observation lens 10 and the object 8 have the same configuration, the description thereof will be omitted.

The reflecting surface of the reflecting mirror 34 in the interferometer 2c,
That is, the facing surface of the beam splitter 33 in the reflecting mirror 34 constitutes a reference surface 341. Further, in order to utilize the phase shift method or the like for the fringe analysis, a piezo element or the like is used in the drive system 35 for driving the reflecting mirror 34. An aplanatic lens is used as the condenser lens 36 in the interferometer 2c.

In the case of the interference measuring apparatus 1c having such a structure, the moving means 39 moves the test object 38 and the reference test object in the optical axis 37 direction and in the direction perpendicular to the optical axis 37 to move the object to be measured. The inspection object 38 and the reference inspection object are installed at predetermined positions.
The light emitted from the light source 30 in the interference measuring device 1c passes through the objective lens 31 and the collimator lens 32 in order, and becomes parallel light expanded to a desired light beam diameter.

This parallel light enters the beam splitter 33, and a part of the parallel light passes through the beam splitter 33.
The remaining portion is reflected by the beam splitter 33 toward the reference surface 341.

The light reflected by the beam splitter 33 is applied to the reference surface 341, reflected by the reference surface 341, and incident on the beam splitter 33 again, and a part of the light passes through the beam splitter 33. This transmitted light is
Via the observation lens 40, the solid-state image sensor (CC
D) It reaches above 42 and becomes reference light.

On the other hand, the light that has passed through the collimator lens 32 and further through the beam splitter 33 enters the condenser lens 36, passes through the condenser lens 36 and is once condensed, and then the object 38 to be inspected. The surface 381 to be inspected is irradiated and reflected by the surface 381 to be inspected. The light reflected by the surface to be inspected 381 returns to the original path, passes through the condenser lens 36, becomes parallel light again, and further enters the beam splitter 33,
A part of the light is reflected by the beam splitter 33 toward the observation lens 40. The reflected light reaches the CCD 42 of the image pickup unit 41 through the observation lens 40 and becomes the test light.

Hereinafter, the operations of the image pickup unit 41, the image processing device, the calculation means, the monitor device, and the memory (for example, how to obtain the correction amount, the correction method, etc.) are the same as those of the interference measuring device 1a. Illustration and description are omitted.

Next, a fourth embodiment of the interference measuring apparatus of the present invention will be described. FIG. 21 is a diagram schematically showing a fourth embodiment of the interference measuring apparatus of the present invention. In the case of this interference measuring apparatus 1d, a reference test object (not shown) is installed at the position of the test object 59 as in the case of the interference measuring apparatus 1a, and interference measurement is performed to obtain a correction amount. An interferometer 1d shown in the figure is a Twyman-Green interferometer (hereinafter referred to as an interferometer) 2
d, an image pickup unit 62 that is an interference fringe detection unit, an image processing device that includes an A / D converter and an image memory (not shown), a calculation unit, a monitor device, and a memory that is a storage unit. .

In this case, the image pickup section 6 of the interference measuring apparatus 1d
2. The image processing device, the calculation means, the monitor device, and the memory are respectively the image pickup unit 1 of the interference measurement device 1a.
1, image processing device 12, calculation means 13, monitor device 1
4 and the memory 15 have the same configuration, the description thereof will be omitted. Further, the reference object of the interference measuring device 1d has the same configuration as the reference object 80 of the interference measuring device 1a, and therefore its explanation is omitted.

The interferometer 2d in the interference measuring device 1d is
Light source 51, objective lens 52, collimator lens 53
A beam splitter 54, a reflecting mirror 55 as a reference member, a drive system 56 for driving the reflecting mirror 55, and a diverging lens as a diverging optical member (a lens having negative power).
57 and a test object 59 that also serves as a reflecting member
It has a moving means 60 that can move in the direction of the optical axis 58 and a direction perpendicular to the optical axis 58, an adjustment amount control means (not shown), and an observation lens 61.

In this case, the light source 51 of the interferometer 2d, the objective lens 52, the collimator lens 53, the moving means 60, the adjustment amount control means, the observation lens 61 and the object 59 are respectively the light source 3 of the interferometer 2a, Since the objective lens 4, the collimator lens 5, the moving unit 9, the adjustment amount control unit 43, the observation lens 10 and the object 8 have the same configuration, the description thereof will be omitted.

The reflecting surface of the reflecting mirror 55 in the interferometer 2d,
That is, the facing surface of the beam splitter 54 in the reflecting mirror 55 constitutes a reference surface 551. Further, in order to use the phase shift method or the like for the fringe analysis, for example, a piezo element or the like is used in the drive system 56 that drives the reflecting mirror 55. An aplanatic lens is used as the diverging lens 57 in the interferometer 2d.

In the case of the interference measuring apparatus 1d having such a structure, the moving means 60 moves the test object 59 and the reference test object in the direction of the optical axis 58 and in the direction perpendicular to the optical axis 58 to move the object to be measured. The inspection object 59 and the reference inspection object are installed at predetermined positions.
The light emitted from the light source 51 in the interference measurement device 1d passes through the objective lens 52 and the collimator lens 53 in order, and becomes parallel light expanded to a desired light beam diameter. The parallel light enters the beam splitter 54, a part of the parallel light passes through the beam splitter 54, and the remaining part is reflected by the beam splitter 54 toward the reference surface 551 side.

The light reflected by the beam splitter 54 is applied to the reference surface 551, reflected by the reference surface 551, and incident on the beam splitter 54 again, and a part of the light passes through the beam splitter 54. This transmitted light is
Through the observation lens 61, the solid-state image sensor (CC
D) It reaches above 63 and becomes the reference light. On the other hand, the beam splitter 54 is transmitted through the collimator lens 53.
The light that has passed through enters the divergent lens 57. The divergent light transmitted through the diverging lens 57 is the surface 591 to be inspected of the object 59 to be inspected.
And is reflected by the surface 591 to be inspected. Test surface 59
The light reflected by 1 returns to the original path, passes through the divergence lens 57, becomes parallel light again, and is incident on the beam splitter 54. Part of the light is reflected by the beam splitter 54 toward the observation lens 61 side. This reflected light reaches the CCD 63 of the image pickup section 62 through the observation lens 61 and becomes the test light.

Hereinafter, the operations of the image pickup unit 62, the image processing device, the calculation means, the monitor device, and the memory (for example, how to obtain the correction amount, the correction method, etc.) are the same as those of the interference measuring device 1a. Illustration and description are omitted. The interference measuring apparatus 1d having such a configuration is used for measuring an object to be inspected having a concave surface having a relatively large curvature radius.

In each of the above embodiments, the Fizeau interferometers 2a and 2a are used as the interferometers of the interferometer.
b, Twyman-Green type interferometers 2c and 2d are used, but the interferometer in the present invention is not limited to these.
In addition, the interferometer may be configured using various interferometers.

Further, in each of the above-described embodiments, when obtaining the correction amount (measurement of the reference object), an aplanatic condensing lens or a diverging lens is used as the converging optical member or the diverging optical member of the interferometer. However, the condensing optical member or the diverging optical member in the present invention is not limited to these, and the condensing optical member or the diverging optical member may have a configuration capable of condensing or diverging incident light. It can be anything. For example, a condensing lens or a diverging lens that does not satisfy the sine condition may be used as the condensing optical member or the diverging optical member of the interferometer.

Further, in each of the above-mentioned embodiments, as the moving means, the moving means 9 and the reflecting mirror capable of moving the test object 8 and the reference test object 80 in the direction of the optical axis 73 and the direction perpendicular to the optical axis 73, respectively. A moving means 25 capable of moving 24 in the direction of the optical axis 26 and a direction perpendicular to the optical axis 26, and a moving means capable of moving the test object 38 and the reference test object in the optical axis 37 direction and the direction perpendicular to the optical axis 37. 39, the inspection object 59 and the reference inspection object on the optical axis 58
However, the moving means in the present invention is not limited to the moving means 60 which can move in the direction perpendicular to the optical axis 58.

For example, the moving means in the present invention relatively moves the condensing point of the object (reflecting member) and the condensing point of the condensing optical member in the optical axis direction and the direction perpendicular to the optical axis. What can be done, what can be moved relative to the condensing point of the inspection object (condensing optical member) and the condensing point of the reflecting member in the optical axis direction and the direction perpendicular to the optical axis, the inspection object ( The condensing point of the reflection member),
What can relatively move the focal point (virtual image) of the diverging optical member in the optical axis direction and the direction perpendicular to the optical axis, or the focal point of the test object (divergent optical member) and the condensing point of the reflecting member. Any structure may be used as long as it can be moved relative to the optical axis direction and the direction perpendicular to the optical axis.

Further, as the measurement of the test object in the present invention, for example, the surface shape of an optical element such as a lens or a mold,
Examples include measurement of transmitted wavefront aberration, and measurement of wavefront aberration of the output wavefront of the optical disk device.

Further, the reference object in the present invention corresponds to the object, for example, if the object is a lens, a lens is used as the reference object and the object is a reflective surface. If it has, a reference object having a reflecting surface is used.

In each of the above embodiments, the correction amount is an approximate linear expression, but the correction amount in the present invention is not limited to this. For example, in the case of defocus, W ₂₀ and W
_{For n0} (for example, W ₂₀ and W ₄₀ , W ₂₀ and W _60, etc.), a plurality of combinations may be stored as a table. In the case of tilt, W _1m and W _nm (for example, W ₁₁ and W ₆₀ ) may be stored.
₃₁ , W ₁₁ and W ₅₁ , W ₁₂ and W ₃₂ , W ₁₂ and W _52, etc.) may be stored as a table.

Further, in each of the above-described embodiments, the interference measurement of the reference object for obtaining the correction amount is performed at three installation positions, but the present invention is not limited to three positions. In this case, the interferometric measurement of the reference object for obtaining the correction amount is
Generally, any number of installation positions may be used if there are two or more.

Further, in each of the above-described embodiments, the correction amount is obtained in advance, the correction amount coefficient is stored in the memory, and the correction amount coefficient is read from the memory and corrected each time the interference measurement of the test object is performed. However, in the present invention, for example, the correction amount may be obtained each time the interference measurement of the test object is performed.

Further, in each of the above embodiments, in the case of defocus, only the 4th and 6th order aberrations are corrected.
The order of the aberration to be corrected in the present invention is not limited to the above embodiment. That is, in the case of defocusing, the aberration orders corrected in the present invention can be any combination as long as they are even orders of four or more. In addition,
When correcting aberrations of even-numbered orders of 8th and higher, for example, the correction may be performed in the same manner as in the case of correcting the 4th-order and 6th-order aberrations in the above-described embodiment.

Further, in each of the embodiments, in the case of tilt, only the third-order and fifth-order aberrations are corrected, but the order of the aberrations to be corrected in the present invention is not limited to the above-mentioned embodiments. That is, in the case of tilt, the aberration orders corrected in the present invention can be arbitrarily combined as long as they are odd orders of three or more. In addition, when correcting the aberrations of the 7th and higher odd orders, for example, the correction may be performed in the same manner as the case of correcting the 3rd and 5th order aberrations in the above-described embodiment.

Further, in the present invention, only one of the correction of the aberrations of the fourth and higher even orders related to the defocus and the correction of the aberrations of the third and higher order related odds regarding the tilt may be performed, or the defocus may be performed. The correction of the even-numbered aberrations of the fourth order or higher regarding the tilt and the correction of the aberrations of the odd-order higher than the third order related to the tilt may be performed.

Further, in each of the above embodiments, the height of incidence on the condensing optical member or the diverging optical member in the measurement of the reference object,
Although the correction is performed by the difference from the incident height on the condensing optical member or the divergent optical member in the measurement of the test object, for example, the incident height on the condensing optical member or the divergent optical member in the measurement of the reference object is performed. Such correction may be omitted when the incident heights on the converging optical member and the diverging optical member in the measurement of the test object are the same.

Further, in each of the above embodiments, the correction of subtracting the aberration of the interferometer itself from the measurement value is performed, but in the present invention, the correction of the aberration of the interferometer itself may be omitted.

Further, in the present invention, the test object and the reference test object may be separate, and the reference test object may be the test object. When the reference test object is the test object,
The measurement value when obtaining the correction amount may be used as the measurement value of the test object, and in addition to the measurement when obtaining the correction amount,
The test object may be newly measured. Although the present invention has been described above based on the illustrated configuration example, the present invention is not limited to this.

[0230]

As described above, according to the interference measuring apparatus and the interference measuring method of the present invention, even when there is a setting error of the test object such as Difukas and tilt in the measurement of the aberration of the test object, Highly accurate measurement can be performed without performing accurate alignment that eliminates setting errors.

In this case, in particular, when a relatively bright condensing lens or a diverging lens or a condensing lens or a diverging lens that does not satisfy the sine condition is used as the condensing optical member or the diverging optical member of the interferometer. As compared with the case where the correction is not performed in the present invention, the measurement accuracy is significantly improved. That is, the same accuracy can be obtained without using an expensive aplanatic lens.

When the reference object and the object to be inspected are different, if the correction amount is obtained once and stored in the memory, the correction amount is stored in the memory each time the object is measured. Since it can be read out and used, when measuring a test object, it is only necessary to measure the test object and at a single installation position,
The work can be simplified and speeded up in a mass production process in which a large number of test objects are measured. Further, when the reference test object is the test object, it is not necessary to replace the reference test object and re-install the test object after obtaining the correction amount.

[Brief description of drawings]

FIG. 1 is a diagram schematically showing a first embodiment of an interference measuring device of the present invention.

FIG. 2 is a diagram schematically showing a first embodiment of the interference measuring apparatus of the present invention.

FIG. 3 is a diagram showing a configuration example of a condenser lens substantially satisfying a sine condition.

FIG. 4 is a diagram showing a configuration example of a condenser lens in which a sine condition is not satisfied.

FIG. 5 is a graph (aberration diagram) showing spherical aberration and sine conditions of a condenser lens substantially satisfying the sine condition.

FIG. 6 is a graph (aberration diagram) showing spherical aberration and a sine condition of a condenser lens that does not satisfy the sine condition.

FIG. 7 is a graph showing the relationship between the fourth-order and even-order aberrations caused by defocus in a condenser lens that substantially satisfies the sine condition, and the incident height (h).

FIG. 8 is a graph showing the relationship between the fourth-order and even-order aberrations caused by defocus in a condenser lens that does not satisfy the sine condition and the incident height (h).

FIG. 9 is a graph showing the relationship between the third-order and higher odd-order aberrations caused by tilt in a condenser lens that substantially satisfies the sine condition, and the incident height (h).

FIG. 10 is a graph showing the relationship between the third-order and higher odd-order aberrations caused by tilt in a condenser lens that does not satisfy the sine condition, and the incident height (h).

FIG. 11 is a diagram schematically showing a first embodiment of the interference measuring apparatus of the present invention.

FIG. 12 is a graph showing the relationship between W ₂₀ and W ₄₀ in the present invention.

FIG. 13 is a graph showing the relationship between W ₂₀ and W ₆₀ in the present invention.

FIG. 14 is a diagram schematically showing a first embodiment of the interference measuring apparatus of the present invention.

FIG. 15 shows the operation of the interferometer when obtaining the correction amount for defocus and the case of performing the aberration measurement of the surface to be inspected of the object in the present invention. 3 is a flowchart showing the operation of the interference measuring device when correcting the error.

FIG. 16 shows the operation of the interferometer when obtaining the correction amount for defocus and the case of performing the aberration measurement of the surface to be inspected of the object in the present invention. 3 is a flowchart showing the operation of the interference measuring device when correcting the error.

FIG. 17 shows the operation of the interferometer when obtaining the correction amount for tilt in the present invention and the case where the aberration measurement of the surface to be inspected of the object to be inspected is performed. It is a flowchart which shows operation | movement of the interference measuring apparatus at the time of amending.

FIG. 18 shows the operation of the interferometer when obtaining the correction amount for tilt in the present invention and the case where the aberration measurement of the surface to be inspected of the object is performed, and only the third-order and fifth-order aberrations are detected. It is a flowchart which shows operation | movement of the interference measuring apparatus at the time of amending.

FIG. 19 is a diagram schematically showing a second embodiment of the interference measuring device of the present invention.

FIG. 20 is a diagram schematically showing a third embodiment of the interference measuring apparatus of the present invention.

FIG. 21 is a diagram schematically showing a fourth embodiment of the interference measuring device of the present invention.

[Explanation of symbols]

 1a, 1b, 1c, 1d Interferometer 2a, 2b Fizeau interferometer 2c, 2d Twyman-Green interferometer 3 Light source 4 Objective lens 5 Collimator lens 6 Half mirror 7 Standard lens 71 Reference surface 711 Driving means 73 Optical axis 75 Condensing Point 8 Test Object 80 Reference Test Object 81 Test Surface 810 Reference Spherical Surface (Reference Test Surface) 85 Curvature Center 850 Curvature Center 9 Moving Means 10 Observation Lens 11 Imaging Unit 12 Image Processing Device 13 Computing Means 14 Monitor Device 15 Memory for exclusive use of data 16 Rays 17 Solid-state imaging device (CCD) 18 Light source 19 Objective lens 20 Collimating lens 21 Half mirror 22 Planar prototype 221 Reference surface 222 Driving means 23 Test lens 24 Reflecting mirror 25 Moving means 26 Optical axis 27 Observation Lens 28 Imaging unit 29 Solid-state imaging device (CCD) 30 light source 31 objective lens 32 collimator lens 33 beam splitter 34 reflecting mirror 341 reference surface 35 drive system 36 condensing lens 37 optical axis 38 test object 381 test surface 39 moving means 40 observation lens 41 imaging unit 42 solid-state image sensor (CCD) ) 43 adjustment amount control means 45 interference fringe 47 interference fringe 51 light source 52 objective lens 53 collimator lens 54 beam splitter 55 reflecting mirror 551 reference surface 56 drive system 57 divergence lens 58 optical axis 59 test object 591 test surface 60 moving means 61 Observation lens 62 Imaging unit 63 Solid-state imaging device (CCD) 101 to 114 steps 301 to 314 steps

Claims (24)

[Claims] 1. The light from a light source is divided into two, one is used as a reference light from a reference surface, and the other is used as a test light from a test object, and the reference light and the test light are superimposed. An interference measuring device for obtaining a phase difference between the reference light and the test light based on the interference fringe, and obtaining the interference fringe, wherein the interference fringe is an approximate polynomial for specifying the phase difference. A first means for developing a value corresponding to the coefficient of each term of the approximate polynomial, based on the numerical aperture of the effective light flux that enters into the test area or exits from the test area, and a reference test object In the state where a setting error is given to the relative position with respect to the interferometer, the setting error amount is changed to perform the interference measurement at least twice, and the measurement value of the reference object obtained by the first means. Second means for obtaining the correction amount of the aberration based on In the interference measurement, the interference measurement device further comprises a third means for correcting the measured value of the test object obtained by the first means based on the correction amount. 2. The interference measuring apparatus according to claim 1, wherein the approximate polynomial is the equation (1) shown in the following mathematical expression 1. [Equation 1] 3. The interference measuring apparatus according to claim 1, wherein the interference measuring apparatus has a condensing optical member in an optical path of the test light. 4. The setting error is given at least in the optical axis direction of the condensing optical member, and the measured value to be corrected is a coefficient of an even-order term of 4th order or more in the approximation polynomial. An interferometer according to item 1. 5. The correction amount is obtained by using a coefficient W ₂₀ of a quadratic term of the approximation polynomial to represent a coefficient of an even-order term of 4th order or more in the approximation polynomial by a linear function. The interference measurement device described. 6. The third means calculates a coefficient W _n0 ′ of an even-order term of the approximate polynomial in the object under test as
The interference measurement apparatus according to claim 5, wherein the interference measurement apparatus is corrected by the equation (13). [Equation 2] 7. The setting error is given at least in a direction perpendicular to the optical axis of the condensing optical member, and the measured value to be corrected is a coefficient of an odd-order term of third order or more in the approximate polynomial. The interferometric measuring device according to claim 3. 8. The correction amount is a first-order term of the approximate polynomial.
Coefficient of₁₁And W ₁₂Using each of the
The coefficient of the odd-order terms of the third order or higher in the term expression is a linear function
The interference measuring apparatus according to claim 7, which is represented. 9. The third means calculates a coefficient W _nm ′ of an odd-order term of the approximate polynomial in the test object as
The interference measuring apparatus according to claim 8, wherein the interference measuring apparatus is corrected by the equation (25). [Equation 3] 10. The interference measuring apparatus according to claim 1, wherein the reference test object is a test object. 11. The light from the light source is divided into two, one is used as the reference light from the reference surface, and the other is used as the test light from the test object, and the reference light and the test light are superimposed. An interference measurement method for detecting a phase difference between the reference light and the test light based on the interference fringe, together with obtaining an interference fringe, wherein a relative position of a reference test object with respect to the interference measurement device is provided. In the state where the setting error is given, the setting error amount is changed and the interference measurement is performed at least twice to obtain a plurality of interference fringes, and the interference fringes are developed into an approximate polynomial for specifying the phase difference, Based on the numerical aperture of the effective light flux incident on the region or emitted from the region to be inspected, the value corresponding to the coefficient of each term of the approximate polynomial is obtained, and the aberration is corrected based on the measured value of the reference object. Calculate the amount, and in the interferometric measurement of the test object, based on the correction amount Interference measurement method characterized by correcting the measured value of the test object. 12. The interference measuring method according to claim 11, wherein the test light has passed through a condensing optical member. 13. The setting error is given at least in the optical axis direction of the condensing optical member, and the measured value to be corrected is a coefficient of an even-order term of 4th order or more in the approximation polynomial. The interference measurement method described in. 14. The correction amount is obtained by using a coefficient W ₂₀ of a quadratic term of the approximation polynomial to represent a coefficient of an even-order term of a fourth order or higher in the approximation polynomial as a linear function. Interference measurement method described. 15. The interference measuring method according to claim 14, wherein the coefficient W _n0 ′ of the even-order term of the approximate polynomial in the test object is corrected by the equation (13) shown in the following Expression 4. [Equation 4] 16. The setting error is given at least in a direction perpendicular to the optical axis of the condensing optical member, and the measured value to be corrected is a coefficient of an odd-order term of third order or more in the approximate polynomial. The interference measurement method according to claim 12. 17. The correction amount represents a coefficient of an odd-order term of a third order or higher in the approximate polynomial as a linear function using each of the coefficients W ₁₁ and W ₁₂ of the primary term of the approximate polynomial. The interference measuring method according to claim 16. 18. The interference measuring method according to claim 17, wherein the coefficient W _nm ′ of the odd-order term of the approximate polynomial in the test object is corrected by the equation (25) shown in the following Expression 5. [Equation 5] 19. The interference measuring method according to claim 11, wherein an object to be inspected is used as the reference object to be inspected. 20. The light from the light source is divided into two, one of which is reflected by a reference surface to be a reference light, and the other of which is made into a convergent light or a divergent light by an optical member and made incident on a surface to be inspected. As the test light by reflecting on the surface, while obtaining the interference fringes by superimposing the reference light and the test light, the phase difference between the reference light and the test light based on the interference fringes. An interference measuring device for detecting, wherein the interference fringes are developed into an approximate polynomial that specifies the phase difference, and based on the numerical aperture of an effective light beam that is incident on or emitted from a test region, the approximation A first means for obtaining a value corresponding to the coefficient of each term of the polynomial, and a setting error in the relative position of the reference surface to be measured with respect to the interferometer is changed at least twice. The group obtained by the first means is measured by interferometry. Second means for obtaining a correction amount of aberration based on the measured value of the surface to be inspected, and, in interference measurement of the surface to be inspected, based on the correction amount, the second means of the surface to be inspected obtained by the first means. An interferometric measuring apparatus, comprising: a third means for correcting a measured value. 21. The interferometer according to claim 20, wherein the optical member is a standard lens having the reference surface. 22. The interferometer according to claim 20, wherein the optical member is a lens having a positive power. 23. The interferometer according to claim 20, wherein the optical member is a lens having negative power. 24. The light from the light source is divided into two, one of which is used as a reference light, and the other of which is transmitted as an inspection light by passing through an inspection object having an action of converging or diverging a light beam. An interference measuring device for detecting the phase difference between the reference light and the test light based on the interference fringes, while obtaining the interference fringes by superimposing the test light, the interference fringes, A value that corresponds to the coefficient of each term of the approximate polynomial is developed based on the numerical aperture of an effective light beam that enters the test area or that exits from the test area. And a setting error is given to the relative position of the reference object having the action of converging or diverging the light beam with respect to the interferometer, the setting error amount is changed to perform the interference measurement at least twice. Said obtained by said first means Based on the measured values of the quasi-specimen, second to determine the amount of correction of aberrations
And a third means for correcting the measurement value of the test object obtained by the first means in the interferometric measurement of the test object having the action of converging or diverging a light beam. An interferometric measuring device comprising: