JPH0443902A - Interference measuring instrument and detecting method of alignment thereof - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention utilizes interference fringes formed by the interference effect of light to accurately measure the shape of flat surfaces, spherical surfaces, and aspheric surfaces such as lenses and mirrors. The present invention relates to an interference measurement device.

[Conventional technology]

In general, literature on detection devices that measure the surface shape of optical elements on the order of less than the wavelength of light includes, for example, Utility Model Application Publication No.
There is a publication No. 67514. The technique disclosed in this publication will be explained with reference to FIGS. 5 and 6.

In FIG. 5, light emitted from a light source 1 passes through a beam expander 2, enters a beam splitter 3, and is split into a reference beam and a measurement beam, each of which is placed on a reference surface 4.
and the surface to be inspected 6, and the reflected light beams are respectively made to enter the beam splitter 3 again and overlap each other to form interference fringes on the image sensor 9 via the imaging lens 8, and are displayed on the display unit 12. . If the reference plane 4 is tilted at this time, interference fringes are obtained on the display section 12. That is, Fig. 6 (
4) As shown in (b) and (C), an image with a large number of interference fringes is obtained, and the alignment of the interferometer is detected and measured by visually counting the number and inclination of these fringes one by one. be.

Furthermore, as a document on the above-mentioned method of changing to visual inspection, there is, for example, Japanese Patent Application Laid-Open No. 1-185404. The technology disclosed in this publication receives interference fringes with an image sensor, outputs them as an interference fringe image signal, and superimposes them with reference fringe image data stored in one image storage means using a calculation means to generate a moiré fringe image signal. The alignment of the interference needle is detected from the period of moiré fringes that change according to the adjustment of the inclination of the reference plane.

[Problem to be solved by the invention]

However, the technique disclosed in the former publication, that is, the method of visually counting the number and inclination of interference fringes to detect the alignment of the interferometer, requires very troublesome detection work and is difficult to perform delicate operations. There was a problem that highly accurate alignment could not be obtained.

Furthermore, the alignment detection method using moire fringes according to the latter publication requires a storage means for storing reference fringe image data and a signal processing circuit for electrically detecting the period of moire fringes. There were problems in terms of cost and quality.

The present invention has been made in view of the above problems, and aims to provide an interference measuring device that can detect and adjust the alignment of an interferometer with high precision and at high speed, and a method for detecting the alignment. be.

[Means to solve the problem]

An overview of the present invention will be explained based on the drawings.

FIG. 1 is a block diagram showing the basic configuration of an interference measuring device according to the present invention.

As shown in the figure, reflected light from the reference surface 4 of the interferometer 14 and reflected light from the test surface 6 held by the alignment adjustment section 7 having a holding section that can adjust the tilt angle and move in the optical axis direction. The interference fringes formed by the interference with the alignment adjustment section 7 and changed by the adjustment of the alignment adjustment section 7 are detected by the interference fringe detection section 9, and the output is processed by the calculation processing section 11 to calculate the wavefront aberration. The wavefront aberration obtained in the processing unit 11 is expanded into a Zernike polynomial,
The X-direction tilt, Y-direction tilt, and defocus amounts are calculated using coefficients corresponding to the X-direction tilt, X-direction tilt, and defocus components, and are displayed on the display unit 12.

[Effect]

The operation of the above configuration will be explained using mathematical formulas.

Wavefront aberration at pupil coordinates (Xi, Yj) is (Xi).

Yj ) and expand it to the 9th term with Zernike polynomial 2, in polar coordinates (ρ, Q) format, W (Xi, Yj) - Co + C + ρ cos θ + C1 ρs
inθ+Cx(2ρ" 1)+C, p"cos
2θ0C, ρ"5in2θ+ CbC3p" -2)
It is expressed as acosθ+C7(3ρ"-2)psinθ+c*(6ρ4-6ρ2+1)...■.(
However, from the formula ρ=, r711 lower CoP), Seidel's aberration as shown below can be calculated, W (X i, Yj) = (Co Cs+ Ca
)+(C+-2C*)pcosθ・X direction tilt+(
C22Ct) ps+nθ・Y direction tilt+(2C3
-6C,)ρ2...7177 at defocus 10F"
cos (2θ--)ρo...as+31teh +C
7cos(θ-β)ρ3°°° coma +60. ρ4
...Third spherical aberration [however, a = tan-'
(Cs/Ca)β=taN'(ct/ci))"・
(2) Each coefficient C, ~C1 is determined by the method of small squares.

According to Equation 0, there are three wavefront aberrations that are caused by alignment errors of the interferometer: tilt in the X direction, tilt in the X direction, and defocus, and their magnitudes are given as follows.

Tilt amount in the X direction C, -2C.

Tilt amount in the Y direction Cz 2Ct tear t - scrapl 2 Cx 6 C* + (75-C7) These alignment amounts are adjusted by the alignment adjustment section 7 so that they are equal to or less than a predetermined target value.

〔Example〕

An interference measuring device and an alignment method thereof according to the present invention will be explained based on examples.

In the drawings, the same configurations or members in FIG. 1 and each embodiment are denoted by the same reference numerals, and the description thereof will be given in the first drawing and will be omitted hereinafter.

(First Embodiment) FIG. 2 is a front view schematically showing the configuration of a first embodiment of the interference measuring device according to the present invention.

The interferometer in this embodiment is an example applied to a Twyman Green type interferometer.

The light emitted from the light source 1 shown in the figure passes through a beam expander 2 and enters a beam splitter 3, where it is split into two, a reference beam and a measurement beam, and a reference plane disposed on each optical axis. 4 and the condenser lens 5, the light enters the surface to be inspected 6 and is reflected.

Each of the reflected light beams enters the beam splitter 3 again and is superimposed to form interference fringes on the image sensor 9 via the imaging lens 8.

The interference fringes formed on the image sensor 9 are input to the arithmetic processing section 11 via the A/D converter 10, and
Calculate the amounts of X-direction tilt, The adjustment is performed by the alignment adjustment unit 7 which has a holder at the end that can be moved in the Z direction, and the result is displayed on the display unit 12.

The target value is determined based on the surface accuracy of the surface to be inspected 6, the adjustment accuracy of the alignment adjustment section 7, and the like.

According to this embodiment with the above configuration, since the alignment amount is given quantitatively, highly accurate alignment fine adjustment can be performed.

(Second Embodiment) FIG. 3 is a front view schematically showing the configuration of a second embodiment of the interference measuring device according to the present invention.

The structure of the interferometer in this embodiment is an example applied to a Twyman-Green interferometer as in the first embodiment.

The alignment control unit 13 is configured to control the alignment adjustment unit 5 according to the amounts of the X-direction tilt, the X-direction tilt, and the defocus determined by (2) explained in FIGS. 1 and 2 above. . That is, by using a piezo element or the like in the adjustment drive section, fine adjustment of the alignment becomes possible.

With the above configuration, alignment adjustment can be performed automatically and high-speed alignment adjustment is also possible.

(Third Embodiment) FIG. 4 is a front view schematically showing the configuration of a third embodiment of the interference measuring device according to the present invention.

The configuration of the interferometer in this example is different from the first and second examples described above, and shows an example that is applicable to a Fizeau type interference needle.

It is constructed so that the light incident on the beam splitter 3 shown in FIG. 2 in the first embodiment is divided into two, and the resulting light beams are incident on the reference surface 4 and the test surface 6, respectively, and reflected. However, in this embodiment, as shown in FIG. It is configured to interfere with the reflected light reflected by the .

According to this embodiment with the above configuration, since the reference surface light flux and the measurement light flux pass through the same bus, the optical system can be made compact, and
It has advantages such as being able to reduce internal aberrations due to optical path differences.

〔Effect of the invention〕

According to the present invention having the above configuration and method, the measured wavefront aberration is expanded into a Zernike polynomial, and the expansion coefficient is used to detect the alignment amount, thereby making it possible to perform quantitative and highly accurate alignment. Furthermore, since the amount of alignment can be quantitatively detected, automatic alignment of the interferometer becomes possible by feeding back the value to the alignment control device.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the basic configuration of an interference measurement device according to the present invention. FIG. 2 is a front view schematically showing the configuration of a first embodiment of the interference measurement device according to the present invention. FIG. 3 is a front view schematically showing the configuration of a second embodiment of the interference measuring device according to the present invention. FIG. 4 is a front view schematically showing the configuration of a third embodiment of the interference measurement device according to the present invention. FIG. 5 is a front view schematically showing the configuration of a conventional interferometer. FIGS. 6(a), 6(b), and 6(C) are photographs of moiré fringes. l...Light source 2...Beam expander 3...Beam splinter 4...Reference surface 5...Focused beam 6...Test surface 7...Alignment adjustment unit 8...Result Image lens 9... Image sensor 10... A/D converter 11... Arithmetic processing section 12... Display section 13... Alignment control section 14... Interference needle Fig. 1

Claims (4)

[Claims] (1) An interferometer that makes a light beam emitted from a light source incident on a reference surface and a surface to be measured, and forms interference fringes by interfering with the reflected light; an interference fringe detection means that detects the interference fringes; The wavefront aberration between the reference surface and the test surface is calculated based on the output of the interference fringe detection means, and the wavefront aberration resulting from the calculation is expressed as Ze.
The present invention is characterized by comprising: arithmetic processing means for calculating the alignment amount of the interferometer by expanding it into a rnike polynomial, and an alignment adjustment means provided with a movable holding part for adjusting the tilt of one of the test surface and the reference surface. Interference measuring device. (2) an interferometer that divides the light beam emitted from a light source into two, makes one light beam incident on a reference surface and the other light beam on a test surface, and forms interference fringes by interfering with the reflected light; An interference fringe detection means for detecting the interference fringes, a wavefront aberration between the reference surface and the test surface is calculated based on the output of the interference fringe detection means, and the wavefront aberration resulting from the calculation is expanded into a Zernike polynomial. 1. An interference measurement device comprising: arithmetic processing means for determining the alignment amount of an interferometer; and alignment adjustment means provided with a movable holding section for adjusting the tilt of one of the test surface and the reference surface. (3) Alignment control means for controlling the tilt angle of one of the reference surface and the test surface according to the alignment amount determined by the arithmetic processing means for adjusting the tilt angle and movement in the optical axis direction. The interference measuring device according to claim 1 or claim 2, characterized in that: (4) Interference fringes that detect the interference fringes formed by dividing the light beam emitted from the light source into two, making one of the light beams incident on the reference surface and the other light beam on the test surface, and interfering with the reflected light. Based on the output of the detection means, the wavefront aberration between the reference surface and the test surface is expanded into a Zernike polynomial, and using the expansion coefficients C_0 to C_2, K_1=C_1-2C_4, K_2=C_2-2C_7
K_3=2C_3-6_8±√(C_4^2+C_3^
2), and adjusts the X-direction tilt, Y-direction tilt, and defocus so that these amounts are equal to or less than predetermined target values.