JP2005249575A - Interference measuring method and interferometer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an interference measuring method capable of acquiring data on luminance distributions of a plurality of significant interference fringes on which errors caused by environmental changes are not superposed. <P>SOLUTION: The interference measuring method includes procedures (11, 12, and 16) for dividing luminous flux to be projected to a surface to be inspected and a reference surface into a plurality of luminous fluxes (L<SB>1</SB>-L<SB>4</SB>) having different angles of light projection so as to simultaneously generate a plurality of interference fringes having phases different from one another and procedures (14, 18, and 15) for detecting the plurality of interference fringes simultaneously generated by the procedures. Even when environmental changes have occurred, only required differences (required phase differences) thereby occur between luminance distributions of the plurality of simultaneously generated interference fringes, on which errors caused by the environmental changes are not superposed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an interference measurement method and an interferometer for measuring a surface shape, and more particularly to an interference measurement method and an interferometer for acquiring luminance distribution data of a plurality of interference fringes having different phases as measurement data.

Measurement (interference measurement) using an interferometer is applied to highly accurate measurement of the surface shape (Non-Patent Document 1, etc.).
In this interference measurement, in order to improve measurement accuracy, luminance distribution data of a plurality of interference fringes having different phases are acquired as measurement data.
There are several methods for changing the phase of the interference fringes (fringed scanning). The optical path difference between the light beam emitted from the reference surface (reference light beam) and the light beam emitted from the test surface (test light beam) There are a method of changing by moving the inspection surface, a method of changing the wavelengths of the light beams instead of changing the optical path difference, and the like.

If the luminance distribution of interference fringes is detected a plurality of times during such fringe scanning, a plurality of significant interference fringe luminance distribution data having different phases can be acquired. If analysis (fringe analysis) is performed based on the luminance distribution data, the shape of the test surface based on the shape of the reference surface can be obtained with high accuracy.
Daniel Malacara, “Optical Shop Testing”, 2nd edition, published by Wiley-Interscience, p. 510-513

However, if an environmental change (vibration, air fluctuation, light source output change, etc.) occurs during fringe scanning, an unnecessary difference occurs between the luminance distribution data, resulting in an error. This error due to environmental changes cannot be eliminated by fringe analysis.
Therefore, an object of the present invention is to provide an interference measurement method and an interferometer that can acquire luminance distribution data of a plurality of significant interference fringes on which errors due to environmental changes are not superimposed.

The interference measurement method according to claim 1, wherein a plurality of light beams to be projected on the test surface and the reference surface are formed into light beams having different projection angles so that a plurality of interference fringes having different phases occur simultaneously. And detecting a plurality of interference fringes simultaneously generated by the procedure.
The interferometer according to claim 2, wherein a plurality of light beams to be projected onto the test surface and the reference surface are formed into light beams having different projection angles so that a plurality of interference fringes having different phases occur simultaneously. And a detection optical system for detecting each of the plurality of interference fringes generated at the same time.

An interferometer according to a third aspect of the present invention is the interferometer according to the second aspect, wherein the light projecting optical system includes an angle adjusting device for adjusting a relationship between light projection angles of the plurality of light beams. It is characterized by that.
The interferometer according to claim 4 is the interferometer according to claim 2 or 3, wherein the detection optical system includes a separation system that separates the plurality of interference fringes and a plurality of occurrence positions separated from each other. And a single image sensor that collectively detects the interference fringes.

The interferometer according to claim 5 is the interferometer according to claim 2 or 3, wherein the detection optical system includes a separation system for separating the plurality of interference fringes and a plurality of occurrence positions separated from each other. And a plurality of image sensors that individually detect the interference fringes.
The interferometer according to claim 6 is the interferometer according to any one of claims 2 to 5, wherein the light projecting optical system branches the light beam emitted from a single light source into a plurality of light beams. A branching system is provided.

  The interferometer according to claim 7 is the interferometer according to any one of claims 2 to 6, wherein the light projection optical system includes a plurality of incident light amount distributions on the test surface. An optical path adjustment system is provided for adjusting the arrangement relationship of the optical paths of the respective light beams so as to match each other.

  According to the present invention, an interference measurement method and an interferometer that can acquire luminance distribution data of a plurality of significant interference fringes on which errors due to environmental changes are not superimposed are realized.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
[Embodiment]
The present embodiment is an embodiment of an interferometer and an interference measurement method using the interferometer.
First, the configuration of the interferometer will be described.
As shown in FIG. 1, the interferometer includes a laser light source (having its wavelength λ) 11, a beam expander 12, a light projecting unit 16, a beam splitter (half mirror) 13, an imaging lens 14, and detection. Unit (corresponding to a separation system in claims) 18, an image pickup device (corresponding to an image sensor in claims) 15, and the like. Data output from the imaging device 15 is taken into a computer (not shown).

Among these, the laser light source 11, the beam expander 12, and the light projecting unit 16 correspond to the light projecting optical system in the claims, and the imaging lens 14, the detection unit 18, and the imaging device 15 are the detection optical system in the claims. Corresponding to
The light projecting unit 16 includes a beam splitter 161, two polarizing beam splitters 162 and 163, four plane reflecting mirrors (first reflecting mirror 171, second reflecting mirror 172, third reflecting mirror 173, and fourth reflecting mirror 174. ) Is provided.

Among these, the beam splitter 161 and the polarization beam splitters 162 and 163 correspond to the branching system in the claims.
At least three of the first reflecting mirror 171, the second reflecting mirror 172, the third reflecting mirror 173, and the fourth reflecting mirror 174 are supported by a stage (not shown) (corresponding to the angle adjusting device in the claims). The posture can be adjusted. This stage is a highly accurate stage generally used for alignment of optical elements.

The test object 1 and the Fizeau member 2 are set on the interferometer having the above-described elements.
Next, the behavior of each light beam in this interferometer will be described.
As shown in FIG. 1, the light beam emitted from the laser light source 11 is converted into a parallel light beam having an appropriate size by the beam expander 12 and then enters the beam splitter 161 in the light projecting unit 16.

The light beam incident on the beam splitter 161 is branched into two light beams of reflected light and transmitted light, and one light beam and the other light beam are incident on the polarization beam splitters 162 and 163, respectively.
The light beam incident on the polarization beam splitter 162 is branched into two light beams of reflected light and transmitted light (hereinafter referred to as a first light beam L ₁ and a second light beam L ₂ ) according to the polarization direction, and the first light beam is split. The light beam L ₁ and the second light beam L ₂ are incident on the reflecting surface 171a of the first reflecting mirror 171 and the reflecting surface 172a of the second reflecting mirror 172, respectively.

The light beam incident on the polarizing beam splitter 163 is also branched into two light beams of reflected light and transmitted light (hereinafter referred to as a third light beam L ₃ and a fourth light beam L ₄ ) according to the polarization direction, and third. The light beam L ₃ and the fourth light beam L ₄ are incident on the reflecting surface 173 a of the third reflecting mirror 173 and the reflecting surface 174 a of the fourth reflecting mirror 174, respectively.
The first light beam L ₁ and the second light beam L ₂ are reflected by the reflecting surfaces 171a and 172a, reenter the polarization beam splitter 162, and then enter the beam splitter 161.

The third light beam L ₃ and the fourth light beam L ₄ are reflected by the reflecting surfaces 173a and 174a, reenter the polarization beam splitter 163, and then enter the beam splitter 161.
The first light beam L ₁ , the second light beam L ₂ , the third light beam L ₃ , and the fourth light beam L ₄ incident on the beam splitter 161 are transmitted or reflected (transmitted in FIG. 1) through the beam splitter 13, and then the Fizeau member 2. Is incident on.

The first part of the light beam L ₁ the light beam L _1r, second part of the light beam L ₂ light beams L _2r, a third part of the light beam L ₃ light beams L _3r, the part of the fourth light beam L _four-beam L _4r is reflected by the reference surface r of the Fizeau member 2 and returns to the beam splitter 13 as a wavefront corresponding to the shape of the reference surface r (hereinafter, these light beams L _1r , L _2r , L _3r , L _4r are Are referred to as “first reference beam”, “second reference beam”, “third reference beam”, and “fourth reference beam”, respectively).

First other part of the light beam L ₁ the light beam L _1o, second other part of the light beam L ₂ light beams L _2o, third other part of the light beam L ₃ light beams L _3o, fourth light flux L ₄ The other part of the light beam L _4o passes through the Fizeau member 2 and then enters the test surface o of the test object 1 at the same angle as the incident angle to the reference surface r.
The light beams L _1o , L _2o , L _3o , and L _4o incident on the test surface o are reflected by the test surface o, become wavefronts according to the shape of the test surface o, and pass through the Fizeau member 2. 13 (hereinafter, these light beams L _1o , L _2o , L _3o , and L _4o are respectively referred to as “first test light beam”, “second test light beam”, “third test light beam”, “fourth test light”. This is referred to as “test light flux”.)

Incidentally, the present interferometer in which the test object 1 and the Fizeau member 2 are inserted side by side in the optical path in this way is a Fizeau interferometer.
The first reference light beam L _1r and the first test light beam L _1o (= first light beam L ₁ ) returned to the beam splitter 13 pass through the imaging lens 14 and the detection unit 18 (details will be described later) in order. incident on 15, to produce an interference pattern S _1.

The second reference light beam L _2r and the second test light beam L _2o (= second light beam L ₂ ) returned to the beam splitter 13 are also sequentially passed through the imaging lens 14 and the detection unit 18 (details will be described later). incident on 15, to produce an interference pattern S _2.
The third reference light beam L _3r and the third test light beam L _3o (= third light beam L ₃ ) returned to the beam splitter 13 are also sequentially passed through the imaging lens 14 and the detection unit 18 (details will be described later). incident on 15, to produce an interference pattern S _3.

The fourth reference light beam L _4r and the fourth test light beam L _4o (= fourth light beam L ₄ ) that have returned to the beam splitter 13 also pass through the imaging lens 14 and the detection unit 18 (details will be described later) in order. incident on 15, to produce an interference pattern S _4.
An imaging surface (not shown) of the imaging element in the imaging device 15 is disposed at a position conjugate with the test surface o with respect to the imaging lens 14.

The luminance distributions of the interference fringes S ₁ , S ₂ , S ₃ , and S ₄ that occur on the imaging surface include information on the shape of the test surface o based on the reference surface r. Data output from the imaging device 15 to a computer (not shown) is luminance distribution data of these interference fringes S ₁ , S ₂ , S ₃ , S ₄ .
Next, details of each part of the interferometer will be described.
First, in this interferometer, the arrangement angle θ ₁ of the first reflecting mirror 171 (incident angle of the first light beam L ₁ with respect to the reflecting surface 171a) and the arrangement angle θ ₂ of the second reflecting mirror 172 (reflection of the second light beam L ₂ ). The incident angle with respect to the surface 172a), the arrangement angle θ ₃ of the third reflecting mirror 173 (the incident angle of the third light beam L ₃ with respect to the reflecting surface 173a), the arrangement angle θ ₄ of the fourth reflecting mirror 174 (the reflection of the fourth light beam L ₄ ). (Incident angle with respect to the surface 174a) satisfies the formula (1).
₂ kd (cosθ ₂ −cosθ ₁ ) = π / 2
2 kd (cosθ ₃ −cosθ ₁ ) = π,
2 kd (cosθ ₄ −cosθ ₁ ) = 3π / 2 (1)
Here, k is the wave number (k = 2π / λ) of the light beam emitted from the light source 11, and d is the optical distance between the reference surface r and the test surface o.

Incidentally, in consideration of a general value of the wavelength λ of the light source 11 and a general value of the size of each part of the interferometer, it is between θ ₁ , θ ₂ , θ ₃ , and θ ₄ that satisfies this equation (1). The difference is slight (up to several minutes).
Therefore, in FIG. 1, the arrangement angle theta ₁ of the first reflecting mirror 171, an arrangement angle theta ₂ of the second reflecting mirror 172, an arrangement angle theta ₃ of the third reflection mirror 173, an arrangement angle theta of the fourth reflecting mirror 174 ₄ was shown as if all were "0".

The arrangement angle of the first reflecting mirror 171 is θ ₁ , the arrangement angle of the second reflecting mirror 172 is θ ₂ , the arrangement angle of the third reflecting mirror 173 is θ ₃ , and the arrangement angle of the fourth reflecting mirror 174 is θ ₄ . At a certain time, the incident angle of the first light beam L ₁ with respect to the reference surface r and the test surface o, the incident angle of the second light beam L ₂ with respect to the reference surface r and the test surface o, the third with respect to the reference surface r and the test surface o. The incident angle of the light beam L _{3 and} the incident angle of the fourth light beam L ₄ with respect to the reference surface r and the test surface o can also be expressed as θ ₁ , θ ₂ , θ ₃ , and θ ₄ , respectively (see FIG. 2A).

According to Equation (1), these incident angles θ ₁ , θ ₂ , θ ₃ , and θ ₄ are different from each other.
If θ ₁ , θ ₂ , θ ₃ , and θ ₄ are different from each other, as shown in FIG. 2B, the condensing point F ₁ of the first light beam L ₁ by the imaging lens 14 and the imaging lens 14 a converging point F ₂ of the second light flux L ₂ by a converging point F ₃ of the third light flux L ₃ by the imaging lens 14, a focal point F ₄ of the fourth light beam L ₄ by the image forming lens 14 is Shift.

In the present interferometer, the first reflecting mirror 171, the second reflecting mirror 172, and the second reflecting mirror F ₁ , F ₂ , F ₃ , and F ₄ are two-dimensionally distributed as shown in FIG. The inclination directions of the third reflecting mirror 173 and the fourth reflecting mirror 174 are appropriately selected.
Further, according to the equation (1), the phase difference generated between the interference fringes S ₁ , S ₂ , S ₃ , S ₄ is π / 2, π, 3π / 2. The reason is shown below.

First, when the arrangement angle of the n reflector is theta _n, as shown in FIG. 2 (a), the optical path difference between the n reference light beam L _nr and the n test light beam L _no, the table in 2Kdcosshita _n Is done.
Therefore, the luminance distribution I _n (x, y) of the interference pattern S _n by the n-th light flux L _n is expressed as equation (2).
I _n (x, y) = I ₀ (x, y) + A ₀ (x, y) cos [ψ ₀ (x, y) −ψ _r (x, y) +2 kd cos θ _n ] (2)
Where ψ ₀ (x, y) is the shape of the test surface o, ψ _r (x, y) is the shape of the reference surface r, I ₀ is the 0th-order component of the luminance distribution, and A ₀ is the luminance amplitude.

Therefore, the luminance distribution I ₁ of the interference pattern S ₁ (x, y), the luminance distribution I ₂ of the interference pattern S ₂ (x, y), the luminance distribution I ₃ of the interference pattern S ₃ (x, y), the interference pattern S ₄ luminance distribution I ₄ (x, y) are respectively represented as formula (3).
I ₁ (x, y) = I ₀ (x, y) + A ₀ (x, y) cos [ψ ₀ (x, y) −ψ _r (x, y) +2 kd cos θ ₁ ],
I ₂ (x, y) = I ₀ (x, y) + A ₀ (x, y) cos [ψ ₀ (x, y) −ψ _r (x, y) +2 kd cos θ ₂ ],
I ₃ (x, y) = I ₀ (x, y) + A ₀ (x, y) cos [ψ ₀ (x, y) −ψ _r (x, y) +2 kd cos θ ₃ ],
I ₄ (x, y) = I ₀ (x, y) + A ₀ (x, y) cos [ψ ₀ (x, y) −ψ _r (x, y) +2 kd cos θ ₄ ] (3)
Substituting equation (1) into equation (3), the phase difference between interference fringe S ₁ and interference fringe S ₂ is π / 2, the phase difference between interference fringe S ₁ and interference fringe S ₃ is π, It can be seen that the phase difference between the interference fringes S ₁ and S ₄ is 3 / 2π.

Next, the detection unit 18 will be described in detail.
As shown in FIGS. 3A and 3B, the detection unit 18 includes a quadrangular pyramid-shaped separation element 18 s and four planar reflecting mirrors 181, 182, 183, and 184.
In the separation element 18s, the surface 18s ₁ corresponding to four sides of the quadrangular _{pyramid, 18s 2, 18s 3, 18s} 4 is in the respective reflecting surfaces.

The posture of the separating element 18s is set so that the reflecting surfaces 18s ₁ , 18s ₂ , 18s ₃ , 18s ₄ face the imaging lens 14 side.
These reflective surfaces 18s _1, 18s _2, 18s _3, substantially at the center of the 18s _4, the focal point F ₁ of the first light flux L ₁ emitted from the imaging lens 14, the focal point F ₂ of the second light flux L _2, the third light flux L ₃ of the focal point F _3, the focal point F ₄ of the fourth light flux L ₄ are positioned respectively.

The reflecting surfaces 18s ₁ , 18s ₂ , 18s ₃ , 18s ₄ deflect the first light beam L ₁ , the second light beam L ₂ , the third light beam L ₃ , and the fourth light beam L ₄ in different directions.
The plane reflecting mirrors 181, 182, 183, and 184 have the first light beam L ₁ , the second light beam L ₂ , the third light beam L ₃ , and the fourth light beam L ₄ in the direction of the imaging device 15 as shown in FIG. To deflect.
By the action of such a detection unit 18, as shown in FIG. 4, the interference pattern S ₁ of the first light flux L _1, the interference pattern S ₂ of the second light flux L _2, the interference pattern S by the third light flux L _{3 3,} the interference pattern S ₄ according to the fourth light flux L ₄ can be reliably separated on the imaging surface 15a of the image pickup device 15.

Next, interference measurement using this interferometer will be described.
In the interference measurement, the above interferometer is driven.
A computer (not shown) takes in one luminance distribution data output at the same timing from the imaging device 15 of this interferometer, and the luminance distribution data of the interference fringes S ₁ , S ₂ , S ₃ , S _{4 from} the luminance distribution data. Are extracted individually.

Here, the phase difference between the interference fringes S ₁ and S ₂ , the phase difference between the interference fringes S ₁ and S ₃ , and the phase difference between the interference fringes S ₁ and S ₄ are respectively π / 2 and π according to the above-described equation (1). , 3π / 2.
The computer uses a fringe analysis suitable for the luminance distribution data of the interference fringes S ₁ , S ₂ , S ₃ , S ₄ having such a phase difference (for example, a well-known fringe analysis such as a 4-bucket method). Apply.
According to this fringe analysis, the shape (ψ ₀ (x, y) −ψ _r (x, y)) of the test surface o based on the reference surface r is _expressed as the wave number k and the 0th-order component I _{0 of the} luminance distribution. It can be obtained with high accuracy irrespective of (x, y) and luminance amplitude A ₀ (x, y).

Next, effects of the present interferometer and the interference measurement method will be described.
The interferometer includes a light projecting optical system such as a light projecting unit 16, and light beams L ₁ , L ₂ , L having different light projecting angles from each other are projected onto the test surface o and the reference surface r. to _3, L ₄ has a plurality of. As a result, a plurality of interference fringes S ₁ , S ₂ , S ₃ , and S ₄ having different phases are generated at the same time.

Further, the interferometer is provided with a detection optical system such as a detection unit 18 and detects the luminance distribution of the interference fringes S ₁ , S ₂ , S ₃ , and S ₄ that are generated at the same time.
Therefore, even if an environmental change occurs in the interferometer, only a necessary difference (necessary phase difference) occurs between the luminance distribution data of the interference fringes S ₁ , S ₂ , S ₃ , and S ₄ that occur at the same time. No error due to environmental changes is superimposed.

That is, the luminance distribution data of the interference fringes S ₁ , S ₂ , S ₃ , S ₄ acquired by the interference measurement using the present interferometer is a plurality of significant interference fringes in which errors due to environmental changes are not superimposed. It is data of.
Therefore, according to this interference measurement, the shape of the test surface o based on the reference surface r can be obtained with high accuracy without being affected by the environmental change of the interferometer.

Further, in this interferometer, since at least three postures among the first reflecting mirror 171, the second reflecting mirror 172, the third reflecting mirror 173, and the fourth reflecting mirror 174 can be adjusted, the light beams L ₁ and L ₂ are adjusted. , L ₃ , L ₄ can be adjusted with respect to the incident angle (light projection angle) with respect to the test surface o.
Therefore, even when the optical distance d between the reference surface r and the test surface o and the wavelength λ of the light source 11 are changed in various ways, the interferometer satisfies the same expression (1) and has the same effect. Can be obtained.

In addition, this interferometer is provided with a detection unit 18 for separating the occurrence positions of the plurality of interference fringes S ₁ , S ₂ , S ₃ , S ₄ , and the interference fringes S ₁ , S ₂ , S ₃ , S _{4 are provided.} And the single imaging device 15 that collectively detects the number of points of the imaging device 15 is minimized.
In addition, since the interferometer includes a light projecting unit 16 that branches a light beam emitted from a single light source 11 into a plurality of parameters, parameters (wave number k, zero-order component I of luminance distribution) determined by the characteristics of the light source 11 are provided. ₀ , luminance amplitude A ₀ ) can be more reliably shared among the plurality of interference fringes S ₁ , S ₂ , S ₃ , S ₄ . That is, this interferometer can more reliably acquire a plurality of significant luminance distribution data necessary for obtaining the shape of the test surface o with high accuracy.

[Modification of Embodiment]
In this interferometer, as shown in FIG. 5, an imaging lens (corresponding to the optical path adjustment system in claims) 19 is inserted between the test surface o and the reference surface r and the light projecting unit 16. For the imaging lens 19, the test surface o and the reflection surface 171a, the test surface o and the reflection surface 172a, the test surface o and the reflection surface 173a, and the test surface o and the reflection surface 174a may be set in a conjugate relationship.

The reason will be described below. Here, two representative reflecting surfaces 171a and 172a, two light beams L ₁ and L ₂ , and two interference fringes S ₁ and S ₂ will be described based on FIG. 6 (the other two reflecting surfaces and the other two reflecting surfaces). The same applies to one light beam and the other two interference fringes.)
Since the reflecting surfaces 171a and 172a are illuminated by the light flux from the common light source 11, even if intensity spots are generated in the light flux, as shown in the upper part of FIGS. The incident light amount distribution D1 on the surface 171a and the incident light amount distribution D2 on the reflecting surface 172a are substantially equal.

However, when the imaging lens 19 is not inserted, as shown in FIG. 6 (a), the light beam L ₁ and the light beam L ₂ is progressed slightly shifted, outside on the surface to be detected o. Therefore, as shown in the lower part of FIG. 6 (a), 'and the light flux incident light quantity distribution relative to the test surface o the L ₂ D2' light beam L ₁ incident light quantity distribution D1 for test surface o and are different.
On the other hand, even when the imaging lens 19 is inserted, as shown in FIG. 6B, the light beam L ₁ and the light beam L ₂ travel while being shifted little by little. Overlap on the test surface o. Therefore, as shown in the lower part of FIG. 6 (b), 'and the incident light intensity distribution for the test surface o of the light beam L ₂ D2' incident light intensity distribution D1 for test surface o of the light beam L ₁ and is consistent ( In other words, the amount of incident light at the same position on the test surface o matches between the light beam L ₁ and the light beam L ₂ .

Thus, if the incident light quantity distributions D1 ′ and D2 ′ match, the zero-order component I ₀ (x, y) of the luminance distribution between the interference fringes S ₁ caused by the light flux L ₁ and the interference fringes S ₂ caused by the light flux L ₂ is obtained. ) Can be shared more reliably.
As a result, a plurality of significant luminance distribution data necessary for obtaining the shape of the test surface o with high accuracy can be acquired more reliably.

Needless to say, when the intensity variation of the light beam emitted from the light source 11 is sufficiently small, the imaging lens 19 described here is unnecessary.
In this interferometer, a beam splitter (half mirror) may be used instead of the polarizing beam splitter 162 or 163 (see FIGS. 1 and 5).
Further, in this interferometer, instead of the branch system (beam splitter 161, polarization beam splitter 162, 163) shown in FIGS. 1 and 5, a single unit having these functions as shown in FIG. A prism 261 may be applied. In FIG. 7, a light projecting unit to which such a prism 261 is applied is denoted by reference numeral 26.

In this interferometer, at least one of the light projecting units 16 and 26 shown in FIGS. 1, 5, and 7 and the detection unit 18 shown in FIGS. 1 and 5 is a general-purpose interferometer. On the other hand, it may be configured to be detachable. If such a unit is prepared, a general-purpose interferometer can be used as the present interferometer.
In this interferometer, the detection unit 28 shown in FIG. 8 may be applied instead of the detection unit 18 shown in FIG.

When this detection unit 28 is applied, the condensing point F _{1 of} the first light beam L ₁ emitted from the imaging lens 14, the condensing point F _{2 of} the second light beam L ₂ , and the condensing point of the third light beam L ₃ . point F _3, 4 such that the focal point F ₄ of the light beam L ₄ is one-dimensionally distributed as shown in FIG. 8 (a), the first reflecting mirror 171 with respect to the light beam from the light source 11, the second reflecting mirror 172, The tilt directions of the third reflecting mirror 173 and the fourth reflecting mirror 174 are appropriately selected.

As shown in FIGS. 8A and 8B, the detection unit 28 includes a separation element 28s and four planar reflecting mirrors 281, 282, 283, and 284.
The separation element 28 s has four reflecting surfaces 28 s ₁ , 28 s ₂ , 28 s ₃ , and 28 s ₄ that are inclined in different directions and arranged in a line.
The posture of the separation element 28 s is set so that the four reflecting surfaces 28 s ₁ , 28 s ₂ , 28 s ₃ , and 28 s ₄ face the imaging lens 14 side.

The condensing points F ₁ , F ₂ , F ₃ , and F ₄ are located at substantially the centers of the reflecting surfaces 28 s ₁ , 28 s ₂ , 28 s ₃ , and 28 s ₄ of the separation element 28 s, respectively.
The reflecting surfaces 28s ₁ , 28s ₂ , 28s ₃ , and 28s ₄ deflect the first light beam L ₁ , the second light beam L ₂ , the third light beam L ₃ , and the fourth light beam L ₄ in different directions. The plane reflecting mirrors 281, 282, 283, and 284 have their first light beam L ₁ , second light beam L ₂ , third light beam L ₃ , and fourth light beam L _4, as shown in FIG. Deflect in the direction.

Such a detection unit 28 also functions in the same manner as the detection unit 18 shown in FIG.
In addition, the interferometer is provided with only one imaging device 15, but as shown in FIGS. 9A and 9B, interference fringes S ₁ , S ₂ , S ₃ , and S ₄ are provided. A plurality of imaging devices 15 that individually detect may be provided. In that case, the plane reflecting mirrors 181, 182, 183 and 184 shown in FIG. 3 and the plane reflecting mirrors 281, 282, 283 and 284 shown in FIG. 8 can be omitted.

Further, in this interferometer, the number of interference fringes that occur simultaneously is set to “4”, but “2”, “3”, or “5” depends on the accuracy required for calculating the shape of the test surface o. It may be “the number above”.
However, in order to calculate the shape with high accuracy regardless of the wave number k, the 0th-order component I ₀ (x, y) of the luminance distribution, and the luminance amplitude A ₀ (x, y), the number of interference fringes is “3 or more. Need to be "number of".
Incidentally, when the number is “3”, a triangular pyramid-shaped separation element 38s (the number of reflection surfaces is “3”) as shown in FIG. 10 can be used as the separation element in the detection unit.

The phase difference between the interference fringes S ₁ , S ₂ , S ₃ , and S ₄ that occur simultaneously is set to π / 2, π, 3π / 2, and 2π, but the number of interference fringes is “5”. In some cases, for example, π / 2, π, 3π / 2, 2π, 5π / 2 (that is, an integer multiple of π / 2) is set.
Alternatively, the phase difference of each interference fringe may be set to a value other than an integer multiple of π / 2. However, setting to an integer multiple of π / 2 is advantageous because the calculation of fringe analysis is simplified.

In FIG. 1 and FIG. 5, the optical paths of the plurality of light beams L ₁ , L ₂ , L ₃ , and L ₄ are arranged on the same plane, but they may not be arranged on the same plane.
Further, in this interference measurement method, the intensities of the light beams L ₁ , L ₂ , L ₃ , and L ₄ are common (the zero-order component I ₀ (x, y) of the luminance distribution is the interference fringes S ₁ , S ₂ , S ₃ and S ₄ ). However, they may be measured separately, and a correction operation based on the measurement result may be added to the above-described fringe analysis.

It is a block diagram of this interferometer. (A) is a figure which shows the space | interval d of the to-be-tested surface o and the reference surface r, and the incident angle (theta) _n of the nth light beam to the to-be-tested surface o. (B) is a diagram showing a relationship between a light beam _{L 1, L 2, L 3} , the focal point F ₁ of _{L 4, F 2, F 3} , F 4. (A) is the side view which looked at the unit 18 for a detection from the imaging lens 14 side. FIG. 4B is a perspective view of the detection unit 18. Is a diagram showing the arrangement of the interference pattern _{S 1, S 2, S 3} , S 4 on the imaging surface 15a. It is a block diagram of this interferometer which inserted the imaging lens 19. FIG. (A) is a conceptual diagram showing an optical relationship between the reflecting surfaces 171a and 172a and the surface to be examined o in a state where the imaging lens 19 is not inserted. FIG. 5B is a conceptual diagram showing an optical relationship between the reflection surfaces 171a and 172a and the test surface o in a state where the imaging lens 19 is inserted. FIG. 6 is a configuration diagram around a prism 261 that can be applied to the present interferometer instead of the light projecting unit 16. (A) is the side view which looked at the detection unit 28 applicable to this interferometer instead of the detection unit 18 from the imaging lens 14 side. (B) is a perspective view of the detection unit 28. (A) is a side view (a side view seen from the imaging lens 14 side) showing a detection optical system including a plurality of imaging devices 15 and separation elements 18s. (B) is a side view (a side view seen from the imaging lens 14 side) showing a detection optical system composed of a plurality of imaging elements 15 and separation elements 28s. It is a perspective view of the separation element 38s applicable when the number of the interference fringes generated simultaneously is three.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Test object 2 Fizeau member 11 Laser light source 12 Beam expander 16 Projection unit 13,161 Beam splitter 14 Imaging lens 18 Detection unit 15 Imaging device 162,163 Polarization beam splitter 171 First reflector 172 Second reflection Mirror 173 Third reflecting mirror 174 Fourth reflecting mirror 171a, 172a, 173a, 174a Reflecting surface

Claims (7)

A procedure for making a plurality of light beams to be projected onto the test surface and the reference surface into light beams having different projection angles so that a plurality of interference fringes having different phases occur at the same time;
A method for detecting a plurality of interference fringes simultaneously generated by the procedure, respectively. A light projecting optical system that multiplexes light beams to be projected onto the test surface and the reference surface into light beams having different light projection angles so that a plurality of interference fringes having different phases occur at the same time;
An interferometer comprising: a detection optical system that detects each of the plurality of interference fringes generated simultaneously. The interferometer according to claim 2, wherein
The projection optical system is:
An interferometer, comprising: an angle adjusting device for adjusting a relationship between projection angles of the plurality of light beams. The interferometer according to claim 2 or claim 3,
In the detection optical system,
An interferometer, comprising: a separation system that separates the plurality of interference fringes; and a single image sensor that collectively detects the plurality of interference fringes separated from each other. The interferometer according to claim 2 or claim 3,
In the detection optical system,
An interferometer, comprising: a separation system that separates the plurality of interference fringes; and a plurality of imaging elements that individually detect the plurality of interference fringes separated from each other at an occurrence position. In the interferometer according to any one of claims 2 to 5,
In the light projecting optical system,
An interferometer, comprising: a branching system that branches the light beam emitted from a single light source into a plurality of parts. In the interferometer according to any one of claims 2 to 6,
In the light projecting optical system,
An interferometer, comprising: an optical path adjustment system that adjusts an arrangement relationship of optical paths of the respective light beams so that an incident light amount distribution on the test surface is matched between the plurality of the light beams.

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