JPH10281738A - Method and equipment for measuring interference - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and an equipment for measuring interference in which a shape including a level difference exceeding the wavelength or an absolute distance can be measured accurately at high speed. SOLUTION: A laser light source 60 emits laser a light having a plurality of wavelengths. A light reflected by a surface 4a to be measured interferes with a light reflected by a prototype plane 64 and image pickup tubes 671 -67n detect the fringe pattern image for respective wavelengths individually. A computer 9 selects a set of m-th,..., first wavelengths (m>=2) such that the combined wavelength of a set of two wavelengths selected from among the plurality of wavelengths decreases gradually. Subsequently, the absolute distance between the prototype plane 64 and the surface 4a to be measured is operated roughly and sequentially from the set of m-th wavelength to the set of first wavelength for each set of wavelength based on the phase distribution difference between fringe images corresponding to two wavelengths. Finally, the absolute distance between the prototype plane 64 and the surface 4a to be measured is operated accurately based on the phase distribution of one of a plurality of wavelengths and the rough absolute distance of the first set of wavelength.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an interference measurement method and an interference measurement apparatus for measuring the shape of an object by utilizing the interference phenomenon of light waves, and more particularly, to a method of using light waves of at least three kinds of wavelengths to exceed the wavelength. The present invention relates to an interference measurement method and an interference measurement apparatus for measuring a shape including a step or an absolute distance between a measurement target surface exceeding a wavelength and an interferometer with high accuracy and high speed.

[0002]

2. Description of the Related Art Measurements utilizing the interference phenomenon of light waves are widely used in the field of high-precision measurement because non-contact measurement is possible with an accuracy of light wavelength, that is, submicron or more. The following are known as a measuring method. (1) Two-beam interferometry (hereinafter referred to as "conventional example 1") (2) Two-wavelength interferometry (hereinafter referred to as "conventional example 2") (3) White light interferometry (hereinafter referred to as "conventional example 3")

(Conventional Example 1) In the two-beam interference method, a reference wavefront reflected by a highly accurate ideally formed reference surface called a prototype and a wavefront to be measured reflected by the surface to be measured interfere with each other. (For example, "Optical S"
"hop Testing 2nd Edition",
D. Edited by Malacara, John Wiley &
Sons, Inc. Published, (1992), Chapter 14,
p. 501-591).

FIG. 7 shows a flow for explaining the two-beam interference method. First, an interference fringe generated by causing interference between a reference wavefront reflected by a reference surface and a measurement target wavefront reflected by a measurement target surface is detected as light intensity shown in Expression (1) (ST1). I (x, y) = a (x, y) + b (x, y) × cos {φ (x, y) + δ} (1) where I (x, y) is the light intensity representing interference fringes a (x, y): bias component b (x, y): amplitude of interference fringe intensity φ (x, y): phase distribution of detection target δ: initial phase determined by arrangement

Next, a phase distribution (here, a wrapped phase distribution) is obtained (this step is referred to as “interference fringe phase analysis”).
That. ) (ST2).

FIGS. 8A and 8B are diagrams for explaining how the phases are wrapped. FIG. 8A shows the actual phase, and FIG. 8B shows the wrapped phase. . Due to the periodic nature of the interference phenomenon shown in the above equation (1), only the phase folded (wrapped phase) in the interval of 2π is directly detected. That is, there is uncertainty in the portion exceeding one cycle of the interference fringes. In other words, interferometry is
This is the act of obtaining φ (x, y) from I (x, y) in the above equation (1). However, cos that appears when obtaining φ (x, y)
Since the inverse function of is a multivalent function, the actual phase φ cannot be determined uniquely as shown in FIG. An integer representing this multiple is referred to as “strip order”.), But is only a fractional component less than one wavelength.

Next, a fringe order ng (x, y) is obtained (this step is called "phase unwrapping") (ST).
3). Phase unwrapping is not mathematically unique. In phase unwrapping, assuming that the surface to be measured is "smooth", the fringe order is determined by trial and error so that the overall shape becomes smooth after phase unwrapping. In addition, algorithms for automatically performing such trial and error have been energetically developed in recent years (for example, TR Judge & P.E.
J. Bryanton-Cross: "A Revi
ew of Phase Unwrapping Te
chneques in Fringe Analyss
is ", Optics and Lasers in
Engineering, vol. 21, (199
4), p. 199-239). Stripe order ng (x, y)
Then, the actual unwrapped phase distribution φ (x, y) is obtained by the following equation (2). φ (x, y) = ng (x, y) × 2π + ψs (x, y) (2) where ng (x, y): fringe order (strictly integer) ψs: fractional phase information less than 2π

Finally, the phase is converted into an actual shape (distance) (ST4). To convert equation (2) into a unit of the actual shape (distance) instead of the phase, λ /
Multiplying by 2π gives equation (3). φ (x, y) × λ / 2π = ng (x, y) × λ + ψs (x, y) × λ / 2π (3) where φ (x, y) × λ / 2π is a precise absolute distance h (x, y)
, Ψs (x, y) × λ / 2π is a fractional component hs less than one wavelength
If (x, y), equation (3) becomes equation (4). h (x, y) = ng (x, y) × λ + hs (x, y) (4) The shape (distance) of the surface to be measured can be obtained from equation (4).

(Conventional Example 2) The two-wavelength interferometry performs interference measurement by using light of two wavelengths simultaneously (for example, Yukihiro Ishii and Ribu).
n Onodera: "Two-wavelength
laser-diode interferometry
ry that uses phase-shifti
ng technologies ", Optics Let
ters, vol. 16, No. 19, (1991),
p. 1523-1525). The contour lines of the shading of the interference fringes (Moire fringes) formed by the two wavelengths are given by Equation (5).
合成 (corresponding to the measurable range in the present invention). Λ = λ ₁ × λ ₂ / | λ ₁ −λ ₂ | (5) where λ ₁ , λ ₂ : two wavelengths to be used. Therefore, the range corresponding to one cycle of interference fringes without uncertainty is: In the ordinary two-beam interferometry, λ = wavelength, whereas in the two-wavelength interferometry, it is enlarged to Λ. Therefore, in the range of Λ wider than λ, it is possible to measure a step exceeding the wavelength and a shape including the absolute distance between the interferometer exceeding the wavelength and the measurement target surface. For example, when two red lights having wavelengths of 660 nm and 670 nm are used, the combined wavelength Λ is 44220 n
m = 44.22 μm, and it is possible to measure a shape including a step and an absolute distance up to 44.22 μm. this is,
This is equivalent to 66 times the range of a normal two-beam interferometer. And, the smaller the wavelength difference | λ ₁ −λ ₂ |
The measurable Λ increases.

(Conventional Example 3) The white light interferometry performs interference measurement using a white light or a light source having a low coherency close to the white light (for example, Kumiko Mats).
ui and Satoshi Kawadata: "Fr
inge-scanning white-light
microscope for surface p
rofile measurement and ma
terial identification ”, Pr
oc. of SPIE, vol. 1720, (199
2), p. 124-132). The coherent length of light generally used in white light interferometry is about several μm, and interference fringes appear only in that range. Further, even within the range of several μm where the interference fringes appear, it is possible to accurately detect a position where the absolute distance between the prototype and the measurement target surface where the change in the contrast of the interference fringes is the maximum and the interference fringe peaks is 0. .
Therefore, in shape measurement using the white light interferometry, the distance between the prototype and the surface to be measured is continuously changed by some method, and locations where the absolute distance between the prototype and the surface to be measured become 0 are sequentially mapped. To obtain the entire measurement data. Usually, mapping is performed by linearly scanning the distance between the interferometer and the measurement object in a direction along the optical axis. When white interference is used in this way, it is possible to measure a step exceeding a wavelength or a shape including an absolute distance between an interferometer exceeding a wavelength and an object surface over a wide range of about 100 μm with an accuracy on the order of nm.

[0011]

However, the conventional example 1
According to the luminous flux interferometry, when the measurement target surface includes a step exceeding the wavelength, the assumption of smoothness cannot be used, so that phase unwrapping cannot be performed, and the flow of interference measurement cannot be completed. . Also, phase unwrapping is only determined so that the relative fringe order relationship of the wrapped phase is smooth, so the absolute fringe order cannot be determined, and the absolute distance between the interferometer and the surface to be measured is determined. Cannot be measured. That is, in the two-beam interference method, since the range in which the absolute distance is reliably obtained is limited to one wavelength or less, there is a disadvantage that it is impossible to measure a shape including a step exceeding the wavelength or the absolute distance.

Further, the two-wavelength interferometry of Conventional Example 2 is a method of increasing the contour line period itself of the interference fringe density, so that if the measurable range 大 き く is increased, the measurement accuracy is reduced in proportion to it, and the submicron However, there is a drawback that high-precision measurement exceeding is extremely difficult.

According to the white light interferometry of Conventional Example 3, when sequentially mapping locations where the absolute distance between the prototype and the surface to be measured is 0, the distance between the prototype and the surface to be measured is mechanically changed. Since a large number of interference fringe images are recorded while being continuously changed, it takes time to collect interference fringes alone. In addition, the computer processing for extracting the shape information takes a long time because the number of images is large. For this reason, there is a disadvantage that the measurement requires a long time. Therefore, it is used when high-speed measurement is required, such as when measuring a changing target surface, when measuring in a vibration environment, or when measuring a large number of surface areas. It is not possible. Furthermore, in order to store a large number of images, it is necessary to prepare a large amount of memory and an external storage device. For example, the above Mat
In Sui et al., 256 images are collected for one measurement. However, even if this is performed at the highest video rate, it takes 8.5 seconds. Actually, since the distance between the prototype and the surface to be measured is continuously changed mechanically, the distance may be further reduced. Further, a device for collecting a high-definition image such as an interference fringe at a high speed such as a video rate is expensive. Furthermore, if one interference fringe image is
Resolution 512 × 5, which can be generally achieved with a V camera
Even if 12 pixels and 256 gradations (8 bits) are sampled, 512 × 512 × 8 × 256 = 64 for 256 sheets
Mbyte. Even with the widespread use of large-capacity memories, it is still expensive to realize a computer environment that can handle such data. Of course, when it is necessary to collect interference fringes with higher definition, since the image is two-dimensional data, an extremely large amount of memory is required. For example, with the spread of HDTV and the spread of high-definition displays for personal computers, 10
Although an image of about 00 × 1000 pixels is becoming uncommon, if interference fringes are collected from an image of that class, a memory capacity of 256 Mbytes, which is four times the above, is required for only one measurement data.

Accordingly, an object of the present invention is to provide an interference measuring method and an interference measuring apparatus capable of measuring a shape including a step exceeding a wavelength and including an absolute distance with high accuracy and high speed.

[0015]

SUMMARY OF THE INVENTION In order to achieve the above object, the present invention irradiates light waves of at least three kinds of wavelengths onto a reference surface and a surface to be measured to cause interference at each of the at least three kinds of wavelengths. The interference fringe images of the at least three types of wavelengths generated by the interference are individually detected, and two wavelengths are grouped from the at least three types of wavelengths so that the composite wavelength of the two wavelengths is sequentially reduced. , M-th
To a first set of wavelengths (where m ≧ 2), and based on a phase distribution difference between the interference fringe images corresponding to the two wavelengths, a set of the m-th to first wavelengths is selected. The approximate absolute distance between the reference surface and the measurement target surface is sequentially calculated from the m-th wavelength set to the first wavelength set, and the approximate absolute distance corresponding to one of the at least three wavelengths is calculated. Calculating a precise absolute distance between the reference surface and the measurement target surface based on a phase distribution of an interference fringe image and the approximate absolute distance of the first set of wavelengths. I will provide a.

According to another aspect of the present invention, there is provided a light source for irradiating at least three types of light waves on a reference surface and a surface to be measured, and a light wave of at least three wavelengths reflected on the reference surface. An optical system that causes the light waves of the at least three types of wavelengths reflected by the measurement target surface to interfere with each other for each of the at least three types of wavelengths; and the at least three types of light waves generated by the interference of the light waves of the at least three types of wavelengths. Interference fringe image detecting means for individually detecting interference fringe images of wavelengths, and m-th to m-th interference wavelengths such that a combined wavelength of the two wavelengths is sequentially reduced as a set of two wavelengths from the at least three wavelengths. One set of wavelengths (where m ≧
Based on a selection means for selecting 2) and a phase distribution difference between the interference fringe images corresponding to the two wavelengths.
A rough calculation means for sequentially calculating a rough absolute distance between the reference surface and the measurement target surface from the m-th wavelength set to the first wavelength set for each of the wavelength sets; A precise absolute distance between the reference surface and the measurement target surface based on the phase distribution of the interference fringe image corresponding to one of the wavelengths and the approximate absolute distance of the first set of wavelengths. The present invention provides an interference measurement device characterized by having precise calculation means for calculating the following.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows an interference measuring apparatus according to a first embodiment of the present invention. This interferometer 1 has a horizontally arranged table 2 and a column 3 erected on the table 2, and mounts a piezo stage 5 on the table 2 for vertically moving an object 4 to be measured. The column 3 is provided with an interferometer 6.

The interferometer 6 has a plurality of wavelengths λ.₁,
λ_Two,. . , Λ_n(Where n is an integer of 3 or more)
A laser light source 60 that simultaneously oscillates laser light;
Collimator lens that converts laser light from source 60 into parallel light
61 and a part of the parallel light from the collimator lens 61.
First half mirror 62A that reflects light toward the fixed object 4 side
And arranged on the measurement object 4 side of the first half mirror 62A
And has the same imaging performance as a normal microscope objective.
An objective lens 63, a plane prototype 64 as a reference plane,
Part of the light from the objective lens 63 is guided to the object 4 to be measured,
Second half mirror 6 for guiding the remaining part to flat prototype 64
2B, the surface (measurement object surface) 4a of the measurement object 4 and the plane
The light reflected by the prototype 64 is reflected by the second half mirror 62.
Returning to B, the wavelength is calculated from the superposed interference light
λ₁, Λ_Two,. . , Λ_n-1And separate each light
The first, second,. . , And (n-1) th dichroic
Cook mirror 65 ₁, 65_Two,. . , 65_n-1And each wavelength
λ₁, Λ_Two,. . , Λ_n-1Through the imaging lens 66
, 1st, 2nd,. . , And (n−
1) Imaging tube 67₁, 67_Two,. . , 67_n-1And the second
(N-1) dichroic mirror 65_n-1Penetrated
Wavelength λ_nN-th image of the light through the imaging lens 66
Imaging tube 67_nAnd The objective lens 63,
With the plane prototype 64 and the second half mirror 62B,
A so-called Michelson interferometer is configured.

Further, the interference measuring apparatus 1 converts a piezo driver 7 for driving the piezo stage 5 and image signals of interference fringes from the _{first to n-th} imaging tubes 67 _{1 to} 67 _n into digital interference fringe image data. An image digitizer 8 to be converted,
A computer 9 controls the piezo driver 7 and obtains the shape of the surface 4a to be measured based on digital data from the image digitizer 8. Note that 9a
Is a computer main body provided with a control unit for controlling the entire apparatus 1, 9b is a display for displaying the measurement results, and 9c is a keyboard.

FIG. 2 is a flowchart showing the operation of the interference measuring apparatus 1 according to the first embodiment. First, the control unit in the computer main body 9a controls the piezo driver 7 to move the measurement object 4 in the vertical direction by the phase shift method (for example, fringe scanning interference measurement method), and the interferometer 6 and the measurement object surface 4a , While changing the distances by λ / 4, the wavelengths λ ₁ , λ ₂ ,. . , Lambda interference fringe image data of four for each _{n I ab (x, y)} ( where, a = 1,2, .., n , b =
1, 2, 3, 4) are detected (ST11). Since the interference fringe image data has unknown values of a (x, y), b (x, y) and φ (x, y) as shown in the equation (1) described in the related art, δ Is obtained by obtaining at least three pieces of interference fringe image data by changing the value of φ, x (x, y) can be obtained.
Each wavelength λ ₁ ,
λ ₂ ,. . , The case of obtaining the four interference fringe image data for each lambda _n. Specifically, λ ₁ ... I ₁₁ (x, y), I ₁₂ (x, y), I ₁₃ (x, y), I ₁₄ (x, y) λ ₂ ... I ₂₁ (x, y), I ₂₂ (x, y), I ₂₃ (x, y), I ₂₄ (x, y). . . λ _n ... I _n1 (x, y), I _n2 (x, y), I _n3 (x, y), I
Detect _n4 (x, y).

Here, a case where one piece of interference fringe image data is obtained will be described. A plurality of wavelengths λ ₁ , λ ₂ ,. . , Λ _n are collimated by the collimator lens 61, a part of the light is reflected by the first half mirror 62 A, and reaches the objective lens 63. The light from the objective lens 63 is
Is partially guided to the measurement target surface 4a by the half mirror 62B, and the remaining part is guided to the flat prototype 64. The light reflected by the measurement target surface 4a and the light reflected by the plane prototype 64, respectively, returns to the second half mirror 62B again, where it is superposed and becomes interference light. A part of the interference light emitted from the objective lens 63 passes through the first half mirror 62A and reaches the _first dichroic mirror 651. The first to (n-1) th dichroic mirrors 65 _{1 to} 65 _n-1 transmit the wavelengths λ ₁ , λ ₂ ,. . , Λ _n-1 are reflected and separated. Therefore, each wavelength λ ₁ , λ ₂ ,. . , Λ _n-1 passes through the imaging lens 66 to the corresponding first, second,. . ,
, Image pickup tube 67 _1, 67 ₂ and the (n-1). . , 6
The light having the wavelength λ _n that has reached 7 _n−1 and transmitted through the (n−1) -th dichroic mirror 65 _n−1 reaches the _n- th imaging tube 6767 _n via the imaging lens 66. In this manner, the image of the interference fringe caused by only the light of the wavelength λ _{1 in} the _first imaging tube 67 _{1 and} the image of the interference fringe caused by the light of the wavelength λ ₂ alone in the second imaging tube 67 ₂ are simultaneously and individually light- is detected as an intensity, hereinafter, similarly, the (n-1) th images only due to the interference fringe light of pickup tube 67 _n-1 at a wavelength of lambda _n-1 of the wavelength in the imaging tube 6767 _n of the n lambda _n The images of the interference fringes due to only the light are detected individually and simultaneously as the light intensity. Wavelength λ ₁ ,
λ ₂ ,. . The image signal of the interference fringes detected at each lambda _n is
The image is converted into digital interference fringe image data by the image digitizer 8 and transferred to a control unit in the computer main body 9a. The control unit controls the wavelengths λ ₁ , λ ₂ ,. . , Lambda every _n 4 sheets of the interference fringe image data I _ab (x, y) obtains the, based on the interference fringe image data I _ab (x, y), performs calculation as described below, the interferometer A distance (hereinafter, also simply referred to as “absolute distance”) between the measurement target 6 and the measurement target surface 4a is obtained.

In order to satisfy the following equations (6 ₁ ), (6 ₂ ), (6 ₃ ) (hereinafter collectively referred to as equation (6)), a plurality of wavelengths λ ₁ , λ ₂ ,. . , Λ _n and two wavelengths λ _ij (where i = 1, 2,..., M, m is an integer of 2 or more, j =
1, 2, and λ _i1 <λ _i2 ) as one set, and select the first to m-th wavelength sets (ST12). This selection may be made by a control unit in the computer main body 9a based on a program or by an operator. Λ _i-1> Rhg _i (however, i = 2,3, .., m ) ... (6 1) λ x / k> Rhg 1 ... (6 2) Rhg 1 <Rhg 2 <. . . <Rhg _m ... (6 ₃₎ However, Λ _i-1: (i-1) -th wavelength pairs (lambda _(i-1) 1,
lambda _(i1) absolute distance measurable range of the synthetic wavelength (schematic of ₂₎₎ rhG _i: the set of wavelength of the i (λ _i1, λ _i2 Summary by) Absolute distance measurement accuracy of lambda _x: more Wavelength λ ₁ ,
λ ₂ ,. . , Λ _n , the wavelength used for calculating the absolute absolute distance k: 2 for measurement by reflection, 1 for measurement by transmission Specifically, 具体_m-1 = λ _{(m-1) 2} × λ _{(m-1) 1} / [k ｛λ _{(m-1) 2-} λ _{(m-1) 11} ]> Rhg _m . . . _{Λ 2 = λ 22 × λ 21} / [k {λ 22 over _{λ 21}]> Rhg 3 Λ} 1 = λ 12 × λ 11 / [k {λ 12 over λ _11}]> Rhg ₂

FIG. 3 is a view for explaining a method of calculating the absolute distance between the interferometer 6 and the surface 4a to be measured. When the first to m-th wavelength pairs are selected so as to satisfy the above equation (6), for all possible i, the composite wavelength of the i-th wavelength pair (measurable range of absolute distance) Λ _i Some λ _i2 ×
λ _i1 / [k {λ _i2 −λ _i1 }] is always the absolute absolute distance measurement accuracy Rhg _{(i + 1) in the (i + 1)} -th set of wavelengths.
Be larger. Therefore, as shown in FIG. 3, the approximate absolute distance hg _m (x, x) based on the _m-th set of wavelengths (λ _m1 , λ _m2 ) having the widest approximate absolute distance measurable range Λ _m .
From y), a combination of wavelengths with a narrower range and higher precision, ie, (λ _{(m-1) 1} , λ _{(m-1) 2} ),. . ,
The approximate absolute distances hg _m-1 (x, y),... Based on (λ ₂₁ , λ ₂₂ ), (λ ₁₁ , λ ₁₂ ). . , Hg ₂ (x, y), hg ₁ . As a result, the plurality of wavelengths λ ₁ ,
λ ₂ ,. . , It is possible to obtain the absolute distance schematic with a precision that can determine the fringe order of the interference fringes resulting from interference fringes of at least one wavelength lambda _x of lambda _n.

Next, using the interference fringe image data detected in step ST11, step ST1 is calculated by the following equation (7).
The phase distribution ψ _ij (x, y) (where i = 1, 2,..., M, j = 1, 2) is calculated for each wavelength λ _ij selected in Step 2 (ST13). ψ _ij (x, y) = arctan [{I _ij4 (x, y) −I _ij2 (x, y)} / {I _ij1 (x, y) −I _ij3 (x, y)}] (7) Since arctan is a multivalent function, ψ _ij (x, y) is obtained as a phase folded into a 2π section, that is, a wrapped phase, as described above.

Next, using the phase distribution ψ _ij (x, y) obtained in step ST13, the approximate absolute distance hg _m (m) of the m-th wavelength set (λ _m1 , λ _m2 ) is obtained by the following equation (8). x, y) is calculated (ST14). hg _m (x, y) = ｛ψ _m1 (x, y) −ψ _m2 (x, y)｝ / ｛2π × k (1 / λ _m1 −1 / λ _m2 )… (8)

FIG. 4 is a diagram for explaining the principle of measuring the approximate absolute distance. As shown in the figure, λ of the i-th wavelength set corresponding to the same location (point of interest) on the measurement target surface
The phase difference between the interference fringe of _{i1 and} the interference fringe of λ _i2 changes depending on the absolute distance between the target point on the surface to be measured and the prototype.
Therefore, the absolute distance can be obtained from the phase difference. The amount of change is a periodic function, and its period (combined wavelength Λ _i ) is two wavelengths λ _{i1 that} are different from each other as in the two-wavelength interferometry.
And λ _i2 , the following equation (5 ′) as in the above equation (5)
Given by Λ _i = λ _i1 × λ _i2 / | λ _i1 −λ _i2 | That is, the range in which the absolute distance is obtained is Λ _i of the measurement range expanded from the 2π section (λ _i1 , λ _i2 ).
The absolute distance obtained in this manner has poor accuracy as compared with the ordinary two-beam interferometry, like the two-wavelength interferometry. In this sense, the absolute distance is approximate, but it is possible to give sufficient accuracy to determine the fringe order.

Here, the reason why hg _m (x, y) in the above equation (8) is a rough absolute distance will be described below. The relationship between the wrapped phase ψ and the actual absolute distance or shape h is expressed by the following equation (9). h · (2π × k) / λ = ψ + 2π × N (9) where k: 2 for reflection measurement, 1 for transmission measurement N: fringe order at wavelength λ は when measurement is performed by reflection Since the light waves reciprocate, the phase difference is doubled even at the same distance difference, and k = 2. This means that the distance indicated by one fringe of interference fringes (interval of interference fringes)
Corresponds to twice the difference between reflection and transmission. Next, λ _m1
The above equation (9) is created with respect to and λ _m2 , and is subtracted and arranged to obtain equation (10).

(Equation 5) (10) Here, ΔN _m (x, y) is the difference between the stripe order by λ _m1 and the stripe order by λ _m2 , that is, ΔN _m (x, y) = N (λ _m1 )
(x, y) −N (λ _m2 ) (x, y). h is Λ _m = λ _m1 × λ
_m2 / | λ _{m1 -λ m2} | time than small, λ _m1 of fringe order N
(Lambda _m1) and lambda _{m @ 2} of fringe order N (λ _m2) are equal, .DELTA.N _m =
It becomes 0. If set to be larger than the appropriate range lambda _m, this is satisfied. At this time, the hg
Equation (8) is obtained. However, h is replaced with hg in order to clearly indicate that the information is rough information.

Next, k is set to m-1 (ST15),
The phase distribution ψ _ij (x, y) obtained in step ST13 and the approximate absolute distance hg _m (x, y) obtained in step ST14
Is used to calculate the fringe order difference ΔN _(m−1) (x, y) of the _(m−1) -th wavelength set by the following equation (11) (ST16).

(Equation 6) (11) Equation (11) is obtained by substituting m for m-1 and h for hg in Equation (10) to obtain ΔN _(m-1) (x, y), that is, λ
_{It is} nothing but a solution of the difference between the fringe order of _{(m-1) 1 and} the fringe order of λ _{(m-1) 2} . However, while ΔN _(m−1) (x, y) is a strictly integer, a function T [] that takes the nearest integer is adopted in consideration of hg including an error. As shown in FIG. 3, if Λ _(m-1) > Rhg _m holds, ΔN _(m-1) (x, y) can be determined without error.

Next, using the phase distribution _{ij ij} (x, y) obtained in step ST13 and the fringe order difference ΔN _(m-1) (x, y) obtained in step ST16, the following equation (12) is obtained. By the (m
The approximate absolute distance hg _(m-1) (x, y) of the set of wavelengths of -1) is calculated (ST17).

(Equation 7) (12) The reason why the expression (12) is established is the same as that of the expression (10).

Next, until k = 1 (ST18), k
Is set to k-1 (ST19), and in the same manner, ΔN _(m−2) (x, y),. . , ΔN ₂ (x, y), ΔN
₁ (x, y) is obtained (ST16), and hg _(m-2) (x, y)
,. . , Hg ₂ (x, y) and hg ₁ (x, y) (S
T17).

Next, the plurality of wavelengths λ ₁ , λ ₂ ,... Used for the interference are finally determined using the approximate absolute distance hg ₁ (x, y) obtained in step ST17. . , Λ _n , the fringe order N (x, y) at one wavelength λ _x is calculated by the following equation (13) (ST20). N (x, y) = T [k × hg 1 (x, y) / λ x -ψ x (x, y) / (2π)] ... (13) Equation (13), in formula (9), h is hg (x, y), λ
Is λ ₁ , and ψ is ψ _x, and nothing is solved for N (x, y). However, considering that N (x, y) is a strictly integer and hg ₁ includes an error, a function T [] taking the closest integer is adopted. As shown in FIG. 3, if λ _x / k> Rhg ₁ holds, N (x, y) can be determined without error.

Finally, using the fringe order N (x, y) obtained in step ST20, a precise absolute distance h (x, y) of the surface to be measured is calculated by equation (14) (ST21). h (x, y) = λ x / k × [ψ x (x, y) / (2π) + N (x, y)] ... (14) Equation (14) is a formula similar to the formula (9) . Where x, y
Represents orthogonal coordinates representing the position of a plane substantially perpendicular to the center normal of the measurement target plane.

Then, the control section in the computer main body 9a displays the obtained precise absolute distance h (x, y) on the display 9b.
To be displayed.

According to the first embodiment, the following effects can be obtained. (B) A plurality of wavelengths λ ₁ , λ ₂ ,. . , Λ _n , the first to m-th wavelength groups are selected as one set, and the approximate absolute distance is sequentially obtained from the set of wavelengths having the longest combined wavelength, so that the absolute distance h is obtained. Range Λ _m is 2
It is much wider than wavelength interferometry, and a single wavelength λ ₁ , λ
₂ ,. . Allows measurement of inclusive shape step or absolute distance exceeding lambda _n. (B) Since the precise absolute distance h (x, y) is finally obtained based on the phase distribution ψ _x (x, y) of one wavelength λ _x and the fringe order N (x, y), The absolute distance h (x, y) can be obtained with the same accuracy as the two-beam interference method.

FIG. 5 shows an interference measuring apparatus according to a second embodiment of the present invention. Components having the same functions as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. The interference measurement device 1 according to the second embodiment is configured to perform interference measurement using three types of wavelengths. That is, the laser light source 60 uses, for example, an argon ion laser that simultaneously oscillates three types of first, second, and third wavelengths λ ₁ , λ ₂ , and λ ₃ , and uses 476 as the first wavelength λ _1. .5Nm, second wavelength lambda ₂ as 488 nm, as a third wavelength lambda ₃ 514.
A resonator in the laser light source 60 is set so as to simultaneously oscillate laser beams having three wavelengths of 5 nm. Also,
The dichroic mirror 65 converts the interference light into a first wavelength λ.
_{A first} dichroic mirror 65 ₁ that separates and reflects ₁
And it reflects the second wavelength lambda ₂ from the interference light, the second using a dichroic mirror 65 ₂ for transmitting the third wavelength lambda _3, an image pickup tube 67, corresponding to each wavelength lambda _1, lambda _2, lambda ₃ to the first image pickup tube 67 _1, the second image pickup tube 67 _2, 3 using the image pickup tube 67 _3.

Next, the operation of the interference fringe measuring apparatus 1 according to the second embodiment will be described. First, the computer body 9a
As described in the first embodiment, the control unit controls the piezo driver 7 to move the measurement object 4 in the vertical direction by the phase shift method (for example, the fringe scanning interference measurement method), and While changing the distance between the total 6 and the measurement target surface 4a by λ / 4, four pieces of interference fringe image data are taken in for each of the wavelengths λ ₁ , λ ₂ , and λ ₃ .

Next, the interference is set so as to satisfy the above equation (6).
Wavelengths λ used for₁, Λ_Two, Λ _ThreeTwo wavelengths from
The first and second wavelength sets are selected as one set. here
Then, as the first set of wavelengths (λ₁, Λ_Three), The second wave
As a set of lengths (λ₁, Λ_Two) Is selected. This place
In this case, the combined wavelength of each wavelength group (measurable range)
Λ ₁, Λ_TwoAnd approximate absolute distance measurement accuracy Rhg₁,
Rhg_TwoIs as follows: The first set of wavelengths (λ₁, Λ_Three): Λ₁= 2.91 μm Rhg₁= 0.064 μm The second set of wavelengths (λ₁, Λ_Two): Λ_Two= 29.6 μm Rhg_Two= 5.53 μm

Next, using the acquired interference fringe image data, by the equation (7), each wavelength lambda _1, lambda _2, the phase distribution [psi ₁ every _{λ 3 (x, y),} ψ 2 (x, y) and ψ ₃ (x, y). ψ ₁ (x, y) = arctan [｛I ₁₄ (x, y) −I ₁₂ (x, y)｝ / ｛I
_{11 (x, y) -I 13} (x, y)}] ψ 2 (x, y) = arctan [{I 24 (x, y) -I 22 (x, y)} / {I
_{21 (x, y) -I 23} (x, y)}] ψ 3 (x, y) = arctan [{I 34 (x, y) -I 32 (x, y)} / {I
₃₁ (x, y) -I ₃₃ (x, y)｝]

Next, the approximate absolute distance hg ₂ (x, y) of the second set of wavelengths (λ ₁ , λ ₂ ) is calculated by the above equation (8). hg ₂ (x, y) = ｛ψ ₁ (x, y) −ψ ₂ (x, y)｝ / ｛2 π × k
(1 / λ ₁ −1 / λ ₂ )｝

Next, according to the above equation (11), the first wavelength
Set (λ₁, Λ_Three) Fringe order difference ΔN ₁Calculate (x, y)
You.

(Equation 8)

Next, the approximate absolute distance hg ₁ (x, y) of the first wavelength pair (λ ₁ , λ ₃ ) is calculated by the above equation (12).

(Equation 9)

Next, a plurality of wavelengths are calculated by the above equation (13).
λ₁, Λ_Two, Λ_ThreeFor example, λ _ThreeFringe order N
Calculate (x, y). N (x, y) = T [k × hg₁(x, y) / λ₁−ψ_Three(X,
y) / (2π)]

Finally, the precise absolute distance h (x, y) of the surface 4a to be measured is calculated using the above equation (14). h (x, y) = λ _x / k × [ψ ₃ (x, y) / (2π) + N (x,
y)]

Then, the control unit in the computer main body 9a displays the obtained precise absolute distance h (x, y) on the display 9b.
To be displayed.

According to the second embodiment, the following effects can be obtained. (B) Phase measurement accuracy: 2π / 100, wavelength accuracy: 0.5 n
Under the condition of m, a precise absolute distance h (x, y) having a measurable range of 0.257 μm and a measurement accuracy of 0.0025 μm was obtained. (B) The measurable range is as wide as 29.6 μm, and
The measurement accuracy was as high as 0.0025 μm. Therefore, it is possible to measure a shape including steps or absolute distances exceeding the wavelengths λ ₁ , λ ₂ , λ ₃ . (C) A phase shift method (fringe scanning interferometry) that takes in four interference fringe image data for each wavelength while changing the distance between the interferometer 6 and the measurement target surface 4a by λ / 4. Therefore, the shape can be measured at high speed. Furthermore, since the imaging tubes 67A, 67B, and 67C capable of detecting light intensity in a two-dimensional area are used as a means for detecting interference fringes, a measurement of a certain range of the measurement target surface 4a is performed at one time. And high-speed measurement becomes possible. Therefore, in the conventional white light interferometry, which required a minimum of 8.5 seconds, the present apparatus 1 can greatly reduce the time within one second. (E) Unlike white interference, a signal can be obtained in a wide range, so that a signal for initial adjustment of the relative position and orientation between the measurement target surface and the interferometer can be obtained in a wider range. Therefore, it is possible to easily adjust the initial position and orientation, which is extremely difficult in the white light interferometry. (F) Since measurement can be performed in a short time, it can be used without a vibration isolator even in places where there is vibration or noise, such as a factory site.

FIG. 6 shows an interference measuring apparatus according to a third embodiment of the present invention. Components having the same functions as those in the first embodiment are denoted by the same reference numerals, and detailed description thereof will be omitted. The interference measuring apparatus 10 includes a horizontally arranged table 11, a pair of columns 12, 12 erected on the table 11, a rail 13 </ b> A and a straight section 13 </ b> B provided between the pair of columns 12, 12. And a piezo stage 5 for vertically moving the measurement object 4 on the table 11.
The interferometer 16 is provided in the rectilinear section 13B, and the interferometer 16 is moved in the horizontal direction by the rectilinear stage 13 to scan on the measurement target surface 4a to measure a wide area.

The interferometer 16 has a first wavelength λ₁Analogy
First laser light that emits a laser beam of 675.1 nm, for example
Source 160₁And the second wavelength λ_TwoFor example, 686.2
laser light source 160 that emits laser light of nm
_TwoAnd the third wavelength λ_ThreeFor example, a 688.2 nm laser
Third laser light source 160 that emits laser light_ThreeAnd the first
Laser light source 160₁To convert laser light from
Collimator lens 161 ₁And the second laser light source 16
0_TwoCollimator laser that converts the laser beam from
161_TwoAnd the third laser light source 160_ThreeLeh from
Third collimator lens 161 that converts the light into parallel light
_ThreeAnd the first laser light source 160₁The first wavelength λ from₁
Of the second laser light source 160_TwoSecond from
Wavelength λ_TwoLight, and the third laser light source 160_ThreeFrom
The third wavelength λ of_ThreeDichroic that reflects the light of the sun
Mirror 162₁And the second laser light source 160_TwoThe first from
Wavelength of 2 _TwoThe third laser light source 160_Three
The third wavelength λ from_ThreeDichroic light that transmits light
Ick mirror 162_TwoAnd the first, second and third cores
Meter lens 161₁, 161_Two, 161_ThreeParallel from
A first half-mirror that reflects a part of the light to the measurement object 4 side
163A and the measurement pair of the first half mirror 163A.
It is arranged on the elephant 4 side and is similar to a normal microscope objective lens.
An objective lens 164 having an imaging performance;
4 as a reference plane arranged between the object 4 and the object 4 to be measured.
A part of the light from the surface prototype 165 and the objective lens 164 is measured.
Guide to fixed object 4 and guide the rest to plane prototype 165
Second half mirror 163B and surface of measurement object 4
(Measurement target surface) Reflected by 4a and plane prototype 165, respectively
The laser beam returns to the second half mirror 163B, where it
The superimposed interference light is imaged via the imaging lens 166.
A color CCD camera 167 is provided. The objective
Lens 164, plane prototype 165 and second half mirror
-163B constitutes a so-called Mirau interferometer.

First, second and third laser light sources 160
₁ , 160 ₂ and 160 ₃ are color CCD cameras 167
Λ ₁ (= 675.1 nm), λ
₂ (= 686.2 nm) and λ ₃ (= 688.2 nm) are selected.

The interference measuring apparatus 10 includes a piezo driver 7 for driving the piezo stage 5 and a
Stage driver 17 for driving the
The image digitizer 8 converts the interference fringe image signal from the D camera 167 into digital interference fringe image data, the piezo driver 7 and the linear stage driver 17 are controlled, and measurement is performed based on the digital data from the image digitizer 8. A computer 9 for determining the shape of the target surface 4a.

Next, an interference measuring device according to a third embodiment will be described.
The operation of the device 10 will be described. First, obtain the interference fringe image data.
Get. That is, the first laser light source 160₁Emitted from
First wavelength λ₁Laser light and second laser light source
160_TwoWavelength λ emitted from_TwoLaser light,
Third laser light source 160_ThreeWavelength λ emitted from
_ThreeThe laser light of the first, second and third collimator lasers
161₁, 161 _Two, 161_ThreeThrough the first dike
Loic mirror 162₁Layered. The first dichro
Ick mirror 162₁Three wavelengths λ from₁, Λ_Two,
λ_ThreeIs partially reflected by the first half mirror 163A.
Is reflected by the measurement target surface 4a and the prototype 165,
Similarly to the first embodiment, the first half mirror 16
Return to 3A as interference light. The light from the Mirau interferometer is
After reaching the color CCD camera 167 via the imaging lens 166,
Reach. The color CCD camera 167 emits light of different wavelengths.
Has the function of individually detecting
1 wavelength λ₁A first interference fringe image by only the light of
Wavelength λ_TwoA second interference fringe image using only the light of
Wavelength λ_Three3rd interference fringe image by only light of
Is detected. Wavelength λ₁, Λ_Two, Λ_ThreeDryness detected for each
The image signal of the interference fringe is digitalized by the image digitizer 16.
The data is converted to data and transferred to the computer 9. Measurement
Interference fringe image data is obtained for a certain range of the target surface 4a.
Then, the computer 9 operates the straight-stage driver 1
7 is controlled and the interferometer 16 is leveled by the
In the same direction, and obtain the interference fringe image data
Embed.

Next, the interference is satisfied so as to satisfy the above equation (6).
Wavelengths λ used for₁, Λ_Two, Λ _ThreeTwo wavelengths from
The first and second wavelength sets are selected as one set. here
Then, as the first set of wavelengths (λ₁, Λ_Three), The second wave
As a set of lengths (λ₁, Λ_Two). In this case,
Synthetic wavelength (measurable range) using a set of wavelengths₁, Λ _Two
And approximate absolute distance measurement accuracy Rhg₁, Rhg
_TwoIs as follows: The first set of wavelengths (λ₁, Λ_Three): Λ₁= 17.7 μm Rhg₁= 0.25 μm The second set of wavelengths (λ₁, Λ_Two): Λ_Two= 118.1 μm Rhg_Two= 1.87 μm, the phase distribution for each wavelength is the same as in the second embodiment.
ψ₁(x, y), ψ_Two(x, y), ψ_Three(x, y) and calculate the second
Approximate absolute distance hg of a set of wavelengths_Two(x, y) and the first
Approximate absolute distance hg of a set of wavelengths₁(x, y)
Wavelength λ₁, Λ_Two, Λ_ThreeFor example, λ_ThreeStripes in
The number N (x, y) is calculated, and the measurement order is determined based on the fringe order N (x, y).
The precise absolute distance h (x, y) of the elephant surface 4a is calculated. Soshi
The control unit in the computer body 9a
The absolute distance h (x, y) is displayed on the display 9b.

According to the third embodiment, under the conditions of phase measurement accuracy: 2π / 100, wavelength accuracy: 0.01 nm, the measurement range is 0.334 μm, and the measurement accuracy is 0.00.
A precise absolute distance h (x, y) of 34 μm was obtained. Also,
Two-dimensional color C as an interference fringe detecting means having a wavelength selecting function having both functions of a wavelength selecting means and an interference fringe detecting means.
Since the CD camera 167 is provided, it is not necessary to separately provide a wavelength selection unit, and a compact, lightweight, and inexpensive apparatus can be realized.

The present invention is not limited to the above embodiment, but various embodiments are possible. For example, by averaging the distances of components of less than one wavelength of each wavelength of the shape of the measurement target surface calculated based on the wrapped phase obtained for each wavelength, components of less than one wavelength of each wavelength are calculated. May be determined with high accuracy. As the average, an appropriate one such as a simple arithmetic average, a weighted arithmetic average, or a geometric mean may be selected according to the purpose. In the above embodiment, a method of acquiring four interference fringe image data is adopted as the phase shift method, but a method of acquiring three or five interference fringe images may be employed. According to the method of acquiring three images, the measurement can be performed at a higher speed although the influence of an error is greater than the method of acquiring four images. According to the method of acquiring 5 sheets, 4
Although it takes more calculation time than the method of acquiring sheets, the influence of errors is reduced. Further, as a phase shift method, a phase shift electronic moiré method for changing δ without changing the distance between the interferometer and the surface to be measured (“Laser Science Research”, No. 13)
(1991)). According to this, it is not necessary to change the distance between the interferometer and the surface to be measured, and higher speed can be achieved. Further, in the above embodiment, when the distance between the interferometer and the measurement target surface is changed, the measurement target surface side is moved, but the interferometer side may be moved. Further, the third interferometer 6 of the second embodiment
The interferometer 16 of the second embodiment may be used for the interferometer 16 of the third embodiment. Further, in the third embodiment, a configuration using light waves of four or more wavelengths may be adopted.

[0055]

As described above, according to the present invention, a set of a plurality of wavelengths is set so that the composite wavelength of the two wavelengths becomes smaller sequentially by setting two wavelengths as a set from the plurality of wavelengths used for the interference. Since the selected absolute wavelengths are sequentially obtained from the set of wavelengths having the longer combined wavelengths, the range in which the absolute distances are obtained is significantly wider than that of the conventional two-wavelength interferometry. Further, a phase distribution of one wavelength among a plurality of wavelengths used for the interference,
Since the precise absolute distance is obtained based on the approximate absolute distance of a set of the shortest wavelengths of the synthetic wavelength, the conventional two
The absolute distance can be measured with the same accuracy as the light beam interferometry. In addition, the number of images taken during measurement is significantly smaller than that of the white light interferometry, and the detection of interference fringes at two different wavelengths is performed simultaneously and in parallel, so that the measurement speed is dramatically higher than in the past. Becomes possible. Therefore, it is possible to measure a shape including a step exceeding a wavelength and an absolute distance with high accuracy and at high speed.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of an interference measurement device according to a first embodiment of the present invention.

FIG. 2 is a flowchart illustrating an operation of the interference measurement device according to the first embodiment.

FIG. 3 is a diagram for explaining an operation of the interference measurement device according to the first embodiment.

FIG. 4 is a diagram for explaining a principle of obtaining an approximate absolute distance by the interference measurement device according to the first embodiment.

FIG. 5 is a configuration diagram of an interference measurement device according to a second embodiment of the present invention.

FIG. 6 is a configuration diagram of an interference measurement device according to a third embodiment of the present invention.

FIG. 7 is a flowchart illustrating a two-beam interference method.

FIG. 8 is a diagram for explaining how the phases are wrapped.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Interferometer 2 Table 3 Pillar 4 Measurement object 4a Measurement object surface 5 Piezo stage 6 Interferometer 60 Laser light source 61 Collimator lens 62A First half mirror 63 Objective lens 64 Planar prototype 62B Second half mirror 65 _1st 1 dichroic mirror 65 ₂ second dichroic mirror 66 imaging lens 67 ₁ first imaging tube 67 ₂ second imaging tube 67 ₃ third imaging tube 7 piezo driver 8 image digitizer 9 computer 9a computer body 9b display 9c Keyboard 10 Interferometer 11 Table 12 Pillar 13A Rail 13B Straight section 13 Straight stage 16 Interferometer 160 ₁ First laser light source 160 ₂ Second laser light source 160 ₃ Third laser light source 161 ₁ First collimator lens 161 ₂ The second collimator 'S 161 ₃ third collimator lens 162 ₁ first dichroic mirror 162 ₂ second dichroic mirror 163A first half mirror 163B second half mirror 164 objective lens 165 plane prototype 166 imaging lens 167 color CCD camera 17 Straight stage driver

Claims (12)

[Claims] 1. An interference fringe image of at least three wavelengths generated by the interference by irradiating light waves of at least three wavelengths onto a reference surface and a surface to be measured and causing interference at each of the at least three wavelengths. Are individually detected, and a set of the m-th to first wavelengths (where m ≧ 2) is set such that two wavelengths from the at least three kinds of wavelengths are set as a set and the composite wavelength of the two wavelengths is sequentially reduced. ), And based on the phase distribution difference between the interference fringe images corresponding to the two wavelengths, from the m-th wavelength set to the first wavelength for each of the m-th to first wavelength sets. The approximate absolute distance between the reference plane and the measurement target plane is sequentially calculated up to a set, the phase distribution of the interference fringe image corresponding to one of the at least three wavelengths, and the first wavelength Based on the approximate distances of the above set of Interferometric method characterized by calculating a precise absolute distance between the reference surface and the measurement target surface. 2. The method according to claim 2, wherein the selection of the set of the m-th to first wavelengths is
The composite wavelengths of the (m-1) to first wavelength sets are respectively
Rei_m-1,. . , Λ_Two, Λ₁Of the m-th to first wavelengths
The measurement accuracy of the above-mentioned approximate absolute distance of each set is Rh
g_m, Rhg_m-1,. . , Rhg _Two, Rhg, said few
At least one of the three wavelengths is λ_xThen
Come, Λ_i-1> Rhg_i(However, i = 2,3, ...,
m) λ_x/ K> Rhg₁(However, k: 2 for reflection measurement,
1) Rhg for transmission measurement₁<Rhg_Two<. . . <Rhg_m 2. The interferometer according to claim 1, wherein the interferometer is configured to satisfy the following relationship.
Measurement method. 3. The calculation of the approximate absolute distance is performed at the i-th wavelength.
The two wavelengths constituting the set of _i1, Λ_i2(However, i
= 1, 2,. . , M), (i + 1) -th wavelength set
Hg the absolute distance of_{(i + 1)}(x, y), the i-th wavelength set
The phase distribution difference is_i1(x, y) −ψ_i2(x, y)
The fringe order difference ΔN of the ith wavelength set_i(x, y) isWhere T []: nearest integer k: 2 for reflection measurement, 1 for transmission measurement, and the approximate absolute distance hg of the i-th wavelength set_i(x, y)
To2. The interference measurement method according to claim 1, wherein the calculation is performed by: 4. The precise absolute distance calculation includes calculating the approximate absolute distance of the _first set of wavelengths as hg ₁ (x, y), one of the plurality of wavelengths as λ _x , and the wavelength λ _x The phase distribution of ψ
_x (x, y) when a, fringe order N (x, y) in the wavelength lambda _x and N (x, y) = T [k × hg 1 (x, y) / λ x -ψ x (x ,
y) / (2π)] where T []: nearest integer k: 2 for reflection measurement and 1 for transmission measurement, and calculates the precise absolute distance h (x, y) as h (x , y) = λ _x / k × [ψ _x (x, y) / (2π) + N (x,
y)], wherein k is 2 for reflection measurement and 1 for transmission measurement. 5. The calculation of the precise absolute distance includes obtaining a plurality of the precise absolute distances using a plurality of wavelengths of the at least three types of wavelengths, and calculating an average of the plurality of the precise absolute distances. The interference measurement method according to claim 1, wherein the precise absolute distance is calculated by taking the absolute distance. 6. A light source for irradiating light waves of at least three types of wavelengths to a reference surface and a measurement target surface; light sources of the at least three types of wavelengths reflected by the reference surface and the at least three light waves reflected by the measurement target surface. An optical system that causes light waves of different wavelengths to interfere with each other for each of the at least three wavelengths, and interference that individually detects interference fringe images of the at least three wavelengths generated by interference of the light waves of the at least three wavelengths. A fringe image detecting means, and a set of m-th to first wavelengths (where m ≧ 2, such that two wavelengths from the at least three types of wavelengths are a set, and a composite wavelength of the two wavelengths is sequentially reduced. ), And based on a phase distribution difference between the interference fringe images corresponding to the two wavelengths, the m-th wavelength set to the first to the first wavelength set for each of the m-th to first wavelength sets. Wavelength pairs A rough calculating means for sequentially calculating a rough absolute distance between the reference surface and the measurement target surface; a phase distribution of the interference fringe image corresponding to one of the at least three wavelengths; An interference measurement apparatus, comprising: a precision calculation unit configured to calculate a precise absolute distance between the reference surface and the measurement target surface based on the approximate absolute distance of one set of wavelengths. 7. The method according to claim 1, wherein the selecting means is configured to select the (m-1) to first
Are respectively set to 合成_m−1 ,. . , Λ
₂ , ₁ , and the measurement accuracy of the approximate absolute distance of the set of the m-th to first wavelengths is Rhg _m , Rh, respectively.
g _m−1 ,. . , Rhg ₂ , Rhg, where λ _x is one of the at least three wavelengths, Λ _i-1 > Rh g _i (where i = 2, 3,..., M) λ _x / k > Rhg ₁ (where k: 2 for reflection measurement,
1) Rhg ₁ <Rhg ₂ <. . . <Interference measuring apparatus according to claim 6, wherein the configuration of performing so as to satisfy the relation of rhG _m. 8. The rough calculation means calculates the rough absolute distance by using the two wavelengths forming the i-th wavelength set as λ _i1 , λ _i2 (where i = 1, 2,. , M), (i +
The approximate absolute distance of the wavelength set of 1) is hg _{(i + 1)} (x, y),
The phase distribution difference of the i-th wavelength set is represented by ψ _i1 (x, y) −ψ
_i2 (x, y), the fringe order difference Δ of the i-th wavelength set
N _i (x, y) is given by Where T []: the nearest integer k: 2 for reflection measurement, 1 for transmission measurement, and the approximate absolute distance hg _i (x, y) of the i-th wavelength set is calculated as follows: Equation 4 7. The interference measurement method according to claim 6, wherein the calculation is performed by: 9. The precise absolute distance calculation means calculates the precise absolute distance by calculating the approximate absolute distance of the first set of wavelengths as h.
g ₁ (x, y), the plurality of single wavelength lambda _x of the wavelength, the wavelength lambda when the phase distribution of _x and [psi _x (x, y), the wavelength lambda fringes at _x degree N ( x, y) by N (x, y) = T [k × hg ₁ (x, y) / λ _x −ψ _x (x, y
y) / (2π)] where T []: nearest integer k: 2 for reflection measurement and 1 for transmission measurement, and calculates the precise absolute distance h (x, y) as h (x , y) = λ _x / k × [ψ _x (x, y) / (2π) + N (x,
y)], wherein k is 2 for reflection measurement and 1 for transmission measurement. 10. The at least one precision operation means comprises:
7. The configuration according to claim 6, wherein a plurality of said precise absolute distances are obtained by using a plurality of wavelengths of the wavelengths of said kind, and said precise absolute distance is calculated by averaging said plurality of said precise absolute distances. Interferometer. 11. The apparatus according to claim 6, wherein said interference fringe image detecting means uses an imaging means for detecting light intensity in a two-dimensional area.
The interference measurement device as described. 12. An interference measuring apparatus according to claim 6, wherein said interference fringe image detecting means uses a two-dimensional color CCD camera.