JPH11218411A - Measurement method for interference and measurement device of interference - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable measuring accurately and in high speed the shape including level difference or absolute distance exceeding wavelength by obtaining fractional wavelength shape information obtained from phase distribution calculated based on interference fringes image on a reference surface and measuring object surface and accurate absolute shape information of the measuring object surface from an integer in an integral multiple component of a wavelength obtained from the outline information of the absolute distance. SOLUTION: Two kinds of laser lights with different wavelengths are reflected on a plane standard (reference surface) and a measuring object surface, respective interference lights are picked up with 2 imaging tubes and the images of the interference fringes are forwarded to the control part 90 of a computer. The control part 90 calculates phase distribution Φ1 and Φ2 of each wavelength with a phase calculation mean 92 based on interference image data Ia and Ib . On this basis, an outline shape calculation means 93 calculates the outline information hg of absolute distance between the measuring object surface and the plane standard, outputs to an integer detection means 94 and calculates an integer ng. On the other hand, a fractional shape information calculation means 95 outputs the fractional shape information hs based on the phase distribution Φ1 and Φ2 . An accurate absolute shape calculation means 96 calculates integral accurate absolute shape information h based on the integer ng and fractional shape information hs.

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 an interference measurement with a step exceeding a wavelength or a measurement target surface exceeding a wavelength. The present invention relates to an interference measurement method and an interference measurement device for measuring a shape including an absolute distance from a meter at high accuracy and at 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 measurement target wavefront reflected by a measurement target surface 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. 8 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).

FIG. 9 shows how the phases are wrapped.
FIG. 3A shows the actual phase, and FIG. 3B 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, the interference measurement is an act of obtaining φ (x, y) from I (x, y) in the above equation (1). However, φ
Since the inverse function of cos that appears when obtaining (x, y) is a multivalent function, the actual phase φ cannot be determined uniquely, as shown in FIG. Can be formed only from fractional components of less than one wavelength excluding an integral multiple of the wavelength (an integer representing the multiple is referred to as “strip order”).

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 calculated using 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 × k) gives equation (3). However, k is 2 in the case of measurement by reflection, and 1 in the case of measurement by transmission. In the case of reflection, the light reciprocates and the optical path difference doubles, so that a coefficient k = 2 is applied. φ (x, y) × λ / (2π × k) = ng (x, y) × λ / k + ψs (x, y) × λ / (2π × k) (3) where φ (x , y) × λ / (2π × k) represents the optical path difference itself, and corresponds to comprehensive precise absolute shape information h (x, y). Further, ψs (x, y) × λ / (2π × k) is set as fraction shape information hs (x, y) which is a fraction component of less than one wavelength. At this time, equation (3) becomes equation (4). h (x, y) = ng (x, y) × λ / k + hs (x, y) (4) The shape (distance) of the surface to be measured can be obtained from equation (4).

<Conventional Example 2> In the two-wavelength interferometry, interference measurement is performed by simultaneously using light of two wavelengths (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).
Appears for each Λ (synthetic wavelength) represented by {= 1 / {(1 / λ ₁ −1 / λ ₂ ) × k} = λ ₁ × λ ₂ / {(λ ₂ −λ ₁ ) × k} (5) where λ ₁ , λ ₂ : used Two wavelengths k: 2 for measurement by reflection and 1 for measurement by transmission Therefore, the range corresponding to one cycle of interference fringes without uncertainty is λ = wavelength in a normal two-beam interference method. On the other hand, 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, in the case of transmission measurement using two red lights having wavelengths of 660 nm and 670 nm, the combined wavelength Λ is 4
4220 nm = 44.22 μm, and 44.22 μm
It is possible to measure shapes including steps up to and absolute distance. This is equivalent to 66 times the range of a normal two-beam interferometer. The smaller the wavelength difference (λ ₂ −λ ₁ ), the larger the measurable Λ range.

<Conventional Example 3> In the white light interferometry, interference measurement is performed using a white light or a light source having low coherency close thereto (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 light beam interferometry, when the surface to be measured 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 only determines the relative fringe order relationship of the wrapped phase so that 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 within one wavelength, 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 the conventional example 2 is a method of increasing the contour line period itself of the interference fringe density, so that when the measurable range Λ is increased, the measurement accuracy is reduced in proportion thereto, There is a drawback that highly accurate measurement exceeding a micron becomes 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, 100
An image of about 0 × 1000 pixels is becoming uncommon, but if interference fringes are collected from an image of that class,
The memory capacity of the 256 Mbyte class which is doubled is required for only one measurement data.

Accordingly, an object of the present invention is to provide an interference measurement method and an interference measurement apparatus capable of measuring a shape including a step exceeding a wavelength and including an absolute distance with high accuracy and at high speed without causing a measurement error. Is to do.

[0015]

In order to achieve the above object, the present invention irradiates a light wave of a first wavelength and a light wave of a second wavelength to a reference surface and a surface to be measured, and reflects the light wave at the reference surface. The lightwave of the first wavelength and the lightwave of the first wavelength reflected on the surface to be measured or the lightwave of the first wavelength transmitted through the surface to be measured interfere with each other, and the second light reflected on the reference surface.
A first step of interfering the light wave of the wavelength and the light wave of the second wavelength reflected on the measurement target surface or transmitted through the measurement target surface, and the interference generated by the interference of the light wave of the first wavelength. A second step of individually detecting an interference fringe image of a first wavelength and an interference fringe image of the second wavelength caused by interference of the light wave of the second wavelength; and an interference fringe of the first wavelength. The first phase distribution wrapped in the 2π section of the measurement target wavefront is calculated based on the image, and the second phase distribution wrapped in the 2π section of the measurement target wavefront is calculated based on the interference fringe image of the second wavelength. the third step and, the first wavelength lambda ₁ for calculating the phase distribution, the second
Is λ ₂ (λ ₂ > λ ₁ ), and the first phase distribution is ψ
₁ (x, y), when the second phase distribution is ψ ₂ (x, y), the absolute distance between the reference plane and the measurement target surface over a predetermined measurement range expanded from the section of 2π If the distance of summary information hg (x, y) of _{0 ≦ (ψ 1 (x,} y) -ψ 2 (x, y)), hg (x, y) = {ψ 1 (x, y) -ψ ₂ (x, y)｝ / ｛(2π ×
k) · (1 / λ ₁ −1 / λ ₂ )｝ where k: 2 for measurement by reflection, 1 for measurement by transmission x, y: Coordinate components of a plane roughly along the measurement target surface ( If ψ ₁ (x, y) −ψ ₂ (x, y)) <0, then hg (x, y) = ｛ψ ₁ (x, y) −ψ ₂ (x, y) + 2π｝ / ｛(
2π × k) · (1 / λ ₁ −1 / λ ₂ )｝, and the first and second steps
Based on any one of the phase distributions, the precise fraction shape information hs _j (x, y)
Hs _j (x, y) = ψ _j (x, y) × λ _j / (2π × k), where j: a fifth step of obtaining a wavelength by a subscript 1 or 2; The fringe order ng _j (x, y) for the first wavelength λ ₁ or the second wavelength λ ₂ is obtained using the general information hg (x, y),
The precise absolute shape information h _j (x, y) of the surface to be measured is given by h _j (x, y) = ng _j (x, y) × λ _j / k + hs _j (x, y), where j: wavelength And a sixth step of determining by subscript 1 or 2 to be distinguished.

In order to achieve the above object, the present invention provides a light source for irradiating a light wave of a first wavelength and a light wave of a second wavelength to a reference surface and a surface to be measured, and the first light reflected by the reference surface. And the light wave of the second wavelength reflected on the measurement target surface, or interferes with the light wave of the first wavelength transmitted through the measurement target surface, and the light wave of the second wavelength reflected on the reference surface and the measurement target An optical system that reflects light on the surface or interferes with the lightwave of the second wavelength transmitted through the surface to be measured, and an interference fringe image of the first wavelength generated by interference of the lightwave of the first wavelength, and Interference fringe image detecting means for individually detecting the interference fringe image of the second wavelength generated by the interference of the light wave of the second wavelength; and 2π of the wavefront to be measured based on the interference fringe image of the first wavelength. The first phase wrapped in the interval of Thereby calculating the cloth, and the phase calculating means for calculating a second phase distribution is wrapped in the interval 2π being measured wavefront based on the interference fringe image of the second wavelength, the first wavelength lambda ₁ , The second wavelength is λ ₂ (λ
₂ > λ ₁ ), when the first phase distribution is ψ ₁ (x, y) and the second phase distribution is ψ ₂ (x, y), a predetermined measurement expanded from the section of 2π Over a range, the approximate information hg (x, y) of the absolute distance between the reference plane and the measurement target plane is set to 0.
≤ (ψ ₁ (x, y) −ψ ₂ (x, y)), then hg (x, y) = ｛ψ ₁ (x, y) −ψ ₂ (x, y)｝ / ｛(2π ×
k) · (1 / λ ₁ −1 / λ ₂ )｝ where k: 2 for measurement by reflection, 1 for measurement by transmission x, y: Coordinate components of a plane roughly along the measurement target surface ( If ψ ₁ (x, y) −ψ ₂ (x, y)) <0, then hg (x, y) = ｛ψ ₁ (x, y) −ψ ₂ (x, y) + 2π｝ / ｛(
2π × k) · (1 / λ ₁ −1 / λ ₂ )｝, and the precise fraction shape information hs _j (x, y) is converted to hs _j (x, y) = ψ _j (x , y) × λ _j / (2π × k) where j is a fraction shape information calculating means operated by a subscript 1 or 2 for discriminating the wavelength, and the approximate information hg (x, y) of the absolute distance is used. The fringe order ng _j (x, y) for the first wavelength λ ₁ or the second wavelength λ ₂
And the fringe order detecting means for detecting the absolute absolute shape information h _j (x, y) is given by h _j (x, y) = ng _j (x, y) × λ _j / k + hs _j (x, y) , J: means for calculating a precise absolute shape obtained by subscript 1 or 2 for distinguishing wavelengths.

[0017]

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

The interferometer 6 includes a laser light source 60 such as an argon ion laser for simultaneously oscillating two types of laser light having a _first wavelength λ ₁ and a second wavelength λ ₂ , and a laser light source 6.
Collimator lens 61 for converting laser light from 0 to parallel light
A first half mirror 62A that reflects a part of the parallel light from the collimator lens 61 to the measurement object 4 side, and a first half mirror 62A that is arranged on the measurement object 4 side of the first half mirror 62A,
An objective lens 63 having the same imaging performance as a normal microscope objective lens, a plane prototype 64 as a reference plane, and a part of the light from the objective lens 63 are guided to the measurement object 4 and the remaining part is Second half mirror 62B leading to flat prototype 64
Then, the light reflected by the surface (measurement surface) 4a of the measurement object 4 and the light reflected by the plane prototype 64 return to the second half mirror 62B, and the interference light generated by being superimposed there is converted to the first wavelength λ. a dichroic mirror 65 for sorting the _first light and the second wavelength lambda ₂ of the light, a first image pickup tube 67A to the first wavelength lambda ₁ of the light through the first imaging lens 66A imaging, the 2
And a second imaging tube 67B for imaging the light having the wavelength λ ₂ through the second imaging lens 66B. In addition, the objective lens 63, the plane prototype 64, and the second half mirror 62
B constitutes a so-called Michelson interferometer.

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 and second image pickup tubes 67A and 67B into digital interference fringe image data. Image digitizer 8
And the piezo driver 7 is controlled, and based on the digital data from the image digitizer 8, the measurement target surface 4a
And a computer 9 for determining the shape of In addition,
9a is a computer main body including a control unit 90 described later,
9b is a display for displaying the measurement results, and 9c is a keyboard.

The laser light source 60 has a first wavelength λ.₁As
488 nm (blue), second wavelength λ _Two514.5 as
Simultaneously oscillates laser light of two wavelengths of nm (green)
The resonator in the laser light source 60 is set so that
Specifically, an etalo appropriately selected for a normal laser resonator
Is adjusted by inserting the button.

The dichroic mirror 65 has a wavelength selecting function, and is configured to transmit light of a _first wavelength λ ₁ of 488 nm and reflect light of a second wavelength λ ₂ of 514.5 nm. ing.

FIG. 2 is a functional block diagram of the computer 9. The computer body 9a includes a CPU that controls the entire device 1 and an RO that stores a program for the CPU.
M and a control unit 90 including a RAM and the like for storing various information necessary for obtaining the shape of the measurement target surface 4a. The control unit 90 performs a process of calculating precise absolute shape information of the measurement target surface 4 a based on the interference fringe image data from the image digitizer 8. It has a phase calculating means 92, a rough shape calculating means 93, a fringe order detecting means 94, a fraction shape information calculating means 95, and a precise absolute shape calculating means 96.

Next, each of the means 91 to 96 of the control unit 90 will be described.
Will be described. The interference fringe image acquiring unit 91 uses a piezo driver 7 by a phase shift method (for example, a fringe scanning interference measurement method).
Is controlled to move the object 4 in the vertical direction, and while changing the distance between the interferometer 6 and the object surface 4a by λ / 4, four interference fringe image data are taken in for each wavelength.

The phase calculating means 92 calculates the phase distribution of the _first wavelength λ ₁ based on the interference fringe image data acquired by the interference fringe image acquiring means 91 using the following equations (6) and (7). ψ ₁ (x, y) and the phase distribution of the second wavelength λ ₂ ψ ₂ (x, y)
Is calculated. ψ ₁ (x, y) = arctan [｛Ia ₄ (x, y) −Ia ₂ (x, y)｝ / ｛Ia ₁ (x, y) −Ia ₃ (x, y)｝]… (6) ψ ₂ (x, y) = arctan [｛Ib ₄ (x, y) −Ib ₂ (x, y)｝ / ｛Ib ₁ (x, y) −Ib ₃ (x, y)｝] (7) Since arctan is a multivalent function, as described above, ψ ₁ (x, y) and ψ ₂ (x, y) are obtained as wrapped phases, that is, wrapped phases of 2π. In addition, the acquired four interference fringe image data of the first wavelength λ ₁ are represented by Ia ₁ (x, y), Ia ₂ (x, y), Ia ₃ (x, y), Ia
₄ (x, y), and similarly, the four interference fringe image data of the second wavelength λ ₂ are obtained as Ib ₁ (x, y), Ib ₂ (x, y), Ib ₃ (x, y), Ib
b ₄ (x, y).

The rough shape calculating means 93 is provided with the phase calculating means 9.
Based on ψ ₁ (x, y) and ψ ₂ (x, y) obtained by the calculation unit 2, each point of the measurement target surface 4 a and the prototype 6 are calculated by using equations (8) and (9).
It calculates approximate information hg (x, y) of the absolute distance to the object 4 (the optical distance between the prototype 64 and the surface 4a to be measured), and outputs the calculation result to the fringe order detecting means 94. (i) 0 ≦
_{(Ψ 1 (x, y)} -ψ 2 (x, y)) if, hg (x, y) = {ψ 1 (x, y) -ψ 2 (x, y)} / {(2π × k ) · (1 / λ ₁ −1 / λ ₂ )｝ (8) where k: 2 for reflection measurement, 1x for transmission measurement, y: coordinates of a plane roughly along the surface to be measured If the component (ii) (ψ ₁ (x, y) −ψ ₂ (x, y)) <0, hg (x, y) = ｛ψ ₁ (x, y) −ψ ₂ (x, y) + 2π ｝ / ｛(2π × k) · (1 / λ ₁ −1 / λ ₂ )｝… (9)

As shown in FIG. 3, the same location on the surface to be measured
First wavelength λ corresponding to (point of interest) ₁Interference fringes and the second
Wavelength λ_TwoIs different from the interference fringe of the measurement target surface 4a.
Varies with the absolute distance between the target point of
You. Therefore, the absolute distance can be obtained from the phase difference.
Wear. The change amount is a periodic function, and the period is two waves
Two different wavelengths λ as in long interferometry₁And λ_TwoAgainst
Thus, it is given by the following equation, which is the same as equation (5). Λ = 1 / ｛(1 / λ₁−1 / λ_Two) × k｝ = λ₁× λ_Two/ ｛(Λ_Two−λ₁) × k｝ That is, the range for which the absolute distance is determined is in the interval of 2π
(Λ₁Or λ_Two) For a given measurement range
Λ. The absolute distance obtained in this way is
As with the negotiation method, the accuracy is lower than that of the ordinary two-beam interferometry.
No. In this sense, the absolute distance is rough information, but the fringe order
Can be given sufficient accuracy to determine
Here, hg (x, y) in the above equations (8) and (9) is the absolute distance.
The reason for the summary information is as follows. Wrapped position
The relationship between the phase ψ and the actual absolute distance or the shape h is given by the equation (1)
0). hg · (2π × k) / λ = ψ + 2π × N (10) where k: 2 for reflection measurement, 1 for transmission measurement N: fringe order at wavelength λ は when measurement is performed by reflection , Because the light wave goes back and forth
The phase difference is doubled even at the distance difference, and k = 2. this
That is, the distance indicated by one fringe of interference fringes (interval of interference fringes)
Corresponds to twice the difference between reflection and transmission. Next, λ₁
And λ_TwoFormula (10) above is calculated for
When rearranging, it becomes Formula (11). hg = {1 / (2π × k)} ・ [｛(ψ₁−ψ_Two) + 2π × ΔN｝ / (1 / λ₁−1 / λ_Two)] (11) where ΔN = N (λ₁) -N (λ_Two).

FIG. 4 shows ΔN with respect to hg when the approximate information hg (x, y) of the absolute distance is uniformly obtained from the above equation (8).
The state of is shown. This method focuses on the property that { ₁ (x, y) − { ₂ (x, y)} is approximately proportional to the absolute distance hg (x, y). At this time, the proportional coefficient is 1 / ｛(2π × k) · (1 / λ
₁ −1 / λ ₂ )｝. However, when the relationship between hg (x, y) and { ₁ (x, y) − { ₂ (x, y)} is actually plotted, the result is as shown in FIG. Are the same, but deviate by a constant as indicated by reference numeral 40 in FIG. Therefore, h is uniformly obtained by the equation (8).
If g (x, y) is calculated, the measurement will be erroneous under some of the above conditions.

FIG. 5 shows the state of ΔN with respect to hg.
hg is 0 and Λ = λ₁× λ_Two/ ｛(Λ _Two−λ₁) × k｝
Λ when taking a value between₁Fringe order N (λ₁) And λ_TwoStripes
Order N (λ_Two) May be 0 or 1.
I understand. Further comparing this with FIG. 4, hg is 0 and ０
= Λ₁× λ_Two/ ｛(Λ_Two−λ₁) × k｝
In that case, ｛ψ₁(x, y) −ψ_Two(x, y) と き に when｝ is positive
N is 0, ｛ψ₁(x, y) −ψ_TwoΔn when (x, y) 負 is negative
Is found to be 1. Equation (1)
Substituting into 1) yields equations (8) and (9).

The fringe order detecting means 94 is based on hg (x, y) obtained by the rough shape calculating means 93 and ng ₁ (x, y) or ng ₁ (x, y) so as to satisfy the equations (12) and (13). ng ₂
(x, y) defines one of fringe order ng ₁ for one single wavelength of lambda ₁ or lambda ₂ (x, y) or fringe order ng ₂
(x, y) is calculated. {Ng ₁ (x, y) +1} × λ ₁ > hg (x, y) ≧ ng ₁ (x, y) × λ ₁ (12) {ng ₂ (x, y) +1} × λ ₂ > hg (x, y) ≧ ng ₂ (x, y) × λ ₂ (13)

Based on 情報₁ (x, y) or ψ ₂ (x, y) obtained by the phase calculating means 92,
The following equation (14) is used to calculate fractional shape information hs _j (x, y), which is a fractional component of less than one wavelength of λ ₁ or λ ₂ . hs _j (x, y) = ψ _j (x, y) × λ _j / (2π × k) (14) where j is a suffix 1 or 2 k for distinguishing a wavelength k: 2 for reflection measurement, transmission For measurement 1

The precise absolute shape calculating means 96 calculates the fringe order ng _j (x, y) obtained by the fringe order detecting means 94 and the fraction shape information hs _j (x, y) obtained by the fraction shape information calculating means 95. On the basis of this, comprehensive accurate absolute shape information h (x, y) is calculated using the following equation (15). h _j (x, y) = ng _j (x, y) × λ _j / k + hs _j (x, y) (15) where j: a suffix 1 or 2 for distinguishing wavelength k: 2 for reflection measurement , For transmission measurement 1

Next, the operation of the present apparatus 1 will be described. First,
Interference fringe image acquisition means 9 of control unit 90 in computer 9
1 controls the piezo driver 7 to move the measurement object 4 in the vertical direction by a phase shift method (for example, fringe scanning interference measurement method), and sets the distance between the interferometer 6 and the measurement object surface 4a to λ.
Four interference fringe image data are taken in for each wavelength while changing by / 4.

Here, a case where one piece of interference fringe image data is obtained will be described. The laser light having two wavelengths λ ₁ and λ ₂ emitted from the laser light source 60 is collimated by a collimator lens 61 and is converted into a first half mirror 62.
Part of the light is reflected by A and reaches the objective lens 63. A part of the light from the objective lens 63 is guided to the measurement target surface 4a by the second 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, is again reflected by the second half mirror 6
It returns to 2B, where it is superimposed and becomes interference light. Part of the light emitted from the objective lens 63 is the first half mirror 6.
The light passes through 2A and reaches the dichroic mirror 65. Therefore, the light having a wavelength of 488 nm reaches the first image pickup tube 67A via the first imaging lens 66A, and has a wavelength of 488 nm.
The light of 4.5 nm passes through the second imaging lens 66B to the second
Reaches the imaging tube 67B. In this manner, the image of the interference fringe caused by only the light having the wavelength of 488 nm in the first imaging tube 67A and the image of the interference fringe caused by only the light having the wavelength of 514.5 nm in the second imaging tube 67B are individually and simultaneously obtained as the light intensity. Is detected. The image signal of the interference fringe detected for each wavelength is
The image is converted into digital interference fringe image data by the image digitizer 8 and transferred to the control unit 90 in the computer 9. Thus, the interference fringe image acquiring unit 9 of the control unit 90
1 acquires four pieces of interference fringe image data for each wavelength and outputs the data to the phase calculating means 92. The interference fringe image data is represented by a (x, y), as shown in Expression (1) described in the related art.
Since b (x, y) and φ (x, y) are unknown quantities, if δ is changed to obtain at least three pieces of interference fringe image data, φ (x, y)
Here, four interference fringe image data are acquired in consideration of calculation accuracy and calculation speed.

Next, based on the interference fringe image data obtained by the interference fringe image obtaining means 91, the phase calculating means 92 calculates the first wavelength λ ₁ based on the above-mentioned equations (6) and (7). The phase distribution ψ ₁ (x, y) and the phase distribution ψ ₂ (x, y) of the second wavelength λ ₂
y), and outputs the calculation result to the rough shape calculating means 93 and the fraction shape information calculating means 95.

Next, the rough shape calculating means 93 uses the above equations (8) and (9) based on ψ ₁ (x, y) and ψ ₂ (x, y) obtained by the phase calculating means 92. To calculate the approximate information hg (x, y) of the absolute distance between each point of the surface 4a to be measured and the prototype 64 (the difference between the optical distance between the prototype 64 and the surface 4a to be measured), and calculate the calculation result. It is output to the fringe order detecting means 94.

Next, based on hg (x, y) obtained by the rough shape calculating means 93, the fringe order detecting means 94 calculates the above equation (12).
And ng ₁ (x, y) or ng ₂ (x, y) is determined so as to satisfy Expression (13), and the fringe order ng ₁ (x, y) for one single wavelength of λ ₁ or λ ₂ is determined. y) or the stripe order ng ₂ (x, y) is calculated, and the calculation result is output to the precise absolute shape calculation means 96.

Next, the fraction shape information calculating means 95 uses the above equation (14) to calculate λ ₁ based on, ₁ (x, y) or ψ ₂ (x, y) obtained by the phase calculating means 92. Alternatively λ fraction shape information is a fractional component of less than one wavelength of ₂ hs _k (x, y) is calculated, and outputs the calculation result to the precise absolute shape calculation unit 96.

Next, the precise absolute shape calculating means 96 calculates
The stripe order ng obtained by the number detection means 94 _j(x, y) and fractional forms
Fraction shape information hs obtained by the shape information calculating means 95_j(x, y)
Based on the above, a comprehensive precision absolute shape is calculated using the above equation (15).
Calculate information h (x, y)

The control unit 90 obtains the determined absolute absolute shape information h.
(x, y) is displayed on the display 9b.

According to the first embodiment, the following effects can be obtained. (A) Since two wavelengths λ ₁ and λ ₂ are used, the lens ら れ る for which the absolute distance h is obtained becomes wide (9475 nm / 2 =
4.737 μm. In the present embodiment, since it is a reflection measurement, it is divided by two. ), It is possible to measure shapes including steps and absolute distances exceeding the wavelengths λ ₁ and λ ₂ . (B) Phase distribution of a single wavelength of either λ ₁ or λ ₂ ψ
₁ (x, y) or ψ ₂ (x, y)
Since s _j (x, y) is obtained, a fraction component of one wavelength or less can be obtained with high accuracy. Since this method is equivalent to the ordinary two-beam interference method, an accuracy of about λn / 50 can be easily obtained (where λn is λ ₁ or λ ₂ ). As a result, precise absolute shape information h of the surface to be measured is obtained.
(x, y) can be obtained. (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 a higher speed than in the white light interferometry. Further, as means for detecting interference fringes, 2
Image pickup tubes 67A, 67 capable of detecting light intensity in a dimensional area
Since B is used, it is possible to perform a measurement for a certain range of the measurement target surface 4a at one time, and high-speed measurement becomes possible. Accordingly, in the white light interferometry of Conventional Example 3, the shortest is 8.
According to the present apparatus 1, the time required for 5 seconds can be significantly shortened within 1 second. (D) The measurement error of the outline information hg (x, y) of the absolute distance is the first
And the first and second wavelengths λ ₁ , λ ₂ are smaller than the interval of the longer interference fringe of the second wavelengths λ ₁ , λ 2.
_{Since 2} is selected in advance, the determination of the fringe order can be reliably performed with the required accuracy, so that an error due to an error in the fringe order determination can be prevented. (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. (G) The above measurement can be accurately performed within a predetermined range without exception.

FIG. 6 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 apparatus 10 includes a horizontally arranged table 11, a pair of columns 12, 12 erected on the table 11, a rail 13A and a straight section 13B extending 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 λ ₁ of 48
A first laser light source 160A that emits 8 nm (blue) laser light, and a second laser light source 160B that emits 514.5 nm (green) laser light as the second wavelength λ _2.
A first collimator lens 161A for converting laser light from the first laser light source 160A into parallel light, a second collimator lens 161B for converting laser light from the second laser light source 160B into parallel light, and a first collimator lens 161B. Laser light source 160A
From the dichroic mirror 162 that transmits the light of the first wavelength λ ₁ from the second laser light source and reflects the light of the second wavelength λ ₂ from the second laser light source 160B, and the first and second collimator lenses 161A and 161B. A first half mirror 163A that reflects a part of the parallel light to the object 4 to be measured
And an objective lens 164 arranged on the measurement object 4 side of the first half mirror 163A and having the same imaging performance as a normal microscope objective lens, and arranged between the objective lens 164 and the measurement object 4 Plane prototype 165 as reference plane
And a second half mirror 163B that guides a part of the light from the objective lens 164 to the measurement target 4 and guides the remaining part to the flat prototype 165, and the surface of the measurement target 4 (measurement target surface).
4a and the laser beam respectively reflected by the plane prototype 165
And a color CCD camera 167 that captures the superposed interference light via an imaging lens 166. Note that the objective lens 165,
The plane prototype 165 and the second half mirror 163B constitute a so-called Mirau interferometer.

The first and second laser light sources 160A, 160A
For 60B, the first and second wavelengths λ ₁ and λ ₂ that can be separated by the color CCD camera 167 are selected. For example, the first laser light source 160A is capable of resolving as a first wavelength λ ₁ into a B signal of the color CCD camera 167,
Selected to emit 8nm (blue) laser light,
The second laser light source 160B can be decomposed into the G signal of the color CCD camera 167 as the second wavelength λ ₂ 514.
It is selected so as to emit 5 nm (green) laser light.

The interference measuring device 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, the operation of the apparatus 10 will be described. The process up to the capture of the interference fringe image data into the computer will be described below. First, the laser light of the first wavelength λ ₁ emitted from the first laser light source 160A and the laser light of the second wavelength λ ₂ emitted from the second laser light source 160B are first and second Collimator lens 161A, 1
After passing through 61B, they are overlapped by the dichroic mirror 162. The light containing two wavelengths from the dichroic mirror 162 is partially reflected by the first half mirror 163A, reflected by the measurement target surface 4a and the prototype 165, and is again reflected by the first half mirror 163A as in the first embodiment. The light returns to the first half mirror 163A as interference light. Light emitted from the Mirau interferometer reaches the color CCD camera 167 via the imaging lens 166. Since the color CCD camera 167 has a function of individually detecting light having different wavelengths as an image, the first interference fringe image using only the light having the first wavelength λ _{1 and} the light having the second wavelength λ ₂ are provided. Only the second interference fringe images are detected individually and simultaneously. The image signal of the interference fringe detected for each wavelength is
It is converted into digital data by the image digitizer 16,
It is transferred to the computer 9. When the interference fringe image data is obtained for a certain range of the measurement target surface 4a, the computer 9 controls the straight-ahead stage driver 17 to move the interferometer 16 by the straight-ahead stage 13 by a predetermined distance in the horizontal direction. Import image data. The interference fringe image data captured as described above is stored in a computer 9
Are processed in the same manner as in the first embodiment.

According to the second embodiment, since the two-dimensional color CCD camera 167 is provided as the interference fringe detecting means having the wavelength selecting function having the functions of the wavelength selecting means and the interference fringe detecting means, the wavelength selecting operation is performed. There is no need to provide a separate means, and a small, lightweight and inexpensive device can be realized.

FIG. 7 shows an interference measuring apparatus according to a third embodiment of the present invention. Note that components having the same functions as those of the first and second embodiments are denoted by the same reference numerals, and detailed description thereof is omitted. The interferometer 20 includes a horizontally arranged table 11, a pair of columns 12, 12 erected on the table 11, a rail 13A and a straight section 13B extending between the pair of columns 12, 12. And a rectilinear stage 13 composed of
The piezo stage 5 for vertically moving the pedestal is mounted, and an interferometer 26 is provided on the linear portion 13B of the linear stage 13.
Is moved in the horizontal direction by the rectilinear stage 13 to scan the surface 4a to be measured, thereby making it possible to measure a wide area.

The interferometer 26 sets the first wavelength λ ₁ to 63
A first semiconductor laser light source 260A that emits 7 nm (red 1) laser light, and a second wavelength λ ₂ of 676 nm
A second semiconductor laser light source 260B that emits the (red 2) laser light, a first shutter 268A that controls transmission blocking of light from the first laser light source 260A, and light from the second laser light source 260B Shutter 268B for controlling transmission blocking of light, and first collimator lens 2 for converting laser light from first laser light source 260A into parallel light.
61A, a second collimator lens 261B that converts the laser light from the second laser light source 260B into parallel light,
And a half mirror 262 that transmits a part of the parallel light from the second collimator lenses 161A and 161B and reflects a part of the parallel light, thereby combining the two parallel lights.
And the first and second collimator lenses 261A, 261
A half mirror 263 that reflects a part of the parallel light from the first mirror 1B to the measurement object 4 side, and an objective lens that is arranged on the measurement object 4 side of the half mirror 263 and has the same imaging performance as a normal microscope objective lens. H.264 and objective lens 264
A plane prototype 265 as a reference plane disposed between the object and the measurement target 4, and a part of light from the objective lens 264 is guided to the measurement target 4, and the remaining part is guided to the plane prototype 265. The laser light reflected by the half mirror 269, the surface (measurement target surface) 4 a of the measurement target 4, and the plane prototype 265 returns to the half mirror 269, and the superposed interference light is transmitted through the imaging lens 266 via the imaging lens 266. CCD camera 267 for imaging
And In addition, the objective lens 264 and the plane prototype 2
The 65 and the half mirror 269 constitute a so-called Mirau interferometer.

The opening and closing of the first shutter 268A and the second shutter 268B are controlled by a computer through the control unit 90, so that the light of the first semiconductor laser light source 260A and the light of the second semiconductor laser light source 260B are transmitted or transmitted. It can be cut off.

The interference measuring device 20 includes a piezo driver 7 for driving the piezo stage 5 and a
, A digitizer 8 for converting an image signal of an interference fringe from the CCD camera 267 into digital interference fringe image data, a piezo driver 7 and a driver 17 for a rectilinear stage. A computer 9 for obtaining the shape of the surface 4a to be measured based on digital data from the digitizer 8;

Next, the operation of the apparatus 20 will be described. The process up to the capture of the interference fringe image data into the computer will be described below. First, the first shutter 268A is opened and the second shutter 268B is closed. At this time, only the laser light of the first wavelength λ ₁ emitted from the first laser light source 260A passes through the first collimator lens 261A and the half mirror 262, and is partially reflected by the half mirror 263 to be measured. Reflected by the surface 4a and the prototype 265,
It returns to the half mirror 269 again and interferes. Further, the light of wavelength λ ₁ emitted from the Mirau interferometer reaches the CCD camera 267 via the imaging lens 266. CCD camera 267
Detects a first interference fringe image using only the light of the first wavelength λ ₁ . Next, the first shutter 268A is closed and the second shutter
The shutter 268B is opened. At this time, only the laser light of the second wavelength λ ₂ emitted from the second laser light source 260B is applied to the second collimator lens 261B and the half mirror 2
After passing through 62, a part thereof is reflected by the half mirror 263, reflected by the measurement target surface 4 a and the prototype 265, and returns to the half mirror 269 again to interfere. Further, the light of wavelength λ ₂ emitted from the Mirau interferometer reaches the CCD camera 267 via the imaging lens 266. This time, the CCD camera 267
A second interference fringe image is detected using only the light of the second wavelength λ ₂ . Image signals of interference fringes detected for each of the wavelengths λ ₁ and λ ₂ are converted into digital data by an image digitizer 8 and transferred to a computer 9. When the interference fringe image data is obtained for a certain range of the measurement target surface 4a, the computer 9 controls the straight-ahead stage driver 17 to move the interferometer 16 by the straight-ahead stage 13 by a predetermined distance in the horizontal direction. Import image data. The interference fringe image data captured as described above is processed by the computer 9 in the same manner as in the first embodiment.

According to the third embodiment, since the wavelength of the light source is switched in time series, two imaging optical systems as in the first embodiment become unnecessary, and two imaging optical systems are used. Errors due to misalignment between systems are eliminated.
In the second embodiment, the two imaging optical systems are built in the color CCD camera 167 and thus are inexpensive, but errors due to misalignment are not completely eliminated. Also, depending on the selection of the two wavelengths, it may be difficult to design and manufacture a dichroic mirror. For example, in order to widen the measurement range 表 represented by the above formula (5), it is necessary to select a combination of light sources having close wavelengths, but it is difficult to realize a filter that discriminates such light having close wavelengths. . In such a case, the first and second embodiments are difficult to realize, but according to the third embodiment, they can be realized without difficulty. As described above, according to the third embodiment, it is possible to realize an inexpensive and high-precision apparatus that can freely combine wavelengths.

The present invention is not limited to the above embodiment, but various embodiments are possible. For example, the fraction shape information obtained for each wavelength hs _k (x, y) new fractional shape information arithmetic mean of hs ₀ (x, y) may be used as. 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. The averaging effect can improve accuracy. 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 five images, the calculation time is longer than that of the method of acquiring four images, but the influence of an error is reduced. In addition, as a phase shift method, a phase shift electronic moiré method that changes 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 interferometer 16 of the second embodiment may be used as the interferometer 6 of the first embodiment, and the interferometer 6 of the first embodiment may be used as the interferometer 16 of the second embodiment.
May be used. In the above embodiment, the light wave of the first wavelength reflected by the reference surface and the light wave of the first wavelength reflected by the measurement target surface interfere with each other, and the light wave of the second wavelength reflected by the reference surface Although the light wave of the second wavelength reflected on the surface to be measured interferes with the light wave of the first wavelength reflected on the reference surface and the light wave of the first wavelength transmitted through the object to be measured, The light wave of the second wavelength reflected by the surface may interfere with the light wave of the second wavelength transmitted through the measurement object.

[0054]

As described above, according to the present invention, since two different wavelengths are used, the range in which the absolute distance can be obtained is as wide as that of the conventional two-wavelength interferometry.
In addition, over the 2π section of the wavefront to be measured, precise shape information of the surface to be measured, that is, a fractional component of one wavelength or less is determined with high accuracy, and precise absolute shape information is determined based on the fractional component and the fringe order. Therefore, the shape can be measured with the same accuracy as that of the conventional two-beam interference method. 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 of two different wavelengths is performed simultaneously and in parallel. Becomes possible. Further, such measurements can be made accurately and without failure within a widened predetermined range. Therefore, it is possible to measure a shape including a step or an absolute distance exceeding a wavelength with high accuracy and at high speed without causing a measurement error.

[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 functional block diagram of a control unit of the interference measurement device according to the first embodiment.

FIG. 3 is a diagram illustrating a principle of obtaining approximate information of an absolute distance by the interference measurement device according to the first embodiment.

FIG. 4 is a diagram for explaining how a wrap phase difference { ₁ (x, y) − { ₂ (x, y)} is proportional to the approximate information hg (x, y) of the absolute distance.

FIG. 5 is a diagram showing a state of a fringe order difference ΔN with respect to general information hg (x, y) of absolute distance.

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

FIG. 7 is a configuration diagram of an interference measurement device according to a third embodiment of the present invention.

FIG. 8 is a flowchart for explaining a two-beam interference method as a conventional interference measurement method.

9A is a diagram illustrating an actual phase, and FIG. 9B is a diagram illustrating a wrapped phase.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Interferometer 2 Table 3 Pillar 4 Object 4a Object to be measured 5 Piezo stage 6 Interferometer 7 Piezo driver 8 Image digitizer 9 Computer 9a Computer body 9b Display 9c Keyboard 10 Interferometer 11 Table 12 Column 13A Rail 13B Straight section 13 Straight Stage 16 Interferometer 17 Straight Stage Driver 26 Interferometer 60 Laser Light Source 61 Collimator Lens 62A First Half Mirror 63 Objective Lens 64 Planar Plate 62B Second Half Mirror 65 Dichroic Mirror 66A First Imaging Lens 66B Second imaging lens 67A First imaging tube 67B Second imaging tube 90 Control unit 91 Interference fringe image acquisition unit 92 Phase calculation unit 93 Schematic shape calculation unit 94 Stripe order detection unit 95 Fractional shape information calculation Means 96 Precise absolute shape calculation means 160A First laser light source 160B Second laser light source 161A First collimator lens 161B Second collimator lens 162 Dichroic mirror 163A First half mirror 163B Second half mirror 164 Objective lens 165 Planar prototype 166 Imaging lens 167 Color CCD camera 260A First semiconductor laser light source 260B Second semiconductor laser light source 261A First collimator lens 261B Second collimator lens 262 Half mirror 263 Half mirror 264 Objective lens 265 Flat prototype 266 Imaging lens 267 CCD camera 268A First shutter 268B Second shutter 269 Half mirror

Claims (11)

[Claims] 1. A light wave of a first wavelength and a light wave of a second wavelength are irradiated on a reference surface and a measurement target surface, and the light wave of the first wavelength reflected on the reference surface and the light wave on the measurement target surface are reflected. Or while interfering with the light wave of the first wavelength transmitted through the surface to be measured, the light wave of the second wavelength reflected by the reference surface and reflected by the surface to be measured, or transmitted through the surface to be measured. A first step of interfering with the light wave of the second wavelength, and an interference fringe image of the first wavelength generated by the interference of the light wave of the first wavelength, and interference of the light wave of the second wavelength. A second step of individually detecting the generated interference fringe image of the second wavelength, and a first phase distribution wrapped in a 2π section of the wavefront to be measured based on the interference fringe image of the first wavelength And calculating the second wavelength A third step of calculating a second phase distribution wrapped in a 2π section of the wavefront to be measured based on the interference fringe image; and λ ₁ for the _first wavelength and λ ₂ (λ ₂ >
λ ₁ ), when the first phase distribution is ψ ₁ (x, y) and the second phase distribution is ψ ₂ (x, y), over a predetermined measurement range expanded from the section of 2π. The approximate information hg (x, y) of the absolute distance between the reference plane and the measurement target plane is 0 ≦
If (ψ ₁ (x, y) −ψ ₂ (x, y)), then hg (x, y) = ｛ψ ₁ (x, y) −ψ ₂ (x, y)｝ / ｛(2π ×
k) · (1 / λ ₁ −1 / λ ₂ )｝ where k: 2 for measurement by reflection, 1 for measurement by transmission x, y: Coordinate components of a plane roughly along the measurement target surface ( If ψ ₁ (x, y) −ψ ₂ (x, y)) <0, then hg (x, y) = ｛ψ ₁ (x, y) −ψ ₂ (x, y) + 2π｝ / ｛(
2π × k) · (1 / λ ₁ −1 / λ ₂ )｝, and the first and second steps
Based on any one of the phase distributions, the precise fraction shape information hs _j (x, y)
Hs _j (x, y) = ψ _j (x, y) × λ _j / (2π × k), where j: a fifth step of obtaining a wavelength by a subscript 1 or 2; The fringe order ng _j (x, y) for the first wavelength λ ₁ or the second wavelength λ ₂ is obtained using the general information hg (x, y),
The precise absolute shape information h _j (x, y) of the surface to be measured is given by h _j (x, y) = ng _j (x, y) × λ _j / k + hs _j (x, y), where j: wavelength And a sixth step of obtaining the subscript by using the subscript 1 or 2 to be distinguished. 2. The method according to claim 1, wherein the step (b) includes the step of obtaining the precise fraction shape information hs based on the first phase distribution ψ ₁ (x, y).
₁ (x, y) and a second phase distribution ψ ₂ (x, y) the determined precise fractional shape information hs ₂ (x, y) based on the respective precise fractional shape information hs ₁ (x, y _2. The interference measurement method according to claim 1, wherein the average value of hs ₂ (x, y) is used for the calculation in step 6. 3. The method according to claim 1, wherein the first step is performed such that a measurement error of the approximate information hg (x, y) of the absolute distance is smaller than a distance indicated by one fringe of the interference fringe of the second wavelength. The method according to claim 1, wherein the first and second wavelengths are selected. 4. The apparatus according to claim 1, wherein said second step uses an imaging means for detecting light intensity in a two-dimensional area as means for detecting the interference fringe images of the first and second wavelengths.
The interference measurement method described. 5. The method according to claim 1, wherein the first step irradiates the light source of the first and second wavelengths to the reference surface and the measurement target surface by switching the light source in a time-series manner. 2. The interference measurement method according to claim 1, wherein the interference fringe image of the first wavelength and the interference fringe image of the second wavelength are detected by a common detection unit. 6. A light source for irradiating a lightwave of a first wavelength and a lightwave of a second wavelength to a reference surface and a measurement target surface, and a light source of the first wavelength reflected by the reference surface and the measurement target surface. Reflecting or interfering with the lightwave of the first wavelength transmitted through the surface to be measured, and reflecting the lightwave of the second wavelength and the lightwave of the second wavelength reflected on the reference surface, or the surface to be measured. An optical system that interferes with the transmitted light wave of the second wavelength, an interference fringe image of the first wavelength generated by the interference of the light wave of the first wavelength, and interference of the light wave of the second wavelength Interference fringe image detecting means for individually detecting the generated interference fringe image of the second wavelength, and a first phase wrapped in a 2π section of the wavefront to be measured based on the interference fringe image of the first wavelength Calculating the distribution and the second Phase calculating means and the first wavelength lambda ₁ for calculating a second phase distribution wrapped in the interval 2π being measured wavefront based on the length of the interference fringe image, the second wavelength lambda ₂ ( λ ₂ >
λ ₁ ), when the first phase distribution is ψ ₁ (x, y) and the second phase distribution is ψ ₂ (x, y), over a predetermined measurement range expanded from the section of 2π. The approximate information hg (x, y) of the absolute distance between the reference plane and the measurement target plane is 0 ≦
If (ψ ₁ (x, y) −ψ ₂ (x, y)), then hg (x, y) = ｛ψ ₁ (x, y) −ψ ₂ (x, y)｝ / ｛(2π ×
k) · (1 / λ ₁ −1 / λ ₂ )｝ where k: 2 for measurement by reflection, 1 for measurement by transmission x, y: Coordinate components of a plane roughly along the measurement target surface ( If ψ ₁ (x, y) −ψ ₂ (x, y)) <0, then hg (x, y) = ｛ψ ₁ (x, y) −ψ ₂ (x, y) + 2π｝ / ｛(
2π × k) · (1 / λ ₁ −1 / λ ₂ )｝, and the precise fraction shape information hs _j (x, y) is converted to hs _j (x, y) = ψ _j (x , y) × λ _j / (2π × k) where j is a fraction shape information calculating means operated by a subscript 1 or 2 for distinguishing a wavelength, and the absolute information hg (x, y) is used. Fringe order n for the first wavelength λ ₁ or the second wavelength λ ₂
fringe order detecting means for detecting g _j (x, y); and converting the precise absolute shape information h _j (x, y) into h _j (x, y) = ng _j (x, y) × λ _j / k + hs _j (x, y) where j: a precise absolute shape calculating means obtained by subscript 1 or 2 for distinguishing wavelengths. 7. The accurate fraction shape information h based on the first phase distribution ψ ₁ (x, y).
s ₁ (x, y) and the second phase distribution ψ ₂ (x, y) the determined precise fractional shape information hs ₂ (x, y) based on the respective precise fractional shape information hs ₁ (x, 7. The interference measuring apparatus according to claim 6, wherein the average value of y) and hs ₂ (x, y) is used for the calculation by the precise absolute shape calculating means. 8. The method according to claim 1, wherein the light source is configured to output approximate information hg of the absolute distance.
7. The interference measurement according to claim 6, wherein the first and second wavelengths are selected such that a measurement error of (x, y) is smaller than a distance indicated by one fringe of the interference fringe of the second wavelength. apparatus. 9. An interference measuring apparatus according to claim 6, wherein said interference fringe image detecting means uses an image pickup means for detecting light intensity in a two-dimensional area. 10. An interference measuring apparatus according to claim 6, wherein said interference fringe image detecting means uses a two-dimensional color CCD camera. 11. The optical system irradiates light waves of the first and second wavelengths to the reference surface and the measurement target surface by switching the light source in time series, and the interference fringe image detecting means includes: 7. The interference measurement apparatus according to claim 6, wherein the interference fringe image of the first wavelength and the interference fringe image of the second wavelength are detected by a common imaging unit.