JP2000074618A - Method and instrument for measuring interference - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a method and instrument for interference measurement which can measure a shape including a step and an absolute distance exceeding a wavelength fast with high precision without any mismeasurement. SOLUTION: Laser light sources 60A, 60B, and 60C emit lights of three kinds of wavelength. The laser light reflected by a plane standard 64 and the laser light reflected by an object surface 4a to be measured interfere with each other and image pickup tubes 67A, 67B, and 67C individually detect interference fringe images by wavelengths. A computer 9 sets 1st to (m)th pairs of wavelengths selected out of three kinds of wavelengths so that the composite wavelengths of the pairs gradually increase, sequentially calculates outline information on the absolute distance between the plane standard 64 and object surface 4a to be measured by using arithmetic expressions corresponding to whether a phase distribution difference between interference fringe image of two wavelengths corresponding to the 1st to (m)th pairs is plus or minus according to the phase distribution difference, and calculates precise information on the absolute distance between the plane standard 64 and object surface 4 to be measured according to the phase distribution of one 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 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. (Eg, “Optical Shop Testi
ng 2nd Edition ”, edited by D. Malacara, John Wiley & Sons,
Inc., (1992), Chapter 14, p.501-591).

FIG. 8 shows a flow for explaining the two-beam interference method. First, an interference fringe generated by interfering the two of the reference wavefront reflected by the reference surface and the measurement target wavefront reflected by the measurement target surface is detected as the 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): 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 means I (x, y) in the above equation (1).
Is the act of finding φ (x, y) from However, since the inverse function of cos that appears when obtaining φ (x, y) is a multivalent function, the actual phase φ cannot be determined uniquely as shown in FIG. Can be obtained only the fractional component of less than one wavelength excluding an integral multiple of the wavelength (an integer representing this multiple is called “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, TRJudge & PJBryanston-Cr
oss: ”A Review of Phase Unwrapping Techniques in F
ringe Analysis ”, Optics and Lasers in Engineering,
vol. 21, (1994), pp. 199-239). After determining the fringe order ng (x, y), the actual unwrapped phase distribution φ (x, y) is determined 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 (x, y): less than 2π Fractional phase information

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 / (2
π × k) to obtain 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, light reciprocates and the optical path difference doubles, so that the coefficient k = 2. 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, the expression
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> The two-wavelength interferometry performs interference measurement by using light of two wavelengths simultaneously (for example, Yukihiro Ishii and Ribun Onodera: "Two-wavele").
ngth laser-diode interferometry that use phase-shi
fting techniques ”, Optcs Letters, vol. 16, No. 19, (199
1), pp. 1523-1525). Contour lines of shading of interference fringes (Moire fringes) formed by two wavelengths appear for each Λ (synthetic wavelength) represented by Expression (5). Λ = 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 to do. k: 2 in the case of measurement by reflection, 1 in the case of measurement by transmission. Therefore, the range corresponding to one cycle of interference fringes without uncertainty is λ = wavelength in the ordinary two-beam interference method. However, 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> The white light interferometry performs interference measurement using a white light or a light source having low coherency close thereto (for example, Kumiko Matsui and Sato).
shi Kawata: "Fringe-scanning white-light microsco
pe for suface profile measurement andmaterial iden
tification ”, Proc. of SPIE, vol. 1720, (1992), 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 the interference measurement cannot be completed. In addition, since phase unwrap is determined only to make the relative fringe order relationship of the wrapped phase smooth, the absolute fringe order cannot be determined, and the absolute distance between the interferometer and the surface to be measured is measured. Can not do it. 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 drawback 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 high-precision measurement exceeding a micron becomes impossible.

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. further,
In order to store and store a large number of images, a large amount of memory and external storage must be prepared, which makes the apparatus expensive. For example, in the document of Matsui et al., 256 images are collected for one measurement, and even if this is performed at the highest video rate, it takes 8.5 seconds. Actually, the distance between the prototype and the surface to be measured is mechanically continuously changed. 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. Further, even if one interference fringe image is sampled at a resolution of 512 × 512 pixels and 256 gradations (8 bits), which is generally achievable with a recent TV camera, the 256 images have 512 × 512 pixels. 51
2 × 8 × 256 = 64 Mbytes. 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 high-definition televisions and the spread of high-definition displays of personal computers, images of about 1000 × 1000 pixels are becoming more and more unusual. Memory capacity 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 or 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 light waves of at least three kinds of wavelengths onto a reference surface and a measurement object surface, and reflects the at least three kinds of light waves reflected by the reference surface. A first step of interfering with each wavelength a light wave of a wavelength and a light wave of the at least three wavelengths reflected or transmitted by the surface to be measured, and at least three kinds of interference fringes generated by the interference of the first step A second step of individually detecting images; and a step of detecting the image of the measurement target surface based on the at least three types of interference fringe images.
a third step of calculating, for each wavelength, at least three types of phase distributions wrapped in an interval of π;
A fourth step of setting first to m-th (where m ≧ 2) sets such that two wavelengths selected from the kinds of wavelengths are taken as one set, and the combined wavelengths of the one set of wavelengths are sequentially increased; Based on the phase distribution difference between the interference fringe images of the two wavelengths corresponding to the first to m-th sets, the first to m-th sets using an arithmetic expression corresponding to the sign of the phase distribution difference. A fifth step of sequentially calculating the approximate information of the absolute distance between the reference plane and the measurement target plane from the m-th to the first set for each of the m-th to the first sets, corresponding to one of the at least three wavelengths; A sixth step of calculating precise information on an absolute distance between the reference plane and the measurement target plane based on the phase distribution of the interference fringe image and the approximate information on the absolute distance according to the first set. An interference measurement method is provided. According to the above configuration, the range of the absolute distance to be obtained is widened by sequentially calculating the approximate information of the absolute distance from the largest synthetic wavelength. Further, by calculating the approximate information of the absolute distance using an arithmetic expression corresponding to the sign of the phase distribution difference, measurement errors can be avoided. In addition, by calculating precise information of the absolute distance based on the phase distribution of one wavelength, the shape can be measured with high accuracy.

In order to achieve the above object, the present invention provides a light source for irradiating light waves of at least three wavelengths 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 for interfering with the light waves of at least three wavelengths reflected or transmitted by the surface to be measured for each wavelength, and at least three interference fringe images generated by the interference of the light waves of at least three wavelengths. An interference fringe image detecting means, a phase calculating means for calculating at least three kinds of phase distributions wrapped in a 2π section of the wavefront to be measured based on the at least three kinds of interference fringe images, The first to m-th (where m ≧ 2) sets are set such that two wavelengths selected from three types of wavelengths are set as a set and the combined wavelength of the set of wavelengths is sequentially increased. Setting means for determining, based on a phase distribution difference between the interference fringe images of the two wavelengths corresponding to the first to m-th sets, using an arithmetic expression corresponding to the sign of the phase distribution difference. First calculating means for sequentially calculating the approximate information of the absolute distance between the reference plane and the measurement target surface from the m-th to the first set for each of the first to m-th sets; Based on the phase distribution of the interference fringe image corresponding to one of the wavelengths and the approximate information of the absolute distance of the first set, precise information on the absolute distance between the reference plane and the measurement target plane is calculated. There is provided an interference measurement device comprising: a second calculation unit. According to the above configuration, the first calculating means sequentially calculates the approximate information of the absolute distance from the largest synthetic wavelength,
The range of the required absolute distance is widened. Further, the first calculating means calculates the approximate information of the absolute distance by using an arithmetic expression according to the sign of the phase distribution difference, thereby avoiding a measurement error. Further, the second calculating means calculates precise information of the absolute distance based on the phase distribution of one wavelength, so that the shape can be measured with high accuracy.

[0017]

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

The interferometer 6 includes a first laser light source 60A that oscillates light of a _first wavelength λ ₁ , a second laser light source 60B that oscillates light of a _second wavelength λ ₂ , and a third wavelength a laser light source 60C that oscillates lambda ₃ of the light, the laser light source 60A~6
Collimator lens 6 for converting laser light from 0C into parallel light
1A to 61C, a bending mirror 69 that bends the parallel light from the collimator lens 61A, and first and second half mirrors 62A that combine a part of the parallel light from the collimator lenses 61A to 61C to form a parallel beam. 62
B and a third half mirror 68A that reflects parallel light from the three laser light sources 60A to 60C to the measurement object 4 side.
An objective lens 63 arranged on the measurement object 4 side of the first half mirror 68A and having the same imaging performance as a normal microscope objective lens, and 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,
Fourth half mirror 6 for guiding the remaining part to flat prototype 64
8B, the surface (measurement target surface) 4a of the measurement target object 4 and the light reflected by the plane prototype 64 are reflected by the fourth half mirror 68.
Returning to B, where the interference light produced by superimposed and the dichroic mirror 65B for selectively reflecting the third wavelength lambda ₃ of the light, the second transmitted through the dichroic mirror 65B
The second wavelength lambda ₂ of the wavelength lambda ₁ of the wavelength lambda ₂ light and first
Dichroic mirror 65A for selectively reflecting light
And a first imaging tube 67A for imaging light of the first wavelength λ ₁ via the first imaging lens 66A, and light of the second wavelength λ ₂ via the second imaging lens 66B. A second imaging tube 67B for imaging is provided, and a third imaging tube 67C for imaging light of the third wavelength λ ₃ via the third imaging lens 66C. The plane prototype 64 and the fourth half mirror 6
8B constitutes a so-called Michelson interferometer.

The interference measuring apparatus 1 also includes a piezo driver 7 for driving the piezo stage 5 and digital interference fringe image signals of the interference fringes from the first, second and third image pickup tubes 67A, 67B and 67C. The image digitizers 8A, 8B, 8C for controlling the piezo driver 7 and the image digitizers 8A, 8B, 8C
And a computer 9 for obtaining the shape of the measurement target surface 4a based on the digital data from the computer.

The first laser light source 60A has a first wavelength λ ₁
670 nm (red light 1), the second laser light source 60
B The second 685nm as the wavelength lambda ₂ (red light 2), the third laser light source 60C is 785n as the third wavelength lambda ₃
It oscillates m (near infrared light) laser light. Semiconductor lasers that achieve this are already commercially available. By way of example, a semiconductor laser of HL6713G Hitachi, Ltd. in the first wavelength lambda ₁ of the light source, a semiconductor laser manufactured by the same company HL6726MG the second wavelength lambda ₂ of the light source, the third the company manufactured HL7853MG semiconductor laser it can be used for the wavelength lambda ₃ of the light source. Of course, the semiconductor laser is not limited to this, and any laser having a similar oscillation wavelength may be used. Such products are also sold by other companies. Further, an external resonator type semiconductor laser whose wavelength can be varied may be used. An example of such is the 6300 Velo from NewFocus, USA.
There are city Series series and so on. Since the output and wavelength of a semiconductor laser fluctuate depending on the injection current and temperature, it is desirable to precisely control the injection current and temperature.

The dichroic mirrors 65A and 65B are
It has a wavelength selection function. Dichroic mirror 65A
Is configured such that light of a first wavelength λ ₁ of 670 nm is transmitted and light of a second wavelength λ ₂ of 685 nm is reflected. The dichroic mirror 65B transmits the light of the first wavelength λ ₁ of 670 nm and the light of the second wavelength λ ₂ of 685 nm, and transmits the light of the third wavelength λ ₃ of 785 nm.
nm light is reflected.

FIG. 2 shows the functions of the computer 9. The computer 9 includes a CPU that controls the entire device 1 and C
The ROM includes a ROM in which a PU program is stored, a RAM that stores various types of information necessary to determine the shape of the measurement target surface 4a, and the like. The computer 9 performs processing for calculating precise information on the absolute distance of the measurement target surface 4a based on the interference fringe image data from the image digitizers 8A, 8B, and 8C. 91,
It has a phase calculating means 92, a general distance information calculating means 93, a fringe order detecting means 94, a fringe order difference detecting means 95 and a precise distance information calculating means 96.

Next, each of the means 91 to 91 of the computer 9 will be described.
96 will be described.

The interference fringe image acquiring means 91 uses the phase shift method (for example, fringe scanning interference measurement method) to perform the piezo driver 7 operation.
To move the object 4 to be measured in the vertical direction, and to capture four interference fringe image data for each wavelength while changing the optical path difference between the interferometer 6 and the object surface 4a by λ / 4. .

The phase calculating means 92 is an interference fringe image obtaining means.
Based on the interference fringe image data acquired by 91, the following equation (6)
 , Equation (7) and Equation (8), the first wavelength λ₁Rank
Phase distributionψ₁(x, y) and the second wavelength λ_TwoPhase distribution of
_Two(x, y) and the third wavelength λ_ThreePhase distribution of_ThreeCalculate (x, y)
Is what you do. ψ₁(x, y) = arctan [｛Ia_Four(x, y) −Ia_Two(x, y)｝ / ｛Ia₁(x, y) −Ia_Three(x, y)｝]… (6) ψ_Two(x, y) = arctan [｛Ib_Four(x, y) −Ib_Two(x, y)｝ / ｛Ib₁(x, y) −Ib_Three(x, y)｝]… (7) ψ_Three(x, y) = arctan [｛Ic_Four(x, y) −Ic_Two(x, y)｝ / ｛Ic₁(x, y) −Ic_Three(x, y)｝]… (8) Since arctan is a multivalent function,
ψ₁(x, y), ψ_Two(x, y) and ψ_Three(x, y) is folded into 2π intervals
Phase as the returned phase,
It is. Further, the acquired first wavelength λ₁Four interference fringes
Image data Ia ₁(x, y), Ia_Two(x, y), Ia_Three(x, y), Ia_Four(x,
y), also the second wavelength λ_TwoOf the four interference fringe image data
Ib₁(x, y), Ib_Two(x, y), Ib_Three(x, y), Ib_Four(x, y), third wavelength
λ_ThreeOf four interference fringe image data of Ic₁(x, y), Ic_Two(x, y),
I c_Three(x, y), Ic_Four(x, y).

The approximate distance information calculating means 93 is selected from ψ ₁ (x, y), ψ ₂ (x, y) and ψ ₃ (x, y) obtained by the phase calculating means 92 by a procedure described later. The wrap phase of the combination i (i = 1, 2) of two different wavelengths is ψa
When (x, y) and ψb (x, y) are used, the absolute distance between each point of the surface 4a to be measured and the prototype 64 (the optical distance between the prototype 64 and the surface 4a to be measured) using Expression (9). This calculates the approximate information hg (x, y) of the target distance) and outputs the calculation result to the fringe order detecting means 94. However, it is selected so that λa <λb. However, in the present embodiment, two combinations of i = 1 and 2 are used as combinations for selecting two wavelengths from three wavelengths. _{hg (i) (x, y} ) = Λ i / k × [{ψ i1 (x, y) -ψ i2 (x, y)} / (2π) + ΔN i (x, y)] ... (9) provided that , Λ _i are defined by equation (10). { _I = 1 / {(1 / λa−1 / λb) × k} = λa × λb / {(λb−λa) × k} (10)

FIG. 3 shows the principle of obtaining the approximate information of the absolute distance. As shown in the figure, the wavelength λ of the combination of the wavelengths of interest corresponding to the same location (point of interest) on the surface to be measured.
The phase difference between the interference fringe a and the interference fringe having the wavelength λb changes depending on the absolute distance between the target point on the measurement target surface 4 a and the prototype 64. Therefore, the absolute distance can be obtained from the phase difference. The amount of change is a periodic function, the period corresponds to the lambda _i of like the two-wavelength interferometry formula (10).
That is, the range in which the absolute distance is determined is Λ _i of the predetermined measurement range expanded from the 2π section (λa or λb). 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 obtained in this way is rough information, but it is possible to provide sufficient accuracy for determining the stripe order difference and the stripe order described later.

Here, the reason why hg _(i) (x, y) obtained by the above equations (9) and (10) is an absolute distance will be described below. The relationship between the wrapped phase ψ and the actual absolute distance or shape h is generally represented by Expression (11) (a general principle expression). h · (2π × k) / λ = ψ + 2π × N (11) where k: 2 for reflection measurement, 1 for transmission measurement N: Fringe order measurement at wavelength λ by reflection Since the light wave reciprocates, the phase difference is doubled even at the same distance difference, and k = 2. This corresponds to the fact that the distance (interval of the interference fringes) indicated by one fringe of the interference fringes differs twice between reflection and transmission. Next, the above equation (11) is created for λa and λb, and is subtracted and rearranged to obtain equation (12). h = {1 / (2π × k)} · [｛(ψa−ψb) + 2π × ΔN _i ｝ / (1 / λa−1 / λb)] (12) where ΔN = N (λa ) -N (λb). When this is rearranged, it matches Equations (9) and (10), and it can be seen that hg _(i) (x, y) in Equation (11) represents an absolute distance. formula
Since (9) has a form in which λ in Equation (4) is replaced by Λ _i , the range is widened by Λ _i / λ times, but the accuracy also deteriorates. It is for this reason to be brief.

The general theory of calculating the approximate distance information is as described above.
There are three wavelengths λ₁, Λ_Two, Λ _ThreeSelected from
The lens whose approximate absolute distance is to be determined from the two combinations
If J covers the distance to be measured sufficiently, the fringe order
Calculate approximate distance information without having to separately measure difference ΔN
Can be This is described below. Here is the table
For simplicity, the wavelength combination index i
(1, 2) is omitted.

FIG. 4 shows the difference in wrap phase ｛ψ ₁ (x, y) −ψ ₂ when the distance h of the point of interest on the measurement target surface 4 a is changed.
(x, y)｝. Although it is in a roughly proportional relationship, it can be seen that there is a discontinuous difference in some places. Considering the case where the measurement target distance under consideration is within the measurement range, it can be seen that the lap phase difference changes discontinuously at the boundary between the positive and negative cases. I understand.

FIG. 5 shows a plot of the fringe order difference ΔN at this time. From the figure, it can be seen that there is a rule that ΔN = 0 when the wrap phase difference is positive and ΔN = 1 when the wrap phase difference is negative. Therefore, when the measurement target distance is within the measurement range, by determining whether the wrap phase difference is positive or negative, the fringe order difference ΔN can be determined by itself, and the approximate distance information can be calculated. . This is to determine whether ΔN _i (x, y) is 0 or 1 and calculate approximate distance information using equation (9). The approximate distance information calculating means 93 also performs this processing. is there. Specifically, Λ
In the case of the second combination of the wavelengths in which
_{g (2) (x, y} ) if a _{0 ≦ {ψ 2 (x,} y) -ψ 3 (x, y)}, hg (2) (x, y) = {ψ 2 (x, y) −ψ ₃ (x, y)｝ / ｛(2π × k) ・
If (1 / λ ₂ −1 / λ ₃ )｝ ｛ψ ₂ (x, y) −ψ ₃ (x, y)｝ <0, then hg ₍₂₎ (x, y) = ｛ψ ₂ (x, y) −ψ ₃ (x, y) +2 π｝ / ｛(2
π × k) · (1 / λ ₂ −1 / λ ₃ )｝.

縞 is maximized by the fringe order difference detecting means 95
As well as the combination of wavelengths for i = 1
For fringes, determine the fringe order difference as follows:
Can be. First of all, the combination of i = 2 wavelengths has already
Low degree hg₍₂₎(x, y) is required
You. Equation (9) is established for the first combination, and the right side is hg
₍₂₎Replace with (x, y), hg₍₂₎(x, y) = Λ₁/ K × [｛ψ₁₁(x, y) −ψ₁₂(x, y)｝ / (2π) + ΔN₁(x, y)] ... (13) By transforming equation (13), the following equation (14) is obtained, from which the wave
The fringe order difference in the first combination of lengths can be determined.
You. ΔN₁(x, y) = round [hg₍₂₎(x, y) × k / Λ₁− ｛Ψ₁₁(x, y) −ψ₁₂(x, y)｝ / (2π)] (14) Here, round [] is a function that returns the closest integer.
The above is the contents of the processing in the fringe order difference detecting means 95.
You.

By the way, in order for an integer to be correctly determined by round [], round [] is taken [hg ₍₂₎ (x, y) × k /
The error of Λ ₁ − ｛ψ ₁₁ (x, y) −ψ ₁₂ (x, y)｝ / (2π)] is 1
/ 2. ｛｛Ψ ₁₁ (x, y) −ψ ₁₂
Since (x, y)｝ / (2 π) is a wrap phase and has very high accuracy, this means that the error σhg of hg _(2)
(2) indicates that σhg ₍₂₎ <k / (2 × Λ ₁ ) (15) needs to be satisfied.

In the present embodiment, the case where i = 1, 2 has been described. However, even if the number of wavelengths is increased and the maximum value of i is further increased, i is similarly decreased by one from m. However, hg _(i) (x, y) and ΔN _i (x, y) can be obtained alternately and sequentially. However, similarly to Expression (15), it is necessary to select a combination of wavelengths so as to satisfy the accuracy condition of the approximate information of the absolute distance.

The fringe order detecting means 94 uses hg ₍₁₎ (x, y) finally obtained by the rough shape calculating means 93 and a wrap phase ψ _j (x, y) of any of the three wavelengths. , (J is 1,
N _J (x, y) = round [hg ₍₁₎ (x, y) × k / λ _j −ψ _j (x, y) / (2π)]… (16) The fringe order for the wavelength λ _j (x, y) is obtained.
For fringe order is determined correctly by the formula (16), in a manner similar to the equation (15), the error Shigumahg ₍₁₎ of hg _{(1) is, σhg (1) <k /} (2 × λ j) ... (17 ) Is required.

The precise distance information calculating means 96 calculates N _j (x, y) obtained by the fringe order detecting means 94 and hg finally obtained.
₍₁₎ (x, y) and wrap phase of any of the three wavelengths ψ
_{Using j} (x, y), hs _j (x, y) = λ _j / k × ｛ψ _j (x, y) / (2π) + N _j (x, y)… (18) Information hs _j (x, y) of the absolute distance is obtained. Equation (18) is equivalent to equation (4) for a two-wavelength interference fringe known to have high accuracy. Therefore, the same accuracy as that of the two-wavelength interferometry can be maintained even though the range is widened. In other words, by utilizing the property that the fringe order is strictly an integer, errors can be discarded and high accuracy can be achieved.

Next, how to select a combination of wavelengths will be described.
I do. Λ as the first combination_Two= 685 nm and λ_Three= 7
85 nm as the second combination₁= 670nm and λ
_Three= 685 nm. Also for precise information calculation of absolute distance
The wrap phase and fringe order used are λ_Three= 785nm
I will choose one. In this case,₁= 2.6
9 μm, Λ_Two= 15.3 μm, Δ₁<Λ_TwoTo
The condition of the present invention is satisfied. At this time, lap phase measurement
2π / 50 for accuracy and 0.02 nm for wavelength accuracy
Assuming the theoretical calculation, hs_jIs 3σ (σ is the standard
0.007 μm in hg₍₁₎Error Rhg₁Is
0.076 μm, hg₍₂₎Error Rhg _TwoIs 0.434
μm. This satisfies the conditions of equations (15) and (17).
You.

FIG. 6 shows the above situation. The total measurement accuracy is ± 0.007 μm and the measurement range is 15.3 μm. Of course, the combination of wavelengths is not limited to this. Depending on the selection, the range can be further widened while maintaining high accuracy.

Here, to show the superiority of the present invention, what happens if only two wavelengths can be used will be examined. First, when only the combination of 685 nm and 785 nm is used, the condition of Expression (17) is satisfied, but the range is only 2.69 μm. Next, 670 nm and 685 nm
When only the combination of is used, the apparent range is 15.3μ
Although it seems to be wide as m, it does not satisfy the condition of Expression (17) (there is only two combination wavelengths and therefore only one combination index), so that the fringe order cannot be determined correctly and measurement cannot be performed.

Next, the operation of the device 1 according to the first embodiment will be described. First, the interference fringe image acquiring means 91 in the computer 9 controls the piezo driver 7 by a phase shift method (for example, fringe scanning interference measurement method) to control the measurement object 4.
Is moved in the vertical direction, and four interference fringe image data are taken in for each wavelength while changing the optical path difference between the interferometer 6 and the measurement target surface 4a by λ / 4.

Here, one piece of interference fringe image data is acquired.
Will be described. First to third laser light sources 6
Three wavelengths emitted from 0A, 60B and 60C
λ₁, Λ _Two, Λ_ThreeLaser light consisting of
Beams 61A, 61B, and 61C are collimated and collimated.
The parallel light from the lens 61A is folded by the folding mirror 69.
From the collimator lenses 61A to 61C.
A part of the parallel light is first and second half mirrors 62A,
The beams are multiplexed at 62B and folded at the third half mirror 68A.
And reaches the objective lens 63. Objective lens 6
The light from 3 is partially measured by a fourth half mirror 68B.
It is led to the elephant surface 4a, and the rest is guided to the flat prototype 64.
You. Light reflected by the measurement target surface 4a and the plane prototype 64, respectively.
Returns to the fourth half mirror 68B again, where
And become interference light. The light emitted from the objective lens 63 is
Is transmitted through the third half mirror 68A to form the third half mirror 68A.
Wavelength λ_ThreeDichroic mirror that selectively reflects light
Reach 65B. Therefore, light having a wavelength of 785 nm
Reaching the third imaging tube 67C via the third imaging lens 66C
I do. On the other hand, the wave transmitted through the dichroic mirror 65B
The light having a length of 685 nm and a wavelength of 670 nm is converted to a second wavelength λ._Two
Dichroic mirror 65A that selectively reflects light
To reach. Accordingly, light having a wavelength of 685 nm is not reflected on the second
The light reaches the second image pickup tube 67B via the lens 66B,
The light of 670 nm passes through the first imaging lens 66A and is
Reaches the imaging tube 67A. Thus, the first shooting
In the image tube 67A, interference fringes caused only by light having a wavelength of 670 nm
In the second image pickup tube 67B, an image is formed of light having a wavelength of 685 nm.
The image of the interference fringes is only the wavelength in the third imaging tube 67C.
The images of interference fringes caused only by the light of 785 nm
Detected as light intensity. Of interference fringes detected for each wavelength
The image signal is decoded by the image digitizers 8A, 8B and 8C.
Digital interference fringe image data,
Is forwarded to Thus, the interference in the computer 9
The fringe image acquiring means 91 outputs four interference fringe image data for each wavelength.
And outputs it to the phase calculation means 92. This interference fringe
Image data is expressed as shown in equation (1) described in the prior art.
In addition, a (x, y), b (x, y) and φ (x, y) are unknown quantities.
To obtain at least three interference fringe image data by changing δ
Then, φ (x, y) can be obtained. Here,
Considering the calculation accuracy and calculation speed, four interference fringe image
Data.

Next, based on the interference fringe image data obtained by the interference fringe image obtaining means 91, the phase calculating means 92
Using the equations (6), (7) and (8), the wrap phase distribution of the first wavelength λ ₁の₁ (x, y) and the wrap phase distribution of the second wavelength λ ₂ ψ ₂ (x, y) and the wrap phase distribution of the third wavelength λ ₃ ψ
₃ (x, y) is calculated, and the calculation result is output to the approximate distance information calculating means 93, the fringe order difference detecting means 95, the fringe order detecting means 94, and the precise distance information calculating means 96.

Next, a first combination of wavelengths (λ ₂ = 685)
nm and λ ₃ = 785 nm) and a second combination of wavelengths (λ ₁
= 670 nm and λ ₃ = 685 nm), the approximate distance information based on the first combination of wavelengths having relatively high accuracy is finally obtained by using the approximate distance information calculating means 93 and the fringe order difference detecting means 95 alternately. And outputs the calculation result to the fringe order detecting means 94.

That is, as described above, first, in the approximate distance information calculating means 93, the wrap phase distribution ψ ₂ (x, y) output by the phase calculating means 92 for the second combination of wavelengths in a wide range. Using ψ ₃ (x, y), 0 ≦ ｛ψ ₂ (x, y
y) −ψ ₃ (x, y)｝, then hg ₍₂₎ (x, y) = ｛ψ ₂ (x, y) −ψ ₃ (x, y)｝ / ｛(2π × k) ·
(1 / λ ₂ −1 / λ ₃ )｝ ｛ψ ₂ (x, y) −ψ ₃ (x, y)｝ <0, then hg ₍₂₎ (x, y) = ｛ψ ₂ (x, y) −ψ ₃ (x, y) +2 π｝ / ｛(2
Approximate distance information is calculated according to (π × k) · (1 / λ ₂ −1 / λ ₃ )｝, and is output to the fringe order difference detecting means 95.

In the fringe order difference detecting means 95, the approximate distance information hg ₍₂₎ (x,
y), the fringe order difference ΔN ₁ (x, y) in the first combination of wavelengths is calculated using Expression (14), and the approximate distance information calculating means 93 is calculated.
Output to

The approximate distance information calculating means 93 calculates the fringe order difference ΔN ₁ (x, y) in the combination 1 of the wavelengths output from the fringe order difference detecting means 95 by using equations (9) and (10). The approximate distance information hg ₍₁₎ (x, y) in the wavelength combination 1 is calculated and output to the fringe order detecting means 94.

In the fringe order detecting means 94, the phase calculating means 9
Lap phase distribution output from 2 ２ _Three(x, y) and the approximate distance
First combination of wavelengths output from separation information calculating means 93
Approximate distance information hg in₍₁₎From (x, y), use equation (16)
And λ_ThreeFringe order N at_ThreeTo calculate the precise distance information
Output to output means 96. Here, λ_ThreeWas used, but other
Λ₁Or λ_TwoMay be.

In the precise distance information calculating means 96, the wrap phase distribution ψ ₃ (x, y) output from the phase calculating means 92 and
From the fringe order N _{3 at} λ ₃ output from the fringe order detecting means 94, the comprehensive precision distance information hs is calculated using Expression (18).
₃ Calculate (x, y). Here, λ ₃ is used, but other λ ₃
It may be ₁ or λ _2.

The computer 9 calculates the precise distance information h
Output and display s ₃ (x, y).

According to the first embodiment, the following effects can be obtained.
Fruit is obtained. (B) Outline of absolute distance in order from the largest synthetic wavelength
By calculating the information, the lens of the absolute distance required
The area becomes wider (Λ_Two= 15.3 μm. In this embodiment,
K = 2. ), A step that greatly exceeds the wavelength
It is possible to measure shapes including differences and absolute distances. (B) λ_ThreeSingle wavelength phase distribution 波長_Threebased on (x, y)
Close distance information hs_ThreeSince (x, y) is obtained, the ordinary two luminous flux
Measurement can be performed with high accuracy equivalent to the interferometry. λ
_ThreeAccuracy of about / 50 can be easily obtained. (C) The optical path difference between the interferometer 6 and the surface 4a to be measured is λ / 4 each.
While changing, four interference fringe image data are acquired for each wavelength.
Phase shift method (fringe scanning interferometry)
Therefore, it is necessary to measure the shape faster than white light interferometry
Becomes possible. Furthermore, as means for detecting interference fringes,
Image pickup tubes 67A, 6 capable of detecting light intensity in a two-dimensional area
7B and 67C, one of the measurement target surfaces 4a is used.
Measurement of the fixed range can be performed at once, and high-speed measurement
Can be determined. Therefore, in the white light interferometry of Conventional Example 3,
What took 8.5 seconds at the shortest, according to this device 1,
It can be greatly reduced within one second. (D) Absolute distance summary information hg₍₁₎The measurement error of (x, y) is
Third wavelength λ_ThreeLess than k divided by
, The first, second and third wavelengths λ₁, Λ_Two, Λ _ThreeWhen,
Preselecting a first combination and a second combination of wavelengths
Make sure that the fringe order is determined with the required accuracy.
Can prevent errors due to erroneous fringe order determination.
You. (E) Outline information hg of absolute distance₍₂₎The measurement error of (x, y) is
The first combination of wavelengths (λ_Two= 685 nm and λ_Three= 785
(nm), the approximate information of the absolute distance hg₍₁₎(x, y)
Ji₁Is less than what is divided by k
Second and third wavelengths λ₁, Λ_Two, Λ_ThreeAnd the first of the wavelengths
Since the combination of and the second combination are selected in advance,
Judgment of fringe order difference can be performed reliably with required accuracy
Therefore, it is possible to prevent an error due to an error in the fringe order difference determination. (F) Unlike white interference, signals can be obtained over a wide range.
For initial adjustment of the relative position and orientation of the interferometer with the surface to be measured.
Signal can be obtained in a wider range. That
The initial position, which was extremely difficult in white light interferometry
Force adjustment can be easily performed. (G) Since measurement can be performed in a short time, vibration and noise
Can be used without a vibration isolator even in places with sound
You. (H) Perform the above measurements accurately within the specified range without exception.
It is possible to do.

FIG. 7 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. This interferometer 1 includes a horizontally arranged table 2, a pair of columns 3 and 3 erected on the table 2, and a rail 13A erected between the pair of columns 3 and 3.
A piezo stage 5 for vertically moving the object 4 to be measured is placed on the table 11;
B, an interferometer 16 is provided, and the interferometer 16 is
And scans the surface 4a to be measured while moving in the horizontal direction to measure a wide area.

The interferometer 16 sets the first wavelength λ ₁ to 67
A first laser light source 60A that emits 0 nm (red light 1) laser light, and a second laser light source 60B that emits 685 nm (red light 2) laser light as the second wavelength λ ₂
A third laser light source 60C having a _third wavelength λ ₃ of 785 nm (near infrared light), a first shutter 70A for controlling transmission and blocking of light from the first laser light source 60A, and a second A second shutter 70B for controlling transmission and blocking of light from the laser light source 60B; a third shutter 70C for controlling transmission and blocking of light from the third laser light source 60C;
To convert the laser light from the laser light source 60A into parallel light.
Collimator lens 61A and second laser light source 60B
A second collimator lens 61B for converting the laser light from the first laser light into parallel light, a third collimator lens 61C for converting the laser light from the third laser light source 60C to the parallel light, and a light from the first laser light source 60A. By reflecting a part of the parallel light from the bending mirror 69 and a part of the parallel light from the second and third collimator lenses 61B and 61C, the parallel light from all the laser light sources 60A to 60C is multiplexed as a result. The half mirrors 62A and 62B, the half mirror 68A that reflects a part of the parallel light from all the laser light sources 60A to 60C to the measurement target 4 side, and the half mirror 68A are disposed on the measurement target 4 side of the half mirror 68A. Objective lens 63 having the same imaging performance as a microscope objective lens
A plane prototype 64 as a reference plane disposed between the objective lens 63 and the measuring object 4; a part of light from the objective lens 63 guided to the measuring object 4; The half mirror 68B leading to the prototype 64, the surface (measurement target surface) 4a of the object 4 to be measured, and the laser beams respectively reflected by the plane prototype 64 return to the half mirror 68B and form an image of the interference light superimposed there. And a CCD camera 167 that captures an image via the lens 66. The so-called Mirau interferometer is constituted by the objective lens 63, the plane prototype 64, the half mirror 68B, and the surface 4a of the measurement object 4.

First shutter 70A, second shutter 7
0B and the third shutter 70C are controlled by a computer to open and close the first laser light source 6C.
0A, the light of the second laser light source 60B or the light of the third laser light source 60C can be transmitted or blocked. Further, the interference measuring device 1 converts the image signal of the interference fringe from the piezo driver 7 for driving the piezo stage 5, the driver 17 for the rectilinear stage to drive the rectilinear stage 13 and the CCD camera 167 into digital interference fringe image data. While controlling the image digitizer 8 to be converted, the piezo driver 7 and the straight stage driver 17,
A computer 9 for obtaining the shape of the surface 4a to be measured based on digital data from the image digitizer 8;

Next, the operation of the apparatus 1 according to the second embodiment will be described.
Explain the work. The interference fringe image data of the computer
The process up to the loading into 9 will be described below. First, the first system
The shutter 70A is opened and the second shutter 70B and the third shutter 70B are opened.
The shutter 70C is closed. At this time, the first laser light source 60
First wavelength λ emitted from A₁Laser light only
After passing through the first collimator lens 61A and the mirror 69, the
A part of the light is reflected by the mirror 68A and the surface 4a to be measured is measured.
And reflected by the prototype 64, returning to the half mirror 68B and interfering.
I do. Furthermore, the wavelength λ from the Mirau interferometer₁The light of the
The light reaches the CCD camera 167 via the image lens 66. C
The CD camera 167 has a first wavelength λ₁No. only by the light
One interference fringe image is detected. Next, in the same manner,
The shutter 70B is opened and the first shutter 70A and the third shutter
Is closed, the second wavelength λ _TwoThe second only by the light of
Are detected. Finally, a third shutter
The shutter 70C is opened and the first shutter 70A and the second shutter
Is closed, the third wavelength λ_ThreeThe third only by the light of
Are detected. Of interference fringes detected for each wavelength
The image signal is converted into digital data by the image digitizer 8
It is converted and transferred to the computer 9. Measurement target surface 4
When the interference fringe image data is obtained for a certain range of a,
The computer 9 controls the driver 17 for the straight-ahead stage
To move the interferometer 16 in the horizontal direction
After moving by a fixed distance, the interference fringe image data is similarly captured.
The interference fringe image data acquired as described above is
The same processing is performed in the computer 9 as in the first embodiment.

According to the second embodiment, since the wavelengths of the light sources are switched in time series, three imaging optical systems as in the first embodiment are not required, and three imaging optical systems are not required. Errors due to misalignment between systems are eliminated.
Depending on the selection of the three wavelengths, it may be difficult to design and manufacture a dichroic mirror. For example, the above equation (5)
It is necessary to select a combination of light sources having close wavelengths in order to widen the measurement range さ れ る represented by, but it is difficult to realize a filter that discriminates such light having close wavelengths. In such a case, the first embodiment is difficult to realize, but according to the second embodiment, it can be realized without difficulty. As described above, according to the second embodiment, it is possible to realize an inexpensive and high-precision apparatus that can freely combine wavelengths.

Note that the present invention is not limited to the above embodiment, and various embodiments are possible. For example, in the above-described 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. 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))
Reference). 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.

[0057]

As described above, according to the present invention, since the approximate information of the absolute distance is sequentially obtained from the largest synthetic wavelength, the range of the obtained absolute distance is different from that of the conventional two-wavelength interferometry. It becomes wider than equivalent. Further, over the 2π section of the wavefront to be measured, precise distance information of the surface to be measured, that is, the phase of one wavelength is obtained with high accuracy, and precise information of the absolute distance is obtained based on this phase distribution 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 to be collected at the time of measurement is significantly smaller than that of the white light interferometry, and by detecting interference fringes of three different wavelengths simultaneously and in parallel, the speed is dramatically higher than that of the conventional method. Measurements are made possible and 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 computer of the interference measurement apparatus according to the first embodiment.

FIG. 3 is a diagram for explaining 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 the wrap phase difference { ₁ (x, y) − { ₂ (x, y)} is proportional to the absolute information hg (x, y);

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 diagram for explaining the principle of selection of a combination of wavelengths in the interference measurement device according to the first embodiment.

FIG. 7 is a configuration diagram of an interference measurement device according to a second 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 Measurement object 4a Measurement object surface 5 Piezo stage 6 Interferometer 7 Piezo driver 8A First image digitizer 8B Second image digitizer 8C Third image digitizer 9 Computer 13 Straight stage 13A Rail 13B Linear unit 16 Interferometer 17 Linear stage driver 60A First laser light source 60B Second laser light source 60C Third laser light source 61A First collimator lens 61B Second collimator lens 61C Third collimator lens 62A First Half mirror 62B Second half mirror 63 Objective lens 64 Plane prototype 65A First dichroic mirror 65B Second dichroic mirror 66 Imaging lens 66A First imaging lens 66B Second imaging lens 66C Imaging lens 67A first imaging tube 67B second imaging tube 67C third imaging tube 68A third half mirror 68B fourth half mirror 69 mirror 70A first shutter 70B second shutter 70C third Shutter 91 Interference fringe image acquisition means 92 Phase calculation means 93 Approximate distance information calculation means 94 Stripe order detection means 95 Stripe order difference detection means 96 Precision distance information calculation means 167 CCD camera

Continued on front page F-term (reference) 2F064 AA09 FF02 GG20 GG22 HH03 HH08 HH09 2F065 AA04 AA25 AA45 AA53 BB05 DD06 FF01 FF04 FF51 GG06 GG23 JJ03 JJ05 JJ19 JJ26 LL20 LL30 MM07 QNN02 PP02

Claims (14)

[Claims] 1. A light wave of at least three kinds of wavelengths is irradiated on a reference surface and a measurement object surface, and the light waves of at least three kinds of wavelengths reflected on the reference surface and the at least three light waves reflected or transmitted on the measurement object surface. A first step of causing light waves of different wavelengths to interfere with each other for each wavelength; and at least three light waves generated by the interference of the first step.
A second step of individually detecting the types of interference fringe images; and, based on the at least three types of interference fringe images, at least three types of phase distribution wrapped in a 2π section of the measurement target surface for each wavelength. A third step of calculating; and a first to m-th (where m ≧ 2) such that two wavelengths selected from the at least three types of wavelengths are set as a set, and a combined wavelength by the set of wavelengths is sequentially increased. A fourth step of setting a set of the above, and an operation according to the sign of the phase distribution difference based on the phase distribution difference between the interference fringe images of the two wavelengths corresponding to the first to m-th sets. A fifth step of sequentially calculating approximate information of an absolute distance between the reference plane and the measurement target plane from the mth to the first set for each of the first to mth sets using an equation; Supports one of the wavelengths A sixth step of calculating precise information on an absolute distance between the reference plane and the measurement target plane based on the phase distribution of the interference fringe image and the approximate information on the absolute distance according to the first set. An interference measurement method comprising: 2. The method according to claim 1, wherein the fourth step comprises:
λ_i1, Λ_i2Where the composite wavelength is_i= Λ_i1・ Λ
_i2/ (Λ_i2−λ_i1) (Where i =
1, 2,. . . m), the fifth step is that the composite wavelength is the largest Δm
Are respectively set to λ_m1, Λ_m2(Λ_m2
> Λ_m1), The wavelength λ_m1, Λ_m2The phase distribution of _m1(x, y)
 , Ψ_m2(x, y), the reference plane and the object to be measured
Outline information hg of the absolute distance to the surface_(m)(x, y) is 0 ≦ ｛ψ_m1
(X, y) −ψ_m2(x, y) 、 then hg_(m)(x, y) = ｛ψ_m1(X, y) −ψ_m2(x, y)｝ / ｛(2
π × k) ・ (1 / λ_m1−1 / λ_m2)｝ ｛Ψ_m1(X, y) −ψ_m2If (x, y)｝ <0, hg_(m)(x, y) = ｛ψ_m1(x, y) −ψ_m2(x, y) +2 π｝ /
｛(2π × k) ・ (1 / λ_m1−1 / λ_m2)｝ Where k: 2 for measurement by reflection, measurement by transmission
In the fixed case, 1 x, y: obtained by the coordinate components of a plane roughly along the surface to be measured, and approximate information hg of the absolute distance based on the m-th set._(m)(x, y)
And the composite wavelength is the second largest._m-1Make up the first
m−1 set of wavelengths λ_{(m-1) 1}, Λ_{(m-1) 2}(Λ_{(m-1 ) 2}> Λ
_{(m-1) 1}) Phase distribution_{(m-1) 1}(x, y), ψ_{(m-1) 2}(x,
y), the fringe order difference ΔN in the (m−1) th set
_m-1(X, y) is ΔN_m-1(X, y) = round [hg_(m)(x, y) × k / Λ_m-1-
｛Ψ_{(m-1) 1}(x, y) −ψ_{(m-1) 2}(x, y)｝ / (2 π)] where Λ_m-1: Second in the m-1 wavelength set
Large synthetic wavelength round []: obtained by a function that returns the closest integer, and the fringe order difference ΔN in the m-1st set_m-1(X,
y) and the respective phase distributions に よ る of the m-1st set.
_{(m-1) 1}(x, y), ψ_{(m-1) 2}From (x, y), the reference plane and the front
Summary information hg of the absolute distance from the surface to be measured_(m-1)(X,
y) to hg_(m-1)(X, y) = Λ_m-1/ k × [｛ψ_{(m-1) 1}(x, y) -ψ
_{(m-1) 2}(x, y)｝ / (2 π) + ΔN_m-1(x, y)], and hg from i = m−2 to 1_{(i + 1)}using (x, y)
ΔN_i(x, y), and the ΔN_ihg using (x, y)
_(i)2. The interferometer according to claim 1, wherein (x, y) is sequentially obtained.
Method. 3. The method according to claim 1, wherein the step ₍ c) comprises the step of: determining the approximate information hg ₍₁₎ (x, y) of the absolute distance according to the first set;
Phase distribution に_よる_j (x, y) by one of the wavelengths λ _j
From (j = 1, 2, 3), the stripe order N _j (x, y) is changed to N _j (x, y) = round [hg ₍₁₎ (x, y) × k / λ _j −ψ _j ( x,
y) / (2π)], from the fringe order N _j (x, y) and the phase distribution ψ _j (x, y) by the one wavelength λ _j , the reference plane and the measurement target plane Hs _j (x, y) = λ _j / k × ｛ψ _j (x, y) / (2π) + N _j (x,
y) The interference measuring method according to claim 2, wherein the method is obtained by｝. 4. The method according to claim 1, wherein the sixth step is performed by the at least three
Determining precise information of at least two of the absolute distances based on a phase distribution of at least two wavelengths of the wavelengths of the type, determining an average value of the precise information of the absolute distances,
The interference measurement method according to claim 2, wherein the average value is used as precise information of the absolute distance. 5. The method according to claim 1, wherein the fourth step is the i-th (i =
1, 2,. . summary information hg of the absolute distance by the set of m)
_(i) A configuration in which the sets are set such that the error σhg _(i) (x, y _{) of} (x, y) satisfies σhg _(i) (x, y) <Λ _m-1 / 2 Claim 1
The interference measurement method described. 6. The method according to claim 1, wherein said second step is performed by said at least three steps.
2. The interference measurement method according to claim 1, wherein an imaging means for detecting light intensity in a two-dimensional area is used as means for detecting interference fringe images of different wavelengths. 7. The method according to claim 1, wherein at least three light sources are switched in time series to irradiate the reference surface and the measurement target surface with the light waves of the at least three types of wavelengths. 2. The interference measurement method according to claim 1, wherein the interference fringe images of at least three types of wavelengths are detected by a common detection unit. 8. A light source for irradiating light waves of at least three kinds of wavelengths to a reference surface and a surface to be measured, and a light wave of at least three kinds of wavelengths reflected by the reference surface and reflected or transmitted by the surface to be measured. An optical system that causes light waves of at least three kinds of wavelengths to interfere with each other for each wavelength; an interference fringe image detecting unit that individually detects at least three kinds of interference fringe images generated by interference of the light waves of at least three kinds of wavelengths; Based on the at least three types of interference fringe images, phase calculating means for calculating at least three types of phase distribution wrapped in a 2π section of the wavefront to be measured, and two wavelengths selected from the at least three types of wavelengths Setting means for setting the first to m-th (where m ≧ 2) sets such that the composite wavelength of the set of wavelengths is sequentially increased as one set; Based on the phase distribution difference between the interference fringe images of the two wavelengths corresponding to the m sets, the m-th to m-th sets are used for each of the first to m-th sets using an arithmetic expression corresponding to the sign of the phase distribution difference. First calculating means for sequentially calculating the approximate information of the absolute distance between the reference surface and the measurement target surface from the first to the first set; and the interference fringe image corresponding to one of the at least three wavelengths. And second calculating means for calculating precise information on the absolute distance between the reference plane and the measurement target plane based on the phase distribution of the first set and the general information on the absolute distance in the first set. Characteristic interference measurement device. 9. The setting means sets the set of wavelengths to λ._i1,
λ_i2Where the composite wavelength is _i= Λ_i1・ Λ_i2/
(Λ_i2−λ_i1) (Where i = 1,
2,. . . m), the first calculating means calculates the maximum of the synthetic wavelength Δm
Λ is the m-th set of wavelengths_m1, Λ_m2(Λ_m2>
λ_m1), The wavelength λ_m1, Λ_m2The phase distribution of_m1(x, y),
ψ_m2When (x, y), the reference surface and the measurement target surface
Summary information hg of the absolute distance of_(m)(x, y) is 0 ≦ ｛ψ_m1(X,
 y) -ψ_m2(x, y) 、 then hg_(m)(x, y) = ｛ψ_m1(X, y) −ψ_m2(x, y)｝ / ｛(2
π × k) ・ (1 / λ_m1−1 / λ_m2)｝ ｛Ψ_m1(X, y) −ψ_m2If (x, y)｝ <0, hg_(m)(x, y) = ｛ψ_m1(X, y) −ψ_m2(x, y) +2 π｝ /
｛(2π × k) ・ (1 / λ_m1−1 / λ_m2)｝ Where k: 2 for measurement by reflection, measurement by transmission
In the fixed case, 1 x, y: calculated by the coordinate components of a plane roughly along the surface to be measured, and the synthesized wavelength is the second largest._m-1To
The fringe order difference ΔN in the (m−1) th set to constitute_m-1(X,
y) and the respective phase distributions に よ る by the (m−1) -th set
_{(m-1) 1}(x, y), ψ_{(m-1) 2}From (x, y), the reference plane and the front
Summary information hg of the absolute distance from the surface to be measured_(m-1)(X,
y) to hg_(m-1)(X, y) = Λ_m-1/ k × [｛ψ_{(m-1) 1}(x, y) -ψ
_{(m-1) 2}(x, y)｝ / (2 π) + ΔN_m-1(x, y)], and hg from i = m−2 to 1
_{(i + 1)}ΔN using (x, y)_i(x, y), and the ΔN_i
hg using (x, y)_(i)Approximate distance to obtain (x, y) sequentially
Calculating means; and approximate information hg of the absolute distance by the m-th set_(m)(x, y)
And the composite wavelength is the second largest._m-1Make up the first
m-1 wavelength λ_{(m-1) 1}, Λ_{(m-1) 2}(Λ_{(m-1) 2}>
λ_{(m-1) 1}) Phase distribution_{(m-1) 1}(x, y), ψ
_{(m-1) 2}From (x, y), the fringe order difference Δ in the (m−1) th set
N_m-1(X, y) is ΔN_m-1(X, y) = round [hg_(m)(x, y) × k / Λ_m-1-
｛Ψ_{(m-1) 1}(x, y) −ψ_{(m-1) 2}(x, y)｝ / (2 π)] where Λ_m-1: Second in the m-1 wavelength set
Large synthetic wavelength round []: Calculated by a function that returns the closest integer, and hg from i = m-2 to 1
_{(i + 1)}ΔN using (x, y)_iStripe order difference calculation for (x, y)
Output means and a first set obtained by the fringe order difference calculation means.
Summary information hg of the absolute distance₍₁₎(x, y)
At least one wavelength λ of the three wavelengths_jPhase distribution
_j(x, y) (j = 1,2,3) and the stripe order N
_j(x, y) is N_j(x, y) = round [hg₍₁₎(x, y) × k / λ_j−ψ_j(x,
y) / (2π)], and the second calculating means calculates the fringe order N_j(x, y) and
Wavelength λ of one of at least three wavelengths_jPhase component
Cloth_j(x, y) (j = 1,2,3)
Accurate information on the absolute distance between the surface and the surface to be measured is given by hs_j(x, y) = λ_j/ k × ｛ψ_j(x, y) / (2π) + N_j(x,
y) Claims having a means for calculating a precise distance obtained by｝
8. The interference measurement device according to 8. 10. The fringe order calculating means and the precise distance calculating means obtain at least two pieces of precise information of the absolute distance for at least two wavelengths of the at least three kinds, and obtain the precise information of the absolute distances. The interference measurement apparatus according to claim 8, wherein an average value of the absolute distance is obtained, and the average value is used as precise information of the absolute distance. 11. The method according to claim 11, wherein the setting means sets the i-th one (i = 1, 2).
2,. . summary information hg of the absolute distance by the set of m)
_(i) A configuration in which the sets are set such that the error σhg _(i) (x, y _{) of} (x, y) satisfies σhg _(i) (x, y) <Λ _m-1 / 2 Claim 8
The interference measurement device as described. 12. The apparatus according to claim 8, wherein said interference fringe image detecting means uses an image pickup means for detecting light intensity in a two-dimensional area.
The interference measurement device as described. 13. An interference measuring apparatus according to claim 8, wherein said interference fringe image detecting means uses a two-dimensional color CCD camera. 14. An optical system for interfering with a light wave, comprising at least three light sources, switching the at least three light sources in time series and irradiating the at least three wavelengths to the reference surface and the measurement target surface. 9. The interference measurement apparatus according to claim 8, wherein the interference fringe image detecting unit detects the interference fringe images of the at least three wavelengths by a common imaging unit.