JP2013044669A - Method and device for measuring surface shape - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem in which it is necessary to additionally install extraction means for obtaining a plurality of monochromatic light beams of different wavelengths in measurement of a surface shape in which an interference fringe is generated with reflection light beams from a measurement object surface and a reference surface for obtaining a phase of each pixel for each monochromatic light beam so as to measure the surface shape.SOLUTION: A surface shape measurement method, a plurality of monochromatic light beams of different wavelengths are radiated to the measurement object surface and the reference surface via radiation means, and the surface height and surface shape of the measurement object surface are obtained on the basis of an intensity of an interference fringe generated by reflection light beams returning in a same optical path while respectively reflected by both of the measurement object surface and the reference surface. The radiation means extracts a plurality of monochromatic light beams having optional and different wavelengths from the radiation light having a wide band wavelength characteristic by using an acoustic-optical filter, and radiates the plurality of monochromatic light beams in a mixed and simultaneous manner.

Description

  The present invention relates to a method and / or means for selectively extracting a plurality of monochromatic lights having different wavelengths used in a surface shape measuring method and apparatus.

  In the surface shape measurement method and apparatus capable of accurately determining the uneven step on the measurement target surface at high speed, the reference surface is arranged in an obliquely inclined posture at an arbitrary angle with respect to the traveling direction of the light. Interference fringes are generated by reflected light returning from the reference surface on the same optical path. The intensity value of each pixel of the interference fringe is imaged with a CCD camera, and the CPU uses the expression for obtaining the interference fringe waveform, and for each pixel to be calculated, the intensity value of each pixel and the intensity value of the neighboring pixel Assuming that the DC component, AC amplitude, and phase of the interference fringe waveform contained in each pixel are the same, the phase of each pixel is obtained for each monochromatic light, and the surface height candidate value group is obtained from that phase. Then, the surface height was obtained from the candidate value group of multiple wavelengths, and the surface shape was measured (see, for example, Patent Document 1 and Patent Document 2).

JP2007 / 088889 JP 2008-209404 A

  In the background art, monochromatic light output from a monochromatic light source or a plurality of monochromatic lights having different wavelengths are used as the light source. In particular, in the surface shape measurement described in Patent Document 1 using a monochromatic light output from a monochromatic light source, the maximum step difference (measurement range) that can be measured is limited to λ / 2, which is half the wavelength λ of monochromatic light. Therefore, it was difficult to take a wide measurement range.

  Further, in the surface shape measurement described in Patent Document 2 using a plurality of monochromatic lights having different wavelengths, a configuration using a plurality of monochromatic light sources having different wavelengths that output different wavelengths may be used, or output from a white light source and a white light source. The light source may be composed of optical means using extraction means for extracting a plurality of monochromatic lights having different predetermined wavelengths.

However, the light source having the above configuration has the following problems.
As described above, when a plurality of light sources are used, the number of light sources for each wavelength that requires equipment costs and running costs (replenishment of consumables, power supply, etc.) is required.
In addition, when trying to obtain a plurality of monochromatic lights having different wavelengths from a single light source, it is necessary to transmit the extraction means extracted from the light source. Light cannot be irradiated efficiently.

  Furthermore, when the number of monochromatic lights having different wavelengths is three or more, the number of extraction means becomes multistage, and the loss increases. Moreover, when changing the wavelength of monochromatic light, the light source or the filter itself must be changed. Furthermore, when increasing the number of wavelengths of monochromatic light, it is necessary to increase the number of light sources, filters, and extraction means.

  The invention of the first surface shape measuring method of the present application states that "a plurality of monochromatic lights having different wavelengths are irradiated to the measurement target surface and the reference surface via the irradiation means, and reflected from both the measurement target surface and the reference surface to be the same. In the surface shape measuring method for obtaining the surface height and surface shape of the surface to be measured based on the intensity value of the interference fringes generated by the reflected light returning from the optical path, the irradiating means is acousto-optic from irradiation light having a broadband wavelength characteristic. It comprises an irradiating means for extracting a plurality of monochromatic lights having different wavelengths using a filter and simultaneously irradiating them. "

  That is, in response to the above-described problem with the light source to be irradiated, as a light source for multi-wavelength interference measurement, a light source including a wavelength characteristic covering a wide area, for example, a visible region to a near infrared region (wavelength of about 400 nm to 1,000 nm) ( Specifically, using a technique combining a halogen lamp light source or a white laser light source and an optical filter capable of transmitting single-band light of a plurality of different wavelengths, the multiple wavelength interference measurement A method for measuring the surface shape of an object to be measured is provided by taking an image for use in one shot and individually decomposing it using a decomposing means.

  Further, the invention of the second surface shape measuring method of the present application is, “Using the measurement result of the reflection intensity of each monochromatic light obtained by irradiating the surface of the monochromatic light while scanning the wavelength of the monochromatic light in advance, A plurality of monochromatic lights having different wavelengths with respect to the surface to be measured are selected and irradiated to perform surface shape measurement. ”

  In other words, when measuring the surface shape that irradiates a plurality of monochromatic lights with different wavelengths, there are many individual measurement objects that possess many optical characteristics. Depending on the optical film thickness, the reflection intensity may be lowered depending on the optical film thickness. Even in such a case, in order to accurately measure the surface shape, the surface shape measuring method described in the first invention is used to selectively extract a plurality of monochromatic lights having different wavelengths simultaneously. By using the acousto-optic filter, the operator can arbitrarily set multiple monochromatic lights with different required wavelengths, so the irradiation of the monochromatic light obtained by irradiating while scanning the monochromatic light wavelength in advance. Using the measurement result of intensity, a plurality of monochromatic lights having different wavelengths with respect to the measurement target surface are selected, and the surface shape is measured using them.

  In addition, the invention of the third surface shape measuring apparatus of the present application states that “a plurality of monochromatic lights having different wavelengths are irradiated to the measurement target surface and the reference surface through the irradiation means and reflected from both the measurement target surface and the reference surface. In the surface shape measuring device for determining the surface height and surface shape of the measurement target surface based on the intensity value of the interference fringes generated by the reflected light returning from the same optical path, the irradiating means is adapted to irradiate the irradiation light having a broadband wavelength characteristic, It comprises an irradiation means for extracting a plurality of monochromatic lights having different wavelengths using an acousto-optic filter and simultaneously irradiating them.

  That is, in response to the above-described problem with the light source to be irradiated, as a light source for multi-wavelength interference measurement, a light source including a wavelength characteristic covering a wide area, for example, a visible region to a near infrared region (wavelength of about 400 nm to 1,000 nm) ( Specifically, using a means that combines a halogen lamp light source or a white laser light source and an acousto-optic filter capable of transmitting monochromatic light of plural bands having different wavelengths, a plurality of monochromatic lights having different wavelengths are simultaneously used. To provide an apparatus capable of measuring the surface shape of a measurement object by irradiating mixed images, capturing the image for multi-wavelength interference measurement in one shot, and individually analyzing the captured image data. .

  In addition, the invention of the fourth surface shape measuring device of the present application, “using the measurement result of the reflection intensity of each monochromatic light obtained by irradiating the surface of the measuring object while scanning the wavelength of the monochromatic light in advance, A plurality of monochromatic lights having different wavelengths with respect to the surface to be measured are selected and irradiated, and the surface shape is measured. ”

  That is, when measuring the surface shape that irradiates a plurality of monochromatic lights with different wavelengths n, there are many individual measurement objects that possess many optical characteristics, and the color of the measurement object surface remains unchanged at the initially set wavelength. Depending on the optical film thickness, the reflection intensity may be reduced depending on the optical film thickness. Even in such a case, in order to accurately measure the surface shape, the surface shape measuring device according to the third invention is used to selectively extract a plurality of monochromatic lights having different wavelengths simultaneously. By using an acousto-optic filter, the operator can arbitrarily set the required multiple monochromatic lights, so irradiate while scanning the monochromatic light wavelength in advance, and measure the reflected intensity of each monochromatic light obtained Using the result, a plurality of monochromatic lights having different wavelengths with respect to the measurement target surface are selected, and the surface shape measurement is performed using the selected monochromatic light.

  In addition, by using an acousto-optic filter, the measurer can arbitrarily set a plurality of monochromatic lights having different wavelengths to be used, so the measurer must perform the measurement without replacing the members of the illumination device. Can do.

  By using the above-described method and / or means, even when a plurality of monochromatic lights having different wavelengths are selected from irradiation light exhibiting broadband wavelength characteristics, the number of members of the illuminating device is only one, and light source management is facilitated. . In addition, if a plurality of light sources are required, the number of light sources can be handled by one as compared with the case of preparing light sources corresponding to the number of monochromatic lights, and light source management becomes easy.

  In addition, by using an acousto-optic filter as an optical filter capable of transmitting a plurality of monochromatic lights in arbitrary bands having different wavelengths, the measurer can arbitrarily set a plurality of monochromatic lights having different wavelengths to be used. Measurer shall perform measurement without being affected by the decrease in sensitivity due to reflectivity even when measuring by using monochromatic light with the optimal wavelength suitable for the object to be measured without replacing the components of the lighting device. Can do.

  Since the operator can arbitrarily set the combination of wavelengths of multiple monochromatic lights to be used, it is possible to easily optimize the combination of multiple monochromatic lights with different wavelengths during measurement and easily change measurement conditions. can do.

  When the number of monochromatic lights having different wavelengths is increased, the number of monochromatic lights within the band of the light source to be used and the number of monochromatic lights that are possible due to the characteristics of the acoustooptic filter (in the currently used acoustochemical filter, six kinds of monochromatic lights are used. Can be obtained without adding a function of a light source or an acousto-optic filter. However, it is necessary that the image pickup apparatus on the image pickup means side has a configuration for holding a decomposition unit that can decompose a plurality of monochromatic lights having different wavelengths.

It is a figure which shows schematic structure of the surface shape measuring apparatus which concerns on a present Example. It is a flowchart which shows the process in a surface shape measuring apparatus. It is a figure which shows schematic structure of an acoustooptic filter. It is a figure which shows the captured image data of a measurement object surface. It is a figure which shows the x-axis direction luminance change of a captured image. It is a figure which shows that the range of (phi) can be specified using the code | symbol information of sin (phi) cos (phi). It is a figure which shows extraction of real surface height. It is a figure which shows the measurement result at the time of measuring a steep level difference using an Example apparatus. The relationship figure of the thickness of a measuring object, the wavelength of irradiated light, and a reflectance.

  Embodiments of the present invention will be described below with reference to the drawings.

  In addition, as a present Example, the surface as described in the prior art document cited in this specification including the example which measured the surface height and surface shape of the measurement object whose surface is substantially flat using interference fringes. The shape measuring device will be described as an example.

  FIG. 1 is a diagram showing a schematic configuration of a surface shape measuring apparatus according to an embodiment of the present invention. This surface shape measuring apparatus has a plurality of specific wavelength bands on a substantially flat measurement object 30 having fine uneven steps on the surface of a semiconductor wafer, liquid crystal panel, plasma display panel, magnetic film, glass substrate or metal film. The optical system unit 1 which irradiates monochromatic light, the control system unit 2 which controls the optical system unit 1, and the holding table 40 which mounts and holds the measuring object 30 are provided.

  The optical system unit 1 measures an illuminating device 10 that outputs a plurality of monochromatic lights having different wavelengths toward the measurement target surface 30A and the reference surface 15, a collimator lens 11 that converts the monochromatic lights into parallel light, and measures both monochromatic lights. A half mirror 13 that reflects light from the direction of the measurement object 30 while reflecting in the direction of the object 30, and an objective lens 14 that condenses a plurality of monochromatic lights having different wavelengths reflected by the half mirror 13; The monochromatic light that has passed through the objective lens 14 is divided into reference light that reflects to the reference surface 15 and measurement light that passes to the measurement target surface 30A, and is reflected by the reference light reflected by the reference surface 15 and the measurement target surface 30A. The beam splitter 17 that re-assembles the measured light and generates interference fringes, and the imaging lens 1 that forms a plurality of monochromatic lights having different wavelengths, the reference light and the measuring light being combined. If, and an imaging device 19 for imaging the object surface 30A with the interference fringes.

The illumination device 10 includes a light source 10A that emits irradiation light having a broadband wavelength, an acoustooptic filter 10B, and a light guide 10C. As the light source 10A of the present embodiment, for example, a white light source including an incandescent bulb or a halogen lamp is used. By passing through the acoustooptic filter 10B, a plurality of monochromatic lights having different wavelengths are selectively extracted in a state where a plurality of monochromatic lights having different wavelengths are mixed at the same time. The light source outputs a plurality of monochromatic lights having different wavelengths. For example, the first wavelength is wavelength λ ₁ = 470 nm, the second wavelength is wavelength λ ₂ = 560 nm, and the third wavelength is wavelength λ ₃ = 600 nm.

  As shown in FIG. 3, the acousto-optic filter 10 </ b> B of this embodiment includes a tellurium dioxide crystal 101, a sound absorbing material 102, a transducer 103, and an oscillator 104. It utilizes anisotropic Bragg diffraction of light generated by the transverse ultrasonic wave 105 made of monochromatic light, and extracts a plurality of monochromatic lights having different wavelengths from light having a broad wavelength at high speed, and passes through the light guide 10C. The collimating lens 11 can be irradiated.

Here, the light guide 10C is a substantially cylindrical light guide that guides a plurality of monochromatic lights having different wavelengths in the main scanning direction after passing through the acoustooptic filter 10B shown in FIG. In order to quickly send a plurality of monochromatic lights having different wavelengths to the rear collimating lens 11.
In addition, the illuminating device 10 is corresponded to the irradiation means of this invention.

  The half mirror 13 reflects parallel light composed of a plurality of monochromatic lights having different wavelengths from the collimating lens 11 toward the measurement object 30, while allowing reflected light returned from the measurement object 30 to pass therethrough.

  The objective lens 14 is a lens that focuses on the measurement target surface 30 </ b> A that focuses a plurality of incident monochromatic light beams having different wavelengths.

  The beam splitter 17 separates a plurality of monochromatic lights with different wavelengths collected by the objective lens 14 into reference light that is reflected by the reference surface 15 and measurement light that is reflected by the measurement target surface 30A. Further, the reference light and the measurement light that are reflected on each surface and return on the same optical path are combined again, thereby generating interference for each wavelength of the plurality of monochromatic lights having different wavelengths. The beam splitter 17 corresponds to the branching means of the present invention.

  The reference surface 15 has a mirror-finished surface, and is attached in an obliquely inclined posture with respect to the traveling direction of the reference light composed of a plurality of monochromatic lights having different wavelengths. The reference light composed of a plurality of monochromatic lights having different wavelengths reflected by the reference surface 15 reaches the beam splitter 17 and is reflected by the beam splitter 17.

In addition, by attaching the reference surface 15 in a slanting posture in front and back with respect to the traveling direction of the reference light composed of a plurality of monochromatic lights having different wavelengths, a plurality of monochromatic colors can be obtained from the arrival distance of the reference light composed of the plurality of monochromatic lights having different wavelengths. The distance until the reflected light composed of light reaches the imaging device 19 varies depending on the position of the reflecting surface. This is equivalent to moving the reference surface 15 and changing the distance L ₁ between the reference surface 15 and the beam splitter 17.

  Further, the measurement light composed of a plurality of monochromatic lights having different wavelengths that have passed through the beam splitter 17 is condensed toward the focal point and reflected by the measurement target surface 30A. The reflected measurement light composed of a plurality of monochromatic lights having different wavelengths reaches the beam splitter 17 and passes through the beam splitter 17.

In the beam splitter 17, reference light composed of a plurality of monochromatic lights having different wavelengths and measurement light composed of a plurality of monochromatic lights having different wavelengths are gathered again. In this case, the distance L ₁ between the reference surface 15 and the beam splitter 17, the optical path difference by the difference in distance between the distance L ₂ between the object surface 30A and the beam splitter 17 is caused. In accordance with the optical path difference, the reference light composed of a plurality of monochromatic lights having different wavelengths and the measurement light composed of a plurality of monochromatic lights having different wavelengths interfere with each other of the wavelengths of the plurality of monochromatic lights having different wavelengths.

  The imaging device 19 captures an image of the measurement target surface 30A that is projected by measurement light including a plurality of monochromatic lights having different wavelengths. At this time, since the reference surface 15 is inclined, an interference fringe that is a spatial variation in luminance due to interference for each wavelength of a plurality of monochromatic lights is captured in the captured image of the measurement target surface 30A. Here, the imaging device 19 serving as an observation unit holds a decomposing unit for each wavelength of monochromatic light, and image data obtained by separating interference fringes for each wavelength of monochromatic light is obtained. The captured image data is collected by the memory 21 of the control system unit 2. Further, as will become clear later, the drive unit 24 of the control system unit 2 is configured to move the optical system unit 1 in the x, y, and z axis directions in FIG. Further, the imaging device 19 captures images of the measurement target surface 30 </ b> A and the convex portion (concave portion) 30 </ b> B of the measurement target surface at a predetermined sampling timing, and the image data is collected by the control system unit 2. The imaging device 19 corresponds to the imaging unit of the present invention.

  The imaging device 19 in the present embodiment may be configured to hold a decomposing unit capable of decomposing a plurality of monochromatic lights having different wavelengths. For example, a CCD solid-state imaging device, a MOS image sensor, a CMOS image sensor, a photoelectric imaging tube, There are avalanche electron multiplication effect imaging tubes and EB-CCDs.

  The control system unit 2 performs overall control of the entire surface shape measuring apparatus and CPU 20 for performing predetermined arithmetic processing, and various data and programs such as image data and arithmetic results sequentially collected by the CPU 20. A memory 21 to be stored, an input unit 22 such as a mouse or a keyboard for inputting other setting information such as a sampling timing and an imaging area, and a monitor 23 for displaying an image of the measurement target surface 30A and the like. Further, it is configured by a computer system including a drive unit 24 configured by a drive mechanism such as a three-axis drive type servo motor that drives the optical system unit 1 to move up, down, left, and right in accordance with an instruction from the CPU 20. ing. The CPU 20 corresponds to the calculation means in the present invention.

  The CPU 20 is a so-called central processing unit, and controls the imaging device 19, the memory 21, and the driving unit 24, and includes a measurement target surface 30 </ b> A including interference fringes for a plurality of monochromatic lights having different wavelengths captured by the imaging device 19. On the basis of the image data, the surface shape is obtained from the phase calculation unit 25 that performs calculation processing for obtaining the surface height of the measurement object 30, the code determination unit 26 described later, and a plurality of obtained surface height data. An image data creation unit 27 is provided. The processing of the phase calculation unit 25 and the image data creation unit 27 in the CPU 20 will be described later. Further, the CPU 20 is connected to a monitor 23 and an input unit 22 such as a keyboard and a mouse, and the operator observes an operation screen displayed on the monitor 23 and receives various setting information from the input unit 22. Make input. Further, the monitor 23 displays a surface image of the measurement target surface 30A, a concavo-convex shape, and the like as numerical values and images.

  The drive unit 24 is a device that moves, for example, the optical system unit 1 in the x, y, and z axis directions illustrated in FIG. 1 to a desired imaging location. The drive unit 24 is configured by a drive mechanism including, for example, a triaxial drive type servo motor that drives the optical system unit 1 in the x, y, and z axis directions in accordance with instructions from the CPU 20. In the present embodiment, the optical system unit 1 is operated. For example, the holding table 40 on which the measurement object 30 is placed may be changed in the three orthogonal axes. Further, there may be two or less moving axes or none.

  Hereinafter, processing performed in the entire surface shape measuring apparatus, which is a characteristic part of the present embodiment, will be described with reference to a flowchart shown in FIG.

  In the present embodiment, the case where the reference surface 15 is inclined as shown in FIG. 1 will be described as an example. In this case, the captured image is as shown in FIG. In the present embodiment, the case of the x-axis direction will be described as an example in order to simplify the description.

<Step S <b>1> The measurement data acquisition CPU 20 drives a drive system such as a stepping motor (not shown) to move the drive unit 24 to the imaging region of the measurement object 30 of the optical unit 1. When the imaging position is determined, the optical system unit 1 simultaneously outputs a plurality of monochromatic lights λ ₁ , λ _2, and λ ₃ having different wavelengths through the acousto-optic filter 10B from the light emitted from the light source 10A of the illumination device 10. The plurality of monochromatic lights are collected by the light guide 10 </ b> C and directed to the half mirror 13.

The imaging device 19 operates in conjunction with the output of a plurality of monochromatic lights having different wavelengths. For example, the measurement target surface 30A having the convex portion (concave portion) 30B of the measurement target surface shown in FIG. . Image data of interference fringes for each of a plurality of monochromatic lights on the measurement target surface 30A acquired by this imaging is stored in the memory 21. That is, the memory 21 stores, for each of the plurality of monochromatic lights generated by the reference light composed of the plurality of monochromatic lights on the reference surface 15 in the tilted posture and the reflected light composed of the plurality of monochromatic lights reflected by the measurement target surface 30A. Interference fringe image data is stored for different wavelengths of monochromatic light. At this time, the propagation distances (two times L ₁ ) of the plurality of monochromatic lights reflected on the reference surface 15 regularly vary based on the reflection position on the reference surface 15.

Accordingly, in the flat portion in the measurement target surface 30A, the propagation distance (twice L ₂ ) of the reflected light composed of a plurality of monochromatic lights from the measurement target surface 30A does not vary at the measurement location. Interference fringes composed of a plurality of monochromatic lights in the image picked up by (1) appear spatially and regularly in the image pickup surface in accordance with the inclination direction and angle of the reference surface 15. Reflected light composed of a plurality of monochromatic light from a plurality of (two times L ₁₎ propagation distance of the reference light comprising monochromatic light with the measurement target surface 30A from the interference fringes reference plane 15 for each wavelength of the plurality of monochromatic light the propagation distance difference lambda _1/2 = 235 nm of the (L 2 × _{2), λ 2/2 =} 280nm and λ _3/2 = 300nm appears one cycle each made.

  On the other hand, as shown in FIG. 1, the interference fringes for each wavelength of a plurality of monochromatic lights are shifted at a portion where the height or depression of the measurement target surface 30 </ b> A varies, that is, at the convex portion (concave portion) 30 </ b> B of the measurement target surface. Appears as irregular stripes.

<Step S2> The interference light intensity value acquisition CPU 20 captures the intensity value of each pixel stored in the memory 21, that is, the interference light intensity value for each of a plurality of monochromatic lights having different wavelengths on the measurement target surface 30A from the image data. At this time, in the vicinity of the pixel numbers 255 and 355 shown in FIG. 5 in which the heights of the measurement target surface 30A and the convex portions (concave portions) 30B of the measurement target surface fluctuate, the spatial pattern of interference fringes for each wavelength of a plurality of monochromatic lights. It appears as an irregular stripe pattern whose phase is shifted (for example, in the X-axis direction in this embodiment of FIG. 5).

<Step S3> Calculation of Phases φ1, φ2, and φ3 in Pixel Units for Each Wavelength The phase calculation unit 25 of the CPU 20 sets the phase of the pixel to be calculated on the measurement target surface 30A to the pixel adjacent to the pixel ( In this embodiment, it is obtained using a calculation algorithm determined in advance using the light intensity value of each interference fringe for each wavelength of a plurality of monochromatic lights (pixels adjacent in the X-axis direction). Specifically, the light intensity value of the interference fringe in the pixel to be calculated and the pixel adjacent to the pixel is applied to an expression for obtaining the interference fringe waveform (fitting) to obtain the phase.

First, the intensity value of the interference fringe light in the pixel to be calculated is described as the following equation (1).

g (x) = a (x) + b (x) cos {2πfx + φ (x)} (1)

Here, x is the position coordinate of the pixel to be calculated, a (x) is a direct current component included in the interference fringe waveform, b (x) is an alternating current component (amplitude of vibration component) included in the interference fringe waveform, and (Referred to as “AC amplitude” as appropriate), f is a spatial frequency component of the interference fringe g (x), and φ (x) is a phase to be calculated corresponding to a predetermined pixel on the measurement target surface 30A. Note that the position coordinates of the pixel to be calculated are expressed in two dimensions (x, y), but in this embodiment, the y coordinates are omitted to simplify the description.

Next, since adjacent pixels are shifted by a minute distance Δx in the x-axis direction from the pixel to be calculated, the light intensity value of the interference fringes is expressed by the following equation (2).

g (x + Δx) = a (x + Δx) + b (x + Δx) cos {2πf (x + Δx)
+ Φ (x + Δx)} (2)
Here, in this embodiment, since the pitch between the pixel to be calculated and the adjacent pixel is a minute distance, it is assumed that the DC component, AC amplitude, and phase included in the interference fringe extending over each pixel are equal, and The relational expressions (3) to (5) are used.

a (x) = a (x + Δx) = a (3)
b (x) = b (x + Δx) = b (4)
φ (x) = φ (x + Δx) = φ (5)
Here, a, b, and φ are constants.

By assuming the relational expressions (3) to (5) above, the expressions (1) and (2) can be replaced as the following expressions (1a) and (2a).

g (x) = a + bcos (2πfx + φ) (1a)
g (x + Δx) = a + bcos {2πf (x + Δx) + φ} (2a)

Next, the equations (1a) and (2a) are modified to create the following equations (6) and (7).

G (x) = g (x) −a = bcos {2πfx + φ} (6)
G (x + Δx) = g (x + Δx) −a = bcos {2πf (x + Δx) + φ} (7)

Next, equations (6) and (7) are transformed into the following equations (8) and (9) by the addition theorem.

G (x) = bcos (2πfx + φ)
= B {cos (2πfx) cosφ−sin (2πfx) sinφ} (8)
G (x + Δx) = bcos {2πf (x + Δx) + φ}
= B [cos {2πf (x + Δx)} cosφ−sin (2πfx + Δx) sinφ]
.... (9)

Next, these equations (8) and (9) are represented by the determinant (10).

なお、Ａは、次のように表される。

A is expressed as follows.

ここで、行列（１０）の左辺からＡの逆行列を掛けて展開することにより、次式（１１）、（１２）を求める。

Here, the following equations (11) and (12) are obtained by multiplying the left side of the matrix (10) by the inverse matrix of A and expanding.

これら上記式（１１）、（１２）を利用し、次式（１３）を得ることができる。なお、ここで、上記ｂｓｉｎφおよびｂｃｏｓφのそれぞれをｂｓｉｎφ＝Ｓおよびｂｃｏｓφ＝Ｃとし、さらにｔａｎφ＝Ｓ／Ｃとすると、

φ＝ａｒｃｔａｎ｛Ｓ／Ｃ｝＋ｎ’π・・・・・・・・（１３）

となる。なお、ｎ’は、整数である。

By using these equations (11) and (12), the following equation (13) can be obtained. Here, if each of bsinφ and bcosφ is bsinφ = S and bcosφ = C, and tanφ = S / C,

φ = arctan {S / C} + n′π (13)

It becomes. Note that n ′ is an integer.

Here, the CPU 20 further includes a code determination unit 26, and the code determination unit 26 refers to the code information of sin φ and cos φ. If this code information is used, the existence range of φ can be expanded from π to 2π from the combination of the signs of sin φ and cos φ. FIG. 6 is a specific diagram for specifying the range of φ with reference to the sign information of sin φ and cos φ as shown in Expression (13). Therefore, using the sign information of sin φ and cos φ, equation (13) can be expressed by the following equation (14).

φ = arctan {S / C} + 2nπ (14)

It becomes. Note that n is an integer.

Therefore, if G (x) and the spatial frequency f of the interference fringe waveform are known, the phase φ can be obtained by Expression (14). G (x) is composed of the luminance information g (x) and g (x + Δx) of the pixel and the direct current component a of the interference fringe waveform, so that g (x) and g (x + Δx), the direct current component a of the interference fringe waveform, interference If the spatial frequency f of the fringe waveform is known, φ can be obtained by the equation (14). That is, the respective phases φ ₁ , φ _2, and φ ₃ for the wavelengths λ ₁ , λ _2, and λ ₃ are obtained using the above arithmetic expressions.

  g (x) and g (x + Δx) can be obtained as luminance information of the pixels of the imaging device 19.

  The DC component a of the interference fringe waveform is, for example, a method of setting an average value of luminance of all pixels observed by the imaging device 19, a method of setting an average value of neighboring pixels of the phase calculation target pixel, or a method of measuring reflectance in advance. Etc. can be obtained.

  Further, the spatial frequency f of the interference fringe waveform is obtained, for example, by a method of obtaining from the installation angle of the reference surface 15 or a method of obtaining from the number of interference fringes in the screen of the interference fringe waveform when a flat surface is observed as the measurement object 30 in advance. Can be sought.

<Step S4> The surface height z ₁ , z _2, and z ₃ calculation CPU 20 for each wavelength of the pixel unit is a calculation target pixel calculated for each of the wavelengths λ ₁ , λ _2, and λ ₃ from the above equation (14). Phase φ ₁ (x), φ ₂ (x) and φ ₃ (x) are substituted into equation (15), and the respective heights z ₁ (x), z ₂ (x) and z ₃ (x) are substituted. Ask.

z (x) = [φ (x) / 4π] λ + z ₀ ... (15)

Note that z ₀ is the reference height of the measurement object 30.

Here, when the wavelength is λ, there are candidate value groups of solutions having different surface heights of different orders n for each range of λ / 2. Thus, three wavelengths lambda _1, lambda ₂ and lambda ₃ candidate value group of the solution of the surface height when using as in the present embodiment, lambda _1/2 of the two candidate values group, lambda _2/2 and lambda periodically exists for each range of _3/2 least common multiple.

  Since there is only one surface height to be obtained, a common height is obtained as an actual height from all candidate value groups. That is, among the candidate values of the surface height solution obtained for each candidate value group, the closest height is defined as the actual height.

For example, a group of candidate values for a wavelength λ ₁ that exists periodically is shown in FIG. 7A, a group of candidate values for a solution of wavelength λ ₂ is shown in FIG. 7B, and a solution candidate value group of a wavelength λ ₃ is As shown in FIG. Here, the portions corresponding to the measurement target surface 30A, which is the lower part of the measurement target 30 shown in FIG. 1, are the X-axis pixel numbers 0 to 254 and 356 to 512, and the convex portions (recesses) of the measurement target surface ) 30B is the center X-axis pixel number 255 to 355. Therefore, both candidate value groups are compared for each pixel, and the ones whose surface heights are substantially the same are extracted. That is, the measurement target surface 30A, which is one of the lower portions, has a height z ₁ of the order n1 = 0 of the wavelength λ ₁ , a height z ₂ of the order n2 = 0 of the wavelength λ _2, and an order n3 = 0 of the wavelength λ _3. because of the height z ₃ coincide, this value and the actual height. The convex portion (concave portion) 30B of the other measurement target surface has a height z ₁ of the order n1 = 16 of the wavelength λ ₁ , a height z ₂ of the order n2 = 13 of the wavelength λ _2, and an order n3 = 12 of the wavelength λ _3. Is substantially equal to the height z ₃ , so this value is taken as the actual height.

That is, from the phases φ ₁ (x), φ ₂ (x) and φ ₃ (x) measured at wavelengths λ ₁ , λ ₂ and λ ₃ based on this principle, the following equations (15a), (15b) and ( Each surface height is obtained by 15c).

_{z 1 (x) = [φ} 1 (x) / 2π + n 1] · (λ 1/2) ······· ··· (15a)
_{z 2 (x) = [φ} 2 (x) / 2π + n 2] · (λ 2/2) ·········· (15b)
_{z 3 (x) = [φ} 3 (x) / 2π + n 3] · (λ 3/2) ········· (15c)

<Step S5> further calculates the actual height Z of the pixel, using the above three _equations, and _n 1, _{n 2} and _{n 3} the difference each other and z 1, _{z 2} and _{z 3} are minimized The actual height Z is determined by substituting it into the above three equations and obtaining any one of z ₁ , z ₂ and z ₃ .
_Or, z 1, the average value of the _{z 2} and _{Z 3} may be the actual height Z.

<Step S6> Completion of calculation for all pixels?
CPU20 repeats the process of step S3-S6 until the calculation of a phase and height is complete | finished about all the pixels, and calculates | requires a phase and surface height.

<Step S7> The image data creation unit 27 of the surface shape display CPU 20 creates a display image of the measurement target surface 30A and the convex portion (concave portion) 30B of the measurement target surface from the calculated information of the actual surface height. Then, based on the information created by the image data creation unit 27, the CPU 20 displays information on the surface height of the measurement object 30 on the monitor 23 as shown in FIG. A three-dimensional or two-dimensional image based on the height information is displayed. The operator can grasp the shape of the convex portion (concave portion) 30B of the measurement target surface on the surface of the measurement target surface 30A by observing these displays. Thus, the measurement process of the surface shape of the measurement target surface 30A is completed.

  As described above, in the process of calculating the intensity value of the interference fringe light for each pixel and the intensity values of a plurality of neighboring pixels from the image data captured by the imaging device 19, the direct current included in the interference fringe waveform of each pixel. The simultaneous comparison is performed assuming that the component a (x), the AC amplitude b (x), and the phase φ (x) are equal for each pixel, thereby canceling the DC component and the AC amplitude of the interference fringes in each pixel. be able to.

  Therefore, since the surface height of the measurement target surface 30A can be measured without using a low-pass filter, the surface height of the steep edge portion of the measurement target surface 30A is accurately obtained as shown in FIG. be able to. As a result, the surface shape of the measurement target surface 30A can be accurately measured.

Further, a candidate value group of the surface height of the measurement object 30 is obtained for each of a plurality of monochromatic lights having different wavelengths from the obtained phase, and a common height is obtained from each candidate group as an actual height. Since the actual height is obtained from a wider candidate range than the surface height is obtained from the phase, the accuracy can be obtained more accurately. Moreover, the upper limit of the height which can be measured with the combination of the wavelength to be used can be made high. For example, if the difference between the wavelengths λ ₁ , λ _2, and λ ₃ is reduced, a higher uneven step can be detected.

  Moreover, since the surface height of the measuring object 30 is calculated | required from a phase, the uneven | corrugated state of a surface can also be discriminate | determined.

  Furthermore, since the reflected light composed of a plurality of monochromatic lights having different wavelengths output at the same time can be detected at the same time, the surface height and the surface shape of the measuring object 30 can be measured, so that the working efficiency can be improved. Above, description of the flowchart which shows the process in the surface shape measuring apparatus of FIG. 2 is completed.

Next, the present invention is not limited to the embodiment described above, and can be modified as follows.
For example, in the above-described embodiment, white light from the light source 10A of the illumination device 10 is incident on the acousto-optic filter 10B to extract a plurality of monochromatic lights having different wavelengths and enter the light guide 10C. The white light from the light source 10A is directly incident on the light guide path 10C, and the white light interference light obtained by combining the white light reference light and the white light measurement light is acoustically generated on the optical path on which the image pickup apparatus 19 is incident. An optical means may be provided that installs the optical filter 10B and extracts interference light composed of a plurality of monochromatic lights having different wavelengths for each of the plurality of monochromatic lights.

  By the way, in the description of the flowchart showing the processing using the surface shape measuring device of FIG. 2 described above, the white light from the light source 10A of the illumination device 10 is irradiated to the measurement target surface 30A through the acoustooptic filter 10B and the light guide path 10C. However, an example using the function that the wavelengths of a plurality of monochromatic lights having different wavelengths to be used can be arbitrarily set by using the acousto-optic filter 10B, which is a feature of the present application, will be described below.

  Some measurement objects 30 that perform surface shape measurement have many optical characteristics. For example, at the stage of irradiating the measurement target surface 30A using the illumination device 10 and imaging using the imaging device 19, depending on the color of the measurement target surface 30A, the measurement target surface 30A is irradiated with monochromatic light having a specific wavelength. There is a case where it has a characteristic of absorbing light, and there is a case where it is desired to change the wavelength of monochromatic light used for measurement to an optimum wavelength. As another example, when there is a transparent thin film on the measurement target surface 30A, depending on the optical film thickness, it may have a characteristic of absorbing irradiation light of monochromatic light of a specific wavelength. There is a case where it is desired to change the wavelength of light to an optimum wavelength.

  In those cases, before the start of the surface measurement, the measurement target surface 30A is irradiated in advance while scanning the wavelength of the monochromatic light in advance, and the measurement result of the obtained reflection intensity of each monochromatic light is used to obtain the measurement target. A plurality of monochromatic lights having different wavelengths with respect to the surface 30A are selected, and the surface shape is measured. At this time, the switching of the wavelength can be easily changed by adopting the acousto-optic filter 10B.

Specifically, when there is a transparent thin film on the measurement target surface 30A, as shown in FIG. 9, there is a phenomenon in which the reflectance varies with a change in the wavelength of irradiation light. Therefore, as described above, it is necessary to select the wavelength of monochromatic light having a high reflectance as the wavelength of monochromatic light to be irradiated. For example, measurement is also performed for three types of monochromatic light wavelengths selected according to the description of the flowchart of FIG. 2 (in the above case, λ ₁ = 470 nm, λ ₂ = 560 nm, and λ ₃ = 600 nm are selected). Depending on the target surface 30A, in the case where the wavelength on the vertical axis of the graph of FIG. 9 is the wavelength of the low reflectance, the monochromatic light is set so that the wavelength of λ ₁ , λ ₂ or λ ₃ becomes a portion with the high reflectance. The surface shape can be measured with higher accuracy if the wavelength is shifted. Such a rough response is possible in the surface shape measuring apparatus having the configuration of the present invention to which the acousto-optic filter 10B that can freely change the wavelength of monochromatic light used in the illumination apparatus 10 shown in FIG. 1 is applied.

DESCRIPTION OF SYMBOLS 1 ... Optical system unit 2 ... Control system unit 10 ... Illuminating device 10A / Light source 10B / Acousto-optic filter 10C / Light guide 101 / Terrel dioxide crystal 102 / Sound absorbing material 103 / Transducer 104 / Oscillator 105 / Wavelength Different transverse wave ultrasonic waves 106 / light having a broad wavelength
107 ・ Non-selection light 108 ・ Multiple monochromatic lights 11 with different wavelengths ・ Colloidal lens 13 ・ Half mirror 14 ・ Object lens 15 ・ Reference surface 17 ・ Beam splitter 18 ・ Image forming lens 19 ・ Image pickup device 20..CPU
21 ·· Memory 22 · · Input unit 23 · · Monitor 24 · · Drive unit 25 · · Phase calculation unit 26 · · Sign determination unit 27 · · Image data creation unit 30 · · Measurement object 30A · Measurement object surface 30B · Convex part (concave part) of measurement target surface
40 ・ ・ Holding table

Claims (4)

Based on the intensity value of interference fringes generated by reflected light that irradiates the measurement target surface and the reference surface with a plurality of monochromatic lights having different wavelengths through the irradiation means, reflects from both the measurement target surface and the reference surface, and returns on the same optical path In the surface shape measuring method for obtaining the surface height and surface shape of the measurement target surface,
Surface shape characterized in that the irradiating means comprises irradiating means for extracting a plurality of monochromatic lights having different wavelengths from an irradiating light having a broadband wavelength characteristic by using an acousto-optic filter and simultaneously irradiating them. Measuring method. In the surface shape measuring method according to claim 1,
Irradiate while scanning the wavelength of monochromatic light on the surface to be measured in advance, and use the resulting measurement results of the reflected intensity of each monochromatic light to select multiple monochromatic lights with the optimal wavelength for the surface to be measured And measuring the surface shape by irradiating them. Based on the intensity value of interference fringes generated by reflected light that irradiates the measurement target surface and the reference surface with a plurality of monochromatic lights having different wavelengths through the irradiation means, reflects from both the measurement target surface and the reference surface, and returns on the same optical path In the surface shape measuring device for determining the surface height and surface shape of the measurement target surface,
Surface shape characterized in that the irradiating means comprises irradiating means for extracting a plurality of monochromatic lights having different wavelengths from an irradiating light having a broadband wavelength characteristic by using an acousto-optic filter and simultaneously irradiating them. measuring device. In the surface shape measuring apparatus according to claim 3,
Irradiate while scanning the wavelength of monochromatic light on the surface to be measured in advance, and use the resulting measurement results of the reflected intensity of each monochromatic light to select multiple monochromatic lights with the optimal wavelength for the surface to be measured And a surface shape measuring apparatus configured to perform surface shape measurement by irradiating them.

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