JP4701387B2 - Measuring apparatus and method, and program - Google Patents

Description

  The present invention relates to a measuring apparatus, method, and program, and more particularly, to a measuring apparatus, method, and program capable of quickly measuring the shape of an object to be measured.

  The present inventors have previously proposed that the intensity of the light source is adjusted by the zone plate according to the incident angle of the light beam to the object to be measured, and the height of the object to be measured is measured (for example, non- Patent Document 1).

Synthetic spatial coherence function for optical tomography and profilometry: simultaneous- International Conference on Optics & Optoelectronics realization of longitudinal coherence scan and phase shift 110-117, Proc.SPIE Vol.4777 (2002,8)

  However, in the previous proposal, as shown in FIG. 1, the light intensity corresponding to the incident angle is set based on the spatial frequency γ and the phase β corresponding to the sparse density of the transparent zone and the opaque zone of the zone plate. Therefore, when trying to measure the height of the object to be measured finely, there is a problem that the number of zone plates must be increased. Specifically, when N phases of M frequencies are measured, the number of zone plates is M × N.

  As a result, since scanning using all of them is performed, there is a problem that the measurement takes time.

  The present invention has been made in view of such a situation, and enables measurement processing to be performed quickly.

The measuring apparatus of the present invention corresponds to the depth of field of the lens of the observation system until the in-focus position of the observation system is set to the first reference position of the measurement range and then reaches the second reference position of the measurement range. The setting means that sequentially moves by the amount, the selection means that sequentially selects a zone plate of a predetermined frequency at each in-focus position, and the intensity is adjusted to a value corresponding to the incident angle using the selected zone plate. Using each of the measuring means for irradiating the object to be measured to measure the detected intensity and the zone plate sequentially selected by the selecting means , the amplitude is calculated based on the detected intensity measured by the measuring means. It calculated the distribution of coherence obtained by dividing the average value, based on the frequency of the zone plate in which the maximum value is obtained for the coherence, and a calculating means for calculating the height of the object to be measured, selected The stage selects a zone plate that is defined so that the initial phase is determined based on the product of 2π, which is a constant representing one period, the frequency of the carrier signal detected as the detection intensity, and the frequency of the zone plate. characterized in that it.

Fourier transform means for Fourier transforming the detected intensity, extraction means for extracting the 0th order spectrum and the −1st order or + 1st order spectrum from the spectrum obtained by the Fourier transform, and the extracted 0th order spectrum and the −1st order or + 1st order spectrum. An inverse Fourier transform means for performing an inverse Fourier transform on the spectrum , and the computing means is obtained by performing an inverse Fourier transform on the zeroth order spectrum for a value obtained by performing an inverse Fourier transform on the −1st order or + 1st order spectrum. By dividing by this value , the coherence distribution can be obtained, and the height of the object to be measured can be calculated based on the frequency of the zone plate from which the maximum coherence value was obtained .

The measurement method of the present invention corresponds to the depth of field of the lens of the observation system until the in-focus position of the observation system is set to the first reference position of the measurement range and then reaches the second reference position of the measurement range. The setting step for sequentially moving by the corresponding amount, the selection step for sequentially selecting a zone plate of a predetermined frequency at each in-focus position, and using the selected zone plate, the intensity is adjusted to a value corresponding to the incident angle. Using each of the measurement step of irradiating the object to be measured to measure the detection intensity, and each of the zone plates sequentially selected by the process of the selection step , based on the detection intensity measured by the process of the measurement step , its amplitude is divided by the average value of the calculated distribution of the resulting coherence, based on the frequency of the zone plate in which the maximum value is obtained for the coherence, the height of the object to be measured Look including a calculation step of calculating, determination processing relating to the selection step, the initial phase, on the basis of 2π is a constant representing one period, the frequency of the carrier signal is detected as a detected intensity, and the product of the frequency of the zone plate A zone plate that is defined to be selected is selected .

The program of the present invention corresponds to the depth of field of the lens of the observation system until the in-focus position of the observation system is set to the first reference position of the measurement range and then reaches the second reference position of the measurement range. A setting step that sequentially moves minute by minute, a selection step that sequentially selects a zone plate of a predetermined frequency at each in-focus position, and light whose intensity is adjusted to a value according to the incident angle using the selected zone plate a measuring step of measuring a detected intensity by irradiating the object to be measured, with each of the sequentially selected zone plate by the process of the selection step, based on the detected intensity measured respectively by the processing of the measurement step, the We obtain a distribution of the resulting coherence by dividing the magnitude in the average value, based on the frequency of the zone plate in which the maximum value is obtained for the coherence, of the measured object height And a computation step of computing, processing of the selection step, the initial phase, 2 [pi is a constant representing one cycle, based on the product of the frequency of the carrier signal is detected as the detected intensity, and zone plate determined A control process for selecting a zone plate defined as described above is executed by a computer.

In the measurement apparatus, method, and program of the present invention, after the in-focus position of the observation system is set to the first reference position of the measurement range, the lens of the observation system is reached until it reaches the second reference position of the measurement range. It is sequentially moved by an amount corresponding to the depth of field, and a zone plate of a predetermined frequency is sequentially selected at each in-focus position, and the intensity is adjusted to a value corresponding to the incident angle using the selected zone plate. The detection intensity is measured by irradiating the object to be measured, and the coherence obtained by dividing the amplitude by the average value based on the measured detection intensity using each of the selected zone plates. And the height of the object to be measured is calculated based on the frequency of the zone plate from which the maximum coherence value is obtained . A zone plate is selected that is defined so that the initial phase is determined based on the product of 2π, which is a constant representing one cycle, the frequency of the carrier signal detected as the detection intensity, and the frequency of the zone plate.

  According to the present invention, the height can be measured. In particular, according to the present invention, the height measurement process can be quickly performed using the zone plate.

  FIG. 2 shows a configuration example of the measuring apparatus 10 to which the present invention is applied. This measuring apparatus 10 adjusts the intensity of light from the light source 11 to a value corresponding to the incident angle θ by using a zone plate-like light source distribution 41 formed on the diffusion plate 20 based on the zone plate 15a. The surface height of the measurement object 25 is measured.

  11 is a laser, 12 is a beam expander, 13, 17, 19 and 22 are lenses, 14 and 16 are polarizing plates, 15 is a spatial light modulator (SLM), and 15 a is a zone displayed on the spatial light modulator 15. A plate, 18 is a pinhole, and 20 is a diffusion plate.

  Reference numeral 21 denotes a motor, 23 denotes a beam splitter, 24 denotes a reference surface, 25 denotes an object to be measured, 26 denotes an imaging lens, 27 denotes a driving device for the imaging lens 26, 28 denotes a detector, and 29 denotes a detector driver.

  30 is a personal computer (PC), 31 is an SLM control driver. The personal computer 30 is configured to include a zone plate generating unit 61 shown in FIG. 3 and a measurement processing unit 101 shown in FIG. 4, and each unit will be described later.

  Reference numeral 41 denotes a light intensity distribution corresponding to the density of the transparent and opaque portions of the zone plate 15a formed on the surface of the diffusion plate 20, and functions as a secondary light source (planar light source). Therefore, in the following, 41 is referred to as a secondary light source. Reference numeral 42 denotes a focus point of the imaging lens 26, and 43 denotes a conjugate image of the focus point of the imaging lens 26.

  The laser beam emitted from the laser 11 is expanded in beam diameter by the beam expander 12, converted into a parallel beam by the lens 13, and then enters the polarizing plate 14.

  The polarizing plate 14 and the polarizing plate 16 transmit linearly polarized light, and both are disposed with the SLM 15 interposed therebetween so that the transmission directions thereof are perpendicular or parallel to each other.

  The SLM (spatial light modulator) 15 is configured to be able to display an image by an LCD (Liquid Crystal Display) that constitutes a large number of pixels, and the LCD according to a signal from a control driver 31 controlled by the personal computer 30. The optical characteristics (change in amplitude and intensity due to absorption, phase change due to refractive index, rotation of polarized light) are changed. That is, when the light beam incident through the polarizing plate 14 is irradiated onto the LCD, light corresponding to the optical characteristics is emitted through the polarizing plate 16.

  In the case of this example, a zone plate for forming a zone plate-shaped light intensity distribution (secondary light source) 41 on the diffusion plate 20 (a large number of concentric circles of transparent and opaque portions are drawn alternately. The light intensity transmittance of the SLM 15 is controlled so that the image 15a is displayed.

  The light beam emitted through the polarizing plate 16 is converged by the lens 17 and enters the pinhole 18. The pinhole 18 smoothes and smooths the contours of the discrete pixels constituting the SLM 15 appearing in the image of the zone plate 15a (light intensity distribution 41). The light emitted from the pinhole 18 is converted into a parallel beam by the lens 19. The parallel beam is incident on the diffusion plate 20.

  The diffuser plate 20 has a number of minute irregularities formed on the surface thereof, and is a translucent disk-like member that diffuses light. The diffuser plate 20 diffuses a parallel beam from the lens 19 (a zone plate-shaped light intensity distribution). A secondary light source is generated and emitted to the lens 22.

  The diffusion plate 20 is rotated by a motor 21. By rotating the diffusion plate 20 in this way, the phase of each point (point light source) of the secondary light source 41 having a zone plate-like intensity distribution generated on the diffusion plate 20 changes randomly and at high speed. The phase difference between the point light sources does not become constant, and the point light source becomes a spatially incoherent light source.

  In other words, when the zone plate 15a is projected on the SLM 15 on the diffusing plate 20, a secondary light source 41 having a light intensity distribution corresponding to the light intensity transmittance of the zone plate 15a is formed. A low-coherence light beam having a light source intensity corresponding to the light intensity distribution is emitted.

  The light beam emitted from each point light source of the secondary light source 41 formed on the diffusion plate 20 is converted into a parallel beam by the lens 22 and enters the beam splitter 23.

  The beam splitter 23 divides the incident parallel beam into two, irradiates one light beam on the reference surface 24 (mirror surface), and irradiates the object 25 to be measured with the other.

  That is, as shown in FIG. 5, the light beam is incident on the reference surface 24 and the measured object 25 at a predetermined incident angle θ.

  By the way, diffused light is emitted from the secondary light source 41. The incident angle θ of the light beam on the reference surface 24 and the measured object 25 is a value corresponding to the emission position (radius from the center) on the secondary light source 41 (diffuser plate 20), as shown in FIG. It becomes. That is, a plurality of light beams having different incident angles θ are incident on the reference surface 24 and the measured object 25. In FIG. 5, for the sake of simplicity, only the light beam at the incident angle θa is shown at the point P1 and the point P11, but actually, the surface 25a of the measured object 25 including the point P1 and the point P11 is shown on the surface 25a. A plurality of light beams having different incident angles θ are incident.

  Since the center of the secondary light source 41 is located on the optical axis of the lens 22, a position (point A and point D or point B and point on the secondary light source 41 that is symmetric with respect to the optical axis). The exit angles of the beams from C) are the same, and the incident angle θ to the measured object 25 is also the same. Further, since the secondary light source 41 is disposed on the distance f of the lens 22, the beam emitted from each point on the secondary light source 41 becomes a parallel beam after passing through the lens 22.

  Returning to FIG. 2, the light beam applied to the reference surface 24 is reflected by the reference surface 24, and the light beam applied to the measured object 25 is reflected by the measured object 25. The reflected light (reference light) from the reference surface 24 and the reflected light (signal light) from the object to be measured 25 are combined by the beam splitter 23 and enter the imaging lens 26.

  For example, as shown in FIG. 5, the light beam 151 is a combination of the signal light reflected by the point P 1 on the surface 25 a of the object 25 and the reference light reflected by the point P 3 on the reference surface 24. 153A enters the imaging lens 26.

  A light beam 153B obtained by combining the signal light reflected by the point P11 on the surface 25a of the object 25 to be measured and the reference light reflected by the point P13 on the reference surface 24 by the light beam 151 is the imaging lens 26. Is incident on.

  As described above, since a plurality of light beams having different incident angles are incident on the surface 25a including the point P1 and the point P11, a plurality of synthesized lights are incident on the imaging lens 26 from the point P1 and the point P11. Incident.

  The imaging lens 26 images the light beam incident from the beam splitter 23 on the sensor array surface (not shown) of the detector 28.

  The driving device 27 is controlled by the personal computer 30 and moves the imaging lens 26 in the optical axis direction so that the focus point 42 of the imaging lens 26 is focused on the surface 25a of the object 25 to be measured.

  The detector 28 generates an image signal of an image formed by the imaging lens 26.

  The driver 29 drives the detector 28, reads the image signal detected by the detector 28, and outputs it to the personal computer 30.

  The personal computer 30 generates the zone plate 15 a and executes the height measurement process of the object to be measured 25 based on the image signal read from the detector 28.

  Next, the measurement principle in the measurement apparatus 10 will be described.

  The detector 28 forms an image of light obtained by combining the signal light and the reference light by the imaging lens 26. The intensity (hereinafter referred to as detection intensity) Idet of each pixel of this image is a signal light generated when light from each point light source forming the secondary light source 41 is reflected from the measured object 25 and the reference surface 24. Intensity of interference fringes generated by the reference light (hereinafter referred to as interference intensity) Iint is added independently.

  The interference intensity Iint becomes stronger or weaker by overlapping the signal light having the predetermined light source intensity Is and the reference light with a predetermined phase difference. The phase difference between the signal light and the reference light has a magnitude corresponding to the optical path difference between the signal light and the reference light, and the optical path difference is determined by the unevenness (height h) of the measured object 25 and the incident angle θ. .

  For example, the interference intensity Iint of the interference light 153A between the signal light reflected at the point P1 on the surface 25a of the object 25 to be measured and the reference light reflected at the point P3 on the reference surface 24 by the light beam 152 in FIG. Since the optical path difference is L1 + L2, the intensity is obtained when the light beam 151 and the light beam 152 interfere with each other with a phase difference having a magnitude corresponding to the optical path difference of L1 + L2.

  L1 represents the distance between the points P2 and P3, and L2 represents the distance between the points P3 and P1. The point P 2 is a point on the light beam 152 corresponding to the point P 1 of the light beam 151, and the point P 3 is a reflection point on the reference surface 24 of the light beam 152.

  Further, the interference intensity Iint of the interference light 153B between the signal light reflected by the light beam 151 at the point P11 on the surface 25a of the measured object 25 and the reference light reflected by the point P13 on the reference surface 24 is expressed by the optical path Since the difference is L11 + L12, the intensity is obtained when the light beam 151 and the light beam 152 interfere with each other with a phase difference having a magnitude corresponding to the optical path difference of L11 + L12. L11 represents the distance between the points P12 and P13, and L12 represents the distance between the points P13 and P11.

  That is, the detection intensity Idet of each pixel of the image formed on the detector 28 is the sum of the interference intensities Iint of the interference light incident from the corresponding points on the surface 25a, as shown in Expression (1). Each interference intensity Iint is determined by the light source intensity Is, the incident angle θ, and the height h of the signal light and the reference light.

  In the present invention, as shown in FIG. 7A, the incident angle θ is controlled to change within a predetermined range. As shown in FIG. 7B, only light of one incident angle θA is not used.

  However, as is clear from the equation (1), when the light source intensity Is is constant regardless of the incident angle θ as shown in FIG. 8A, the interference intensity corresponds to the incident angle θ as shown in FIG. 8B. Even if Iint is changed, the detected intensity Idet is the sum of the interference intensities Iint, and as shown in FIG. 8C, becomes a constant value regardless of the change in height.

  Therefore, for example, if the light source intensity Is of the light beam is adjusted to a value corresponding to the incident angle θ as shown in FIG. 9A in accordance with the change of the interference intensity Iint with respect to the incident angle θ at the height hi shown in FIG. 9B (change) 9C, the maximum value of the detected intensity Idet can be obtained from the point of the height hi as shown in FIG. 9C. That is, when the measured object 25 is scanned using the light source, the height of the point where the maximum value of the detected intensity Idet is obtained can be set to the height hi (the height of the measured object 25 can be measured). ). The height hi is expressed by the following formula.

  As described above, in the present invention, the light source intensity Is of the light beam is set to the incident angle θ in accordance with the change of the interference intensity Iint with respect to the incident angle θ at the height h for each height h to be measured. The zone plate 15a to be changed to a corresponding value (FIG. 9A) (a two-dimensional light source 41 having such a light source intensity distribution is formed) is generated in advance, and 2 formed by each of the generated zone plates 15a. The height of the measured object 25 is measured by scanning the measured object 25 with the next light source 41 (hereinafter, described as scanning the measured object 25 with the zone plate 15a as appropriate).

  For example, as shown in FIG. 10, the light source intensity Is of the light beams 211 and 221 changes to a value corresponding to the incident angle θ in accordance with the change of the interference intensity Iint with respect to the incident angle θ on the surface 25a1 having the height h11. The zone plate 15a-3 (frequency γa1) for forming the secondary light source 41 to be generated is generated, and the light beams 211, 221 and the like are adjusted in accordance with the change of the interference intensity Iint with respect to the incident angle θ on the surface 25a2 having the height h12. The zone plate 15a-2 (frequency γa2) for forming the secondary light source 41 whose light source intensity Is changes to a value corresponding to the incident angle θ is generated, and interference with the incident angle θ at a height h10 (not shown) is generated. A zone plate 15a-1 in which the secondary light source 41 is formed in which the light source intensity Is changes to a value corresponding to the incident angle θ according to the change of the intensity Iint is generated, and the incident angle θ at a height h13 (not shown). According to the change of interference intensity Is If the zone plate 15a-4 for forming the secondary light source 41 in which the light source intensity Is changes to a value corresponding to the incident angle θ is generated, the object to be measured 25 is scanned with the zone plate 15a. Thus, the points at heights h10, h11, h12, and h13 can be detected.

  In this way, height measurement is performed.

  Next, the zone plate 15a generation process will be described with reference to FIG. 11. First, parameters necessary for generating the zone plate 15a will be described.

  As described above, for example, as shown in FIG. 12, at each of the heights h0..., The heights hi,. When the zone plates 15a-0,..., 15a-N forming the secondary light source 41 are generated, the light source intensity Is of the beam changes to a value corresponding to the incident angle θ. When the object to be measured 25 is scanned by the zone plate 15a, the detection intensity Idet from the measurement point 0 of the height h0,..., The measurement point i of the height hi,. The maximum value of is obtained.

  Here, “the light source intensity Is of the light beam changes to a value corresponding to the incident angle θ according to the change of the interference intensity Iint with respect to the incident angle θ” means that the interference intensity Iint is small as shown in FIG. The incident angle (incident angles θ0, θ2 in FIG. 13B) and the light source intensity Is decreases (incident angles θ1, θ3, etc. in FIG. 13A) and the interference intensity Iint increases. , Θ4, etc.) to increase the light source intensity Is (incident angles θ0, θ2, θ4, etc. in FIG. 13A), that is, the light source intensity so that the peaks and valleys of the light source intensity Is and the interference intensity Iint coincide with each other. It means that Is changes. Thus, by making the light source intensity Is correspond to the interference intensity Iint, a positive peak value can be brought about in the detection intensity Idet (FIG. 13C).

  This also means that the frequency and phase of change of the light source intensity Is with respect to the incident angle θ coincide with the frequency and phase of change of the interference intensity Iint with respect to the incident angle θ.

  The light source intensity Is of the secondary light source 41 is changed by changing the phase β of the zone plate 15a. For example, as shown in FIG. 14A, the light source intensity of a predetermined frequency γ (the light intensity of the two-dimensional light source 41 formed by the zone plate 15a having the frequency γ) Is is a cosine wave (or sine wave) function curve whose frequency monotonically increases. It is prescribed by. FIG. 14B shows a part of FIG. 14A enlarged in phase (horizontal axis). For example, point A, point B, and point C on the light source intensity Is shown in FIG. 14A correspond to point A, point B, and point C of equal intensity on the cosine function curve shown in FIG. 14B, respectively.

  Then, when the phase of the cosine function curve shown in FIG. 14B is shifted by the amount of δβ (referred to as a phase shift of δβ), new cosine function curves as shown by dotted lines are obtained, and the intensities at points A, B, and C are obtained. Fluctuate and become points A ′, B ′, and C ′ on the new cosine function curve. Points A, B, and C are shifted by δA, δB, and δC, respectively.

  A new cosine function curve in the case of such a phase shift is as shown by a solid line in FIG. 14C.

  When this phase shift is 180 degrees, the peak of the original light source intensity Is (FIG. 13A) becomes a valley and the valley becomes a peak as shown in FIG. 15A, and the peak of the light source intensity Is as shown in FIG. 15B. And valleys correspond to the valleys and peaks of the interference intensity Iint. In this case, since the large interference intensity Iint is removed from the detection intensity Idet, the detection intensity Idet is minimized as shown in FIG.

  Generally speaking, when the zone plate 15a having a predetermined spatial frequency γ is phase-shifted, the detection intensity Idet of the secondary light source 41 increases or decreases according to the cosine function. As shown in FIG. 16, the phase difference between the peak (Pp) and valley (Pv) of the cosine fluctuation is 180 degrees.

From the above, the detection intensity Idet of the secondary light source 41 when the zone plate 15a is phase-shifted can be expressed by Expression (2). In equation (2), a is the average value (DC component) of the detection intensity Idet, b (γ) is the amplitude of the AC component, and is a value that is half the difference between the peak and valley of the detection intensity Idet. . γ is the frequency of the zone plate 15a (secondary light source 41), β is its initial phase, and φ is the initial phase of the detection intensity Idet determined by the set positions of the measured object 25 and the reference surface 24.
Idet = a (γ) + b (γ) cos (β + φ) (2)

In addition, Formula (2) becomes the same value as Formula (1), when the change of the light source intensity Is with respect to incident angle (theta) is represented by Formula (3). R in the formula (3) is a distance from the center of the zone plate 15a (secondary light source 41).
Is = 1 + cos (γr ² + β) (3)

  That is, according to the equation (2), since the frequency γ and the phase β of the zone plate 15a (secondary light source 41) can be controlled independently, the scanning of the zone plate 15a is performed by scanning the frequency γ and the phase shift for each frequency γ. This can be done separately for scanning. Even if the frequency γ and the frequency of the change in the interference intensity Iint match, the detection intensity Idet does not become maximum unless the phases match each other, but the phase of the zone plate 15a of the frequency γ is shifted to thereby increase the light source intensity. If the phase of the change of Is matches the phase of the change of the interference intensity Iint, the maximum value of the detected intensity Idet can be obtained from the point of the surface 25a of the measured object 25 where the interference intensity Iint changes. it can.

  Further, by dividing b (γ) in equation (2) by a (γ), a coherence function (contrast) is obtained. Therefore, in the present invention, instead of detecting the maximum value of the detection intensity Idet, the coherence function ( The maximum value of (contrast) (= b (γ) / a (γ)) is detected.

  Since the height of the peak of the detection intensity Idet may fluctuate due to the change in the light amount of the laser light source or the influence of noise, the position where the maximum value appears (height h) may deviate from the actual position.

  If the coherence function is detected, even if the light quantity variation occurs, the variation is canceled by taking the ratio by the division, and the location (height h) of the maximum value of the accurate coherence function is detected. be able to. That is, the detection of the coherence function can increase the S / N ratio of the system as compared with the case of detecting the detection intensity Idet.

  There are roughly two coherence function detection methods, the Fourier transform method and the phase shift method.

  In the Fourier transform method, the phase β is scanned with respect to each frequency γ of the zone plate 15a to be scanned, as shown in FIG. 17A, with 0 to 360 ° as one cycle, and scanning is repeated several times, as shown in FIG. 17B. Such a detection intensity Idet is obtained. The detected intensity Idet is Fourier transformed.

  By this Fourier transform, as shown in FIG. 17C, a zero-order spectrum 251, a −1 order spectrum 252, and a +1 order spectrum 253 are obtained. Then, the coherence is calculated from the ratio of the −1st order spectrum 252 (or the + 1st order spectrum 253 (the magnitude represents b (γ) / 2) and the 0th order spectrum 251 (the magnitude represents the average value a (γ)). Is calculated.

  On the other hand, in the phase shift method, the initial phase β of the zone plate 15a is phase-shifted by a phase step amount that is equally divided into the number of steps equal to or greater than the number of unknowns in the equation (2), thereby scanning for one cycle. A coherence function is calculated by analyzing the simultaneous equations obtained thereby.

  By the way, in the Fourier transform method and the phase shift method, as described above, a phase shift for each frequency γ of the zone plate 15a is required (at least three or more phase shifts are required). That is, if the number of the frequency γ of the zone plate 15a is M and the number of phase shifts (the number of scanned phases) for each frequency γ is N, only M × N zone plates 15a are required.

  That is, if the data is obtained by individually changing the frequency γ and the phase β of the zone plate 15a and the Fourier transform method or the phase shift method is applied as it is, it takes time for the entire scanning of the zone plate 15a and a long time scanning. This makes it easier to receive noise from the outside world and increases the amount of calculation.

Therefore, in the present invention, the initial phase β and the frequency γ are set in a linear relationship as shown in, for example, the equation (4), so that the scanning of the frequency γ and the shift of the phase β are performed simultaneously. That is, the phase β also changes linearly corresponding to the frequency γ, and the phase shift is also performed in accordance with the scanning of the frequency γ. In this way, there is no need to perform a phase shift separately, so that the amount of data can be reduced and the processing speed can be increased.
β = 2πfcγ (4)

  In this case, when the frequency γ of the zone plate 15a is scanned, a carrier signal as shown in FIG. 18 is detected as the detection intensity Idet (Equation (2)) of each pixel of the observation image. When the spatial frequency γ being scanned does not correspond to a signal having a carrier frequency of the actual height frequency fc, the coherence is small, so that the carrier amplitude is small, but the spatial frequency γ corresponds to the actual height. Since the coherence is large, the carrier amplitude is also large. That is, the amplitude of the carrier signal represents the magnitude of coherence.

  Therefore, when the Fourier transform method is used to detect the amplitude of the carrier fringes and the detected intensity Idet in FIG. 18 is Fourier transformed, the carrier fringes are cosine signals. Therefore, the explanation will be given with reference to FIG. Thus, three spectra are obtained.

  The distance between the −1st order spectrum 252 (or the + 1st order spectrum 253) and the 0th order spectrum 251 corresponds to the carrier fringe frequency fc, and the −1st order spectrum 252 (or the + 1st order spectrum 253) is extracted and reversed. If Fourier transform is performed, the amplitude b (γ) of the detected intensity Idet can be obtained.

In order to extract the −1st order spectrum 252 (or the + 1st order spectrum 253) and the 0th order spectrum 251, it is necessary that the spectra do not overlap. That is, as shown in FIGS. 19 and 20, each of the −1st order spectrum 252 and the + 1st order spectrum 253 must be positioned between the 0th order spectrum 251 and the left and right boundary lines 254 and 255 of the data. In order to completely separate the −1st order spectrum 252 and the + 1st order spectrum 253 from the 0th order spectrum 251, the carrier fringe frequency fc is equal to the width fv of the −1st order spectrum 252 and the + 1st order spectrum 253. Must be 1/2 or more. That is, it is necessary to satisfy Expression (5).
fc ≧ fv / 2 (5)

Further, if the −1st order spectrum 252 and the + 1st order spectrum 253 exceed the data boundary lines 254 and 255, the outer part of the spectrum boundary line is cut at the boundary line, and the complete spectrum is not obtained. The fringe frequency fc needs to be (fs-fv) / 2 or less. That is, it is necessary to satisfy Expression (6). Here, fs is a sampling rate for scanning the plate frequency γ.
fc ≦ (fs−fv) / 2 (6)

Further, as shown in FIG. 21, when the width fv of the −1st order spectrum 252 and the + 1st order spectrum 253 exceeds half the sampling rate fs of the frequency γ, the inside of the −1st order spectrum 252 and the + 1st order spectrum 253 overlap. Alternatively, the outer side exceeds the data boundary line, and a spectrum having a complete amplitude cannot be obtained. Therefore, it is necessary to satisfy Expression (7).
2fc ≦ fs / 2 (7)

From the above, the independent −1st order spectrum 252 and + 1st order spectrum 253 cannot be extracted unless the sampling rate fs of the frequency γ, the spectrum amplitude fv, and the frequency fc of the carrier fringes satisfy Expression (8).
fv / 2 ≦ fc ≦ (fs−fv) / 2
2fc ≦ fs / 2 (8)

  That is, if Expression (8) is satisfied, the amplitude distribution b (γ) of the detection intensity Idet is obtained by obtaining the inverse Fourier transform of the −1st order spectrum 252 (or the + 1st order spectrum 253). Furthermore, the average value distribution a (γ) of the detection intensity Idet is obtained by obtaining the 0th-order inverse Fourier transform. Then, coherence is obtained by b (γ) / a (γ). Note that a (γ) is the total intensity of the secondary light source 41, and is a direct current component of the detection intensity Idet. When the frequency γ of the zone plate 15a changes, the value of a changes slightly, so a is a function of (γ). Can be expressed as However, since it is smaller than the amplitude change of the detection intensity Idet, it may be a substantially constant value (a (γ) = a).

As described above, the initial phase β and the frequency γ (= h / λf ² ) have the relationship shown in the equation (4), and fc needs to satisfy the equation (8). Therefore, in the present invention, the zone plate 15a is generated by the phase β and the frequency γ that satisfy such conditions.

  Next, a configuration example of the zone plate generation unit 61 (FIG. 3) of the personal computer 30 will be described.

  The width determining unit 81 determines the width fv of the Fourier spectrum. The scanning step determination unit 82 determines the scanning step Δγ of the frequency γ of the zone plate 15a. The frequency determining unit 83 satisfies the equation (8) with the relationship between the width fv determined by the width determining unit 81 and the sampling frequency fs that is the reciprocal of the scanning step Δγ determined by the scanning step determining unit 82. The frequency fc is determined.

  The generation unit 84 calculates the phase β from the frequency γ and the carrier fringe frequency fc determined by the frequency determination unit 83 according to the equation (4), and generates the zone plate 15a having the frequency γ and the calculated phase β. To do.

  Next, a configuration example of the measurement processing unit 101 (FIG. 4) of the personal computer 30 that executes the height measurement processing of the measured object 25 by the zone plate 15a generated by the zone plate generation unit 61 will be described.

  The mode setting unit 111 sets the mode of measurement processing executed by the measurement processing unit 101.

  The rotating unit 112 controls the motor 21 (FIG. 2) to rotate the diffusion plate 20. The irradiation unit 113 drives the laser 11 to irradiate the laser beam.

  The focusing unit 114 performs a focusing process. The setting unit 115 sets the in-focus position of the observation system (imaging lens 22, driving device 27, detector 28) to a predetermined reference position. The display unit 116 displays the image formed on the detector 28.

  The load unit 117 selects one zone plate 15 a having a predetermined frequency γ and loads it onto the spatial light modulator 15 via the control driver 31. The measurement unit 118 measures the detection intensity Idet of each pixel of the image (observation image) imaged on the detector 28 and stores the measurement result in the storage unit 119.

  The determination unit 120 selects one pixel of the observation image stored in the storage unit 119, the selection unit 121 selects a focus position, and the reading unit 122 selects the pixel selected by the determination unit 120. The measured value at the in-focus position selected by the unit 121 is read from the storage unit 119.

  The conversion unit 123 performs a Fourier transform on the measurement value read from the reading unit 122 or performs an inverse Fourier transform on the −1st order spectrum or the + 1st order spectrum and the 0th order spectrum of the spectrum obtained by the Fourier transform. The extraction unit 124 extracts a −1st order spectrum, a + 1st order spectrum, and a 0th order spectrum from the spectrum obtained by the Fourier transform in the conversion unit 123.

  The calculation unit 125 calculates coherence from b (γ) and a (γ) obtained by the inverse Fourier transform of the −1st order spectrum or the + 1st order spectrum in the conversion unit 123 and the 0th order spectrum, and the calculated coherence. Find the maximum value of. The computing unit 125 computes the surface height of the measured object 25 corresponding to the pixel from the frequency γ corresponding to the obtained maximum value of coherence.

  With reference to the flowchart of FIG. 11, the generation process of the zone plate 15a will be described. This process is performed by the zone plate generator 61 shown in FIG.

In step S11, the width determining unit 81 of the zone plate generating unit 61 determines the width fv of the Fourier spectrum. Note that fv is a value obtained by squaring the maximum value Rmax of the radius of the illumination range of the zone plate 15a as shown in the equation (9). The width fv can also be estimated by preliminary experiments (including simulation).
fv = Rmax ² (9)

In step S12, the scanning step determination unit 82 measures the scanning step Δγ of the frequency γ of the zone plate 15a by the detection unit Δh of the height of the measured object and the measured object as shown in the equation (10). The wavelength is determined based on the wavelength λ of the light source used and the focal length f (FIG. 6) of the observation system lens 22 for observing the object to be measured.
1 / fs = Δγ = Δh / λf ² (10)

  In step S13, the frequency determining unit 83 determines the carrier fringe frequency fc that satisfies the equation (8) under the relationship between the width fv calculated in step S11 and the sampling frequency fs calculated in step S12. .

  In step S14, the generation unit 84 calculates the phase β from the frequency γ and the carrier fringe frequency fc determined in step S13 according to the equation (4).

  The generation unit 84 generates the zone plate 15a having the frequency γ and the calculated phase β.

  The zone plate 15a is generated as described above.

  Next, the height measurement process of the measured object 25 by the zone plate 15a generated as described above will be described with reference to a flowchart. When the height distribution of the object to be measured 25 is wide and all the surfaces 25a do not fall within one depth of field, the user sets the auto mode. In this case, the process of measuring the height while scanning the depth of field by the focus scanning shown in FIGS. 22 and 23 (auto mode measurement process) is performed. This process is executed by the measurement processing unit 101 of the personal computer 30 shown in FIG. Mode setting is performed by the mode setting unit 111.

  In step S <b> 51, the rotation unit 112 of the measurement processing unit 101 of the personal computer 30 controls the motor 21 to rotate the diffusion plate 20.

  Next, in step S52, the irradiation unit 113 drives the laser 11 to emit laser light.

  In step S53, the setting unit 115 sets the in-focus position of the observation system to the first reference position in the measurement range. That is, the setting unit 115 drives the driving device 27 to move the imaging lens 26 in the vertical direction as shown in FIG. 26 so that the focus point of the imaging lens 26 is set to the first reference position Pa in the measurement range. Set to. The focusing unit 114 performs focusing processing at that position. Thus, if the object to be measured 25 has a surface having a height corresponding to the first reference position Pa, the object is focused on that height.

  The focusing lens 26 is focused in this way if the observation point A and the observation point B can be focused on the surface 25a of the measured object 25 as shown in FIG. The intensity Idet is the sum of the interference intensity Iint of the interference light from that point, and is a value corresponding to the height h. In the example of FIG. 24, the interference light of the light beam 271 having the incident angle θ1 and the interference light of the light beam 272 having the incident angle θ2 are incident from the observation point A having the height h21, and from the observation point B having the height h22. The interference light of the light beam 271 having the incident angle θ1 and the interference light of the light beam 272 having the incident angle θ2 are incident.

  On the other hand, as shown in FIG. 25, when the observation point D is not focused on the surface 25a of the measured object 25 (when focused at a position above the surface 25a), the detected intensity Idet at that time is a point Since this is the sum of the interference intensities Iint including interference light from a plurality of points A, B, and C incident on D, it does not become a value corresponding only to the height h.

  As a result, there is no problem if the surface 25a is a mirror surface, but if the surface 25a is a rough surface, the height cannot be measured. By focusing, the height can be measured even if the surface 25a is a rough surface.

  Next, in step S54, the display unit 116 displays the image formed on the detector 28.

  In step S <b> 55, the load unit 117 selects one zone plate 15 a having the predetermined frequency γ (the zone plate 15 a generated by the generation processing described with reference to FIG. 11), and the spatial light modulator 15 via the control driver 31. To load.

  For example, in the example of FIG. 27A, the zone plate 15a-1 having the frequency γ1 is first loaded.

  Next, in step S56, the measurement unit 118 measures the detection intensity Idet of each pixel of the image (observation image) imaged on the detector 28, and stores the measurement result in the storage unit 119 in step S57.

  In this way, for example, in the example of FIG. 27A, the detection intensity Idet of each pixel of the image IM1 is measured, and the measurement result is stored in the storage unit 119.

  In step S58, the loading unit 117 determines whether or not all target zone plates 15a have been selected. If it is determined that there are still unselected zone plates 15a, the load unit 117 returns to step S55, Zone plate 15a (zone plate 15a of other frequency γ) is selected and loaded into the spatial light modulator 15. Thereafter, the processing after step S56 is similarly performed.

  That is, in the example of FIG. 27A, zone plates 15a-2 (not shown) to 15a-m are selected in order, and the detection intensity of each pixel of the observed images IM2 (not shown) to IMm on the selected zone plate 15a. Each Idet is stored in the storage unit 119.

  If it is determined in step S58 that all the zone plates 15a have been selected, the process proceeds to step S59, where the setting unit 115 determines whether or not the in-focus position has been moved to the second reference position Pb (FIG. 26). If it is determined that the position has not been moved yet, the process proceeds to step S60, and the in-focus position is moved in the direction of the second reference position Pb in the measurement range by one step.

  Thereafter, the process returns to step S54, and the subsequent processing is similarly performed.

  That is, at the different in-focus positions, as shown in FIG. 27A, the detection intensity Idet of each pixel of the observation pixels on each zone plate 15a is stored in the storage unit 119.

  As shown in FIG. 28, the distance of one step for moving the in-focus position is FPi in the depth of field at the predetermined in-focus position and the depth of field FP (i + in the next in-focus position). The distance of 1) is set to be equal to or smaller than the depth of field.

  Returning to FIG. 22, when it is determined in step S59 that the in-focus position has moved to the second reference position Pb, the process proceeds to step S61 (FIG. 23), and the determination unit 120 performs each observation stored in the storage unit 119. One pixel corresponding to each of the images is selected.

  In step S62, the selection unit 121 selects one in-focus position. In step S63, the reading unit 122 selects each of the zone plates 15a at the in-focus position selected in step S62 of the pixel selected in step S61. The measurement value of the detection intensity Idet at the time of selection is read from the storage unit 119.

  For example, when the pixel A shown in the example of FIG. 27A is selected in step S61, the detection intensity Idet of the pixel A when the zone plate 15a is selected at the in-focus position selected in step S62 is read out. As a result, a detection intensity Idet as shown on the leftmost side of FIGS. 27B and 29 is obtained.

  Next, in step S64, the conversion unit 123 performs a Fourier transform on the measurement value read in step S63 (S64 in FIG. 29). FIG. 29 schematically shows the processing of a predetermined step, and corresponding steps in FIG. 29 indicate corresponding portions.

  In step S65, the extraction unit 124 extracts the −1st order spectrum and the 0th order spectrum from the spectrum obtained by the Fourier transform in step S64 (S65 in FIG. 29).

  Next, in step S66, the conversion unit 123 performs inverse Fourier transform on the −1st order spectrum and the 0th order spectrum extracted in step S65 to obtain b (γ) and a (γ) (S66 in FIG. 29).

  In step S67, the calculation unit 125 calculates coherence (= b (γ) / a (γ)) from b (γ) and a (γ) calculated in step S66 (S67 in FIG. 29).

  Next, in step S68, the calculation unit 125 obtains the maximum value of coherence. That is, the maximum value of the coherence at the time of selecting each zone plate 15a at the in-focus position selected in step S62 for the pixel selected in step S61 is obtained.

  Next, in step S69, the selection unit 121 determines whether or not there is an in-focus position that has not yet been processed. If it is determined that there is an in-focus position that has not yet been processed, the selection unit 121 returns to step S62 and proceeds to the next step. The in-focus position is selected, and the processing after step S63 is similarly performed.

  If it is determined in step S69 that there is no unprocessed in-focus position, the process proceeds to step S70, and the calculation unit 125 obtains the largest coherence value from among the coherence maximum values corresponding to each in-focus position.

In step S71, the calculation unit 125 calculates the frequency γ corresponding to the largest coherence maximum value (acquires the frequency γ of the zone plate 15a from which the maximum value was obtained), and in step S72, corresponds to the frequency γ. The height h to be calculated is calculated (h = γλf ² ).

  In step S73, it is determined whether or not there is a pixel that has not yet been processed. If it is determined that there is a pixel that has not yet been processed, the process returns to step S61 to select the next pixel, and step S62. Subsequent processing is similarly performed.

  If it is determined in step S73 that there is no unprocessed pixel, the process proceeds to step S74, and the calculation unit 125 calculates the shape of the measured object 25 based on the height of each pixel calculated in step S72.

  In step S75, the display unit 116 displays an image corresponding to the shape calculated in step S74 as a measurement image.

  As described above, the height (shape) of each part of the surface of the measured object 25 is measured.

  For example, within a predetermined depth of field, as shown in FIG. 30, a point pi having a height hi at which the interference intensity Iint changes to the maximum at the frequency γ1, and a height hk at which the interference intensity int changes to the maximum at the frequency γ2. When the point pk exists, the pixel corresponding to the point pi can obtain a spectrum distribution having the maximum amplitude when scanning with the zone plate 15a-i having the frequency γ1, so that the height of the point pi from the frequency γ1 is obtained. Can be calculated. Also, since the spectrum corresponding to the maximum amplitude is obtained from the pixel corresponding to the point pk when scanning with the zone plate 15a-k having the frequency γ2, the height of the point pk can be calculated from the frequency γ2.

  In this example, since the depth of field is scanned by the focus scanning, a coherence distribution is obtained by scanning both the focus and the frequency γ of the zone plate 15a as shown in FIG. The appearing location shows the actual height of the object surface. That is, in the example of FIG. 31A, the height of the object surface is obtained from the frequency γ1, and in the example of FIG. 31B, the height of the object surface is obtained from the frequency γk.

  As described above, the phase of the zone plate 15a is defined by the frequency γ (equation (4)), and the scanning by the phase shift is automatically performed, so that the measurement process can be performed quickly. That is, in the present invention, the number of scans (number of zone plates) is only the number (M) of frequencies γ, and therefore N = 3 at least as compared with the conventional case (FIG. 1) (M × N). Then, the data amount can be reduced to 1/3 or less.

  In the present specification, the step of describing the program provided by the recording medium is not limited to the processing performed in chronological order according to the described order, but is not necessarily performed in chronological order. It also includes processes that are executed individually.

It is a figure explaining the conventional height measuring method. It is a block diagram which shows the structural example of the measuring apparatus 10 to which this invention is applied. 4 is a block diagram illustrating a configuration example of a zone plate generation unit 61. FIG. 3 is a block diagram illustrating a configuration example of a measurement processing unit 101. FIG. It is a figure explaining incident angle (theta). It is another figure explaining incident angle (theta). It is a figure which shows the example of light source intensity Is. It is a figure which shows the example of detection intensity Idet. It is a figure which shows the other example of detection intensity Idet. It is a figure which shows the example of height detection. It is a flowchart explaining a zone plate production | generation process. It is a figure which shows the other example of height detection. It is a figure which shows the other example of height detection. It is a figure explaining a phase shift. It is a figure which shows the other example of height detection. It is another figure explaining a phase shift. It is a figure which shows the other example of height detection. It is a figure explaining the amplitude of a carrier. It is a figure which shows a Fourier-transform result. It is a figure which shows another Fourier-transform result. It is a figure which shows another Fourier-transform result. It is a flowchart explaining a height measurement process. It is another flowchart explaining a height measurement process. It is a figure explaining focus scanning. It is another figure explaining focus scanning. It is a figure explaining depth of field. It is a figure explaining height measurement processing. It is another figure explaining depth of field. It is another figure explaining a height measurement process. It is another figure explaining a height measurement process. It is another figure explaining a height measurement process.

Explanation of symbols

  11 laser, 12 beam expander, 13, 17, 19, 22 lens, 14, 16 polarizing plate, 15 spatial light modulator (SLM), 15a zone plate 18 pinhole, 20 diffuser plate, 21 motor, 23 beam splitter, 24 reference plane, 25 object to be measured, 26 imaging lens, 27 driving device, 28 detector, 29 detector driver, 30 personal computer, 31 SLM control driver, 41 zone plate

Claims (4)

In a measuring apparatus that measures the height of an object to be measured by adjusting the intensity of the light source to a value corresponding to the incident angle by the zone plate-shaped light intensity distribution formed based on the zone plate,
After the in-focus position of the observation system is set to the first reference position of the measurement range, it is sequentially moved by an amount corresponding to the depth of field of the lens of the observation system until it reaches the second reference position of the measurement range. Setting means to
Selection means for sequentially selecting the zone plates of a predetermined frequency at each of the in-focus positions;
Measuring means for irradiating the object to be measured with light whose intensity is adjusted to a value corresponding to an incident angle using the selected zone plate, and measuring the detected intensity;
Using each of the zone plates sequentially selected by the selection means, based on the detection intensity respectively measured by the measurement means, obtain a distribution of coherence obtained by dividing the amplitude by the average value, A calculation means for calculating the height of the object to be measured based on the frequency of the zone plate from which the maximum value of the coherence was obtained;
It said selection means, initial phase, 2 [pi is a constant representing the one period, the frequency of the carrier signal is detected as the detected intensity, and the so defined that is determined based on the product of the frequency of the zone plate The zone plate is selected. Fourier transform means for Fourier transforming the detected intensity;
Extraction means for extracting a zeroth-order spectrum and a −1st-order or + 1st-order spectrum from a spectrum obtained by Fourier transform;
An inverse Fourier transform means for performing an inverse Fourier transform on the extracted 0th order spectrum and −1st order or + 1st order spectrum;
Further comprising
The computing means is
By dividing the value obtained by inverse Fourier transform of the −1st order or + 1st order spectrum by the value obtained by inverse Fourier transform of the 0th order spectrum, the distribution of the coherence is obtained, The measuring apparatus according to claim 1, wherein the height of the object to be measured is calculated based on the frequency of the zone plate from which the maximum value is obtained. In the measuring method of the measuring device for measuring the height of the object to be measured by adjusting the intensity of the light source to a value corresponding to the incident angle by the zone plate-shaped light intensity distribution formed based on the zone plate,
After the in-focus position of the observation system is set to the first reference position of the measurement range, it is sequentially moved by an amount corresponding to the depth of field of the lens of the observation system until it reaches the second reference position of the measurement range. A setting step to
A selection step of sequentially selecting the zone plates of a predetermined frequency at each of the in-focus positions;
A measurement step of irradiating the object to be measured with light whose intensity is adjusted to a value according to an incident angle using the selected zone plate, and measuring the detected intensity;
Using each of the zone plates sequentially selected by the process of the selection step, the coherence obtained by dividing the amplitude by the average value based on the detected intensity respectively measured by the process of the measurement step. Calculating a distribution and calculating a height of the object to be measured based on the frequency of the zone plate from which the maximum value of the coherence is obtained, and
The process of selection steps, initial phase, defined as determined based on 2π is a constant representing one period, the frequency of the carrier signal is detected as the detected intensity, and the product of the frequency of the zone plate A measuring method comprising: selecting the zone plate that is provided. In the program of the measuring apparatus for measuring the height of the object to be measured by adjusting the intensity of the light source to a value corresponding to the incident angle by the zone plate-shaped light intensity distribution formed based on the zone plate,
After the in-focus position of the observation system is set to the first reference position of the measurement range, it is sequentially moved by an amount corresponding to the depth of field of the lens of the observation system until it reaches the second reference position of the measurement range. A setting step to
A selection step of sequentially selecting the zone plates of a predetermined frequency at each of the in-focus positions;
A measurement step of irradiating the object to be measured with light whose intensity is adjusted to a value according to an incident angle using the selected zone plate, and measuring the detected intensity;
Using each of the zone plates sequentially selected by the process of the selection step, the coherence obtained by dividing the amplitude by the average value based on the detected intensity respectively measured by the process of the measurement step. Calculating a distribution and calculating a height of the object to be measured based on the frequency of the zone plate from which the maximum value of the coherence is obtained, and
The process of selection steps, initial phase, defined as determined based on 2π is a constant representing one period, the frequency of the carrier signal is detected as the detected intensity, and the product of the frequency of the zone plate A program for causing a computer to execute a control process of selecting the zone plate being performed.

Images