CN103791853A - Microstructure measuring device and measuring method based on color strip information processing - Google Patents

Abstract

Provided are a microstructure measuring device and measuring method based on color strip information processing. The system is provided with a Zeiss optical microscope and an input light source halogen lamp, a scanning mechanism connected with a computer is arranged at the sample scanning end of the Zeiss optical microscope, a CCD color camera and an image collecting card connected with the CCD color camera are arranged at the signal collecting end of the Zeiss optical microscope in sequence, and the image collecting card is further connected with the computer. The method comprises the steps of carrying out bayer inverse transformation on a set of original images collected by the CCD color camera, obtaining the light intensity values of different scanning positions R, G and B, calculating the phase position information of channels R, G and B, determining the position of a zero optical path difference, obtaining height information corresponding to pixel points, obtaining height information corresponding to different pixel points, and finally obtaining the surface appearance of an object. The CCD color camera is used for collecting fringe images with white light, the influence of environment noise can be effectively reduced, and measurement precision is improved.

Description

Microstructure measuring system and measuring method based on color fringe information processing

Technical field

The present invention relates to a kind of microstructure measuring system.Particularly relate to microstructure measuring system and measuring method based on color fringe information processing that a kind of CCD of use color camera gathers white-light fringe image.

Background technology

In field of micro-Na manufacture, reliability and the quality influence of the surface topography of micro-nano device to system is remarkable.For example, the electromechanical properties such as capacitance that the surface topography of MEMS capacitor two parallel plate electrodes can appreciable impact capacitor, magnitude of voltage, Electric Field Distribution, and then have influence on performance and the yield rate of MEMS capacitor element.In addition, the surface topography of micro-nano device can reflect the technological parameter in process, is the important evidence that process is monitored, diagnosed.Thereby the precision measurement of Microstructures Topography is significant.

In micro-nano field tests, white light interferometric technology is a kind of important contactless measurement.In test process, this technology does not form the damage to testee surface, also has advantages of that measurement range is large, measuring accuracy is high.Mainly be divided into two kinds for the algorithm of white light interference signal processing: a kind of is by the light distribution of analysis white light interference signal, obtains the pattern of testee, and main algorithm has gravity model appoach, polynomial fitting method etc.; Another kind is the pattern that obtains object by the phase information of white light interference signal, and main algorithm has Fourier transform, Wavelet Transform etc.

In the process of collection white-light fringe, normally used is CCD black and white camera, is three-dimensional and utilize CCD color camera can make the image information of obtaining by two-dimensional expansion, i.e. the information of R, G, tri-passages of B.

e.

utilize 3-CCD color camera to obtain white light interference image Deng people, but due to the interference signal blue wave band spectral energy gathering a little less than, so only used the information analysis of R, two passages of G to obtain the pattern of testee; The methods of people based on windowing Fourier transform such as Suodong Ma, analyze by the image of the R to the collection of 3-CCD color camera, G, tri-passages of B, have obtained the pattern of testee; Compared to the 3-CCD color camera of realizing coloured image by prismatic decomposition and obtaining, the method cost that single CCD color camera obtains coloured image by Baeyer (Bayer) filtering is more cheap, the people such as Zden ě k Buchta based on experimental verification use single CCD color camera to gather white light interference image, and then analyze the feasibility that obtains object dimensional pattern.

Summary of the invention

Technical matters to be solved by this invention is that a kind of microstructure measuring system and measuring method based on color fringe information processing that can effectively reduce Environmental Noise Influence, improve measuring accuracy is provided.

The technical solution adopted in the present invention is: a kind of microstructure measuring system based on color fringe information processing, include Zeiss optical microscope, the light source input end of Zeiss optical microscope is provided with Halogen lamp LED, the Sample Scan end of Zeiss optical microscope is provided with for sample is carried out to vertical scanning, and the scanning mechanism being connected with computing machine, the signals collecting end of Zeiss optical microscope is disposed with CCD color camera and the image pick-up card being connected with CCD color camera, and described image pick-up card also connects computing machine.

Between described Zeiss optical microscope and described Halogen lamp LED, be provided with the white balance optical filter for reducing the light transmission of wave band beyond blue wave band.

Include and the object lens nanometer positioning device and the piezo controller being connected with described object lens nanometer positioning device of the corresponding setting of Sample Scan end of described Zeiss optical microscope at described scanning mechanism, described piezo controller connects computing machine by RS232, described object lens nanometer positioning device is connected on Mirau type interference objective, described Mirau type interference objective and the corresponding setting of sample being arranged on experiment table.

Measuring method for the microstructure measuring system based on color fringe information processing of the present invention, comprises the steps:

1) one group of original image of CCD color camera collection is carried out to Baeyer inverse transformation, obtain real color image information;

2) extract respectively R, the G and the B passage intensity signal that are converted the arbitrary pixel of coloured image obtaining by step 1), and then obtain the light intensity value of different scanning position R, G, B;

3) selecting the Morlet small echo female small echo as wavelet transformation, to step 2) R, the G obtaining, the light intensity value of B passage do One Dimension Continuous Wavelet Transform, utilizes transformation results to calculate the phase information of R, G, B passage;

4) R, G step 3) being obtained, the phase information of B passage, based on the evaluation function of structure

the preliminary position of determining zero optical path difference;

5) choose the phase information of near R, G zero optical path difference, B passage, the phase information of described R, G, B passage is done to least square fitting and obtain zero optical path difference position optimal estimation value, accurately determine the position of zero optical path difference;

6) the zero optical path difference position optimal estimation value of utilizing step 5) to obtain, obtains step 2) elevation information that described pixel is corresponding;

7) other pixel that step 1) is converted to the coloured image obtaining is done and step 2 respectively) to the identical processing of step 6), put corresponding elevation information thereby obtain different pixels, finally obtain the surface topography of object.

Step 2) described R, the G of arbitrary pixel and the light intensity value of B be to be obtained by following formula:

$I_m\left(z\right)=I_{0m}+{\mathrm{\γ}}_m{I}_{0m}g(z-z_0)\cos \left[\frac{4\mathrm{\π}(z-z_0)}{{\mathrm{\λ}}_{\mathrm{cm}}}\right]---\left(1\right)$

Wherein, m is expressed as R, G, B, represents R, G, the B passage of CCD color camera; I _0mrepresent background light intensity; γ _mrepresent fringe visibility; λ _cmrepresent the centre wavelength of light source in respective channel; Z represents the position of object lens nanometer positioning device vertical scanning, and in the time that the two light beam light path differences that interfere are zero, the positional representation at object lens nanometer positioning device place is z ₀, referred to as zero optical path difference position; G (z _m-z ₀) be relevant envelope item.

Described relevant envelope item is expressed as

$g(z-z_0)=\exp [-{\left(\frac{z-z_0}{l_{\mathrm{cm}}}\right)}^2]---\left(2\right)$

Wherein, l _cmrepresent the coherent length of light source in respective channel.

R, G described in step 3), B channel phases information are to obtain by following three steps:

The first step, selects the female small echo of Morlet small echo as wavelet transformation,

Second step, to I _m(z) carrying out One Dimension Continuous Wavelet Transform obtains:

$W_m(a,b)={\∫}_{-\∞}^{+\∞}{I}_m\left(z\right){\mathrm{\ψ}}_{\mathrm{ab}}^{*}\left(z\right)\mathrm{dz}---\left(3\right)$

Wherein, female small echo that ψ (z) is wavelet transformation, a, b represents respectively scale factor and the shift factor of wavelet transformation, ${\mathrm{\ψ}}_{\mathrm{ab}}\left(z\right)=\frac{1}{\sqrt{a}}\mathrm{\ψ}\left(\frac{z-b}{a}\right),$ * be conjugate operation symbol;

The 3rd step, R, G, B channel phases information

pass through W _mthe argument of (a, b)

Obtain, wherein, a ₀, b ₀for W _mcorresponding scale factor and shift factor when the mould value of (a, b) is maximum, Re[W _m(a ₀, b ₀)] and Im[W _m(a ₀, b ₀)] represent respectively W _m(a ₀, b ₀) real part and imaginary part.

Described in step 6), utilize zero optical path difference position optimal estimation value, obtain step 2) elevation information H that described pixel is corresponding is to obtain by following formula:

H=H′+z ₀ (5)

Wherein, H '=N Δ, Δ represents sweep span, N is scanning step number corresponding to sampling light intensity maximum value position, z ₀for the optimal estimation value of zero optical path difference position.

Microstructure measuring system and measuring method based on color fringe information processing of the present invention, use CCD color camera to gather white-light fringe image, compared with using traditionally gray level image measurement object appearance, can effectively reduce the impact of neighbourhood noise, improve measuring accuracy.

Accompanying drawing explanation

Fig. 1 is the one-piece construction schematic diagram of microstructure measuring system of the present invention;

Fig. 2 a does not use white balance optical filter, the relative intensity schematic diagram of R, G, B light intensity;

Fig. 2 b uses white balance optical filter, the relative intensity schematic diagram of R, G, B light intensity;

Fig. 3 is the process flow diagram of the inventive method;

Fig. 4 a is the R passage surface of intensity distribution of certain pixel;

Fig. 4 b is the G passage surface of intensity distribution of certain pixel;

Fig. 4 c is the B passage surface of intensity distribution of certain pixel;

Fig. 5 is near R, G, the B channel phases distribution plan of certain pixel zero light path position;

Fig. 6 is evaluation function schematic diagram.

In figure

Embodiment

Below in conjunction with embodiment and accompanying drawing, microstructure measuring system and the measuring method based on color fringe information processing of the present invention is described in detail.

As shown in Figure 1, microstructure measuring system based on color fringe information processing, include Zeiss optical microscope 2, the light source input end of Zeiss optical microscope 2 is provided with the Halogen lamp LED 1 with wide spectral characteristic, the Sample Scan end of Zeiss optical microscope 2 is provided with for sample 9 is carried out to vertical scanning, and the scanning mechanism being connected with computing machine 8, the signals collecting end of Zeiss optical microscope 2 is disposed with the CCD color camera 6 that the model of Basler company is avA1600-65kc, the PCI-1428 image pick-up card 7 of the NI company being connected with CCD color camera 6, realize the collection of image, described image pick-up card 7 also connects computing machine 8, can in computing machine, observe image.The software section that computing machine has comprised system, mainly comprises the collection that uses LabVIEW to realize image and uses MATLAB to realize the processing of data.Between described Zeiss optical microscope 2 and described Halogen lamp LED 1, be provided with the white balance optical filter 11 for reducing band of light transmissivity beyond blue wave band.

As shown in Fig. 2 a, Fig. 2 b, add a white balance optical filter at lighting source place, can play the effect that reduces its all band (except blue wave band) optical transmission rate.While not using white balance optical filter in Fig. 2 a, the light signal signal to noise ratio (S/N ratio) of blue wave band is very low; After using optical filter in Fig. 2 b, reflect the output intensity by increasing light source, light intensity green and blue wave band is enhanced, the light intensity of red wave band is attenuated, the signal to noise ratio (S/N ratio) of green and blue wave band spectrum is improved, simultaneously, CCD camera in saturated, has not improved the utilization factor of signal because of the increase of light source output intensity.

Described scanning mechanism includes and the object lens nanometer positioning device 4 of the corresponding setting of Zeiss optical microscope 2 Sample Scan end and the piezo controller 5 being connected with described object lens nanometer positioning device 4, the product that the model that described object lens nanometer positioning device 4 selects PI company to produce is PIP-721.CL, the product that the model that piezo controller 5 selects PI company to produce is E-509.C1A, described piezo controller 5 connects computing machine 8 by RS232, described object lens nanometer positioning device 4 is connected on Mirau type interference objective 3, described Mirau type interference objective 3 adopts the Mirau type interference objective of being produced by Nikon company, and (enlargement ratio is 10X, numerical aperture N.A. is 0.30), described interference objective 3 and the corresponding setting of sample 9 being arranged on experiment table 10.

As shown in Figure 3, microstructure measuring system and the measuring method based on color fringe information processing of the present invention, comprises the steps:

1) one group of original image of CCD color camera collection is carried out to Baeyer inverse transformation, obtain real color image information;

2) extract respectively that to convert the R(of the arbitrary pixel of coloured image obtaining by step 1) red), G(is green) and B(indigo plant) passage intensity signal, and then obtain the light intensity value of different scanning position R, G, B;

R, the G of described arbitrary pixel and the light intensity value of B are to be obtained by following formula:

$I_m\left(z\right)=I_{0m}+{\mathrm{\γ}}_m{I}_{0m}g(z-z_0)\cos \left[\frac{4\mathrm{\π}(z-z_0)}{{\mathrm{\λ}}_{\mathrm{cm}}}\right]---\left(1\right)$

Wherein, m is expressed as R, G, B, represents R, G, the B passage of CCD color camera; I _0mrepresent background light intensity, the DC component of reflection light intensity; γ _mrepresent fringe visibility; λ _cmrepresent the centre wavelength of light source in respective channel; Z represents the position of object lens nanometer positioning device vertical scanning, and in the time that the two light beam light path differences that interfere are zero, the positional representation at object lens nanometer positioning device place is z ₀, this position is referred to as zero optical path difference position; G (z _m-z ₀) be relevant envelope item, determined in the spectral signature of respective channel by light source.

The light source Halogen lamp LED using in experiment all presents at the spectrum of R, G, B passage the feature that Gauss (Gauss) distributes, thereby described relevant envelope item is expressed as

$g(z-z_0)=\exp [-{\left(\frac{z-z_0}{l_{\mathrm{cm}}}\right)}^2]---\left(2\right)$

Wherein, l _cmrepresent the coherent length of light source in respective channel, in R, G, B passage, only at zero optical path difference position z ₀near the distribution that just has interference fringe.

3) selecting the Morlet small echo female small echo as wavelet transformation, to step 2) R, the G obtaining, the light intensity value of B passage do One Dimension Continuous Wavelet Transform, utilizes transformation results to calculate the phase information of R, G, B passage;

Described R, G, B channel phases information are to obtain by following three steps:

The first step, selects the female small echo of Morlet small echo as wavelet transformation,

due to signal I _mpresent the feature of Gaussian distribution, and Morlet small echo is in fact formed by Gaussian function modulation, so select the female small echo of Morlet small echo as wavelet transformation.

Second step, to I _m(z) carrying out One Dimension Continuous Wavelet Transform obtains:

$W_m(a,b)={\∫}_{-\∞}^{+\∞}{I}_m\left(z\right){\mathrm{\ψ}}_{\mathrm{ab}}^{*}\left(z\right)\mathrm{dz}---\left(3\right)$

Wherein, female small echo that ψ (z) is wavelet transformation, a, b represents respectively scale factor and the shift factor of wavelet transformation, ${\mathrm{\ψ}}_{\mathrm{ab}}\left(z\right)=\frac{1}{\sqrt{a}}\mathrm{\ψ}\left(\frac{z-b}{a}\right),$ * be conjugate operation symbol;

The 3rd step, R, G, B channel phases information

pass through W _mthe argument of (a, b)

Obtain, wherein, a ₀, b ₀for W _mcorresponding scale factor and shift factor when the mould value of (a, b) is maximum, Re[W _m(a ₀, b ₀)] and Im[W _m(a ₀, b ₀)] represent respectively W _m(a ₀, b ₀) real part and imaginary part, as shown in Figure 5.By to I _m(z) carry out the W that One Dimension Continuous Wavelet Transform obtains _m(a, b) reflected ψ _abwith I _mdegree of correlation.The variation of scale factor a has reflected signal I _mthe variation of frequency, the variation of shift factor b has reflected signal I _mthe variation of displacement, by the continuous variation of scale factor a and shift factor b, can try to achieve at different frequency and displacement place ψ _abwith I _mthe size of degree of correlation.At a certain scanning position place, work as ψ _aband I (z) _m(z) degree of correlation is the highest, i.e. W _mwhen the mould value of (a, b) is maximum, W _mthe argument of (a, b) is the I of this scanning position place _m(z) phase value.

4) R, G step 3) being obtained, the phase information of B passage, the evaluation function of the structure based on as shown in Figure 6

the preliminary position of determining zero optical path difference, now evaluation function has minimum value in zero optical path difference position;

5) choose the phase information of near R, G zero optical path difference, B passage, the phase information of described R, G, B passage is done to least square fitting and obtain zero optical path difference position optimal estimation value, accurately determine the position of zero optical path difference.

In actual measurement process, measuring error makes the zero optical path difference position of R, G, B not at same position place, for obtaining the optimal estimation value of zero optical path difference position, uses least square method to determine.

The phase information of R, G, B passage can be expressed as

wherein, A _m=4 π/λ _cm, B _m=-4 π z ₀/ λ _cm.According to principle of least square method, zero optical path difference position z ₀optimal estimation value can be

while having minimum value, try to achieve, now need to satisfy condition

Can obtain zero optical path difference position z ₀optimal estimation value be

${\mathrm{<figure-callout\; id="0"\; label="z"\; filenames="HDA0000459050710000012.png,HDA0000459050710000021.png"\; state="\{\{state\}\}">z</figure-callout>}}_0=-\frac{A_R{B}_R+A_G{B}_G+A_B{B}_B}{A_{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HDA0000459050710000042.png,HDA0000459050710000051.png"\; state="\{\{state\}\}">R</figure-callout>}}^2+A_{\mathrm{<figure-callout\; id="2"\; label="G"\; filenames="HDA0000459050710000042.png,HDA0000459050710000051.png"\; state="\{\{state\}\}">G</figure-callout>}}^2+A_B^2}---\left(6\right)$

Determine A _m, B _mmethod as follows: first tentatively determine the position of zero optical path difference by evaluation function EF, and then to the sampled point in zero order fringe

analyze.Sampled point

meet funtcional relationship

According to principle of least square method, the A in formula (7) _m, B _mrelational expression meets the following conditions:

Can obtain

Can try to achieve A _m, B _mnumerical value, and then try to achieve zero optical path difference position z ₀optimal estimation value.Optimal estimation value z ₀be confined in zero order fringe, its essence is the deviate of sampling light intensity maximum value position and zero optical path difference position.

6) the zero optical path difference position optimal estimation value of utilizing step 5) to obtain, obtains step 2) elevation information that described pixel is corresponding, described elevation information H obtains by following formula:

H=H′+z ₀ (10)

Wherein, H '=N Δ, Δ represents sweep span, N is scanning step number corresponding to sampling light intensity maximum value position, z ₀for the optimal estimation value of zero optical path difference position.

7) other pixel that step 1) is converted to the coloured image obtaining does and step 2 respectively) to the identical processing of step 6), put corresponding elevation information thereby obtain different pixels, finally obtain the surface topography of object.

The present invention utilizes single CCD color camera to gather the image of white light interference color fringe.In addition, be different from the method for windowed FFT, because the theory of wavelet transformation is ripe day by day, apply increasingly extensive, the present invention has selected continuous wavelet transform method to analyze the image information of R, G, tri-passages of B, thereby obtains physical dimension and the surface topography of testee.

Claims (8)

1. the microstructure measuring system based on color fringe information processing, include Zeiss optical microscope (2), it is characterized in that, the light source input end of Zeiss optical microscope (2) is provided with Halogen lamp LED (1), the Sample Scan end of Zeiss optical microscope (2) is provided with for sample (9) is carried out to vertical scanning, and the scanning mechanism being connected with computing machine (8), the signals collecting end of Zeiss optical microscope (2) is disposed with CCD color camera (6) and the image pick-up card (7) being connected with CCD color camera (6), described image pick-up card (7) also connects computing machine (8).

2. the microstructure measuring system based on color fringe information processing according to claim 1, it is characterized in that, between described Zeiss optical microscope (2) and described Halogen lamp LED (1), be provided with the white balance optical filter (11) for reducing the light transmission of wave band beyond blue wave band.

3. the microstructure measuring system based on color fringe information processing according to claim 1, it is characterized in that, include and the object lens nanometer positioning device (4) and the piezo controller (5) being connected with described object lens nanometer positioning device (4) of the corresponding setting of Sample Scan end of described Zeiss optical microscope (2) at described scanning mechanism, described piezo controller (5) connects computing machine (8) by RS232, described object lens nanometer positioning device (4) is connected on Mirau type interference objective (3), described Mirau type interference objective (3) and the corresponding setting of sample (9) being arranged on experiment table (10).

4. for a measuring method for the microstructure measuring system based on color fringe information processing described in claim 1～3 any one, it is characterized in that, comprise the steps:

1) one group of original image of CCD color camera collection is carried out to Baeyer inverse transformation, obtain real color image information;

2) extract respectively R, the G and the B passage intensity signal that are converted the arbitrary pixel of coloured image obtaining by step 1), and then obtain the light intensity value of different scanning position R, G, B;

3) selecting the Morlet small echo female small echo as wavelet transformation, to step 2) R, the G obtaining, the light intensity value of B passage do One Dimension Continuous Wavelet Transform, utilizes transformation results to calculate the phase information of R, G, B passage;

4) R, G step 3) being obtained, the phase information of B passage, based on the evaluation function of structure the preliminary position of determining zero optical path difference;

5) choose the phase information of near R, G zero optical path difference, B passage, the phase information of described R, G, B passage is done to least square fitting and obtain zero optical path difference position optimal estimation value, accurately determine the position of zero optical path difference;

6) the zero optical path difference position optimal estimation value of utilizing step 5) to obtain, obtains step 2) elevation information that described pixel is corresponding;

7) other pixel that step 1) is converted to the coloured image obtaining is done and step 2 respectively) to the identical processing of step 6), put corresponding elevation information thereby obtain different pixels, finally obtain the surface topography of object.

5. measuring method according to claim 4, is characterized in that step 2) described R, the G of arbitrary pixel and the light intensity value of B be to be obtained by following formula:

$I_m\left(z\right)=I_{0m}+{\mathrm{\&gamma;}}_m{I}_{0m}g(z-z_0)\cos \left[\frac{4\mathrm{\&pi;}(z-z_0)}{{\mathrm{\&lambda;}}_{\mathrm{cm}}}\right]---\left(1\right)$

Wherein, m is expressed as R, G, B, represents R, G, the B passage of CCD color camera; I _0mrepresent background light intensity; γ _mrepresent fringe visibility; λ _cmrepresent the centre wavelength of light source in respective channel; Z represents the position of object lens nanometer positioning device vertical scanning, and in the time that the two light beam light path differences that interfere are zero, the positional representation at object lens nanometer positioning device place is z ₀, referred to as zero optical path difference position; G (z _m-z ₀) be relevant envelope item.

6. measuring method according to claim 5, is characterized in that, described relevant envelope item is expressed as

$g(z-z_0)=\exp \left[{-\left(\frac{z-z_0}{l_{\mathrm{cm}}}\right)}^2\right]---\left(2\right)$

Wherein, l _cmrepresent the coherent length of light source in respective channel.

7. measuring method according to claim 4, is characterized in that, R, G, B channel phases information described in step 3) are to obtain by following three steps:

The first step, selects the female small echo of Morlet small echo as wavelet transformation,

Second step, to I _m(z) carrying out One Dimension Continuous Wavelet Transform obtains:

$W_m(a,b)={\&Integral;}_{-\&infin;}^{+\&infin;}{I}_m\left(z\right){\mathrm{\&psi;}}_{\mathrm{ab}}^{*}\left(z\right)\mathrm{dz}---\left(3\right)$

Wherein, female small echo that ψ (z) is wavelet transformation, a, b represents respectively scale factor and the shift factor of wavelet transformation, ${\mathrm{\&psi;}}_{\mathrm{ab}}\left(z\right)=\frac{1}{\sqrt{a}}\mathrm{\&psi;}\left(\frac{z-b}{a}\right),$ * be conjugate operation symbol;

The 3rd step, R, G, B channel phases information

pass through W _mthe argument of (a, b)

Obtain, wherein, a ₀, b ₀for W _mcorresponding scale factor and shift factor when the mould value of (a, b) is maximum, Re[W _m(a ₀, b ₀)] and Im[W _m(a ₀, b ₀)] represent respectively W _m(a ₀, b ₀) real part and imaginary part.

8. measuring method according to claim 4, is characterized in that, utilizes zero optical path difference position optimal estimation value described in step 6), obtains step 2) elevation information H that described pixel is corresponding is to obtain by following formula:

H=H′+z ₀ (5)

Wherein, H '=N Δ, Δ represents sweep span, N is scanning step number corresponding to sampling light intensity maximum value position, z ₀for the optimal estimation value of zero optical path difference position.

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