CN105865370A - White-light scanning interferometry measurement method and system - Google Patents

Abstract

The invention relates to a white-light scanning interferometry measurement method and system. The system comprises a white-light scanning module, a calibration module, a fixed flat plate and a piezoelectric ceramic micro displacement platform, wherein the white-light scanning module comprises a white light source, a Kohler illumination system, a first beam splitter, a second beam splitter, a first microobjective, a second microobjective, an imaging lens, first, second, third, fourth and fifth plane mirrors and a first single-color black-and-white image sensor; the calibration module comprises a laser and a second single-color black-and-white image sensor. According to the system and the method, the central wavelength of a light source is not required to be calibrated, the calculation accuracy is not affected by enveloping shapes of interference signals, the anti-noise performance is good, and the method and the system can be widely applied to signal processing of white-light scanning interferometry measurement.

Description

A kind of white light scanning interferometric method and system

Technical field

The present invention relates to white light scanning and interfere measuring three-dimensional morphology field, be specifically related to a kind of based on generalized correlation The white light scanning interferometric method of time delay estimation and system.

Background technology

White light scanning interferes the three-dimensional shaped being widely used in micro-object as a kind of 3 D measuring method Looks are measured and rough object surfaces degree is measured.Along with the development of sophisticated manufacturing, need some apparent heights are jumped Become and carry out measuring three-dimensional morphology from hundreds of nanometer to objects such as the MEMS of hundreds of micron, semiconductor chips. Currently used sonde-type measuring method such as atomic force microscope and step instrument all have some limitations, It is not suitable for the measuring three-dimensional morphology of this type objects.

Further, white light scanning interferometry technology compensate for phase hit between Single wavelength interferometry consecutive points The shortcoming that can not obtain correct result during more than measurement wavelength half, expands the range of Single wavelength interferometry. White light scanning interferometry technology not only have in Single wavelength interferometry to testee noncontact, not damaged, The advantage such as high-resolution, high accuracy, additionally it is possible to have interruption, graded relatively big (big exactly to surface itself In record light wave wavelength) object measure, as having step, the object of defective hole structure.White light is swept Retouch interferometry, in fields such as D surface contouring, automatically processing, industrial detection, control of product quality, there is weight Want meaning and wide application prospect.

White light scanning interferes use broad spectrum light source to be illuminated, and has shorter being concerned with for comparing monochromatic light Length, so that interference fringe can only appear in the least spatial dimension.When the light path measuring light and reference light When difference is zero, there is maximum in interference signal, also referred to as zero optical path difference position.This zero optical path difference position is just Representing the relative altitude information of measured surface corresponding data point, the relative altitude of all data points has been combined into survey Take temperature the overall pattern in face.In white light scanning interferometry, the method for zero optical path difference location positioning is a research Focus, has had a lot of method to be in succession suggested.The most commonly used method has the most several, it may be assumed that center of gravity Method, Fourier transformation method, Hilbert transform method, Fourier's frequency-domain analysis method, continuous wavelet becomes Change method and Light bulb phase-shift interfering method.Center of gravity method is by calculating the method positioned zero of white light interference signal center of gravity Optical path difference position, it calculates speed, but it can be only applied on symmetric form signal, and computational accuracy Affected by noise bigger.Fourier transformation method and Hilbert transform method by Fourier transformation or are wished You ask for white light interference signal envelope at Bert conversion, positioned zero optical path difference position by the way of the envelope extreme value of location Put.Although this two classes method can obtain envelope peak, but their noiseproof feature is more weak.Fourier's frequency domain Analysis method is carried out by the way of Fourier transformation extracts phase place by dialogue optical interference signals thus asks for zero light path Difference position, this algorithm computational accuracy is higher, however it is necessary that the centre wavelength of Calibrating source, and the process of calculating is multiple Miscellaneous.The method computational accuracy of continuous wavelet transform is high, and anti-noise ability is relatively strong, but the envelope shape to interference signal Shape there are certain requirements.Light bulb phase-shift interfering method have references to the operational approach of Single wavelength phase shift art, and this method is suitable for In processing the smoother object in surface, and bigger error can be brought when phase shift interval is chosen inaccurate.

Above-mentioned many white light scannings interfere zero optical path difference localization method all to there is respective limitation, have Certain scope of application.Therefore, design one is more accurate, more simply, extracts white light interference zero light faster The method of the position of path difference, builds the system that a kind of light path system is simple and direct, interferogram sampling operating process is easy, For reduce measurement system complexity, reduce measure and calculate the time, improve certainty of measurement, accelerate measure speed Degree is significantly.

Summary of the invention

In view of this, it is necessary to propose a kind of white light scanning interferometry side based on generalized correlation for time delay estimation Method and system.

A kind of white light scanning interferometer measuration system, including white light scanning module, scaling module, fixed flat planar, with And piezoelectric ceramics micro-displacement platform, described white light scanning module includes a white light source；One Kohler illumination system System；One the first beam splitter and second beam splitter, the light that described light source sends is after Kohler illumination system Enter the first beam splitter and be divided into object light and reference light；One the first microcobjective and a second micro-thing Mirror；First beam splitter is between described Kohler illumination system and the second microcobjective；Imaging len and first, Second, third, fourth, fifth plane mirror；One first monochromatic black white image sensor, described reference Light is incident on the first plane mirror by the first microcobjective, and described object light is entered by the second microcobjective Penetrate at object under test, again each via first, second microcobjective after object light and reference light reflection, and then converge Interfering after the first beam splitter, interference image is the first monochromatic black white image sensor via imaging len Gathered.Described scaling module includes a laser instrument；One second monochromatic black white image sensor.Described sharp The laser that light device sends incides the second beam splitter, by the second beam splitter via the 5th, after fourth plane reflecting mirror The laser of outgoing interferes via after the second plane mirror, the 3rd plane mirror, its interference bar produced Stricture of vagina is gathered by the second monochromatic black white image sensor；Described fixed flat planar is used for fixing object to be measured；Described pressure Electroceramics micro-displacement platform is used for driving object under test to be subjected to displacement.

A kind of white light scanning interferometric method, it uses above-mentioned white light scanning interferometer measuration system, described method Including: gather white light interference figure and laser interference figure that a series of object under test produces, use laser interference figure meter Calculate the stepping of piezoelectric ceramics micro-displacement platform, demarcate the scanning stepping that white light scanning is interfered；Choose white light interference A bit on figure, carries out Fourier transformation process to this light intensity signal；Filter window is set to described Fourier Frequency spectrum carries out spectral filtering；Calculate the light intensity signal of all pixels and selected pixel light intensity signal successively The relative displacement of zero optical path difference position；Calculate object under test apparent height.

Relative to prior art, described method and system, can by white light source during asking for signal time delay To regard a signal source as, corresponding different pixels point interference strength signal is considered as in space different receptor The homology signals with noise received, substitutes by calculating the process of interference strength signal time delay between pixel Each pixel interference strength signal individually carries out conversion process and asks for the process of zero optical path difference position, thus nothing Needing the centre wavelength of Calibrating source, and computational accuracy is not affected by the envelope shape of interference signal, noiseproof feature is strong, Can be widely applied in the signal processing of white light scanning interferometry.

Accompanying drawing explanation

In order to be illustrated more clearly that technical scheme, below by embodiment required use attached Figure is briefly described, it should be apparent that, the accompanying drawing in describing below is only some embodiments of the present invention, For those of ordinary skill in the art, on the premise of not paying creative work, it is also possible to according to these Accompanying drawing obtains other accompanying drawing.

The white light scanning based on generalized correlation for time delay estimation that Fig. 1 provides for first embodiment of the invention interferes survey The structural representation of amount system.

The schematic flow sheet of the white light scanning interferometric method that Fig. 2 provides for second embodiment of the invention.

Detailed description of the invention

Below in conjunction with the accompanying drawing in the embodiment of the present invention, the technical scheme in the embodiment of the present invention is carried out clearly Chu, it is fully described by.

First embodiment

As it is shown in figure 1, the white light scanning interferometer measuration system 500 that first embodiment of the invention provides includes white Photoscanning module 100, scaling module 200, for fix the fixed flat planar 40 of object 30 to be measured, piezoelectricity pottery Porcelain micro-displacement platform 50 and piezoelectric ceramics controller 60.

Wherein said white light scanning module 100 includes: 101, Kohler illumination system of a white light source 102, first beam splitter 103 and 104, first microcobjective 105 and of second beam splitter Individual second microcobjective 106, the monochromatic black white image sensor 108 of imaging len 107, first.

Wherein said scaling module 200 includes a laser instrument 201；First plane mirror 202, second is flat Face reflecting mirror the 203, the 3rd plane mirror 204, fourth plane reflecting mirror the 205, the 5th plane mirror 206, Second monochromatic black white image sensor 208.

In Z-direction (first direction), described first beam splitter 103 is positioned at described Kohler illumination system 102 and second between microcobjective 106；In Y direction (second direction, Y-axis is perpendicular to Z axis), Described first beam splitter 103 is between described imaging len 107 and the first microcobjective 105.

It addition, in the Z-axis direction, described second microcobjective the 106, the 3rd plane mirror 204, fixing Flat board 40 (and object to be measured 30) and piezoelectric ceramics micro-displacement platform 50 be positioned at the first beam splitter 103 and Between second beam splitter 104.

In the present embodiment, described white light source 101 is a halogen tungsten lamp white light source.Described laser instrument 201 Be wavelength be the He-Ne laser instrument of 632.8nm.

During work, the light that described halogen tungsten lamp white light source 101 sends enters after Kohler illumination system 102 collimates It is incident upon the first beam splitter 103, is divided into reference light L1 and object light L2.

Described reference light L1 is incident on the first plane mirror 202 by the first microcobjective 105, described Object light L2 is incident on object under test 30, object light L2 and reference light L1 reflection by the second microcobjective 106 After again each via first, second microcobjective 105,106, and then gather after the first beam splitter 103 occur Interfering, interference image is gathered by the first monochromatic black white image sensor 108 via imaging len 107.

In the present embodiment, described object under test 30 and the second plane mirror 203 are by fixed flat planar 40 Fixing, specifically object under test 30 and the second plane mirror 203 lays respectively at described fixed flat planar 40 Both sides.During use, adjust object under test 30 and make it have identical vertical sweep with the second plane mirror 203 Retouch displacement.

In the present embodiment, in addition to the side that the second plane mirror 203 is positioned at the second beam splitter 104, The other both sides of the second beam splitter 104, are respectively provided with the 3rd plane mirror 204, fourth plane reflecting mirror 205。

The laser that He-Ne laser instrument 201 sends is incident via the 5th, after fourth plane reflecting mirror 206,205 To the second beam splitter 104, by the laser of the second beam splitter 104 outgoing via the second plane mirror 203, Interfering after three plane mirrors 204, its interference fringe produced is by the second monochromatic black white image sensor 208 are gathered.

In the present embodiment, first, second beam splitter 103,104 is the beam splitter that two parameters are the same；The The enlargement ratio of one microcobjective 105 and the second microcobjective 106 is 10, and numerical aperture is 0.25.

First monochromatic black white image sensor 108 and the second monochromatic black white image sensor 208 are two specifications Identical imageing sensor.

It addition, object under test 14 specifically uses the OA that MEMSCAP company produces in the present embodiment MEM103 type MEMS.

During use, in white light scanning optical interference circuit, piezoelectric ceramics micro-displacement platform 50 drive object under test 30, it is achieved measure the scanning of object under test 30 vertical direction.Point from Measuring Object 30 surface differing heights The light of reflection is reaching interference zero optical path difference position the most in the same time with reference light.

Thus, measure object under test 30 apparent height to determine, if to realize by extracting zero optical path difference position The accurate measurement of measuring targets 30 height, it is necessary to the displacement of piezoelectric ceramics micro-displacement platform 50 is entered Row Accurate Calibration, in the present invention use laser interference demarcate method, by the second plane mirror 203 with treat Survey object 30 to be fixed by fixed flat planar 40, under the driving of piezoelectric ceramics micro-displacement platform 50, determinand Body 30 and the second plane mirror 203 have identical vertical scanning displacement, only need to measure the second plane reflection The vertical scanning displacement of mirror 203, the vertical scanning displacement of the most available corresponding object under test 30.

During reality is measured, piezoelectric ceramics micro-displacement platform 50 is (by piezoelectric ceramics Micro displacement controller 60 Controlled) often move once, the first black white image sensor 108 and the second black white image sensor 208 meeting Respectively adopting piece image, the first black white image sensor 108 collects the white light comprising object under test 30 information Interference fringe, the second black white image sensor 208 collects laser interferencefringes.Extracted by phase-shift phase and calculate Method, the interference fringe collecting the second black white image sensor 208 carries out calculating and can obtain micrometric displacement and sweep Retouch platform and often move the interference fringe phase-shift phase once produced, thus calculate the displacement of correspondence.Use this side Method can realize the Accurate Calibration to piezoelectric ceramics micrometric displacement scan table displacement.

And the white light interference image that the first black white image sensor 108 is collected, choose in interferogram One pixel, extracts the light intensity function of this pixel, successively by the light intensity letter of all pixels on interferogram Number all light intensity functions with selected pixels point calculate displacement difference by Generalized Correlation Algorithm for Time Delay Estimation, permissible Obtain relative displacement between each pixel and selected pixel zero optical path difference position, thus obtain object under test Height, implement and will be described in detail in a second embodiment.

Second embodiment

Please also refer to Fig. 2, will will be in conjunction with the accompanying drawings and embodiments to based on correlated time delay in conjunction with the present embodiment The white light scanning interferometric method estimated is described further, and it uses first embodiment institute in the method The white light scanning interferometer measuration system 500 stated measures, and comprises the steps of S101 S106.

Step S101, the white light interference figure gathering the generation of a series of object under test and laser interference figure, use sharp Optical interference calculates the stepping of piezoelectric ceramics micro-displacement platform 50, the scanning stepping that demarcation white light scanning is interfered:

When specifically measuring, computer is used to drive the first monochromatic black white image sensor 108 and the second monochromatic black and white Imageing sensor 208 gathers a series of white light interference figure comprising object under test 30 information and laser interference simultaneously Figure.

Phase-shift phase extraction algorithm is used (to see document " Two step demodulation algorithm based on the orthogonality of diamond diagonal vectors》Applied Physics B 119:387–391 (2015)), laser interference figure is calculated, obtain object under test 30 piezoelectric ceramics micro-displacement platform 50 every The mobile interference fringe phase-shift phase once produced, thus demarcate the scanning stepping that white light scanning is interfered.

Step S102, a bit chosen on white light interference figure, carried out at Fourier transformation this light intensity signal Reason:

Such as, selected pixels point (x₀,y₀) light intensity signal I (x₀,y₀, z) can be expressed as:

$I(x_0,y_0,z)=a(x_0,y_0)+b(x_0,y_0)g\[z-h(x_0,y_0)\]cos\{\frac{4\mathrm{\π}}{{\mathrm{\λ}}_0}\[z-h(x_0,y_0)\]\}+\mathrm{\η}---\left(1\right)$

Wherein, (x₀,y₀) representing single pixel coordinate in interferogram, z is that micro positioner is along optical axis Scan position, h (x₀,y₀) represent Measuring Object apparent height distribution, a (x₀,y₀) it is background intensity, b(x₀,y₀) it is modulation amplitude, g [z-h (x₀,y₀)] it is the envelope function of interference signal.λ₀Middle cardiac wave for light source Long, η is the random noise in experiment.Here ignore the impact of additional phase delay.

Light intensity signal represented by formula (1) is carried out Fourier transformation obtain:

In formula, G (x₀,y₀,f_z) it is the Fourier transformation frequency spectrum of g (z).

Step S103, filter window is set the Fourier spectrum in step S102 is carried out spectral filtering.

Specifically, arrange the filter window H (f being led to rectangular filter window combination by two center band_z), filter Except background item frequency spectrum in (2) formula, eliminating partial noise, this process can be expressed as:

Step S104, extract the light intensity signal of all pixels and carry out converting Filtering Processing.

In the present embodiment, all pixels (x, light intensity signal y) is illustrated as:

$I(x,y,z)=a(x,y)+b(x,y)g\[z-h(x,y)\]cos\{\frac{4\mathrm{\π}}{{\mathrm{\λ}}_0}\[z-h(x,y)\]\}+\mathrm{\η}---\left(4\right)$

Light intensity signal represented by formula (4) is carried out Fourier transformation obtain:

Filtered window H (f_zResult after) is:

Step S105, calculate the light intensity signal of all pixels and zero light of selected pixel light intensity signal successively The relative displacement of path difference position:

(3) formula and (6) formula are proceeded as follows:

Wherein * represents complex conjugate.To C (f_z) carry out inverse Fourier transform, obtain:

From the principle of generalized correlation for time delay estimation, whenWhen obtaining maximum, nowIt is (x, y) pixel and (x₀,y₀) the zero optical path difference position relative displacement Δ h of pixel.And (8) formula obtains maximum The reason that can obtain zero optical path difference position relative displacement Δ h is as follows:

$\begin{array}{c}R\left(z_{f_z}\right)\≈\{b(x_0,y_0)g\[z-h(x_0,y_0)\]\cos \{\frac{4\mathrm{\π}}{{\mathrm{\λ}}_0}\[z-h(x_0,y_0)\]\left\}\right\}\⊗\\ \{b(x,y)g\[-z-h(x,y)\]\cos \{\frac{4\mathrm{\π}}{{\mathrm{\λ}}_0}\[-z-h(x,y)\]\left\}\right\}\end{array}---\left(9\right)$

In formula,Represent convolution.By formula (8), we can beIt is expressed as:

$\begin{array}{c}R\left(z_{f_z}\right)\≈b(x_0,y_0)b(x,y){\∫}_{-\mathrm{\∞}}^{+\mathrm{\∞}}g\[z-h(x_0,y_0)\]\cos \{\frac{4\mathrm{\π}}{{\mathrm{\λ}}_0}\[z-h(x_0,y_0)\]\}\×\\ g\[z_{f_z}+z-h(x,y)\]\cos \{\frac{4\mathrm{\π}}{{\mathrm{\λ}}_0}\[z_{f_z}+z-h(x,y)\]\}dz\end{array}---\left(10\right)$

If Δ h=h is (x, y)-h (x₀,y₀) it is (x, y) pixel and (x₀,y₀) the zero optical path difference position phase of pixel To displacement, then (10) formula can be expressed as:

$\begin{array}{c}R\left(z_{f_z}\right)\≈b(x_0,y_0)b(x,y){\∫}_{-\mathrm{\∞}}^{+\mathrm{\∞}}g\[z-h(x_0,y_0)\]\cos \{\frac{4\mathrm{\π}}{{\mathrm{\λ}}_0}\[z-h(x_0,y_0)\]\}\×\\ g\[z-h(x_0,y_0)+(z_{f_z}-\mathrm{\Δ}h)\]\cos \{\frac{4\mathrm{\π}}{{\mathrm{\λ}}_0}\[z-h(x_0,y_0)+(z_{f_z}-\mathrm{\Δ}h)\]\}dz\end{array}---\left(11\right)$

From (11), formula can draw, whenTime,Obtain maximum.

Step S106, calculating object under test apparent height:

Calculate the relative displacement of all pixels and the zero optical path difference position of selected pixels point successively, be i.e. equivalent to Calculate the apparent height of object under test.

So far, the method and system 500 proposed by the present invention, can be from a series of white light interferences collected In figure, recover the three-dimensional appearance of object under test.

In sum, described method and system 500 are during asking for signal time delay, by white light source 101 Regarding a signal source as, corresponding different pixels point interference strength signal is considered as in space different receptor and connects The homology signals with noise received, substitutes often by calculating the process of interference strength signal time delay between pixel Individual pixel interference strength signal individually carries out conversion process and asks for the process of zero optical path difference position, thus without Demarcate the centre wavelength of white light source 101, and computational accuracy is not affected by the envelope shape of interference signal, anti- Performance of making an uproar is strong, can be widely applied in the signal processing of white light scanning interferometry.

Compared with prior art, present invention have the advantage that

(1) for Single wavelength measuring method, the method that the present invention provides can realize graded The measurement of larger object, considerably increases measurement scope, has expanded the application of interferometry.

(2) zero optical path difference location algorithm is interfered to need the light intensity to single pixel relative to other white light scannings Signal carries out conversion process, and zero optical path difference position extraction process is converted to by extensively by the method that the present invention proposes Justice Time Delay Estimation Based asks for the interference signal relative displacement problem between different pixels.It addition, the present invention The method proposed is simple to operate, and computational accuracy is high, and noise robustness is strong, it is not necessary to the centre wavelength of Calibrating source, And the envelope shape no requirement (NR) of dialogue optical interference signals.

(3) system 500 that the inventive method uses is simple, to piezoelectricity by the way of Single wavelength laser phase shift The scanning stepping of pottery micro-displacement platform is demarcated, and this mode carries out stepping demarcation than by electricity feedback Method more accurate.

The above is the preferred embodiment of the present invention, it is noted that for the ordinary skill of the art For personnel, under the premise without departing from the principles of the invention, it is also possible to make some improvements and modifications, these change Enter and retouching is also considered as protection scope of the present invention.

Claims (7)

1. a white light scanning interferometer measuration system, it is characterised in that described system include white light scanning module, Scaling module, fixed flat planar and piezoelectric ceramics micro-displacement platform, wherein said white light scanning module includes:

One white light source；

One Kohler illumination system；

One the first beam splitter and second beam splitter, the light that described light source sends is through Kohler illumination system Rear entrance the first beam splitter is also divided into object light and reference light；

One the first microcobjective and second microcobjective；First beam splitter is positioned at described Kohler illumination system Between system and the second microcobjective；

One imaging len and the first, second, third, fourth, the 5th plane mirror；And

One first monochromatic black white image sensor, described reference light is incident on first by the first microcobjective On plane mirror, described object light is incident on object under test, object light and reference light reflection by the second microcobjective After again each via first, second microcobjective, and then interfere after converging in the first beam splitter, interferogram As being gathered by the first monochromatic black white image sensor via imaging len；

Wherein said scaling module includes:

One laser instrument；

One second monochromatic black white image sensor, the laser that described laser instrument sends via the 5th, fourth plane Incide the second beam splitter after reflecting mirror, by the laser of the second beam splitter outgoing via the second plane mirror, Interfering after three plane mirrors, its interference fringe produced is adopted by the second monochromatic black white image sensor Collection；

Wherein said fixed flat planar is used for fixing object to be measured；Described piezoelectric ceramics micro-displacement platform is used for driving Object under test is subjected to displacement.

2. a kind of white light scanning interferometer measuration system as claimed in claim 1, it is characterised in that described light Source is a halogen tungsten lamp white light source.

3. a kind of white light scanning interferometer measuration system as claimed in claim 1, it is characterised in that described sharp Light device is He-Ne laser instrument.

4. a kind of white light scanning interferometer measuration system as claimed in claim 1, in a first direction, described First beam splitter is between described Kohler illumination system and the second microcobjective.

5. white light scanning interferometer measuration system as claimed in claim 4 a kind of, it is characterised in that with the In the second direction that one direction is perpendicular, described first beam splitter is positioned at described picture lens and the first microcobjective Between.

6. a kind of white light scanning interferometer measuration system as claimed in claim 1, it is characterised in that first shows The enlargement ratio of speck mirror and the second microcobjective is 10, and numerical aperture is 0.25.

7. a white light scanning interferometric method, it uses the white light scanning as described in claim 1-6 to interfere Measurement system, it is characterised in that described method includes:

Gather white light interference figure and laser interference figure that a series of object under test produces, use laser interference figure meter Calculate the stepping of piezoelectric ceramics micro-displacement platform, demarcate the scanning stepping that white light scanning is interfered；

Choose a bit on white light interference figure, this light intensity signal is carried out Fourier transformation process；

Filter window is set described Fourier spectrum is carried out spectral filtering；

The light intensity signal extracting all pixels carries out converting Filtering Processing；

Calculate the light intensity signal of all pixels and the zero optical path difference position phase of selected pixel light intensity signal successively To displacement；And

Calculate object under test apparent height.