CN104501739A - Multimode interference confocal microscope system - Google Patents

Abstract

The present invention provides a multi-mode interference confocal microscope system, which is characterized in that it includes: three light sources, respectively a red light source, a green light source and a blue light source; ; The collimating light homogenizer refracts the light emitted by the color separation light combiner into collimated and uniform light; the total reflection prism makes the light emit in a predetermined direction; the spatial light modulator performs specific illumination light field modulation on the light; The controller controls each light source and spatial light modulator separately; the beam splitter prism emits the light in the vertical direction; the objective lens irradiates the light on the surface of the measured object and collects the reflected light on the surface of the measured object; The light converges at the focal point of the tube lens; the imaging detector forms the surface image of the measured object from the light gathered by the tube lens; and the phase shifter, connected with the objective lens, is used to move the position of the objective lens, wherein the objective lens is a Mirau interference objective lens and Any of the brightfield microscope objectives.

Description

Multimode Interferometric Confocal Microscopy System

technical field

The invention relates to the field of precision three-dimensional measurement, in particular to an interference confocal microscope system capable of realizing multi-mode switching and having good measurement adaptability.

Background technique

With the development of micro-fabrication technology, micro-circuits, micro-optical components, micro-machines and other micro-structures are constantly appearing, which makes the demand for measuring the surface topography of micro-structures more and more urgent. The microstructured surface is a complex three-dimensional structure composed of microscopic structural units, and its measurement generally requires direct or indirect microscopic magnification, and requires high lateral resolution and vertical resolution. At the same time, unlike the measurement of smooth surfaces, the measurement of microstructured surfaces not only measures the roughness or flaws of the surface, but also measures the contour, shape deviation and position deviation of the surface.

Interferometric microscopy is the product of the combination of optical interferometry and microscopic systems. By adding a microscopic magnification vision system to the interferometer, the lateral resolution of the interferogram is improved, enabling it to measure the three-dimensional surface topography of the microstructure . With the development of computer technology, modern control technology and image processing technology, interferometric microscopy has emerged monochromatic light phase-shift interferometry (PSI) and white light vertical scanning interferometry (VSI) with measurement accuracy at the nanometer level. Compared with other surface topography measurement methods, interference microscopy has the advantages of rapidity and non-contact, and can cooperate with environmental loading systems to complete structural surface topography measurements under vacuum, pressure, and heating environments. Electromechanical systems and micro-opto-electromechanical systems have been widely used in the measurement of structural surface topography.

Monochromatic light phase-shift interferometry (PSI) is a phase measurement method based on monochromatic light interference. The height information of the sample surface is extracted by measuring and analyzing the interference phase Φ of the interferogram. The PSI method generally uses a micro-displacement device such as a piezoelectric ceramic (PZT) to generate a shift in the phase Ф of the interferogram, and uses the light intensity values of more than three phase-shifted interferograms to obtain the height value of the sample surface. Monochromatic light interference fringes have periodicity. If the height of two adjacent points exceeds 1/4 wavelength, that is, the interferometric phase value exceeds π, then a certain interferogram light intensity value may correspond to a different optical path difference value. Therefore, the PSI method cannot measure the step structure whose height exceeds 1/4 wavelength of the monochromatic light.

White light vertical scanning interferometry (VSI) is a vertical scanning measurement method based on white light interference, which extracts the height information of the sample surface by measuring and analyzing the zero optical path difference position of the interferogram. Since white light is a broadband light source, the white light interferogram is the superposition of the interference of different wavelengths of light. Due to the short coherence distance of white light, some characteristic parameters such as light intensity and contrast will reach the maximum value when the interferogram is at the position of zero optical path difference. Therefore, the VSI method scans the measured surface to obtain a series of different height values by precisely moving the measurement plane M. The interferogram, and then apply the white light interference processing algorithm to extract the vertical zero optical path difference position of each point on the measured surface, and then restore the three-dimensional shape of the measured surface. Compared with the PSI method, the VSI method overcomes the shortcomings of the limited step height measurement, but its measurement accuracy is currently lower than that of the PSI method.

The confocal microscope technique acquires slice images at different heights on the surface of the sample, and then calculates the position of the peak light intensity of each slice image to obtain the three-dimensional surface topography of the measured object. In the confocal microscope system, the point light source, the surface of the measured object and the small hole in front of the detector are mutually conjugated. Through the scanning mechanism, the confocal microscope can image all the points on the entire surface of the measured object, and then obtain the image of the entire plane through image fusion processing; or use structured light to achieve surface imaging, the accuracy is slightly worse than point imaging, but the speed Much faster. The three-dimensional confocal image not only has a higher lateral resolution than ordinary microscopes, but also has a more prominent advantage in that it has a strong ability to resolve axial details of objects, especially suitable for the measurement of rough sample surfaces.

However, due to the diversity of the surface of the measured object, different algorithms need to be applied to samples with different surface roughness levels or step heights. At present, there is no algorithm that can adapt to any situation. Therefore, there is a need for a three-dimensional microscopic measurement system that can have multiple measurement methods at the same time. In this way, regardless of the characteristics of the measured object, a suitable algorithm can be used to obtain the surface topography.

Contents of the invention

The present invention aims at the above problems, and aims to provide a multi-mode interference confocal microscope system, which can switch appropriate measurement modes according to the measurement needs of the measured object to measure the surface of the measured object.

In order to achieve the above object, the present invention adopts the following technical solutions:

The present invention provides a multi-mode interference confocal microscope system, which is characterized in that it includes: three light sources, respectively a red light source, a green light source and a blue light source; , which is composed of a reflective mirror that transmits red light and reflects green light and a reflector that transmits red light and reflects blue light, which are arranged across each other; a collimating light homogenizer refracts the light emitted by the color separation light combiner into collimated and uniform light; The total reflection prism emits light in a predetermined direction through refraction and reflection; the spatial light modulator receives the light emitted by the total reflection prism and performs specific illumination light field modulation on the light, and the light modulated by the illumination light field passes through the total reflection The prism emits out; the controller controls the opening of each light source separately, and controls the spatial light modulator to select a specific illumination light field modulation; the beam splitting prism receives the light emitted after passing through the total reflection prism, and makes the light emit in a vertical direction; The objective lens receives the light emitted from the dichroic prism and irradiates the light on the surface of the measured object, collects the reflected light on the surface of the measured object, makes the reflected light go out in the opposite direction, and passes through the dichroic prism; the tube lens receives the light passing through the dichroic prism light, and make the light converge at the focus of the tube lens through refraction; the imaging detector, located at the focus of the tube lens, forms the surface image of the measured object from the light converged by the tube lens; and a phase shifter, connected with the objective lens, for Move the position of the objective lens, wherein the objective lens is any one of the Mirau interference objective lens and the bright field microscope objective lens,

When using the monochromatic light working mode, the controller controls any one of the red light source, green light source and blue light source to emit light, and the other two light sources do not emit light, and the controller sets the spatial light modulator to a fully open state As a mirror, the objective lens is a Mirau interference objective;

When using the white light scanning interference mode, the controller controls the three light sources to emit light at the same time, and output white light after passing through the color separation light combiner. At the same time, the spatial light modulator is set to a fully open state as a reflector, and the objective lens is a Mirau interference objective lens;

When using the monochromatic light confocal measurement working mode, the controller controls any one of the red light source, green light source and blue light source to emit light, and the other two light sources do not emit light. At the same time, the pixel state of the spatial light modulator is controlled to be black and white. Any one of the square wave and sinusoidal fringes, so that the light entering the spatial light modulator is modulated into structured light, and the objective lens is a bright field microscope objective lens.

Function and Effect of Invention

According to the multi-mode interference confocal microscope system involved in the present invention, because the controller controls a single light source to emit light, and controls the spatial light modulator to be in a fully open state, as a reflector, and uses a Mirau interference objective lens as an objective lens, the detection can be made The interference light is received by the detector to obtain the interference image of the measured object under the irradiation of monochromatic light; the three light sources are controlled to emit light at the same time through the controller, and white light is output after passing through the color separation light combiner, and the spatial light modulator is controlled to be fully open, as Reflector, and Mirau interference objective lens is used as the objective lens, so that the detector can receive interference light and obtain the interference image of the measured object under white light irradiation; the controller controls a single light source to emit light, and controls the spatial light modulator to be black and white interval square wave or sinusoidal fringes and generate the required phase shift, and use the bright field microscope objective as the objective lens to obtain the slice image of the measured object at the focal plane of the objective lens, and then use the phase shifter to control the focus of the bright field microscope objective Surface position, the surface topography of the measured object can be obtained through the slice images at different heights of the measured object, so the multi-mode interference confocal microscope system can switch between multiple measurement modes, according to the surface characteristics and measurement of the measured object Need, select the appropriate measurement mode and algorithm, so as to have good measurement adaptability.

Description of drawings

Fig. 1 is a schematic structural diagram of the multi-mode interference confocal microscope system in the embodiment.

Detailed ways

The multi-mode interference confocal microscope system involved in the present invention will be described in detail below with reference to the accompanying drawings.

Fig. 1 is a schematic structural diagram of the multi-mode interference confocal microscope system in the embodiment.

As shown in Figure 1, a multi-mode interference confocal microscope system 10 includes a light source 11, a light source 12, a light source 13, a color separation light combiner 14, a collimation light homogenizer 15, a total reflection prism 16, a spatial light modulator 17, and a controller 18. A dichroic prism 19 , an objective lens 20 , a tube lens 21 , an imaging detector 22 and a phase shifter 23 .

The light source 11 , the light source 12 and the light source 13 are respectively a red light source 11 , a green light source 12 and a blue light source 13 , which can respectively emit monochromatic light.

The color separation light combiner 14 is formed by a reflective mirror that transmits red light and reflects green light and a reflector that transmits red light and reflects blue light intersects each other, and can combine the light emitted by the three light sources into one bundle.

The collimating and homogenizing device 15 is used to refract the light emitted by the color separation and combining device 14 into collimated and uniform light.

The total reflection prism 16 emits light in a predetermined direction through refraction and reflection.

The spatial light modulator 17 receives the light emitted by the total reflection prism 16, and performs specific illumination light field modulation on the light, and the modulated light passes through the total reflection prism 16 vertically and then is emitted.

The controller 18 is respectively connected with the light source 11, the light source 12, the light source 13 and the spatial light modulator 17, and is used to respectively control the opening of the three light sources, and control the spatial light modulator 17 to perform specific illumination light field modulation.

The dichroic prism 19 receives the light modulated by the spatial light modulator 17 and emitted from the total reflection prism 16, and makes the light emit in a vertical direction.

The objective lens 20 receives the light emitted from the dichroic prism 19 and irradiates the light on the surface of the measured object 24 (not shown in the figure), collects the reflected light on the surface of the measured object 24, makes the reflected light reversely emit, and passes through the dichroic prism 19. Objective 20 is switchable between a Mirau interference objective and a brightfield microscope objective.

The tube lens 21 receives the light passing through the dichroic prism 19 and converges the light at the focal point of the tube lens 21 .

The imaging detector 22 is located at the focal point of the tube lens 21 , receives the light collected by the tube lens 21 and forms a surface image of the measured object 24 .

The phase shifter 23 is connected with the objective lens 20 for controlling the movement of the objective lens 20 .

When using the monochromatic light working mode, the controller 18 controls any one of the red light source 11, the green light source 12, and the blue light source 13 to emit light, and the other two light sources do not emit light. At the same time, the controller 18 controls the spatial light modulator 17 is set to a fully open state as a mirror, and the objective lens 20 is a Mirau interference objective lens 20 . Mirau interference objective lens 20 divides the received monochromatic light into two beams of light, respectively illuminates the reference plane (not shown in the figure) of Mirau interference objective lens 20 and the surface of the measured object 24, and is reflected by the reference plane and the measured object 24 The light interferes, is collected by the Mirau interference objective lens 20, passes through the dichroic prism 19, is refracted by the tube lens 21, and is received by the detector 22 to obtain an interference image of monochromatic light.

The light intensity value obtained by each pixel on the detector 22 can be expressed as the following formula:

I(x,y)＝A+Bcos[φ(x,y)+θ] (1)

In the formula, A is the background light intensity, B is the degree of modulation, (x, y) is the phase difference between the reflected light on the reference plane and the reflected light on the surface of the measured object 24 in the interference system, and θ is the control of the reference plane on the micro-displacement device The phase shift value performed below.

It can be seen that there are three unknowns in formula (1), and at least three equations are needed to solve it. The final phase value obtained by the N-step interferometric phase shift algorithm is related to the intensity of the interfering light in each frame. Expressed as: φ=f(I ₁ ,I ₂ ,...,I _n ) (2)

Through formula (1) and formula (2), the wrapped phase value of each point of the interference image can be obtained, and its range is [-π, π], and then the continuous phase value of all pixels can be obtained by using the street wrapping algorithm , these phase values correspond to the relative heights of the surface of the measured object 24 .

When using the white light scanning interference mode, the controller 18 controls the red light source 11, the green light source 12 and the blue light source 13 to emit light at the same time, and output white light after passing through the color separation light combiner 14, and at the same time set the spatial light modulator 17 to fully open State As a mirror, the objective lens 20 is a Mirau interference objective lens 20 . The Mirau interference objective lens 20 divides the received white light into two beams of light, which are respectively irradiated to the reference plane (not shown in the figure) of the Mirau interference objective lens 20 and the surface of the measured object 24, the light reflected by the reference plane and the measured object 24 When the interference occurs, it is collected by the Mirau interference objective lens 20, passes through the dichroic prism 19, is refracted by the tube lens 21, and is received by the detector 22 to obtain a white light interference image.

The light intensity value obtained by each pixel on the detector 22 is the superposition of formula (1) in a certain wavelength range, expressed as:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; z</span>}}<span\; class="notranslate">\; =</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; +</span>\underset{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}}{\overset{{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}}{<span\; class="notranslate">\; \&Integral;</span>}}\mathrm{<span\; class="notranslate">\; \&psi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&lambda;</span>}<span\; class="notranslate">\; )</span>\mathrm{<span\; class="notranslate">\; cos</span>}\frac{\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; z</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}\mathrm{<span\; class="notranslate">\; d\&lambda;</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In the formula, λ _c is the central wavelength of white light, 2λ _b is the wavelength bandwidth of white light, and ψ(λ) is the energy distribution of incident light on the detector 22 with respect to wavelength λ.

Due to the short coherence distance of white light interference, the light intensity contrast of the interferogram reaches the maximum at the position of zero optical path difference. Through the precise movement of the micro-displacer in the z-axis direction, a series of interferograms with different z-values are obtained. The zero optical path difference position in the vertical direction of each point on the surface of the measured object 24 is extracted by using the white light interference algorithm, and then the surface topography of the measured object 24 is restored.

When using the monochromatic light confocal measurement working mode, the controller 18 controls any one of the red light source 11, the green light source 12, and the blue light source 13 to emit light, and the other two light sources do not emit light, and simultaneously controls the spatial light modulator 17. The pixel state is a square wave or sinusoidal stripes with black and white intervals, so that the light entering the spatial light modulator 17 is modulated into structured light. The objective 20 is a bright field microscope objective 20 .

The bright-field microscope objective lens 20 irradiates the structured light onto the surface of the measured object 24, and then collects the light reflected by the surface of the measured object 24. The light passes through the dichroic prism 19, is refracted by the cylinder lens 21, and is received by the detector 22. A surface image of the measured object 24 is obtained.

On the sample surface, the illumination square is distributed as:

S(x ₀ ,y ₀ )＝1+mcos(νx ₀ +θ ₀ ) (4)

where m is the degree of modulation, _θ0 is an arbitrary spatial phase, ν is the normalized spatial frequency, and ν is related to the spatial frequency of the actual fringe image. After being modulated by the spatial light modulator 17, the light intensity formula that can be obtained on the detector 22 is:

I(x,y)＝I ₀ +I _c cosθ ₀ +I _s sinθ ₀ (5)

In the formula, I ₀ is the light field imaging under uniform illumination, and I _c and I _s are the additional light intensity amplitudes of the fringe pattern.

The pixel state of the spatial light modulator 17 is generated by the controller 18 The detector 22 receives the reflected light from the surface of the measured object 24 to obtain the second image of the measured object, and then the controller 18 causes the pixel state of the spatial light modulator 17 to generate a second The phase shift amount is obtained to obtain the third image of the measured object. thus get and When is the corresponding three images I ₁ , I ₂ and I ₃ . Then by formula (3), formula (4) and formula (5), obtain the optical tomographic image of the measured object 24 at the focal plane of the bright field microscope objective lens 20:

${\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; p</span>}}<span\; class="notranslate">\; =</span>{<span\; class="notranslate">\; [</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; ]</span>}^{\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 6</span>}<span\; class="notranslate">\; )</span>$

Then, the phase shifter 23 is used to raise and lower the bright field microscope objective lens 20, and the measured object 24 is scanned longitudinally to obtain slices at different heights of the measured object, thereby obtaining the three-dimensional surface topography of the measured object 24.

Function and effect of embodiment

According to the multi-mode interference confocal microscope system of this embodiment, because the single light source is controlled by the controller to emit light, and the spatial light modulator is controlled to be in a fully open state, as a reflector, and the Mirau interference objective lens is used as the objective lens, the detector can be made Receive the interference light to obtain the interference image of the measured object under the irradiation of monochromatic light; control the three light sources to emit light at the same time through the controller, output white light after passing through the color separation light combiner, and control the spatial light modulator to be fully open, as a reflection mirror, and use the Mirau interference objective lens as the objective lens, the detector can receive the interference light, and the interference image of the measured object under white light irradiation can be obtained; the single light source is controlled by the controller to emit light, and the spatial light modulator is controlled to be black and white. Wave or sinusoidal fringes and generate the required phase shift, and use the bright field microscope objective as the objective lens to obtain the slice image of the measured object at the focal plane of the objective lens, and then use the phase shifter to control the focal plane of the bright field microscope objective position, the surface topography of the measured object can be obtained through slice images at different heights of the measured object, so the multi-mode interference confocal microscope system can switch between multiple measurement modes, according to the characteristics of the surface of the measured object and measurement needs , choose the appropriate measurement mode and algorithm, so it has good measurement adaptability.

Of course, the multi-mode interference confocal microscope system involved in the present invention is not limited to the structures described in the above embodiments. The above is only a basic description of the concept of the present invention, and any equivalent transformation made according to the technical solution of the present invention shall fall within the scope of protection of the present invention.

Claims (1)

1. A multi-mode interference confocal microscope system, characterized in that, comprising: Three light sources, namely red light source, green light source and blue light source; The color separation light combiner combines the light emitted by the light source into one bundle, which is composed of a reflective mirror that transmits red light and reflects green light and a reflector that transmits red light and reflects blue light, and is arranged to cross each other; A collimating light homogenizer, which refracts the light emitted by the color separation light combiner into collimated and uniform light; A total reflection prism, through refraction and reflection, causes the light to emit towards a predetermined direction; The spatial light modulator receives the light emitted by the total reflection prism and performs specific illumination light field modulation on the light, and the light modulated by the illumination light field is emitted after passing through the total reflection prism; a controller, respectively controlling the turning on of each of the light sources, and controlling the spatial light modulator to select the specific illumination light field modulation; The dichroic prism receives the light emitted after passing through the total reflection prism, so that the light is emitted towards the vertical direction; The objective lens receives the light emitted from the dichroic prism and irradiates the light on the surface of the measured object, collects the reflected light on the surface of the measured object, makes the reflected light reversely emit, and passes through the dichroic prism; a tube lens, receiving the light passing through the dichroic prism, and converging the light at the focal point of the tube lens through refraction; an imaging detector, located at the focal point of the tube lens, forming a surface image of the measured object from the light converged by the tube lens; and a phase shifter, connected to the objective lens, for moving the position of the objective lens, Wherein, the objective lens is any one of the Mirau interference objective lens and the bright field microscope objective lens, When using the monochromatic light working mode, the controller controls any one of the red light source, the green light source, and the blue light source to emit light, and the other two light sources do not emit light, and at the same time The controller sets the spatial light modulator to a fully open state as a mirror, and the objective lens is a Mirau interference objective lens; When using the white light scanning interference working mode, the controller controls the three light sources to emit light at the same time, and outputs white light after passing through the color separation light combiner, and at the same time sets the spatial light modulator to a fully open state as a reflector, The objective lens is a Mirau interference objective lens; When using the monochromatic light confocal measurement working mode, the controller controls any one of the red light source, the green light source and the blue light source to emit light, and the other two light sources do not emit light, At the same time, the pixel state of the spatial light modulator is controlled to be any one of square waves and sinusoidal fringes with black and white intervals, so that the light incident on the spatial light modulator is modulated into structured light, and the objective lens is bright field micro objective lens.