CN105466358A - Chromatography microscopic measurement method for parallel optical lines - Google Patents

Abstract

The invention discloses a parallel optical line tomographic microscopic measurement method, which belongs to the technical field of optical microscopic imaging and precision measurement. The present invention first utilizes <maths num="0001"> </maths> Calculate the microscopic tomographic image field of the standard plane mirror, in which I ₁ , I ₂ and I ₃ are three structured light modulation image fields respectively, draw the center point of the microscopic tomographic image field obtained by the above calculation The corresponding axial tomographic response intensity curve; then intercept the one-sided linear interval of the curve, establish a theoretical correlation model between the intensity field and the height of the sample surface, obtain a measurement calibration linear curve, and form a height-intensity lookup table; and then replace the standard plane The mirror is the actual sample to be tested. According to the height-intensity lookup table, the surface height values of all points in the microscopic image field are obtained in a single scan, and the tomographic detection of the three-dimensional structure of the sample surface within a certain axial range is realized. The invention can be used for rapid detection of non-axial mechanical scanning, parallel and three-dimensional tomography.

Description

A parallel optical line tomography microscopic measurement method

Technical field:

The invention belongs to the technical field of optical microscopic imaging and precision measurement, and in particular relates to a parallel optical line tomographic microscopic measurement method.

Background technique:

Optical microscopic measurement devices have played an important role in promoting the process of human understanding and understanding of the microscopic scientific world. In the middle and late 1950s, M. Minsky, a postdoctoral fellow at Harvard University, invented a brand new optical microscopic device, that is, the common Focus microscope, which uses point illumination and point detection, and introduces a point-by-point scanning structure to realize three-dimensional imaging of the internal structure of the sample. In 1997, on the basis of long-term research and exploration in the field of confocal microscopy, M.A.A.Neil and T.Wilson of Oxford University in the United Kingdom proposed structured illumination microscopy (see M.Neil, R.Juskaitis, T.Wilson. Method of obtaining optical sectioning by using structured light in conventional microscopy. Optics Letters, 1997, 22 (24): 1905-1907), which is a parallel optical tomographic microscopy technique that can be realized with minor changes on the basis of ordinary optical microscope systems, including ordinary white light source illumination, no (co- Focus) physical pinholes, non-point-by-point scanning, etc., through optical fringe modulation, demodulation and other steps to achieve optical tomography, and proved that its axial optical tomography characteristics are similar to ordinary single-point scanning confocal microscopes.

The current structured illumination microscopy technology generally drives a one-dimensional physical grating through a micro-displacement worktable to generate a mechanical step-scanning phase shift, projects the cosine intensity fringes to the sample space to be tested, and uses the grating fringes with different initial phases to analyze the surface morphology of the sample. Or internal structure modulation; CCD is used to detect the modulated light field carrying object structure information respectively. Generally, after collecting 3 images, through mathematical operation processing, the ordinary wide-field image and optical tomographic image are demodulated and separated from the detected light field. .

To sum up, the existing microscopic measurement technology generally uses mechanical step scanning, which not only reduces the measurement efficiency, but also affects the measurement accuracy. The above problems limit the application range of structured illumination microscopic technology. The present invention utilizes the basic device of the micro-micro-technique of structured illumination to realize single scan line tomography measurement.

Invention content:

The purpose of the present invention is to overcome the mechanical step scanning process of the sample to be tested, finally realize non-contact, non-scanning, wide-field parallel optical stereoscopic tomographic imaging and measurement, and provide a parallel optical line tomographic microscopic measurement method, a single scan can realize the three-dimensional tomographic detection of the surface topography of the sample within a certain axial range.

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

A parallel optical line tomography microscopic measurement method, comprising the following steps:

1) Select the standard flat mirror as the standard measurement sample;

2) Use a one-dimensional Z-direction piezoelectric ceramic precision translation stage to step and scan the plane mirror along the axis, and perform steps 3) and 4) at each axial position;

3) Use a precision stepping motor to move the one-dimensional transmission grating along the X-axis direction, and collect three structured light-modulated image fields, I ₁ , I ₂ and I ₃ , respectively. The three structured-light modulated image fields correspond to parallel optical line tomography. Image fields after structured light phase shifts of 0, 2π/3 and 4π/3 in the micro-measurement device;

4) Based on the three image fields obtained in step 3), by the expression $I_{\sec t}=\frac{\sqrt{2}}{3}\sqrt{{(I_2-I_1)}^2+{(I_3-I_1)}^2+{(I_3-I_2)}^2}$ Calculate the microtomography image field I _sect ;

5) Every time step 3) is executed, the expression I _sect described in step 4) is used to calculate the microtomography image field, and draw the axial tomography response intensity curve corresponding to the central point in the above image field;

6) Intercepting the one-sided linear interval of the curve described in step 5), establishing a theoretical correlation model between the intensity field and the height of the sample surface, obtaining a measurement calibration linear curve, and forming a height-intensity lookup table;

7) Replace the standard flat mirror with the actual sample to be tested, repeat steps 2) and 3), and obtain the surface height values of all points in the image field according to the height-intensity lookup table obtained in step 6), and realize a single scan. Complete the detection of the three-dimensional tomographic structure of the sample surface within the axial range.

The beneficial effects of the present invention are: a parallel optical line tomography microscopic measurement method provided by the present invention, based on the theoretical measurement model of wide field line tomography established by diffraction optics and Fourier optics theory, realizes axial-free mechanical scanning , Parallel, rapid three-dimensional tomography detection, overcomes the problem of axial mechanical step-scanning of the sample to be tested, and the best axial resolution can reach the order of several nanometers (corresponding to the case of a large numerical aperture microscopic objective lens). The present invention can be used for non-axial mechanical scanning, parallel, rapid detection of three-dimensional tomography, in the aspects of non-contact, high-resolution, fast tomographic imaging and measurement of three-dimensional surface topography of micro-nano devices such as micro-mechanics, micro-electronics, and micro-optics Provide a new and effective measurement method.

The present invention is significantly different from the existing non-interference differential confocal measurement technology (see literature Chau-HwangLee, JyhpyngWang. Noninterferometricdifferentialconfocalmicroscopywith2-nmdepthresolution. OpticsCommunications, 1997, 135: 233-237), the present invention adopts structured light illumination stripe modulation and demodulation The technology is a parallel chromatography method, while the prior art uses a common confocal scanning measurement device, which is a point-scanning chromatography method, so horizontal two-dimensional mechanical scanning must be performed.

Description of drawings:

Fig. 1 is a structural schematic diagram of a structured light illumination parallel optical line tomography microscopic measurement device.

Among them: 1—incoherent light illumination source, 2—narrow-band filter, 3—stepping motor, 4—one-dimensional transmission grating, 5—first tube mirror, 6—beam splitter, 7—microscopic objective lens, 8— Object to be measured, 9—PZT, 10—second tube mirror, 11—CCD.

Fig. 2 is the theoretical calculation curve of the axial tomography response of the structured light microscopy imaging system.

detailed description:

The present invention will be further described below in conjunction with the accompanying drawings and embodiments.

As shown in Figure 1, the parallel optical line tomography microscopic measurement device includes an incoherent light illumination source 1, a narrow-band filter 2, a stepping motor 3, a one-dimensional transmission grating 4, a first tube mirror 5, and a beam splitter 6 , a microscope objective lens 7, a one-dimensional PZT9, a second tube lens 10 and a CCD11; wherein, the light emitted by the incoherent light illumination source 1 passes through the narrow-band filter 2, the one-dimensional transmission grating 4, and the first tube lens 5 successively , is reflected by the beam splitter 6, and is focused on the surface of the object to be measured 8 placed on the one-dimensional PZT9 through the microscope objective 7 to form structured light illumination; 6. After the second tube mirror 10, the illuminating light beam is focused on the focal plane of the CCD11; the stepper motor 3 is used to control the lateral movement of the one-dimensional transmission grating 4 to complete the three-step phase shift of the one-dimensional transmission grating 4, respectively are 0, 2π/3 and 4π/3, and the CCD11 collects three image fields of I ₁ , I ₂ and I ₃ accordingly; the one-dimensional PZT9 is used to control the movement of the object 8 to be measured in the vertical direction.

A parallel optical line tomography microscopic measurement method of the present invention uses a one-dimensional transmission grating 4 to modulate the incident quasi-parallel light beam to form a striped grating structure illumination, and then microscopically images the grating stripes to the microscope through an incoherent optical imaging filter system. At the focal plane of the objective lens 7, through spatial filtering, cosine intensity distribution illumination stripes are generated to modulate the surface topography of the sample; the reflected or scattered light emitted from the surface of the object to be measured 8 is captured by the infinity imaging system and the second tube mirror 10 focal length. The CCD11 at the plane position detects the light intensity and collects the image field _I1 ; the lateral position of the illumination straight stripe grating is moved by the stepper motor 3, and the displacement of 1/3 and 2/3 of the grating period d is respectively moved, and the image field is collected respectively by the CCD11 I ₂ and I ₃ ; according to the structured light microtomography theory, there are

$\left\{\begin{array}{c}{\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; c</span>}\mathrm{<span\; class="notranslate">\; o</span>}\mathrm{<span\; class="notranslate">\; no</span>}\mathrm{<span\; class="notranslate">\; v</span>}}<span\; class="notranslate">\; =</span>\frac{{\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">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 3</span>}}}{\mathrm{<span\; class="notranslate">\; 3</span>}}\\ {\mathrm{<span\; class="notranslate">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; sec</span>}\mathrm{<span\; class="notranslate">\; t</span>}}<span\; class="notranslate">\; =</span>\frac{\sqrt{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 3</span>}}\sqrt{{<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">\; 1</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">\; 3</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">\; 2</span>}}<span\; class="notranslate">\; +</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">\; I</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}\end{array}\right.<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

According to the formula (1), the ordinary optical image field I _conv and the optical tomographic image field I _sect can be obtained through the mathematical operation of the image fields I ₁ , I ₂ and I ₃ .

Using the scalar diffraction theory, the normalized axial tomographic response I(u) of the structured illumination microscopic imaging system under incoherent illumination conditions is approximated as

$\mathrm{<span\; class="notranslate">\; I</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>\frac{\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; J</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; w</span>}\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; )</span>}{\mathrm{<span\; class="notranslate">\; w</span>}\mathrm{<span\; class="notranslate">\; u</span>}}<span\; class="notranslate">\; |</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In the formula, J ₁ (·) is the first-order Bessel function of the first kind; the parameter w is

w＝ _2υω (1- _υω /2)(3)

In the formula, υ _ω =λMω/sinα is the normalized spatial frequency; ω=1/d is the real spatial frequency of the one-dimensional illumination grating stripe (d is the grating period); λ is the central wavelength of the illumination source; M is the structured light illumination The miniature multiple of the system; NA=sinα is the numerical aperture of the microscopic objective lens; the normalized axial displacement optical coordinate u is

$\mathrm{<span\; class="notranslate">\; u</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; \&pi;</span>}}{\mathrm{<span\; class="notranslate">\; \&lambda;</span>}}\mathrm{<span\; class="notranslate">\; z</span>}{\mathrm{<span\; class="notranslate">\; sin</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; \&alpha;</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

In the formula, z is the real coordinate of the axial displacement.

Based on formula (1) to formula (4), the specific measurement process of a kind of parallel optical line tomography microscopic measurement method of the present invention is:

1) Select the standard flat mirror as the standard measurement sample;

2) Use a one-dimensional Z-direction piezoelectric ceramic precision translation stage to step and scan the plane mirror along the axis, and perform steps 3) and 4) at each axial position;

3) Use a precision stepping motor to move the one-dimensional transmission grating along the X-axis direction, and collect three structured light-modulated image fields, I ₁ , I ₂ and I ₃ , respectively. The three structured-light modulated image fields correspond to parallel optical line tomography. The image field after the structured light phase shift of 0, 2π/3 and 4π/3 in the micro-measurement device is calculated by the formula (1) to obtain the microtomography image field I _sect ;

4) Every time step 3) is executed, formula (1) is used to calculate the microtomography image field, and the axial tomography response intensity curve corresponding to the center point in the image field is drawn;

5) Intercepting the one-sided linear interval of the curve described in step 4), establishing a theoretical correlation model between the intensity field and the height of the sample surface, obtaining a measurement calibration linear curve, and forming a height-intensity lookup table;

6) Replace the standard flat mirror with the actual sample to be tested, repeat steps 2) and 3), and obtain the surface height values of all points in the image field according to the height-intensity lookup table obtained in step 5), and realize a single scan. Complete the detection of the three-dimensional tomographic structure of the sample surface within a certain axial range.

Example:

Figure 2 shows the change law of the axial tomographic response curve of the structured illumination microscopic imaging system with the normalized spatial frequency υ _ω . When υ _ω =1, ω=(sinα/λ)/M, the axial layer The narrowest analytical response curve corresponds to the best axial resolution, that is, I(u)=|2J ₁ (u)/u|, and the ideal confocal axial tomographic response I _conf (u)=sinc ² [u/ (2π)] compared to (shown by the dotted line in the figure), its full width at half maximum (FWHM) is narrower. Intercept the linear interval of the above curve (as shown in the dotted line box in Figure 2), establish a theoretical correlation model between the intensity field and the height of the sample surface, and realize the three-dimensional tomography of the sample surface morphology within a certain axial range within a single scan. Structural detection.

According to the theoretical analysis of the present invention, design optical system parameters as shown in table 1, adopt wavelength λ=532nm, axial tomographic resolution utilizes the full width at half maximum (FWHM) estimation of axial response curve, and lateral resolution utilizes Ray Estimated by the criterion of 0.61λ/NA, the lateral resolution has not been improved because the grating rotation frequency has not been modulated.

Table 1 Structured illumination microscopic imaging system parameters

The specific embodiment of the present invention has been described above in conjunction with the accompanying drawings, but these descriptions can not be interpreted as limiting the scope of the present invention, the protection scope of the present invention is defined by the appended claims, any claims on the basis of the present invention All modifications are within the protection scope of the present invention.

Claims (1)

1. a parallel optical line chromatography microscopic measuring method, is characterized in that, comprise the following steps:

1) selection standard plane mirror is canonical measure sample;

2) utilize one dimension Z-direction piezoelectric ceramics precision displacement table along axle step-scan plane mirror, at each axial location, perform step 3) and 4);

3) utilize precision stepper motor to move one dimension transmission grating along X-direction, gather I respectively ₁, I ₂and I ₃three width structured lights modulation image fields, the image field of three width structured lights modulation image fields respectively in corresponding parallel optical line chromatography micro-measurement apparatus behind structured light phase shift 0,2 π/3 and 4 π/3;

4) based on step 3) the three width image fields that obtain, by expression formula $I_{\sec t}=\frac{\sqrt{2}}{3}\sqrt{{(I_2-I_1)}^2+{(I_3-I_1)}^2+{(I_3-I_2)}^2}$ Calculate micro tomography image field I _sect;

5) often perform step 3) once, adopt step 4) described in expression formula I _sectcalculate micro tomography image field, and draw axial chromatography response intensity curve corresponding to central point in above-mentioned image field;

6) step 5 is intercepted) single-sided linear of described curve is interval, set up the theoretical correlation model of intensity field and sample surfaces height, obtain Measurement and calibration linearity curve, height of formation---intensity lookup tables;

7) standard of replacement plane mirror is actual testing sample, repeat step 2) and 3), according to step 6) gained height---intensity lookup tables, obtain institute's surface elevation value a little in image field, realize the detection that single sweep operation just can complete sample surface morphology solid chromatography structure in axial range ability.