CN108844492B - Microstructure morphology measurement method and device based on spectral modulation degree depth coding - Google Patents
Microstructure morphology measurement method and device based on spectral modulation degree depth coding Download PDFInfo
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Abstract
The invention discloses a microstructure morphology measuring method and a microstructure morphology measuring device based on spectral modulation degree depth coding. The measured element and the spatial light modulator are in object image conjugation under the central wavelength of the spectral range adopted by measurement; the light beam deflection coupler, the spatial light modulator, the collimation and beam expansion lens, the beam splitter, the axial non-achromatic microscope objective, the imaging lens and the color camera are in a common light path structure. During measurement, firstly pre-calibrating the corresponding relation of spectrum and depth of a system device, then collecting each frame of monochromatic phase-shifting fringe pattern reflected by a measured element through a measuring device to obtain the modulation degree distribution of each monochromatic fringe pattern related to the surface shape of a measured element, and acquiring a coded image; and adopting a Gaussian, quasi-Gaussian or spline model to fit and determine a 'spectrum-modulation degree' relation curve of each point on the surface to be measured, demodulating to obtain depth information of each point on the corresponding surface to be measured, and completing the mechanical-free scanning and full-field non-contact rapid high-precision measurement of the three-dimensional shape distribution microstructure shape of the element to be measured.
Description
Technical Field
The invention relates to a microstructure morphology measurement technology, in particular to a microstructure morphology measurement method and device based on spectral modulation depth coding, and belongs to the technical field of advanced manufacturing and detection.
Background
In the important fields of national economy such as semiconductor manufacturing, artificial intelligence, aerospace, and the like, opto-electro-mechanical elements such as silicon-based wafers, micro-electro-mechanical systems (MEMS), Computer-generated holograms (CGH), and the like, have been widely used. The surfaces of these components often present a complex (mirror-like) microstructure formed by machining, laser/plasma etching, spray coating, and the like. The morphology distribution not only reflects the external characteristics of the element, but also is closely related to the intrinsic characteristics such as hardness, residual stress, service life, damage threshold value and the like. The detection is used as an important ring in the manufacturing and production process of the components, the help can be provided for pre-evaluating and controlling the relevant performance of the components, and the quality of the processing and forming effect of the components is often directly determined by the detection precision. Over the last decade, ultra-precise detection of surface microstructure features of such elements has attracted attention and research of scientists in the related field.
The optical interference microscopic testing technology has the characteristics of non-contact, full-field measurement, high precision and the like, and is widely applied to the precise detection of the microscopic morphology of the optical electromechanical element. In the traditional scheme, laser with good monochromaticity is mostly used as a light source, and the measurement precision can reach the sub-nanometer level by combining the phase-shifting interferometry. However, the requirement that the optical path difference between adjacent measured points is less than a quarter wavelength limits the application of the single-wavelength laser interference microscopic testing technology in the aspect of detecting the three-dimensional topography of (class) mirror surface components with complex microstructures (such as a step shape) on the surface to a certain extent. Although white light interferometry, which has a unique zero-optical path difference position and can perform absolute measurement, is commonly used for high-precision detection of the surface shape of the above-mentioned components, it requires fine scanning in the axial direction by means of a high-precision micro-displacer (e.g., a piezo-electric transducer, PZT). Therefore, the whole measurement time is long, the method is only suitable for detecting a static object plane, and is extremely sensitive to external airflow disturbance, vibration and the like in the scanning process, the structure of the system is complex, and the cost is high.
In contrast, as an incoherent optical detection technology, the three-dimensional topography measurement method based on the fringe modulation degree coding has the advantages of more flexible and controllable measurement process, relatively simple system structure and the like, but in order to obtain the axial surface shape distribution of a measured object, PZT still needs to be used for axial scanning, and the three-dimensional topography measurement method also has the defects of weak external interference resistance, suitability for static measurement and the like. Therefore, how to realize the non-mechanical scanning, full-field non-contact, fast and high-precision measurement of the three-dimensional topography distribution of the optical-mechanical-electrical element with a complex (mirror-like) microstructure on the surface without significantly increasing the complexity and cost of the system structure is a research hotspot and trend in the field.
Disclosure of Invention
Aiming at the defects in the prior art, the invention provides a method and a device which can realize the quick and accurate measurement of (class) mirror microstructure, in particular to a discontinuous (class) mirror microstructure element with complex surface shape change without a mechanical scanning component.
The technical scheme for realizing the aim of the invention is to provide a microstructure morphology measuring device based on spectral modulation degree depth coding, which comprises a broad spectrum light source, a light beam coupler, a spectral modulation gating device, a dodging coupler, a light beam turning coupler, a spatial light modulator, a collimation beam expanding lens, a beam splitter, an axial non-achromatic microobjective, an objective table, an imaging lens, a color camera, a computer and a controller; the computer is respectively connected with the controller and the color camera; the measured element is arranged on the objective table, and the measured element and the spatial light modulator are in object image conjugation under the central wavelength of the spectral range adopted by measurement; the light beam deflection coupler, the spatial light modulator, the collimation and beam expansion lens, the beam splitter, the axial non-achromatic microscope objective, the imaging lens and the color camera are in a common light path structure; polychromatic light emitted by the broad spectrum light source is uniformly incident to the spectrum modulation gating device through the light beam coupler, the spectrum regulation and control output end of the controller is connected with the spectrum modulation gating device, the spectrum modulation gating device sequentially outputs monochromatic light with specific wavelength in the spectral range for measurement, and incident monochromatic light field signals which are uniformly distributed in space are obtained through the uniform light coupler and the light beam deflection coupler and are incident to the spatial light modulator; the spatial light modulator is positioned on the front focal plane of the collimation beam expanding lens, the coded image output end of the controller is connected with the spatial light modulator, the spatial light modulator outputs a spatial coded monochromatic sine stripe light field signal, and the spatial light modulator is coupled to the collimation beam expanding lens by the light beam deflection coupler to become parallel light which is incident to the surface of the beam splitter; the beam splitter reflects parallel monochromatic sinusoidal stripe light into the axial non-achromatic microscope, the parallel monochromatic sinusoidal stripe light irradiates the surface of a measured element, the monochromatic sinusoidal stripe light reflected by the measured surface sequentially passes through the axial non-achromatic microscope objective and the beam splitter and is coupled to the target surface of the color camera through the imaging lens, and the color camera transmits acquired image data to the computer.
The spectrum modulation gating device is an acousto-optic modulator and a spectrum modulation gating system based on a dispersion element and a spatial light modulator; the spatial light modulator is a digital micromirror device and silicon-based liquid crystal; the wide-spectrum light source is a halogen lamp, a white light LED and a super-continuum spectrum laser; the color camera is a color three-chip CCD or CMOS camera.
The technical scheme of the invention also provides a microstructure morphology measurement method based on spectral modulation depth coding, which comprises the following steps:
first step, "pre-calibration of spectrum-depth" correspondence:
(1) the spectral modulation gating device is used for gating and filtering polychromatic light emitted by the broad-spectrum light source, monochromatic light with specific wavelength is output and is uniformly irradiated to the spatial light modulator through the uniform light coupler and the light beam turning coupler;
(2) synchronously regulating and controlling the spatial light modulator, outputting monochromatic light signals which are uniformly distributed in space, and irradiating the monochromatic light signals to a standard plane reflector on an objective table through a light beam deflection coupler, a collimation beam expanding lens, a beam splitter and an axial non-achromatic microscope objective;
(3) the standard plane reflector is driven by the piezoelectric ceramic micro-displacer to perform axial scanning along the optical axis direction of the microscope objective, a monochromatic light signal is reflected to enter the axial non-achromatic microscope objective and the beam splitter, the wavelength value of the light signal is received and measured by the spectrometer, and the axial moving position of the piezoelectric ceramic micro-displacer when the monochromatic light signal reaches the peak value in the scanning process is recorded;
(4) repeating the steps (1) to (3) along the direction from short wave to long wave or in the reverse direction in the spectral range used for measurement to obtain a group of spectrum-depth data, obtaining a corresponding relation curve of the spectrum-depth by utilizing a polynomial or spline fitting method, and completing pre-calibration;
and secondly, acquiring a coded image: placing the element to be measured on an object stage, and adjusting the position of the object stage along the axial direction and the radial direction to ensure that the element to be measured and the spatial light modulator are in object image conjugation under the central wavelength in the spectral range used for measurement; filtering polychromatic light emitted by the broad spectrum light source along the direction from short wave to long wave or in the reverse direction by using the spectrum modulation gating device, sequentially outputting monochromatic light with specific wavelength, and uniformly irradiating the monochromatic light to the spatial light modulator through the uniform light coupler and the light beam turning coupler; synchronously regulating and controlling the spatial light modulator, sequentially outputting corresponding monochromatic phase-shifted sine fringe pattern light field signals, and irradiating the light field signals to the surface of a measured element through a light beam deflection coupler, a collimation beam expanding lens, a beam splitter and an axial non-achromatic microscope objective; the controller controls the color camera to synchronously acquire each frame of monochromatic phase-shifting fringe pattern reflected by the tested element and transmit the monochromatic phase-shifting fringe pattern to the computer for storage and processing;
thirdly, coded image demodulation: processing each obtained monochromatic phase-shift fringe pattern by using a random phase-shift algorithm to obtain modulation degree distribution of each monochromatic light fringe pattern related to the surface shape of the measured piece; adopting a Gaussian, quasi-Gaussian or spline model to fit and determine a 'spectrum-modulation degree' relation curve of each point on a surface to be measured, utilizing the characteristic that the modulation degree of each monochromatic light stripe reaches maximum at the focal plane position (namely the depth position of the point to be measured), and demodulating to obtain the depth coding spectrum information of each point; and (3) demodulating to obtain depth information of each point on the corresponding surface to be measured according to a spectrum-depth relation curve obtained by the first step of pre-calibration to obtain the microstructure morphology of the element to be measured, and completing the mechanical scanning-free full-field non-contact rapid high-precision measurement of the three-dimensional morphology distribution of the element to be measured.
In the technical scheme of the invention, the spectral range used for measurement is an ultraviolet band, a visible light band or an infrared band.
The principle of the invention is as follows: based on the traditional three-dimensional shape measuring method based on stripe modulation degree coding, monochromatic parallel lights with different wavelengths are focused on different axial depth positions through an axial non-achromatic optical system in a one-to-one correspondence mode, the modulation degree of each monochromatic light stripe changes along with the axial depth and reaches a maximum value at the focal plane position (namely the depth position of a point to be measured), and unique coding among the modulation degree, the spectrum and the depth is achieved.
Compared with the prior art, the invention has the remarkable advantages that:
1. the measuring device provided by the invention does not need an axial mechanical scanning component, realizes unique coding between spectrum, modulation degree and depth from system hardware by virtue of a spectrum modulation gating module, a spatial light modulator and an axial non-achromatic microobjective, thereby completing full-field, non-contact, rapid and accurate measurement of (class) mirror microstructures, particularly discontinuous (class) mirror microstructure elements with complex surface shape changes, effectively inhibiting measurement errors caused by scanning movement of the mechanical component, and improving the controllability and anti-interference capability of the system.
2. The spectral modulation degree depth coding algorithm provided by the invention utilizes monochromatic parallel lights with different wavelengths to be focused on different axial depth positions in a one-to-one correspondence manner through an axial non-achromatic optical system, and the modulation degree of each monochromatic light stripe changes along with the axial depth and reaches an extreme value near the focal plane position, so that unique coding among spectrum, modulation degree and depth is realized on the basis of a measurement principle, and thus, time consumption, easy external interference and axial mechanical scanning with low flexibility in the traditional three-dimensional shape measurement method based on stripe modulation degree coding are avoided, the introduced measurement error is effectively reduced, and the detection efficiency is improved.
Drawings
Fig. 1 is a schematic structural diagram of a microstructure topography measuring apparatus based on spectral modulation depth coding according to an embodiment of the present invention;
FIG. 2 is a graph of the spectrum-depth relationship provided by an embodiment of the present invention;
FIG. 3 is a spectrum-modulation relationship curve according to an embodiment of the present invention.
Wherein: 1. a broad spectrum light source; 2. a beam coupler; 3. a spectral modulation gate; 4. a light homogenizing coupler; 5. a beam-folding coupler; 6. a spatial light modulator; 7. a collimating beam expanding lens; 8. a beam splitter; 9. an axial non-achromatic microobjective; 10. a measured element; 11. an object stage; 12. an imaging lens; 13. a color camera; 14. a data transmission control line; 15. a computer; 16. and a controller.
Detailed Description
The microstructure topography measuring apparatus and method based on spectral modulation depth coding according to the present invention will be further described in detail with reference to the accompanying drawings and embodiments.
Example 1
Referring to fig. 1, it is a schematic structural diagram of a microstructure topography measuring apparatus based on spectral modulation depth coding according to this embodiment. The measuring device comprises a broad spectrum light source 1, a light beam coupler 2, a spectrum modulation gating device 3, a dodging coupler 4, a light beam turning coupler 5, a spatial light modulator 6, a collimation beam expanding lens 7, a beam splitter 8, an axial non-achromatic microscope objective 9, an objective table 11, an imaging lens 12, a color camera 13, a data transmission control line 14, a computer 15 and a controller 16.
Polychromatic light emitted by the broad spectrum light source 1 is uniformly incident to the spectrum modulation gating device 3 through the light beam coupler 2, monochromatic light with specific wavelength is sequentially output by the spectrum modulation gating device 3 in a measuring spectrum range, and incident monochromatic light field signals which are uniformly distributed in space are obtained through the uniform light coupler 4 and the light beam turning coupler 5 and are incident to the spatial light modulator 6; the spatial light modulator 6 is positioned at the front focal plane position of the collimation beam expanding lens 7, the coded image output end of the controller 16 is connected with the spatial light modulator 6, the spatial light modulator 6 outputs a spatial coded monochromatic sinusoidal fringe light field signal, and the spatial coded monochromatic sinusoidal fringe light field signal is coupled to the collimation beam expanding lens 7 by the light beam deflection coupler 5 to become parallel light which is incident to the surface of the beam splitter 8; the beam splitter 8 reflects parallel monochromatic sinusoidal stripe light into the axial non-achromatic microobjective 9, the parallel monochromatic sinusoidal stripe light irradiates the surface of a tested element 10 on the objective table 11, the monochromatic sinusoidal stripe light reflected by the tested surface sequentially passes through the axial non-achromatic microobjective 9 and the beam splitter 8 and is coupled to the target surface of the color camera 13 through the imaging lens 12, and the color camera 13 transmits acquired image data to the computer. The position of the object stage 11 can be changed in the axial and radial directions so that the measured element 10 located thereon and the spatial light modulator 6 are in object-image conjugation at the central wavelength in the spectral range used for measurement; a light beam deflection coupler 5, a spatial light modulator 6, a collimation beam expanding lens 7, a beam splitter 8, an axial non-achromatic microscope objective 9, an imaging lens 12 and a color camera 13 are in a common light path structure; the computer 15 is connected with the controller 16 and the color camera 13 through a data transmission control line 14, and realizes the regulation and control of the light field signals output by the spectral modulation gate 3 and the spatial light modulator 6 and the synchronous control of the image data collected and transmitted by the camera 13 by utilizing the programming based on the Visual C + + 2010 compiler.
In this embodiment, the spectral modulation gate 3 is an acousto-optic modulator (AOTF), which can regulate and control polychromatic light and sequentially output monochromatic light with specific wavelength; the spatial light modulator 6 is a Digital Micromirror Device (DMD) and can realize the modulation of the spatial distribution of an incident light field; the axial non-achromatic microscope objective 9 can focus monochromatic parallel light with different wavelengths at different depth positions along the axial direction; the broad spectrum light source 1 is a halogen lamp, a white light LED or a super-continuum spectrum laser; the light beam coupler 2 is a structural device consisting of a lens, a reflector or an optical fiber; the light homogenizing coupler 4 is an integrating sphere or an integrating rod; the beam folding coupler 5 is a Total Internal Reflection (TIR) prism; the beam splitter 8 is a 1:1 semi-transparent semi-reflective beam splitter prism; the color camera 13 is a color three-chip CCD camera; the spectral range used for measurement is ultraviolet band, visible band or infrared band.
By using the apparatus shown in fig. 1, the present embodiment provides a microstructure topography measurement method based on depth coding of spectral modulation degree, which includes the following three steps:
first, the system is pre-calibrated. Before measurement, the system device needs to be pre-calibrated according to the corresponding relation of spectrum-depth:
1) the spectral modulation gating device 3 is used for gating and filtering polychromatic light emitted by the broad spectrum light source 1, monochromatic light with specific wavelength is output, and the monochromatic light is uniformly irradiated to the spatial light modulator 6 through the uniform light coupler 4 and the light beam turning coupler 5;
2) synchronously regulating and controlling the spatial light modulator 6 by using software programmed on the basis of a Visual C + + 2010 compiler, outputting monochromatic light signals which are uniformly distributed in space, and irradiating the monochromatic light signals to a standard plane reflector on an objective table through a light beam deflection coupler 5, a collimation beam expanding lens 7, a beam splitter 8 and an axial non-achromatic microscope objective 9;
3) the standard plane mirror is driven by the piezoelectric ceramic micro-displacer to perform axial scanning along the optical axis direction of the microscope objective 9, a monochromatic light signal is reflected to enter the axial non-achromatic microscope objective 9 and the beam splitter 8, the wavelength value of the light signal is received and measured by the spectrometer, and the axial moving position of the piezoelectric ceramic micro-displacer when the monochromatic light signal reaches the peak value in the scanning process is recorded;
4) repeating the above process along the direction from short wave to long wave (or reverse direction) in the spectrum range for measurement to obtain a group of 'spectrum-depth' data, determining the 'spectrum-depth' relation curve of the system device by utilizing polynomial or spline fitting technology, and completing the pre-calibration of the system.
Since monochromatic parallel lights with different wavelengths pass through the axial non-achromatic microscope objective 9 to be focused on different axial depth positions in a one-to-one correspondence manner, namely the correspondence relationship between the spectrums and the depths is as shown in the following formula (1):
z=f(λ) (1)
wherein,f(.) is a single-valued function,zindicating the axial depth. Referring to fig. 2, a spectrum-depth relationship curve is provided for an embodiment of the present invention, wherein the horizontal axis represents the wavelength domain λ (from left to right, short wave to long wave direction), and the vertical axis represents the depthz. Due to the influence of factors such as installation error and nonlinear axial dispersion of optical elements, nonlinear corresponding relation is often presented between spectrum and depth, and the single-valued function can be more accurately represented by polynomial or spline fitting technology in the calibration process of the measurement system devicef(•)。
And secondly, acquiring a coded image. During measurement, the position of the object stage 11 is adjusted along the axial direction and the radial direction, so that the measured element 10 positioned on the object stage and the spatial light modulator 6 are in object-image conjugation under the central wavelength in the spectral range (ultraviolet band, visible light band or infrared band) used for measurement; filtering polychromatic light emitted by the broad spectrum light source 1 by using a spectrum modulation gating device 3 along the direction from short wave to long wave (or reverse direction), sequentially outputting monochromatic light with specific wavelength, and uniformly irradiating the monochromatic light to a spatial light modulator 6 through a uniform light coupler 4 and a light beam turning coupler 5; synchronously regulating and controlling the spatial light modulator 6 by using software developed based on a Visual C + + 2010 compiler, sequentially outputting corresponding monochromatic phase-shifted sinusoidal fringe pattern light field signals, and irradiating the signals to the surface of a tested element 10 through a light beam deflection coupler 5, a collimation beam expanding lens 7, a beam splitter 8 and an axial non-achromatic microscope objective 9; the color camera 13 cooperates with the controller 16 to collect each frame of monochromatic phase-shift fringe pattern reflected by the tested element 10, and transmits the fringe pattern to the computer 15 for storage and processing;
in the embodiment, the adopted method is based on the traditional three-dimensional shape measurement method based on fringe modulation degree coding, monochromatic parallel lights with different wavelengths are focused on different axial depth positions in a one-to-one correspondence mode through an axial non-achromatic microscope objective 9, the modulation degree of each monochromatic light fringe changes along with the axial depth and reaches a maximum value at the focal plane position (namely the depth position of a point to be measured), and unique coding among the modulation degree, the spectrum and the depth is realized.
The method specifically comprises the following steps: based on the time domain equal step phase shift technology, the output of monochromatic phase shift sine fringe pattern light field signals is sequentially realized from short wavelength to long wavelength (or reversely) in a spectral range used for measurement by changing the light field intensity distribution of a spatial light modulator 6 and by means of a broad spectrum light source 1, a light beam coupler 2, a uniform light coupler 4 and a light beam turning coupler 5. The light intensity distribution of each frame of monochromatic phase-shift fringe pattern collected by the color camera 13 and reflected by the tested element 10 is shown in formula (2):
wherein (A), (B), (C), (D), (C), (x, y) Being the image coordinates on the target surface of the color camera 13,
is the fringe phase associated with the three-dimensional profile of the measured element 10,
is shown asmThe central wavelength of the individual monochromatic lights,
，Mfor measuring the number of monochromatic lights (in the present example) in the spectral range used (ultraviolet, visible or infrared band)M=30），
And
respectively representmA single colorThe background component and modulation degree distribution of the light stripe pattern,
is as followsnThe amount of phase shift of the steps is,
，
，Nis the phase shift step number (in the present embodiment)N= 4). Since the "spectrum-depth" has a corresponding relationship as shown in formula (1), the light intensity distribution of the monochromatic phase-shift fringe pattern obtained by the color camera 13 for each frame can be expressed as shown in formula (3):
wherein,
as a function of single value
The inverse function of (a) is,
is as followsmCentral wavelength of monochromatic light
Corresponding axial depth. Because the modulation degree of each monochromatic light stripe varies with the axial depth and reaches a maximum value near the position of the focal plane. Therefore, the maximum position of the fringe modulation degree in the wavelength domain corresponding to any point on the tested element 10 is the depth coding spectrum information of the point, and unique coding among the spectrum, the modulation degree and the depth is realized.
And thirdly, demodulating the coded image. Processing each obtained monochromatic phase-shift fringe pattern by using a random phase-shift algorithm to obtain each monochromatic fringe pattern related to the surface shape of the tested piece 10Distribution of modulation degree of
(ii) a Determining a 'spectrum-modulation degree' relation curve of each point on a surface to be measured based on Gaussian, Gaussian-like or spline model fitting, and demodulating depth coding spectrum information of each point by utilizing the characteristic that the modulation degree of each monochromatic light stripe reaches maximum at the focal plane position (namely the depth position of the point to be measured)
(ii) a Then combines the spectrum-depth relation curve obtained by the preliminary calibration of the first step
And demodulating the depth information of each point on the corresponding surface to be measured, and finally completing the mechanical scanning-free full-field non-contact rapid high-precision measurement of the three-dimensional shape distribution of the element 10 to be measured.
Referring to FIG. 3, a spectrum-modulation relationship curve of a point on the device under test 10 is provided for an embodiment of the present inventionB(lambda) with the abscissa representing the wavelength domain lambda (short to long wave direction from left to right) and the ordinate the normalized fringe modulation, determined during demodulation based on gaussian, gaussian-like or spline model fittingB(lambda) to determine the spectral position lambda corresponding to the maximum value of the curve1Combining with the 'spectrum-depth' relation curve
The depth (height) information of the point can be obtainedz 1。
Claims (7)
1. A microstructure morphology measuring device based on spectral modulation degree depth coding is characterized in that: the device comprises a wide-spectrum light source (1), a light beam coupler (2), a spectrum modulation gating device (3), a uniform light coupler (4), a light beam turning coupler (5), a spatial light modulator (6), a collimation and beam expansion lens (7), a beam splitter (8), an axial non-achromatic micro objective (9), an objective table (11), an imaging lens (12), a color camera (13), a data transmission control line (14), a computer (15) and a controller (16); the computer (15) is respectively connected with the controller (16) and the color camera (13) through a data transmission control line (14); the measured element (10) is arranged on the objective table (11), and the measured element (10) and the spatial light modulator (6) are in object image conjugation under the central wavelength of the spectral range adopted by measurement; a light beam deflection coupler (5), a spatial light modulator (6), a collimation and beam expansion lens (7), a beam splitter (8), an axial non-achromatic microscope objective (9), an imaging lens (12) and a color camera (13) are in a common light path structure; complex color light emitted by a broad spectrum light source (1) is uniformly incident to a spectrum modulation gating device (3) through a light beam coupler (2), a spectrum regulation and control output end of a controller (16) is connected with the spectrum modulation gating device (3), the spectrum modulation gating device (3) sequentially outputs monochromatic light with specific wavelength in a measurement spectrum range, and incident monochromatic light field signals which are uniformly distributed in space are obtained through a uniform light coupler (4) and a light beam turning coupler (5) and are incident to a spatial light modulator (6); the spatial light modulator (6) is located at the front focal plane position of the collimation beam expanding lens (7), the coded image output end of the controller (16) is connected with the spatial light modulator (6), the spatial light modulator (6) outputs a spatial coded monochromatic sine stripe light field signal, and the spatial coded monochromatic sine stripe light field signal is coupled to the collimation beam expanding lens (7) through the light beam turning coupler (5) to become parallel light which is incident to the surface of the beam splitter (8); the device comprises a beam splitter (8), an axial non-achromatic microscope objective (9), a tested element (10), an imaging lens (12), a color camera (13), and a computer, wherein the beam splitter (8) reflects parallel monochromatic sinusoidal stripe light, the parallel monochromatic sinusoidal stripe light enters the axial non-achromatic microscope objective (9) and then irradiates the surface of the tested element (10), the monochromatic sinusoidal stripe light reflected by the tested surface sequentially passes through the axial non-achromatic microscope objective (9) and the beam splitter (8) and is coupled to the target surface of the color camera (13), and the color camera (13) transmits acquired image data to the computer.
2. The microstructure topography measuring device based on spectral modulation degree depth coding according to claim 1, characterized in that: the spectrum modulation gating device is an acousto-optic modulator.
3. The microstructure topography measuring device based on spectral modulation degree depth coding according to claim 1, characterized in that: the spatial light modulator is a digital micro-mirror device or a silicon-based liquid crystal.
4. The microstructure topography measuring device based on spectral modulation degree depth coding according to claim 1, characterized in that: the wide-spectrum light source is a halogen lamp, a white light LED or a super-continuum spectrum laser.
5. The microstructure topography measuring device based on spectral modulation degree depth coding according to claim 1, characterized in that: the color camera is a color three-chip CCD or CMOS camera.
6. A microstructure morphology measurement method based on spectral modulation depth coding is characterized by comprising the following steps:
first step, "pre-calibration of spectrum-depth" correspondence:
(1) the spectral modulation gating device is used for gating and filtering polychromatic light emitted by the broad-spectrum light source, monochromatic light with specific wavelength is output and is uniformly irradiated to the spatial light modulator through the uniform light coupler and the light beam turning coupler;
(2) synchronously regulating and controlling the spatial light modulator, outputting monochromatic light signals which are uniformly distributed in space, and irradiating the monochromatic light signals to a standard plane reflector on an objective table through a light beam deflection coupler, a collimation beam expanding lens, a beam splitter and an axial non-achromatic microscope objective;
(3) the standard plane reflector is driven by the piezoelectric ceramic micro-displacer to perform axial scanning along the optical axis direction of the microscope objective, a monochromatic light signal is reflected to enter the axial non-achromatic microscope objective and the beam splitter, the wavelength value of the light signal is received and measured by the spectrometer, and the axial moving position of the piezoelectric ceramic micro-displacer when the monochromatic light signal reaches the peak value in the scanning process is recorded;
(4) repeating the steps (1) to (3) along the direction from short wave to long wave or in the reverse direction in the spectral range used for measurement to obtain a group of spectrum-depth data, obtaining a corresponding relation curve of the spectrum-depth by utilizing a polynomial or spline fitting method, and completing pre-calibration;
and secondly, acquiring a coded image: placing the element to be measured on an object stage, and adjusting the position of the object stage along the axial direction and the radial direction to ensure that the element to be measured and the spatial light modulator are in object image conjugation under the central wavelength in the spectral range used for measurement; filtering polychromatic light emitted by the broad spectrum light source along the direction from short wave to long wave or in the reverse direction by using the spectrum modulation gating device, sequentially outputting monochromatic light with specific wavelength, and uniformly irradiating the monochromatic light to the spatial light modulator through the uniform light coupler and the light beam turning coupler; synchronously regulating and controlling the spatial light modulator, sequentially outputting corresponding monochromatic phase-shifted sine fringe pattern light field signals, and irradiating the light field signals to the surface of a measured element through a light beam deflection coupler, a collimation beam expanding lens, a beam splitter and an axial non-achromatic microscope objective; the controller controls the color camera to synchronously acquire each frame of monochromatic phase-shifting fringe pattern reflected by the tested element and transmit the monochromatic phase-shifting fringe pattern to the computer for storage and processing;
thirdly, coded image demodulation: processing each obtained monochromatic phase-shift fringe pattern by using a random phase-shift algorithm to obtain modulation degree distribution of each monochromatic light fringe pattern related to the surface shape of the measured piece; adopting a Gaussian, quasi-Gaussian or spline model to fit and determine a 'spectrum-modulation degree' relation curve of each point on a surface to be detected, and demodulating to obtain depth coding spectrum information of each point; and demodulating to obtain depth information of each point on the corresponding surface to be measured according to the spectrum-depth relation curve obtained by the first step of pre-calibration to obtain the microstructure appearance of the element to be measured.
7. The microstructure topography measuring method based on spectral modulation depth coding according to claim 6, characterized in that: the spectral range used for measurement is ultraviolet band, visible light band or infrared band.
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