CN115235344B - Vortex beam-based measurement system and height measurement method - Google Patents
Vortex beam-based measurement system and height measurement method Download PDFInfo
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- CN115235344B CN115235344B CN202210631487.8A CN202210631487A CN115235344B CN 115235344 B CN115235344 B CN 115235344B CN 202210631487 A CN202210631487 A CN 202210631487A CN 115235344 B CN115235344 B CN 115235344B
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- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
Abstract
The invention provides a measuring system and a height measuring method based on vortex beams, which belong to the field of optical measurement and imaging, wherein the measuring system comprises a multi-wavelength laser module, a measuring illumination module, a vortex reference module, a focusing optical module, an image acquisition module, a data processing module and an external output module; the measuring method comprises the steps of arranging a measuring system, collecting sample information and calculating the height; according to the method, based on the spatial phase distribution characteristics of vortex beams, the height value variation is converted into the rotation quantity of the interference pattern around the optical axis, and the rotation quantity is obtained by using a four-step phase shift method, so that the height value variation is obtained; compared with the traditional methods such as short coherence measurement, projection differential measurement and the like, the height measurement scheme has smaller data volume, higher sampling frequency and higher time resolution; can be popularized and applied in the fields of semiconductors, chips and the like which need high-precision measurement and real-time measurement.
Description
Technical Field
The invention belongs to the field of high-precision measurement, and particularly relates to a vortex beam-based measurement system and a height measurement method, which can be applied to the fields of semiconductors, chips, PCBs, FPBs and the like needing high-precision measurement.
Background
With the development of industrial technology, the industry has higher and higher requirements on real-time high-precision height measurement, especially in the fields of nano-scale high-precision measurement related to semiconductors, chips and the like, and the main height measurement schemes at present mainly include the following steps:
1. short coherence
The interference light intensity of the short coherent light source is very sensitive to the optical path difference, and the accurate measurement of the height can be realized by fitting and searching the peak position of the light intensity envelope curve, but in the sampling process, a certain scanning time is required, and the real-time work cannot be performed;
2. multi-view geometry
The multi-view geometry method can be used for positioning three-dimensional coordinates of a spatial point in real time through spatial position relations among a plurality of optical systems, so that height measurement is realized. For single-point height measurement, point laser is generally used for realizing, but the measurement accuracy of submicron level can only be realized at present under the restriction of device performance and size;
3. common interferometry
The common interferometry method is generally used for measuring the relative position of a single plane, and can realize absolute position measurement only under the condition of a scanning reference mirror, and can not measure the morphology of a discontinuous surface;
4. oblique beam horizontal offset method
In a microscope system, by utilizing the high NA characteristic of a microscope objective, off-axis illumination with a large angle can be realized, when the parallelism of illumination beams is good, the horizontal position of the illumination beams irradiated on a sample is in direct proportion to the defocusing amount of the sample, and the defocusing amount (real-time measurement of the height) can be realized by monitoring the horizontal position. The method is influenced by the NA of the microscope objective, and the measuring precision is about 50nm when NA is 0.9.
5. Application of vortex rotation
Vortex light is a hollow light beam with a spiral phase wavefront and a phase singular point, the light intensity of the light wave at the phase singular point is zero, and the phases are spirally distributed around the singular point along the direction perpendicular to the propagation direction. The vortex beam has orbital angular momentum, enabling manipulation of particles and measurement of micro-deformations. The Gaussian beam can be changed into the vortex beam through the vortex phase plate, and the method can be applied to micro-measurement fields such as microlithography, super-resolution display, micro-deformation, displacement, space distance, three-dimensional surface type measurement and the like. However, existing vortex measurement schemes are limited to obtaining the desired results by unwrapping after final results are acquired using a CCD. This solution does not meet the high precision and real-time requirements of industrial levels.
In summary, the current measurement method is difficult to simultaneously consider the requirements of high-precision measurement and real-time measurement, and in order to meet the field requirements of high-precision measurement and real-time measurement of semiconductors, chips and the like, an optical height measurement scheme which is simultaneously required by precision and real-time needs to be developed.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention aims to provide a vortex beam-based measuring system and a height measuring method, which can solve the problems.
Design principle: the method comprises the steps of providing multi-wavelength laser, providing reference light and measuring light, obtaining sample height information through data processing calculation through a double detector or a sensor array based on vortex light beams, and achieving the effect of achieving both precision and efficiency. For a vortex beam, there is a circumferential phase distribution of its wavefront (see fig. 1 a).
When the vortex beam interferes coaxially with the plane beam, the interference image is sinusoidally distributed in the circumferential direction (see fig. 1b, 1 c).
Four light intensity detectors (with angle intervals of 90 degrees) are uniformly distributed along the circumferential direction by taking the center of the interference pattern as an axis, and the light intensity I (I) corresponding to each sensor is obtained according to an interference light intensity calculation formula 1 /I 2 /I 3 /I 4 ). According to the load value of the vortex beam, a four-step phase shift method is adopted to calculate the phase difference phi of the two interference beams, and then the height delta z of the sample relative to the initial position is calculated.
The specific scheme is as follows.
The measuring system based on the vortex beam comprises a multi-wavelength laser module, a measuring illumination module, a vortex reference module, a focusing optical module, an image acquisition module, a data processing module and an external output module; the multi-wavelength laser module is used for providing lasers with various wavelengths; the measuring illumination module and the vortex reference module are arranged at the downstream of the multi-wavelength laser module to form two light path branches: the measuring illumination module is used for providing partial lasers with various wavelengths as measuring light to a measured sample after passing through the focusing optical module and collecting sample information; the vortex reference module carries out vortex modulation on the rest of multiple wavelength lasers, and the formed multipath single wavelength vortex rotation is provided for the image acquisition module as reference light after beam combination; the focusing optical module is arranged at the light path downstream of the measurement illumination module and is used for providing the measurement light of the measurement illumination module for the measured sample and then reflecting the measurement light to form a sample surface and transmitting the sample surface to the image acquisition module through a detection light path; the image acquisition module respectively detects and collects reference light and measuring light with sample surface measurement information according to wavelength; the data processing module is used for collecting measurement information of the image acquisition module and calculating sample height information; and the external output module is used for outputting and displaying the height information calculated by the data processing module.
Further, the multi-wavelength laser module comprises a multi-wavelength laser, a collimation beam expander and a first polaroid which are sequentially arranged; the collimating beam expander is used for collimating and expanding the laser beams with multiple wavelengths emitted by the multi-wavelength laser; the first polaroid modulates the collimated and expanded laser beams with multiple wavelengths into linear polarized light.
Further, the measurement illumination module comprises a spectroscope, a reflecting polarizer and a quarter wave plate which are sequentially arranged; the spectroscope is used for transmitting part of the multi-wavelength laser as measuring light; the reflection polarizer and the quarter wave plate are used for sequentially transmitting the measuring light passing through the spectroscope to the focusing optical module; the quarter wave plate is used for modulating the polarization states of the incident measuring light and the reflected measuring light, and is matched with half-wave loss of sample reflection to realize that the polarization state of the measuring light rotates by 90 degrees, so that the reflected measuring light is totally reflected by the reflecting polarizer.
Further, the vortex reference module comprises a half-wave plate, a first dichroic mirror, a first vortex phase plate, a second reflecting mirror, a second vortex phase plate, a third reflecting mirror and a second dichroic mirror; the half-wave plate is used for rotating the polarization direction of the multi-wavelength laser of the spectroscope reflection part by 90 degrees; the first dichroic mirror is used for splitting the multi-wavelength laser beam after the spectroscope into two single-wavelength Gaussian beams; the two single-wavelength Gaussian beams respectively pass through the first vortex phase plate and the second vortex phase plate and then become vortex beams with a charge value of l=1; the second dichroic mirror is used for combining two vortex beams with the charge value of l=1 as reference light, and transmitting the reference light to the image acquisition module after being transmitted through the reflecting polarizer.
Further, the image acquisition module adopts an area array detector or adopts a plurality of detector array modules; each detector array module includes a plurality of detector arrays, a third dichroic mirror, and a second polarizer; the second polarizer is used for modulating the reference light transmitted through the reflecting polarizer and the reflected measuring light; the third dichroic mirror is used for splitting the multi-wavelength light beam modulated by the second polaroid into single-beam light with multiple wavelengths, and the single-beam light is received and collected by the corresponding detector array.
Further, the measuring system further comprises an extinction module, wherein the extinction module is arranged at the spectroscope and used for eliminating stray light emitted through the spectroscope and improving the signal-to-noise ratio of the system.
The invention also provides a height measurement method based on the vortex beam, which comprises the following steps:
arranging a measuring system: arranging a measuring system according to the foregoing;
sample information collection: assuming that the phase difference corresponding to the initial position is 2pi×n, the light intensity collected by each light intensity detector is respectively:
wherein Ip is the light intensity collected by the p-th light intensity detector, I 0 For the light intensity of the reference beam and the measuring beam, I 1 /I 2 /I 3 /I 4 The light intensity of the four light intensity detectors, δz is the height value of the sample relative to the initial position, λ is the wavelength of the detected light, and l is the charge value of the vortex beam;
height calculation: and according to the load value of the vortex beam, a four-step phase shift method is adopted to calculate the phase difference phi of the two interference beams, and then the height delta z of the sample relative to the initial position is calculated.
Further, the height calculation includes a discontinuously varying sample height calculation and a continuously varying sample height calculation; for samples that vary discontinuously, the altitude calculation uses dual wavelength unwrapped phase information; for continuously changing samples, the height calculation uses a method of accumulating counts.
Compared with the prior art, the invention has the beneficial effects that: according to the method, based on the spatial phase distribution characteristics of vortex beams, the height value variation is converted into the rotation quantity of the interference pattern around the optical axis, and the rotation quantity is obtained by using a four-step phase shift method, so that the height value variation is obtained; compared with the traditional methods such as short coherence measurement, projection difference measurement and the like, the height measurement scheme has smaller data volume, higher sampling frequency and higher time resolution; can be popularized and applied in the fields of semiconductors, chips and the like which need high-precision measurement and real-time measurement.
Drawings
FIG. 1 is a schematic diagram of spatial phase distribution, coaxial optical interference pattern and circumferential light intensity distribution of a vortex beam;
FIG. 2 is a schematic diagram of the optical path of a vortex beam based measurement system of the present invention;
fig. 3 is a schematic view of a detector array comprising four light intensity detectors.
In the figure:
10. a multi-wavelength laser module; 11. a multi-wavelength laser; 12. a collimation beam expander; 13. a first deflection plate; 14. a first mirror;
20. a measurement illumination module; 21. a beam splitter; 22. a reflective polarizer; 23. a quarter wave plate;
30. a vortex reference module; 31. a half-wave plate; 32. a first dichroic mirror; 33. a first vortex phase plate; 34. a second mirror; 35. a second scroll phase plate; 36. a third mirror; 37. a second dichroic mirror;
40. a focusing optical module;
50. an image acquisition module; 51. a detector array; 52. a third dichroic mirror; 53. a second polarizing plate;
60. a data processing module;
70. an external output module;
80. and a extinction module.
Detailed Description
For the purpose of making the objects, technical solutions and advantages of the embodiments of the present invention more apparent, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention, and it is apparent that the described embodiments are some embodiments of the present invention, but not all embodiments of the present invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Measuring system based on vortex light beam
Referring to fig. 2, the measuring system based on the vortex beam comprises a multi-wavelength laser module 10, a measuring illumination module 20, a vortex reference module 30, a focusing optical module 40, an image acquisition module 50, a data processing module 60, an external output module 70 and an extinction module 80. Integrally, including laser sources, vortex modulated light paths, interferometry, etc., constitute vortex-based height measurement schemes.
Wherein the multi-wavelength laser module 10 is used for emitting or providing laser light with various wavelengths. Specifically, the multi-wavelength laser module 10 includes a multi-wavelength laser 11, a collimator-expander 12, and a first polarization plate 13, which are sequentially arranged. The collimator-expander 12 is used to collimate and expand the multiple wavelength lasers emitted by the multi-wavelength laser 11. The first polarizer 13 modulates the collimated and expanded laser beams with various wavelengths into linear polarized light.
Finally, the multi-wavelength laser module 10 provides linearly polarized modulated multi-wavelength lasers (λ1, λ2, … … λi, i being a positive integer of ≡2).
Further, the multi-wavelength laser module 10 further includes a first mirror 14 for changing the outgoing light path, so as to reduce the system space.
In one example, the first mirror 14 normal is disposed at 45 ° to the incident light.
Wherein, the measuring illumination module 20 and the vortex reference module 30 are arranged downstream of the multi-wavelength laser module 10, forming two optical path branches: the measurement illumination module 20 is configured to provide a part of the laser beams with multiple wavelengths as measurement light to the sample to be measured through the focusing optical module 40, and is configured to collect sample information; the vortex reference module 30 carries out vortex modulation on the rest of the multiple-wavelength laser, and the formed multipath single-wavelength vortex light is provided as reference light to the image acquisition module 50 after being combined.
Specifically, the measurement illumination module 20 includes a beam splitter 21, a reflecting polarizer 22, and a quarter wave plate 23, which are arranged in this order. The spectroscope 21 is used for transmitting a part of the multi-wavelength laser light as measurement light; the reflecting polarizer 22 and the quarter wave plate 23 are used to sequentially transmit the measurement light passing through the beam splitter 21 to the focusing optical module 40.
The quarter wave plate 23 is used for modulating the polarization states of the incident measurement light and the reflected measurement light, and is matched with the half-wave loss of the sample reflection to realize that the polarization state of the measurement light rotates by 90 degrees, so that the reflected measurement light is totally reflected by the reflecting polarizer 22.
Specifically, vortex reference module 30 includes half-wave plate 31, first dichroic mirror 32, first vortex phase plate 33, second mirror 34, second vortex phase plate 35, third mirror 36, and second dichroic mirror 37. The half-wave plate 31 is used for rotating the polarization direction of the multi-wavelength laser light of the reflecting part of the spectroscope 21 by 90 degrees; the first dichroic mirror 32 is used for splitting the multi-wavelength laser beam passing through the beam splitter 21 into two single-wavelength gaussian beams.
Further, the two single-wavelength gaussian beams pass through the first vortex phase plate 33 and the second vortex phase plate 35 respectively, and become vortex beams with a load value of l=1.
The second and third mirrors 34, 36 are used to redirect a single wavelength gaussian beam passing before and after the second vortex phase plate 35.
Further, the second dichroic mirror 37 is configured to combine two vortex beams with a load value of l=1 as reference light, and transmit the combined beams to the image acquisition module 50 after being fully transmitted by the reflective polarizer 22.
The focusing optical module 40 is disposed downstream of the optical path of the measurement illumination module 20, and is configured to provide the measurement light of the measurement illumination module 20 to the sample to be measured, and reflect the measurement light to form a sample surface, and provide the sample surface to the image acquisition module 50 via a detection optical path.
Specifically, the focusing optical module 40 employs an afocal optical system or a telescopic system. Depending on the difference in measurement/monitoring requirements, different configurations may be selected, such as: 1) Uniform media or free space; 2) A microscopic imaging system consisting of a microscope barrel and a microscope objective; 3) A beam shrinking or expanding system.
Wherein, the image acquisition module 50 respectively detects and collects reference light and measuring light with sample surface measuring information according to wavelength; the image acquisition module 50 employs an area array detector or employs a plurality of detector array modules.
When a plurality of detector array modules are employed, each detector array module includes a plurality of detector arrays 51, a third dichroic mirror 52, and a second polarizer 53; the plurality of detector arrays 51 are denoted SA1, SA2, … … SAj, j being a positive integer of > 2, see the example of FIG. 1 where j is taken to be 2, i.e. two detector arrays are employed.
The second polarizing plate 53 is used to modulate the reference light transmitted through the reflecting polarizer 22 and the reflected measuring light; the third dichroic mirror 52 is used for splitting the multi-wavelength light beam modulated by the second polarizer 53 into single-beam light of a plurality of wavelengths, and receiving the acquisition by the corresponding detector array 51.
Further, each of the detector arrays 51 includes a plurality of light intensity detectors PD1, PD2, PD3 … … PDm uniformly arranged in the circumferential direction with the interference pattern center as an axis, where m is a positive integer greater than or equal to 3.
In one example, the light intensity detector is in the form of, but not limited to, a photodiode or the like.
Referring to the example in fig. 3, m is taken to be 4, i.e., each detector array 51 includes four light intensity detectors: PD1, PD2, PD3, PD4, two adjacent light intensity detectors are angularly spaced 90 deg..
The data processing module 60 is used for acquiring measurement information of the image acquisition module 50, i.e. the area array detector or the plurality of detector arrays, and calculating sample height information.
Wherein the external output module 70 externally outputs and displays the height information calculated by the data processing module 60.
The extinction module 80 of the measurement system is disposed at the beam splitter 21, and is used for eliminating stray light emitted from the beam splitter 21 and improving the signal-to-noise ratio of the system.
The matting module 80 can take a variety of matting schemes including, but not limited to, the following forms: 1) A light absorbing surface having an angle with the optical axis; 2) The outgoing beam is reflected outside the system.
Depending on the application requirements, the measurement system may choose a variety of configurations: single wavelength/multiple wavelength, beam expansion/contraction, number of detectors, etc.
The system comprises the following specific operation steps:
1. the multi-wavelength laser light emitted by the multi-wavelength laser 11 is collimated and expanded, then enters a first polarizer 13 (linear polarizer), and is modulated into linear polarization;
2. polarized light is deflected by the first reflecting mirror 14 (M1) and is incident to the 50/50 spectroscope 21, one beam is used as measuring light to irradiate the surface of a sample, and the other beam is used as reference light to enter a vortex modulation light path;
3. in the vortex modulation light path, the fast axis direction of the half-wave plate 31 forms an included angle of 45 degrees with the polarization direction of the light beam, and the polarization direction rotates by 90 degrees after the light beam passes through;
4. after passing through the first dichroic mirror 32 (DM 1), the light beam becomes two single-wavelength gaussian light beams, and is incident to the vortex phase plate, respectively: a first scroll phase plate 33 (VPP 1) and a second scroll phase plate 35 (VPP 2);
5. after the vortex phase delay by the first vortex phase plate 33 (VPP 1) and the second vortex phase plate 35 (VPP 2), the gaussian beam becomes a vortex beam with a charge value of l=1;
6. the two vortex beams are combined after passing through a second dichroic mirror 37 (DM 2), and enter a detection light path after passing through a reflecting polarizer 22;
7. after passing through the reflective polarizer 22, the measuring beam is incident on the sample surface or the focusing optical system of the focusing optical module 40;
8. the surface of the sample reflects the measuring beam to the reflecting polarizer 22 and enters the detection light path together with the reference beam;
9. the reference beam and the measuring beam are modulated by the second polarizer 53 and split by the third dichroic mirror 52, and then respectively enter the detector arrays SA1 and SA2;
10. the data processing module 60 collects the measured values of the detectors on the detector arrays SA1 and SA2 in real time, then calculates sample height information, and outputs the height information to an external system.
The measuring system converts the height information into the rotation angle of the interference pattern around the optical axis by utilizing the spatial phase distribution characteristic of the vortex beam, and forms an interference measuring module by using a plurality of high-speed point light intensity detectors, so that the real-time detection of the height information is realized.
Height measurement method based on vortex beam
A height measurement method based on vortex beam includes:
arranging a measuring system: arranging the measuring system, the multi-wavelength laser module 10 adopts a dual-wavelength laser, and each detector array 51 of the image acquisition module 50 comprises four light intensity detectors (PD 1, PD2, PD3 and PD 4);
sample information collection: assuming that the phase difference corresponding to the initial position is 2pi×n, the light intensities collected by the four light intensity detectors (PD 1, PD2, PD3, PD 4) are respectively:
wherein I is 0 For the light intensity of the reference beam and the measuring beam, I 1 /I 2 /I 3 /I 4 The light intensity of the four light intensity detectors, δz is the height value of the sample relative to the initial position, λ is the wavelength of the detected light, and l is the charge value of the vortex beam;
height calculation: taking l=1, the phase difference of the four light intensity detectors isThe phase difference phi of the two interference beams is obtained by a four-step phase shift method:
further, the height value delta z of the sample relative to the initial position is obtained:
because phi is E [0,2 pi ], the maximum measuring range of the structure is only 0.5lambda, and the requirements of applications such as automatic focusing/surface type measurement and the like cannot be met. To increase the measurement range, the following method may be employed:
further, the height calculation includes a discontinuously varying sample height calculation and a continuously varying sample height calculation;
for a sample with discontinuous delta z change, a multi-wavelength heterodyne unpacking method is used for the height calculation, and a dual-wavelength system is taken as an example, and dual-wavelength unpacking phase information is used for the height calculation; specifically, if the wavelengths of the two detection beams are respectively lambda 1 、λ 2 The system measurement range is increased to
Accordingly, by selecting an appropriate wavelength, the detection range can be extended to several micrometers to several tens of micrometers.
For samples with continuously varying δz, the height calculation uses a method of accumulating counts.
For applications such as non-pattern wafer surface type detection and displacement table motion precision measurement, the sample delta z is continuously changed, and a continuous counting method can be adopted to expand the measurement range. In theory, the measurement range of this scheme is not limited.
The whole scheme utilizes the spatial phase distribution characteristic of vortex light beams to convert the height information into the rotation angle of an interference pattern around an optical axis, and a plurality of high-speed point light intensity detectors are used for forming an interference measurement module, so that the real-time detection of the height information is realized.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention, and are not limited thereto; although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: the technical scheme described in the foregoing embodiments can be modified or some technical features thereof can be replaced by equivalents; such modifications and substitutions do not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims (9)
1. A vortex beam based measurement system, characterized by: the measuring system comprises a multi-wavelength laser module (10), a measuring illumination module (20), a vortex reference module (30), a focusing optical module (40), an image acquisition module (50), a data processing module (60) and an external output module (70);
the multi-wavelength laser module (10) is used for providing lasers with multiple wavelengths;
the measuring illumination module (20) and the vortex reference module (30) are arranged at the downstream of the multi-wavelength laser module (10) to form two light path branches: the measuring illumination module (20) is used for providing partial laser with various wavelengths as measuring light to a measured sample through the focusing optical module (40) and collecting sample information; the vortex reference module (30) carries out vortex modulation on the rest laser with multiple wavelengths, and the formed multipath single-wavelength vortex rotation is provided for the image acquisition module (50) as reference light after beam combination;
the vortex reference module (30) comprises a half-wave plate (31), a first dichroic mirror (32), a first vortex phase plate (33), a second reflecting mirror (34), a second vortex phase plate (35), a third reflecting mirror (36) and a second dichroic mirror (37); the half-wave plate (31) is used for rotating the polarization direction of the multi-wavelength laser of the reflecting part of the spectroscope (21) by 90 degrees; the first dichroic mirror (32) is used for splitting the multi-wavelength laser beam which is subjected to the beam splitting mirror (21) into two single-wavelength Gaussian beams; two single-wavelength Gaussian beams respectively pass through the first vortex phase plate (33) and the second vortex phase plate (35) and then become vortex beams with a load value of l=1; the second dichroic mirror (37) is used for taking a vortex beam combination of two beams with a charge value of l=1 as reference light, and transmitting the reference light to the image acquisition module (50) after being transmitted through the reflecting polarizer (22);
the focusing optical module (40) is arranged at the downstream of the light path of the measuring illumination module (20) and is used for providing the measuring light of the measuring illumination module (20) to the measured sample and then reflecting the measuring light to form a sample surface and transmitting the sample surface to the image acquisition module (50) through a detection light path;
the image acquisition module (50) respectively detects and collects reference light and measuring light with sample surface measurement information according to wavelengths;
the data processing module (60) is used for acquiring measurement information of the image acquisition module (50) and calculating sample height information;
the external output module (70) outputs and displays the height information calculated by the data processing module (60) externally.
2. The measurement system of claim 1, wherein: the multi-wavelength laser module (10) comprises a multi-wavelength laser (11), a collimation beam expander (12) and a first polaroid (13) which are sequentially arranged;
the collimating and beam expanding device (12) is used for collimating and expanding the laser beams with multiple wavelengths emitted by the multi-wavelength laser (11);
the first polaroid (13) modulates the collimated and expanded laser beams with multiple wavelengths into linear polarized light.
3. The measurement system according to claim 2, wherein: the measuring illumination module (20) comprises a spectroscope (21), a reflecting polarizer (22) and a quarter wave plate (23) which are sequentially arranged;
the spectroscope (21) is used for transmitting part of the multi-wavelength laser light as measuring light;
the reflecting polarizer (22) and the quarter wave plate (23) are used for sequentially transmitting the measuring light passing through the spectroscope (21) to the focusing optical module (40);
the quarter wave plate (23) is used for modulating the polarization states of incident measuring light and reflected measuring light, and the polarization states of the measuring light are rotated by 90 degrees by matching with half-wave loss of sample reflection, so that the reflected measuring light is totally reflected by the reflecting polarizer (22).
4. The measurement system of claim 1, wherein: the focusing optical module (40) adopts an afocal optical system or a telescopic system.
5. The measurement system of claim 1, wherein: the image acquisition module (50) adopts an area array detector or adopts a plurality of detector array modules;
each detector array module includes a plurality of detector arrays (51), a third dichroic mirror (52), and a second polarizer (53);
the second polarizer (53) is used for modulating the reference light transmitted through the reflecting polarizer (22) and the reflected measuring light;
the third dichroic mirror (52) is used for splitting the multi-wavelength light beam modulated by the second polaroid (53) into single-beam light with multiple wavelengths, and the single-beam light is received and collected by the corresponding detector array (51).
6. The measurement system of claim 5, wherein: each detector array (51) comprises a plurality of light intensity detectors PD1, PD2, PD3 … … PDm which are uniformly arranged along the circumferential direction by taking the center of the interference pattern as an axis, wherein m is a positive integer greater than or equal to 3.
7. The measurement system of claim 5, wherein: the measuring system further comprises an extinction module (80), wherein the extinction module (80) is arranged at the spectroscope (21) and is used for eliminating stray light emitted through the spectroscope (21) and improving the signal-to-noise ratio of the system.
8. A vortex beam-based height measurement method, the method comprising:
arranging a measuring system: -arranging the measuring system according to any of the claims 1-7, wherein the multi-wavelength laser module (10) employs a dual wavelength laser, each detector array (51) of the image acquisition module (50) comprising four light intensity detectors (PD 1, PD2, PD3, PD 4);
sample information collection: assuming that the phase difference corresponding to the initial position is 2pi×n, the light intensities collected by the four light intensity detectors (PD 1, PD2, PD3, PD 4) are respectively:
wherein I is 0 For the light intensity of the reference beam and the measuring beam, I 1 /I 2 /I 3 /I 4 The light intensity of the four light intensity detectors, δz is the height value of the sample relative to the initial position, λ is the wavelength of the detected light, and l is the charge value of the vortex beam;
height calculation: taking l=1, the phase difference of the four light intensity detectors isUsing four-step phase shift method to obtain two interference light beam phase difference phi:
further, the height value delta z of the sample relative to the initial position is obtained:
9. the height measurement method according to claim 8, wherein: the height calculation includes a discontinuously varying sample height calculation and a continuously varying sample height calculation;
for samples that vary discontinuously, the altitude calculation uses dual wavelength unwrapped phase information;
for continuously varying samples, the height calculation uses a method of accumulating counts.
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