Nanometer length metering system and method based on chromium atomic transition frequency

Abstract

The invention discloses a nanometer length metering system and method based on chromium atom transition frequency, and belongs to the field of nanometer length metering, the nanometer length metering system comprises a physical wavelength reference and a working standard substance, the physical wavelength reference is a 425.55 nm laser wavelength locked to a chromium atom (7S3-> 7P4) transition spectral line, and the working standard substance is a laser wavelength locked to a chromium atom (7S3-> 7P4) transition spectral line. The working standard substance is chromium self-tracing series gratings prepared by using an atomic photoetching method, grating periods are traced to a physical wavelength reference, and the chromium self-tracing series gratings comprise a one-dimensional chromium self-tracing grating and a two-dimensional chromium self-tracing grating. According to the nanometer length metering system based on the chromium atom transition frequency, the chromium atom transition frequency, which is a natural constant, is materialized to the chromium self-traceability grating in a laser convergence atom deposition manner, so that the grating has independent traceability and ultrahigh accuracy and consistency at the same time.

Description

Technical Field

[0001] The invention relates to the field of nanometer length measurement, and in particular to a nanometer length measurement system and method based on chromium atom transition frequency. Background Art

[0002] Nanotechnology studies the material world in the range of 0.1nm to 100nm. In the era of ultra-precision advanced manufacturing, innovation and technological progress in cutting-edge technologies such as nanomaterials, nanoelectronics, nanodynamics, and nanobiology are inseparable from nanotechnology. Nanometrology is a precision measurement technology at the nanoscale and is the basic support for advanced nanomanufacturing technology.

[0003] Traceability is a fundamental issue in nano-metrology. In the field of nano-length metrology, traceability is essential to achieve accurate, reliable and mutually comparable measurements, so that the measurement results can be associated with the reference standard through an uninterrupted traceability chain. Therefore, nano-measurement must build a complete length measurement system that can be traced back to the definition of "meter". The nano-metrology length traceability chain generally consists of the following parts: ① Definition of SI units; ② Implementation of reference standards; ③ Transfer of reference standards to the measurement system. Usually, the reference standard and the measurement process will affect the uncertainty of the measurement results. In addition, in different length measurement applications, the measurement range and accuracy requirements vary greatly. Therefore, the nano-metrology length traceability chain needs to be continuously optimized and enriched to meet higher requirements.

[0004] In the new definition of the International System of Units, which officially came into effect on May 20, 2019, seven natural constants were used to define seven basic units. Using basic constants as the basis for understanding and defining basic concepts in nature is the core idea of ​​realizing the definition of "meter". When measuring nanometer lengths, a certain basic constant should be used as the length reference, that is, the source of the length traceability chain. At present, the international community generally uses a standard wavelength or standard frequency in a vacuum with a specified uncertainty as the reference for length traceability. Among them, the most commonly used wavelength is the laser wavelength generated by an iodine-stabilized helium-neon laser: 632.99121258nm (relative uncertainty is 2.1×10 -11 ). However, the laser interferometer using the 633nm wavelength standard has the problem of poor adaptability to the wavelength environment and is difficult to meet widespread needs. At the same time, due to the large number of traceability links and the long traceability chain, the error accumulation in the transmission process is large, the long-term stability is insufficient, and it is difficult to meet the requirements of value flattening. The length traceability method newly recommended by the International Conference on Weights and Measures based on the silicon {220} crystal plane spacing d220 in a vacuum environment of 22.5°C has limited measurable feature sizes, and it is difficult to obtain true atomic resolution within a larger imaging range. Therefore, the development of different nano-metrology systems based on new physical constants can be an important expansion and effective supplement to the existing nano-metrology systems. Summary of the invention

[0005] The purpose of the present invention is to provide a nanometer length measurement system and method based on the transition frequency of chromium atoms to solve the problems mentioned in the background technology.

[0006] To achieve the above object, the present invention provides a nanometer length measurement system based on the transition frequency of chromium atoms, including a physical wavelength reference and a working standard substance, wherein the physical wavelength reference is locked to the chromium atom ( 7 S3 → 7 The working standard material is a chromium self-traceable series grating prepared by atomic lithography, and the grating period is traced back to the physical wavelength standard. The chromium self-traceable series grating includes a one-dimensional chromium self-traceable grating and a two-dimensional chromium self-traceable grating.

[0007] Preferably, the wavelength locking device of the physical wavelength reference comprises a laser, a tunable titanium sapphire laser, an external cavity frequency doubler and a femtosecond optical frequency comb which are arranged in sequence. The light emitted by the laser passes through the tunable titanium sapphire laser to obtain a tuned laser. The output light of the titanium sapphire laser is then tunably coupled to the external cavity frequency doubler. The generated laser is locked to the chromium atom ( 7 S3 → 7 P4) transition lines.

[0008] Preferably, the preparation process of the one-dimensional chromium self-traceable grating comprises the following steps: The metal powder is heated to a sublimation state in a vacuum environment and an atomic beam is drawn out in a leakage flow manner; The jet atomic beam passes through a frequency-stabilized laser to lock the laser wavelength to the transition frequency of the two energy levels of the chromium atom; The beam of chromium atoms is collimated by the cooling effect of the laser field; The collimated chromium atomic beam is subjected to spatial periodic distribution control by a laser standing wave field, and the propagation direction of the chromium atomic beam is perpendicular to the propagation direction of the laser standing wave field. A substrate on which chromium atoms are deposited is placed at a suitable position away from the laser standing wave field, so that periodically distributed chromium atoms are deposited on the substrate to form a one-dimensional chromium self-traceable grating structure.

[0009] Preferably, the preparation process of the two-dimensional chromium self-traceable grating comprises the following steps: Based on the atomic lithography technology, the first atomic lithography is performed on the substrate to obtain a one-dimensional atomic lithography deposited grating sample; The aperture is used to keep the convergent light pointing and the plane normal vector pointing of the one-dimensional atomic lithography deposition grating template unchanged, the one-dimensional atomic lithography deposition grating template is rotated, and it is ensured that there is an overlap between the area to be deposited and the deposited area of ​​the metal atomic beam, and the one-dimensional atomic lithography deposition grating template is perpendicular to the mirror surface of the deposition mirror, and the orientation of the mirror is adjusted so that the normal vector direction is parallel to the direction of the incident convergent light; The standing wave field formed by the converging light is adjusted so that the spatial height overlaps with the area where the metal atomic beam is to be deposited. A second atomic lithography is performed on the one-dimensional atomic lithography deposition grating template to form a two-dimensional chromium self-traceable grating structure.

[0010] The present invention also provides a nanometer length measurement method based on the transition frequency of chromium atoms, comprising the following steps: A self-traceable grating interferometer precision displacement measurement system is established with working standard materials as the core. The self-traceable grating interferometer precision displacement measurement system includes three optical path structures: homodyne, heterodyne and self-mixing. Based on the physical wavelength, a laser interferometer precision displacement measurement system is established that can be traced back to the 425.55nm physical wavelength standard. The self-traceable grating interferometer precision displacement measurement system and the laser interferometer precision displacement measurement system traceable to the 425.55nm physical wavelength standard are applied to the field of nanometer length measurement.

[0011] Preferably, the homodyne structure includes a coherent light source, a photoelectric detection module, a self-traceable grating and a signal processing module, which are connected in sequence. The self-traceable grating is arranged on the displacement motion platform to be measured. The laser generated by the coherent light source is transmitted through the photoelectric detection module, and then incident on the self-traceable grating, where it diffracts with the self-traceable grating, returns to the photoelectric detection module to continue to propagate, and enters the signal processing module. The signal processing module collects the interference signal to obtain the motion displacement and motion direction.

[0012] Preferably, the heterodyne structure includes a single-frequency laser module, a frequency shift module, a heterodyne displacement measurement module, a self-traceable grating and a signal processing module. The single-frequency laser module generates a single-frequency laser, which passes through the frequency shift module to obtain two linearly polarized lights with different frequencies and mutually orthogonal polarization states, forming a heterodyne light source. The heterodyne laser passes through the heterodyne displacement measurement module and is incident on the self-traceable grating. The diffracted light returns to the heterodyne displacement measurement module along the original optical path to obtain a measurement signal and a reference signal with displacement information. Finally, the signal processing module calculates the phase difference between the two signals and performs displacement conversion.

[0013] Preferably, the self-mixing structure includes a single-frequency laser module, a one-dimensional self-traceable grating, a detection module and a signal processing module. The single-frequency laser module generates a single-frequency laser, and the detection module receives the laser self-mixing interference signal information fed back by the one-dimensional self-traceable grating. The signal processing module uses a normalization algorithm to restore the signal and combines a phase unwrapping algorithm and a Hilbert transform algorithm to reconstruct the nano-displacement signal.

[0014] Preferably, the laser interferometer precision displacement measurement system traceable to the 425.55 nm physical wavelength standard includes a single-frequency laser module, a beam interference module, a photoelectric detection module and a signal processing module.

[0015] Preferably, the self-traceable grating interferometer precision displacement measurement system and the laser interferometer precision displacement measurement system traceable to the 425.55nm physical wavelength standard can verify their measurement capabilities through a comparison platform, which includes a laser interferometer moving mirror, a one-dimensional chromium self-traceable grating, a mechanical adapter module and a piezoelectric ceramic drive module.

[0016] Therefore, the present invention adopts the above-mentioned nanometer length measurement system and method based on the transition frequency of chromium atoms, which has the following beneficial effects: (1) The natural constant of chromium atomic transition frequency is materialized onto a chromium one-dimensional nano-grating by laser convergence atomic deposition, so that the grating can be directly traced back to the natural constant, with both independent traceability and ultra-high accuracy, consistency and uniformity; (2) In accordance with the principle of traceability requirements for metrological calibration, the use of chromium self-traceable gratings can achieve direct calibration, and has strong resistance to environmental interference and small error accumulation. It is suitable for comprehensive applications in nanometer length measurement and is a powerful supplement to the existing nanometer length value transfer system. (3) The grating interferometer based on the grating of the standard material is used for metrological applications. The traceability chain is short and the error accumulation is small. At the same time, the problem that the precision displacement measurement is easily disturbed by the change of the refractive index of the air is overcome, and the complete independent nanometer length metrology method with the grating interferometer as the core is expanded.

[0017] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a flow chart of a nanometer length measurement method based on chromium atom transition frequency according to an embodiment of the present invention; Figure 2 Schematic diagram of the preparation process of a one-dimensional chromium self-traceable grating according to an embodiment of the present invention; Figure 3 This is an AFM image of the diamond grating structure of the two-dimensional chromium self-traceable grating according to an embodiment of the present invention (the rotation angle θ is 60 degrees); Figure 4 Schematic diagram of a self-traceable homodyne grating interferometry precision displacement measurement system according to an embodiment of the present invention; Figure 5 Schematic diagram of a laser interferometer precision displacement measurement system based on a 425.5 nm physical wavelength standard according to an embodiment of the present invention.

[0019] Reference numerals

[0020] 1. Coherent light source; 2. Photoelectric detection module; 3. Self-traceable grating; 4. Displacement motion platform; 5. Signal processing module. DETAILED DESCRIPTION

[0021] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0022] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0023] Example

[0024] like Figure 1-3 As shown, the present invention provides a nanometer length measurement system based on the transition frequency of chromium atoms, including a physical wavelength reference and a working standard material, wherein the physical wavelength reference is locked to the chromium atom ( 7 S3 → 7 P4) transition line of 425.55nm laser wavelength. Chromium atomic transition line ( 7 S3 → 7 P4) corresponds to a wavelength of 425.55nm, which is a constant in nature.

[0025] The wavelength locking device of the physical wavelength reference includes a 532nm laser, a tunable titanium sapphire laser, an external cavity frequency doubler and a femtosecond optical frequency comb. The specific laser generation process is as follows: a laser that can pump 532nm laser is used as the pump source of the tunable titanium sapphire laser to obtain a laser tuned to 851nm wavelength; the output light of the titanium sapphire laser is then coupled to the external cavity frequency doubler to generate a 425.55nm wavelength laser; based on the induced fluorescence effect, the 425.55nm wavelength laser is locked to the chromium atom ( 7 S3 → 7 P4) transition lines.

[0026] The one-dimensional chromium self-traceable grating in the working standard material is prepared by laser convergence atomic deposition. The specific preparation process is: the atomic lithography system is evacuated to a vacuum, the atomic furnace is heated to sublimate the high-purity chromium powder in it and eject it in the form of an atomic beam, the ejected atomic beam passes through a frequency-stabilized laser to lock the laser wavelength at the transition frequency of the two energy levels of the chromium atom, the cooling laser standing wave field perpendicular to the atomic furnace cools and collimates the ejected atomic beam, and the collimated atomic beam passes through a slit and then is air-cooled under the action of the convergent laser standing wave field. The propagation direction of the chromium atomic beam is perpendicular to the propagation direction of the laser standing wave field. A substrate (i.e., a silicon substrate) on which chromium atoms are deposited is placed at a suitable distance from the laser standing wave field, so that the periodic distribution of chromium atoms is deposited on the silicon substrate. The period of the converged laser standing wave field is half of the laser wavelength, so the chromium grating has a period of λ / 2 in the direction of the standing wave field, that is, the theoretical value is 212.7705±0.0049nm. After 2.5 hours of deposition, a one-dimensional chromium self-traceable grating with a peak-to-valley height of 30nm can be obtained.

[0027] The preparation process must ensure that the laser wavelength is always locked on the chromium transition frequency, otherwise it will be impossible to obtain a working standard material grating that meets the requirements. In addition, the light cutting ratio of the focused laser standing wave field on the substrate silicon wafer is controlled within 50%.

[0028] The dimensions of the working standard material are as follows: the grating vector direction is greater than 3mm, the grating line direction is greater than 0.4mm, and the grating peak-to-valley height is greater than 30nm.

[0029] The one-dimensional chromium self-traceable grating in the working standard material has a fixed value of 212.781nm±0.008nm, which can be directly used to calibrate a commercial scanning electron microscope. The average pitch value measured by the scanning electron microscope at that position is calculated using the actual magnification of the instrument. The scale correction factor of the scanning electron microscope is corrected based on the deviation between the pitch value obtained by the scanning electron microscope and the fixed value of the one-dimensional chromium self-traceable grating.

[0030] The preparation process of the two-dimensional chromium self-traceable grating in the working standard material includes the following steps: Based on the atomic lithography technology, the first atomic lithography is performed on the substrate to obtain a one-dimensional atomic lithography deposited grating sample; By using the limiting function of the aperture, the convergent light direction and the plane normal vector direction of the one-dimensional atomic lithography grating template are kept unchanged, the grating template is rotated by an angle θ, and it is ensured that there is an overlap between the area to be deposited and the deposited area of ​​the metal atom beam, and the grating template is perpendicular to the mirror surface of the deposition mirror, and the orientation of the mirror is adjusted so that the normal vector direction is parallel to the direction of the incident convergent light; The standing wave field formed by the converging light is adjusted so that the spatial height overlaps with the area to be deposited by the metal atomic beam. A second atomic lithography is performed on the one-dimensional atomic lithography deposition grating template to form a two-dimensional atomic grating diamond grid structure, and one of the inner angles of the diamond is equal to the rotation angle θ.

[0031] Atomic lithography technology based on the transition frequency of chromium atoms provides an effective way to establish a new nanometer length measurement system. Atomic lithography technology mainly uses the dipole force of the laser standing wave field to manipulate the atomic movement, so that the cooled chromium atomic beam passes through the laser standing wave field to form a periodic grating structure on the substrate. Since the atomic deposition position strictly corresponds to the trough or antinode position of the laser standing wave field, the period of the structure is strictly traced back to the laser wavelength and has self-traceability. Taking the one-dimensional chromium atomic lithography grating as an example, the one-dimensional chromium atomic lithography grating with an actual fixed value of 212.781nm±0.008nm has been verified to have extremely high pitch accuracy and sample consistency, both in the order of 0.001nm. Self-traceable standard materials have successfully solved the problem of long traceability chain errors caused by the long dependence of grating values ​​on laser wavelength fixed values, shortening the nanometer length measurement traceability chain in various precision instruments and processing technologies, and providing important support for the flattening application of self-traceable gratings.

[0032] At present, based on the chromium transition frequency, a variety of self-traceable grating standard materials such as 1D212.8nm, 2D212.8nm, and 1D106.4nm have been prepared using atomic lithography technology and soft X-ray interferometry technology. They can be directly used as calibration standards for offline calibration of various high-precision measuring instruments such as scanning probe microscopes and scanning electron microscopes; at the same time, an ultra-precision displacement sensor based on self-traceable gratings has been developed. On the basis of achieving direct traceability, the robustness has been greatly improved, and on-site embedded nano-metrology can be realized. It has demonstrated sub-nanometer ultra-precision displacement measurement capabilities. Atomic force microscopes, accelerometers, grating pitch calibration devices and other metrological test instruments built on the basis of self-traceable grating ultra-precision displacement sensors can be applied to the field of nano-length metrology. Therefore, the nano-length metrology system based on the chromium atomic transition frequency has a flat and all-round application prospect in the field of nano-metrology.

[0033] The present invention also provides a nanometer length measurement method based on the transition frequency of chromium atoms, comprising the following steps: A self-traceable grating interferometric precision displacement measurement system is established with working standard materials as the core; Based on the physical wavelength, a laser interferometer precision displacement measurement system is established that can be traced back to the 425.55nm physical wavelength standard. According to the actual scene requirements, the self-traceable grating interferometer precision displacement measurement system and the laser interferometer precision displacement measurement system traceable to the 425.55nm physical wavelength standard are applied to the field of nanometer length measurement.

[0034] A self-traceable grating interferometry precision displacement measurement system is established with working standard materials as the core, including three optical path structures: homodyne, heterodyne and self-mixing.

[0035] like Figure 4 The homodyne structure includes a coherent light source 1, a photoelectric detection module 2, a self-traceable grating 3 and a signal processing module 5. The coherent light source 1, the photoelectric detection module 2 and the signal processing module 5 are connected in sequence. The self-traceable grating 3 is set on the displacement motion platform 4 to be measured. The laser generated by the coherent light source 1 is transmitted through the photoelectric detection module 2, and then incident on the self-traceable grating 3, diffracts with the self-traceable grating 3, returns to the photoelectric detection module 2 to continue to propagate, and enters the signal processing module 5. The signal processing module 5 collects the interference signal to obtain the motion displacement and motion direction.

[0036] Working principle of the homodyne structure: build a homodyne optical path structure, fix the working standard material grating on the three-dimensional adjustment frame, and fix the adjustment frame to the nano-displacement stage (displacement motion platform 4); fix the displacement stage to the optical platform, and use the grating diffraction method to adjust the grating shape so that the grating vector direction is parallel to the optical platform surface, and the grating line is perpendicular to the optical platform surface; based on the standard material grating, install the homodyne Littrow grating interferometer displacement measurement system; input a triangle wave signal to the displacement stage to make it move, and then debug the interferometer system to realize the displacement data reading.

[0037] The heterodyne structure includes a single-frequency laser module, a frequency shift module, a heterodyne displacement measurement module, a self-traceable grating and a signal processing module. The single-frequency laser module generates a single-frequency laser, which passes through the frequency shift module to obtain two linearly polarized lights with different frequencies and mutually orthogonal polarization states, forming a heterodyne light source. The heterodyne laser passes through the heterodyne displacement measurement module and is incident on the self-traceable grating. The diffracted light returns to the heterodyne displacement measurement module along the original optical path to obtain a measurement signal and a reference signal with displacement information. Finally, the signal processing module calculates the phase difference between the two signals and performs displacement conversion.

[0038] The self-mixing structure includes a single-frequency laser module, a one-dimensional self-traceable grating, a detection module and a signal processing module. The structure is built based on the Littrow diffraction optical path. The single-frequency laser module generates a single-frequency laser. The detection module receives the laser self-mixing interference signal information fed back by the one-dimensional self-traceable grating. The signal processing module uses a normalization algorithm to restore the signal and combines the phase unwrapping algorithm and the Hilbert transform algorithm to reconstruct the nano-displacement signal.

[0039] The original displacement signal of the homodyne and heterodyne self-traceable grating interferometer precision displacement measurement system built with working standard materials as the core is 106.4nm, and the displacement resolution can reach 0.1nm.

[0040] like Figure 5 Based on the physical wavelength as the core, a laser interferometer precision displacement measurement system traceable to the physical wavelength benchmark of 425.55nm is established, including a single-frequency laser module, a beam interference module, a photoelectric detection module and a signal processing module. The beam interference module constructs a spatially symmetrical, common-path multi-beam interference system. Based on the orthogonal phase solution method, the shortest geometric distance fitting method is used to suppress the nonlinear error of the interference precision displacement measurement system.

[0041] The self-traceable grating interferometry precision displacement measurement system built around working standard materials and the laser interferometry precision displacement measurement system based on the physical wavelength and traceable to the physical wavelength benchmark of 425.55nm can verify their measurement capabilities through comparative measurements. The comparison platform is designed based on the piezoelectric ceramic nano-displacement platform, which includes a laser interferometer moving mirror, a one-dimensional chromium self-traceable grating, a mechanical adapter module and a piezoelectric ceramic drive module. The mechanical adapter module ensures that the laser interferometer moving mirror is orthogonal to the one-dimensional chromium self-traceable grating, and that their centers are in the same plane.

[0042] Therefore, the present invention adopts the above-mentioned nanometer length measurement system and method based on the transition frequency of chromium atoms, and uses laser convergence atomic deposition to materialize the natural constant of the transition frequency of chromium atoms onto the chromium one-dimensional nano grating, so that the grating can be directly traced back to the natural constant, with both independent traceability and ultra-high accuracy, consistency and uniformity.

[0043] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A nanometer length measurement system based on chromium atomic transition frequency, characterized in that: It includes a physical wavelength reference and a working standard substance, wherein the physical wavelength reference is locked to the chromium atom ( 7 S3 → 7 The working standard material is a chromium self-traceable series grating prepared by atomic lithography, and the grating period is traced back to the physical wavelength standard. The chromium self-traceable series grating includes a one-dimensional chromium self-traceable grating and a two-dimensional chromium self-traceable grating.

2. The nanometer length measurement system based on chromium atom transition frequency according to claim 1, characterized in that: The wavelength locking device of the physical wavelength reference comprises a laser, a tunable titanium sapphire laser, an external cavity frequency doubler and a femtosecond optical frequency comb which are arranged in sequence. The light emitted by the laser passes through the tunable titanium sapphire laser to obtain a tuned laser. The output light of the titanium sapphire laser is then tunably coupled to the external cavity frequency doubler. The generated laser is locked to the chromium atom ( 7 S3 → 7 P4) transition lines.

3. The nanometer length measurement system based on chromium atom transition frequency according to claim 1, characterized in that: The preparation process of the one-dimensional chromium self-traceable grating comprises the following steps: The metal powder is heated to a sublimation state in a vacuum environment and an atomic beam is drawn out in a leakage flow manner; The jet atomic beam passes through a frequency-stabilized laser to lock the laser wavelength to the transition frequency of the two energy levels of the chromium atom; The beam of chromium atoms is collimated by the cooling effect of the laser field; The collimated chromium atomic beam is subjected to spatial periodic distribution control by a laser standing wave field, and the propagation direction of the chromium atomic beam is perpendicular to the propagation direction of the laser standing wave field. A substrate on which chromium atoms are deposited is placed at a suitable position away from the laser standing wave field, so that periodically distributed chromium atoms are deposited on the substrate to form a one-dimensional chromium self-traceable grating structure.

4. The nanometer length measurement system based on chromium atom transition frequency according to claim 1, characterized in that: The preparation process of the two-dimensional chromium self-traceable grating comprises the following steps: Based on the atomic lithography technology, the first atomic lithography is performed on the substrate to obtain a one-dimensional atomic lithography deposited grating sample; The aperture is used to keep the convergent light pointing and the plane normal vector pointing of the one-dimensional atomic lithography deposition grating template unchanged, the one-dimensional atomic lithography deposition grating template is rotated, and it is ensured that there is an overlap between the area to be deposited and the deposited area of ​​the metal atomic beam, and the one-dimensional atomic lithography deposition grating template is perpendicular to the mirror surface of the deposition mirror, and the orientation of the mirror is adjusted so that the normal vector direction is parallel to the direction of the incident convergent light; The standing wave field formed by the converging light is adjusted so that the spatial height overlaps with the center of the area to be deposited by the metal atomic beam, and a second atomic lithography is performed on the one-dimensional atomic lithography deposition grating template to form a two-dimensional chromium self-traceable grating structure.

5. A nanometer length measurement method based on the transition frequency of chromium atoms, applied to the nanometer length measurement system as described in claims 1-4, characterized in that: The following steps are involved: A self-traceable grating interferometer precision displacement measurement system is established with working standard materials as the core. The self-traceable grating interferometer precision displacement measurement system includes three optical path structures: homodyne, heterodyne and self-mixing. Based on the physical wavelength, a laser interferometer precision displacement measurement system is established that can be traced back to the 425.55nm physical wavelength standard. The self-traceable grating interferometer precision displacement measurement system and the laser interferometer precision displacement measurement system traceable to the 425.55nm physical wavelength standard are applied to the field of nanometer length measurement.

6. The nanometer length measurement method based on chromium atom transition frequency according to claim 5, characterized in that: The homodyne structure includes a coherent light source, a photoelectric detection module, a self-traceable grating and a signal processing module. The coherent light source, the photoelectric detection module and the signal processing module are connected in sequence. The self-traceable grating is arranged on the displacement motion platform to be measured. The laser generated by the coherent light source is transmitted through the photoelectric detection module, and then incident on the self-traceable grating, diffracts with the self-traceable grating, returns to the photoelectric detection module to continue to transmit, and enters the signal processing module. The signal processing module collects interference signals to obtain the motion displacement and motion direction.

7. The nanometer length measurement method based on chromium atom transition frequency according to claim 5, characterized in that: The heterodyne structure includes a single-frequency laser module, a frequency shift module, a heterodyne displacement measurement module, a self-traceable grating and a signal processing module. The single-frequency laser module generates a single-frequency laser, which passes through the frequency shift module to obtain two linearly polarized lights with different frequencies and mutually orthogonal polarization states, forming a heterodyne light source. The heterodyne laser passes through the heterodyne displacement measurement module and is incident on the self-traceable grating. The diffracted light returns to the heterodyne displacement measurement module along the original optical path to obtain a measurement signal and a reference signal with displacement information. Finally, the signal processing module calculates the phase difference between the two signals and performs displacement conversion.

8. The nanometer length measurement method based on chromium atom transition frequency according to claim 5, characterized in that: The self-mixing structure includes a single-frequency laser module, a one-dimensional self-traceable grating, a detection module and a signal processing module. The single-frequency laser module generates a single-frequency laser, and the detection module receives the laser self-mixing interference signal information fed back by the one-dimensional self-traceable grating. The signal processing module uses a normalization algorithm to restore the signal and combines a phase unwrapping algorithm and a Hilbert transform algorithm to reconstruct the nano-displacement signal.

9. The nanometer length measurement method based on chromium atom transition frequency according to claim 5, characterized in that: The laser interferometer precision displacement measurement system traceable to the 425.55nm physical wavelength standard includes a single-frequency laser module, a beam interference module, a photoelectric detection module and a signal processing module. The single-frequency laser module generates a single-frequency laser, and the beam interference module obtains the displacement information of the moving part. The photoelectric detection module receives the interference signal information, and the signal processing module uses the restored signal to solve the nano displacement signal.

10. The nanometer length measurement method based on chromium atom transition frequency according to claim 5, characterized in that: The self-traceable grating interferometer precision displacement measurement system and the laser interferometer precision displacement measurement system traceable to the 425.55nm physical wavelength standard can verify their measurement capabilities through a comparison platform, which includes a laser interferometer moving mirror, a one-dimensional chromium self-traceable grating, a mechanical adapter module and a piezoelectric ceramic drive module. The laser interferometer moving mirror and the one-dimensional chromium self-traceable grating are fixedly mounted on the mechanical adapter module at the same time, the mechanical adapter module is fixed on the piezoelectric ceramic drive module, the piezoelectric ceramic drives the mechanical adapter module to move, and the laser interferometer and the self-traceable grating interferometer simultaneously measure the motion displacement, and the performance verification is achieved by comparing the measurement results.

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