A method for preparing a direct traceable grating with high diffraction efficiency

Abstract

The present invention discloses a method for preparing a direct traceability grating with high diffraction efficiency, belonging to the field of high-precision grating manufacturing. The method comprises the following steps: 1) generating a neutral atomic beam in a vacuum using a high-temperature thermal evaporation method; 2) reducing the lateral motion velocity of the neutral atomic beam using laser Doppler cooling; 3) converging the atomic beam using a laser standing wave field and depositing it vertically onto a substrate to form a direct traceability grating structure; and 4) sequentially depositing a metal film and a protective film on the surface of the direct traceability grating using a thermal evaporation method to obtain a standard sample of a direct traceability grating with high diffraction efficiency. The present invention provides a method for preparing a direct traceability grating with high diffraction efficiency, which can significantly improve the diffraction efficiency of the direct traceability grating, is simple to operate, and does not destroy the self-traceability of the direct traceability grating.

Description

Technical Field

[0001] The present invention relates to the field of high-precision grating manufacturing, and in particular to a method for preparing a direct traceability grating with high diffraction efficiency. Background Art

[0002] Ultra-precision displacement technology is a key technology in the fields of precision engineering and nanotechnology. It allows us to accurately measure and control very small distances. Among various ultra-precision displacement technologies, grating interferometry instrument measurement has the advantages of high precision, high resolution, stability, good repeatability, non-contact measurement, wide dynamic range and strong environmental adaptability. It is particularly suitable for high-precision fields such as integrated circuits.

[0003] Gratings play a crucial role in grating interferometers, impacting not only measurement accuracy but also the reliability and applicability of the system. Specifically, gratings must possess the following characteristics: 1. High-precision periodicity: The grating's periodicity must be highly consistent; any slight variation in period will directly impact the interferometer's measurement accuracy. Therefore, the grating's manufacturing process requires extremely high precision to ensure uniform spacing across each grating line. 2. High linearity: Grating linearity is crucial for accurate measurement results. This means the lines on the grating must be evenly spaced across the entire measuring range, without distortion or bowing. 3. Good thermal stability: The grating material should have a low coefficient of thermal expansion to reduce measurement errors caused by temperature fluctuations. Maintaining stable grating dimensions and spacing in environments with fluctuating temperatures is crucial for maintaining high-precision measurements. 4. High resistance to environmental interference: The grating should be resistant to environmental factors such as humidity, dust, and chemical corrosion, ensuring long-term stable operation without compromising performance. 5. High reflectivity or transmittance: The reflectivity or transmittance of the grating must be high enough to ensure sufficient light intensity for interference, thereby obtaining a clear and reliable interference pattern. 6. Mechanical stress resistance: Gratings may be affected by mechanical stress during installation or long-term use. Good mechanical stress resistance ensures the stability and lifespan of the grating. Therefore, high-performance grating interferometers place very strict requirements on the grating. These requirements ensure that the interferometer can provide high-precision and high-stability measurement results, directly affecting the performance and application range of the grating interferometer.

[0004] The characteristics of direct traceable gratings meet the above requirements very well. Specifically: 1. During the preparation process of the direct traceable grating, the grating period corresponds to the period of the standing wave field formed by the laser passing through the reflector, and the laser wavelength is locked to the atomic energy level transition constant. Therefore, the period of the grating is strictly traced back to the atomic energy level transition constant, and the periodicity and high linearity of the grating can be guaranteed. 2. The grating can be deposited on different substrates according to different needs. For example, it can be deposited on zero expansion glass when thermal stability is required. 3. In terms of resistance to environmental interference, taking the direct traceable grating prepared with chromium as the material as an example, the dense oxide layer on the surface of the chromium grating makes the grating significantly resistant to environmental interference and can cope with various complex environments. In addition, due to its high accuracy and consistency, the direct traceable grating can be used in the grating interferometer without calibration, which greatly reduces the transmission and accumulation of uncertainty.

[0005] The directly traceable grating interferometer is a nano-displacement sensor that uses a chromium atom photolithography grating as a physical reference. Its displacement measurement reference is directly traceable to the chromium atomic transition frequency. It has the core feature of realizing the flattened transfer of "natural physical reference-displacement measurement reference" while taking into account the advantages of the grating interferometer in terms of environmental resistance and robustness. However, the current directly traceable grating has low diffraction efficiency, which limits the performance of the directly traceable grating interferometer. Low diffraction efficiency will lead to low laser interference contrast, thus affecting the stability of the measurement. On the other hand, the original directly traceable grating was only used statically, and the preparation process only focused on the periodic stability of the grating under static conditions. Now that directly traceable gratings are beginning to be used dynamically, new requirements are placed on the diffraction efficiency of the preparation process. In addition, when the directly traceable grating is calibrated using the diffraction method, the diffraction efficiency also needs to be improved.

[0006] Before this, in order to improve the diffraction efficiency of direct traceability gratings, the peak-to-valley height of the grating was usually optimized to increase the diffraction efficiency of the grating. However, there is an upper limit to the diffraction efficiency improved by this method, and the improvement effect on the use of direct traceability grating interferometers is very limited.

[0007] The fabrication of directly traceable gratings with high diffraction efficiency has far-reaching significance for advancing the development of precision measurement technology, promoting the application of advanced technologies, and accelerating the translation of scientific research results, in terms of improving measurement accuracy and efficiency, promoting the miniaturization and integration of optical instruments, and enhancing system stability and reliability. Therefore, it is necessary to develop new methods for fabricating directly traceable gratings with high diffraction efficiency (while ensuring that the grating spacing is not affected). Summary of the Invention

[0008] The purpose of the present invention is to provide a method for preparing a direct traceability grating with high diffraction efficiency, which significantly improves the grating diffraction efficiency without changing the direct traceability of the grating.

[0009] To achieve the above object, the present invention provides a method for preparing a direct traceable grating with high diffraction efficiency, comprising the following steps:

[0010] S1. Generate neutral atom beam in vacuum based on high-temperature thermal evaporation method;

[0011] S2, using laser Doppler cooling to reduce the lateral motion speed of the neutral atom beam;

[0012] S3, using a laser standing wave field to converge the atomic beam and deposit it vertically onto the substrate to form a direct traceability grating structure;

[0013] S4. A metal film and a protective film are sequentially deposited on the surface of the direct traceability grating by thermal evaporation to obtain a direct traceability grating standard sample with high diffraction efficiency.

[0014] Preferably, step S1 is specifically as follows: placing the direct traceability grating preparation material into a high-temperature evaporation source crucible, evacuating the vacuum chamber to a high vacuum condition, placing a small hole at a certain distance from the crucible as a pre-collimation hole, and forming a neutral atomic beam with a certain divergence angle through the pre-collimation hole.

[0015] Preferably, in step S1, the temperature stability of the high-temperature evaporation source is controlled within ±0.1%, and the vacuum degree of the evaporation chamber is better than 2E-6 Pa.

[0016] Preferably, in step S1, the preparation material of the direct traceability grating includes chromium, iron or aluminum, and the purity thereof is not less than 99.5%.

[0017] Preferably, step S2 is specifically as follows: using a laser with a certain detuning amount from the atomic transition frequency to act perpendicularly on the moving direction of the neutral atomic beam, and then returning to the original path through a reflector to cool the transverse velocity of the neutral atomic beam to a limit, thereby reducing the transverse velocity of the atomic beam.

[0018] Preferably, step S3 is specifically as follows: using a laser beam that has a certain detuning amount from the atomic transition frequency, converging it through a convex lens to obtain converged deposition light, and then returning it through a reflector to form a stable laser standing wave field, and periodically regulating the neutral atomic beam to form a direct traceable grating structure that can be traced back to the atomic transition frequency.

[0019] Preferably, in step S3, when the laser frequency of the laser beam is positively or negatively detuned relative to the atomic transition frequency, the laser beam is deposited at a node or antinode position of the laser standing wave field, and the frequency stability of the deposited laser wavelength is maintained within the order of 100 kHz, while the direction of the laser is strictly orthogonal to the neutral atom beam.

[0020] Preferably, in step S3, the substrate material is indium phosphide, silicon and zero-expansion glass, and the laser standing wave field is a one-dimensional standing wave field or a two-dimensional standing wave field.

[0021] Preferably, step S4 is specifically as follows: firstly depositing a layer of metal film on the surface of the direct traceability grating by thermal evaporation coating method, then replacing the coating material, and continuing to evaporate the outermost protective film, and finally obtaining a direct traceability grating with high diffraction efficiency.

[0022] Preferably, in step S4, the metal film material includes silver, aluminum or gold, the protective film is a derivative material of magnesium fluoride or silicon, the metal film thickness is half the peak-to-valley height of the direct traceability grating, and the protective film thickness is one-quarter the peak-to-valley height of the direct traceability grating.

[0023] Therefore, the present invention adopts the above-mentioned method for preparing a direct traceability grating with high diffraction efficiency, which has the following beneficial effects: it can significantly improve the diffraction efficiency of the direct traceability grating, is simple to operate, and at the same time does not destroy the self-traceability of the direct traceability grating.

[0024] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the structure of the direct traceability grating prepared by the present invention;

[0026] Figure 2 This is a flow chart of a method for preparing a direct traceable grating with high diffraction efficiency according to the present invention;

[0027] Reference numerals

[0028] 1. Chromium atomic beam; 2. Cooling light; 3. Collimated atomic beam; 4. Converging deposition light; 5. Self-traceable chromium grating structure; 6. Substrate; 7. Metal film vapor; 8. Metal film; 9. Protective film vapor; 10. Protective film. DETAILED DESCRIPTION

[0029] 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, not all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings herein 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 of 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.

[0030] 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, it does not need to be further defined or explained in subsequent drawings.

[0031] Example

[0032] like Figure 1-2 As shown, a method for preparing a directly traceable grating with high diffraction efficiency is provided. The method is based on laser convergence atomic deposition technology and thermal evaporation coating technology to prepare a directly traceable grating with high diffraction efficiency. The grating is a small pitch traceable standard material with a scale of 100 nanometers or less. The specific steps of the method are as follows:

[0033] S1. Generate neutral atom beam in vacuum based on high-temperature thermal evaporation method.

[0034] The direct traceability grating preparation material is placed in a high-temperature evaporation source crucible, the vacuum chamber is evacuated to a high vacuum condition, and a small hole is placed at a certain distance from the crucible as a pre-collimation hole. A neutral atomic beam with a certain divergence angle can be formed through the pre-collimation hole.

[0035] The preparation material of the direct traceability grating is one of the metals such as chromium Cr, iron Fe or aluminum Al, and its purity is not less than 99.5%.

[0036] Taking chromium atoms as an example, a chromium atomic beam 1 is generated via thermal evaporation. The temperature stability of the high-temperature evaporation source must be controlled within ±0.1% to ensure beam flux stability, and the evaporation chamber vacuum is maintained at better than 2E-6 Pa. For chromium, a pre-collimation aperture with a diameter of 6 mm is located 60 cm from the beam nozzle to pre-align the atomic beam.

[0037] S2. Use laser Doppler cooling to reduce the transverse motion speed of the neutral atom beam.

[0038] A laser with a certain detuning amount from the atomic transition frequency is used to act perpendicularly on the direction of motion of the neutral atomic beam, and then returns along the original path through a reflector, cooling the lateral velocity of the neutral atomic beam to the limit, thereby reducing the lateral velocity of the atomic beam and preparing for the subsequent laser convergence of atoms. The key to the above cooling process is that the laser direction needs to be orthogonal to the central motion direction of the neutral atomic beam, and the laser frequency needs to have an appropriate detuning amount from the neutral atomic transition frequency. Another laser beam is added at the farther end of the neutral atomic beam as a detection light to interact with the neutral atoms to produce fluorescence. The cooling effect is judged by observing the degree of influence of the intervention and non-intervention of the cooling light 2 on the intensity and width of the fluorescence.

[0039] Cooling light 2 is relative to chromium atoms 7 S 3 →7 P 4 A laser beam with a certain detuning amount in the transition frequency decelerates the lateral velocity of the atomic beam based on the Doppler cooling principle, thereby achieving the purpose of collimating the atomic beam. The collimated atomic beam 3 undergoes laser Doppler cooling. During the cooling process, it is necessary to ensure that the two cooling light beams 2 return along the original path while being orthogonal to the atomic beam, so that the cooling effect of the atomic beam is optimized. The two cooling light beams 2 refer to the incident laser beam and the laser beam reflected back by the reflector, which are essentially the same laser beam, but the optical path of the reflected laser beam needs to coincide with the incident laser beam and both cooling light beams 2 are perpendicular to the atomic beam. The power of the cooling light 2 needs to be selected based on the actual cooling effect.

[0040] The detuning amount of the laser is controlled at half the natural line width of the atomic transition frequency, and the two cooling light beams 2 are adjusted to be orthogonal to the atomic beam to achieve the best cooling effect on the left and right sides.

[0041] S3. The atomic beam is converged by using a laser standing wave field and vertically deposited onto the substrate 6 to form a direct traceability grating structure, wherein the laser standing wave field is locked to the atomic transition frequency and has a certain detuning amount relative to it.

[0042] A laser beam that is detuned from the atomic transition frequency is converged through a convex lens to obtain converged deposition light 4, which is then returned along the same path through a reflector to form a stable laser standing wave field. The neutral atomic beam is periodically regulated to form a direct traceable grating structure that can be traced back to the atomic transition frequency.

[0043] The converged deposition light 4 is relative to the chromium atom 7 S 3 → 7 P 4 A laser beam with a transition frequency detuned by -250 MHz is converged by a convex lens, aligning its direction with the cooling beam 2 while returning along its original path to form a stable laser standing wave field. The collimated atomic beam 3 passes through the standing wave field formed by the converging light and is deposited at the nodes of the standing wave, ultimately forming a self-traceable chromium grating structure 5 on a substrate 6.

[0044] When the laser frequency of the laser beam is positively or negatively detuned relative to the atomic transition frequency, the laser beam is deposited at the node or antinode position of the laser standing wave field, and the frequency stability of the deposited laser wavelength must be maintained within the order of 100 kHz. At the same time, the direction of the laser should be strictly orthogonal to the neutral atomic beam.

[0045] The substrate 6 is made of indium phosphide (InP), silicon (Si), zero-expansion glass, and the like.

[0046] The laser standing wave field can be a one-dimensional standing wave field or a two-dimensional standing wave field.

[0047] The detuning amount of the laser depends on the transition energy level of the material used, and the direction of the converging laser beam and the cooling light 2 must be consistent.

[0048] S4. A metal film 8 and a protective film 10 are sequentially deposited on the surface of the direct traceability grating by using a thermal evaporation method to obtain a direct traceability grating standard sample with high diffraction efficiency.

[0049] A metal film 8 is first deposited on the surface of the direct traceability grating by thermal evaporation coating method, and then the coating material is replaced and the outermost protective film 10 is continuously evaporated to finally obtain a direct traceability grating with high diffraction efficiency.

[0050] Specifically, a metal film vapor 7 is uniformly deposited on the surface of a direct traceability grating. There is no need to add converging light to periodically control the atoms, so there are no requirements for the lateral velocity of the atoms; only uniformity of the vapor deposition is required. The metal film 8 uniformly deposited on the surface of the direct traceability grating increases the reflectivity of incident light. A protective film vapor 9 is uniformly deposited on the surface of the metal film 8 to form a protective film 10. The result is a direct traceability grating with high diffraction efficiency, increasing its first-order diffraction efficiency from 7% before coating to 21% after coating, a threefold increase.

[0051] The metal film 8 is made of silver, aluminum, or gold. The protective film 10 is made of magnesium fluoride, MgF2, or a silicon derivative, SiO. x The thickness of the metal film 8 is usually half of the peak-to-valley height of the direct traceability grating, and the thickness of the protective film 10 is one quarter of the peak-to-valley height of the direct traceability grating.

[0052] Therefore, the present invention adopts the above-mentioned method for preparing a direct traceability grating with high diffraction efficiency, which can significantly improve the diffraction efficiency of the direct traceability grating, is simple to operate, and does not destroy the self-traceability of the direct traceability grating.

[0053] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. 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 solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A method for preparing a direct traceable grating with high diffraction efficiency, characterized in that: The following steps are involved: S1. Generate neutral atom beam in vacuum based on high-temperature thermal evaporation method; S2, using laser Doppler cooling to reduce the lateral motion speed of the neutral atom beam; S3, using a laser standing wave field to converge the atomic beam and deposit it vertically onto the substrate to form a direct traceability grating structure; S4. Using thermal evaporation to sequentially deposit a metal film and a protective film on the surface of the direct traceability grating to obtain a direct traceability grating standard sample with high diffraction efficiency; Step S1 specifically comprises: placing the direct traceability grating preparation material into a high-temperature evaporation source crucible, evacuating the vacuum chamber to a high vacuum condition, and placing a small hole at a certain distance from the crucible as a pre-collimation hole. A neutral atomic beam with a certain divergence angle can be formed through the pre-collimation hole; In step S1, the temperature stability of the high-temperature evaporation source is controlled within ±0.1%, and the vacuum degree of the evaporation chamber is better than 2E-6 Pa; Step S2 specifically comprises: using a laser with a certain detuning amount from the atomic transition frequency to act perpendicularly on the direction of motion of the neutral atomic beam, and then returning along the original path through a reflector, thereby cooling the transverse velocity of the neutral atomic beam to a limit, thereby reducing the transverse velocity of the atomic beam; the detuning amount of the laser is controlled to be half the natural line width of the atomic transition frequency, and at the same time, the two cooling beams are adjusted to be orthogonal to the atomic beam; Step S3 specifically comprises: using a laser beam that is detuned from the atomic transition frequency by a certain amount, converging it through a convex lens to obtain a converged deposition light, and then returning it through a reflector to form a stable laser standing wave field, and periodically regulating the neutral atomic beam to form a directly traceable grating structure that can be traced back to the atomic transition frequency; In step S3, when the laser frequency of the laser beam is positively or negatively detuned relative to the atomic transition frequency, the laser beam is deposited at a node or antinode of the laser standing wave field, and the frequency stability of the deposition laser wavelength is maintained within the order of 100 kHz. At the same time, the direction of the laser is strictly orthogonal to the neutral atom beam. In step S4, the metal film material is silver, aluminum or gold, the protective film is a derivative material of magnesium fluoride or silicon, the metal film thickness is half of the direct traceability grating peak-to-valley height, and the protective film thickness is one-quarter of the direct traceability grating peak-to-valley height.

2. The method for preparing a direct traceable grating with high diffraction efficiency according to claim 1, wherein: In step S1, the direct traceability grating is made of a material selected from the group consisting of chromium, iron, and aluminum, and its purity is not less than 99.5%.

3. The method for preparing a direct traceable grating with high diffraction efficiency according to claim 1, wherein: In step S3, the substrate material is indium phosphide, silicon and zero-expansion glass, and the laser standing wave field is a one-dimensional standing wave field or a two-dimensional standing wave field.

4. The method for preparing a direct traceable grating with high diffraction efficiency according to claim 1, wherein: Step S4 specifically comprises: first coating a metal film on the surface of the direct traceability grating by thermal evaporation coating method, then replacing the coating material, and continuing to evaporate the outermost protective film, finally obtaining a direct traceability grating with high diffraction efficiency.

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