Preparation method of direct traceability grating with high diffraction efficiency

Abstract

The invention discloses a preparation method of a direct traceability grating with high diffraction efficiency, which belongs to the field of high-precision grating manufacturing, and comprises the following steps: 1) generating a neutral atom beam in vacuum based on a high-temperature thermal evaporation method; 2) reducing the transverse movement speed of the neutral atom beam by adopting laser Doppler cooling; 3) converging the atomic beams by using a laser standing wave field, and vertically depositing the atomic beams on the substrate to form a direct traceability grating structure; and 4) sequentially evaporating a metal film and a protective film on the surface of the direct traceability type grating by using a thermal evaporation method to obtain the direct traceability type grating standard template with high diffraction efficiency. The invention provides the preparation method of the direct traceability type grating with high diffraction efficiency, the diffraction efficiency of the direct traceability type grating can be remarkably improved, the operation is simple, and meanwhile, the self-traceability of the direct traceability type grating cannot be damaged.

Description

Technical Field

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

[0002] Ultra-precision displacement technology is a key technology in the field of precision engineering and nanotechnology. It allows us to accurately measure and control very small distances. Among various ultra-precision displacement technologies, grating interferometer 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 vital role in grating interferometers. They not only affect the measurement accuracy, but also determine the reliability and scope of application of the system. Specifically, gratings need to have the following characteristics: 1. High-precision periodicity: The periodicity of the grating needs to be highly consistent. Any slight period change will directly affect the measurement accuracy of the interferometer. Therefore, the manufacturing process of the grating requires extremely high precision to ensure that the spacing of each grating line is uniform and consistent. 2. High linearity: The linearity of the grating is crucial to ensure the accuracy of the measurement results. This means that the lines on the grating must be evenly distributed throughout the entire measurement range without distortion or bending. 3. Good thermal stability: The grating material should have a low thermal expansion coefficient to reduce measurement errors caused by temperature changes. In an environment with temperature fluctuations, the size and spacing of the grating remain stable, which is very important for maintaining high-precision measurements. 4. High resistance to environmental interference: The grating should be able to resist the influence of environmental factors such as humidity, dust, and chemical corrosion to ensure long-term stable operation without affecting its performance. 5. High reflectivity or transmittance: The reflectivity or transmittance of the grating needs to be high enough to ensure sufficient light intensity to participate in the interference, so as to obtain a clear and reliable interference pattern. 6. Mechanical stress resistance: The grating may be affected by mechanical stress during installation or long-term use. Good mechanical stress resistance can ensure the stability and life of the grating. Therefore, high-performance grating interferometers have very strict requirements on gratings. These requirements ensure that the interferometer can provide high-precision and high-stability measurement results, which directly affects the performance and application range of the grating interferometer.

[0004] The characteristics of direct traceability gratings meet the above requirements very well. Specifically: 1. During the preparation process of direct traceability gratings, the grating period corresponds to the standing wave field period 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 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 environmental interference resistance, taking the direct traceability grating made of chromium as an example, the dense oxide layer on the surface of the chromium grating makes the grating have significant environmental interference resistance and can cope with various complex environments. In addition, due to its high accuracy and consistency, the direct traceability grating can be used in the grating interferometer without calibration, which greatly reduces the transmission and accumulation of uncertainty.

[0005] The direct traceability grating interferometer is a nano-displacement sensor that uses a chromium atom photolithography grating as a physical reference. Its displacement measurement reference is directly traced back to the chromium atom transition frequency. It has the core feature of realizing the flattened transmission of "natural physical reference-displacement measurement reference", while taking into account the advantages of grating interferometer's strong resistance to environmental interference and robustness. However, the current direct traceability grating has low diffraction efficiency, which limits the performance of the direct traceability 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 direct traceability grating was only used statically, and everyone's preparation process only focused on the periodic stability of the grating under static conditions. Now the direct traceability grating has begun to be used dynamically, which has new requirements for the diffraction efficiency of the preparation process. In addition, when the direct traceability grating is calibrated by the diffraction method, the diffraction efficiency also needs to be improved.

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

[0007] From the perspective of improving measurement accuracy and efficiency, promoting the miniaturization and integration of optical instruments, and improving the stability and reliability of the system, the preparation method of high diffraction efficiency direct traceability grating has far-reaching significance for promoting the development of precision measurement technology, promoting the application of high-tech, and accelerating the transformation of scientific research results. Therefore, it is necessary to develop a new method for preparing high diffraction efficiency direct traceability grating (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 traceability 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 vertically deposit it onto a substrate to form a direct traceability grating structure;

[0013] S4. A metal film and a protective film are sequentially deposited on the surface of a 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 a neutral atomic beam with a certain divergence angle can be formed through the pre-collimation hole.

[0015] Preferably, in step S1, the temperature stability of the high-temperature evaporation source is controlled at ±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 type grating includes chromium, iron or aluminum, and the purity thereof is not less than 99.5%.

[0017] Preferably, step S2 specifically includes: using a laser with a certain detuning amount from the atomic transition frequency to act vertically on the moving direction of the neutral atomic beam, and then returning along the original path through a reflector to cool the lateral velocity of the neutral atomic beam to a limit, thereby reducing the lateral 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 convergent 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 traceability 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 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 a layer of metal film is coated 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 is continuously evaporated to finally obtain 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 of the peak-to-valley height of the direct traceability grating, and the protective film thickness is one-quarter of 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 A schematic diagram of the structure of preparing a direct traceability grating according to the present invention;

[0026] Figure 2 It 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. Converged 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, 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.

[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, further definition and explanation thereof is not required in subsequent drawings.

[0031] Example

[0032] like Figure 1-2 As shown, a method for preparing a direct traceability 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 direct traceability grating with high diffraction efficiency. The grating is a small pitch traceability standard material of a hundred 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 direct traceability type grating is made of a material selected from 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, the chromium atomic beam 1 is generated by thermal evaporation, in which the temperature stability of the high-temperature evaporation source is controlled at ±0.1% to ensure the flux stability of the atomic beam, and the vacuum degree of the evaporation chamber is better than 2E-6 Pa. For the chromium element, the position of the pre-collimation hole is 60 cm away from the atomic beam nozzle, and the pre-collimation hole diameter is 6 mm, and the atomic beam is pre-collimated.

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

[0038] A laser with a certain detuning amount from the atomic transition frequency is used perpendicularly to the direction of motion of the neutral atom beam, and then returns along the original path through a reflector to cool the lateral velocity of the neutral atom beam to a limit, thereby reducing the lateral velocity of the atom 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 atom beam, and the laser frequency needs to have an appropriate detuning amount from the neutral atom transition frequency. Another laser beam is added at the farther end of the neutral atom beam as a detection light to interact with the neutral atoms to produce fluorescence, and 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 The 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 optimal. 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 the two cooling light beams 2 are perpendicular to the atomic beam. The power of the cooling light 2 needs to be selected in combination with 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 is 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 through a reflector to form a stable laser standing wave field. The neutral atomic beam is periodically regulated to form a direct traceability 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 The laser beam with a transition frequency of -250Mhz detuning is converged by a convex lens, and the direction of the laser beam is consistent with the direction of the cooling light 2, while returning along the 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 node of the standing wave, and finally forms a self-traceable chromium grating structure 5 on the 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 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 atom beam.

[0045] The substrate 6 material used is indium phosphide InP, silicon Si, zero expansion glass, etc.

[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 focusing 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 type grating by using a thermal evaporation method to obtain a direct traceability type grating standard sample with high diffraction efficiency.

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

[0050] Specifically, the metal film vapor 7 is uniformly deposited on the surface of the direct traceability grating. There is no need to add converging light to periodically control the atoms. Therefore, there is no requirement for the lateral velocity of the atoms, and only the uniformity of the evaporation is required. The metal film 8 obtained by uniform evaporation on the surface of the direct traceability grating can increase the reflectivity of the incident light. The protective film vapor 9 is uniformly evaporated on the surface of the metal film 8 to obtain the protective film 10. Finally, a direct traceability grating with high diffraction efficiency is obtained, and the first-order diffraction efficiency of the direct traceability grating is increased from 7% before coating to 21% after coating, which is three times the original.

[0051] The metal film 8 is made of silver Ag, aluminum Al or gold Au and the protective film 10 is made of magnesium fluoride MgF2 or silicon derived material SiO x The thickness of the metal film 8 is usually half of the peak-to-valley height of the direct-traceable grating, and the thickness of the protective film 10 is one-fourth of the peak-to-valley height of the direct-traceable 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 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 method for preparing a direct traceability 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 vertically deposit it onto a substrate to form a direct traceability grating structure; S4. A metal film and a protective film are sequentially deposited on the surface of a direct traceability grating by thermal evaporation to obtain a direct traceability grating standard sample with high diffraction efficiency.

2. The method for preparing a direct traceability grating with high diffraction efficiency according to claim 1, characterized in that: 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 a neutral atomic beam with a certain divergence angle can be formed through the pre-collimation hole.

3. The method for preparing a direct traceability grating with high diffraction efficiency according to claim 2, characterized in that: In step S1, the temperature stability of the high-temperature evaporation source is controlled at ±0.1%, and the vacuum degree of the evaporation chamber is better than 2E-6 Pa.

4. The method for preparing a direct traceability grating with high diffraction efficiency according to claim 2, characterized in that: In step S1, the direct traceability type 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%.

5. The method for preparing a direct traceability grating with high diffraction efficiency according to claim 1, characterized in that: Step S2 specifically includes: using a laser with a certain detuning amount from the atomic transition frequency to act vertically on the moving direction of the neutral atomic beam, and then returning along the original path through a reflector to cool the lateral velocity of the neutral atomic beam to the limit, thereby reducing the lateral velocity of the atomic beam.

6. The method for preparing a direct traceability grating with high diffraction efficiency according to claim 1, characterized in that: 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 convergent 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 traceability grating structure that can be traced back to the atomic transition frequency.

7. The method for preparing a direct traceability grating with high diffraction efficiency according to claim 6, characterized in that: 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 the node or antinode of the laser standing wave field, and the frequency stability of the deposited laser wavelength must be maintained within the order of 100 kHz, while the direction of the laser is strictly orthogonal to the neutral atom beam.

8. The method for preparing a direct traceability grating with high diffraction efficiency according to claim 6, characterized in that: 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.

9. The method for preparing a direct traceability grating with high diffraction efficiency according to claim 1, characterized in that: Step S4 is specifically as follows: firstly a layer of metal film is coated on the surface of the direct traceability type grating by thermal evaporation coating method, and then the coating material is replaced, and the outermost protective film is continuously evaporated to finally obtain a direct traceability type grating with high diffraction efficiency.

10. The method for preparing a direct traceability grating with high diffraction efficiency according to claim 9, characterized in that: 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 peak-to-valley height of the direct traceability grating, and the protective film thickness is one quarter of the peak-to-valley height of the direct traceability grating.

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