A multi-step periodic grating structure and a preparation method thereof

Abstract

The present invention discloses a multi-step periodic grating structure and a preparation method thereof, relating to the technical field of micro-displacement detection. It includes a periodic multi-step grating structure. Each period of the multi-step grating structure includes a substrate and a four-step grating structure. The four-step grating structures are all arranged on the substrate. According to the order from right to left within a single period, the four-step grating structures are respectively the first-step grating structure, the second-step grating structure, the third-step grating structure, and the fourth-step grating structure, which are layer structure arrays of three different heights. The present invention realizes the regulation and weakening of the zero-order diffracted light through structural improvement, so as to achieve the effect of improving the stability of the laser in the detection system. The multi-step periodic grating structure prepared by the corresponding preparation method has the function of weakening the zero-order light regulation, can realize a certain range of light intensity regulation, is convenient for preparation and integration, has a high diffraction efficiency, and can be applied to the field of integrated high-precision displacement detection.

Description

Technical Field

[0001] The present invention relates to the technical field of micro-displacement detection, in particular to a multi-step periodic grating structure and a preparation method thereof. Background Art

[0002] With the rapid progress of precision instrument manufacturing, aerospace and microelectronics manufacturing, the demand for ultra-precision displacement detection accuracy in various precision manufacturing fields has continued to increase. Among a series of ultra-precision displacement detection technologies, diffraction grating interferometry micro-displacement detection technology has attracted widespread attention from industry insiders due to its low cost, high detection accuracy and integration potential.

[0003] At present, the main problem to be solved in the diffraction grating interferometric micro-displacement detection technology is the further improvement of detection stability. Among them, the unstable fluctuation of the light source caused by the reflection of the zero-order diffraction light of the metal grating is particularly prominent. Therefore, it is necessary to realize the modulation of the zero-order diffraction reflection light through the improved design of the grating structure to improve the stability of the detection system. Summary of the invention

[0004] In order to improve the stability of diffraction grating interference type micro-displacement detection, the present invention provides a multi-step periodic grating structure and a preparation method thereof.

[0005] The present invention is realized by the following technical scheme: a multi-step periodic grating structure, including a periodic multi-step grating structure, each period of the multi-step grating structure includes a substrate and a four-step grating structure, the four-step grating structure is arranged on the substrate, and the four-step grating structure is respectively a first step grating structure, a second step grating structure, a third step grating structure, and a fourth step grating structure in the order from right to left in a single period. The main factor interfering with the stability of the displacement detection system is the vertical reflection of the reflected zero-order diffraction light back into the laser emission cavity. The present invention realizes the regulation and weakening of the zero-order diffraction light through structural improvement, so as to achieve the effect of improving the stability of the laser of the detection system.

[0006] The first step grating structure includes a first transmission layer and a first metal reflection layer, wherein the first metal reflection layer is coated on the first transmission layer; the material refractive index of the first transmission layer is 1.4-1.9, and the material reflectivity of the first metal reflection layer is 0.5-1.0; the period of the first step grating structure is 0.5 μm-2 μm; the thickness of the first transmission layer h a Refractive index of the transmitting material n satisfy , to meet the optical path difference required for destructive interference in the medium; the overall thickness of the first metal reflection layer is 100 nm to 300 nm, including an oxide absorption layer with a thickness of 20 to 80 nm; the reflectivity of the oxide absorption layer is 0.1 to 0.3; λ is the wavelength of the laser source. The first transmission layer can be integral with or in close contact with the substrate.

[0007] The second stepped grating structure includes a second transmission layer, which is in close contact with or integral with the first transmission layer; the second transmission layer is made of the same material as the first transmission layer, and the thickness of the second transmission layer h a is related to the refractive index of the transmission material n to meet ; the period of the second stepped grating structure is 0.5 μm to 2 μm. The second transmission layer can also be integral with or in close contact with the substrate.

[0008] The third stepped grating structure includes a third metal reflection layer, which is coated on the substrate; the third metal reflection layer has the same material and thickness as the first metal reflection layer, and the period of the third stepped grating structure is 0.5 μm to 2 μm.

[0009] The fourth stepped grating structure is the substrate, without a transmission layer and a metal reflection layer, and the period of the fourth stepped grating structure is 0.5 μm to 2 μm.

[0010] Preferably, the third stepped grating structure has the same period and duty cycle as the first stepped grating structure; the fourth stepped grating structure has the same duty cycle as the second stepped grating structure.

[0011] Preferably, the first stepped grating structure, the second stepped grating structure, the third stepped grating structure and the fourth stepped grating structure have the same duty cycle.

[0012] Preferably, the first transmission layer and the second transmission layer are made of materials with good light transmittance, and the light transmittance is > 95%. BF33 glass can be used, but it is not limited to BF33 glass. The first metal reflection layer and the third metal reflection layer are made of chromium oxide and chromium, and the set laser source wavelength λ is 850 nm, but it is not limited to this wavelength.

[0013] The present invention also provides a preparation method for a multi-stepped periodic grating structure, and the obtained product is a multi-stepped periodic grating structure. The method includes the following steps:

[0014] 1) Provide a transparent substrate, which has good light transmittance, and its light transmittance is greater than 95%;

[0015] 2) Design a photoresist mask that meets the periodicity and can be used to fabricate a multi-layer structure with a four-step grating structure;

[0016] 3) First, fabricate the third-step grating structure. Use a photoresist mask complementary to the target grating structure, spin coating speed, and complete high-precision patterning transfer by controlling the exposure dose and development dose. Expose, develop, etch, deposit, and strip the substrate. Etch the transparent substrate to the etching depth of the third-step grating structure to make it meet the target depth of the wavelength and refractive index relationship. Then, at the etched target depth of the transparent substrate, use physical vapor deposition or chemical vapor deposition to deposit a metal reflective layer on the surface of the etched target position, and analyze and evaluate the metal thickness through surface measurement technology to see if it meets the expected standard; Remove the photoresist mask and the excess metal reflective layer, and evaluate the photoresist mask residue to ensure that it does not interfere with the subsequent lithography process;

[0017] 4) Fabricate the first-step grating structure. Prepare a photoresist mask that matches the formed transparent substrate. Similarly, by controlling the spin coating speed, film thickness, exposure dose, and drying temperature, according to the thickness required for the first transmission layer in the first-step grating structure 1 as , etch the corresponding depth at the target position on the substrate surface through anisotropic etching technology; Then deposit a metal reflective layer on the surface of the etched target position, and analyze and evaluate the metal thickness through surface measurement technology to see if it meets the expected standard; Remove the photoresist mask and the excess metal reflective layer, and evaluate the photoresist mask residue to ensure that it does not interfere with the subsequent lithography process;

[0018] 5) Use precision-designed and manufactured masks and lithography technology to prepare a photoresist mask that matches the formed transparent substrate. Control the spin coating speed, film thickness, exposure and development dose, and drying temperature. According to the height of the second transmission layer of the second-step grating structure as , use anisotropic etching technology to etch the target depth of the fourth-step grating structure at the target position of the fourth-step grating structure 4 on the substrate surface;

[0019] 6) Remove the photoresist mask to complete the fabrication of the second-step grating structure and the fourth-step grating structure, and perform surface inspection and evaluation after completion.

[0020] Preferably, the transparent substrate is BF33 glass, but is not limited to BF33 glass.

[0021] Preferably, the photoresist mask uses positive photoresist with a thickness of 2 μm, but is not limited to positive photoresist.

[0022] Preferably, the metal reflective layer is made of chromium oxide and chromium metal, and the method used is physical vapor deposition (PVD) method or chemical vapor deposition method; and the mask and the excess metal reflective layer are removed by a lift-off process. All methods or substances used are not limited to the preferred methods or substances given, and means with the same function can be used to replace them. The set values are not fixed and can be changed.

[0023] Preferably, the thickness of the metal reflective layer is measured by a surface measurement method, the evaluation of the photoresist mask residue is carried out by microscopy, and the method for measuring the etching depth is to use a profilometer for depth measurement and evaluation. All methods are not limited to the preferred methods given, and means with the same function can be used to replace them.

[0024] Compared with the prior art, the present invention has the following beneficial effects: The multi-step periodic grating structure and its preparation method provided by the present invention have the effect of weakening the zero-order light regulation for the prepared multi-step periodic grating structure, can achieve light intensity regulation within a certain range, are easy to prepare and integrate, have a high diffraction efficiency, and can be applied to the field of integrated high-precision displacement detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 Schematic diagram of the photolithography step for preparing the third-step grating structure provided by a specific embodiment of the present invention.

[0026] Figure 2 Schematic diagram of the etching step for preparing the third-step grating structure provided by a specific embodiment of the present invention.

[0027] Figure 3 Schematic diagram of the metal deposition result for preparing the third-step grating structure provided by a specific embodiment of the present invention.

[0028] Figure 4 Schematic diagram of the photolithography step for preparing the first-step grating structure provided by a specific embodiment of the present invention.

[0029] Figure 5 Schematic diagram of the etching step for preparing the first-step grating structure provided by a specific embodiment of the present invention.

[0030] Figure 6 Schematic diagram of the metal deposition result for preparing the first-step grating structure provided by a specific embodiment of the present invention.

[0031] Figure 7 Schematic diagram of the photolithography step for preparing the fourth-step grating structure provided by a specific embodiment of the present invention.

[0032] Figure 8 Schematic diagram of the etching step for preparing the fourth-step grating structure and the second-step grating structure provided by a specific embodiment of the present invention.

[0033] Figure 9 Schematic diagram of the multi-step periodic grating structure model provided by a specific embodiment of the present invention.

[0034] The markings in the figure are as follows: 1 - the first stepped grating structure, 2 - the second stepped grating structure, 3 - the third stepped grating structure, 4 - the fourth stepped grating structure, 101 - the first transmission layer, 102 - the first metal reflection layer, 201 - the second transmission layer, 301 - the third metal reflection layer. Specific embodiments

[0035] The present invention will be further described below in conjunction with specific embodiments.

[0036] A multi-step periodic grating structure, as Figure 9 shown: It includes a periodic multi-step grating structure. Each period of the multi-step grating structure includes a substrate and a four-step grating structure. The four-step grating structures are all arranged on the substrate. In the order from right to left within a single period, the four-step grating structures are the first stepped grating structure 1, the second stepped grating structure 2, the third stepped grating structure 3, and the fourth stepped grating structure 4 respectively; the first stepped grating structure 1 includes a first transmission layer 101 and a first metal reflection layer 102, and the first metal reflection layer 102 is coated on the first transmission layer 101; the refractive index of the material of the first transmission layer 101 is 1.4 to 1.9, and the reflectivity of the material of the first metal reflection layer 102 is 0.5 to 1.0; the period of the first stepped grating structure 1 is 0.5 μm to 2 μm; the thickness h a and the refractive index of the transmission material n satisfy ; the overall thickness of the first metal reflection layer 102 is 100 nm to 300 nm, including an oxide absorption layer with a thickness of 20 to 80 nm; the reflectivity of the oxide absorption layer is 0.1 to 0.3; λ is the wavelength of the laser source; the second stepped grating structure 2 includes a second transmission layer 201, and the second transmission layer 201 is in a close or integral relationship with the first transmission layer 101; the second transmission layer 201 and the first transmission layer 101 are made of the same material, and the thickness h a and the refractive index of the transmission material n satisfy ; The period of the second stepped grating structure 2 is 0.5 μm to 2 μm; the third stepped grating structure 3 includes a third metal reflection layer 301, the third metal reflection layer 301 is coated on the substrate, and the materials and thicknesses of the third metal reflection layer 301 and the first metal reflection layer 102 are the same. The period of the third stepped grating structure 3 is 0.5 μm to 2 μm; the fourth stepped grating structure 4 is a substrate without a transmission layer and a metal reflection layer, and the period of the fourth stepped grating structure 4 is 0.5 μm to 2 μm.

[0037] In this embodiment, the following preferred solutions are adopted: the duty ratios of the third stepped grating structure 3 and the first stepped grating structure 1 are the same; the duty ratios of the fourth stepped grating structure 4 and the second stepped grating structure 2 are the same. In this embodiment, the duty ratios of the first stepped grating structure 1, the second stepped grating structure 2, the third stepped grating structure 3, and the fourth stepped grating structure 4 are all 25%; the first transmission layer 101 and the second transmission layer 201 are made of materials with good light transmittance, and the light transmittance is > 95%. The first metal reflection layer 102 and the third metal reflection layer 301 are made of chromium oxide and chromium; and the set laser source wavelength λ is 850 nm; the substrate used in this embodiment is BF33 glass, with a refractive index n of 1.45 and a light transmittance > 95%, which can ensure less diffraction efficiency loss; and a multi-stepped periodic grating structure is prepared on this substrate; the thickness of the first transmission layer 101 of the first stepped grating structure 1 is 146 nm, and the overall thickness of the first metal reflection layer 102 is 105 nm, including a 20-nm oxide absorption layer. The period of the first stepped grating structure 1 is 1 μm; the height of the second stepped grating structure 2 is 472 nm, and the period is 1 μm; the period of the third stepped grating structure 3 is 1 μm, and the period of the fourth stepped grating structure 4 is 1 μm.

[0038] The preparation method of the above multi-stepped periodic grating structure specifically includes the following steps:

[0039] 1) According to the target size, design the layout required for preparing the multi-layer structure and prepare a mask plate; select positive photoresist, and the spin coating speed needs to be considered in combination with the etching method used. The thickness of the photoresist is controlled at a relatively thin thickness, such as 2 μm. Further, complete the high-precision pattern transfer by controlling the exposure dose and the development dose duration, and complete the preparation of the photoresist mask G1 by drying at an appropriate temperature, as Figure 1 shown;

[0040] 2) According to the height of the array unit of the second stepped grating structure 2 being , anisotropic etching technology is required to etch a depth of 472 nm at the target position G3 on the substrate surface as Figure 2 shown. After this step, perform depth measurement and evaluation with a profilometer;

[0041] 3) In this embodiment, physical vapor deposition (PVD) technology or chemical vapor deposition (CVD) technology can be used to deposit 20 nm of chromium oxide and 85 nm of chromium metal on the grating surface as the third metal reflective layer 301. The metal thickness is analyzed and evaluated by surface measurement technology to determine whether it meets the expected standard;

[0042] 4) Use the lift-off process to remove the photoresist mask and the excess metal reflective layer to complete the preparation of the third stepped grating structure as shown in G4 in Figure 3 This step requires evaluating the photoresist mask residue by microscopy to ensure that it does not interfere with the subsequent lithography process;

[0043] 5) Use precision-designed and manufactured mask plates and lithography technology to complete the second pattern transfer and the preparation of the photoresist mask as shown in G5 in Figure 4 This step also requires controlling the spin coating speed, the thickness of the photoresist, the exposure dose, and the drying temperature; according to the thickness of the first transmissive layer 101 of the first layer structure array being etch at a depth of 326 nm at the target position on the substrate surface as shown in G6 in Figure 5 by anisotropic etching technology;

[0044] 6) Use PVD technology to deposit 20 nm of chromium oxide and 85 nm of chromium metal on the entire surface as the Figure 6 first metal reflective layer 102 shown in G7 in

[0045] but not limited to this metal thin film manufacturing technology, metal / oxide materials, and corresponding thicknesses, and analyze and evaluate the metal thickness by surface measurement technology to determine whether it meets the expected standard; Figure 6 7) Use the lift-off process to remove the mask and the excess metal reflective layer to complete the preparation of the first stepped grating structure 1 as shown in

[0046] This step also requires evaluating the photoresist mask residue by microscopy to ensure that it does not interfere with the subsequent lithography process; Figure 7 8) Use precision-designed and manufactured mask plates and lithography technology to complete the third pattern transfer and the preparation of the photoresist mask as shown in G8 in This step also requires controlling the spin coating speed, the thickness of the photoresist, the exposure and development dose, and the drying temperature; according to the height of the second layer structure array unit being

[0047] etch at a depth of 472 nm at the target position G9 on the substrate surface by further anisotropic etching technology; Figure 8 9) Remove the photoresist mask to complete the preparation of the fourth stepped grating structure 4 shown in G10 in

[0048] It should be noted that the grating structure described in this embodiment has the function of weakening the zero-order light regulation, can achieve light intensity regulation within a certain range, is convenient for preparation and integration, has a high diffraction efficiency, and can be applied to the field of integrated high-precision displacement detection.

[0049] It can be understood that the above embodiments are merely exemplary embodiments adopted to illustrate the principle of the present invention. However, the present invention is not limited thereto. For those of ordinary skill in the art, various modifications and improvements can be made without departing from the spirit and essence of the present invention, and these modifications and improvements are also regarded as the protection scope of the present invention.

Claims

1. A multi-step periodic grating structure, characterized in that: It includes a periodic multi-step grating structure. Each periodic multi-step grating structure includes a substrate and a four-step grating structure. The four-step grating structures are all disposed on the substrate. The four-step grating structures are, in order from right to left within a single period, the first-step grating structure (1), the second-step grating structure (2), the third-step grating structure (3), and the fourth-step grating structure (4); The first stepped grating structure (1) includes a first transmission layer (101) and a first metal reflection layer (102), and the first metal reflection layer (102) is coated on the first transmission layer (101); the refractive index of the material of the first transmission layer (101) is 1.4 to 1.9, and the reflectivity of the material of the first metal reflection layer (102) is 0.5 to 1.0; the period of the first stepped grating structure (1) is 0.5 μm to 2 μm; the thickness of the first transmission layer (101) h a and the refractive index of the transmission material n satisfies ; the overall thickness of the first metal reflection layer (102) is 100 nm to 300 nm, including an oxide absorption layer with a thickness of 20 to 80 nm; the reflectivity of the oxide absorption layer is 0.1 to 0.3; λ is the wavelength of the laser source; The second stepped grating structure (2) includes a second transmissive layer (201), and the second transmissive layer (201) is in a close contact or integral relationship with the first transmissive layer (101); the second transmissive layer (201) and the first transmissive layer (101) are made of the same material, and the thickness of the second transmissive layer (201) h a is related to the refractive index of the transmissive material n satisfies ; the period of the second stepped grating structure (2) is 0.5 μm to 2 μm; The third-step grating structure (3) includes a third metal reflection layer (301). The third metal reflection layer (301) is coated on the substrate. The materials and thicknesses of the third metal reflection layer (301) and the first metal reflection layer (102) are the same. The period of the third-step grating structure (3) is 0.5 μm to 2 μm; The fourth-step grating structure (4) is the substrate, without a transmission layer and a metal reflection layer. The period of the fourth-step grating structure (4) is 0.5 μm to 2 μm.

2. The multi-step periodic grating structure according to claim 1, wherein: The periods and duty cycles of the third-step grating structure (3) and the first-step grating structure (1) are the same; the duty cycles of the fourth-step grating structure (4) and the second-step grating structure (2) are the same.

3. The multi-step periodic grating structure according to claim 1, wherein: The duty cycles of the first-step grating structure (1), the second-step grating structure (2), the third-step grating structure (3), and the fourth-step grating structure (4) are the same.

4. A multi-step periodic grating structure according to claim 1, characterized in that: The first transmission layer (101) and the second transmission layer (201) are made of materials with good light transmittance, and the light transmittance is > 95%. The first metal reflection layer (102) and the third metal reflection layer (301) are made of chromium oxide and chromium; and the set laser source wavelength λ is 850 nm.

5. A preparation method of a multi-step periodic grating structure, characterized in that: The product obtained is the multi-step periodic grating structure in claim 1; the following steps are included: 1) Provide a transparent substrate, which has good light transmittance and its light transmittance is greater than 95%; 2) Design a photoresist mask plate that meets the periodicity and can be used to prepare a multi-layer structure of a four-step grating structure; 3) First, prepare the third-step grating structure (3). Use a photoresist mask template complementary to the target grating structure, the spin coating speed, and by controlling the exposure dose and development dose, complete the high-precision pattern transfer. Expose, develop, etch, deposit, and strip the substrate. Etch the transparent substrate to the etching depth of the third-step grating structure (3) so that it meets the target depth of the wavelength and refractive index relationship. Then, at the target depth etched on the transparent substrate, use physical vapor deposition technology or chemical vapor deposition to deposit a metal reflection layer on the surface of the etched target position, and analyze and evaluate the metal thickness through surface measurement technology to see if it meets the expected standard; Remove the photoresist mask plate and the excess metal reflection layer, and evaluate the photoresist mask residue to ensure that it does not interfere with the subsequent lithography process; 4) Prepare the first stepped grating structure (1), and prepare a photoresist mask template that matches the already formed transparent substrate. Similarly, by controlling the spin coating speed, film thickness, exposure dose, and drying temperature, according to the thickness required for the first transmission layer (101) in the first stepped grating structure (1) to be , etch the corresponding depth at the target position on the substrate surface through anisotropic etching technology; then deposit a metal reflection layer on the surface of the etched target position, and analyze and evaluate the metal thickness through surface measurement technology to see if it meets the expected standard; Remove the photoresist mask plate and the excess metal reflection layer, and evaluate the photoresist mask residue to ensure that it does not interfere with the subsequent lithography process; 5) A photoresist mask template matching the formed transparent substrate is prepared by using a precisely designed and manufactured mask plate and photolithography technology. The spin coating speed, film thickness, exposure and development dose, and drying temperature are controlled. According to the thickness of the second transmission layer (201) of the second stepped grating structure (2) being , an anisotropic etching technology is used to etch the fourth stepped grating structure (4) with a target depth at the target position of the fourth stepped grating structure (4) on the substrate surface; 6) Remove the photoresist mask to complete the preparation of the second-step grating structure (2) and the fourth-step grating structure (4), and perform surface detection and evaluation after completion.

6. The preparation method of a multi-step periodic grating structure according to claim 5, characterized in that: The transparent substrate is BF33 glass.

7. The preparation method of a multi-step periodic grating structure according to claim 5, characterized in that: The photoresist mask plate uses positive photoresist with a thickness of 2 μm.

8. The preparation method of a multi-step periodic grating structure according to claim 5, characterized in that: The metal reflective layer uses chromium oxide and chromium metal, and the method used is physical vapor deposition (PVD) method or chemical vapor deposition method; and the lift-off process is used to remove the mask and the excess metal reflective layer.

9. The preparation method of a multi-step periodic grating structure according to claim 5, characterized in that: The thickness of the metal reflective layer is measured by surface measurement method, the evaluation of the photoresist mask residue is carried out by microscopy, and the method for measuring the etching depth is to use a profilometer for depth measurement and evaluation.

10. Use of a multi-step periodic grating structure according to claim 1, characterized in that: It has a zero-order light regulation weakening effect and is applied to integrated high-precision displacement detection.

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