Preparation method of two-dimensional surface relief grating

Abstract

The invention provides a preparation method of a two-dimensional surface relief grating, which comprises the following steps of: firstly, preparing a first-dimensional surface relief grating on the surface of a substrate to obtain the substrate with the first-dimensional surface relief grating; then, continuously preparing a second-dimensional surface relief grating on the substrate with the first-dimensional surface relief grating, and obtaining a two-dimensional surface relief grating on the substrate; wherein the set groove depth of the first-dimension surface relief grating is 1000-1500 nm, and the set groove depth of the second-dimension surface relief grating is 300-450 nm; the grid line direction of the first-dimension surface relief grating is perpendicular to the grid line direction of the second-dimension surface relief grating. According to the preparation method of the two-dimensional surface relief grating, the prepared two-dimensional surface relief grating is high in diffraction efficiency and has the polarization selection characteristic.

Description

Technical Field

[0001] The present invention belongs to the technical field of grating preparation, and particularly relates to a method for preparing a two-dimensional surface relief grating. Background Art

[0002] With the advent of the Internet + and big data 5G era, the concept of the metaverse has become popular, and fields such as wearable devices, smart homes, and education and teaching have developed rapidly, bringing development opportunities to augmented reality (AR) technology.

[0003] AR products are regarded as the next epoch-making terminal devices after smartphones. Head-mounted, handheld, and spatial displays are currently the three main types of AR products. Among them, AR glasses have attracted much attention due to their lightweight and convenient characteristics.

[0004] Currently, relatively mature AR glasses technical solutions are mainly divided into the prism solution, the birdbath solution, the free-form surface solution, the off-axis holographic lens solution, and the light guide solution.

[0005] The light guide is considered the main optical solution for consumer-grade AR glasses lenses due to its thin and light characteristics and high penetration of external light.

[0006] Among them, light guides can generally be divided into geometric waveguides and diffractive waveguides. Diffractive waveguides are divided into volume holographic grating waveguides and surface relief grating waveguides.

[0007] The surface relief gratings used in existing surface relief grating waveguides have a one-dimensional surface relief grating structure, as shown in Figure 1 shown. There is also a two-dimensional surface relief grating structure, as shown in Figure 2 shown. The two-dimensional surface relief grating structure is composed of two one-dimensional surface relief grating structures. In the existing two-dimensional surface relief grating structure, the groove depths of the two one-dimensional surface relief grating structures are the same.

[0008] Research has found that if the groove depths of the two one-dimensional surface relief grating structures in the two-dimensional surface relief grating structure are different and the grating line directions are perpendicular (as shown in Figure 3 shown), the diffraction efficiency of the grating is high and it has polarization selection characteristics. Therefore, there is an urgent need to provide a method for preparing a two-dimensional surface relief grating structure, and the groove depths of the two one-dimensional surface relief grating structures in the prepared two-dimensional surface relief grating structure are different and the grating line directions are perpendicular. Summary of the Invention

[0009] In order to meet the needs of the existing technology, the present invention provides a method for preparing a two-dimensional surface relief grating.

[0010] The present invention is realized through the following technical solutions:

[0011] The present invention provides a method for preparing a two-dimensional surface relief grating, comprising the following steps:

[0012] Prepare a first-dimension surface relief grating on the surface of a substrate to obtain a substrate with a first-dimension surface relief grating;

[0013] Continue to prepare a second-dimension surface relief grating on the substrate with the first-dimension surface relief grating to obtain a two-dimensional surface relief grating on the substrate;

[0014] Wherein, the set groove depth of the first-dimension surface relief grating is 1000 - 1500 nm, and the set groove depth of the second-dimension surface relief grating is 300 - 450 nm;

[0015] The grating line direction of the first-dimension surface relief grating is perpendicular to the grating line direction of the second-dimension surface relief grating.

[0016] Further, preparing a first-dimension surface relief grating on the surface of a substrate to obtain a substrate with a first-dimension surface relief grating includes the following steps:

[0017] Spin-coat a photoresist with a first set thickness on the substrate to obtain a substrate provided with a first photoresist mask;

[0018] Perform a first beam interference exposure operation on the first photoresist mask on the substrate, so that the illuminated part of the first photoresist mask is in a fully exposed state, and obtain a first photoresist mask with changed properties on the substrate;

[0019] Perform a first development operation on the first photoresist mask with changed properties on the substrate to obtain a first photoresist grating mask on the substrate, and obtain a substrate with a first photoresist grating mask;

[0020] Etch the substrate with the first photoresist grating mask, and after the etching is completed, clean the residual photoresist on the surface of the substrate to obtain a substrate with a first-dimension surface relief grating.

[0021] Further, spin-coating a photoresist with a first set thickness on the substrate to obtain a substrate provided with a first photoresist mask includes the following steps:

[0022] Place the substrate in a spin coater;

[0023] Drop a first set amount of photoresist onto the upper surface of the substrate;

[0024] Drive the spin coater to rotate to drive the substrate to perform a first spin coating rotation, so that the upper surface of the substrate is uniformly coated with the photoresist having the first set thickness to obtain a substrate provided with a first photoresist mask.

[0025] Further, during the process of driving the spin coater to rotate and drive the substrate to perform the first spin coating rotation, the initial rotation speed of the spin coater is 300 - 500 r / min, the duration of the initial rotation speed is 5 - 8 s, the working rotation speed of the spin coater is 3500 - 4500 r / min, and the duration of the working rotation speed is 50 - 70 s.

[0026] Further, the first set thickness of the photoresist is determined according to the set groove depth parameter of the first - dimension surface relief grating and the etching selectivity ratio between the photoresist and the substrate.

[0027] Further, perform a first - beam interference exposure operation on the first photoresist mask on the substrate, so that the illuminated part of the first photoresist mask is in a fully exposed state, and obtain a first photoresist mask with changed properties on the substrate, including the following steps:

[0028] Fix the substrate provided with the first photoresist mask in the holographic exposure system at a first set angle, and irradiate the substrate provided with the first photoresist mask through a first exposure field forming light and dark fringes by beam interference, so that the illuminated part of the first photoresist mask is in a fully exposed state, and obtain a first photoresist mask with changed properties on the substrate;

[0029] Among them, the first set angle is determined based on the grating line direction of the first - dimension surface relief grating.

[0030] Further, perform a first development operation on the first photoresist mask with changed properties on the substrate, and obtain a first photoresist grating mask on the substrate, and obtain a substrate with a first photoresist grating mask, including the following steps:

[0031] Immerse the first photoresist mask with changed properties on the substrate in the developer for the first development operation, and the corresponding part of the first photoresist mask is eroded by the developer, and obtain a first photoresist grating mask on the substrate, and obtain a substrate with a first photoresist grating mask.

[0032] Further, determine the duty ratio of the first photoresist grating mask according to the set duty ratio of the first - dimension surface relief grating;

[0033] Based on the duty ratio of the first photoresist grating mask, control the following parameters of the first - beam interference exposure operation and the first development operation:

[0034] In the first - beam interference exposure operation, the exposure amount received by the illuminated part of the first photoresist mask on the substrate under the first exposure field;

[0035] In the first development operation, the development time of the first photoresist mask with changed properties on the substrate in the developer.

[0036] Further, the light-exposed part of the first photoresist mask being in a fully exposed state means that, in the light-exposed part of the first photoresist mask, the first photoresist mask with the first set thickness on the substrate can be completely dissolved after the first beam interference exposure operation and the first development operation.

[0037] Further, etching the substrate with the first photoresist grating mask, and after the etching is completed, cleaning the photoresist residue on the surface of the substrate to obtain a substrate with a first-dimension surface relief grating, includes the following steps:

[0038] Using an ion beam etching machine to etch the substrate with the first photoresist grating mask, copying the topography distribution of the first photoresist grating mask onto the substrate, controlling the first etching time of the ion beam etching machine for etching the substrate with the first photoresist grating mask, and obtaining a first-dimension surface relief grating with the set groove depth on the substrate;

[0039] Cleaning the photoresist residue on the surface of the substrate to obtain a substrate with a first-dimension surface relief grating with the set groove depth.

[0040] Further, continuing to prepare a second-dimension surface relief grating on the substrate with the first-dimension surface relief grating, and obtaining a two-dimensional surface relief grating on the substrate, includes the following steps:

[0041] Spin-coating a second photoresist with a second set thickness on the substrate with the first-dimension surface relief grating, and the photoresist filling the non-structural regions of the first-dimension surface relief grating to obtain a substrate with a second photoresist mask;

[0042] Performing a second beam interference exposure operation on the second photoresist mask on the substrate, such that the light-exposed part of the second photoresist mask in the structural regions of the first-dimension surface relief grating is in a fully exposed state and the light-exposed part of the second photoresist mask in the non-structural regions of the first-dimension surface relief grating is in a partially exposed state, and obtaining a second photoresist mask with changed properties on the substrate;

[0043] Performing a second development operation on the second photoresist mask with changed properties on the substrate, and obtaining a second photoresist grating mask on the substrate to obtain a substrate with a second photoresist grating mask;

[0044] Etching the substrate with the second photoresist grating mask, and after the etching is completed, cleaning the photoresist residue on the surface of the substrate to obtain a two-dimensional surface relief grating on the substrate.

[0045] Further, a photoresist with a second set thickness is spin-coated on a substrate having a first-dimension surface relief grating, and the non-structural regions of the first-dimension surface relief grating are filled with the photoresist to obtain a substrate provided with a second photoresist mask, including the following steps:

[0046] Place the substrate having the first-dimension surface relief grating into a spin coater;

[0047] Drop a second set amount of photoresist onto the side of the substrate having the first-dimension surface relief grating;

[0048] Drive the spin coater to rotate to drive the substrate having the first-dimension surface relief grating to perform a second spin coating rotation, so that the side of the substrate having the first-dimension surface relief grating is uniformly coated with the photoresist having the second set thickness, and the non-structural regions of the first-dimension surface relief grating are filled with the photoresist, to obtain a substrate provided with a second photoresist mask.

[0049] Further, during the process of driving the spin coater to rotate to drive the substrate having the first-dimension surface relief grating to perform a second spin coating rotation, the initial rotation speed of the spin coater is 350 - 450 r / min, the duration of the initial rotation speed is 6 - 8 s, the working rotation speed of the spin coater is 2200 - 2500 r / min, and the duration of the working rotation speed is 50 - 70 s.

[0050] Further, the second set thickness of the photoresist is the distance between the side where the photoresist contacts the air and the side where the photoresist contacts the top surface of the structural region of the first-dimension surface relief grating;

[0051] The second set thickness of the photoresist is determined according to the set groove depth parameter of the second-dimension surface relief grating and the etching selectivity ratio between the photoresist and the substrate.

[0052] Further, perform a second beam interference exposure operation on the second photoresist mask on the substrate, so that the illuminated part of the second photoresist mask in the structural region of the first-dimension surface relief grating is in a fully exposed state and the illuminated part of the second photoresist mask in the non-structural region of the first-dimension surface relief grating is in a partially exposed state, to obtain a second photoresist mask with changed properties on the substrate, including the following steps:

[0053] Fix the substrate provided with the second photoresist mask in the holographic exposure system at a second set angle, and irradiate the substrate provided with the second photoresist mask through a second exposure field formed by beam interference with light and dark fringes, so that the illuminated part of the second photoresist mask in the structural region of the first-dimension surface relief grating is in a fully exposed state and the illuminated part of the second photoresist mask in the non-structural region of the first-dimension surface relief grating is in a partially exposed state, to obtain a second photoresist mask with changed properties on the substrate;

[0054] Among them, the second set angle is determined based on the grating line direction of the second-dimensional surface relief grating.

[0055] Further, perform a second development operation on the second photoresist mask with changed properties on the substrate to obtain a second photoresist grating mask on the substrate, and obtain a substrate with a second photoresist grating mask, including the following steps:

[0056] Immerse the second photoresist mask with changed properties on the substrate in a developer for the second development operation. The corresponding part of the second photoresist mask is eroded by the developer, and a second photoresist grating mask is obtained on the substrate, and a substrate with a second photoresist grating mask is obtained.

[0057] Further, determine the duty cycle of the second photoresist grating mask according to the set duty cycle of the second-dimensional surface relief grating;

[0058] Based on the duty cycle of the second photoresist grating mask, control the following parameters of the second beam interference exposure operation and the second development operation:

[0059] In the second beam interference exposure operation, the exposure amount received by the illuminated part of the second photoresist mask on the substrate under the second exposure field;

[0060] In the second development operation, the development time of the second photoresist mask with changed properties on the substrate in the developer.

[0061] Further, the illuminated part of the second photoresist mask in the structural area of the first-dimensional surface relief grating is in a completely exposed state: for the illuminated part of the second photoresist mask in the structural area of the first-dimensional surface relief grating, the second photoresist mask with the second set thickness on the substrate can be completely dissolved after the second beam interference exposure operation and the second development operation;

[0062] The illuminated part of the second photoresist mask in the non-structural area of the first-dimensional surface relief grating is in an incompletely exposed state: for the illuminated part of the second photoresist mask in the non-structural area of the first-dimensional surface relief grating, after the second beam interference exposure operation and the second development operation of the second photoresist mask, the non-structural area of the first-dimensional surface relief grating still has photoresist.

[0063] Further, etch the substrate with the second photoresist grating mask, and after the etching is completed, clean the photoresist residue on the substrate surface to obtain a two-dimensional surface relief grating on the substrate, including the following steps:

[0064] In the position area on the substrate surface with the first-dimension surface relief grating, use an ion beam etching machine to etch the substrate with the second photoresist grating mask, copy the topography distribution of the second photoresist grating mask onto the substrate, control the second etching time of the ion beam etching machine for etching the substrate with the second photoresist grating mask, and obtain the second-dimension surface relief grating with the set groove depth on the substrate;

[0065] Clean the photoresist remaining on the substrate surface to obtain a two-dimensional surface relief grating on the substrate.

[0066] Compared with the prior art, the technical solution of the present invention has the following beneficial effects:

[0067] The present invention provides a method for preparing a two-dimensional surface relief grating. First, prepare a first-dimension surface relief grating on the substrate surface to obtain a substrate with the first-dimension surface relief grating; then, continue to prepare a second-dimension surface relief grating on the substrate with the first-dimension surface relief grating to obtain a two-dimensional surface relief grating on the substrate; wherein, the set groove depth of the first-dimension surface relief grating is 1000 - 1500 nm, and the set groove depth of the second-dimension surface relief grating is 300 - 450 nm; the grating line direction of the first-dimension surface relief grating is perpendicular to the grating line direction of the second-dimension surface relief grating. Specifically, the present invention first prepares the above-mentioned first-dimension surface relief grating on the substrate surface through the operations of spin coating, exposure, development, etching, and cleaning for the first time to obtain a substrate with the first-dimension surface relief grating, and then realizes the preparation of the above-mentioned second-dimension surface relief grating on the substrate through the operations of spin coating, exposure, development, etching, and cleaning for the second time on the substrate with the first-dimension surface relief grating, so as to prepare a two-dimensional surface relief grating on the substrate. The prepared two-dimensional surface relief grating has high diffraction efficiency and polarization selection characteristics.

[0068] The method for preparing a two-dimensional surface relief grating provided by the present invention, in the process of preparing a second-dimensional surface relief grating on a substrate having a first-dimensional surface relief grating, the step of spin-coating a photoresist with a second set thickness on the substrate having the first-dimensional surface relief grating to obtain a substrate provided with a second photoresist mask ensures that the photoresist fills the non-structural regions of the first-dimensional surface relief grating. The step of performing a second-beam interference exposure operation on the second photoresist mask on the substrate, by controlling the exposure amount of the illuminated portion of the second photoresist mask in the structural regions of the first-dimensional surface relief grating and controlling the exposure amount of the illuminated portion of the second photoresist mask in the non-structural regions of the first-dimensional surface relief grating, makes the illuminated portion of the second photoresist mask in the structural regions of the first-dimensional surface relief grating in a fully exposed state and the illuminated portion of the second photoresist mask in the non-structural regions of the first-dimensional surface relief grating in a partially exposed state. Furthermore, after developing the second photoresist mask, it is ensured that the substrate still has photoresist in the non-structural regions of the first-dimensional surface relief grating. Thus, in the process of ion etching the substrate to obtain the second-dimensional surface relief grating, the photoresist in the non-structural regions of the first-dimensional surface relief grating on the substrate etches and protects the grating structures such as the groove depth of the first-dimensional surface relief grating already prepared on the substrate. Description of the Drawings

[0069] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0070] Figure 1 Stereogram of an exemplary existing one-dimensional surface relief grating structure;

[0071] Figure 2 Stereogram of an exemplary existing two-dimensional surface relief grating structure;

[0072] Figure 3 Stereogram of an exemplary two-dimensional surface relief grating structure composed of two one-dimensional surface relief grating structures with different groove depths and perpendicular grating line directions;

[0073] Figure 4 Schematic diagram for explaining the structural parameters of an exemplary surface relief grating structure;

[0074] Figure 5 Overall concept flowchart of the method for preparing a two-dimensional surface relief grating provided by the present invention;

[0075] Figure 6 Overall schematic flowchart for preparing a first-dimensional surface relief grating on the substrate surface;

[0076] Figure 7 It is a schematic optical path diagram of a dual-beam exposure system;

[0077] Figure 8 It is a schematic structural diagram of a substrate with a second photoresist mask formed by spin-coating a photoresist with a second set thickness on a substrate having a first-dimensional surface relief grating;

[0078] Figure 9 It is a schematic structural diagram after exposure and development of the illuminated part of the second photoresist mask on the substrate.

[0079] Among them, 1 - laser, 2 - first wave plate, 3 - beam splitting prism, 4 - second wave plate, 5 - first mirror, 6 - second mirror, 7 - third mirror, 8 - first microscope objective, 9 - second microscope objective, 10 - first pinhole, 11 - second pinhole, 12 - first collimating lens, 13 - second collimating lens. Specific embodiments

[0080] Next, the technical solutions of the present invention will be clearly and completely described in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative efforts fall within the scope of protection of the present invention.

[0081] In this article, terms such as "first", "second" and other similar terms do not intend to imply any order, quantity or importance, but are only used to distinguish different elements. In this article, terms such as "a", "one" and other similar terms do not intend to indicate that there is only one of the described things, but indicate that the relevant description is only directed to one of the described things, and the thing may have one or more. In this article, terms such as "comprising", "including" and other similar terms are intended to represent a logical relationship and should not be regarded as representing a spatial structure relationship. For example, "A includes B" is intended to mean that logically B belongs to A, rather than indicating that B is located inside A in space. In addition, the meanings of terms such as "comprising", "including" and other similar terms should be regarded as open-ended rather than closed-ended. For example, "A includes B" is intended to mean that B belongs to A, but B does not necessarily constitute all of A, and A may also include other elements such as C, D, E, etc.

[0082] In this document, the terms "embodiment", "this embodiment", "preferred embodiment", and "an embodiment" do not mean that the relevant description only applies to a specific embodiment, but rather that these descriptions may also apply to one or more other embodiments. Those skilled in the art should understand that in this document, any description made for a certain embodiment can be substituted, combined, or otherwise combined with the relevant descriptions in one or more other embodiments. The new embodiments generated by such substitution, combination, or other combination are easily conceivable by those skilled in the art and fall within the protection scope of the present invention.

[0083] In the description herein, the meaning of "a plurality" is at least two, such as two, three, etc., unless otherwise specifically defined.

[0084] As Figure 4 shown, for an exemplary surface relief grating structure, in combination with the illustration, the surface relief grating structure has the following structural parameters:

[0085] 1. Grating line width;

[0086] 2. Grating period;

[0087] 3. Duty cycle of the grating: grating line width / grating period;

[0088] 4. Grating structure area;

[0089] 5. Grating non-structure area, and the non-structure area has a groove depth.

[0090] As mentioned above, it has been found that if the groove depths of two one-dimensional surface relief grating structures in a two-dimensional surface relief grating structure are different and the grating line directions are perpendicular, the diffraction efficiency of the grating is high and it has polarization selection characteristics. Therefore, there is an urgent need in the art to provide a method for preparing a two-dimensional surface relief grating structure such that the groove depths of two one-dimensional surface relief grating structures in the prepared two-dimensional surface relief grating structure are different and the grating line directions are perpendicular.

[0091] Therefore, to meet the needs of the existing technology, as Figure 5 shown, the present invention provides a method for preparing a two-dimensional surface relief grating, and the general concept is as follows:

[0092] S1 Prepare a first-dimensional surface relief grating on the surface of the substrate to obtain a substrate with a first-dimensional surface relief grating.

[0093] S2 Continuously prepare a second-dimensional surface relief grating on the substrate with the first-dimensional surface relief grating to obtain a two-dimensional surface relief grating on the substrate.

[0094] Among them, the set groove depth of the first-dimension surface relief grating is 1000 - 1500 nm, and the set groove depth of the second-dimension surface relief grating is 300 - 450 nm.

[0095] The grating line direction of the first-dimension surface relief grating is perpendicular to the grating line direction of the second-dimension surface relief grating.

[0096] Exemplarily, as Figure 6 shown, the steps of preparing the first-dimension surface relief grating on the substrate surface to obtain a substrate with the first-dimension surface relief grating are as follows:

[0097] S1-1 Immerse the substrate in the mixed cleaning solution and clean the substrate with ultrasonic assistance at 70 - 100 °C for 1 - 3 h to obtain a cleaned substrate.

[0098] Among them, the mixed cleaning solution includes concentrated sulfuric acid and hydrogen peroxide.

[0099] The mass ratio of concentrated sulfuric acid to hydrogen peroxide is 1 - 5:1.

[0100] Exemplarily,

[0101] Add the mixed cleaning solution of concentrated sulfuric acid and hydrogen peroxide into the ultrasonic cleaner, and the mass ratio of concentrated sulfuric acid to hydrogen peroxide in the mixed cleaning solution is 3:1.

[0102] Place the substrate in a glassware and put the glassware into the mixed solution in the ultrasonic cleaner.

[0103] Start the ultrasonic cleaner and clean the substrate with ultrasonic assistance at 90 °C for 2 h.

[0104] Cleaning the substrate here can remove the residual impurities on the substrate surface, ensure the cleanliness of the substrate surface, and thus prevent the substrate impurities from affecting the subsequently prepared grating structure.

[0105] S1-2 Perform oxygen ion ashing treatment on the upper surface of the cleaned substrate for 5 - 20 min.

[0106] Exemplarily,

[0107] Put the cleaned substrate into an oxygen ion asher, and the oxygen ions released in the oxygen ion asher bombard the upper surface of the substrate for 10 min.

[0108] Performing oxygen ion ashing treatment on the substrate can improve the hydrophilicity of the substrate and enhance the adhesion of the substrate to the photoresist.

[0109] S1-3 Perform a tackifying treatment on the upper surface of the substrate after the ashing treatment.

[0110] Exemplarily,

[0111] Place the ashed substrate on the spin coater stage, and fix the substrate on the spin coater stage by means of vacuum adsorption.

[0112] Drop the tackifier onto the upper surface of the substrate.

[0113] Drive the spin coater to rotate to drive the substrate to rotate, so that the upper surface of the substrate is uniformly spin-coated with the tackifier.

[0114] Dry the substrate with the upper surface uniformly spin-coated with the tackifier to obtain a substrate with the tackifier firmly attached.

[0115] Exemplarily,

[0116] Here, the tackifier can be the tackifier with the model number RZN-6200.

[0117] The dropping amount of the tackifier is about one dropper.

[0118] The initial rotation speed of the spin coater is 100 - 300 r / min, the duration of the initial rotation speed is 5 - 10 s, the working rotation speed of the spin coater is 2000 - 3000 r / min, and the duration of the working rotation speed is 30 - 80 s.

[0119] S1-4 Spin-coat a photoresist with a first set thickness on the substrate after the tackifying treatment to obtain a substrate with a first photoresist mask set.

[0120] Exemplarily,

[0121] Place the substrate with the tackifier firmly attached into the spin coater, that is, place the substrate with the tackifier firmly attached on the spin coater stage, and fix the substrate on the spin coater stage by means of vacuum adsorption.

[0122] Drop a first set amount of photoresist onto the upper surface of the substrate.

[0123] Drive the spin coater to rotate to drive the substrate to perform a first spin coating rotation, so that the upper surface of the substrate is uniformly coated with a photoresist with a first set thickness to obtain a substrate with a first photoresist mask set.

[0124] Photoresist is a photosensitive substance, and its main components are resin, photosensitive compound and solvent. When exposed to light, the properties of the photoresist itself will change. According to the different situations of the change of the photoresist properties when exposed to light, the photoresist can be divided into positive photoresist and negative photoresist. After the positive photoresist is exposed to light, the photoresist molecules in the exposed part will undergo a chain-breaking reaction and can be dissolved in the developer, while the photoresist molecules in the unexposed part are insoluble in the developer; after the negative photoresist is exposed to light, the photoresist molecules in the exposed part will undergo a cross-linking reaction and are insoluble in the developer, while the photoresist molecules in the unexposed part are soluble in the developer.

[0125] The chain-breaking reaction or cross-linking reaction of the photoresist requires light of a certain wavelength to be absorbed to complete, that is, the photoresist needs to receive a certain exposure amount during exposure to complete the corresponding chemical reaction. During exposure, the exposure amount received by the photoresist is positively correlated with both the exposure light intensity and the exposure time received by the photoresist. During development, the sol amount of the photoresist is positively correlated with the exposure amount.

[0126] The above-mentioned photoresist can be a positive photoresist or a negative photoresist, but a positive photoresist is preferably used.

[0127] The first set thickness of the above-mentioned photoresist is determined according to the set groove depth parameter of the first-dimensional surface relief grating and the etching selectivity ratio between the photoresist and the substrate. Exemplarily, taking the set groove depth parameter of the first-dimensional surface relief grating as 1500 nm and using a positive photoresist of Dow Chemical as an example, the thickness of the photoresist spin-coated on the substrate is controlled at about 1200 nm.

[0128] The first set dispensing amount of the above-mentioned photoresist is related to the selected type of the photoresist and the spin-coated thickness of the photoresist on the substrate. Taking the example of spin-coating a 1200 nm thick photoresist of Dow Chemical on the substrate, the dispensing amount of the positive photoresist is controlled at 5 - 7 ml.

[0129] Exemplarily, during the first spin coating process of driving the spin coater to rotate to drive the substrate, the initial rotation speed of the spin coater is 300 - 500 r / min, the duration of the initial rotation speed is 5 - 8 s, the working rotation speed of the spin coater is 3500 - 4500 r / min, and the duration of the working rotation speed is 50 - 70 s. By controlling the rotation speed and the duration of the rotation speed of the spin coater during the first spin coating process, it can be ensured that the photoresist with the first set dispensing amount dropped on the upper surface of the substrate can be evenly spin-coated on the upper surface of the substrate and the photoresist layer on the substrate has the first set thickness. Taking the example of spin-coating a 1200 nm thick photoresist of Dow Chemical on the substrate, the initial rotation speed of the spin coater is 400 r / min, the working time is 6 s, the working rotation speed of the spin coater is 4000 r / min, and the working time is 60 s.

[0130] S1-5 performs a first beam interference exposure operation on the first photoresist mask on the substrate, so that the illuminated part of the first photoresist mask is in a completely exposed state, and a first photoresist mask with changed properties is obtained on the substrate.

[0131] Exemplarily,

[0132] S1-5-1 sets up a holographic exposure system for the first beam interference exposure operation. The holographic exposure system forms a first exposure field with light and dark alternating fringes through beam interference. Here, the holographic exposure system can use a two-beam exposure system or a Lloyd's mirror exposure system.

[0133] Such asFigure 7 As shown in the figure, it is a schematic optical path diagram of a dual-beam exposure system. The incident beam emitted by the laser 1 enters the first wave plate 2, and after the polarization state is adjusted by the first wave plate, it enters the beam splitting prism 3. The beam splitting prism 3 splits the beam into two beams. The first beam is reflected by the third mirror 7 and then enters the first microscope objective 8. After being focused by the first microscope objective 8, it enters the first pinhole 10. After being filtered by the first pinhole 10, it enters the first collimating lens 12 and becomes the first parallel beam after being collimated by the first collimating lens 12. The second beam passes through the second wave plate 4 to adjust the polarization state, and then is reflected by the first mirror 5 and the second mirror 6 in sequence and enters the second microscope objective 9. After being focused by the second microscope objective 9, it enters the second pinhole 11. After being filtered by the second pinhole 11, it enters the second collimating lens 13 and becomes the second parallel beam after being collimated by the second collimating lens 13. The first parallel beam and the second parallel beam interfere on the surface of the substrate (sample to be exposed) provided with the photoresist mask to form the first exposure field. Among them, the direction along the grating vector is taken as the x direction, the direction along the grating lines is taken as the y direction, and the direction along the normal of the substrate is taken as the z direction.

[0134] S1-5-2 fixes the substrate provided with the first photoresist mask in the holographic exposure system at a first set angle (the first set angle is determined based on the grating line direction of the first-dimensional surface relief grating), and irradiates the substrate provided with the first photoresist mask through the first exposure field with bright and dark fringes formed by beam interference, so that the illuminated part of the first photoresist mask is in a completely exposed state, and the first photoresist mask with changed properties is obtained on the substrate.

[0135] During the process that the first exposure field with bright and dark fringes formed by beam interference irradiates the substrate provided with the first photoresist mask to make the illuminated part of the first photoresist mask in a completely exposed state, the duty cycle of the first photoresist grating mask is determined according to the set duty cycle of the first-dimensional surface relief grating, and the exposure amount received by the illuminated part of the first photoresist mask on the substrate under the first exposure field is controlled based on the duty cycle of the first photoresist grating mask.

[0136] The illuminated part of the first photoresist mask being in a completely exposed state means that in the illuminated part of the first photoresist mask, the first photoresist mask with a first set thickness on the substrate can be completely dissolved after the first beam interference exposure operation and the first developing operation.

[0137] Exemplarily, there are 3 ways to control the exposure amount:

[0138] 1. Under the condition of the same exposure time, adjust the exposure light intensity of the first exposure field, so as to control the exposure amount of the illuminated part of the first photoresist mask in the first exposure field.

[0139] 2. Under the condition that the exposure light intensity distribution in the first exposure field remains unchanged, adjust the exposure time of the illuminated part of the first photoresist mask, so as to control the exposure amount of the illuminated part of the first photoresist mask in the first exposure field.

[0140] 3. At the same time, adjust the exposure light intensity of the first exposure field and the exposure time of the illuminated part of the first photoresist mask, so as to control the exposure amount of the illuminated part of the first photoresist mask in the first exposure field.

[0141] S1-6 Perform a first development operation on the first photoresist mask with changed properties on the substrate to obtain a first photoresist grating mask on the substrate, and obtain a substrate with a first photoresist grating mask.

[0142] Exemplarily,

[0143] Immerse the first photoresist mask with changed properties on the substrate in a developer for the first development operation. The corresponding part of the first photoresist mask is eroded by the developer to obtain a first photoresist grating mask on the substrate, and obtain a substrate with a first photoresist grating mask.

[0144] Taking a positive photoresist as an example,

[0145] Immerse the first photoresist mask with changed properties on the substrate in a developer for the development operation. The illuminated part of the first photoresist mask is eroded and dissolved by the developer to obtain a first photoresist grating mask on the substrate, and obtain a substrate with a first photoresist grating mask.

[0146] During the process of immersing the first photoresist mask with changed properties on the substrate in a developer for the development operation, determine the duty cycle of the first photoresist grating mask according to the set duty cycle of the first-dimensional surface relief grating, and control the development time of the first photoresist mask with changed properties on the substrate in the developer based on the duty cycle of the first photoresist grating mask.

[0147] S1-7 Etch the substrate with the first photoresist grating mask. After the etching is completed, clean the residual photoresist on the surface of the substrate to obtain a substrate with a first-dimensional surface relief grating.

[0148] Exemplarily,

[0149] S1-7-1 Use an ion beam etching machine to etch the substrate with the first photoresist grating mask, copy the topography distribution of the first photoresist grating mask to the substrate, control the first etching time of the ion beam etching machine for etching the substrate with the first photoresist grating mask, and obtain a first-dimensional surface relief grating with the above-mentioned set groove depth on the substrate.

[0150] Here, the first etching time for the ion beam etcher to etch the substrate with the first photoresist grating mask is related to the set groove depth parameter of the first-dimensional surface relief grating on the substrate. Exemplarily, when the set groove depth parameter of the first-dimensional surface relief grating on the substrate is 1500 nm, the first etching time can be controlled at about 1 h.

[0151] S1-7-2 Clean the residual photoresist on the surface of the substrate to obtain a substrate with the first-dimensional surface relief grating having the above set groove depth.

[0152] An example of the cleaning solvent for the residual photoresist on the substrate surface can be acetone solvent.

[0153] Exemplarily, the above-mentioned method for continuously preparing the second-dimensional surface relief grating on the substrate with the first-dimensional surface relief grating to obtain a two-dimensional surface relief grating on the substrate includes the following steps:

[0154] S2-1 Spin-coat a photoresist with a second set thickness on the substrate with the first-dimensional surface relief grating, and the photoresist fills the non-structural regions of the first-dimensional surface relief grating, to obtain a substrate with a second photoresist mask (as Figure 8 shown).

[0155] Exemplarily,

[0156] Place the substrate with the first-dimensional surface relief grating on the spin-coating stage of the spin coater, and fix the substrate on the spin-coating stage by means of vacuum adsorption.

[0157] Drop a second set amount of photoresist onto the side of the substrate with the first-dimensional surface relief grating.

[0158] Drive the spin coater to rotate to drive the substrate with the first-dimensional surface relief grating to perform a second spin coating rotation, so that the side of the substrate with the first-dimensional surface relief grating is uniformly coated with a photoresist with a second set thickness, and the photoresist fills the non-structural regions of the first-dimensional surface relief grating, to obtain a substrate with a second photoresist mask.

[0159] The above-mentioned photoresist can be a positive photoresist or a negative photoresist, but preferably a positive photoresist is used.

[0160] The second set thickness of the above-mentioned photoresist is the distance between the side where the photoresist contacts the air and the side where the photoresist contacts the top surface of the structural region of the first-dimensional surface relief grating. As Figure 8 shown, Figure 8 H in represents the second set thickness of the photoresist.

[0161] In theory, the second set thickness of the photoresist can be determined according to the set groove depth parameter of the second-dimensional surface relief grating and the etching selectivity between the photoresist and the substrate. However, considering that the second photoresist mask on the substrate needs to ensure that the illuminated part in the structural area of the first-dimensional surface relief grating is in a fully exposed state and the illuminated part in the non-structural area of the first-dimensional surface relief grating is in a partially exposed state during the subsequent second-beam interference exposure operation, the second set thickness of the photoresist here is greater than the thickness value determined according to the set groove depth parameter of the second-dimensional surface relief grating and the etching selectivity between the photoresist and the substrate. Exemplarily, the thickness of the photoresist spin-coated on the substrate is controlled at about 1000 nm.

[0162] The above-mentioned second set dispensing amount of the photoresist is related to the selected type of the photoresist and the spin-coated thickness of the photoresist on the substrate. Taking the example of spin-coating a 1000-nm thick positive photoresist from Dow Chemical on the substrate, the dispensing amount of the positive photoresist is controlled at 5 ml.

[0163] Exemplarily, during the process of driving the spinner to rotate to drive the substrate with the first-dimensional surface relief grating to perform the second spin coating, the initial rotation speed of the spinner is 350 - 450 r / min, the duration of the initial rotation speed is 6 - 8 s, the working rotation speed of the spinner is 2200 - 2500 r / min, and the duration of the working rotation speed is 50 - 70 s. By controlling the rotation speed of the spinner and the duration of the rotation speed during the second spin coating process, it can be ensured that the side of the substrate with the first-dimensional surface relief grating is uniformly spin-coated with the photoresist having the second set thickness, and the photoresist fills the non-structural area of the first-dimensional surface relief grating. Taking the example of spin-coating a 1000-nm thick positive photoresist from Dow Chemical on the substrate, the initial rotation speed of the spinner is 400 r / min, the working time is 6 s, the working rotation speed of the spinner is 2200 r / min, and the working time is 60 s.

[0164] S2-2 Perform a second-beam interference exposure operation on the second photoresist mask on the substrate, so that the illuminated part in the structural area of the first-dimensional surface relief grating of the second photoresist mask is in a fully exposed state and the illuminated part in the non-structural area of the first-dimensional surface relief grating is in a partially exposed state, and a second photoresist mask with changed properties is obtained on the substrate.

[0165] Exemplarily,

[0166] S2-2-1 Build a holographic exposure system for the second-beam interference exposure operation. The holographic exposure system forms a second exposure field with light and dark fringes through beam interference. The holographic exposure system here can adopt a two-beam exposure system or a Lloyd's mirror exposure system.

[0167] S2-2-2 Fix the substrate with the second photoresist mask inside the holographic exposure system at a second set angle (the second set angle is determined based on the grating line direction of the second-dimensional surface relief grating), and irradiate the substrate with the second photoresist mask through the second exposure field that forms light and dark alternating fringes by beam interference, so that the illuminated part of the second photoresist mask in the structural area of the first-dimensional surface relief grating is in a fully exposed state and the illuminated part of the second photoresist mask in the non-structural area of the first-dimensional surface relief grating is in a partially exposed state, and a second photoresist mask with changed properties is obtained on the substrate.

[0168] During the process that the substrate with the second photoresist mask is irradiated by the second exposure field that forms light and dark alternating fringes by beam interference, so that the illuminated part of the second photoresist mask in the structural area of the first-dimensional surface relief grating is in a fully exposed state and the illuminated part of the second photoresist mask in the non-structural area of the first-dimensional surface relief grating is in a partially exposed state, determine the duty ratio of the second photoresist grating mask according to the set duty ratio of the second-dimensional surface relief grating, and control the exposure amount received by the illuminated part of the second photoresist mask on the substrate based on the duty ratio of the second photoresist grating mask.

[0169] The illuminated part of the second photoresist mask in the structural area of the first-dimensional surface relief grating being in a fully exposed state means that: for the illuminated part of the second photoresist mask in the structural area of the first-dimensional surface relief grating, the second photoresist mask with a second set thickness on the substrate can be completely dissolved after the second beam interference exposure operation and the second development operation (as Figure 9 shown).

[0170] The illuminated part of the second photoresist mask in the non-structural area of the first-dimensional surface relief grating being in a partially exposed state means that: for the illuminated part of the second photoresist mask in the non-structural area of the first-dimensional surface relief grating, after the second beam interference exposure operation and the second development operation of the second photoresist mask, the non-structural area of the first-dimensional surface relief grating still has photoresist (as Figure 9 shown).

[0171] Exemplarily, there are 3 ways to control the exposure amount:

[0172] 1. Under the condition of the same exposure time, adjust the exposure light intensity of the second exposure field, so as to control the exposure amount of the illuminated part of the second photoresist mask in the second exposure field.

[0173] 2. Under the condition that the exposure light intensity distribution of the second exposure field remains unchanged, adjust the exposure time of the illuminated part of the second photoresist mask, so as to control the exposure amount of the illuminated part of the second photoresist mask in the second exposure field.

[0174] 3. At the same time, adjust the exposure light intensity of the second exposure field and the exposure time of the illuminated part of the second photoresist mask, so as to control the exposure amount of the illuminated part of the second photoresist mask in the second exposure field.

[0175] S2-3 Perform a second development operation on the second photoresist mask with changed properties on the substrate to obtain a second photoresist grating mask on the substrate, and obtain a substrate with a second photoresist grating mask.

[0176] Exemplarily,

[0177] Immerse the second photoresist mask with changed properties on the substrate in a developer for a second development operation. The corresponding part of the second photoresist mask is eroded by the developer to obtain a second photoresist grating mask on the substrate, and obtain a substrate with a second photoresist grating mask.

[0178] Taking a positive photoresist as an example,

[0179] Immerse the second photoresist mask with changed properties on the substrate in a developer for a development operation. The illuminated part of the second photoresist mask is eroded and dissolved by the developer to obtain a second photoresist grating mask on the substrate, and obtain a substrate with a second photoresist grating mask.

[0180] During the process of immersing the second photoresist mask with changed properties on the substrate in a developer for a development operation, determine the duty cycle of the second photoresist grating mask according to the set duty cycle of the second-dimensional surface relief grating, and control the development time of the second photoresist mask with changed properties on the substrate in the developer based on the duty cycle of the second photoresist grating mask.

[0181] S2-4 Etch the substrate with a second photoresist grating mask. After the etching is completed, clean the residual photoresist on the substrate surface to obtain a two-dimensional surface relief grating on the substrate.

[0182] Exemplarily,

[0183] S2-4-1 In the position area on the substrate surface with a first-dimensional surface relief grating, use an ion beam etching machine to etch the substrate with a second photoresist grating mask, copy the topography distribution of the second photoresist grating mask to the substrate, and control the second etching time of the ion beam etching machine for etching the substrate with a second photoresist grating mask to obtain a second-dimensional surface relief grating with the above-mentioned set groove depth on the substrate.

[0184] Here, the second etching time of the ion beam etching machine for etching the substrate with a second photoresist grating mask is related to the set groove depth parameter of the second-dimensional surface relief grating on the substrate. Exemplarily, when the set groove depth parameter of the second-dimensional surface relief grating on the substrate is 400 nm, the second etching time can be controlled at about 26 min.

[0185] S2-4-2 Clean the residual photoresist on the substrate surface to obtain a two-dimensional surface relief grating on the substrate.

[0186] Examples of the cleaning solvent for the residual photoresist on the substrate surface can use acetone solvent.

[0187] The above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those of ordinary skill in the art can still modify the specific implementation manners of the present invention or make equivalent replacements. Any such modifications or equivalent replacements that do not depart from the spirit and scope of the present invention are within the scope of the claims of the present invention pending approval.

Claims

1. A method for preparing a two-dimensional surface relief grating, characterized in that: The steps include: Preparing a first-dimensional surface relief grating on the surface of a substrate to obtain a substrate having a first-dimensional surface relief grating; Continue to prepare a second-dimensional surface relief grating on the substrate having the first-dimensional surface relief grating, so as to obtain a two-dimensional surface relief grating on the substrate; The set groove depth of the first-dimensional surface relief grating is 1000-1500nm, and the set groove depth of the second-dimensional surface relief grating is 300-450nm; The grating line direction of the first-dimensional surface relief grating is perpendicular to the grating line direction of the second-dimensional surface relief grating.

2. The method for preparing a two-dimensional surface relief grating according to claim 1, characterized in that: The method comprises the following steps: preparing a first-dimensional surface relief grating on a substrate surface to obtain a substrate having a first-dimensional surface relief grating: Spin coating a photoresist with a first set thickness on the substrate to obtain a substrate provided with a first photoresist mask; Performing a first light beam interference exposure operation on the first photoresist mask on the substrate, so that the illuminated portion of the first photoresist mask is in a fully exposed state, and obtaining a first photoresist mask with changed properties on the substrate; Performing a first development operation on the first photoresist mask with changed properties on the substrate to obtain a first photoresist grating mask on the substrate, thereby obtaining a substrate having the first photoresist grating mask; The substrate with the first photoresist grating mask is etched, and after the etching is completed, the residual photoresist on the surface of the substrate is cleaned to obtain a substrate with a first-dimensional surface relief grating.

3. The method for preparing a two-dimensional surface relief grating according to claim 2, characterized in that: Spin coating a photoresist with a first set thickness on a substrate to obtain a substrate provided with a first photoresist mask comprises the following steps: placing the substrate into a coating machine; dripping a first set amount of photoresist onto the upper surface of the substrate; The coating machine is driven to rotate to drive the substrate to perform a first coating rotation, so that the upper surface of the substrate is evenly coated with the photoresist having the first set thickness, thereby obtaining a substrate provided with a first photoresist mask.

4. The method for preparing a two-dimensional surface relief grating according to claim 3, characterized in that: In the process of driving the glue spreader to rotate and drive the substrate to perform the first glue spread rotation, the initial speed of the glue spreader is 300-500r / min, the initial speed duration is 5-8s, the working speed of the glue spreader is 3500-4500r / min, and the working speed duration is 50-70s.

5. The method for preparing a two-dimensional surface relief grating according to any one of claims 2 to 4, characterized in that: The first set thickness of the photoresist is determined according to a set groove depth parameter of the first-dimensional surface relief grating and an etching selectivity ratio between the photoresist and the substrate.

6. The method for preparing a two-dimensional surface relief grating according to claim 2, characterized in that: Performing a first light beam interference exposure operation on the first photoresist mask on the substrate so that the illuminated portion of the first photoresist mask is in a fully exposed state, and obtaining a first photoresist mask with changed properties on the substrate, comprises the following steps: The substrate provided with the first photoresist mask is fixedly arranged in the holographic exposure system at a first set angle, and the substrate provided with the first photoresist mask is irradiated by a first exposure field formed by light beam interference with light stripes, so that the illuminated part of the first photoresist mask is in a fully exposed state, and the first photoresist mask with changed properties is obtained on the substrate; The first set angle is determined based on the grating line direction of the first-dimensional surface relief grating.

7. The method for preparing a two-dimensional surface relief grating according to claim 6, characterized in that: Performing a first development operation on the first photoresist mask with changed properties on the substrate to obtain a first photoresist grating mask on the substrate, and obtaining a substrate having the first photoresist grating mask, comprises the following steps: The first photoresist mask with changed properties on the substrate is immersed in a developer to perform a first development operation, and the corresponding part of the first photoresist mask is corroded by the developer to obtain a first photoresist grating mask on the substrate, thereby obtaining a substrate with the first photoresist grating mask.

8. The method for preparing a two-dimensional surface relief grating according to claim 7, characterized in that: determining a duty ratio of the first photoresist grating mask according to a set duty ratio of the first-dimensional surface relief grating; The following parameters of the first light beam interference exposure operation and the first development operation are controlled based on the duty ratio of the first photoresist grating mask: The exposure amount received by the illuminated portion of the first photoresist mask on the substrate in the first exposure field during the first light beam interference exposure operation; In the first development operation, the development time of the first photoresist mask with changed properties on the substrate in the developer.

9. The method for preparing a two-dimensional surface relief grating according to claim 6, characterized in that: The illuminated portion of the first photoresist mask is in a fully exposed state when: in the illuminated portion of the first photoresist mask, the first photoresist mask of the first set thickness on the substrate can be completely dissolved after the first light beam interference exposure operation and the first development operation.

10. The method for preparing a two-dimensional surface relief grating according to claim 2, characterized in that: Etching the substrate with the first photoresist grating mask, and cleaning the residual photoresist on the surface of the substrate after etching to obtain a substrate with a first-dimensional surface relief grating, comprising the following steps: Using an ion beam etcher to etch the substrate with the first photoresist grating mask, copying the topography distribution of the first photoresist grating mask onto the substrate, controlling a first etching time for the ion beam etcher to etch the substrate with the first photoresist grating mask, and obtaining a first-dimensional surface relief grating with the set groove depth on the substrate; The residual photoresist on the surface of the substrate is cleaned to obtain a substrate having a first-dimensional surface relief grating with the set groove depth.

11. The method for preparing a two-dimensional surface relief grating according to claim 1, characterized in that: The second-dimensional surface relief grating is continuously prepared on the substrate having the first-dimensional surface relief grating to obtain a two-dimensional surface relief grating on the substrate, comprising the following steps: Spin-coating a photoresist of a second set thickness on the substrate having the first-dimensional surface relief grating, and the photoresist fills the non-structured area of ​​the first-dimensional surface relief grating, to obtain a substrate provided with a second photoresist mask; Performing a second light beam interference exposure operation on the second photoresist mask on the substrate, so that the illuminated portion of the second photoresist mask in the structure region of the first-dimensional surface relief grating is in a fully exposed state and the illuminated portion of the second photoresist mask in the non-structure region of the first-dimensional surface relief grating is in an incompletely exposed state, thereby obtaining a second photoresist mask with changed properties on the substrate; Performing a second development operation on the second photoresist mask with changed properties on the substrate to obtain a second photoresist grating mask on the substrate, thereby obtaining a substrate having the second photoresist grating mask; The substrate with the second photoresist grating mask is etched, and after the etching is completed, the residual photoresist on the surface of the substrate is cleaned to obtain a two-dimensional surface relief grating on the substrate.

12. The method for preparing a two-dimensional surface relief grating according to claim 11, characterized in that: Spin coating a photoresist of a second set thickness on a substrate having a first-dimensional surface relief grating, and the photoresist fills the non-structured area of ​​the first-dimensional surface relief grating to obtain a substrate provided with a second photoresist mask, comprising the following steps: Putting the substrate having the first-dimensional surface relief grating into a coating machine; Adding a second set amount of photoresist to a side of the substrate having a first-dimensional surface relief grating; The coating machine is driven to rotate and the substrate with the first-dimensional surface relief grating is driven to perform a second coating rotation, so that one side of the substrate with the first-dimensional surface relief grating is evenly coated with the photoresist with the second set thickness, and the photoresist fills the non-structural area of ​​the first-dimensional surface relief grating, thereby obtaining a substrate with a second photoresist mask.

13. The method for preparing a two-dimensional surface relief grating according to claim 12, characterized in that: In the process of driving the glue spreader to rotate and drive the substrate with the first-dimensional surface relief grating to perform the second glue spread rotation, the initial speed of the glue spreader is 350-450r / min, the initial speed duration is 6-8s, the working speed of the glue spreader is 2200-2500r / min, and the working speed duration is 50-70s.

14. The method for preparing a two-dimensional surface relief grating according to any one of claims 11 to 13, characterized in that: The second set thickness of the photoresist is the distance between the side of the photoresist in contact with the air and the side of the photoresist in contact with the top surface of the structure area of ​​the first-dimensional surface relief grating; The second set thickness of the photoresist is determined according to a set groove depth parameter of the second-dimensional surface relief grating and an etching selectivity ratio between the photoresist and the substrate.

15. The method for preparing a two-dimensional surface relief grating according to claim 11, characterized in that: The second photoresist mask on the substrate is subjected to a second light beam interference exposure operation, so that the illuminated portion of the second photoresist mask in the structure region of the first-dimensional surface relief grating is in a fully exposed state and the illuminated portion of the non-structure region of the first-dimensional surface relief grating is in an incompletely exposed state, and a second photoresist mask with changed properties is obtained on the substrate, comprising the following steps: The substrate provided with the second photoresist mask is fixedly arranged in the holographic exposure system at a second set angle, and the substrate provided with the second photoresist mask is irradiated by a second exposure field formed by light beam interference with light stripes, so that the illuminated portion of the second photoresist mask in the structure area of ​​the first-dimensional surface relief grating is in a fully exposed state and the illuminated portion of the second photoresist mask in the non-structure area of ​​the first-dimensional surface relief grating is in an incompletely exposed state, thereby obtaining a second photoresist mask with changed properties on the substrate; The second set angle is determined based on the grating line direction of the second-dimensional surface relief grating.

16. The method for preparing a two-dimensional surface relief grating according to claim 15, characterized in that: Performing a second development operation on the second photoresist mask with changed properties on the substrate to obtain a second photoresist grating mask on the substrate, and obtaining a substrate with the second photoresist grating mask, comprises the following steps: The second photoresist mask with changed properties on the substrate is immersed in a developer for a second development operation, and the corresponding part of the second photoresist mask is corroded by the developer to obtain a second photoresist grating mask on the substrate, thereby obtaining a substrate with the second photoresist grating mask.

17. The method for preparing a two-dimensional surface relief grating according to claim 16, characterized in that: determining a duty ratio of the second photoresist grating mask according to a set duty ratio of the second-dimensional surface relief grating; The following parameters of the second light beam interference exposure operation and the second development operation are controlled based on the duty ratio of the second photoresist grating mask: The exposure amount received by the illuminated portion of the second photoresist mask on the substrate in the second exposure field during the second light beam interference exposure operation; In the second developing operation, the developing time of the second photoresist mask with changed properties on the substrate in the developing solution.

18. The method for preparing a two-dimensional surface relief grating according to claim 15, characterized in that: The second photoresist mask is in a fully exposed state in the illuminated portion of the structure region of the first-dimensional surface relief grating: the second photoresist mask of the second set thickness on the substrate can be completely dissolved after the second light beam interference exposure operation and the second development operation in the illuminated portion of the structure region of the first-dimensional surface relief grating; The second photoresist mask is in an incompletely exposed state in the illuminated portion of the non-structured area of ​​the first-dimensional surface relief grating: the second photoresist mask is in the illuminated portion of the non-structured area of ​​the first-dimensional surface relief grating, and after the second photoresist mask undergoes the second beam interference exposure operation and the second development operation, the non-structured area of ​​the first-dimensional surface relief grating still has photoresist.

19. The method for preparing a two-dimensional surface relief grating according to claim 11, characterized in that: The substrate with the second photoresist grating mask is etched, and after the etching is completed, the residual photoresist on the surface of the substrate is cleaned to obtain a two-dimensional surface relief grating on the substrate, comprising the following steps: In the position area of ​​the substrate surface having the first-dimensional surface relief grating, the substrate having the second photoresist grating mask is etched by an ion beam etcher, the topography distribution of the second photoresist grating mask is copied to the substrate, and the second etching time of the ion beam etcher for etching the substrate having the second photoresist grating mask is controlled to obtain the second-dimensional surface relief grating having the set groove depth on the substrate; The residual photoresist on the substrate surface is cleaned to obtain a two-dimensional surface relief grating on the substrate.

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