Diffractive optical waveguide, method of making and use thereof

Abstract

The application provides a diffraction optical waveguide and a preparation method and application thereof, and the preparation method comprises the following steps: preparing a waveguide to be plated; sequentially forming a first chemical inert polymer layer and a first photoresist layer on a side surface of the waveguide to be plated close to a stamping glue layer; exposing and developing to remove the first chemical inert polymer layer and the first photoresist layer on the diffraction micro-nano structure, so that a waveguide to be plated with a second chemical inert polymer layer and a second photoresist layer is obtained; forming a metal film layer on a side surface of the waveguide to be plated close to the second photoresist layer, and then cleaning to remove the second chemical inert polymer layer, the second photoresist layer and the metal film layer thereon, so that the diffraction optical waveguide is obtained. Through the design of the chemical inert polymer layer and the mutual cooperation of each process step, the preparation method fundamentally solves the problem that the waveguide to be plated prepared by nano-imprinting is yellow on the surface in the photoetching process, and has excellent pattern quality and process compatibility.

Description

Technical Field

[0001] This invention belongs to the field of micro-nano manufacturing technology, specifically relating to a diffractive optical waveguide, its fabrication method, and its application. Background Technology

[0002] Currently, to increase the reflectivity of diffractive waveguides, a metal film layer is typically deposited on the diffractive micro / nano structure region. The fabrication method for diffractive waveguides generally includes the following steps: First, a waveguide with a diffractive micro / nano structure on its surface is provided for coating. Then, a photoresist layer is formed on the surface of the waveguide near the diffractive micro / nano structure. Next, the photoresist layer is exposed and developed to remove it from the diffractive micro / nano structure. Then, a metal film layer is deposited on the surface near the photoresist layer. Finally, the remaining photoresist layer is cleaned to remove it, thereby removing the metal film layer on top of it, retaining the metal film layer on the diffractive micro / nano structure, thus obtaining the diffractive waveguide.

[0003] Nanoimprint lithography (NIM) technology boasts advantages such as high-precision replication, large-area fabrication, and low-cost mass production, making it one of the most widely used micro / nano manufacturing technologies. Therefore, NIM is frequently used to fabricate waveguides with diffractive micro / nano structures. However, after subsequent photolithography processes on the surface of the nanoimprint-fabricated waveguide, a yellowing phenomenon occurs. This not only affects the aesthetics of the diffractive waveguide but, more importantly, impacts its key optical properties such as transmittance, brightness, and luminous efficiency.

[0004] Therefore, developing a method for fabricating diffractive waveguides that can fundamentally solve the problem of surface yellowing caused by photolithography is an urgent problem to be solved in this field. Summary of the Invention

[0005] To address the shortcomings of existing technologies, the present invention aims to provide a diffractive waveguide, its fabrication method, and its application. By designing a chemically inert polymer layer and coordinating various process steps, the fabrication method fundamentally solves the problem of surface yellowing caused by photolithography in waveguides fabricated using nanoimprinting, and exhibits excellent pattern quality and process compatibility.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a method for fabricating a diffractive optical waveguide, the method comprising: Fabrication of a waveguide to be coated; wherein the waveguide to be coated includes a waveguide substrate and an imprinted adhesive layer having a diffraction micro / nano structure disposed on the waveguide substrate; A first chemically inert polymer layer and a first photoresist layer are sequentially formed on the surface of the waveguide to be coated near the imprinted adhesive layer. The waveguide to be coated, having a first chemically inert polymer layer and a first photoresist layer, is exposed and developed to remove the first chemically inert polymer layer and the first photoresist layer from the diffraction micro / nano structure of the waveguide to be coated, thereby obtaining a waveguide to be coated having a second chemically inert polymer layer and a second photoresist layer. A metal film is formed on the surface of the waveguide to be coated, near the second photoresist layer. Then, the second chemically inert polymer layer, the second photoresist layer, and the metal film on the second photoresist layer are removed by cleaning to obtain the diffractive waveguide.

[0007] The present invention has found that the main reasons for the yellowing phenomenon on the surface of the waveguide to be coated by nanoimprint during the photolithography process in the fabrication of diffractive optical waveguides are as follows: 1) The solvent components in the photoresist react with the chemical groups on the surface of the imprinting agent; 2) Some components in the photoresist undergo photocatalytic or thermocatalytic reactions on the surface of the imprinting agent; 3) The imprinting agent has a high surface energy, which leads to uneven wetting of the photoresist and the formation of local accumulation.

[0008] Based on this, the fabrication method of the diffractive waveguide proposed in this invention involves setting a first chemically inert polymer layer on the surface of the waveguide to be coated, near the imprinted resist layer, between the imprinted resist layer and the first photoresist layer. This effectively blocks direct contact between the first photoresist layer and the imprinted resist layer, thereby preventing chemical and / or physical reactions that may cause yellowing, and fundamentally solving the problem of surface yellowing during photolithography. The fabrication method is adaptable to various photoresists, imprinted resists, and process conditions, exhibiting excellent process compatibility and flexibility, and yielding high-quality patterns and high-quality diffractive waveguides.

[0009] In this invention, the term "chemically inert polymer" refers to a polymer that is chemically inert, does not react with imprinting adhesive, does not react with photoresist, does not have photoreactive properties, does not react during the exposure stage, and is soluble in the developer during the development stage.

[0010] As a preferred embodiment of the present invention, the step of preparing the waveguide to be coated includes: A waveguide substrate is provided, and an imprinting adhesive layer is coated on one side surface of the waveguide substrate; The imprinting adhesive is imprinted using a preset imprinting template, and then cured for the first time to form an imprinting adhesive layer with a diffraction micro-nano structure.

[0011] In this invention, the type of waveguide substrate is not specifically limited; any substrate known in the art for use in diffractive waveguides is applicable. For example, the waveguide substrate includes glass.

[0012] Preferably, the refractive index of the imprinting adhesive is 1.80-2.20, for example, it can be 1.82, 1.85, 1.88, 1.90, 1.92, 1.95, 1.98, 2.00, 2.02, 2.05, 2.08, 2.10, 2.12, 2.15 or 2.18, as well as specific point values ​​between the above point values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific point values ​​included in the range.

[0013] As a preferred technical solution of the present invention, the imprinting adhesive is a high refractive index imprinting adhesive with a refractive index of 1.80-2.20, which has a good refractive index matching degree with the waveguide substrate, which helps to reduce interface reflection loss and improve the contrast and optical performance of the diffracted light waveguide coupled image.

[0014] This invention does not impose specific limitations on the composition of the imprinting adhesive. Any imprinting adhesive known in the art that can be used for micro-nano manufacturing, preferably with a refractive index of 1.80-2.20, is applicable to this invention.

[0015] For example, the imprinting adhesive includes any one or a combination of at least two of the following materials: titanium oxide, zirconium oxide, metal oxide nanoparticle-doped polymer, and organic-inorganic hybrid material.

[0016] Preferably, the first curing temperature is 120℃-180℃, for example, it can be 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃ or 175℃, as well as specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0017] Preferably, the first curing time is 30 s - 120 s, for example, it can be 40 s, 50 s, 60 s, 70 s, 80 s, 90 s, 100 s or 110 s, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0018] Preferably, before the step of sequentially forming a first chemically inert polymer layer and a first photoresist layer on the side surface of the waveguide to be coated near the imprinted adhesive layer, the method further includes pre-treatment of the waveguide to be coated, the pre-treatment including cleaning and baking.

[0019] Preferably, the cleaning method includes cleaning the waveguide to be coated using a plasma cleaner.

[0020] Preferably, the cleaning is performed in an oxygen-containing atmosphere to thoroughly remove surface contaminants.

[0021] Preferably, the cleaning time is 1 min to 5 min, for example, it can be 1.5 min, 2 min, 2.5 min, 3 min, 3.5 min, 4 min or 4.5 min, as well as specific point values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific point values ​​included in the range.

[0022] Preferably, the baking is carried out in a protective gas. On one hand, because the imprinting adhesive layer reacts under high-temperature baking and in the presence of oxygen, forming a dense "oxidized skin" or altering its surface energy, the adhesion performance of the imprinting adhesive layer deteriorates, posing a risk of detachment of the first chemically inert polymer layer. Baking in a protective gas prevents cross-linking of the imprinting adhesive layer, maintaining its excellent adhesion performance and preventing the first chemically inert polymer layer from detaching. On the other hand, the imprinting adhesive layer undergoes an oxidation reaction under high-temperature baking and in the presence of oxygen, causing it to yellow or produce polar byproducts. The presence of a protective gas effectively inhibits the oxidation reaction, maintaining the imprinting adhesive layer's excellent optical transparency and chemical purity. Furthermore, particulate contaminants exist in the air; if these contaminants remain on the surface of the imprinting adhesive layer, they can cause surface defects. The injection of the protective gas prevents particulate contaminants from remaining on the surface of the imprinting adhesive layer, thus avoiding surface defects caused by particulate contaminants.

[0023] For example, the protective gas includes nitrogen, helium, argon, etc.

[0024] Preferably, the baking temperature is 120℃-180℃, for example, it can be 125℃, 130℃, 135℃, 140℃, 145℃, 150℃, 155℃, 160℃, 165℃, 170℃ or 175℃, as well as specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0025] Preferably, the baking time is 30 min-120 min, for example, it can be 40 min, 50 min, 60 min, 70 min, 80 min, 90 min, 100 min or 110 min, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0026] As a preferred embodiment of the present invention, the step of forming a first chemically inert polymer layer on the surface of the waveguide to be coated near the imprinted adhesive layer includes: Provide chemically inert polymer coatings; The chemically inert polymer coating is applied to the surface of the waveguide to be coated, near the imprinted adhesive layer, and then cured a second time to obtain the first chemically inert polymer layer.

[0027] Preferably, the chemically inert polymer coating comprises any one or a combination of at least two of polydimethylglutarimide, polymethyl methacrylate, polycarbonate, polystyrene, and polyimide.

[0028] As a preferred embodiment of the present invention, the first chemically inert polymer layer comprises any one or a combination of at least two of polydimethylglutarimide, polymethyl methacrylate, polycarbonate, polystyrene, and polyimide. On one hand, it is a chemically inert material that will not chemically react with inorganic oxides or other components in the imprinting resist layer, nor will it change the composition of the imprinting resist layer. Furthermore, it is located between the imprinting resist layer and the first photoresist layer, effectively preventing direct contact between the first photoresist layer and the imprinting resist layer, thus preventing chemical and / or physical reactions that may cause yellowing. On the other hand, the first chemically inert polymer layer has good chemical stability and mechanical strength, enabling it to adapt to various types of photoresists and process conditions, greatly improving process compatibility and flexibility. Moreover, the introduction of the first chemically inert polymer layer improves the wettability and adhesion of the first photoresist layer, reducing edge defects and peeling phenomena, thereby improving the resolution and fidelity of the pattern.

[0029] Preferably, the viscosity of the chemically inert polymer coating at 24±1℃ is 10 cp - 50 cp, for example, it can be 15 cp, 20 cp, 25 cp, 30 cp, 35 cp, 40 cp or 45 cp, and specific values ​​within the above ranges. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range. By designing the chemically inert polymer coating to have the aforementioned viscosity, on the one hand, it has better fluidity, making the homogenization more uniform, and the formed first chemically inert polymer layer is uniform and flat, which is beneficial to the homogenization of photoresist and the formation of a uniform first photoresist layer, thereby avoiding the problems of poor development and metal film residue caused by defects in the first chemically inert polymer layer and the first photoresist layer. On the other hand, chemically inert polymer coatings with a specific viscosity reduce the stickiness between chemically inert polymer molecules, making the first chemically inert polymer layer easily dissolve by the developer during the development stage. This results in the second photoresist layer and the edges of the second chemically inert polymer layer having good undercut patterns, allowing for a larger process window in the metal film layer setup process.

[0030] It should be noted that the chemically inert polymer coating, in addition to the chemically inert polymer (including any one or a combination of at least two of polydimethylglutarimide, polymethyl methacrylate, polycarbonate, polystyrene, and polyimide), also includes a solvent and optionally additives. For example, the solvent includes cyclopentanone; the additive includes propylene glycol methyl ether acetate, which can adjust the viscosity of the coating. The higher the content of additives in the chemically inert polymer coating, the lower the viscosity of the coating.

[0031] Preferably, the chemically inert polymer coating contains 1-33% by mass of the chemically inert polymer (including any one or a combination of at least two of polydimethylglutarimide, polymethyl methacrylate, polycarbonate, polystyrene, and polyimide), for example, 2%, 5%, 8%, 10%, 12%, 15%, 18%, 20%, 22%, 25%, 28%, or 30%, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range, but preferably 1-20%.

[0032] Preferably, the solvent (preferably cyclopentanone) in the chemically inert polymer coating has a mass content of 65%-90%, for example, it can be 68%, 70%, 72%, 75%, 78%, 80%, 82%, 85% or 88%, and specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0033] Preferably, the mass content of the additive (preferably propylene glycol methyl ether acetate) in the chemically inert polymer coating is 0-2%, for example, it can be 0.1%, 0.3%, 0.5%, 0.8%, 1%, 1.2%, 1.5% or 1.8%, and specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range, but 0.1%-2% is further preferred.

[0034] For example, in the chemically inert polymer coating, the mass content of the chemically inert polymer is 1%-20% (e.g., the mass content of polydimethylglutarimide is 10%-15%, or the mass content of polymethyl methacrylate is 1%-20%), the mass content of cyclopentanone is 65%-90%, and the mass content of propylene glycol methyl ether acetate is 0.1%-2%. By adjusting the amount of each component within the above range, the viscosity of the coating at 24±1℃ can be achieved to be 10 cp-50 cp.

[0035] Preferably, the second curing temperature is 90℃-120℃, for example, it can be 92℃, 95℃, 98℃, 100℃, 102℃, 105℃, 108℃, 110℃, 112℃, 115℃ or 118℃, as well as specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0036] Preferably, the second curing time is 60 s-120 s, for example, it can be 65 s, 70 s, 75 s, 80 s, 85 s, 90 s, 95 s, 100 s, 105 s, 110 s or 115 s, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0037] Preferably, the thickness of the first chemically inert polymer layer is 1 μm-2 μm, for example, it can be 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.7 μm, 1.8 μm or 1.9 μm, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0038] Preferably, the thickness ratio of the first photoresist layer to the first chemically inert polymer layer is (1-1.5):1, for example, it can be 1.05:1, 1.1:1, 1.15:1, 1.2:1, 1.25:1, 1.3:1, 1.35:1, 1.4:1, or 1.45:1, etc. This ensures that the second chemically inert polymer layer and the second photoresist layer obtained by exposure and development have excellent undercut morphology, and prevents collapse at the edges of the second photoresist layer. If the thickness ratio of the first photoresist layer to the first chemically inert polymer layer is too large, the second chemically inert polymer layer will be unable to support the weight of the second photoresist layer and will collapse. After collapse, the second photoresist layer and the imprinting layer will be connected. The subsequently applied metal film layer will be located on the surface of the second photoresist layer and the imprinting layer, and will not be able to form an effective gap, resulting in cleaning difficulties and making it difficult to peel off the metal film layer on the second photoresist layer. If the thickness ratio of the first photoresist layer to the first chemically inert polymer layer is too low, it will be difficult to prevent the developer from dissolving, resulting in a small development process window, failure to form the target undercut, and affecting the pattern size.

[0039] Preferably, the first photoresist layer is a negative photoresist layer.

[0040] Preferably, the step of sequentially forming a first chemically inert polymer layer and a first photoresist layer on the surface of the waveguide to be coated near the imprinted adhesive layer includes: Photoresist is coated onto the first chemically inert polymer layer, and then cured in a third step to obtain the first photoresist layer.

[0041] Preferably, the photoresist is a negative photoresist.

[0042] This invention does not specifically limit the type of negative photoresist; all negative photoresists known in the art are applicable to this invention.

[0043] Preferably, the photoresist includes a chemically amplified photoresist.

[0044] Preferably, the photosensitive wavelength of the photoresist is selected from any one of the g-line (436 nm), h-line (405 nm), i-line (365 nm), KrF (248 nm), or ArF (193 nm). This photosensitive wavelength meets the requirements of pattern resolution (linewidth) and ensures that the resulting second chemically inert polymer layer and second photoresist layer have excellent and intact undercut morphology, guaranteeing the stability of the prepared metal film. Furthermore, during subsequent cleaning and removal, the metal film on the second photoresist layer is completely removed along with the second chemically inert polymer layer and the second photoresist layer, avoiding metal residue in areas outside the diffraction micro / nano structure. If the wavelength is too long, it will lead to reduced resolution, a worse undercut morphology formed by the second chemically inert polymer layer and the second photoresist layer, and adhesion problems between the metal film on the diffraction micro / nano structure and the metal film on the second photoresist layer, thus introducing the risk of metal residue. If the wavelength is too short, the energy from the wavelength cannot penetrate the first photoresist layer evenly, resulting in insufficient reaction of the first photoresist layer. In the subsequent development stage, the first photoresist layer remains, which will block the metal film layer, causing defects in the metal film layer, leading to reduced performance or even scrapping of the diffractive waveguide.

[0045] Preferably, the third curing temperature is 90℃-120℃, for example, it can be 92℃, 95℃, 98℃, 100℃, 102℃, 105℃, 108℃, 110℃, 112℃, 115℃ or 118℃, as well as specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0046] Preferably, the third curing time is 60 s-120 s, for example, it can be 65 s, 70 s, 75 s, 80 s, 85 s, 90 s, 95 s, 100 s, 105 s, 110 s or 115 s, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0047] In this invention, the waveguide to be coated, having a first chemically inert polymer layer and a first photoresist layer, is exposed and developed to remove the first chemically inert polymer layer and the first photoresist layer from the diffraction micro / nano structure. The chemically inert polymer layer remaining on the waveguide to be coated is called the "second chemically inert polymer layer", and the remaining photoresist layer is called the "second photoresist layer".

[0048] Preferably, in the exposure and development process, the exposure energy is 60 mJ / cm². 2 -100 mJ / cm 2 For example, it can be 65mJ / cm 2 70 mJ / cm 2 75 mJ / cm 2 80 mJ / cm 2 85 mJ / cm 2 90 mJ / cm 2 Or 95 mJ / cm 2 As for the specific point values ​​between the above point values, due to space limitations and for the sake of brevity, this invention will not exhaustively list the specific point values ​​included in the range.

[0049] For example, the exposure can be performed using a stepper lithography machine or a contact lithography machine.

[0050] Preferably, the exposure and development process includes a baking step between exposure and development.

[0051] Preferably, the baking temperature is 90℃-120℃, for example, it can be 92℃, 95℃, 98℃, 100℃, 102℃, 105℃, 108℃, 110℃, 112℃, 115℃ or 118℃, as well as specific values ​​between the above points. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0052] Preferably, the baking time is 60 s-120 s, for example, it can be 65 s, 70 s, 75 s, 80 s, 85 s, 90 s, 95 s, 100 s, 105 s, 110 s or 115 s, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0053] Preferably, in the exposure and development process, the developing solution used is an aqueous solution of an alkaline substance.

[0054] Preferably, the developing substance comprises tetramethylammonium hydroxide.

[0055] Preferably, the alkaline substance in the developing solution has a mass content of 1%-5%, for example, it can be 1.5%, 2%, 2.5%, 3%, 3.5%, 4% or 4.5%, and specific point values ​​between the above point values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific point values ​​included in the range.

[0056] Preferably, in the exposure and development process, the development time is 30 s-100 s, for example, 40 s, 50 s, 60 s, 70 s, 80 s, or 90 s, and specific point values ​​within the above ranges. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range. This results in the formation of a well-defined undercut pattern for the second photoresist layer and the second chemically inert polymer layer. During the preparation of the metal film, the metal film on the diffraction micro / nano structure is effectively isolated from the metal film on the second photoresist layer. In the subsequent cleaning and removal process, the metal film on the second photoresist layer will be completely removed along with the peeling of the second chemically inert polymer layer and the second photoresist layer, preventing metal residues outside the diffraction micro / nano structure. If the development time is too short, the undercut formed by the second photoresist layer and the second chemically inert polymer layer will not be obvious, causing the metal film on the diffraction micro / nano structure to adhere to the metal film on the second photoresist layer. This makes it difficult to remove the metal film on the second photoresist layer, resulting in metal residue. If the development time is too long, the undercut formed by the second photoresist layer and the second chemically inert polymer layer will become larger. The edge of the second photoresist layer will collapse due to lack of support, which will also cause the metal film on the diffraction micro / nano structure to adhere to the metal film on the second photoresist layer. This will make it difficult to remove the metal film on the second photoresist layer, resulting in metal residue.

[0057] Preferably, the projection of the second photoresist layer onto the waveguide substrate covers the projection of the second chemically inert polymer layer onto the waveguide substrate.

[0058] Understandably, during the exposure and development process, the unexposed areas of the first photoresist layer are washed away by the developer, exposing the first chemically inert polymer layer. The developer continues to penetrate downwards and interacts with the first chemically inert polymer layer, causing the first chemically inert polymer layer in that area to be washed away. As a result, the projection of the second photoresist layer onto the waveguide substrate overlaps the projection of the second chemically inert polymer layer onto the waveguide substrate, forming a complete undercut pattern. This effectively isolates the metal film layer on the diffractive micro / nano structure from the metal film layer on the second photoresist layer, preventing them from adhering. This effectively avoids the problem of metal entanglement during the fabrication of the metal film layer. In the subsequent cleaning and removal process, the metal film layer on the second photoresist layer is completely removed along with the peeling of the second chemically inert polymer layer and the second photoresist layer, thus avoiding the problem of metal residue after cleaning and removing the metal film layer on the second photoresist layer. This improves the precision and quality of the metal film layer in the diffractive waveguide.

[0059] Preferably, the distance between the projection of the edge of the second photoresist layer and the edge of the second chemically inert polymer layer onto the waveguide substrate is 1 μm-4 μm, for example, it can be 1.2 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.5 μm, 2.6 μm, 2.8 μm, 3 μm, 3.2 μm, 3.4 μm, 3.5 μm, 3.6 μm or 3.8 μm, and specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0060] Preferably, the step of exposing and developing the waveguide to be coated with a first chemically inert polymer layer and a first photoresist layer to remove the first chemically inert polymer layer and the first photoresist layer from the diffraction micro / nano structure of the waveguide to be coated, to obtain a waveguide to be coated with a second chemically inert polymer layer and a second photoresist layer, includes: Using an exposure energy of 60 mJ / cm 2 -100 mJ / cm 2 The lithography machine exposes the first chemically inert polymer layer and the first photoresist layer; The first chemically inert polymer layer and the first photoresist layer after exposure are baked at a temperature of 90℃-120℃ for 60 s-120 s. The first chemically inert polymer layer and the first photoresist layer after baking are developed using a developing solution for 30 s-100 s to remove the first chemically inert polymer layer and the first photoresist layer on the diffraction micro / nano structure of the waveguide to be coated. The distance between the edge of the second photoresist layer and the projection of the edge of the second chemically inert polymer layer on the waveguide substrate is 1 μm-4 μm.

[0061] Preferably, the material of the metal film layer includes any one or a combination of at least two of chromium, aluminum, titanium, platinum, and gold.

[0062] Preferably, the thickness of the metal film is 100 nm-300 nm, for example, it can be 120 nm, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm or 280 nm, as well as specific values ​​between the above values. Due to space limitations and for the sake of brevity, the present invention will not exhaustively list the specific values ​​included in the range.

[0063] Preferably, the step of forming a metal film on the side surface of the waveguide to be coated near the second photoresist layer includes: forming a metal film on the side surface of the waveguide to be coated near the second photoresist layer using a vapor deposition method.

[0064] Preferably, in the vapor deposition method, the area of ​​the vapor-deposited metal film is greater than or equal to the area of ​​the diffraction micro / nano structure.

[0065] Preferably, the step of cleaning to remove the second chemically inert polymer layer, the second photoresist layer, and the metal film layer on the second photoresist layer includes: The second chemically inert polymer layer is removed by cleaning with a cleaning solution, thereby removing the second photoresist layer and metal film layer on the second chemically inert polymer layer.

[0066] Preferably, the cleaning fluid includes N 1-Methylpyrrolidone, acetone, ethanol, isopropanol, or any one or a combination of at least two of them.

[0067] Preferably, the cleaning is performed under ultrasonic conditions.

[0068] More preferably, the cleaning with the cleaning solution includes a first cleaning and a second cleaning performed sequentially; the cleaning solution for the first cleaning includes acetone, and the cleaning solution for the second cleaning includes isopropanol. After cleaning with the cleaning solution, water can also be used for rinsing; after the above cleaning, the second chemically inert polymer layer and the second photoresist layer and metal film layer thereon can be fully removed.

[0069] As a preferred embodiment of the present invention, the method for fabricating the diffractive waveguide specifically includes the following steps: S1. Fabrication of the waveguide to be coated: A waveguide substrate is provided, and an imprinting adhesive layer is coated on one side surface of the waveguide substrate; The imprinting adhesive is imprinted using a preset imprinting template and cured at 120℃-180℃ for 30 s-120 s to form an imprinting adhesive layer with a diffraction micro-nano structure, thus obtaining the waveguide to be coated. The waveguide to be coated is cleaned and then baked in a protective gas at 120℃-180℃ for 30 min-120 min to obtain the pretreated waveguide to be coated. S2. Preparation of the first chemically inert polymer layer: A chemically inert polymer coating is applied to the surface of the waveguide to be coated near the imprinted adhesive layer after pretreatment, and then cured at 90℃-120℃ for 60 s-120 s to obtain a first chemically inert polymer layer with a thickness of 1 μm-2 μm; the chemically inert polymer coating includes any one or a combination of at least two of polydimethylglutarimide, polymethyl methacrylate, polycarbonate, polystyrene, and polyimide; S3. Preparation of the first photoresist layer: Photoresist is coated onto the first chemically inert polymer layer and then cured at 90℃-120℃ for 60 s-120 s to obtain the first photoresist layer; S4, Exposure and Development: Using an exposure energy of 60 mJ / cm 2 -100 mJ / cm 2 The lithography machine exposes the first chemically inert polymer layer and the first photoresist layer. The first chemically inert polymer layer and the first photoresist layer after exposure are baked at 90℃-120℃ for 60 s-120s; The baked first chemically inert polymer layer and first photoresist layer are developed using a developing solution for 30 s-100 s to remove the first chemically inert polymer layer and first photoresist layer from the diffraction micro / nano structure of the waveguide to be coated, resulting in a waveguide to be coated with a second chemically inert polymer layer and a second photoresist layer; the distance between the edge of the second photoresist layer and the projection of the edge of the second chemically inert polymer layer onto the waveguide substrate is 1 μm-4 μm. S5. Preparation of metal film: A metal film layer is prepared on the surface of the waveguide to be coated near the second photoresist layer using a vapor deposition method; the area of ​​the metal film layer is greater than or equal to the area of ​​the region with the diffraction micro / nano structure. S6. Clean and remove the second chemically inert polymer layer, the second photoresist layer, and the metal film layer on the second photoresist layer: The second chemically inert polymer layer is removed by cleaning with a cleaning solution, thereby removing the second photoresist layer and the metal film layer on the second chemically inert polymer layer to obtain the diffractive waveguide; The cleaning fluid includes N 1-Methylpyrrolidone, acetone, ethanol, isopropanol, or any one or a combination of at least two of them.

[0070] As a preferred embodiment of the present invention, in the fabrication method of the diffractive waveguide, the introduction of a first chemically inert polymer layer effectively blocks direct contact between the first photoresist layer and the imprinting resist layer, preventing chemical and / or physical reactions that may cause yellowing. Simultaneously, through optimization of process parameters in steps S2-S4, the resulting second chemically inert polymer layer and second photoresist layer form a clear undercut, effectively avoiding the problem of metal wrapping during the metal film preparation step, and thus avoiding metal residue issues in step S6. Furthermore, the first chemically inert polymer layer possesses good chemical stability and mechanical strength, adapting to various types of photoresists and process conditions, greatly improving process compatibility and flexibility. Moreover, the presence of the first chemically inert polymer layer improves the wettability and adhesion of the first photoresist layer, reducing edge defects and peeling, thereby improving pattern resolution and fidelity. In addition, each step of the fabrication method has a clear process window, facilitating industrial production and large-scale application. Furthermore, the preparation method of the present invention does not impose too many restrictions on the specific composition of materials such as imprinting adhesive and photoresist, and is applicable to a variety of different types of high refractive index imprinting adhesive and different types of photoresist, thus having wide applicability.

[0071] In a second aspect, the present invention provides a diffractive optical waveguide, which is prepared by the preparation method described in the first aspect.

[0072] Thirdly, the present invention provides a display device, the display device comprising the diffractive waveguide described in the second aspect.

[0073] Compared with the prior art, the present invention has at least the following beneficial effects: (1) In the fabrication method of the diffractive waveguide proposed in this invention, a first chemically inert polymer layer is introduced between the imprinting resist layer and the first photoresist layer, effectively blocking direct contact between the first photoresist layer and the imprinting resist layer. This prevents chemical and / or physical reactions that may cause yellowing, fundamentally solving the problem of surface yellowing caused by photolithography in waveguides fabricated by nanoimprinting. The fabrication method can adapt to various photoresists, imprinting resists, and process conditions, exhibiting excellent process compatibility and flexibility, and yielding high-quality patterns and high-quality diffractive waveguides.

[0074] (2) In this invention, by setting the first chemically inert polymer layer and cooperating with the process parameters, the second chemically inert polymer layer and the second photoresist layer obtained by exposure and development form an obvious undercut pattern, which effectively avoids the problem of metal wrapping when preparing the metal film layer, and thus avoids the problem of metal residue after cleaning and removing the metal film layer on the second photoresist layer, thereby improving the fineness and quality of the metal film layer in the diffractive waveguide.

[0075] (3) In this invention, the first chemically inert polymer layer has good chemical stability and mechanical strength, can be matched with a variety of different imprinting adhesives, and can adapt to various types of photoresists and process conditions, exhibiting excellent process compatibility and wide applicability. At the same time, the introduction of the first chemically inert polymer layer improves the wettability and adhesion of the first photoresist layer, reduces edge defects and peeling phenomena, and improves the resolution and fidelity of the pattern.

[0076] (4) In the preparation method of the present invention, a wide range of materials such as photoresist and imprinting adhesive are selected, and each step has a clear process window, which makes it easy to realize industrial production and large-scale application. Attached Figure Description

[0077] Figure 1 A process flow diagram of a method for fabricating a diffractive optical waveguide according to a specific embodiment; Figure 2A A schematic diagram of the process structure for fabricating a diffractive optical waveguide according to a specific embodiment; Figure 2B A schematic diagram of the fabrication process of the diffractive waveguide provided for Comparative Example 1; Figure 3A The image shows the macroscopic morphology of the diffractive waveguide prepared in Example 1. Figure 3B This is a top view of the macroscopic morphology of the diffractive waveguide prepared in Example 2; Figure 3C Top view of the macroscopic morphology of the diffractive waveguide prepared in Example 5; Figure 3D Top view of the macroscopic morphology of the diffractive waveguide prepared in Example 6; Figure 3E The top view of the macroscopic morphology of the diffractive waveguide prepared in Comparative Example 1; Figure 4A A top view of the microstructure of the diffractive waveguide prepared in Example 1; Figure 4B Top view of the microstructure of the diffractive waveguide prepared in Example 7; Figure 4C The top view shows the microstructure of the diffractive waveguide prepared in Comparative Example 1. Figure 5A The optical microscope image of the waveguide to be coated, having a second chemically inert polymer layer and a second photoresist layer, obtained in step S4 of Example 1; Figure 5B The optical microscope test image of the waveguide to be coated with the second photoresist layer obtained in step S3 of Comparative Example 1 is shown. Figure 6A Scanning electron microscope (SEM) image of the waveguide sample with metal coating obtained in step S5 of Example 1; Figure 6B Scanning electron microscope (SEM) image of the waveguide sample with metal coating obtained in step S4 of Comparative Example 1. Detailed Implementation

[0078] To facilitate understanding of the present invention, specific embodiments are provided to further illustrate the technical solution of the present invention. Those skilled in the art should understand that the embodiments are merely illustrative of the present invention and should not be considered as specific limitations thereof.

[0079] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used herein, are intended to cover non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not limited to those elements and may also include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0080] In this invention, features specified as "first" and "second" may explicitly or implicitly include one or more of these features, used to distinguish and describe features, without any order or emphasis. In the description of this invention, unless otherwise stated, "multiple" means two or more.

[0081] In one specific embodiment, the process flow diagram of the fabrication method of the diffractive optical waveguide provided by the present invention is as follows: Figure 1 As shown in the diagram, the process structure is as follows: Figure 2A As shown, it includes the following steps: S1. Fabrication of the waveguide to be coated: A waveguide substrate is provided, and an imprinting adhesive layer is coated on one side surface of the waveguide substrate; The imprinting adhesive is imprinted and cured using a preset imprinting template to form an imprinting adhesive layer with a diffraction micro-nano structure, thereby obtaining the waveguide to be coated. The waveguide to be coated is pretreated as follows: cleaned, and then baked in a protective gas. S2. Preparation of the first chemically inert polymer layer: A chemically inert polymer coating is applied to the surface of the pretreated waveguide near the imprinted adhesive layer, and then cured to obtain a first chemically inert polymer layer. S3. Preparation of the first photoresist layer: Photoresist is coated onto the first chemically inert polymer layer and cured to obtain the first photoresist layer; S4, Exposure and Development: The first chemically inert polymer layer and the first photoresist layer are exposed using a photolithography machine; The first chemically inert polymer layer and the first photoresist layer are baked after exposure; The first chemically inert polymer layer and the first photoresist layer after baking are developed using a developing solution to remove the first chemically inert polymer layer and the first photoresist layer from the diffraction micro / nano structure of the waveguide to be coated, thereby obtaining a waveguide to be coated with a second chemically inert polymer layer and a second photoresist layer. S5. Preparation of metal film: A metal film layer is prepared on the surface of the waveguide to be coated near the second photoresist layer using a vapor deposition method; the area of ​​the metal film layer is greater than or equal to the area of ​​the region with the diffraction micro / nano structure. S6. Clean and remove the second chemically inert polymer layer, the second photoresist layer, and the metal film layer on the second photoresist layer: The second chemically inert polymer layer is removed by cleaning with a cleaning solution, thereby removing the second photoresist layer and the metal film layer on the second chemically inert polymer layer, and obtaining the diffractive waveguide.

[0082] The following will use several embodiments as examples to describe in detail the diffractive optical waveguide and its fabrication method according to the present invention, but the diffractive optical waveguide and its fabrication method according to the present invention are not limited to these embodiments.

[0083] In the following embodiments of the present invention, the imprinting adhesive, photoresist, and chemically inert polymer coating used are all commercially available chemicals.

[0084] Example 1 A diffractive optical waveguide and its fabrication method, the fabrication method specifically including the following steps: S1. Fabrication of the waveguide to be coated: A glass sheet is used as the waveguide substrate. An imprinting adhesive (a titanium-containing organic-inorganic hybrid imprinting adhesive with a refractive index of 1.85) is spin-coated onto one surface of a 4-inch glass sheet. The imprinting adhesive is imprinted using a preset imprinting template. After baking and curing at 150°C for 60 seconds, an imprinting adhesive layer with a diffraction micro-nano structure is formed, and the waveguide to be coated is obtained. The waveguide to be coated is pretreated as follows: first, it is placed in a plasma cleaner and treated in an oxygen atmosphere for 2 minutes; then, it is baked in a nitrogen atmosphere at 150°C for 60 minutes to complete the pretreatment.

[0085] S2. Preparation of the first chemically inert polymer layer: The surface of the waveguide to be coated, which has been pretreated in S1, is coated with a chemically inert polymer coating (polydimethylglutarimide, with a viscosity of 20 cp at 24°C) on the side near the imprinted adhesive layer, and then baked and cured at 110°C for 2 min to obtain a first chemically inert polymer layer with a thickness of 1 μm. S3. Preparation of the first photoresist layer: Photoresist (i-line chemical amplification negative photoresist) is coated on the first chemically inert polymer layer obtained in step S2, and then baked and cured at 110°C for 90 s to obtain a first photoresist layer with a thickness of 1.5 μm. S4, Exposure and Development: The first chemically inert polymer layer and the first photoresist layer were exposed using an i-line lithography machine at an exposure energy of 80 mJ / cm². 2 The exposed first chemically inert polymer layer and first photoresist layer are baked at 110°C for 90 seconds. The baked first chemically inert polymer layer and first photoresist layer are then developed using a developer (2.38% tetramethylammonium hydroxide aqueous solution) for 60 seconds to remove the first chemically inert polymer layer and first photoresist layer from the diffraction micro / nano structure of the waveguide to be coated, resulting in a waveguide to be coated with a second chemically inert polymer layer and a second photoresist layer. The distance between the edge of the second photoresist layer and the projection of the edge of the second chemically inert polymer layer onto the waveguide substrate is 2.5 μm. S5. Preparation of metal film: A 200 nm thick aluminum layer is deposited on the surface of the waveguide to be coated in step S4, near the second photoresist layer, using an evaporation deposition machine. S6. Clean and remove the second chemically inert polymer layer, the second photoresist layer, and the metal film layer on the second photoresist layer: The waveguide with the aluminum layer obtained in step S5 is sequentially cleaned with acetone (under ultrasonic conditions), isopropanol, and pure water to remove the second chemically inert polymer layer, and the second photoresist layer and the aluminum layer on the second chemically inert polymer layer are also removed to obtain the diffractive waveguide.

[0086] The following evaluations were made on the fabrication method and the resulting diffractive waveguide of this embodiment: (1) Observation of surface morphology The macroscopic morphology of the diffracted waveguide prepared by the method provided in this embodiment is shown in the figure below. Figure 3A Its surface shows no yellowing; moreover, after exposure and development in step S4, the second chemically inert polymer layer and the second photoresist layer form a clear undercut pattern, that is, the edge of the second chemically inert polymer layer is recessed within the edge of the second photoresist layer. After metal plating in step S4 and cleaning in step S5, the metal film layer outside the diffraction micro / nano structure region can be effectively removed, and there is no metal residue in the region outside the diffraction micro / nano structure (such as...). Figure 3A and 4A (As shown).

[0087] Furthermore, the waveguide to be coated, which has a second chemically inert polymer layer and a second photoresist layer, obtained by exposure and development in step S4, was observed using an optical microscope. The resulting optical microscope test image is shown below. Figure 5A As shown, by using a specific first chemically inert polymer layer to isolate the first photoresist layer from the imprinting resist layer, the reaction and / or penetration of the photoresist and imprinting resist are avoided, thus preventing the yellowing problem. Furthermore, by using the first chemically inert polymer layer to improve the yellowing problem, there is no need to use dyes, which avoids the problem of insufficient edge reaction during exposure, ensuring the integrity of edge lines and thus guaranteeing the integrity of the microstructure morphology of the diffractive waveguide. Simultaneously, after exposure and development, the first photoresist layer forms an inverted trapezoidal undercut. Combined with the characteristic that the first chemically inert polymer layer does not react with ultraviolet light but is only dissolved by the developer, an opening forms in the first photoresist layer after development. The developer contacts the first chemically inert polymer layer through this opening, thereby expanding the undercut morphology. This well-formed undercut structure after exposure and development of this double-layer structure completely prevents the metal on the second photoresist layer from connecting with the metal on the diffraction micro / nano structure during evaporation. The cleaning process in step S6 completely dissolves the second chemically inert polymer layer and the second photoresist layer, thereby stripping away the metal on the second photoresist layer, ensuring no metal residue remains outside the diffraction micro / nano structure (e.g., Figure 3A and 4A (As shown).

[0088] (2) Image quality analysis The waveguide sample with a metal coating obtained in step S5 of this embodiment was characterized using a scanning electron microscope (SEM). The resulting SEM image is shown below. Figure 6AAs shown, the preparation method solves the yellowing problem while ensuring that the undercut pattern formed by the second chemically inert polymer layer and the second photoresist layer is clear and complete. During metal evaporation, it can effectively block the metal from being deposited around the surface, thus effectively isolating the metal film layer on the diffractive micro / nano structure and the metal film layer on the second photoresist layer without them sticking together. The cleaning process in step S6 removes the second chemically inert polymer layer and the second photoresist layer while also removing the metal film layer on the second photoresist layer, while the effective metal film layer on the diffractive micro / nano structure is retained.

[0089] (3) Repeatability Using the preparation method provided in this embodiment, 10 diffractive waveguides were continuously prepared. The resulting products had uniform surface quality and no yellowing, demonstrating the stability and repeatability of the preparation method.

[0090] Example 2 A diffractive optical waveguide and its fabrication method are disclosed. The difference between the fabrication method and Example 1 is that the imprinting adhesive used in step S1 is an imprinting adhesive with a refractive index of 1.9, and the chemically inert polymer coating used in step S2 is polycarbonate. Other materials, process steps and parameters are the same as in Example 1.

[0091] The fabrication method and the obtained diffractive waveguide of this embodiment are evaluated. The macroscopic morphology of the diffractive waveguide prepared by the fabrication method provided in this embodiment is shown in the figure below. Figure 3B As shown, Example 2 also obtained a high-quality pattern without yellowing, and the obtained diffractive waveguide has no metal residue in the region outside the diffractive micro / nano structure.

[0092] Example 3 A diffractive optical waveguide and its fabrication method are disclosed. The fabrication method differs from that of Example 1 in that the pretreatment process parameters in step S1 are different, as follows: First, the waveguide is placed in a plasma cleaner and treated in an oxygen atmosphere for 2 minutes; then, it is baked in a nitrogen atmosphere at 120°C for 60 minutes to complete the pretreatment. Other materials, process steps, and parameters are the same as in Example 1.

[0093] Example 4 A diffractive optical waveguide and its fabrication method are disclosed. The fabrication method differs from that of Example 1 in that the pretreatment process parameters in step S1 are different, as follows: First, the waveguide is placed in a plasma cleaner and treated in an oxygen atmosphere for 2 minutes; then, it is baked at 180°C in a nitrogen atmosphere for 60 minutes to complete the pretreatment. Other materials, process steps, and parameters are the same as in Example 1.

[0094] During the pretreatment of the waveguide to be coated, baking at 120℃, 150℃, and 180℃ can effectively stabilize the surface of the imprinted adhesive layer without causing thermal degradation. Thermal degradation leads to poor adhesion of the imprinted adhesive layer, resulting in insufficient bonding between the first chemically inert polymer layer and the imprinted adhesive layer, posing a risk of detachment. Furthermore, poor adhesion of the imprinted adhesive layer also affects the bonding force between the metal film layer and the diffractive micro / nano structure. If the metal film layer is not firmly adhered, it will severely affect the performance of the diffractive waveguide. The pretreatment of this invention does not cause thermal degradation, thus avoiding the adverse effects of thermal degradation. Simultaneously, the pretreatment of the waveguide to be coated does not cause yellowing.

[0095] Example 5 A diffractive optical waveguide and its fabrication method, the fabrication method comprising the following steps: S1. Fabrication of the waveguide to be coated: A glass sheet is used as the waveguide substrate. An imprinting adhesive (a titanium-containing organic-inorganic hybrid imprinting adhesive with a refractive index of 1.85) is spin-coated onto one surface of a 4-inch glass sheet. The imprinting adhesive is imprinted using a preset imprinting template. After baking and curing at 150°C for 60 seconds, an imprinting adhesive layer with a diffraction micro-nano structure is formed, and the waveguide to be coated is obtained. The waveguide to be coated is pretreated as follows: first, it is placed in a plasma cleaner and treated in an oxygen atmosphere for 2 minutes; then, it is baked in a nitrogen atmosphere at 150°C for 60 minutes to complete the pretreatment.

[0096] S2. Preparation of the first chemically inert polymer layer: The surface of the waveguide to be coated, which has been pretreated in S1, is coated with a chemically inert polymer coating (polydimethylglutarimide, with a viscosity of 20 cp at 24°C), and then baked and cured at 90°C for 90 s to obtain a first chemically inert polymer layer with a thickness of 1 μm. S3. Preparation of the first photoresist layer: Photoresist (i-line chemical amplification negative photoresist) is coated on the first chemically inert polymer layer obtained in step S2, and then baked and cured at 90°C for 90 s to obtain a first photoresist layer with a thickness of 1.5 μm. S4, Exposure and Development: The first chemically inert polymer layer and the first photoresist layer were exposed using an i-line lithography machine at an exposure energy of 60 mJ / cm². 2The exposed first chemically inert polymer layer and first photoresist layer are baked at 90°C for 90 seconds. The baked first chemically inert polymer layer and first photoresist layer are then developed using a developer (2.38% tetramethylammonium hydroxide aqueous solution) for 75 seconds to remove the first chemically inert polymer layer and first photoresist layer from the diffraction micro / nano structure of the waveguide to be coated, resulting in a waveguide to be coated with a second chemically inert polymer layer and a second photoresist layer. The distance between the edge of the second photoresist layer and the projection of the edge of the second chemically inert polymer layer onto the waveguide substrate is 2.8 μm. S5. Preparation of metal film: A 200 nm thick aluminum layer is deposited on the surface of the waveguide to be coated in step S4, near the second photoresist layer, using an evaporation deposition machine. S6. Clean and remove the second chemically inert polymer layer, the second photoresist layer, and the metal film layer on the second photoresist layer: The waveguide with the aluminum layer obtained in step S5 is sequentially cleaned with acetone (under ultrasonic conditions), isopropanol, and pure water to remove the second chemically inert polymer layer, and the second photoresist layer and the aluminum layer on the second chemically inert polymer layer are also removed to obtain the diffractive waveguide.

[0097] The fabrication method and the obtained diffractive waveguide of this embodiment are evaluated. The macroscopic morphology of the diffractive waveguide prepared by the fabrication method provided in this embodiment is shown in the figure below. Figure 3C As shown, Example 5 also obtained a high-quality pattern without yellowing issues, and in the obtained diffractive waveguide, there are no metal residues in the region outside the diffractive micro / nano structure.

[0098] Example 6 A diffractive optical waveguide and its fabrication method are disclosed. The difference between the fabrication method described in this method and that of Example 5 is that step S2 uses a chemically inert polymer coating with a viscosity of 35 cp at 24±1℃. Other materials, process steps, and parameters are the same as in Example 5.

[0099] The fabrication method and the obtained diffractive waveguide of this embodiment are evaluated. The macroscopic morphology of the diffractive waveguide prepared by the fabrication method provided in this embodiment is shown in the figure below. Figure 3DAs shown, the viscosity of the chemically inert polymer coating at 24±1℃ is 35 cp, exhibiting good fluidity. This results in more uniform spin-coating, forming a smooth and even first chemically inert polymer layer. This facilitates photoresist spin-coating and the formation of a uniform first photoresist layer, thus avoiding defects in the first chemically inert polymer layer and the first photoresist layer that could lead to poor development and metal film residue. Furthermore, this viscosity of the chemically inert polymer coating reduces the intermolecular adhesion of the chemically inert polymer, making the first chemically inert polymer layer easily dissolve by the developer during the development stage. This results in good undercut patterns at the edges of the second photoresist layer and the second chemically inert polymer layer, allowing for a larger process window in the metal film deposition process.

[0100] Example 7 A diffractive optical waveguide and its fabrication method, the fabrication method comprising the following steps: S1. Fabrication of the waveguide to be coated: A glass sheet is used as the waveguide substrate. An imprinting adhesive (a titanium-containing organic-inorganic hybrid imprinting adhesive with a refractive index of 1.85) is spin-coated onto one surface of a 4-inch glass sheet. The imprinting adhesive is imprinted using a preset imprinting template. After baking and curing at 150°C for 60 seconds, an imprinting adhesive layer with a diffraction micro-nano structure is formed, and the waveguide to be coated is obtained. The waveguide to be coated is pretreated as follows: first, it is placed in a plasma cleaner and treated in an oxygen atmosphere for 2 minutes; then, it is baked in a nitrogen atmosphere at 150°C for 60 minutes to complete the pretreatment.

[0101] S2. Preparation of the first chemically inert polymer layer: The surface of the waveguide to be coated, which has been pretreated in S1, is coated with a chemically inert polymer coating (polydimethylglutarimide, with a viscosity of 20 cp at 24°C) on the side near the imprinted adhesive layer, and then baked and cured at 110°C for 2 min to obtain a first chemically inert polymer layer with a thickness of 1 μm. S3. Preparation of the first photoresist layer: Photoresist (i-line chemical amplification negative photoresist) is coated on the first chemically inert polymer layer obtained in step S2, and then baked and cured at 110°C for 90 s to obtain a first photoresist layer with a thickness of 1.2 μm. S4, Exposure and Development: The first chemically inert polymer layer and the first photoresist layer were exposed using an i-line lithography machine at an exposure energy of 80 mJ / cm². 2The exposed first chemically inert polymer layer and first photoresist layer are baked at 110°C for 90 seconds. The baked first chemically inert polymer layer and first photoresist layer are developed using a developer (2.38% tetramethylammonium hydroxide aqueous solution) for 120 seconds to remove the first chemically inert polymer layer and first photoresist layer from the diffraction micro / nano structure of the waveguide to be coated, resulting in a waveguide to be coated with a second chemically inert polymer layer and a second photoresist layer. S5. Preparation of metal film: A 200 nm thick aluminum layer is deposited on the surface of the waveguide to be coated in step S4, near the second photoresist layer, using an evaporation deposition machine. S6. Clean and remove the second chemically inert polymer layer, the second photoresist layer, and the metal film layer on the second photoresist layer: The waveguide with the aluminum layer obtained in step S5 is sequentially cleaned with acetone (under ultrasonic conditions), isopropanol, and pure water to remove the second chemically inert polymer layer, and the second photoresist layer and the aluminum layer on the second chemically inert polymer layer are also removed to obtain the diffractive waveguide.

[0102] The fabrication method and the obtained diffractive waveguide of this embodiment are evaluated. The microstructure of the diffractive waveguide prepared by the fabrication method provided in this embodiment is shown in the figure below. Figure 4B As shown, there is no yellowing phenomenon in the waveguide to be coated with the second chemically inert polymer layer and the second photoresist layer obtained by exposure and development; however, due to the long development time, the undercut of the second chemically inert polymer layer and the second photoresist layer becomes larger, and the edge of the second photoresist layer collapses due to lack of support, causing the metal film layer on the subsequently prepared diffractive micro / nano structure to adhere to the metal film layer on the second photoresist layer. It is difficult to remove the metal film layer on the second photoresist layer, and there is a problem of metal residue in the area outside the diffractive micro / nano structure.

[0103] Example 8 A diffractive optical waveguide and its fabrication method are disclosed. The fabrication method differs from that of Example 7 in that step S3 forms a 2 μm first photoresist layer, and step S4 has a development time of 100 s. Other materials, process steps, and parameters are the same as in Example 7.

[0104] The fabrication method and the resulting diffractive waveguide of this embodiment were evaluated. In the fabrication method provided in this embodiment, there was no yellowing phenomenon in the waveguide to be coated with the second chemically inert polymer layer and the second photoresist layer obtained by exposure and development. However, due to the excessive thickness of the first photoresist layer, the second chemically inert polymer layer could not bear the weight of the second photoresist layer and collapsed. After the collapse, the second photoresist layer and the imprinted resist layer were connected. The subsequently set metal film layer was located on the surface of the second photoresist layer and the imprinted resist layer, and could not form an effective gap, resulting in cleaning difficulties and making it difficult to peel off the metal film layer on the second photoresist layer.

[0105] Comparative Example 1 A diffractive optical waveguide and its fabrication method are disclosed, the process flow diagram of which is shown below. Figure 2B As shown, it includes the following steps: S1. Fabrication of the waveguide to be coated: A glass sheet is used as the waveguide substrate. An imprinting adhesive (a titanium-containing organic-inorganic hybrid imprinting adhesive with a refractive index of 1.85) is spin-coated onto one surface of a 4-inch glass sheet. The imprinting adhesive is imprinted using a preset imprinting template. After baking and curing at 150°C for 60 seconds, an imprinting adhesive layer with a diffraction micro-nano structure is formed, and the waveguide to be coated is obtained. The waveguide to be coated is pretreated as follows: first, it is placed in a plasma cleaner and treated in an oxygen atmosphere for 2 minutes; then, it is baked in a nitrogen atmosphere at 150°C for 60 minutes to complete the pretreatment.

[0106] S2. Preparation of the first photoresist layer: In step S1, the surface of the waveguide to be coated, which has undergone pretreatment, is coated with photoresist (i-line chemical amplification type negative photoresist) on the side near the imprinted adhesive layer, and then baked and cured at 110°C for 90 s to obtain a first photoresist layer with a thickness of 1.5 μm. S3, Exposure and Development: The first photoresist layer was exposed using an i-line lithography machine at an exposure energy of 80 mJ / cm². 2 The first photoresist layer after exposure is baked at 110°C for 90 seconds; the first photoresist layer after baking is developed using a developer (2.38% tetramethylammonium hydroxide aqueous solution) for 60 seconds to remove the first photoresist layer on the diffraction micro / nano structure of the waveguide to be coated, thereby obtaining the waveguide to be coated with a second photoresist layer. S4. Preparation of metal film: A 200 nm thick aluminum layer is deposited on the surface of the waveguide to be coated in step S3, near the second photoresist layer, using an evaporation deposition machine. S5. Clean and remove the second photoresist layer and the metal film layer on the second photoresist layer: The waveguide with the aluminum layer obtained in step S4 is sequentially cleaned with acetone (under ultrasonic conditions), isopropanol, and pure water to remove the second photoresist layer, thereby removing the aluminum layer on the second photoresist layer and obtaining the diffractive waveguide.

[0107] The fabrication method and the resulting diffractive waveguide of this comparative example were evaluated. The macroscopic morphology of the diffractive waveguide prepared in Comparative Example 1 is shown in the figure below. Figure 3E As shown, its surface exhibits obvious luminescence problems; moreover, due to the swirling deposition problem in the evaporated metal, the cleaning process in step S5 cannot effectively remove the metal film layer outside the diffraction micro / nano structure region, resulting in metal residue problems, such as... Figure 4C As shown.

[0108] The optical microscope image of the waveguide to be coated with the second photoresist layer obtained by exposure and development in step S3 of Comparative Example 1 is shown below. Figure 5B As shown, after exposure and development using traditional single-layer photoresist, the edge lines of the pattern appear incomplete and jagged. This is because, in order to solve the yellowing problem, photoresist raw material manufacturers will change the composition of the photoresist (such as dyes). Although this may improve the yellowing problem (or it may not), the addition of dyes will change the proportion of the main components of the photoresist (such as resin). With fixed exposure parameters and photoresist whose proportion has changed, there will inevitably be negative effects such as incomplete reaction. As a result, the parts that should have reacted at the edges did not react sufficiently, forming incomplete jagged edges, which ultimately affects the morphology of the diffractive waveguide microstructure. Furthermore, this dye also affects the reaction between the photoresist and ultraviolet light, resulting in insufficient reaction between the photoacid and the photoresist after exposure. This causes the bottom edge of the second photoresist layer to not be recessed within the top edge, meaning the second photoresist layer does not form an inverted trapezoidal morphology. Consequently, during subsequent metal deposition, the metal layer on the second photoresist layer directly connects to the metal layer on the diffraction micro / nano structure, forming a single piece. This results in the cleaning process in step S5 being unable to completely remove the metal outside the diffraction micro / nano structure region, leaving metal residue. Figure 4C As shown.

[0109] The scanning electron microscope (SEM) image of the waveguide sample with a metal coating obtained in step S4 of Comparative Example 1 is shown below. Figure 6B As shown, since the traditional single-layer photoresist layer cannot form a good undercut after exposure and development, that is, the second photoresist layer does not have an inverted trapezoidal morphology, after the entire surface is coated with a metal film, the metal film on the second photoresist layer will adhere to the metal film on the diffraction micro-nano structure. As a result, the cleaning process in step S5 can only remove the second photoresist layer, while the metal at the corner cannot be torn off and removed, resulting in metal residue in the area outside the diffraction micro-nano structure region.

[0110] Comparing Example 1 and Comparative Example 1, it can be seen that the preparation method provided by the present invention can effectively solve the problem of surface yellowing caused by photolithography in the waveguide to be coated by nanoimprinting. Moreover, in the formed diffractive waveguide, there is no metal residue in the area outside the diffractive micro-nano structure, which ensures the pattern quality and process stability.

[0111] The present invention has been illustrated through the above embodiments, but the present invention is not limited to the above process steps, that is, it does not mean that the present invention must rely on the above process steps to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions of the raw materials used in the present invention, additions of auxiliary components, and selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for fabricating a diffractive optical waveguide, characterized in that, The preparation method includes: Fabrication of a waveguide to be coated; wherein the waveguide to be coated includes a waveguide substrate and an imprinted adhesive layer having a diffraction micro / nano structure disposed on the waveguide substrate; A first chemically inert polymer layer and a first photoresist layer are sequentially formed on the surface of the waveguide to be coated near the imprinted adhesive layer. The waveguide to be coated, having a first chemically inert polymer layer and a first photoresist layer, is exposed and developed to remove the first chemically inert polymer layer and the first photoresist layer from the diffraction micro / nano structure of the waveguide to be coated, thereby obtaining a waveguide to be coated having a second chemically inert polymer layer and a second photoresist layer. A metal film is formed on the surface of the waveguide to be coated, near the second photoresist layer. Then, the second chemically inert polymer layer, the second photoresist layer, and the metal film on the second photoresist layer are removed by cleaning to obtain the diffractive waveguide.

2. The preparation method according to claim 1, characterized in that, The steps for preparing the waveguide to be coated include: A waveguide substrate is provided, and an imprinting adhesive layer is coated on one side surface of the waveguide substrate; The imprinting adhesive is imprinted using a preset imprinting template, and then cured for the first time to form an imprinting adhesive layer with a diffraction micro-nano structure. Preferably, the refractive index of the imprinting adhesive is 1.80-2.20; Preferably, the first curing temperature is 120℃-180℃, and the time is 30 s-120 s; Preferably, before the step of sequentially forming a first chemically inert polymer layer and a first photoresist layer on the surface of the waveguide to be coated near the imprinted adhesive layer, the method further includes pre-treatment of the waveguide to be coated, the pre-treatment including cleaning and baking; Preferably, the cleaning time is 1 min to 5 min; Preferably, the baking is carried out in a protective gas; Preferably, the baking temperature is 120℃-180℃ and the baking time is 30 min-120 min.

3. The preparation method according to claim 1, characterized in that, The step of forming a first chemically inert polymer layer on the surface of the waveguide to be coated near the imprinted adhesive layer includes: Provide chemically inert polymer coatings; The chemically inert polymer coating is applied to the surface of the waveguide to be coated near the imprinted adhesive layer, and then cured a second time to obtain the first chemically inert polymer layer. Preferably, the chemically inert polymer coating comprises any one or a combination of at least two of polydimethylglutarimide, polymethyl methacrylate, polycarbonate, polystyrene, and polyimide; Preferably, the chemically inert polymer coating has a viscosity of 10 cp-50 cp at 24±1℃; Preferably, the second curing temperature is 90℃-120℃, and the time is 60 s-120 s; Preferably, the thickness of the first chemically inert polymer layer is 1 μm-2 μm.

4. The preparation method according to claim 1, characterized in that, The thickness ratio of the first photoresist layer to the first chemically inert polymer layer is (1-1.5):1; Preferably, the first photoresist layer is a negative photoresist layer; Preferably, the step of sequentially forming a first chemically inert polymer layer and a first photoresist layer on the surface of the waveguide to be coated near the imprinted adhesive layer includes: Photoresist is coated onto the first chemically inert polymer layer, and then cured in a third step to obtain the first photoresist layer; Preferably, the photoresist includes a chemically amplified photoresist; Preferably, the photosensitive wavelength of the photoresist is selected from any one of g-line, h-line, i-line, KrF, or ArF; Preferably, the third curing temperature is 90℃-120℃ and the time is 60 s-120 s.

5. The preparation method according to claim 1, characterized in that, The projection of the second photoresist layer onto the waveguide substrate covers the projection of the second chemically inert polymer layer onto the waveguide substrate.

6. The preparation method according to claim 5, characterized in that, The distance between the edge of the second photoresist layer and the projection of the edge of the second chemically inert polymer layer onto the waveguide substrate is 1 μm-4 μm.

7. The preparation method according to claim 6, characterized in that, The step of exposing and developing the waveguide to be coated with a first chemically inert polymer layer and a first photoresist layer to remove the first chemically inert polymer layer and the first photoresist layer from the diffraction micro / nano structure of the waveguide to be coated, to obtain a waveguide to be coated with a second chemically inert polymer layer and a second photoresist layer, includes: Using an exposure energy of 60 mJ / cm 2 -100 mJ / cm 2 The lithography machine exposes the first chemically inert polymer layer and the first photoresist layer; The first chemically inert polymer layer and the first photoresist layer after exposure are baked at a temperature of 90℃-120℃ for 60 s-120 s. The first chemically inert polymer layer and the first photoresist layer after baking are developed using a developing solution for 30 s-100 s to remove the first chemically inert polymer layer and the first photoresist layer on the diffraction micro / nano structure of the waveguide to be coated. The distance between the edge of the second photoresist layer and the projection of the edge of the second chemically inert polymer layer on the waveguide substrate is 1 μm-4 μm.

8. The preparation method according to claim 1, characterized in that, The material of the metal film layer includes any one or a combination of at least two of chromium, aluminum, titanium, platinum, and gold; Preferably, the thickness of the metal film is 100 nm-300 nm; Preferably, the step of forming a metal film on the side surface of the waveguide to be coated near the second photoresist layer includes: forming a metal film on the side surface of the waveguide to be coated near the second photoresist layer using a vapor deposition method; Preferably, the step of cleaning to remove the second chemically inert polymer layer, the second photoresist layer, and the metal film layer on the second photoresist layer includes: The second chemically inert polymer layer is removed by cleaning with a cleaning solution, thereby removing the second photoresist layer and metal film layer on the second chemically inert polymer layer; Preferably, the cleaning fluid includes N 1-Methylpyrrolidone, acetone, ethanol, isopropanol, or any one or a combination of at least two of them.

9. A diffractive optical waveguide, characterized in that, The diffractive waveguide is prepared by the preparation method described in any one of claims 1-8.

10. A display device, characterized in that, The display device includes the diffractive waveguide as described in claim 9.

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