Method for preparing optical lens micro-nano structure photonic crystal anti-reflection surface by electron beam lithography

Abstract

The application relates to the technical field of micro-nano optical manufacturing, and discloses an electron beam lithography preparation method for an optical lens micro-nano structure photonic crystal anti-reflection surface, which comprises the following steps: S1, preparing a composite photoresist containing HSQ, a functional additive C60, a catalytic additive TEA, a main solvent and a gradient-induced cosolvent; S2, cleaning an optical lens substrate; S3, spin coating the photoresist and pre-baking, and utilizing the difference in the volatilization rate of the mixed solvents to make C60 enriched on the surface of the film layer; S4, under the condition that no conductive layer is coated, performing electron beam exposure on the film layer, at this time, C60 dissipates electric charges, and TEA cooperatively catalyzes HSQ crosslinking; S5, developing and removing unexposed areas; and S6, high-temperature baking the developed pattern to form a photonic crystal anti-reflection structure. The application solves the problem of electric charge accumulation on an insulating substrate, does not need a conductive layer, simultaneously improves exposure sensitivity, simplifies the process, and realizes the preparation of a high-fidelity micro-nano structure.

Description

Technical Field

[0001] This invention relates to the field of micro-nano optical manufacturing technology, specifically to a method for preparing anti-reflective surfaces of micro-nano structure photonic crystals for optical lenses using electron beam lithography. Background Technology

[0002] In high-performance optical systems, reflections from the surface of optical lenses lead to light energy loss and stray light interference. By fabricating subwavelength periodic micro / nano structures on the lens surface, highly efficient broadband anti-reflection capabilities can be achieved. Electron beam lithography, with its nanoscale resolution, is the core technique for fabricating such precision optical micro / nano structures.

[0003] However, electron beam lithography faces significant technical challenges when used to fabricate electrically insulating substrates such as optical lenses. Because both the substrate and the photoresist material are electrically insulators, electrons injected during electron beam exposure cannot be promptly conducted away, accumulating rapidly on the exposed surface and forming a significant negative electric field. This charge accumulation effect causes deflection of subsequent incident electron beams, resulting in severe distortions in the exposed pattern, such as positional drift, pattern stretching, and periodic damage, making the fabrication of high-fidelity photonic crystal arrays extremely difficult.

[0004] Currently, the conventional solution is to coat an additional conductive layer on the surface of the photoresist film to dissipate the charge. However, this approach significantly increases the complexity of the process, requiring an additional conductive layer coating step before exposure and a conductive layer removal step after exposure and before development. This not only prolongs the processing cycle but also easily introduces contamination or damages the underlying photoresist pattern.

[0005] Furthermore, while using HSQ negative photoresist, which can be directly thermally converted into a silicon dioxide structure to simplify subsequent etching processes, the low exposure sensitivity of HSQ itself is also a limiting factor. It requires a high electron beam exposure dose to achieve sufficient cross-linking, which not only significantly reduces the processing efficiency of EBL, but also exacerbates the proximity effect, which is also detrimental to the realization of high-density, high-fidelity micro / nano structures. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides an electron beam lithography method for fabricating anti-reflective surfaces of micro / nano-structured photonic crystals for optical lenses. This method solves the problem of severe pattern distortion caused by charge accumulation on insulating substrates such as fused silica in electron beam lithography, as well as the problems of low exposure sensitivity, high required exposure dose, and low processing efficiency of traditional HSQ photoresists.

[0007] To achieve the above objectives, the present invention provides the following technical solution: a method for fabricating anti-reflective surfaces of micro / nano-structured photonic crystals for optical lenses using electron beam lithography, comprising the following steps: S1. Prepare a functionally graded composite photoresist, wherein the composite photoresist comprises a matrix resin, functional additives, catalytic additives, and a mixed solvent system, wherein the mixed solvent system consists of a main solvent and a gradient-inducing co-solvent; S2. Pre-treat the optical lens substrate to remove organic and inorganic contaminants from the substrate surface; S3. Spin-coat the composite photoresist prepared in S1 onto the pretreated substrate surface. Utilize the gradient-induced difference in evaporation rates between the co-solvent and the main solvent to drive the functional additives to form a negative concentration gradient in the vertical direction in the photoresist film. Then, pre-bake the film to remove residual solvent and cure it. S4. No additional conductive layer needs to be coated on the surface of the photoresist film. Electron beam lithography system is used to expose the photonic crystal pattern with electron beam. During the exposure process, functional additives achieve anti-charge accumulation and anti-proximity effect, and promote the cross-linking of the matrix resin in situ with the assistance of catalytic additives. S5. The exposed substrate is developed with a developer to remove the insufficiently exposed photoresist areas. After cleaning and drying, a photonic crystal pattern array is obtained. S6. The substrate with the photonic crystal pattern array is post-calcined and cured to further cross-link and transform the matrix resin, forming a SiO2-based photonic crystal anti-reflection micro / nano structure with embedded functional additives on the surface of the optical lens.

[0008] Preferably, the matrix resin is a hydrogen silsesquioxane.

[0009] Preferably, the functional additive is Buckminster fullerene.

[0010] Preferably, the catalytic additive is a weak base, specifically triethylamine.

[0011] Preferably, in the mixed solvent system, the main solvent is methyl isobutyl ketone or anisole, and the gradient-induced co-solvent is chloroform or toluene.

[0012] Preferably, in step S1, the preparation of the composite photoresist is carried out in a glove box or clean room, and the matrix resin, functional additives, and catalytic additives are completely dissolved in the mixed solvent system by stirring or ultrasonic treatment.

[0013] Preferably, in step S2, the substrate pretreatment involves immersion in Piranha solution, rinsing with deionized water, and drying with nitrogen. Alternatively, the substrate may be subjected to oxygen plasma treatment or coated with HMDS to enhance the adhesion between the photoresist and the substrate.

[0014] Preferably, in step S2, the optical lens substrate is fused silica or high-refractive-index optical glass.

[0015] Preferably, in step S4, the energy of the electron beam used in electron beam lithography is 50-100 keV.

[0016] Preferably, in step S5, the developing solution is a 2.38% TMAH aqueous solution, and the developing method is immersion developing.

[0017] This invention provides a method for fabricating anti-reflective surfaces of micro / nano-structured photonic crystals for optical lenses using electron beam lithography. It offers the following advantages: 1. This invention utilizes a composite functional additive (Bakerminster fullerene C) in a hydrogen silsesquioxane (HSQ) matrix resin. 60 By utilizing the difference in evaporation rates between the main solvent and the gradient-induced co-solvent, spontaneous enrichment of functional additives on the surface of the photoresist film was achieved in the spin-coating step (S3). 60 Its high electron affinity and π-electron conjugation system enable the film surface to dissipate charges in situ, effectively suppressing the charge accumulation effect of electron beam lithography (S4) on insulating substrates such as fused silica, avoiding the resulting pattern distortion, and eliminating the need for additional coating and removal of commercial conductive layers, thus simplifying the process.

[0018] 2. This invention introduces a catalytic additive (triethylamine TEA) into the photoresist composition. This additive, along with functional additive C... 60 It plays a synergistic catalytic role in electron beam lithography (S4). As a weakly basic catalyst, TEA significantly reduces C4. 60 The HSQ crosslinking reaction barrier significantly improves the exposure sensitivity of the photoresist. This effect enables the present invention to complete patterning with a lower electron beam exposure dose, effectively shortening the processing time, while suppressing the adverse effects of the proximity effect on pattern fidelity under high dose.

[0019] 3. Through the synergistic effect of the above-mentioned functional additives, catalytic additives and gradient induction mechanism, this invention ensures the high fidelity of electron beam lithography patterns on insulating substrates. Combined with the final post-calcination step (S6), the prepared SiO2-based composite micro / nano structures (such as photonic crystal arrays) have highly periodic, uniform and regular morphology, thereby achieving excellent broadband anti-reflection performance on the surface of optical lenses and effectively reducing the surface reflection loss of optical devices. Attached Figure Description

[0020] Figure 1 This is a flowchart of the method of the present invention. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0022] Please see the appendix Figure 1 This invention provides a method for fabricating antireflective surfaces of micro / nano-structured photonic crystals for optical lenses using electron beam lithography, specifically including: I. Preparation Example Preparation Example 1: Composite Photoresist Stock Solution R-1 (1) In a Class 100 cleanroom, weigh 3.0 g of hydrogen silsesquioxane (HSQ) solid powder, dissolve it in 80 mL of methyl isobutyl ketone (MIBK) main solvent, and stir with a magnetic stirrer until HSQ is completely dissolved to obtain solution A.

[0023] (2) Weigh 0.015g of Buckminster fullerene (C 60 Dissolve the powder (this amount is 0.5% of the HSQ solid mass) in 20 mL of chloroform (gradient-induced co-solvent), and use ultrasonic oscillation to completely dissolve it to obtain solution B.

[0024] (3) Slowly add solution B to solution A. Then, add 0.003 g of triethylamine (TEA) (this amount is 0.1% of the mass of HSQ solid) to the mixed solution.

[0025] (4) Stir the mixed solution obtained in S3 magnetically at room temperature in the dark for 6 hours to fully homogenize it.

[0026] (5) The homogenized solution was filtered using a 0.2μm-0.2μm polytetrafluoroethylene (PTFE) needle filter to remove potential aggregates and particles, thus obtaining composite photoresist stock solution R-1.

[0027] Preparation Example 2: Composite Photoresist Stock Solution R-2 (1) In a Class 100 cleanroom, weigh 3.0 g of hydrogen silsesquioxane (HSQ) solid powder, dissolve it in 80 mL of methyl isobutyl ketone (MIBK) main solvent, stir to dissolve, and obtain solution A.

[0028] (2) Weigh 0.090g of Buckminster fullerene (C 60 Powder (this amount is 3.0% of the HSQ solid mass) was dissolved in 20 mL of chloroform (gradient-induced co-solvent) and sonicated to obtain solution B.

[0029] (3) Slowly add solution B to solution A. Then, add 0.003 g of triethylamine (TEA) (this amount is 0.1% of the mass of HSQ solid) to the mixed solution.

[0030] (4) The subsequent homogenization and filtration steps are the same as in Preparation Example 1, thus obtaining composite photoresist stock solution R-2.

[0031] Preparation Example 3: Composite Photoresist Stock Solution R-3 (1) In a Class 100 cleanroom, weigh 3.0 g of hydrogen silsesquioxane (HSQ) solid powder, dissolve it in 80 mL of methyl isobutyl ketone (MIBK) main solvent, stir to dissolve, and obtain solution A.

[0032] (2) Weigh 0.015g of Buckminster fullerene (C 60 Dissolve the powder (this amount is 0.5% of the HSQ solid mass) in 20 mL of chloroform (gradient-induced co-solvent), and sonicate to obtain solution B.

[0033] (3) Slowly add solution B to solution A. Then, add 0.015 g of triethylamine (TEA) to the mixed solution (this amount is 0.5% of the mass of HSQ solid).

[0034] (4) The subsequent homogenization and filtration steps are the same as in Preparation Example 1, thus obtaining composite photoresist stock solution R-3.

[0035] Preparation Example 4: Composite Photoresist Stock Solution R-4 (1) In a Class 100 cleanroom, weigh 4.0 g of hydrogen silsesquioxane (HSQ) solid powder, dissolve it in 90 mL of anisole (main solvent), stir to dissolve, and obtain solution A.

[0036] (2) Weigh 0.060g of Buckminster fullerene (C 60 Dissolve the powder (this amount is 1.5% of the HSQ solid mass) in 10 mL of toluene (gradient-induced co-solvent), and sonicate to obtain solution B.

[0037] (3) Slowly add solution B to solution A. Then, add 0.010 g of triethylamine (TEA) to the mixed solution (this amount is 0.25% of the mass of HSQ solid).

[0038] (4) The subsequent homogenization and filtration steps are the same as in Preparation Example 1, thus obtaining composite photoresist stock solution R-4.

[0039] Preparation Example 5: Control photoresist stock solution R-C1 (simulating existing technology) In a Class 100 cleanroom, 3.0 g of silsesquioxane (HSQ) solid powder was weighed and dissolved in 100 mL of methyl isobutyl ketone (MIBK). Subsequent homogenization and filtration steps were the same as in Preparation Example 1. This preparation example does not contain C. 60 It contains no TEA and no gradient-induced co-solvent.

[0040] Preparation Example 6: Control photoresist stock solution R-C2 (lacking functional additive C) 60 ) In a Class 100 cleanroom, the procedures S1, S3, S4, and S5 of Preparation Example 1 were followed, but C was not added in step (3). 60 (That is, S2 is omitted, the amount of MIBK used in S1 is 80 mL, and 20 mL of chloroform is added separately). This prepares a product free of C. 60 However, it contains photoresist stock solution R-C2 containing HSQ, TEA and MIBK / chloroform mixed solvents.

[0041] Preparation Example 7: Control photoresist stock solution R-C3 (lacking catalyst additive TEA) In a Class 100 cleanroom, the procedure of Preparation Example 1 was followed, but triethylamine (TEA) was not added in step S3. This resulted in a product that did not contain TEA but contained HSQ and C. 60 Photoresist stock solution R-C3 with MIBK / chloroform mixed solvent.

[0042] Preparation Example 8: Control photoresist stock solution R-C4 (deletion gradient induced mechanism) In a Class 100 cleanroom, weigh out 3.0g of HSQ powder and 0.015g of C. 60 Powder and 0.003 g TEA. Dissolve all the above components together in 100 mL of methyl isobutyl ketone (MIBK) (excluding gradient-inducing co-solvents chloroform or toluene). Subsequent homogenization and filtration steps are the same as in Preparation Example 1, to obtain photoresist stock solution R-C4.

[0043] II. Implementation Examples Example 1: This embodiment provides a method for fabricating anti-reflection surfaces of micro / nano-structured photonic crystals for optical lenses using electron beam lithography, including the following steps: (1) Take the composite photoresist stock solution R-1 prepared in Preparation Example 1 for later use.

[0044] (2) S2: Take a 4-inch fused silica wafer (optical lens substrate), immerse it in a Piranha solution of H2SO4:H2O2 (volume ratio 3:1), heat and clean it at 120°C for 20 minutes; then rinse it with deionized water for 5 minutes, and finally dry it with high-purity nitrogen.

[0045] (3) S3: Place the substrate treated in S2 on a spin coater, add photoresist stock solution R-1, and set the spin coating program as follows: 500 rpm for 10 seconds (spreading), followed by 3000 rpm for 60 seconds (spin coating); immediately after spin coating, transfer the substrate to a hot plate at 90°C for 3 minutes to form a photoresist film layer.

[0046] (4) S4: The substrate with the film is fed into the electron beam lithography system without coating an additional conductive layer on the surface of the film. The accelerating voltage is set to 80keV and the beam current is 1nA. Exposure is performed according to the preset photonic crystal pattern (e.g., a periodic nanopillar array) with an exposure dose of 2000μC / cm.

[0047] (5) S5: After exposure, immerse the substrate in a 2.38% (w / w) TMAH aqueous solution for 60 seconds (development temperature 22℃); immediately after development, rinse with deionized water for 60 seconds to terminate development, and then dry with high-purity nitrogen to obtain a photonic crystal pattern array.

[0048] (6) S6: Place the substrate with the patterned array in a tube furnace, heat it to 600°C at a rate of 10°C / min under a nitrogen atmosphere (flow rate 1.0L / min), and hold it at that temperature for 60 minutes; then allow it to cool naturally to room temperature to obtain the final photonic crystal anti-reflection micro / nano structure.

[0049] Example 2: This embodiment provides a method for fabricating anti-reflection surfaces of micro / nano-structured photonic crystals for optical lenses using electron beam lithography, including the following steps: (1) Take the composite photoresist stock solution R-2 prepared in Preparation Example 2 for later use.

[0050] (2) S2: Take N-BK7 high refractive index optical glass (optical lens substrate) and perform Piranha cleaning according to step (2) of Example 1; after cleaning and drying, perform additional oxygen plasma treatment (power 80W, treatment for 30 seconds) to enhance adhesion.

[0051] (3) S3: Place the substrate treated in S2 on a spin coater, add photoresist solution R-2, and set the spin coating program to 2000 rpm for 45 seconds; immediately after spin coating, transfer the substrate to a hot plate at 80°C and preheat for 5 minutes.

[0052] (4) S4: The substrate with the film layer is fed into the electron beam lithography system without coating an additional conductive layer on the surface of the film layer. The accelerating voltage is set to 50keV, the beam current is 500pA, and the exposure is performed according to the preset pattern with an exposure dose of 1800μC / cm.

[0053] (5) S5: After exposure, immerse the substrate in a 2.38% (w / w) TMAH aqueous solution for 30 seconds (development temperature 20°C); the subsequent rinsing and drying steps are the same as in Example 1.

[0054] (6) S6: Place the substrate with the patterned array in a rapid thermal annealing furnace (RTA), heat it to 400°C in a nitrogen atmosphere, and hold it for 30 minutes; then cool it to room temperature.

[0055] Example 3: This embodiment provides a method for fabricating anti-reflection surfaces of micro / nano-structured photonic crystals for optical lenses using electron beam lithography, including the following steps: (1) Take the composite photoresist stock solution R-3 prepared in Preparation Example 3 for later use.

[0056] (2) S2: Take a 4-inch fused silica wafer and perform Piranha cleaning and drying according to S2 of Example 1.

[0057] (3) S3: Place the substrate treated in S2 on a spin coater, add photoresist solution R-3, and set the spin coating program to 4000 rpm for 60 seconds; immediately after spin coating, transfer the substrate to a hot plate at 110°C and preheat for 2 minutes.

[0058] (4) S4: The substrate with the film layer is fed into the electron beam lithography system without coating an additional conductive layer on the surface of the film layer. The accelerating voltage is set to 100keV, the beam current is 2nA, and the exposure is performed according to the preset pattern with an exposure dose of 1500μC / cm.

[0059] (5) S5: After exposure, immerse the substrate in a 2.38% (w / w) TMAH aqueous solution for 90 seconds (development temperature 25°C); the subsequent rinsing and drying steps are the same as in Example 1.

[0060] (6) S6: Place the substrate with the patterned array in a tube furnace, heat it to 750°C at a rate of 15°C / min under an argon atmosphere (flow rate 1.0L / min), and hold it at that temperature for 45 minutes; then allow it to cool naturally to room temperature.

[0061] Example 4: This embodiment provides a method for fabricating anti-reflection surfaces of micro / nano-structured photonic crystals for optical lenses using electron beam lithography, including the following steps: (1) Take the composite photoresist stock solution R-4 prepared in Preparation Example 4 for later use.

[0062] (2) S2: Take a 4-inch fused silica wafer, perform Piranha cleaning and drying according to S2 of Example 1; after drying, place the substrate in an HMDS coating oven and perform vapor deposition at 150°C for 20 minutes to enhance adhesion.

[0063] (3) S3: Place the substrate treated in S2 on a spin coater, add photoresist stock solution R-4, and set the spin coating program to 5000 rpm for 60 seconds; immediately after spin coating, transfer the substrate to a hot plate at 100°C and preheat for 3 minutes.

[0064] (4) S4: The substrate with the film layer is fed into the electron beam lithography system without coating an additional conductive layer on the surface of the film layer. The accelerating voltage is set to 100keV, the beam current is 1.5nA, and the substrate is exposed according to the preset pattern with an exposure dose of 1600μC / cm.

[0065] (5) S5: After exposure, immerse the substrate in a 2.38% (w / w) TMAH aqueous solution for 120 seconds (development temperature 22°C); the subsequent rinsing and drying steps are the same as in Example 1.

[0066] (6) S6: Place the substrate with the patterned array in a tube furnace, heat it to 900°C at a rate of 5°C / min under a nitrogen atmosphere, and hold it at that temperature for 60 minutes; then let it cool naturally to room temperature.

[0067] III. Comparative Example Comparative Example 1: The difference compared to Example 1 is as follows: (1) In S1, the control photoresist stock solution R-C1 (containing only HSQ and MIBK) prepared in Preparation Example 5 was used. (2) In S4, before electron beam exposure, an additional commercial conductive layer (e.g., Espacer300Z) must be spin-coated on the surface of the photoresist film. (3) After exposure in S4 and before development in S5, add a step of rinsing with deionized water for 60 seconds to remove the conductive layer. All other steps are the same.

[0068] Comparative Example 2: The difference compared to Example 1 is as follows: (1) In S1, the control photoresist stock solution R-C2 (lacking functional additive C) prepared in Preparation Example 6 was used. 60 ); (2) In S4, due to the missing C 60 To achieve its anti-charge accumulation function, an additional commercial conductive layer must be spin-coated before electron beam exposure. (3) After exposure in S4 and before development in S5, add a step of rinsing with deionized water for 60 seconds to remove the conductive layer. All other steps are the same.

[0069] Comparative Example 3: The difference compared to Example 1 is as follows: (1) In S1, the control photoresist stock solution R-C3 (lacking catalytic additive TEA) prepared in Preparation Example 7 was used. (2) In S4, due to the lack of cross-linking promotion effect of TEA, the electron beam exposure dose is increased to 3500 μC / cm to achieve a considerable degree of curing (2000 μC / cm in Example 1). All other parameters are the same.

[0070] Comparative Example 4: The difference compared to Example 1 is as follows: In S1, the control photoresist stock solution R-C4 prepared in Preparation Example 8 was used (using a single MIBK solvent, a deficiency gradient-induced co-solvent, therefore no negative concentration gradient of functional additives is formed in S3). Everything else was the same.

[0071] IV. Test Examples Part 1: Feasibility Test of the Core Mechanism of this Invention Test Example 1: Verification of the anti-charge accumulation (S4) mechanism (surface potential measurement) 1. Experimental Procedure (1) Take the composite photoresist stock solution R-1 prepared in Preparation Example 1 (used in Example 1) and the control photoresist stock solution R-C2 prepared in Preparation Example 6 (used in Comparative Example 2).

[0072] (2) Take two identical 4-inch fused silica substrates and perform pretreatment according to step S2 in Example 1.

[0073] (3) Using the same spin coating and pre-baking parameters (3000 rpm for 60 seconds; 90°C for 3 minutes), photoresist R-1 and R-C2 were coated on the two substrates respectively to form a film layer with the same thickness.

[0074] (4) Key steps: Neither substrate is coated with any additional conductive layer.

[0075] (5) The two substrates are fed into an electron beam lithography system (accelerating voltage 80keV). A 1mm × 1mm solid square pattern is exposed in the center region of each substrate using the same exposure dose (e.g., 500μC / cm) to ensure that equal amounts of charge are injected.

[0076] (6) After exposure is complete, immediately (within 5 minutes) remove the substrate from the EBL chamber and transfer it to a non-contact electrostatic voltmeter (Kelvin probe, Trek Model 344).

[0077] (7) Measure the surface potential at 5 different locations (point 1 to point 5) in the exposure area (within a 1mm×1mm square) of the two substrates respectively.

[0078] 2. Experimental Data Table 1. Surface potential measurement data after exposure. ; 3. Conclusion The surface potential measurement data shown in Table 1 intuitively verify the anti-charge accumulation technical mechanism in the present invention.

[0079] Comparative Example 2 (using R-C2 photoresist, without functional additive C) 60 After electron beam exposure, the average surface potential of the exposed area of ​​the substrate reached -23.16V. This data shows that, without a charge dissipation path, a large number of injected electrons accumulate on the surface of the insulating fused silica substrate and the photoresist film layer, forming a significant negative electric field. In actual photolithography processes, this high-intensity local electric field is the direct cause of subsequent electron beam path deflection and severe pattern distortion (such as position drift and pattern stretching).

[0080] In contrast, Example 1 (using R-1 photoresist containing functional additive C) 60 The substrate, after being exposed to the same dose of electron beam, exhibits an average surface potential of only -1.14V in the exposed area. This value is close to the background potential of the unexposed area (typically in the range of -0.5V to -1.0V), indicating that the injected charge during the exposure process is dissipated in a timely and efficient manner, without significant charge accumulation.

[0081] This result confirms the effectiveness of functional additive C. 60 Its key role in the present invention. C 60 The molecule's high electron affinity makes it an excellent transient electron-trapping site, effectively capturing injected excess electrons. Meanwhile, C... 60 The unique π-electron conjugation system of molecules allows trapped electrons to conduct short-range between adjacent molecules (such as hopping or tunneling), enabling rapid lateral dissipation of charge within the photoresist film layer. This molecular-scale in-situ charge dissipation mechanism avoids the catastrophic accumulation of local negative potential.

[0082] Therefore, the composite photoresist composition design of the present invention (as shown in Example 1) can effectively suppress the charge accumulation effect of electron beam lithography on the insulating substrate without relying on any external conductive layer (such as commercial conductive adhesive), thus ensuring the fidelity of the lithographic pattern in S4.

[0083] Test Case 2: Validation of the Functional Gradient (S3) Mechanism (Deep Analysis with XPS) 1. Experimental Procedure (1) Take the composite photoresist stock solution R-1 prepared in Preparation Example 1 (used in Example 1, containing a mixed solvent of MIBK / chloroform) and the control photoresist stock solution R-C4 prepared in Preparation Example 8 (used in Comparative Example 4, containing only a single solvent of MIBK).

[0084] (2) Take two identical P-type silicon (Si) wafers (for XPS testing to obtain good conductivity) and perform pretreatment according to S2 in Example 1.

[0085] (3) Using the same spin coating and pre-baking parameters as in Example 1 (3000 rpm for 60 seconds; 90°C for 3 minutes), photoresist R-1 and R-C4 were coated on two silicon wafers to prepare unexposed films for analysis.

[0086] (4) The two samples were sent into an X-ray photoelectron spectrometer (XPS, Thermo Fisher ESCALAB250Xi) using a monochromatic AlKα X-ray source (1486.6eV).

[0087] (5) Argon ions using 2keV energy (Ar + The sample surface is sputtered and peeled layer by layer by a beam, with a sputtering area of ​​2mm×2mm.

[0088] (6) Sputtering was paused at sputtering times of 0s (original surface), 10s, 20s, 30s, 60s, 90s and 120s respectively, and high-resolution energy spectra of C1s, Si2p and O1s were collected in the analysis area.

[0089] (7) Using the instrument's built-in Avantage software, process the acquired energy spectrum data, subtract the influence of adventitious carbon (surface contamination carbon) in the C1s spectrum, and calculate C (derived from C). 60 The atomic percentages of C (and HSQ matrix) and Si (derived from HSQ matrix) are calculated to obtain the C / Si atomic ratio.

[0090] 2. Experimental Data Table 2 XPS depth profile data for C / Si atomic ratio ; 3. Conclusion The XPS depth analysis data in Table 2 verify the effectiveness of the mixed solvent system used in step S3 for the functional additive C. 60 Spatial distribution regulation mechanism.

[0091] Comparative Example 4 used R-C4 photoresist (single MIBK solvent), whose C / Si atomic ratio remained essentially constant throughout the sputtering depth (from 0 s to 120 s), with an average value of approximately 0.147. This data indicates that using a single solvent for spin coating, the functional additive C... 60 It exhibits a uniform bulk phase distribution in the HSQ matrix.

[0092] Example 1 used R-1 photoresist (MIBK / chloroform mixed solvent), which exhibited a significantly different C / Si atomic ratio distribution. At the outermost surface of the film (sputtering time 0 s), the C / Si ratio was as high as 0.42, a value much higher than the average of Comparative Example 4. As the sputtering time increased (i.e., the analysis depth advanced into the film), the C / Si ratio decreased monotonically, dropping to 0.15 after 60 s of sputtering, and eventually stabilizing at 0.14, consistent with the bulk concentration value of Comparative Example 4.

[0093] The results clearly demonstrate that Example 1 utilized the significant difference in evaporation rates between the co-solvent (chloroform) and the main solvent (MIBK) in the S3 spin-coating step. Chloroform, as C... 60 It is a good solvent with much higher volatility than MIBK, and its rapid non-equilibrium evaporation during spin coating drives the solute C 60 directional migration and enrichment towards the membrane-air interface.

[0094] This mechanism spontaneously forms C on the top of the photoresist film layer (i.e., the main area of ​​electron beam injection). 60 The high concentration enrichment layer, while C in the bulk phase of the film layer 60 The concentration was the same as that of the conventional mixing method (Comparative Example 4). This "self-assembled functional gradient" structure allows the functional additive (C) to... 60 The distribution of the charge is highly matched with the area where charge accumulation occurs, thus enabling efficient in-situ charge dissipation with a low average addition amount.

[0095] Test Example 3: Verification of the crosslinking promotion (S4) mechanism (photolithographic contrast curve) 1. Experimental Procedure (1) Take the composite photoresist stock solution R-1 prepared in Preparation Example 1 (used in Example 1, containing TEA) and the control photoresist stock solution R-C3 prepared in Preparation Example 7 (used in Comparative Example 3, without TEA).

[0096] (2) Take two P-type silicon (Si) wafers respectively and perform pretreatment according to S2 in Example 1.

[0097] (3) Using the same spin coating and pre-baking parameters (3000 rpm for 60 seconds; 90°C for 3 minutes), photoresist R-1 and R-C3 were coated onto two silicon wafers respectively. The initial film thickness (T0) of the two samples was measured using an ellipsometry.

[0098] (4) The two substrates are fed into an electron beam lithography system (accelerating voltage 80keV). A series of 100μm×100μm block arrays are exposed on the two samples respectively, with the exposure dose increasing from 500μC / cm to 5000μC / cm (dose step 500μC / cm).

[0099] (5) After exposure, both substrates are simultaneously immersed in a 2.38% (w / w) TMAH aqueous solution for 60 seconds (development temperature 22°C), then rinsed with deionized water for 60 seconds and dried with high-purity nitrogen.

[0100] (6) Use a probe profilometer (DektakXT) to measure the remaining film thickness (Tf) of each dose square after development.

[0101] (7) Calculate the normalized remaining thickness (NRT) at each dose point. The formula is: NRT = Tf / T.

[0102] 2. Experimental Data Table 3. Relationship between exposure dose and normalized residual thickness. ; 3. Conclusion The data in Table 3 (i.e., the original data of the photolithographic contrast curves) verify the in-situ crosslinking promotion mechanism of the catalytic additive (TEA) in the present invention.

[0103] Photoresist sensitivity (D) 50 The exposure dose is defined as the amount required to retain 50% of the film thickness. According to the data in Table 3, the D of Example 1 (R-1 photoresist) 50 The dose was around 1500 μC / cm; while the D of Comparative Example 3 (R-C3 photoresist) 50 The dosage is close to 3000 μC / cm.

[0104] This data indicates that the exposure sensitivity of the R-1 photoresist in Example 1 is significantly higher than that of the R-C3 photoresist in Comparative Example 3. The only component difference between the two photoresists is that R-1 contains the catalytic additive TEA, while R-C3 does not.

[0105] This performance difference is attributed to a synergistic catalytic mechanism in the S4 exposure step. Under electron beam irradiation, the functional additive C 60 Capture electrons to form C60 - Anionic free radicals. In the R-C3 system without TEA, C 60 - Anionic free radicals mainly initiate HSQ (SiHSiH bond) crosslinking through energy transfer or free radical reaction. However, the reaction energy barrier of this process is relatively high, resulting in low overall crosslinking efficiency. A higher exposure dose (such as 3000 μC / cm) is required to make HSQ fully insoluble in the developer.

[0106] In the R-1 system of Example 1, the presence of the catalytic additive TEA (weak base) can effectively activate the SiHSiH bonds in the HSQ matrix, or act as a proton acceptor with C. 60 - Anionic free radicals act, significantly reducing C 60 The energy barrier of the mediated HSQ crosslinking reaction. This in-situ crosslinking promoting effect significantly increases the number of HSQ crosslinking events that can be triggered per unit exposure dose, i.e., improving crosslinking efficiency.

[0107] Therefore, the present invention introduces TEA as a catalytic additive, in conjunction with functional additive C. 60 The synergistic effect effectively enhances the reaction sensitivity of the matrix resin HSQ under electron beam exposure, making the exposure dose required to complete photoresist patterning (such as 2000 μC / cm in Example 1 or 1500 μC / cm in Example 3) significantly lower than that required in systems lacking this catalyst (such as 3500 μC / cm required in Comparative Example 3). This has direct significance for improving the processing efficiency of electron beam lithography.

[0108] Part Two: Overall Performance Comparison Test of the Invention Test Example 4: Anti-reflection performance test of photonic crystal (spectral measurement) 1. Experimental Procedure (1) Take the final samples prepared in Examples 1-4 and Comparative Examples 1-4 (i.e., the substrates that have been cured by baking after S6).

[0109] (2) Take an additional bare fused silica substrate, which is the same as the substrate used in Example 1 but has not undergone any treatment, as a reference.

[0110] (3) Use an ultraviolet-visible-near-infrared (UV-Vis-NIR) spectrophotometer (Agilent Cary 5000) equipped with a 150mm integrating sphere accessory (DRA-2500).

[0111] (4) Use a standard whiteboard (Spectralon) to perform 100% baseline calibration on the integrating sphere and use a light trap (LightTrap) to perform 0% baseline calibration.

[0112] (5) Set measurement parameters: wavelength range 400nm to 1000nm, data interval 1nm, incident angle 8° (near vertical incident).

[0113] (6) Measure the total reflectance (R%) spectra of the bare substrate, samples of Examples 1-4 and Comparative Examples 1-4 respectively.

[0114] (7) To facilitate comparison, the average reflectance of all samples in the 400nm-1000nm band was extracted.

[0115] 2. Experimental Data Table 4 shows the average reflectance of the samples in the 400-1000 nm wavelength range. ; 3. Conclusion The spectral measurement data in Table 4 verify that the photonic crystal structure prepared in this invention has anti-reflection function and reveal the influence of different process components on the final optical performance.

[0116] First, the average reflectance of the samples in Examples 1-4 was significantly lower than 1.5%, far lower than the average reflectance of the bare fused silica substrate (3.54%). This data confirms the complete technical solution of the present invention (S1-S6), which can successfully prepare photonic crystals with specific micro-nano structures on the surface of optical lens substrates, achieving effective anti-reflection function over a wide spectral range.

[0117] Secondly, Comparative Examples 1-4 were compared with Comparative Examples 1 and 2. Both Comparative Example 1 (conventional HSQ) and Comparative Example 2 (HSQ+TEA) did not contain C. 60 The final S6 curing process yields a pure SiO2 micro / nano structure. While these structures also exhibit some antireflectivity (2.48% and 2.53%, respectively), their reflectivity is significantly higher than that of Examples 1-4 (average approximately 1.26%). This difference indicates that the SiO2-based embedded functional additive (C) formed by S6 in this invention... 60 The composite micro / nano structure of C exhibits superior optical performance compared to the pure SiO2 structure. 60 The embedding may have adjusted the optical constants (refractive index or extinction coefficient) of the SiO2 matrix, or formed a more optimized gradient refractive index profile, thereby achieving lower reflectivity.

[0118] Finally, the optical performance analysis of Comparative Examples 3 and 4 verified the necessity of the key mechanism of this invention. Comparative Example 3 (lacking TEA) exhibited an average reflectance as high as 3.81%, attributed to the low sensitivity revealed in Test Example 3. To achieve curing, Comparative Example 3 required a high exposure dose, which exacerbated the proximity effect, leading to excessive expansion of the photoresist exposure area, rough edge lines, and periodic structural distortion. Ultimately, the fabricated micro / nano structure deviated from the optical design and failed to achieve effective anti-reflection.

[0119] Comparative Example 4 (lacking gradient solvent) showed the highest average reflectance (4.07%), even higher than the bare substrate, which may indicate the occurrence of incoherent scattering. This result is consistent with the conclusions of Test Example 2 (C... 60 Corresponding to (not enriched on the surface). Due to C 60 While uniformly dispersed in the bulk phase, its concentration on the surface is insufficient to completely suppress charge accumulation (as shown in Test Example 1), resulting in localized charge accumulation during the S4 exposure process, causing electron beam deflection and pattern distortion. Therefore, the gradient-induced mechanism of S3 is crucial for ensuring the pattern fidelity of S4 and ultimately achieving the final optical performance.

[0120] Test Example 5: Indirect Test of Photonic Crystal Pattern Fidelity (Laser Diffraction) 1. Experimental Procedure (1) This test requires that the pattern prepared in the S4 exposure step be a periodic array (e.g., a two-dimensional nanopillar array with a design period of a=400nm).

[0121] (2) Take the final samples prepared in Examples 1-4 and Comparative Examples 1-4 (after S6).

[0122] (3) Setting up the laser diffraction optical path: Using a HeNe laser (λ=632.8nm) as the light source, after beam expansion and collimation, a parallel beam with a diameter of 3mm is formed.

[0123] (4) Place the sample to be tested vertically in the optical path so that the collimated beam is incident on the photonic crystal pattern area at the center of the sample.

[0124] (5) Place a white screen or CCD detector at a distance of L=50.0cm behind the sample to observe and record the diffraction pattern.

[0125] (6) Qualitative observation: Record the clarity, symmetry and whether there is distortion of the first-order diffraction spot (m=1) in the diffraction pattern.

[0126] (7) Quantitative measurement: Using an optical power meter, measure the total incident light power (Ptotal, measured when the sample is removed) and the power of the first-order diffraction spot (P1). Calculate the first-order diffraction efficiency (DE), DE = P1 / Ptotal.

[0127] 2. Experimental Data Table 5 Laser diffraction pattern quality and first-order diffraction efficiency ; 3. Conclusion The diffraction test results in Table 5 provide indirect evidence of the fidelity of the photolithographic pattern and reveal the combined influence of different technical mechanisms in this invention on the uniformity of the final structure.

[0128] Examples 1-4 all exhibited clear, sharp, and symmetrical diffraction spot arrays, with first-order diffraction efficiencies all exceeding 22% (e.g., Example 3 reached 25.1%). This data demonstrates that the complete process of this invention (S1-S6) can fabricate micro / nano structure arrays with high uniformity and high periodicity fidelity. The clear symmetry of the diffraction spots proves that the S4 exposure step accurately reproduced the designed two-dimensional periodicity, and the structure morphology after S6 curing is regular.

[0129] Comparative Examples 1, 2, and 4 exhibited extremely low diffraction efficiencies (all below 4.5%), and their diffraction patterns displayed characteristics of "severe distortion," "stretching," or "twisting." Comparative Examples 1 and 2 lacked Cg. 60 Comparative Example 4 lacks a gradient-induced mechanism. This is in contrast to Test Example 1 (high surface potential) and Test Example 2 (C). 60 The data (unenriched) show that these diffraction defects can be attributed to charge accumulation that was not effectively suppressed during the S4 exposure process. The accumulated surface potential causes random deflection and drift of the electron beam path during the writing process, severely disrupting the periodicity of the EBL writing pattern. As a result, the final cured structure cannot form an effective diffraction grating, and the diffraction efficiency is therefore extremely low.

[0130] Comparative Example 3 (lacking TEA) also exhibited low diffraction efficiency (6.5%), but its pattern primarily displayed "diffuseness" and "blurred edges" rather than "distortion." This phenomenon is consistent with the findings of Test Example 3 (low sensitivity). Due to the lack of TEA catalysis, S4 required a high exposure dose. The proximity effect introduced by the high dose resulted in poorer linewidth control (CD) and increased edge roughness for structural features such as nanopillars. Although periodicity was maintained (without distortion due to charge accumulation), the deterioration (blurring) of the structural morphology also led to decreased diffraction efficiency and increased background scattering.

[0131] In summary, Test Example 5 confirms the anti-charge accumulation mechanism in the present invention (by C). 60 Both gradient solvent and crosslinking promotion mechanisms (achieved by TEA) are necessary for the preparation of high-fidelity periodic micro / nano structures (i.e., to achieve the optical properties shown in Test Example 4).

[0132] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for fabricating antireflective surfaces of micro / nano-structured photonic crystals for optical lenses using electron beam lithography, characterized in that, Includes the following steps: S1. Prepare a functionally graded composite photoresist, wherein the composite photoresist comprises a matrix resin, functional additives, catalytic additives, and a mixed solvent system, wherein the mixed solvent system consists of a main solvent and a gradient-inducing co-solvent; S2. Pre-treat the optical lens substrate to remove organic and inorganic contaminants from the substrate surface; S3. Spin-coat the composite photoresist prepared in S1 onto the pretreated substrate surface. Utilize the gradient-induced difference in evaporation rates between the co-solvent and the main solvent to drive the functional additives to form a negative concentration gradient in the vertical direction in the photoresist film. Then, pre-bake the film to remove residual solvent and cure it. S4. No additional conductive layer needs to be coated on the surface of the photoresist film. Electron beam lithography system is used to expose the photonic crystal pattern with electron beam. During the exposure process, functional additives achieve anti-charge accumulation and anti-proximity effect, and promote the cross-linking of the matrix resin in situ with the assistance of catalytic additives. S5. The exposed substrate is developed with a developer to remove the insufficiently exposed photoresist areas. After cleaning and drying, a photonic crystal pattern array is obtained. S6. The substrate with the photonic crystal pattern array is post-calcined and cured to further cross-link and transform the matrix resin, forming a SiO2-based photonic crystal anti-reflection micro / nano structure with embedded functional additives on the surface of the optical lens.

2. The method for fabricating the anti-reflection surface of a micro / nano structure photonic crystal for optical lenses using electron beam lithography according to claim 1, characterized in that, The matrix resin is hydrogen silsesquioxane.

3. The method for fabricating the anti-reflection surface of a micro / nano structure photonic crystal for optical lenses using electron beam lithography according to claim 1, characterized in that, The functional additive is Buckminster fullerene.

4. The method for fabricating the anti-reflection surface of a micro / nano structure photonic crystal for optical lenses using electron beam lithography according to claim 1, characterized in that, The catalyst additive is a weak base, specifically triethylamine.

5. The method for fabricating the anti-reflection surface of a micro / nano structure photonic crystal for optical lenses using electron beam lithography according to claim 1, characterized in that, In the mixed solvent system, the main solvent is methyl isobutyl ketone or anisole, and the gradient-induced co-solvent is chloroform or toluene.

6. The method for fabricating the anti-reflection surface of a micro / nano structure photonic crystal for optical lenses using electron beam lithography according to claim 1, characterized in that, In step S1, the composite photoresist is prepared in a glove box or clean room, and the matrix resin, functional additives, and catalytic additives are completely dissolved in the mixed solvent system by stirring or ultrasonic treatment.

7. The method for fabricating the anti-reflection surface of a micro / nano structure photonic crystal for optical lenses using electron beam lithography according to claim 1, characterized in that, In step S2, the substrate pretreatment process involves soaking in Piranha solution, rinsing with deionized water, and drying with nitrogen. Alternatively, the substrate can be treated with oxygen plasma or coated with HMDS to enhance the adhesion between the photoresist and the substrate.

8. The method for fabricating the anti-reflection surface of a micro / nano structure photonic crystal for optical lenses using electron beam lithography according to claim 1, characterized in that, In step S2, the optical lens substrate is fused silica or high-refractive-index optical glass.

9. The method for fabricating the anti-reflection surface of a micro / nano structure photonic crystal for optical lenses using electron beam lithography according to claim 1, characterized in that, In S4, the energy of the electron beam used in electron beam lithography is 50-100keV.

10. The method for fabricating the anti-reflection surface of a micro / nano structure photonic crystal for optical lenses using electron beam lithography according to claim 1, characterized in that, In step S5, the developer is a 2.38% TMAH aqueous solution, and the development method is immersion development.

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