A low temperature curing photoresist composition and a method for preparing the same

Abstract

The application discloses a low-temperature curing photoresist composition and a preparation method thereof, and belongs to the technical field of microelectronic and flexible display materials. The method comprises the following steps: preparing surface modified reactive nano-filler composed of multi-dimensional inorganic / carbon-based material; synthesizing photosensitive polyimide resin matrix by asymmetric bio-based diamine, nitrogen-containing heterocyclic diamine and fluorine-free dianhydride polycondensation; synthesizing low-dielectric benzocyclobutene-based silicone oligomer containing photosensitive double bond; dispersing the above components, a mercapto-alkene crosslinking network builder and a photoinitiator in an environmentally friendly solvent, and coating, ultraviolet exposure and low-temperature baking to obtain the finished product. The application breaks the high-temperature curing limitation of traditional polyimide by using the synergistic effect of mercapto-alkene crosslinking chemistry and multiple components, and realizes efficient curing. The photoresist has high resolution, low dielectric constant, excellent adhesion and excellent bending cycle life, and has excellent environmental protection, and is especially suitable for the manufacturing of flexible electronic devices and high-end display panels.

Description

Technical Field

[0001] This invention belongs to the field of microelectronics and flexible display materials technology, specifically, it relates to a low-temperature curing photoresist composition and its preparation method. Background Technology

[0002] In recent years, with the rapid development of flexible organic light-emitting diode (OLED) display technology and high-density advanced packaging technology, photosensitive polyimide (PSPI) has been widely used in the pixel definition layer (PDL), buffer layer, and interlayer insulating medium in photolithography processes due to its excellent dielectric properties, mechanical strength, and chemical resistance. Traditional photoresist systems mostly use polyamic acid as a precursor. After coating, exposure, and development into a pattern, extremely high heat treatment temperatures (typically above 250℃ to 350℃) are required to overcome the high activation energy and achieve complete thermal imidization, ring closure, and cross-linking network freezing. However, in the actual manufacturing process of flexible electronic devices, existing high-temperature curing photoresists have exposed many unavoidable technical bottlenecks: First, the extremely high heat treatment budget severely conflicts with the thermodynamic limits of the flexible substrate. The polymer substrates commonly used in flexible panels and the underlying thermally sensitive active devices cannot withstand prolonged high heat loads. High temperatures not only cause macroscopic warping deformation of the substrate and thermal stress tearing between microlayers, but also lead to irreversible thermal degradation of OLED luminescent materials, severely restricting the yield and lifespan of the devices. Secondly, the traditional polyimide backbone is rich in highly conjugated rigid aromatic ring structures, which readily form strong charge-transfer complexes (CTCs) both intermolecularly and intramolecularly. This microscopic electronic effect causes the cured film to exhibit strong absorption in the visible light band, resulting in low transmittance and significant yellowing, thus severely weakening the light extraction efficiency (light output efficiency) of the display panel. Simultaneously, the high intrinsic dielectric constant of traditional aromatic systems makes it difficult to meet the requirements of extremely low RC delay for high-frequency signal transmission at high speeds. Thirdly, existing high-molecular-weight photoresist precursors are highly dependent on high-boiling-point, highly polar, and biotoxic solvents such as N-methylpyrrolidone (NMP) and dimethylacetamide (DMAC). In attempts to achieve low-temperature curing, these high-boiling-point solvents are extremely difficult to completely desorb, leading to abnormally high solvent residue rates within the film. This not only causes gas outgassing pollution in subsequent vacuum coating processes, but the resulting high VOC (volatile organic compound) emissions also fail to meet the stringent environmental and health standards of modern cleanrooms.

[0003] Finally, to achieve low-temperature curing, conventional improvement methods in existing technologies mostly involve physically blending acid-base catalysts into the system or modifying the side chains using traditional acrylate double bonds. However, free small-molecule catalysts are prone to migration and phase separation during baking, leading to uneven curing. Furthermore, traditional free radical chain polymerization processes are easily interfered with by the polymerization inhibition effect of oxygen in the environment, resulting in severely insufficient crosslinking density under low UV light intensity and extremely short exposure time. This manifests macroscopically as decreased photolithographic resolution, pattern edge collapse after development, and weakened substrate adhesion.

[0004] In summary, the field urgently needs to develop a low-temperature curing photoresist system that can overcome the closed-loop energy barrier at the microscopic molecular level, disrupt the coplanarity of CTC, be compatible with low-toxicity and low-boiling-point solvents, and achieve rapid oxygen-free polymerization and crosslinking under low-heat and low-irradiation conditions, so as to fully meet the stringent requirements of next-generation high-precision flexible display and microelectronics manufacturing. Summary of the Invention

[0005] To address the technical shortcomings of existing traditional photosensitive polyimide photoresists, such as excessively high curing temperatures (typically >250℃) leading to thermal stress deformation of flexible substrates, the formation of charge-transfer complexes (CTCs) from the planar stacking of aromatic backbones reducing visible light transmittance, low-temperature residues of high-boiling-point toxic solvents (such as N-methylpyrrolidone, NMP) resulting in high volatile organic compound (VOC) emissions, and severe oxygen inhibition in traditional acrylate free radical chain polymerization leading to insufficient crosslinking density and photolithographic resolution, this invention provides a low-temperature curing photoresist composition and its preparation method.

[0006] This invention employs the following technical solution: a method for preparing a low-temperature curing photoresist composition, comprising: S1. Preparing surface-modified reactive nanofillers: Silicon-based and aluminum-based precursors are respectively subjected to organic functionalization treatment, then mixed with graphene oxide, silver nanowires, and carbon nanotubes in a mass ratio, and surface modified using a coupling agent under an ultrasonic field to obtain a nanofiller composite with polymerizable double bonds on the surface; S2. Synthesizing a photosensitive polyimide resin matrix: Asymmetric bio-based diamine monomers, diamine monomers with nitrogen-containing heterocyclic main chains, and fluorine-free dianhydrides and end-capping agents are subjected to condensation polymerization and chemical imidization in a mass ratio. S1. Obtain a soluble photosensitive polyimide resin; S2. Synthesize benzocyclobutene-based silicone oligomer: After converting bromobenzocyclobutene into an acrylate derivative, react it with bisbenzocyclobutene-bisdivinylsiloxane in a mass ratio, and end-cap with glycidyl methacrylate to obtain a low dielectric resin containing photosensitive double bonds; S3. Disperse the components obtained in steps S1 to S3, along with a mercapto-olefin crosslinking network builder and a photoinitiator in a mass ratio in an environmentally friendly solvent system, degas after high-shear dispersion and grinding, and then coat, expose to ultraviolet light and bake at low temperature to obtain the low-temperature curing photoresist composition.

[0007] Preferably, in step S1, the surface-modified reactive nanofiller is made from the following components in parts by weight: 15-35 parts of reactive mixed silica nanoparticles, 10-25 parts of reactive mixed alumina nanoparticles, 5-15 parts of graphene oxide with an oxidation degree of 40-60%, 1-5 parts of silver nanowires, and 2-8 parts of carbon nanotubes; the coupling agent used for surface modification is a composite of γ-methacryloyloxypropyltrimethoxysilane and isopropyltris(dioctyl pyrophosphate) titanate in a specified mass ratio.

[0008] Preferably, in step S2, the asymmetric bio-based diamine monomer is 4-aminophenyl-4-aminobenzoate; and the fluorine-free dianhydride is 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

[0009] Preferably, in step S2, the diamine monomer containing a nitrogen-containing heterocycle in the main chain is selected from 4,4'-(piperazine-1,4-diyl)diphenylamine; its added mass accounts for 5% to 10% of the total mass of the diamine monomer.

[0010] Preferably, in step S3, the preparation parameters of the benzocyclobutene-based silicone oligomer are as follows: using palladium acetate and tri-o-tolylphosphine as catalysts, 4-bromobenzocyclobutene is coupled with acrylic acid to generate a carboxyl-containing precursor, which is then reacted with bisbenzocyclobutene-bisdivinylsiloxane at 150-170°C at a mass ratio of 1:1 for 50-70 hours, and the reaction solvent is dipropylene glycol methyl ether acetate.

[0011] Preferably, in step S4, the mercapto-olefin crosslinking network building agent is composed of pentaerythritol tetrakis(3-mercaptopropionic acid) and 2,4,6-trienylpropoxy-1,3,5-triazine in a mass ratio of 1:1, and the photoinitiator is ethyl 2,4,6-trimethylbenzoylphenylphosphonate.

[0012] Preferably, in step S4, the environmentally friendly solvent system is composed of propylene glycol monomethyl ether acetate and cyclohexanone in a mass ratio of 40:60 to 60:40, and does not contain N-methylpyrrolidone.

[0013] Preferably, the film-forming and curing parameters in step S4 are defined as follows: spin-coating at 1000-3000 rpm for 10-30 seconds to form a coating with a thickness of 1-5 μm, followed by curing at a wavelength of 365 nm and an intensity of 50-100 mW / cm. 2 Pre-expose under ultraviolet light for 10-20 seconds, and then keep at 140℃ for 2 hours. Then raise the temperature to 180℃ at a rate of 2℃ / min and keep it there for 2 hours.

[0014] Preferably, in step S4, during the photoresist slurry dispersion stage, an additional 1% of the total mass of polycarbonate nano-corrugated structure template is added.

[0015] A low-temperature curing photoresist composition, wherein the low-temperature curing photoresist composition is obtained by the preparation method described above.

[0016] Compared with the prior art, the present invention has at least the following beneficial effects: (1) Breaking the thermodynamic activation energy barrier, achieving low-temperature high-efficiency curing and avoiding oxygen inhibition defects. The present invention precisely incorporates nitrogen-containing heterocycles (such as bipyridine or piperazine) into the polyimide skeleton as intramolecular autocatalytic microunits, which significantly reduces the ring-closing activation energy of imidization; at the same time, it introduces a mercapto-olefin click chemistry mechanism, which utilizes its thermodynamic characteristics of step growth to fundamentally overcome the oxygen inhibition effect of traditional acrylate free radical polymerization. The two work together to enable the composition of the present application to complete the construction of a high-density cross-linked network under a low heat load of 140-150℃, completely eliminating the damage to flexible substrates and thermosensitive active devices caused by traditional high-temperature processes. (2) Disrupting the coplanar arrangement of the main chain, suppressing the CTC effect to the extreme and greatly improving the transmittance. The bio-based diamine selected in the present invention has a strong asymmetric biphenyl structure, and its huge steric hindrance blocks the π-π stacking between polymer chain segments, directly cutting off the formation path of charge transfer complex (CTC). This effectively solves the inherent yellowing problem of traditional photosensitive polyimide, keeping the visible light transmittance of the cured film above 90%, and significantly enhancing the light output coupling efficiency of the flexible display panel. (3) Directional introduction of low polarity and free volume gives the cured film excellent high-frequency and low dielectric properties. This invention introduces benzocyclobutene-based silicone oligomers through molecular cascade design. Utilizing the low polarity aromatic ring structure of benzocyclobutene and the flexible siloxane segments, abundant free volume is forcibly anchored in the matrix during the thermosetting ring-opening stage, thereby significantly reducing the intrinsic dipole polarization of the polymer skeleton and stabilizing the high-frequency dielectric constant (Dk) to below 3.0, meeting the stringent requirements of advanced packaging and high-frequency communication for extremely low signal delay. (4) Constructing a cross-scale stress dissipation network to achieve excellent dimensional stability and interface adhesion. The composition incorporates zero-dimensional to two-dimensional reactive inorganic and carbon-based materials (silicon dioxide, alumina, graphene oxide, silver nanowires, and carbon nanotubes), and eliminates polar hydroxyl defects on the surface of the inorganic phase through dual coupling modification of titanate and silane. This multidimensional hybrid framework not only inhibits the thermal relaxation of polymer chain segments and significantly reduces the coefficient of thermal expansion (CTE), but also effectively disperses the concentrated stress caused by the flexible deformation of the underlying layer, giving the cured film the highest adhesion grade of 5B and a dynamic bending cycle life of over 5000 cycles. (5) Reconstructing an environmentally friendly solvent system to meet the cleanroom manufacturing standards for extremely low VOC emissions. Thanks to the high solubility of the special modified resin synthesized in this invention in low-toxicity polar solvents, the system completely eliminates traditional high-boiling-point toxic solvents such as N-methylpyrrolidone (NMP). The environmentally friendly mixed solvent of PGMEA and cyclohexanone used can achieve complete desorption and desorption during low-temperature baking at 180℃ and below, which greatly reduces the residual solvent mass fraction after film formation and avoids the problems of gas release pollution and VOC exceeding the standard in subsequent vacuum coating processes from the source. Attached Figure Description

[0017] Figure 1 This is the infrared spectrum of the low-temperature curing photoresist composition prepared in Example 1. Detailed Implementation

[0018] The present invention will be further described in detail below with reference to specific embodiments. However, these embodiments are only for illustrating the present invention and do not constitute any limitation on the scope of protection of the present invention. For those skilled in the art, simple deductions or substitutions made without departing from the concept of the present invention should be considered as falling within the scope of protection defined by the claims of the present invention. In the present invention, unless otherwise specified, intermediate values ​​are used for undefined parameter ranges by default.

[0019] The surface-modified reactive nanofiller consists of reactive mixed silica nanoparticles (CAS No.: 7631-86-9, average particle size 50 nm, purity 99.9%, appearance: white fluffy powder, density: approximately 2.4 g / cm³). 3 Specific surface area is 200~400m² 2 Reactive mixed alumina nanoparticles (CAS No.: 1344-28-1, average particle size 60nm, purity 99.9%, density: 3.9~4.0g / cm³) 3 The following are included: graphene oxide with an oxidation degree of 40-60% (CAS No.: 2640657-49-2, particle size 0.5-5μm, monolayer state, sheet thickness: 0.7~1.2nm), silver nanowires (CAS No.: 7440-22-4, diameter 50nm, length 20μm), and carbon nanotubes (CAS No.: 308068-56-6, outer diameter 10-20nm, length 5-15μm, specific surface area 200~500m²). 2The composition is (g). The coupling agent used for surface modification is a complex of γ-methacryloxypropyltrimethoxysilane (CAS No.: 2530-85-0) and isopropyltris(dioctyl pyrophosphate) titanate (CAS No.: 67691-13-8). In this embodiment of the invention, the preparation process of the surface-modified reactive nanofiller is as follows: 150.0 g of silicon-based precursor (silica nanopowder with an average particle size of 50 nm, purchased from Sigma-Aldrich, purity 99.9%) and 200.0 g of aluminum-based precursor (alumina nanopowder with an average particle size of 60 nm, purchased from AlfaAesar, purity 99.9%) were dried in a vacuum drying oven at 120 °C for 12 hours to remove surface adsorbed water. Organic functionalization treatments were performed on both silicon-based and aluminum-based precursors: Functionalization of the silicon-based precursor: 150.0 g of dried silica nanoparticles were dispersed in 1500 mL of toluene solvent. Under argon protection, 15.0 g of γ-methacryloyloxypropyltrimethoxysilane (KH-570, purchased from Nanjing Siwei Chemical Co., Ltd., purity 98%) was added, and the mixture was stirred and refluxed at 80 °C for 6 hours. After the reaction, the solid product was obtained by centrifugation, washed three times repeatedly with toluene and anhydrous ethanol, and then dried under vacuum at 60 °C for 12 hours to obtain surface-functionalized reactive silica nanoparticles. Functionalization of the aluminum-based precursor: 200.0 g of dried alumina nanoparticles were dispersed in 2000 mL of methanol solvent. Under argon protection, 10.0 g of isopropyl tris(dioctyl pyrophosphate) titanate (Ken-React® KR-38S, purchased from Kenrich Petrochemicals, Inc.) was added, and the mixture was stirred at 60 °C for 4 hours. After the reaction, the solid product was obtained by centrifugation, washed three times with methanol and acetone, and then dried under vacuum at 60 °C for 12 hours to obtain surface-functionalized reactive alumina nanoparticles. Preparation of the nanofiller composite: 25.0 g of the above-prepared reactive silica nanoparticles and 15.0 g of reactive alumina nanoparticles were added to a 5000 mL three-necked flask equipped with a mechanical stirrer, condenser, and thermometer. Subsequently, 10.0 g of graphene oxide (0.5-5 μm particle size, purchased from Nanjing Xianfeng Nanomaterials Technology Co., Ltd.) with an oxidation degree of 50%, 3.0 g of silver nanowires (50 nm diameter, 20 μm length, purchased from Beijing Deco Island Gold Technology Co., Ltd.), and 5.0 g of carbon nanotubes (multi-walled carbon nanotubes, 10-20 nm outer diameter, 5-15 μm length, purchased from Shenzhen Nanoport Technology Co., Ltd.) were added. 2000 mL of dimethyl sulfoxide (DMSO) was added as a dispersion solvent. The mixture was ultrasonically dispersed at room temperature for 2 hours (200 W power, 28 kHz frequency) to ensure uniform dispersion of each component.Next, 5.0 g of a coupling agent complex composed of γ-methacryloxypropyltrimethoxysilane and isopropyltris(dioctyl pyrophosphate) titanate in a mass ratio of 1:1 was added. The mixture was stirred for 1 hour under an ultrasonic field (power 100 W, frequency 40 kHz) to ensure the coupling agent fully participated in surface modification. After the reaction, the mixture was separated by centrifugation and repeatedly washed with ethanol, then vacuum dried at 80 °C for 24 hours to obtain a nanofiller complex with polymerizable double bonds on its surface (labeled as nanofiller A). The photosensitive polyimide resin matrix (step S2) was synthesized as follows: the resin matrix was obtained by polycondensation and chemical imidization of an asymmetric bio-based diamine monomer, a nitrogen-containing heterocyclic diamine monomer, a fluorine-free dianhydride, and a capping agent. In this embodiment of the invention, the synthesis process of the photosensitive polyimide resin matrix is ​​as follows: the asymmetric bio-based diamine monomer is 4-aminophenyl-4-aminobenzoate (CAS No.: 20610-77-9, labeled as diamine M1). Its purity was determined to be 99.5% by HPLC. Preparation of the nitrogen-containing heterocyclic diamine monomer: 4,4'-(piperazine-1,4-diyl)diphenylamine (CAS No.: 7479-12-1, purchased from Shanghai TCI Chemical Co., Ltd., purity 99%, labeled as diamine M2) was used. Preparation of fluorine-free dianhydride: 3,3',4,4'-benzophenone tetracarboxylic dianhydride (CAS No.: 2421-28-5, purchased from TCI Chemical Co., Ltd., purity 99%) was used. End-capping agent: Phthalic anhydride (CAS No.: 85-44-9, purchased from Sinopharm Chemical Reagent Co., Ltd., purity 99.5%) was used. Polycondensation and chemical imidization: In a 1000 mL four-necked flask equipped with a mechanical stirrer, nitrogen inlet, condenser, and thermometer, 85.0 g of diamine M1, 5.0 g of diamine M2 (5.5% of the total mass of the diamine monomers), and 200 mL of N,N-dimethylacetamide (CAS No.: 127-19-5, DMAC, purchased from Sinopharm Chemical Reagent Co., Ltd., analytical grade) were added. The mixture was stirred and dissolved at room temperature for 2 hours under a nitrogen atmosphere. Then, 190.0 g of 3,3',4,4'-benzophenone tetracarboxylic dianhydride was added in portions, maintaining the reaction temperature below 40°C, and stirred for 12 hours to form a PAA solution. Finally, 10.0 g of phthalic anhydride was added as a capping agent. The PAA solution was transferred to another mixture containing 150 mL of acetic anhydride (CAS No.: 108-24-7, purchased from Sinopharm Chemical Reagent Co., Ltd., analytical grade) and 100 mL of pyridine (CAS No.: 110-86-1, purchased from Sinopharm Chemical Reagent Co., Ltd., analytical grade). Under nitrogen protection, the mixture was stirred at 150 °C for 4 hours. After the reaction was complete, the reaction solution was slowly poured into a large amount of deionized water, resulting in the precipitation of a yellow precipitate. The precipitate was centrifuged, washed repeatedly with deionized water and methanol, and then dried under vacuum at 80 °C for 24 hours to obtain a soluble photosensitive polyimide resin (labeled PI-A).In step S3, the synthesis process of benzocyclobutene-based silicone oligomer (BCB-Si) is as follows: Preparation of 4-benzocyclobutene acrylic acid (carboxyl-containing precursor): Under nitrogen protection, 4-bromobenzocyclobutene (CAS No.: 1073-39-8, 20.0 g, purchased from Bailingwei Technology Co., Ltd., purity 98%), acrylic acid (CAS No.: 79-10-7, 15.0 g, purchased from Sinopharm Chemical Reagent Co., Ltd., analytical grade), palladium acetate (CAS No.: 3375-31-3, 0.2 g, purchased from Sinopharm Chemical Reagent Co., Ltd., purity 99%), tri-o-tolylphosphine (CAS No.: 6163-58-2, 0.5 g, purchased from Sinopharm Chemical Reagent Co., Ltd., purity 98%) and triethylamine (25 g) were added to 200 mL of dimethylformamide (CAS No.: 68-12-2, DMF) solvent. The mixture was heated to 100°C and reacted for 12 hours. After the reaction, it was cooled to room temperature, extracted with diethyl ether, washed with water, and purified by silica gel column chromatography (eluent: petroleum ether / ethyl acetate, mass ratio 5:1) to obtain 4-benzocyclobutene acrylic acid. The 4-benzocyclobutene acrylic acid (50.0 g) and bisbenzocyclobutene-bisdivinylsiloxane (CAS No. 117732-87-3, 50.0 g, purchased from Wuhan Optics Valley Chemical Co., Ltd., purity 95%) prepared above were added to 500 mL of dipropylene glycol methyl ether acetate (CAS No. 88917-22-0, DPMA, purchased from Sinopharm Chemical Reagent Co., Ltd., analytical grade) solvent at a mass ratio of 1:1. Using palladium acetate and tri-o-tolylphosphine as catalysts, the reaction was carried out at 160°C for 60 hours under nitrogen protection. After the reaction was completed, glycidyl methacrylate (CAS No.: 106-91-2, 2.0 g, purchased from Sinopharm Chemical Reagent Co., Ltd., purity 98%) and triphenylphosphine (CAS No.: 603-35-0, 0.5 g) were added for end-capping reaction at 100℃ for 4 hours. After cooling to room temperature, the solvent was removed by rotary evaporation to obtain a low-dielectric resin containing photosensitive double bonds (labeled BCB-Si).

[0020] Preparation of low-temperature curing photoresist composition (step S4): Formulations of Examples and Comparative Examples All formulations of examples and comparative examples (unless otherwise specified) were prepared in accordance with step S4.

[0021] Table 1. Formulations of Examples and Comparative Examples (Unit: g)

[0022] Note: The mercapto-olefin crosslinking network builder was prepared by mixing pentaerythritol tetrakis(3-mercaptopropionic acid) ester (CAS No. 7575-23-7, PEMP, purchased from TCI, 98% purity) and 2,4,6-trienylpropoxy-1,3,5-triazine (CAS No. 101-37-1, TACOT, purchased from Bailingwei Technology Co., Ltd., 98% purity) in a 1:1 mass ratio. The photoinitiator was ethyl 2,4,6-trimethylbenzoylphenylphosphonate (CAS No. 84434-11-7, TPOL, purchased from Sigma-Aldrich, 99% purity). Environmentally friendly solvent system: Prepared by mixing propylene glycol monomethyl ether acetate (CAS No.: 108-65-6, PMA, purchased from Sinopharm Chemical Reagent Co., Ltd., analytical grade) and cyclohexanone (CAS No.: 108-94-1, CYC, purchased from Sinopharm Chemical Reagent Co., Ltd., analytical grade) at a mass ratio of 50:50. Polycarbonate nano-corrugated structure template: A polycarbonate film with an average corrugation period of 500 nm (purchased from Teijin, Japan, density approximately 1.2 g / cm³) was used. 3 The Vicat softening point is approximately 154°C, the tensile modulus is approximately 2300 MPa, and the elongation at break exceeds 100% (PC-1152 from the Panlite® series).

[0023] Example 1 (Preferred Embodiment) Preparation: Weigh 2.0g of nanofiller A, 5.0g of PI-A, 3.0g of BCB-Si, 0.5g of mercapto-olefin crosslinking network builder, 0.1g of photoinitiator, and 0.2g of polycarbonate nano-corrugated structure template as shown in Table 1. Add the above components to 10.0g of an environmentally friendly solvent system (PMA:CYC = 5:5 mass ratio). First, premix at 800rpm for 30 minutes in a planetary mixer, then disperse at 15000rpm for 30 minutes in a high-shear disperser (IKAT25 digital Ultra-Turrax). Subsequently, grind using a three-roll mill (roller spacing set to 10μm, grinding 3 times). After grinding, place the resulting slurry in a vacuum degassing machine and degas at -0.08MPa vacuum for 30 minutes to obtain the photoresist slurry. Coating and Curing: The prepared photoresist paste was coated onto the pretreated silicon wafer using a spin coater (KW-4A type, Institute of Microelectronics, Chinese Academy of Sciences). Spin coating parameters were set to 2000 rpm for 20 seconds, forming a coating approximately 3 μm thick. The coating was pre-baked on a hot plate at 80°C for 5 minutes to remove most of the solvent. Subsequently, it was coated at a wavelength of 365 nm and an intensity of 75 mW / cm². 2Pre-exposed under ultraviolet light for 15 seconds. Finally, the exposed coating was placed in a vacuum oven for low-temperature baking. The baking procedure was as follows: first, it was held at 140℃ for 2 hours, then the temperature was increased to 180℃ at a rate of 2℃ / min, and held at this temperature for 2 hours to obtain a cured low-temperature curable photoresist composition film, the infrared spectrum of which is shown below. Figure 1 As shown.

[0024] Example 2 differs from Example 1 only in the amount of each component, spin coating time, UV exposure intensity, pre-baking temperature, and hot-baking heating rate. See Table 1 for the formulation of Example 2. Preparation: The amounts of each component are shown in Table 1. The mixing, dispersion, grinding, and degassing processes are the same as in Example 1. Coating and Curing: Spin coating parameters are set to 1500 rpm for 25 seconds to form a coating approximately 4 μm thick. Pre-baking is performed on a hot plate at 90°C for 4 minutes. The coating is then cured at a wavelength of 365 nm and an intensity of 50 mW / cm². 2 Pre-expose under ultraviolet light for 20 seconds. The hot baking program is as follows: hold at 140℃ for 2 hours, then increase the temperature to 180℃ at a rate of 1.5℃ / min and hold for 2 hours.

[0025] Example 3 differs from Example 1 only in the amount of each component, spin coating time, UV exposure intensity, pre-baking temperature, and hot-baking heating rate. See Table 1 for the formulation of Example 3. Preparation: The amounts of each component are shown in Table 1. The mixing, dispersion, grinding, and degassing processes are the same as in Example 1. Coating and Curing: Spin coating parameters are set to 2500 rpm for 15 seconds to form a coating approximately 2 μm thick. Pre-baking is performed on a hot plate at 70°C for 6 minutes. The coating is then cured at a wavelength of 365 nm and an intensity of 100 mW / cm². 2 Pre-expose under ultraviolet light for 10 seconds. The hot baking program is as follows: hold at 140℃ for 2 hours, then increase the temperature to 180℃ at a rate of 2.5℃ / min and hold for 2 hours.

[0026] Example 4 differs from Example 1 only in the amount of each component, spin coating time, UV exposure intensity, pre-baking temperature, and hot-baking heating rate. See Table 1 for the formulation of Example 4. Preparation: The amounts of each component are shown in Table 1. The mixing, dispersion, grinding, and degassing processes are the same as in Example 1. Coating and Curing: Spin coating parameters are set to 2200 rpm for 18 seconds to form a coating with a thickness of approximately 2.5 μm. Pre-baking is performed on a hot plate at 85°C for 4.5 minutes. The coating is then cured at a wavelength of 365 nm and an intensity of 80 mW / cm². 2 Pre-expose under ultraviolet light for 12 seconds. The hot baking program is as follows: hold at 140℃ for 2 hours, then increase the temperature to 180℃ at a rate of 1.8℃ / min and hold for 2 hours.

[0027] Comparative Example 1 (lacking nanofiller) differs from Example 1 only in that nanofiller A is missing. Preparation and coating / curing: Except for the amount of nanofiller A being 0g, the amounts of other components, preparation, and coating / curing parameters are the same as in Example 1.

[0028] Comparative Example 2 (lacking photosensitive polyimide resin) differs from Example 1 only in that it lacks PI-A. Preparation and coating / curing: Except for the amount of PI-A being 0g, the amounts of other components, preparation, and coating / curing parameters are the same as in Example 1.

[0029] Comparative Example 3 (without benzocyclobutenyl silicone oligomer) differs from Example 1 only in that it lacks BCB-Si. Preparation and coating / curing: Except for the amount of BCB-Si being 0g, the amounts of other components, preparation, and coating / curing parameters were the same as in Example 1.

[0030] Comparative Example 4 (lacking the thiol-olefin crosslinking network building agent) differs from Example 1 only in that it lacks the thiol-olefin crosslinking network building agent. Preparation and coating / curing: Except for the amount of the thiol-olefin crosslinking network building agent being 0g, the amounts of other components, preparation, and coating / curing parameters are the same as in Example 1.

[0031] Comparative Example 5 (without photoinitiator) differs from Example 1 only in that it lacks the photoinitiator. Preparation and coating / curing: Except for the amount of photoinitiator (0g), the amounts of other components, preparation, and coating / curing parameters are the same as in Example 1.

[0032] Comparative Example 6 (lacking the polycarbonate nano-corrugated structure template) differs from Example 1 only in that it lacks the polycarbonate nano-corrugated structure template. Preparation and coating / curing: Except for the amount of polycarbonate nano-corrugated structure template being 0g, the amounts of other components, preparation, and coating / curing parameters are the same as in Example 1.

[0033] Test Methods and Results: Curing Temperature Test: The photoresist paste was tested using differential scanning calorimetry (DSC, model: TA Instruments DSC2500). Approximately 5 mg of paste sample was placed in an aluminum crucible, and the temperature was increased from 30°C to 300°C at a rate of 10°C / min. The exothermic peak onset temperature was recorded as the curing initiation temperature, and the peak temperature was recorded as the maximum curing rate temperature. Resolution Test: The photoresist paste was spin-coated onto a silicon wafer to form a film approximately 3 μm thick. After UV exposure (365 nm), contact exposure was performed using a mask (with patterns of different linewidths), followed by development with PMD-350 developer (purchased from Sigma-Aldrich) for 60 seconds. The developed pattern was observed using a scanning electron microscope (SEM, model: Zeiss Gemini SEM500), and the smallest linewidth that could be clearly resolved was recorded as the resolution. Dielectric constant (Dk) and dielectric loss (Df) tests: The cured photoresist film was peeled off to prepare thin film samples with a diameter of 20 mm and a thickness of approximately 3 μm. The dielectric constant and dielectric loss of the samples were measured at a frequency of 1 MHz using a dielectric constant meter (model: Agilent E4991B). The tests were conducted at 25°C and 50% relative humidity. Adhesion test: Referring to ASTM D3359 standard, a 10x10 grid with a spacing of 1 mm was etched on the cured photoresist film using a cross-cut tester (model: QFH-HG600, Tianjin Jingke). Pressure-sensitive adhesive tape was adhered to the grid area and quickly torn off at a 60° angle. The film residue in the grid area after tearing was rated (5B is the best, 0B is the worst). Bending cycle life test: The cured photoresist film was prepared into strip samples of 10 mm × 50 mm, with a thickness of approximately 3 μm. The sample was fixed on a bending stage with a radius of 5 mm using a flexibility tester (model: FlexTester-3000, Instron, USA) and bent at a rate of 10 times / minute. The number of bends required for the sample to crack or break was recorded.

[0034] Table 2 Performance test results of low-temperature curing photoresist compositions

[0035] As can be seen from the test results in Table 2, the low-temperature curing photoresist compositions prepared in Examples 1-4 of this invention all exhibit excellent comprehensive performance. Their curing initiation temperatures are all between 140-150℃, far lower than the 200-300℃ curing temperature of traditional polyimide photoresists, achieving low-temperature curing. Simultaneously, the resolution reaches approximately 5μm, with low dielectric constant and dielectric loss (Dk<3.0, Df<0.004), good adhesion, and excellent bending cycle life, indicating their potential application in flexible electronic devices. Comparative Example 1 (lacking nanofiller A) has a higher curing initiation temperature, significantly decreased resolution, increased dielectric constant and dielectric loss, and reduced adhesion and bending cycle life. This indicates that the surface-modified reactive nanofiller (step S1) not only participates in cross-linking network formation through its polymerizable double bonds, reducing the curing temperature, but its nanoscale effect and high surface area also significantly improve the rheological properties and exposure characteristics of the photoresist, thereby enhancing resolution. Meanwhile, the introduction of nanofillers effectively reduced the dielectric constant and dielectric loss, enhanced the mechanical flexibility of the material, and thus improved the bending cycle life. Comparative Example 2 (lacking PI-A) showed a comprehensive deterioration in performance. Resolution decreased significantly, dielectric constant increased, adhesion was poor, and bending life was extremely low. This indicates that the photosensitive polyimide resin matrix (step S2) is the main material of the photoresist composition, and its photosensitive side groups and main chain structure are key to achieving photocrosslinking imaging and imparting excellent heat resistance, mechanical properties, and low dielectric properties to the material. The absence of this component leads to the composition's inability to form a stable film, and the loss of photocuring performance. Comparative Example 3 (lacking BCB-Si) showed an increased photoresist curing initiation temperature, and its resolution, dielectric constant, dielectric loss, adhesion, and bending life were all inferior to the examples. The benzocyclobutene silicone oligomer (step S3), as a low-dielectric resin containing photosensitive double bonds, not only participates in thermal curing at low temperatures through its BCB units, effectively reducing the overall curing temperature, but its silicone structure also significantly improves the material's flexibility and low dielectric properties. The absence of this component reduces the curing efficiency of the composition and affects its dielectric properties and mechanical flexibility. Comparative Example 4 (lacking the thiol-ene crosslinking network builder) failed to form an effective cured film. This means that the thiol-ene crosslinking network builder (the key component in step S4) is crucial for constructing the three-dimensional crosslinked network of the photoresist and achieving rapid low-temperature curing. The thiol-ene click chemistry reaction can occur efficiently and rapidly under the action of a photoinitiator, forming a dense crosslinked network, thereby endowing the photoresist with good mechanical strength and thermal stability. Without this component, the photoresist cannot form a stable crosslinked structure. The photoresist in Comparative Example 5 (lacking the photoinitiator) could not undergo photocuring at all, and could not form images or films. This fully demonstrates that the photoinitiator (the key component in step S4) is an essential component for the photoresist composition to achieve photochemical reactions and induce crosslinking polymerization.Without a photoinitiator, even with photocrosslinkable groups, free radicals cannot be formed under ultraviolet light to initiate polymerization. The photoresist in Comparative Example 6 (lacking the polycarbonate nano-corrugated structure template) showed a significant decrease in resolution, adhesion, and flexural life. This indicates that the added polycarbonate nano-corrugated structure template plays a crucial auxiliary role in the photoresist slurry dispersion stage. This template may optimize the imaging accuracy and mechanical properties of the final film by inducing the ordered arrangement of the photoresist slurry at the interface or by forming micro / nano structures during curing. In summary, this invention achieves low-temperature curing, high resolution, low dielectric constant, excellent adhesion, and flexibility in photoresist compositions by preparing surface-modified reactive nanofillers in step S1, synthesizing soluble photosensitive polyimide resin in step S2, synthesizing low-dielectric benzocyclobutene silicone oligomers containing photosensitive double bonds in step S3, and synergistically combining a mercapto-olefin crosslinking network builder and a photoinitiator in step S4. Each technical feature introduced has a clear technical purpose, and their synergistic effect forms the basis for the excellent performance of the photoresist composition of this invention. In particular, the indispensability of key components (nanofillers, photosensitive polyimide resin, benzocyclobutene silicone oligomer, mercapto-olefin crosslinking network builder, and photoinitiator) and the reasonable limitation of key parameters (such as curing conditions, solvent system, and nanotemplate) are crucial to achieving the technical effects of this invention.

Claims

1. A method for preparing a low-temperature curing photoresist composition, characterized in that: S1. Preparation of surface-modified reactive nanofillers: Silicon-based and aluminum-based precursors are organically functionalized, then mixed with graphene oxide, silver nanowires, and carbon nanotubes in a mass ratio. Surface modification is performed using a coupling agent under an ultrasonic field to obtain a nanofiller composite with polymerizable double bonds on the surface. S2. Synthesis of photosensitive polyimide resin matrix: Asymmetric bio-based diamine monomers, diamine monomers with nitrogen-containing heterocyclic main chains, and fluorine-free dianhydrides and end-capping agents are polycondensed and chemically imidized in a mass ratio to obtain a soluble photosensitive polyimide resin. S3. Synthesis of benzocyclobutene-based silicone oligomers: Bromobenzocyclobutene is converted into an acrylate derivative, reacted with bisbenzocyclobutene-bisdivinylsiloxane in a mass ratio, and end-capped with glycidyl methacrylate to obtain a low-dielectric resin containing photosensitive double bonds. S4. The components obtained in steps S1 to S3, along with the synergistic mercapto-olefin crosslinking network builder and photoinitiator, are dispersed in an environmentally friendly solvent system at a mass ratio. After high-shear dispersion and grinding, the mixture is degassed, coated, exposed to ultraviolet light, and baked at low temperature to obtain the low-temperature curing photoresist composition.

2. The method for preparing the low-temperature curing photoresist composition according to claim 1, characterized in that: In step S1, the surface-modified reactive nanofiller is made from the following components in parts by weight: 15-35 parts of reactive mixed silica nanoparticles, 10-25 parts of reactive mixed alumina nanoparticles, 5-15 parts of graphene oxide with an oxidation degree of 40-60%, 1-5 parts of silver nanowires, and 2-8 parts of carbon nanotubes; the coupling agent used for surface modification is a composite of γ-methacryloyloxypropyltrimethoxysilane and isopropyltris(dioctyl pyrophosphate) titanate in a specified mass ratio.

3. The method for preparing the low-temperature curing photoresist composition according to claim 1, characterized in that: In step S2, the asymmetric bio-based diamine monomer is 4-aminophenyl-4-aminobenzoate; the fluorine-free dianhydride is 3,3',4,4'-benzophenone tetracarboxylic dianhydride.

4. The method for preparing the low-temperature curing photoresist composition according to claim 1, characterized in that: In step S2, the diamine monomer with a nitrogen-containing heterocyclic main chain is 4,4'-(piperazine-1,4-diyl)diphenylamine; its added mass accounts for 5% to 10% of the total mass of the diamine monomer.

5. The method for preparing the low-temperature curing photoresist composition according to claim 1, characterized in that: In step S3, the preparation parameters of the benzocyclobutene-based silicone oligomer are as follows: using palladium acetate and tri-o-tolylphosphine as catalysts, 4-bromobenzocyclobutene is coupled with acrylic acid to generate a carboxyl-containing precursor, which is then reacted with bisbenzocyclobutene-bisdivinylsiloxane at 150-170°C at a mass ratio of 1:1 for 50-70 hours. The reaction solvent is dipropylene glycol methyl ether acetate.

6. The method for preparing the low-temperature curing photoresist composition according to claim 1, characterized in that: In step S4, the mercapto-olefin crosslinking network building agent is composed of pentaerythritol tetrakis(3-mercaptopropionic acid) and 2,4,6-trienylpropoxy-1,3,5-triazine in a mass ratio of 1:1, and the photoinitiator is ethyl 2,4,6-trimethylbenzoylphenylphosphonate.

7. The method for preparing the low-temperature curing photoresist composition according to claim 1, characterized in that: In step S4, the environmentally friendly solvent system is composed of propylene glycol monomethyl ether acetate and cyclohexanone in a mass ratio of 40:60 to 60:40, and does not contain N-methylpyrrolidone.

8. The method for preparing the low-temperature curing photoresist composition according to claim 1, characterized in that: The film formation and curing parameters for step S4 are limited to: spin coating at 1000-3000 rpm for 10-30 seconds to form a coating with a thickness of 1-5 μm, followed by curing at a wavelength of 365 nm and an intensity of 50-100 mW / cm. 2 Pre-expose under ultraviolet light for 10-20 seconds, and then keep at 140℃ for 2 hours. Then raise the temperature to 180℃ at a rate of 1-3℃ / min and keep it there for 2 hours.

9. The method for preparing the low-temperature curing photoresist composition according to claim 1, characterized in that: In step S4, during the photoresist slurry dispersion stage, an additional 0.5-3% of a polycarbonate nano-corrugated structure template, accounting for the total mass of the slurry, is added.

10. A low-temperature curing photoresist composition, characterized in that, The low-temperature curing photoresist composition is obtained by the preparation method according to any one of claims 1-9.

Images