A polyimide material and its preparation method

Abstract

This invention relates to a polyimide material and its preparation method, belonging to the field of polymer materials technology. The invention uses a macromolecular diamine monomer containing PEG segments and 4,4'-diaminodiphenyl ether as a compounded diamine monomer, reacting it with a dianhydride monomer compounded with 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride and 3,3',4,4'-biphenyl tetracarboxylic dianhydride to prepare a polyimide with carboxyl groups in its side chains. Then, the polyimide with carboxyl groups in its side chains is grafted with a photosensitive compound to prepare a photosensitive polyimide material. The PEG-based macromolecular diamine provides excellent solubility, film-forming properties, and low-temperature flexibility; the rigid aromatic diamine improves mechanical strength, thermal stability, and pattern fidelity; the ether-bonded ODPA ensures solubility and uniform crosslinking; and the biphenyl-type BPDA increases modulus, reduces water absorption, and improves resolution.

Description

Technical Field

[0001] This invention relates to a polyimide material and its preparation method, belonging to the field of polymer materials technology. Background Technology

[0002] Polyimide (PI), as a high-performance polymer material, possesses excellent high-temperature resistance, mechanical strength, dielectric properties, and chemical stability, and has been widely used in microelectronics, aerospace, flexible electronics, and other fields. Among them, photosensitive polyimide (PSPI) combines the excellent comprehensive properties of polyimide with its photosensitive characteristics. It can be directly patterned through photolithography processes such as ultraviolet light exposure and development, without the need for additional etching steps. This significantly simplifies the fabrication process of microelectronic devices, reduces production costs, and has become one of the core materials in the field of microelectronics processing.

[0003] Photosensitive polyimides can be divided into two categories based on their development mechanism: positive and negative. Negative photosensitive polyimides, due to the formation of an insoluble cross-linked network after exposure, have high development contrast and better pattern fidelity, making them more suitable for the preparation of high-precision microelectronic patterns. They have irreplaceable advantages in the manufacture of integrated circuits, flexible circuit boards, sensors, and other devices.

[0004] Currently, existing methods for preparing negatively photosensitive polyimides mainly involve introducing photopolymerizable photosensitive groups (such as acrylate groups and styrene groups) into the polyimide molecular chain. Ultraviolet light irradiation causes these photosensitive groups to undergo polymerization and cross-linking reactions, creating a difference in solubility between the exposed and unexposed areas, thereby achieving patterning. However, existing negatively photosensitive polyimide materials still face many technical bottlenecks, making it difficult to meet the demands of high-precision microelectronic processing. (1) The problem of balancing solubility and film formation: Polyimide molecular chains are relatively rigid and usually have poor solubility. To improve solubility, existing technologies often introduce flexible segments into the molecular chain. However, the introduction of flexible segments often leads to a decrease in the rigidity and thermal stability of the material, and may also increase the water absorption rate of the material, affecting the dimensional stability after patterning. If there are insufficient flexible segments, the material will have poor solubility and uneven film formation, which will lead to an increase in exposure dose and development difficulties during the photolithography process, and an increase in the roughness of the pattern edge.

[0005] (2) Insufficient synergy between photosensitivity and overall performance: Existing technologies often employ grafting of a single photosensitizing group or polymerization of a single diamine or dianhydride monomer, making it difficult to achieve synergistic optimization of key indicators such as photosensitivity, pattern resolution, film thickness retention, and water absorption. For example, some materials have high photosensitivity but low pattern resolution and large line edge roughness; some materials have high rigidity and low water absorption but poor solubility and excessive exposure dose, failing to meet both high-precision photolithography and practical application requirements.

[0006] (3) Poor photocrosslinking efficiency and stability: Some photosensitive groups (such as acrylate groups, N-hydroxymethylacrylamide, etc.) are unstable in activity during reaction or storage, and are prone to premature polymerization or crosslinking failure, resulting in a decrease in the photolithography performance of the material; at the same time, the photocrosslinking efficiency of a single photosensitive group is limited, making it difficult to quickly form a dense crosslinking network, resulting in insufficient film thickness retention in the exposure area, and defects such as film layer erosion and linewidth loss during development.

[0007] (4) Lack of synergistic design of compound system: Although existing technologies have attempted to introduce flexible segments or different photosensitive groups, they have not formed a synergistic design of "flexible-rigid" diamine compound and "solubility-size stability" dianhydride compound, which cannot give full play to the advantages of different monomers, making it difficult to break through the comprehensive performance of the material and lacking creativity.

[0008] Therefore, addressing the problems of imbalance between solubility and film-forming properties, insufficient synergy between photosensitivity and overall performance, low photocrosslinking efficiency, and poor pattern resolution and dimensional stability in existing negative photosensitive polyimide materials, it is of great practical significance and industrial application value to develop a negative photosensitive polyimide material and its preparation method that combines excellent film-forming properties, high photosensitivity, high resolution, and low water absorption through monomer compounding and synergistic optimization. This is also a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0009] The purpose of this invention is to provide a polyimide material and its preparation method to solve the problems of unbalanced solubility and film-forming properties, poor pattern resolution and dimensional stability of existing negative photosensitive polyimide materials.

[0010] This invention provides a method for preparing a polyimide material, comprising the following steps: (1) A mixture of bipolar acyl chloride polyethylene glycol and 3,5-diaminobenzoic acid in a solvent at a molar ratio of 1:2 is reacted to obtain a macromolecular diamine monomer; the number average molecular weight of the bipolar acyl chloride polyethylene glycol is 400~4000. (2) A polyamic acid solution is obtained by mixing and reacting a macromolecular diamine monomer, 4,4'-diaminodiphenyl ether, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride in a solvent; then a dehydrating agent and a catalyst are added to the polyamic acid solution to carry out an imidization reaction to obtain a polyimide with carboxyl groups in the side chain; the molar ratio of the macromolecular diamine monomer to 4,4'-diaminodiphenyl ether is 7~9:1~3; the molar ratio of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride to 3,3',4,4'-biphenyltetracarboxylic dianhydride is 2~4:1~3; the total molar amount of the macromolecular diamine monomer and 4,4'-diaminodiphenyl ether is equal to the total molar amount of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride; (3) A polyimide with carboxyl groups on its side chain and a photosensitive compound are mixed and reacted in a solvent under the action of a carboxyl activator to obtain a polyimide material; the photosensitive compound is hydroxyethyl methacrylate or p-aminostyrene; the molar ratio of the carboxyl group in the polyimide with carboxyl groups on its side chain to the molar ratio of the photosensitive compound is 0.8~1:1.

[0011] Preferably, the number-average molecular weight of the di-terminated acyl chloride polyethylene glycol is 800-1000.

[0012] Preferably, the method for mixing and reacting bi-terminated acyl chloride polyethylene glycol with 3,5-diaminobenzoic acid in a solvent is as follows: an anhydrous N-methylpyrrolidone solution of 3,5-diaminobenzoic acid is added dropwise to an anhydrous N-methylpyrrolidone solution of bi-terminated acyl chloride polyethylene glycol at 0-5°C, and then the temperature is raised to 25-30°C to continue the mixing reaction. After precipitation, washing, and drying, a macromolecular diamine monomer is obtained; the dropping rate is 15-20 drops / min; the mixing reaction is continued for 8-10 hours; anhydrous diethyl ether is used for precipitation.

[0013] Preferably, the method for mixing and reacting the macromolecular diamine monomer, 4,4'-diaminodiphenyl ether, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride, and 3,3',4,4'-biphenyltetracarboxylic dianhydride in a solvent is as follows: 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride are added in three portions to a mixture of the macromolecular diamine monomer, 4,4'-diaminodiphenyl ether, and anhydrous N-methylpyrrolidone, and then the mixture is reacted at room temperature for 12-15 hours; the interval between the three additions is 15-20 minutes.

[0014] Preferably, the dehydrating agent is acetic anhydride and the catalyst is pyridine.

[0015] Preferably, the imidization reaction is carried out at a temperature of 100-110°C for 6-8 hours.

[0016] Preferably, after the imidization reaction is completed, the polyimide with carboxyl groups in the side chain is obtained by precipitation, washing, and drying; the precipitate is made of anhydrous ethanol.

[0017] Preferably, the photosensitive compound is hydroxyethyl methacrylate, and the carboxyl activator is composed of 4-dimethylaminopyridine and N,N'-dicyclohexylcarbodiimide; the photosensitive compound is p-aminostyrene, and the carboxyl activator is composed of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide.

[0018] Preferably, the mixing reaction in step (3) is carried out in the dark for 24-28 hours.

[0019] A polyimide material prepared by a method described above.

[0020] The beneficial effects of this invention are as follows: This invention uses a macromolecular diamine monomer containing PEG segments and 4,4'-diaminodiphenyl ether as a compound diamine monomer, and reacts it with a dianhydride monomer compounded with 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride and 3,3',4,4'-biphenyl tetracarboxylic dianhydride to prepare a polyimide with carboxyl groups in the side chain. Then, the polyimide with carboxyl groups in the side chain is grafted with a photosensitive compound to prepare a photosensitive polyimide material. Introducing PEG segments of a specific molecular weight into the main chain can achieve good solubility and film uniformity of the material. PEG-based macromolecular diamines provide excellent solubility, film-forming properties and low-temperature flexibility. Rigid aromatic diamines (ODA) improve mechanical strength, thermal stability and pattern fidelity. Ether-bonded ODPA ensures solubility and crosslinking uniformity. Biphenyl-type BPDA improves modulus, reduces water absorption and improves resolution. The synergistic effect of these four components enables the material to simultaneously achieve optimal performance in terms of exposure sensitivity, pattern resolution, line edge roughness, and water absorption, resulting in comprehensive properties that cannot be achieved by a single component, demonstrating a significant synergistic effect. This invention, through synergistic optimization of the flexibility of the polyimide backbone (PEG segments) and the photoreactive groups of the side chains, successfully obtained a negatively photosensitive polyimide material that combines excellent film-forming properties, high photosensitivity, and high resolution, possessing extremely high application value in the field of microelectronics processing. Detailed Implementation

[0021] The following examples are intended to further illustrate the content of the present invention, rather than to limit the scope of protection of the present invention. Example

[0022] The preparation method of the polyimide material in this embodiment includes the following steps: (1) In a 250 mL three-necked flask equipped with a mechanical stirrer, a constant pressure dropping funnel and a nitrogen protection device, add 5.0 mmol of di-terminated acyl chloride polyethylene glycol (Mn=1000) with a number average molecular weight of 1000 and 30 mL of anhydrous N-methylpyrrolidone, and cool to 0 °C in an ice-water bath; prepare a solution by mixing 10.0 mmol of 3,5-diaminobenzoic acid with 15 mL of anhydrous N-methylpyrrolidone, and then slowly drip the solution through a constant pressure dropping funnel. The solution was added to a three-necked flask at a dropping rate of 20 drops / min, maintaining the reaction temperature at 0°C. After the addition was complete, the ice bath was removed, the temperature was raised to 30°C, and the reaction was stirred for another 8 hours. After the reaction was complete, the reaction solution was slowly added dropwise to 500 mL of anhydrous diethyl ether to precipitate a pale yellow solid. The solid was filtered, and the filter cake was washed three times with diethyl ether. The washed solid was then vacuum dried at 40°C for 12 hours to obtain a macromolecular diamine monomer with a yield of 92.3%. The chemical structure of the macromolecular diamine monomer is as follows: .

[0023] (2) Under nitrogen protection, 2.25 mmol of macromolecular diamine monomer, 0.25 mmol of 4,4'-diaminodiphenyl ether and 25 mL of anhydrous N-methylpyrrolidone were added to a dry 100 mL three-necked flask. The mixture was stirred until the macromolecular diamine monomer was completely dissolved. Then, a mixture of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride and 3,3',4,4'-biphenyl tetracarboxylic dianhydride was added in three portions. The total amount of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride added was 2.0 mmol, and the total amount of 3,3',4,4'-biphenyl tetracarboxylic dianhydride added was 0.5 mmol. The mixture was added every 15 min. After the mixture of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride and 3,3',4,4'-biphenyl tetracarboxylic dianhydride was added, the mixture was stirred at room temperature for 12 h to obtain a viscous polyamic acid (PAA) solution.

[0024] 4.5 mL of acetic anhydride and 2.0 mL of pyridine were added sequentially to a polyamic acid (PAA) solution. The mixture was stirred at room temperature for 30 min, then heated to 100 °C and stirred for another 8 h. After the reaction was complete, the reaction solution was cooled to room temperature and then slowly added dropwise to 500 mL of anhydrous ethanol to precipitate the solid. The solid was filtered, and the filter cake was washed three times with ethanol. The washed filter cake was then vacuum dried at 60 °C for 12 h to obtain polyimide with carboxyl side chains. The yield was 88.5%. The GPC test results (with PS as the standard) were as follows: Mw = 48200, PDI = 1.72.

[0025] (3) Add 2.1 mmol of carboxyl-containing polyimide with side chain carboxyl groups and 30 mL of anhydrous N-methylpyrrolidone to a three-necked flask and stir until the carboxyl-containing polyimide with side chain carboxyl groups is fully dissolved. Then add 0.5 mmol of 4-dimethylaminopyridine and 2.3 mmol of N,N'-dicyclohexylcarbodiimide and activate the carboxyl groups for 30 min in an ice-water bath. Then slowly add the photosensitive compound solution obtained by dissolving 2.3 mmol of photosensitive compound (hydroxyethyl methacrylate) in 30 mL of anhydrous N-methylpyrrolidone to the three-necked flask. After the addition is complete, remove the ice bath and stir the reaction for 24 h in the dark and at a temperature of 25 °C. After the reaction is complete, filter to remove insoluble matter. Slowly add the filtrate to 500 mL of anhydrous ethanol to precipitate. Filter the precipitate and wash the filter cake three times with ethanol. Dry the washed solid under vacuum at 40 °C for 12 h to obtain polyimide material with a yield of 85.2%. Example

[0026] The difference between the preparation method of the polyimide material in this embodiment and the preparation method of the polyimide material in Example 1 is that step (3) of the preparation method of the polyimide material in this embodiment is as follows: Add 2.1 mmol of carboxyl-containing polyimide with side chains and 30 mL of anhydrous N-methylpyrrolidone to a three-necked flask, stir until the carboxyl-containing polyimide with side chains is fully dissolved, then add 2.3 mmol of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and 2.3 mmol of N-hydroxysuccinimide, and activate the carboxyl groups for 60 mL in an ice-water bath. Then, the photosensitive compound solution obtained by dissolving 2.3 mmol of the photosensitive compound (p-aminostyrene) in 30 mL of anhydrous N-methylpyrrolidone was slowly added dropwise to a three-necked flask. After the addition was complete, the ice bath was removed, and the reaction was stirred for 24 h under light-protected conditions and at a temperature of 25 °C. After the reaction was completed, the reaction solution was cooled to room temperature, and the insoluble matter was removed by filtration. The filtrate was slowly added dropwise to 500 mL of anhydrous ethanol, and a precipitate was formed. The precipitate was filtered, and the filter cake was washed three times with anhydrous ethanol. The washed solid was vacuum dried at 40 °C for 12 h to obtain the photosensitive polyimide material with a yield of 83.7%. Example

[0027] The difference between the preparation method of the polyimide material in this embodiment and the preparation method of the polyimide material in Example 1 is that the number average molecular weight of the double-terminated acyl chloride polyethylene glycol in step (1) of the preparation method of the polyimide material in this embodiment is 400, and the Mw of the polyimide with carboxyl side chain prepared in this embodiment is 36500. Example

[0028] The difference between the preparation method of the polyimide material in this embodiment and the preparation method of the polyimide material in Example 1 is that the number average molecular weight of the double-terminated acyl chloride polyethylene glycol in step (1) of the preparation method of the polyimide material in this embodiment is 600, and the Mw of the polyimide with carboxyl side chain prepared in this embodiment is 42100. Example

[0029] The difference between the preparation method of the polyimide material in this embodiment and the preparation method of the polyimide material in Example 1 is that the number average molecular weight of the double-terminated acyl chloride polyethylene glycol in step (1) of the preparation method of the polyimide material in this embodiment is 2000, and the Mw of the polyimide with carboxyl side chain prepared in this embodiment is 52300. Example

[0030] The difference between the preparation method of the polyimide material in this embodiment and the preparation method of the polyimide material in Example 1 is that the number average molecular weight of the double-terminated acyl chloride polyethylene glycol in step (1) of the preparation method of the polyimide material in this embodiment is 4000, and the Mw of the polyimide with carboxyl side chain prepared in this embodiment is 61800.

[0031] Comparative Example 1 The only difference between the preparation method of the polyimide material in this comparative example and the preparation method of the polyimide material in Example 1 is that in step (2) of the preparation method of the polyimide material in this comparative example, the macromolecular diamine monomer is replaced with 3,5-diaminobenzoic acid.

[0032] Comparative Example 2 The difference between the preparation method of the polyimide material in this comparative example and the preparation method of the polyimide material in Example 1 is that step (3) is omitted in the preparation method of the polyimide material in this comparative example. That is, the polyimide material prepared by the preparation method of the polyimide material in this comparative example is the polyimide with carboxyl side chain prepared by step (2) in Example 1.

[0033] Comparative Example 3 The only difference between the preparation method of the polyimide material in this comparative example and the preparation method of the polyimide material in Example 1 is that in step (3) of the preparation method of the polyimide material in this comparative example, hydroxyethyl methacrylate is replaced with hydroxyethyl acrylate.

[0034] Comparative Example 4 The only difference between the preparation method of the polyimide material in this comparative example and the preparation method of the polyimide material in Example 1 is that in step (3) of the preparation method of the polyimide material in this comparative example, hydroxyethyl methacrylate is replaced with pentaerythritol triacrylate.

[0035] Comparative Example 5 The difference between the preparation method of the polyimide material in this comparative example and the preparation method of the polyimide material in Example 1 is that in step (3) of the preparation method of the polyimide material in this comparative example, hydroxyethyl methacrylate is replaced with 4-hydroxybutyl acrylate.

[0036] Comparative Example 6 The difference between the preparation method of the polyimide material in this comparative example and the preparation method of the polyimide material in Example 1 is that in step (3) of the preparation method of the polyimide material in this comparative example, hydroxyethyl methacrylate is replaced with 2-hydroxypropyl methacrylate.

[0037] Comparative Example 7 The only difference between the preparation method of the polyimide material in this comparative example and the preparation method of the polyimide material in Example 1 is that in step (3) of the preparation method of the polyimide material in this comparative example, hydroxyethyl methacrylate is replaced with N-hydroxymethylacrylamide.

[0038] Comparative Example 8 The difference between the preparation method of the polyimide material in this comparative example and the preparation method of the polyimide material in Example 1 is that the amount of macromolecular diamine monomer used in step (2) of the preparation method of the polyimide material in this comparative example is 2.5 mmol, and the amount of 4,4'-diaminodiphenyl ether used is 0 mmol.

[0039] Comparative Example 9 The difference between the preparation method of the polyimide material in this comparative example and the preparation method of the polyimide material in Example 1 is that the amount of macromolecular diamine monomer used in step (2) of the preparation method of the polyimide material in this comparative example is 0 mmol, and the amount of 4,4'-diaminodiphenyl ether used is 2.5 mmol.

[0040] Comparative Example 10 The difference between the preparation method of the polyimide material in this comparative example and the preparation method of the polyimide material in Example 1 is that the total amount of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride added in step (2) of the preparation method of the polyimide material in this comparative example is 2.5 mmol, and the total amount of 3,3',4,4'-biphenyl tetracarboxylic dianhydride added is 0 mmol.

[0041] Comparative Example 11 The difference between the preparation method of the polyimide material in this comparative example and the preparation method of the polyimide material in Example 1 is that the total amount of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride added in step (2) of the preparation method of the polyimide material in this comparative example is 0 mmol, and the total amount of 3,3',4,4'-biphenyl tetracarboxylic dianhydride added is 2.5 mmol.

[0042] Experimental Example To investigate the photosensitivity of the polyimide materials prepared in each example and comparative example, 2.00g of the polyimide materials prepared in each example and comparative example were dissolved in 8.00g of cyclopentanone to prepare a 20wt% solution. Then, 0.06g of photoinitiator Irgacure 651 (benzoyl dimethyl ketal) was added, and the mixture was stirred in the dark for 2h. After filtration through a 0.45μm polytetrafluoroethylene filter membrane, the photosensitizing resin composition was obtained.

[0043] The prepared photosensitive resin composition was spin-coated onto a 4-inch silicon wafer treated with hexamethyldisilazane (HMDS). After pre-baking at 100°C for 3 min, a photosensitive coating with a thickness of 4.5 μm was obtained. Exposure was performed using an i-line (365 nm) exposure machine through a linewidth test mask. After exposure, the coating was back-baked at 110°C for 2 min, followed by development with a 2.38 wt% tetramethylammonium hydroxide (TMAH) aqueous solution for 60 s. The coating was rinsed with deionized water and dried with nitrogen. The developed pattern was then observed using an electron microscope. The film thickness retention rate in the exposed area, pattern resolution (expressed as the minimum clearly resolvable linewidth / spacing), and line edge roughness (LER) were tested. The minimum exposure dose was also recorded. The results are shown in Table 1. The film thickness retention rate in the exposed area = (film thickness in the exposed area after development / initial film thickness) × 100%, reflecting the polymer's resistance to dissolution in the developer; a higher value indicates better development contrast. The minimum exposure dose refers to the minimum exposure energy required to clearly resolve a 5 μm L / S pattern.

[0044] Finally, the photosensitive polyimide materials of each embodiment and comparative example were prepared into a 20wt% cyclopentanone solution, spin-coated onto a silicon wafer, pre-baked at 100℃ for 3 min, and then baked at 110℃ for 2 min. The resulting dry film samples, measuring 20 mm × 20 mm and 4.5 μm in thickness, were then peeled off. Three samples were prepared in parallel for each group, and the average value was calculated after the experiment. The prepared dry film samples were then subjected to water absorption rate testing, and the results are shown in Table 1.

[0045] Table 1 Photolithographic properties of polyimide materials polyimide Film thickness retention rate in the exposed area (%) <![CDATA[Minimum exposure dose (mJ / cm 2 )]]> Graphics resolution (μm) LER(nm) Water absorption rate (%) Example 1 92 200 5 18 0.8 Example 2 90 220 5 25 1.4 Example 3 91 210 5 21 1.3 Example 4 89 200 5 28 1.5 Example 5 85 180 5 35 1.8 Example 6 84 220 5 48 2.3 Comparative Example 1 35 650 10 75 2.1 Comparative Example 2 68 450 5 42 1.6 Comparative Example 3 21 >1000 >20 >100 2.8 Comparative Example 4 76 550 5 90 2.4 Comparative Example 5 65 >1000 >20 >100 2.9 Comparative Example 6 16 >1000 >20 >100 2.7 Comparative Example 7 5 >1500 >20 >100 3.5 Comparative Example 8 85 280 5 35 1.8 Comparative Example 9 70 500 8 60 1.1 Comparative Example 10 88 240 5 28 1.5 Comparative Example 11 82 300 5 40 0.9 As shown in Table 1, the photosensitive polyimide material prepared in this embodiment of the invention has photopolymerizable unsaturated double bonds (such as hydroxyethyl methacrylate, p-aminostyrene, and other photosensitive groups) branched to its sides. Under ultraviolet irradiation, the photosensitive double bonds undergo rapid photoinitiated polymerization and cross-linking reactions, forming a high-density, three-dimensional, insoluble and infusible cross-linked network structure in the exposed area. This cross-linked structure exhibits extremely high stability in alkaline developer, is almost insoluble, does not swell, and is not etched, thus ensuring the complete preservation of the film layer in the exposed area; while the unexposed area does not undergo cross-linking and maintains good alkaline solubility, allowing for effective removal by the developer. Therefore, this embodiment achieves high-contrast patterning with stable preservation of the exposed area and efficient dissolution of the unexposed area, resulting in high pattern fidelity, regular line edges, high film thickness retention, lower minimum exposure dose, and superior pattern resolution.

[0046] The experimental results of Examples 1 and 3-6 show that the PEG molecular weight of 1000 (Example 1) has the best overall performance. If the molecular weight is too low (400, 600), the exposure dose will increase slightly. If the molecular weight is too high (2000, 4000), the hydrophilic chain segment will be too long, causing slight swelling during development and a decrease in the quality of the pattern edge.

[0047] The polyimide prepared in Comparative Example 1 lacks PEG flexible segments, resulting in high material rigidity, poor solubility, and uneven film quality after film formation, leading to a significant increase in exposure dose and difficulty in development.

[0048] The polyimide prepared in Comparative Example 2 contains only carboxyl groups in its side chains and lacks photosensitive groups such as photocrosslinkable unsaturated double bonds. It can only achieve image retention through decarboxylation of the carboxyl groups under light irradiation or weak free radical crosslinking. Due to the low photoreactivity of the carboxyl groups, poor photocrosslinking efficiency, and insufficient crosslinking density, a stable and insoluble crosslinked network structure cannot be quickly formed in the exposed area. This leads to the film layer in the exposed area being easily partially dissolved by the developer during development, resulting in significant linewidth loss, edge burrs, and other defects. Furthermore, due to the low photoreactivity, a higher exposure dose is required to achieve initial image fixation. Therefore, the minimum exposure dose is significantly higher than that of Example 1, which grafted photosensitive groups, resulting in significantly inferior development contrast and pattern formation quality compared to Example 1.

[0049] As can be seen from Example 1 and Comparative Example 3, although the hydroxyethyl methacrylate (HEMA) used in Example 1 and the hydroxyethyl acrylate in Comparative Example 3 have similar structures, the free radicals formed by hydroxyethyl methacrylate are more stable due to the electron-donating effect and steric hindrance effect of α-methyl groups. However, gelation occurred in Comparative Example 3, indicating that the reactivity of acrylates in the system is mismatched, and premature or uncontrollable polymerization may have occurred.

[0050] As can be seen from Example 1 and Comparative Examples 4-5, Comparative Example 4 uses pentaerythritol triacrylate, which, although containing many functional groups, has significant steric hindrance, leading to incomplete cross-linking, resulting in residual substrate and linewidth distortion. Comparative Example 5 uses 4-hydroxybutylacrylate, which has a longer alkyl chain. While it offers some flexibility, this may cause excessive swelling of the film in the developer, resulting in extremely high exposure dose.

[0051] As shown in Examples 1, 2, and Comparative Example 7, Example 2 uses p-aminostyrene linked by amide bonds, and its photosensitivity is comparable to that of the ester-linked HEMA in Example 1 (resolution 5 μm, clear edges), but it has slight burrs and a slightly higher exposure dose, indicating that the ester-linked HEMA has slightly better overall performance in this system. However, the N-hydroxymethylacrylamide in Comparative Example 7 may have unstable N-hydroxymethyl groups under storage or reaction conditions, leading to crosslinking failure and no pattern retention.

[0052] As can be seen from Example 1 and Comparative Examples 8-11, Example 1 uses a PEG-based macromolecular diamine and 4,4'-diaminodiphenyl ether (ODA) as the diamine monomer, and a 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride (ODPA) and 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA) as the dianhydride monomer. Through the synergistic effect of the four, the optimal balance of various performance indicators is achieved, with an exposure area film thickness retention rate of 92% and a minimum exposure dose of only 200 mJ / cm. 2 With a pattern resolution of 5μm, a line edge roughness (LER) as low as 18nm, and a water absorption rate of only 0.8%, the overall performance is significantly better than that of the single monomer system (comparative examples 8-11), fully demonstrating the non-obviousness and synergistic value of the compound system.

[0053] Comparative Example 8 uses only a single PEG-based macromolecular diamine (without ODA). Although it can ensure certain solubility and film-forming properties, and the minimum exposure dose can be maintained within a reasonable range, the lack of rigid aromatic diamine support results in excessive hydrophilicity of the material. This leads to a decrease in film thickness retention in the exposed area to 85%, an increase in LER to 35 nm, an increase in water absorption to 1.8%, slight swelling during development, and a significant decrease in pattern fidelity. This indicates that a single PEG-based macromolecular diamine cannot balance sensitivity and pattern quality.

[0054] Comparative Example 9 used only 4,4'-diaminodiphenyl ether (ODA, a PEG-free macromolecular diamine), which was too rigid, resulting in a significant deterioration in the system's solubility and film uniformity. Its film thickness retention rate in the exposed area was only 70%, and the minimum exposure dose soared to 500 mJ / cm. 2The image resolution dropped to 8μm and the LER reached 60nm. Although the water absorption rate was controlled at 1.1% (better than Comparative Example 8), the photolithography performance could no longer meet the basic requirements of microelectronic processing, highlighting the indispensability of PEG-based macromolecular diamine in improving solubility and reducing exposure dose.

[0055] Comparative Example 10 used only 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride (ODPA, without BPDA). Although the ether bond structure ensured uniform crosslinking, the material modulus and dimensional stability were insufficient, resulting in a decrease in film thickness retention in the exposed area to 88% and an increase in the minimum exposure dose to 240 mJ / cm². 2 With LER increased to 28nm and water absorption rate increased to 1.5%, the overall performance is better than that of comparative examples 8-9, but still significantly worse than that of example 1, indicating that a single ODPA cannot achieve the synergy of high resolution and low water absorption rate.

[0056] Comparative Example 11 used only 3,3',4,4'-biphenyltetracarboxylic dianhydride (BPDA, without ODPA). Although the biphenyl structure effectively reduced water absorption (0.9%, close to Example 1) and improved material rigidity, the decreased solubility led to poorer coating uniformity, resulting in a drop in film thickness retention in the exposed area to 82% and an increase in the minimum exposure dose to 300 mJ / cm². 2 When LER is increased to 40nm, the quality of the pattern edge deteriorates, proving that a single BPDA is difficult to balance solubility and pattern fidelity.

[0057] Based on the data and analysis in Table 1, the polyimide material prepared by this invention exhibits excellent photosensitivity. Firstly, introducing PEG segments with a specific molecular weight (preferably around 1000) into the main chain is crucial for achieving good solubility and film uniformity, effectively avoiding the problems of poor solubility and excessive exposure dose encountered without PEG segments (Comparative Example 1). The PEG chain length needs precise control; too short a length results in insufficient improvement in solubility, while too long a length leads to excessive hydrophilicity and a decline in the quality of the pattern edges.

[0058] Secondly, the structure of the side chain photosensitive group plays a decisive role in photolithography performance. Using methacrylate compounds (such as hydroxyethyl methacrylate) to attach to the side chain via ester bonds (Example 1), compared with other types of olefin monomers (Comparative Examples 3-7), it exhibits the best photocrosslinking activity and stability, achieving low exposure dose, high film thickness retention (92%) and high-fidelity patterns (5μm resolution, steep edges).

[0059] Finally, in the polyimide material prepared by this invention, PEG-based macromolecular diamine provides excellent solubility, film-forming properties, and low-temperature flexibility; rigid aromatic diamine (ODA) enhances mechanical strength, thermal stability, and pattern fidelity; ether-bonded ODPA ensures solubility and crosslinking uniformity; and biphenyl-type BPDA increases modulus, reduces water absorption, and improves resolution. The synergistic effect of these four components enables the material to simultaneously achieve optimal performance in terms of exposure sensitivity, pattern resolution, line edge roughness, and water absorption, achieving comprehensive properties that cannot be achieved by a single component, demonstrating a significant synergistic effect.

[0060] In summary, by synergistically optimizing the flexibility of the polyimide backbone (PEG segment) and the photoreactive groups of the side chains, this invention has successfully obtained a negative photosensitive polyimide material with excellent film-forming properties, high photosensitivity, and high resolution, which has extremely high application value in the field of microelectronics processing.

Claims

1. A method for preparing a polyimide material, characterized in that, Includes the following steps: (1) A mixture of bipolar acyl chloride polyethylene glycol and 3,5-diaminobenzoic acid in a solvent at a molar ratio of 1:2 is reacted to obtain a macromolecular diamine monomer; the number average molecular weight of the bipolar acyl chloride polyethylene glycol is 400~4000. (2) A polyamic acid solution is obtained by mixing and reacting a macromolecular diamine monomer, 4,4'-diaminodiphenyl ether, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride in a solvent; then a dehydrating agent and a catalyst are added to the polyamic acid solution to carry out an imidization reaction to obtain a polyimide with carboxyl groups in the side chain; the molar ratio of the macromolecular diamine monomer to 4,4'-diaminodiphenyl ether is 7~9:1~3; the molar ratio of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride to 3,3',4,4'-biphenyltetracarboxylic dianhydride is 2~4:1~3; the total molar amount of the macromolecular diamine monomer and 4,4'-diaminodiphenyl ether is equal to the total molar amount of 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride; (3) A polyimide with carboxyl groups on its side chain and a photosensitive compound are mixed and reacted in a solvent under the action of a carboxyl activator to obtain a polyimide material; the photosensitive compound is hydroxyethyl methacrylate or p-aminostyrene; the molar ratio of the carboxyl group in the polyimide with carboxyl groups on its side chain to the molar ratio of the photosensitive compound is 0.8~1:

1.

2. The method for preparing the polyimide material according to claim 1, characterized in that, The number-average molecular weight of the di-terminated acyl chloride polyethylene glycol is 800-1000.

3. The method for preparing the polyimide material according to claim 1, characterized in that, The method for mixing and reacting bi-terminated acyl chloride polyethylene glycol with 3,5-diaminobenzoic acid in a solvent is as follows: an anhydrous N-methylpyrrolidone solution of 3,5-diaminobenzoic acid is added dropwise to an anhydrous N-methylpyrrolidone solution of bi-terminated acyl chloride polyethylene glycol at 0-5°C, and then the temperature is raised to 25-30°C to continue the mixing and reaction. After precipitation, washing, and drying, a macromolecular diamine monomer is obtained; the dropping rate is 15-20 drops / min; the mixing and reaction time is continued for 8-10 hours; anhydrous diethyl ether is used for precipitation.

4. The method for preparing the polyimide material according to claim 1, characterized in that, The method for mixing and reacting macromolecular diamine monomer, 4,4'-diaminodiphenyl ether, 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride in a solvent is as follows: 3,3',4,4'-diphenyl ether tetracarboxylic dianhydride and 3,3',4,4'-biphenyltetracarboxylic dianhydride are added in three portions to a mixture of macromolecular diamine monomer, 4,4'-diaminodiphenyl ether and anhydrous N-methylpyrrolidone, and then the mixture is reacted at room temperature for 12-15 hours; the interval between the three additions is 15-20 minutes.

5. The method for preparing the polyimide material according to claim 1, characterized in that, The dehydrating agent is acetic anhydride, and the catalyst is pyridine.

6. The method for preparing the polyimide material according to claim 5, characterized in that, The imidization reaction is carried out at a temperature of 100-110°C for 6-8 hours.

7. The method for preparing the polyimide material according to claim 1, 5, or 6, characterized in that, After the imidization reaction is completed, the product is precipitated, washed, and dried to obtain a polyimide with carboxyl groups in the side chain; the precipitate is obtained using anhydrous ethanol.

8. The method for preparing the polyimide material according to claim 1, characterized in that, The photosensitive compound is hydroxyethyl methacrylate, and the carboxyl activator is composed of 4-dimethylaminopyridine and N,N'-dicyclohexylcarbodiimide; the photosensitive compound is p-aminostyrene, and the carboxyl activator is composed of 1-ethyl-(3-dimethylaminopropyl)carbodiimide hydrochloride and N-hydroxysuccinimide.

9. The method for preparing the polyimide material as described in claim 1 or 8, characterized in that, The mixing reaction in step (3) is carried out in the dark for 24-28 hours.

10. A polyimide material prepared by the method described in any one of claims 1-9.