Preparation process of photosensitive polyimide material

Abstract

The invention discloses a preparation process of a photosensitive polyimide material, and belongs to the technical field of polyimide materials, diphenylethynyl is introduced into a polyamide acid molecule main chain, and a cross-linking point is constructed among the polyamide acid molecule main chains by utilizing photocrosslinking among the diphenylethynyl, so that the photosensitive polyimide material is prepared. A polyimide body solution capable of being developed by alkali liquor is obtained; and filtering, spin-coating, pre-baking, exposing, developing, cleaning and the like to obtain the polyimide material with the photosensitive characteristic. Besides, in order to improve the rate of photosensitive cross-linking reaction between polyamide acid molecular chains, and meanwhile, in order to obtain higher photosensitive sensitivity and maintain the advantage of alkali liquor development, a cross-linking agent and a photoinitiator can be added into the polyamide acid so as to improve the photoreaction efficiency of the polyamide acid. The preparation process of the photosensitive polyimide material solves the technical problem of how to improve the environmental protection property of the photosensitive polyimide material.

Description

Technical Field

[0001] The invention relates to the technical field of polyimide materials, and in particular to a preparation process of a photosensitive polyimide material. Background Art

[0002] Polyimide is widely used in aerospace, automobile, integrated circuit, display and other fields due to its excellent high temperature resistance, high strength, low dielectric, low thermal expansion, chemical corrosion resistance and other properties. However, when polyimide is used in the field of integrated circuit packaging as a stress buffer layer and requires processes such as drawing through holes, it is often necessary to use ordinary photoresist to achieve it. Specifically, the polyimide part that is not protected by the photoresist layer can be etched away first, and then the photoresist layer can be removed to obtain a polyimide pattern. However, this process is relatively complicated; moreover, repeated wet etching operations are likely to affect the pattern quality and reduce the yield. Therefore, photosensitive polyimide came into being.

[0003] Furthermore, the first photosensitive polyimide to be commercially applied is negative photosensitive polyimide, including ester type and ionic type. This type of negative photosensitive polyimide system usually includes components such as polyamic acid matrix, crosslinking agent, photoinitiator, sensitizer and solvent. Among them, the polyamic acid matrix plays a role in providing thermodynamic properties of the pattern after photolithography, but the polyamic acid matrix also has an important influence on the quality of the photolithography pattern, and controlling its molecular weight is also crucial to the photolithography resolution and photosensitivity. Low molecular weight polyamic acid is conducive to accelerating the rate of photoinduced crosslinking between molecular chains and providing higher sensitivity, but this will sacrifice its thermal and mechanical properties to a certain extent.

[0004] Based on this, Chinese patent CN1320032C discloses a negative polyimide photosensitive material and its preparation method. The polyimide photosensitive material is polymerized with 2,4-dihydroxy-m-phenylenediamine hydrochloride, diamine monomer and dianhydride as raw materials to obtain a polyimide containing hydroxyl groups on the molecular chain; then, the hydroxyl groups are esterified with the acyl chloride of acrylic acid and its derivatives to obtain a polyimide photosensitive material with negative photosensitivity. This type of negative polyimide photosensitive material has high photosensitivity and resolution, good thermal properties and organic solubility, and has broad application prospects in the fields of aviation, microelectronics, etc.

[0005] However, the polyimide photosensitive materials and preparation methods disclosed above still have the technical problem of insufficient environmental protection. Specifically, the design of commercial negative photosensitive polyimide systems is mostly through bonding photosensitive small molecules to the molecular chains of polyimide or its precursor, and using the cross-linking reaction between photosensitive small molecules under ultraviolet irradiation to form cross-linking bridges between the molecular chains of polyimide or its precursor; thus, the exposed area is insoluble in the developer, thereby achieving the effect of negative photolithography. However, most of these negative photosensitive systems use organic solvents for development, such as DMAc, DMF, NMP, etc., which is extremely unfavorable from an environmental perspective; moreover, organic solvents will have a certain swelling effect on the cross-linked polyimide or its precursor, which will lead to some negative effects, such as the residual solvent is not easy to volatilize and remove, and the resolution of the negative pattern is reduced. Therefore, the development of negative photosensitive polyimide systems that can be developed with alkaline solutions has gradually been favored by R&D personnel and the market. Summary of the invention

[0006] Based on this, it is necessary to provide a preparation process of a photosensitive polyimide material in order to solve the technical problem of how to improve the environmental protection of the photosensitive polyimide material.

[0007] A preparation process of a photosensitive polyimide material comprises the following steps: S1: Prepare materials according to a preset formula, including: 4,4'-(acetylene-1,2-diyl) diphthalic anhydride, 4,4'-diaminodiphenyl ether, p-phenylenediamine, N,N-dimethylformamide, a crosslinking agent, and a photoinitiator; S2: In a vessel protected by nitrogen, add 4,4'-diaminodiphenyl ether and p-phenylenediamine in a preset ratio, and dissolve the two in a preset amount of N,N-dimethylformamide solvent, and continue to stir; after the diamine monomer is completely dissolved, add 4,4'-(acetylene-1,2-diyl) diphthalic anhydride in a preset ratio in several batches, continue to stir and keep the reaction for 12 hours, and continue to add N,N-dimethylformamide solvent to adjust the solid content of the solution to 20wt%; continue to stir for 0.5h, until the reaction system presents a stable, uniform and transparent viscous solution, stop the reaction, and obtain a polyamic acid solution; S3: adding a crosslinking agent and a photoinitiator to the polyamic acid solution in a preset ratio, and maintaining stirring or performing ultrasonic treatment to make the components in the solution fully mixed; S4: filtering the uniformly mixed solution through a polytetrafluoroethylene membrane filter to remove insoluble impurities and tiny particles in the solution; then, removing bubbles in the solution using a vacuum degassing machine or a static method; S5: Spin coating, spray coating or roller coating are used to evenly coat the filtered solution on the substrate; after coating, the substrate and the material are pre-baked; S6: placing the pre-baked material in a photolithography machine and exposing it to ultraviolet light of a preset wavelength; after exposure, performing a post-baking process to completely cure the polyimide resin and form a stable pattern structure; S7: placing the exposed and cured semi-finished product in a developer to dissolve the unexposed or unnecessary parts after exposure to reveal the desired pattern; after development, rinsing with deionized water and drying to complete the preparation of the photosensitive polyimide material.

[0008] Specifically, in step S1, the proportions of the materials are respectively: 10-18 parts of 4,4'-(acetylene-1,2-diyl)phthalic anhydride, 8-16 parts of 4,4'-diaminodiphenyl ether, 2-4 parts of p-phenylenediamine, 20-35 parts of N,N-dimethylformamide, 2.5-5 parts of crosslinking agent and 2.5-5 parts of photoinitiator, in terms of molar ratio.

[0009] Specifically, in step S1, the proportions of the materials are respectively: 15 parts of 4,4'-(acetylene-1,2-diyl)phthalic anhydride, 12 parts of 4,4'-diaminodiphenyl ether, 3 parts of p-phenylenediamine, 30 parts of N,N-dimethylformamide, 3.5 parts of crosslinking agent and 3.5 parts of photoinitiator, in terms of molar ratio.

[0010] Specifically, the cross-linking agent is at least one of pentaerythritol tetrakis, trimethylolpropane tris or hexaethylene glycol dithiol.

[0011] Specifically, the photoinitiator is 2-hydroxy-2-methyl-1-phenylpropanone or 1-hydroxycyclohexyl phenyl ketone.

[0012] Specifically, in step S5, the coating method is preferably spin coating, and the process parameters of the spin coating are set as: low speed 500 r / min spin coating for 5 s, high speed 6500 r / min spin coating for 30 s.

[0013] Specifically, in step S5, the drying temperature after coating is set to 80° C., and the drying is continued for 300 seconds.

[0014] Specifically, in step S7, development is performed using a TMAH aqueous solution containing 30% isopropyl alcohol at room temperature.

[0015] Specifically, the concentration of the TMAH aqueous solution is 0.25 wt % to 0.36 wt %.

[0016] Specifically, in step S6, the temperature of the post-baking treatment is 330° C. and the duration is 150 seconds.

[0017] In summary, in the preparation process of the photosensitive polyimide material of the present invention, by introducing diphenylethynyl groups into the main chain of polyamic acid molecules, crosslinking points are constructed between the main chains of polyamic acid molecules by photoinduced crosslinking between diphenylethynyl groups, and a polyimide solution that can be developed with alkali solution is obtained; and then by filtering, spin coating, pre-baking, exposing, developing and cleaning it, a polyimide material with photosensitive properties can be obtained. In addition, in order to improve the rate of photosensitive crosslinking reaction between polyamic acid molecular chains, at the same time, in order to obtain higher photosensitivity and retain its alkali solution development advantage, a crosslinking agent and a photoinitiator can be added thereto to improve its photoreaction efficiency. Thus, a three-component negative photosensitive polyimide material is formed by using diphenylethynyl polyamic acid as a film-forming matrix, using polythiol as a crosslinking agent, and doping a certain amount of photoinitiator. It constructs crosslinking points by a click reaction between the alkynyl group of the polyamic acid main chain and the thiol group of the polythiol, thereby reducing the solubility of the polyamic acid in the alkaline solution in the exposure area, and obtaining a negative pattern. The aforementioned process can avoid using an organic solvent for development, so the preparation process of the photosensitive polyimide material of the present invention solves the technical problem of how to improve the environmental protection of the photosensitive polyimide material. DETAILED DESCRIPTION

[0018] In order to make the above-mentioned purpose, features and advantages of the present invention more obvious and easy to understand, the specific implementation mode of the present invention is described in detail below in conjunction with embodiments. In the following description, many specific details are set forth to facilitate a full understanding of the present invention. However, the present invention can be implemented in many other ways different from those described herein, and those skilled in the art can make similar improvements without violating the connotation of the present invention, so the present invention is not limited by the specific embodiments disclosed below.

[0019] Specifically, the preparation process of the photosensitive polyimide material of the present invention comprises the following steps: S1: Prepare materials according to a preset formula, including: 4,4'-(acetylene-1,2-diyl) diphthalic anhydride, i.e. EDPA, 4,4'-diaminodiphenyl ether, i.e. ODA, p-phenylenediamine, i.e. PPD, N,N-dimethylformamide, i.e. DMF, a crosslinking agent, and a photoinitiator; S2: In a vessel protected by nitrogen, add 4,4'-diaminodiphenyl ether and p-phenylenediamine in a preset ratio, and dissolve the two in a preset amount of N,N-dimethylformamide solvent, and continue to stir; after the diamine monomer is completely dissolved, add 4,4'-(acetylene-1,2-diyl) diphthalic anhydride in a preset ratio in several batches, continue to stir and keep the reaction for 12 hours, and continue to add N,N-dimethylformamide solvent to adjust the solid content of the solution to 20wt%; continue to stir for 0.5h, until the reaction system presents a stable, uniform and transparent viscous solution, stop the reaction, and obtain a polyamic acid solution; S3: adding a crosslinking agent and a photoinitiator to the polyamic acid solution in a preset ratio, and maintaining stirring or performing ultrasonic treatment to make the components in the solution fully mixed; S4: Filter the uniformly mixed solution through a precision filter, such as a polytetrafluoroethylene membrane filter, to remove insoluble impurities and tiny particles in the solution; then, use a vacuum degassing machine or a static method to remove bubbles in the solution to ensure the smoothness and quality of the solution during the coating process; S5: Spin coating, spray coating or roller coating are used to evenly coat the filtered solution on the surface of a substrate, such as a silicon wafer, glass, flexible plastic, etc. After coating, the substrate and the material are pre-baked to remove part of the solvent, to initially solidify the coating, and to enhance adhesion to the substrate; the pre-baking temperature and time need to be optimized according to the coating thickness and resin properties; S6: placing the pre-baked material in a photolithography machine and exposing it to ultraviolet light of a preset wavelength; after exposure, performing a post-baking process to completely cure the polyimide resin and form a stable pattern structure; S7: placing the exposed and cured semi-finished product in a developer to dissolve the unexposed or unnecessary parts after exposure to reveal the desired pattern; after development, rinse with deionized water and dry; as needed, further chemical treatment such as etching, metallization or physical treatment such as cutting, packaging, etc. can be performed to complete the preparation of the photosensitive polyimide material.

[0020] Specifically, polyamic acid has good alkaline solubility due to the carboxyl groups on its molecular chain; therefore, directly using polyamic acid as a matrix to construct a negative PSPI system can achieve the purpose of using alkaline aqueous solution for development. The key point of this technical solution is how to establish effective cross-linking points between polyamic acid molecular chains while retaining the carboxyl groups.

[0021] Furthermore, carbon-carbon double bonds have always been an important entry point for polymer chemical photocrosslinking, and some characteristic structures containing carbon-carbon double bonds are often used to construct negative photosensitive polyimide systems, such as chalcone structure 1, cinnamoyl structure, etc. Specifically, the crosslinking bridge is constructed between polyamic acid or polyimide by utilizing its characteristic of photoinduced 2+2 cycloaddition reaction, but the introduction of these double bond structures in the main chain or side chain is likely to reduce the thermodynamic properties of the obtained polyimide pattern.

[0022] Furthermore, the alkynyl-containing structure is also a relatively good photosensitive group, such as diphenylethynyl, which is often used in the field of liquid crystal orientation. Thermal cross-linking between diphenylethynyl groups can also be used to improve the thermal stability and dimensional stability of polyimide, but it has not yet been applied in the field of photosensitive polyimide.

[0023] Therefore, the preparation process of the photosensitive polyimide material of the present invention proposes a method of constructing a negative photosensitive polyimide system by utilizing the photocrosslinking property of diphenylvinylene, which can directly construct a crosslinking bridge between polyamic acid chains, and can retain the carboxyl group to provide the feasibility of alkaline solution development, and on the other hand, the conjugated rigid structure of the diphenylvinylene group itself can also provide better thermodynamic stability for the polyimide. That is, the present invention introduces diphenylvinylene groups into the main chain of the polyamic acid molecule, and utilizes the photoinduced crosslinking between the diphenylvinylene groups to construct crosslinking points between the main chains of the polyamic acid molecule, thereby obtaining an intrinsic negative photosensitive polyimide system that can be developed with alkaline solution.

[0024] Furthermore, in a specific embodiment, in the aforementioned step S1, the preset ratios of the materials, in terms of molar ratio, are: 10 parts of EDPA, 8 parts of ODA, 2 parts of PPD, 20 parts of DMF, 2.5 parts of crosslinking agent and 2.5 parts of photoinitiator.

[0025] Furthermore, in another specific embodiment, in the aforementioned step S1, the preset ratios of the materials, in terms of molar ratio, are: 15 parts of EDPA, 12 parts of ODA, 3 parts of PPD, 30 parts of DMF, 3.5 parts of crosslinking agent and 3.5 parts of photoinitiator.

[0026] Furthermore, in another specific embodiment, in the aforementioned step S1, the preset ratios of the materials, in terms of molar ratio, are: 18 parts of EDPA, 16 parts of ODA, 4 parts of PPD, 35 parts of DMF, 5 parts of crosslinking agent and 5 parts of photoinitiator.

[0027] Specifically, the aforementioned cross-linking agent may be at least one of: pentaerythritol tetrakis, ie, PTM, trimethylolpropane tris, ie, TTM, or hexaethylene glycol dithiol, ie, HDT.

[0028] Specifically, the aforementioned photoinitiator may be: 2-hydroxy-2-methyl-1-phenylpropanone or 1-hydroxycyclohexyl phenyl ketone.

[0029] Specifically, in the aforementioned step S5, the coating method is preferably spin coating, and the process parameters of the spin coating are set as: low speed 500 r / min spin coating for 5 s, high speed 6500 r / min spin coating for 30 s.

[0030] Furthermore, in the aforementioned step S7, the developing condition is: developing with a 0.25-0.36 wt % TMAH aqueous solution containing 30% isopropyl alcohol at room temperature.

[0031] Furthermore, the photosensitive polymer solution needs to be formed by spin coating or slit coating before exposure, and then heat treatment is also required to continue to volatilize the solvent, so as to obtain a stable non-sticky surface film. However, during these heating processes, whether the acetylenic groups on the polyamic acid molecular chain will undergo interchain crosslinking under the action of heat, if it does occur, it will have a certain negative impact on the subsequent UV exposure crosslinking. Therefore, in the aforementioned step S5, the pre-baking temperature is controlled to not exceed 150°C, and the optimal pre-baking process parameters are set as: the drying temperature is 80°C, and the drying is continued for 300 seconds.

[0032] Furthermore, a major factor that determines the photolithography quality of the polyamic acid system is the control of the development conditions. On the one hand, the developer needs to fully wet the polyamic acid film, and the tetramethylammonium hydroxide aqueous solution, i.e., TMAHaq, is added in a manner of isopropyl alcohol to increase the wetting of the polyamic acid film; on the other hand, the concentration of TMAHaq needs to be controlled. Too high alkalinity will cause the exposed cross-linked part of the polyamic acid to dissolve, thereby failing to obtain a clear solubility contrast between the unexposed area and the exposed area, and too low alkalinity will result in a too slow development rate. Therefore, the preparation process of the photosensitive polyimide material of the present invention proposes a technical solution for controlling the concentration of TMAHaq at 0.25w%.

[0033] Furthermore, in the preparation process of the photosensitive polyimide material of the present invention, the prepared polyamic acid solution has a relatively strong absorption of ultraviolet light with a wavelength of 365nm. Therefore, in the aforementioned S6, the pre-baked material can be placed in a photolithography machine and exposed to ultraviolet light with a preset wavelength of 365nm; after exposure, a post-baking treatment is performed; at this time, the post-baking temperature can be set to not less than 300°C, and it is preferably 330°C, so that the polyimide resin can be completely cured to form a stable pattern structure.

[0034] In summary, in the preparation process of the photosensitive polyimide material of the present invention, by introducing diphenylethynyl groups into the main chain of polyamic acid molecules, crosslinking points are constructed between the main chains of polyamic acid molecules by photoinduced crosslinking between diphenylethynyl groups, and a polyimide solution that can be developed with alkali solution is obtained; and then by filtering, spin coating, pre-baking, exposing, developing and cleaning it, a polyimide material with photosensitive properties can be obtained. In addition, in order to improve the rate of photosensitive crosslinking reaction between polyamic acid molecular chains, at the same time, in order to obtain higher photosensitivity and retain its alkali solution development advantage, a crosslinking agent and a photoinitiator can be added thereto to improve its photoreaction efficiency. Thus, a three-component negative photosensitive polyimide material is formed by using diphenylethynyl polyamic acid as a film-forming matrix, using polythiol as a crosslinking agent, and doping a certain amount of photoinitiator. It constructs crosslinking points by a click reaction between the alkynyl group of the polyamic acid main chain and the thiol group of the polythiol, thereby reducing the solubility of the polyamic acid in the alkaline solution in the exposure area, and obtaining a negative pattern. The aforementioned process can avoid using an organic solvent for development, so the preparation process of the photosensitive polyimide material of the present invention solves the technical problem of how to improve the environmental protection of the photosensitive polyimide material.

[0035] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0036] The above-mentioned embodiments only express several implementation methods of the present invention, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that, for ordinary technicians in this field, several variations and improvements can be made without departing from the concept of the present invention, and these all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A process for preparing a photosensitive polyimide material, characterized in that: It includes the following steps: S1: Prepare materials according to a preset formula, including: 4,4'-(acetylene-1,2-diyl) diphthalic anhydride, 4,4'-diaminodiphenyl ether, p-phenylenediamine, N,N-dimethylformamide, a crosslinking agent, and a photoinitiator; S2: In a vessel protected by nitrogen, add 4,4'-diaminodiphenyl ether and p-phenylenediamine in a preset ratio, and dissolve the two in a preset amount of N,N-dimethylformamide solvent, and continue to stir; after the diamine monomer is completely dissolved, add 4,4'-(acetylene-1,2-diyl) diphthalic anhydride in a preset ratio in several batches, continue to stir and keep the reaction for 12 hours, and continue to add N,N-dimethylformamide solvent to adjust the solid content of the solution to 20wt%; continue to stir for 0.5h, until the reaction system presents a stable, uniform and transparent viscous solution, stop the reaction, and obtain a polyamic acid solution; S3: adding a crosslinking agent and a photoinitiator to the polyamic acid solution in a preset ratio, and maintaining stirring or performing ultrasonic treatment to make the components in the solution fully mixed; S4: filtering the uniformly mixed solution through a polytetrafluoroethylene membrane filter to remove insoluble impurities and tiny particles in the solution; then, removing bubbles in the solution using a vacuum degassing machine or a static method; S5: Spin coating, spray coating or roller coating are used to evenly coat the filtered solution on the substrate; after coating, the substrate and the material are pre-baked; S6: placing the pre-baked material in a photolithography machine and exposing it to ultraviolet light of a preset wavelength; after exposure, performing a post-baking process to completely cure the polyimide resin and form a stable pattern structure; S7: placing the exposed and cured semi-finished product in a developer to dissolve the unexposed or unnecessary parts after exposure to reveal the desired pattern; after development, rinsing with deionized water and drying to complete the preparation of the photosensitive polyimide material.

2. The process for preparing the photosensitive polyimide material according to claim 1, characterized in that: In step S1, the proportions of the materials are as follows: 10-18 parts of 4,4'-(acetylene-1,2-diyl)phthalic anhydride, 8-16 parts of 4,4'-diaminodiphenyl ether, 2-4 parts of p-phenylenediamine, 20-35 parts of N,N-dimethylformamide, 2.5-5 parts of a crosslinking agent, and 2.5-5 parts of a photoinitiator, by molar ratio.

3. The process for preparing the photosensitive polyimide material according to claim 2, characterized in that: In step S1, the proportions of the materials are respectively: 15 parts of 4,4'-(acetylene-1,2-diyl)phthalic anhydride, 12 parts of 4,4'-diaminodiphenyl ether, 3 parts of p-phenylenediamine, 30 parts of N,N-dimethylformamide, 3.5 parts of crosslinking agent and 3.5 parts of photoinitiator, in terms of molar ratio.

4. The process for preparing the photosensitive polyimide material according to claim 1, characterized in that: The cross-linking agent is at least one of pentaerythritol tetrakis, trimethylolpropane tris or hexaethylene glycol dithiol.

5. The process for preparing the photosensitive polyimide material according to claim 1, characterized in that: The photoinitiator is 2-hydroxy-2-methyl-1-phenylpropanone or 1-hydroxycyclohexylphenylketone.

6. The process for preparing the photosensitive polyimide material according to claim 1, characterized in that: In step S5, the coating method is preferably spin coating, and the process parameters of spin coating are set as: low speed 500 r / min spin coating for 5 s, high speed 6500 r / min spin coating for 30 s.

7. The process for preparing the photosensitive polyimide material according to claim 6, characterized in that: In step S5, the drying temperature after coating is set to 80°C, and the drying is continued for 300 seconds.

8. The process for preparing the photosensitive polyimide material according to claim 1, characterized in that: In step S7, development is performed at room temperature using a TMAH aqueous solution containing 30% isopropyl alcohol.

9. The process for preparing the photosensitive polyimide material according to claim 8, characterized in that: The concentration of the TMAH aqueous solution is 0.25 wt % to 0.36 wt %.

10. The process for preparing the photosensitive polyimide material according to claim 1, characterized in that: In step S6, the post-baking treatment is performed at a temperature of 330° C. and lasts for 150 seconds.