Negative photosensitive resin composition, microstructure, preparation method and application

Abstract

The invention discloses a negative photosensitive resin composition, a microstructure, a preparation method and application. The negative photosensitive resin composition at least comprises the following components in parts by mass: 100 parts of alkali-soluble resin, 5-50 parts of a cross-linking agent, 0.5-10 parts of a photoacid generator, 0.01-5 parts of an acid diffusion control agent and a proper amount of an organic solvent. Wherein the acid diffusion control agent is 2-phenyl benzimidazole. According to the negative photosensitive resin composition disclosed by the invention, the common defects of pattern side wall inclination, bottom adhesive residue or T-shaped top and the like caused by non-uniform exposure and excessive acid diffusion in the traditional thick film photoetching are overcome by accurately controlling the diffusion of acid; a negative pattern having excellent sidewall steepness (high aspect ratio), high resolution (e.g., 3 [mu] m to 5 [mu] m line width), and high structural fidelity can be formed under a high film thickness condition.

Description

Technical Field

[0001] This invention belongs to the field of photolithography technology, specifically relating to a negative photosensitive resin composition, microstructure, preparation method and application. Background Technology

[0002] In the manufacturing of semiconductor devices, micro-electro-mechanical systems (MEMS), and advanced packaging technologies, photolithography is a crucial process for forming intricate patterned structures. Photolithography uses a negative photosensitive resin composition (also known as photoresist) to transfer a pattern from a mask onto a substrate. Based on the difference in solubility between exposed and unexposed areas after development, photosensitive resins can be classified as positive or negative. Chemically amplified negative photosensitive resin systems work by using a photoacid generator (PAG) to produce an acid catalyst in the exposed area. This acid catalyst then catalyzes a crosslinking reaction between the alkali-soluble resin and a crosslinking agent in the subsequent post-exposure baking (PEB) step, causing the exposed area to form a three-dimensional network structure insoluble in alkaline developer, thus preserving the pattern.

[0003] With the rapid development of advanced packaging technologies (such as wafer-level packaging (WLP) and 2.5D / 3D integration), the requirements for thick-film lithography of key components such as redistribution layers (RDL), copper pillar electroplating masks, and MEMS structures are becoming increasingly stringent. Typically, the film thickness is required to reach tens of micrometers (e.g., 30 to 40 micrometers) while maintaining high resolution and extremely high aspect ratio.

[0004] However, traditional chemically amplified negative photosensitive resin compositions face multiple technical challenges when applied to photolithography with such high film thickness. These challenges mainly focus on the uniform transfer of light energy and the precise control of acid catalysts. The most critical challenge lies in controlling the diffusion behavior of the acid catalyst generated by the photoacid generator during the post-exposure baking (PEB) process. Acid diffusion is the basis of the chemical amplification effect, but in thick films, the diffusion path of acid is significantly prolonged. If left uncontrolled, acid will diffuse excessively into unexposed areas, causing blurring at the edges of exposed areas, resulting in uncontrolled pattern linewidth, line bridging, and especially the formation of "T-topping" structures at the top of the film layer, or "footing" in unexposed areas, severely impairing the fidelity and manufacturability of the microstructure.

[0005] Existing technologies often fail to solve the dynamic balance problem between exposure energy gradient and acid diffusion by simply increasing the concentration of crosslinking agent or PAG. This is especially true when high resolution requirements of 3 μm–5 μm linewidth are needed, where precise limitation of acid diffusion becomes a key bottleneck determining pattern performance. Summary of the Invention

[0006] The purpose of this invention is to provide a negative photosensitive resin composition, microstructure, preparation method and application. The negative photosensitive resin composition can form negative patterns with high resolution (3μm-5μm linewidth), high aspect ratio (6:1 or higher) and excellent sidewall steepness (close to 90 degrees) under high film thickness conditions. It solves the defects in the prior art, such as tilted sidewalls of the pattern, bottom footing and the formation of "T"-shaped structure at the top, caused by light energy attenuation gradient and excessive acid diffusion in thick film lithography (30μm-40μm).

[0007] To achieve the above objectives, a specific embodiment of the present invention provides the following technical solution:

[0008] A negative photosensitive resin composition, wherein the negative photosensitive resin composition comprises at least the following components in parts by weight: 100 parts alkali-soluble resin, 5-50 parts crosslinking agent, 0.5-10 parts photoacid-generating agent, 0.01-5 parts acid diffusion control agent, and an appropriate amount of organic solvent.

[0009] The acid diffusion control agent is 2-phenylbenzimidazole.

[0010] In one or more embodiments of the present invention, the molar ratio of the acid diffusion control agent and the photo-induced acid-producing agent is 0.1:1-2:1.

[0011] In one or more embodiments of the present invention, the alkali-soluble resin is at least one of hydroxystyrene-styrene-acrylate copolymer and hydroxystyrene-styrene-methacrylate copolymer.

[0012] In one or more embodiments of the present invention, the alkali-soluble resin has a weight-average molecular weight of 3,000 g·mol⁻¹. -1 -30,000 g·mol -1 The hydroxyl content is 45 mol%-70 mol%.

[0013] In one or more embodiments of the present invention, the molar percentage of acrylate units or methacrylate units in the alkali-soluble resin is from 5 mol% to 25 mol%.

[0014] In one or more embodiments of the present invention, the crosslinking agent includes at least one selected from melamine derivatives, urea derivatives, styrene-type crosslinking agents, and epoxy resins; and / or,

[0015] The photoacid-producing agent includes at least one of sulfonium salt compounds and iodonium salt compounds; and / or,

[0016] The organic solvent includes at least one of propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, ethyl lactate, cyclohexanone, and γ-butyrolactone; the solid content of the negative photosensitive resin composition is 20wt%-40wt%.

[0017] In one or more embodiments of the present invention, the negative photosensitive resin composition further includes at least one of a surfactant and an adhesion promoter;

[0018] The surfactant includes at least one of nonionic fluorocarbon-based surfactants and siloxane-based surfactants;

[0019] The adhesion promoters include compounds containing silane groups and compounds containing epoxy groups.

[0020] Another specific embodiment of the present invention provides the following technical solution:

[0021] A method for preparing a negative photosensitive resin composition, the method comprising the following steps:

[0022] At least the alkali-soluble resin, crosslinking agent, photoacid-generating agent, and acid diffusion control agent are dissolved in an organic solvent to obtain a negative photosensitive resin composition.

[0023] Another specific embodiment of the present invention provides the following technical solution:

[0024] A microstructure, wherein the raw material of the microstructure is at least a negative photosensitive resin composition.

[0025] In one or more embodiments of the present invention, the aspect ratio of the microstructure is greater than or equal to 6:1; and / or,

[0026] The sidewall steepness of the microstructure is 85°–95°; and / or,

[0027] The microstructure has a linewidth of 3μm-5μm and a thickness of 30μm-40μm.

[0028] Another specific embodiment of the present invention provides the following technical solution:

[0029] A method for preparing a microstructure, the method comprising the following steps:

[0030] The negative photosensitive resin composition is coated on a substrate to form a film layer with a thickness of 30μm-40μm;

[0031] Pre-bake the film layer at 80℃-120℃ for 1-5 minutes;

[0032] The pre-baked film layer is exposed using a patterned mask;

[0033] The exposed film layer is baked at 90℃-130℃ for 1min-5min;

[0034] The microstructure is obtained by developing the microstructure using a developer.

[0035] In one or more embodiments of the present invention, the exposure step uses KrF exposure or i-line exposure, with an exposure dose of 50 mJ·cm⁻¹. -2 -300 mJ·cm -2 ; and / or,

[0036] In the development step, a 2 wt%-3 wt% TMAH aqueous solution is used for development for 30s-180s.

[0037] In one or more embodiments of the present invention, the method for preparing the microstructure further includes the following steps:

[0038] After development with a developer, it is cured at 140℃-200℃.

[0039] Another specific embodiment of the present invention provides the following technical solution:

[0040] Application of a microstructure in semiconductor devices, microelectromechanical systems, and advanced packaging.

[0041] Compared with the prior art, the present invention has the following beneficial effects:

[0042] 1. A breakthrough in high-resolution thick-film lithography (30μm-40μm) was achieved. By optimizing the molecular weight and hydroxyl content of the resin, and using a highly substituted crosslinking agent, the sufficiency and uniformity of the crosslinking reaction within the film layer were ensured. Combined with a key acid diffusion control agent (such as 2-phenylbenzimidazole), the composition can precisely limit the diffusion distance of the acid, effectively overcoming the problems of pattern blurring and linewidth loss caused by excessive acid diffusion in traditional thick films. A fine structure with a linewidth of 3μm-5μm and no obvious defects was stably obtained, with an aspect ratio of over 6:1.

[0043] 2. Excellent pattern contour and structural fidelity were achieved. The precise acid diffusion control mechanism, in particular, prevented excessive cross-linking at the exposure edges and eliminated the "T"-shaped top and bottom footing phenomenon, resulting in a final pattern sidewall steepness of close to 90°±5°, which is crucial for subsequent electroplating or etching processes (such as manufacturing copper pillars or RDLs).

[0044] 3. High process window tolerance, easy to implement industrially. The composition provided by this invention uses readily available components, has a simple preparation method, and the photolithography process parameters (such as pre-baking, PEB temperature and time) are within the industrial standard range, compatible with existing i-line or KrF photolithography equipment, thus improving production efficiency and yield. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0046] Figure 1 This is a schematic diagram of the microstructure in Embodiment 1 of the present invention;

[0047] Figure 2 This is a schematic diagram of the microstructure in Comparative Example 1 of the present invention. Detailed Implementation

[0048] To enable those skilled in the art to better understand the technical solutions in this disclosure, the technical solutions in the embodiments of this disclosure are described clearly and completely below. Obviously, the described embodiments are only some embodiments of this disclosure, and not all embodiments. Based on the embodiments in this disclosure, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this disclosure.

[0049] Existing chemically amplified negative photosensitive resin compositions suffer from light energy attenuation gradients and excessive acid diffusion. These problems lead to defects in thick-film lithography (30μm-40μm), such as tilted sidewalls, bottom footing, and the formation of "T"-shaped structures at the top. To address these defects, this invention provides a chemically amplified negative photosensitive resin composition capable of forming negative patterns with high resolution (3μm–5μm linewidth), high aspect ratio (above 6:1), and excellent sidewall steepness (close to 90 degrees) under high film thickness conditions. Thick-film patterns formed using the negative photosensitive resin composition of this invention can be applied in advanced semiconductor manufacturing and microelectromechanical systems (MEMS), and are particularly suitable for redistribution layer (RDL) insulating layers, passivation layers, and high aspect ratio electroplating masks requiring high precision and reliability.

[0050] One specific embodiment of the present invention provides a negative photosensitive resin composition, which includes at least the following components by weight: 100 parts alkali-soluble resin, 5-50 parts crosslinking agent, 0.5-10 parts photoacid-generating agent, 0.01-5 parts acid diffusion control agent, and an appropriate amount of organic solvent.

[0051] Furthermore, the alkali-soluble resin is the main material for the negative photolithography function of the negative photosensitive resin composition. It is a copolymer of a: hydroxystyrene, b: styrene, and c: acrylate (or methacrylate), preferably a random terpolymer, as shown in the schematic diagram below: This structure is designed to meet the requirements of thick film coating (high solids content at low viscosity) while also taking into account thermal stability, substrate adhesion, and development contrast.

[0052] Component functional analysis was performed on the above structure:

[0053] a: Hydroxystyrene unit (or p-hydroxystyrene, PHS): Provides a phenolic hydroxyl group (-OH), which is the key group that imparts the resin's alkali solubility (solubility in TMAH developer). More importantly, the phenolic hydroxyl group is the active site for crosslinking reactions with crosslinking agents under acid catalysis (such as etherification or alkylation). Its content directly affects the photosensitivity and contrast of the photoresist.

[0054] b: Styrene unit: As a non-polar framework unit, it is used to improve the glass transition temperature (Tg) and mechanical strength of the resin, and enhance its resistance to subsequent etching processes (etching resistance), which is crucial for thick film structures used as electroplating masks.

[0055] c: Acrylic ester unit (or methacrylate unit): This unit acts as an adhesion and flexibility modifier. Introducing acrylates (such as methyl acrylate, ethyl acrylate, butyl acrylate, methyl methacrylate, or isobutyl methacrylate) can reduce the internal stress of the resin, improve adhesion to diverse substrates such as metals or passivation layers, and fine-tune the resin's solubility in solvents and coating rheology, making it suitable for high-solids content and single-pass thick-film spin coating processes.

[0056] Furthermore, the weight-average molecular weight (Mw) of the alkali-soluble resin was precisely controlled at 3,000 g·mol⁻¹. -1 Up to 30,000 g·mol -1 Within the range. If Mw is below 3,000 g·mol⁻¹ -1 The resulting cross-linked film layer lacks sufficient mechanical strength, making it prone to collapse or peeling during development or post-processing, and also has a low heat distortion temperature. If Mw exceeds 30,000 g·mol⁻¹ -1At the desired high solids content of 20 wt%–40 wt%, the viscosity of the composition becomes excessively high, making uniform thick-film spin coating difficult. Furthermore, the diffusion and relaxation of macromolecular segments hinder the penetration of the developer, leading to a decrease in resolution. The most preferred Mw range is 5,000 g·mol⁻¹. -1 Up to 20,000 g·mol -1 .

[0057] Furthermore, the hydroxyl content of the alkali-soluble resin is controlled between 45 mol% and 70 mol%. This content determines the alkali solubility of the resin and the density of crosslinking sites. The preferred range of hydroxyl content is 55 mol% to 65 mol%. Excessive hydroxyl content (e.g., exceeding 70 mol%) will cause the unexposed areas to dissolve too quickly during pre-baking and PEB processes, reducing contrast; excessively low content (e.g., below 45 mol%) will require excessively high exposure doses to achieve sufficient crosslinking, or result in insufficient crosslinking and poor structural fidelity.

[0058] Furthermore, the proportion of acrylate units in the alkali-soluble resin is 5 mol% to 25 mol% of the total molar amount of the copolymer. For example, if a hydroxystyrene-styrene-ethyl acrylate terpolymer is used, the preferred molar ratio is: hydroxystyrene (45 mol%–70 mol%) : styrene (15 mol%–40 mol%) : acrylate (5 mol%–25 mol%). This balance ensures good etching resistance, sufficient alkali solubility, and excellent substrate adhesion to meet the stringent requirements for thick-film patterning in advanced packaging.

[0059] Furthermore, alkali-soluble resins can be obtained by using free radical polymerization reactions of monomers conventional in the art. For example, alkali-soluble resins can be obtained by free radical polymerization of hydroxystyrene (monomer a), styrene (monomer b), and acrylates (monomer c), wherein the molar ratio of monomer a, monomer b, and monomer c can be 65:15:20. The solvent for the polymerization reaction is an alcohol or ester solvent, preferably methanol. The polymerization reaction time is 10-16 hours, preferably 14 hours. After the polymerization reaction is completed, the reaction solution is mixed with pure water to produce a precipitate. The precipitate is dissolved in tetrahydrofuran solvent, and then mixed with pure water again to precipitate. This process is repeated three times. The solid precipitate is then dried in a vacuum oven at a low temperature (40°C-50°C) for 48 hours.

[0060] Furthermore, the function of the crosslinking agent is to react with the hydroxyl groups of the resin under acid catalysis, causing the resin molecules in the exposed area to connect and form a three-dimensional insoluble network. The efficiency of the crosslinking agent is crucial for overcoming the problem of insufficient bottom crosslinking caused by the light energy decay of thick films.

[0061] Furthermore, the crosslinking agent can be at least one of melamine derivatives (such as methylated melamine or butylated melamine), urea derivatives, or styrene-type crosslinking agents, or epoxy resins (such as bisphenol A type epoxy resin or linear phenolic epoxy resin). Melamine derivatives with high reactivity and good thermal stability are preferred.

[0062] The structural diagram of a melamine derivative is as follows: The structural diagram of urea derivatives is as follows: The structural diagram of the styrene-type crosslinking agent is as follows: .

[0063] Preferably, the crosslinking agent is a methoxymethylated melamine resin (e.g., hexamethoxymethylmelamine, HMMM). To ensure rapid and sufficient crosslinking within a limited PEB time even with a relatively low acid concentration on the photoresist substrate at high film thicknesses (30 μm–40 μm), this invention emphasizes the degree of substitution of the crosslinking agent. The degree of methoxymethylation is preferably ≥70%, more preferably ≥80%, to provide more active methoxymethyl sites (-OCH2OCH3) to undergo acid-catalyzed etherification / alkylation reactions with the phenolic hydroxyl groups of the resin. This high degree of substitution is crucial for ensuring sufficient crosslinking at the bottom of the thick film, eliminating "footing" defects, and guaranteeing sidewall steepness.

[0064] Furthermore, the amount of crosslinking agent used is 5–50 parts by weight (relative to 100 parts by weight of the negative photosensitive resin composition), preferably in the range of 10–30 parts by weight. If the amount is less than 5 parts by weight, the crosslinking density is too low and cannot resist the erosion of the developer, resulting in pattern collapse. If the amount exceeds 50 parts by weight, it may cause the unexposed areas to dissolve slowly in the developer (i.e., produce residual adhesive), and may also reduce the storage stability of the composition and increase the brittleness of the film.

[0065] Furthermore, photoacid generators (PAGs) produce strong acids under exposure (KrF or i-line), acting as catalysts for crosslinking reactions. In thick-film lithography, the selection of PAGs must consider their quantum yield and light absorption characteristics. PAGs must have a suitable absorption coefficient at the exposure wavelength to ensure that light energy can penetrate a thickness of 30 μm–40 μm. If the PAG absorption is too strong, light energy will be concentrated only at the top of the film, exacerbating the exposure gradient. Simultaneously, PAGs need to have a high quantum yield to generate a sufficient concentration of acid even at low photon fluxes (bottom of the film).

[0066] Furthermore, PAG is preferably a sulfonium salt compound or an iodonium salt compound, preferably triphenylsulfonium trifluoromethanesulfonate, as shown in the schematic diagram: This sulfonium salt exhibits good efficiency at both i-line (365 nm) and KrF (248 nm) wavelengths. The generated anion—trifluoromethanesulfonate (TfO)—is produced. - — It is a strong acid with high acidity and moderate diffusivity, which is very suitable for driving cross-linking reactions.

[0067] PAG can also be selected from triphenylsulfonium nonafluorobutane sulfonate, diphenyliodonium hexafluoroantimonate, etc. A schematic diagram of the structure of diphenyliodonium hexafluoroantimonate is shown below. .

[0068] Furthermore, the amount of PAG used is 0.5–10 parts by weight (relative to 100 parts by weight of negative photosensitive resin composition), preferably 1–5 parts by weight. Too low a dosage will result in insufficient exposure sensitivity, requiring extremely high dosage; too high a dosage may lead to excessive absorption at the top of the film, exacerbating the light energy gradient, and excessive PAG decomposition products (non-acidic residues) may affect the film performance.

[0069] Furthermore, the acid diffusion control agent is a key innovation of this invention for achieving high-resolution thick-film lithography. In thick films, excessive acid diffusion can lead to blurred edges of the exposed area, forming defects such as a "T"-shaped top (T-topping, caused by acid diffusing upwards to the unexposed top layer) and footing (caused by acid diffusing downwards to the unexposed bottom). The acid diffusion control agent (ADCA), through its weak alkalinity, precisely and locally quenches or captures acid at the edges of the exposed area, thereby limiting the effective diffusion distance (Ld) of the acid.

[0070] In terms of structural requirements and mechanism, ADCA must have a moderate basicity (pKa) to effectively capture strong acids without causing undesirable side reactions with crosslinking agents or resins during the PEB process, and it must also have good thermal stability to adapt to the PEB temperature.

[0071] The preferred acid diffusion control agent is 2-phenylbenzimidazole, the structural diagram of which is shown below: .

[0072] 2-Phenylenibimidazole belongs to the imidazole derivative class. Its nitrogen atom's electron cloud is conjugated by the phenyl and benzene ring structures, making it less basic and having a lower diffusion rate than aliphatic amines (such as triethanolamine). Its advantages are as follows:

[0073] Eliminating T-topping: At the top of the film layer, due to the high exposure, there is a large acid concentration gradient. 2-Phenylenazole can precisely neutralize excess acid at the boundary of the exposed area, preventing acid from horizontally diffusing into the unexposed area during PEB, effectively eliminating the T-topping phenomenon and ensuring the linewidth accuracy at the top of the pattern.

[0074] Enhancing sidewall steepness: By limiting the effective diffusion distance of acid (Ld), the boundary of the crosslinking reaction becomes sharper and more defined, thereby achieving a high aspect ratio structure with a sidewall steepness of nearly 90°±5°.

[0075] Thermal stability: Its high thermal stability ensures that it will not decompose or excessively volatilize during the PEB process at 90℃–130℃, thus maintaining the precision of acid diffusion control.

[0076] Furthermore, the amount of ADCA used is crucial, ranging from 0.01 to 5 parts by weight (relative to 100 parts by weight of the negative photosensitive resin composition), with a preferred range of 0.1 to 2 parts by weight. The amount typically needs to be finely adjusted according to the type of PAG and the molar ratio. If the ADCA amount is less than 0.01 parts by weight, the control effect on acid diffusion is not significant. If the amount exceeds 5 parts by weight, it may lead to excessive quenching of the acid, a sharp decrease in the photosensitivity of the composition, requiring higher exposure doses, or even failure to fully crosslink and form patterns.

[0077] Furthermore, the negative photosensitive resin composition must be dissolved in a suitable organic solvent to form a uniform coating solution. Considering that thick-film lithography requires high solids content (20wt%–40wt%) and excellent leveling properties, the organic solvent must possess the following characteristics: high solubility for all components, low toxicity, moderate evaporation rate, high boiling point, and high purity.

[0078] Preferred organic solvents include at least one of propylene glycol monomethyl ether acetate (PGMEA, also known as PMA), propylene glycol monomethyl ether (PGME), ethyl lactate (EL), cyclohexanone, γ-butyrolactone, etc.

[0079] Propylene glycol monomethyl ether acetate (PGMEA) is preferred as the organic solvent due to its excellent solubility and moderate evaporation rate, making it ideal for thick-film spin coating of high-solids-content solutions. The solids content of the negative photosensitive resin composition is typically controlled between 20 wt% and 40 wt% to ensure that the required film thickness of 30 μm–40 μm can be achieved in a single spin coating.

[0080] Furthermore, the negative photosensitive resin composition may also contain other conventional photoresist additives in an amount of 0.01–5 parts by weight (relative to 100 parts by weight of the negative photosensitive resin composition). These additives may include:

[0081] Surfactants are used to improve the wettability, leveling, and coating uniformity of photoresists on substrates, especially on large wafers or high aspect ratio structures. Examples include nonionic fluorocarbon-based or siloxane-based surfactants.

[0082] Adhesion promoters: For example, compounds containing silane groups (such as hexamethyldisilazane, HMDS) or compounds containing epoxy groups are used to enhance the adhesion between photoresist and silicon wafers, glass or metallization layers (such as Ti / Cu / Ni) and prevent peeling during wet development.

[0083] Dye / Absorbent: If further control over the penetration depth of light in the thick film is required, a small amount of absorbent can be added. However, in this invention, since the PAG and resin structures have been optimized, this step can usually be omitted to simplify the formulation.

[0084] Another specific embodiment of the present invention provides a method for preparing a negative photosensitive resin composition, comprising the following steps:

[0085] Step 1, dissolve the resin.

[0086] Specifically, an accurately weighed alkali-soluble resin is added to a selected organic solvent (preferably PGMEA), and stirred under a nitrogen atmosphere at room temperature or with moderate heating (e.g., 30°C–50°C) until the resin is completely dissolved to form a homogeneous resin mother liquor.

[0087] Step 2: Add crosslinking agent and PAG.

[0088] Specifically, the crosslinking agent and photoacid-producing agent are weighed in the specified proportions and added to the resin mother liquor, and stirring is continued until completely dissolved. Since PAG is photosensitive, this step must be performed under yellow light.

[0089] Step 3: Add acid diffusion control agent.

[0090] Specifically, the key acid diffusion control agent, preferably 2-phenylbenzimidazole, is accurately weighed and added to the solution. Since the amount of ADCA used is extremely small and its impact on acid diffusion is significant, it is essential to ensure the uniformity of its dispersion and dissolution.

[0091] Step 4, mix and homogenize.

[0092] Specifically, the mixture is continuously stirred to ensure that all solid components are completely dissolved, forming a high-concentration homogeneous solution with a solid content of 20wt%–40wt%. The stirring time is typically 4h–24h.

[0093] Step 5, precision filtration.

[0094] Specifically, to remove any micron- or submicron-sized particulate impurities that may be present, this is the final and most critical step in avoiding photolithography defects. The solution is filtered through a series of filters. The final filtration pore size should be 1 μm or smaller. A two- or three-stage filtration system is preferred, for example, a 5 μm pre-filtration followed by a 1 μm filtration, and finally a precision filtration through a 0.2 μm or 0.1 μm PTFE or nylon membrane filter to achieve the ultra-cleanliness standards required for semiconductor manufacturing.

[0095] Another specific embodiment of the present invention provides a microstructure, wherein the raw materials of the microstructure include at least the above-mentioned negative photosensitive resin composition.

[0096] Specifically, the aspect ratio of the microstructure is greater than or equal to 6:1, the sidewall steepness of the microstructure is 85°–95°, and the linewidth of the microstructure is 3μm–5μm.

[0097] Another specific embodiment of the present invention provides a method for preparing a microstructure, comprising the following steps:

[0098] Step ⅰ, Coating.

[0099] Specifically, the negative photosensitive resin composition is applied to a substrate by spin coating, spraying, or die coating. The substrate can be a standard silicon wafer, glass, sapphire substrate, or a metallized substrate with completed metal wiring (e.g., Cu / Ni / Au RDL layer).

[0100] Thickness control: The film thickness is strictly controlled within the range of 30 μm to 40 μm by precisely controlling the spin coating speed (e.g., 500 rpm to 2000 rpm) and the viscosity of the negative photosensitive resin composition (controlled by solid content, 20wt%–40wt%). This high thickness requirement is to meet the needs of advanced encapsulation RDL insulating layers or high aspect ratio electroplating masks. Film thickness uniformity must be ensured within ±5% to guarantee the uniformity of subsequent exposures.

[0101] Step ii, pre-bake (or soft bake).

[0102] Specifically, the coated substrate is placed on a heated plate for pre-baking at 80℃–120℃ for 1–5 minutes. This step aims to remove most of the residual solvent from the photoresist film, densifying the film and preventing defects caused by bubbles or solvent residue during subsequent exposure. A balance needs to be struck in temperature selection: too low a temperature results in insufficient solvent removal; too high a temperature may cause partial cross-linking of the resin in the unexposed state (thermal cross-linking) or decomposition of the photoacid-generating agent, thereby reducing photosensitivity and contrast. Preferred pre-baking conditions are 100℃ for 2–3 minutes.

[0103] Step iii, Exposure.

[0104] Specifically, exposure is performed using a high-intensity lithography machine through a mask with a predetermined precision pattern. The exposure wavelength can be KrF (248nm) or i-line (365nm). Considering the absorption and scattering attenuation of light energy by the thick film, the exposure dose needs to be significantly higher than that of thin-film lithography.

[0105] Dosage setting: Exposure set at 50 mJ·cm -2 Up to 300 mJ·cm -2 Within a wide range.

[0106] Overcoming the gradient: The selection of the exposure dose is crucial for balancing the crosslinking at the top and bottom of the film. Because light energy attenuates significantly by the time it reaches the bottom, a sufficiently high dose (e.g., 150 mJ·cm⁻¹) must be set. -2 This ensures that even at the bottom of a 30–40 μm thick film, PAG generates sufficient acid to drive the crosslinking reaction. Lower dose limit (50 mJ·cm⁻¹) -2 Suitable for highly sensitive formulations, with an upper limit of 300 mJ·cm⁻¹ -2 It is used to compensate for high absorption rates or extremely thick membranes.

[0107] Step iv, Post Exposure Bake (PEB).

[0108] Specifically, this step is the core step for achieving acid-catalyzed crosslinking and acid diffusion control, and involves baking on a heating plate at 90℃–130℃ for 1–5 minutes.

[0109] PEB Mechanism: Temperature and time control the diffusion rate of acid and the rate of chemical reaction in PEB. Excessive temperature or time leads to over-diffusion of acid, resulting in reduced resolution (blurred edges) despite sufficient cross-linking. Insufficient temperature or time results in incomplete cross-linking, leading to insufficient pattern strength.

[0110] Synergistic effect of acid diffusion control: In this step, the acid diffusion controller (2-phenylbenzimidazole) acts precisely at the boundary between the exposed and unexposed areas, limiting the effective diffusion range of the acid (typically within tens of nanometers to one micrometer), thereby ensuring the sharp edges required to form a 3μm–5μm linewidth pattern. Preferred PEB conditions are 110℃–125℃ for 3 minutes.

[0111] Step v, Development.

[0112] Specifically, wet development is performed using a standard alkaline developer, typically a 2.38 wt% aqueous solution of tetramethylammonium hydroxide (TMAH). The development time is 30 to 180 seconds.

[0113] Development Control: The development process must be precisely controlled to ensure complete resin dissolution in unexposed areas while maintaining the integrity of fully cross-linked exposed areas. Longer development times (e.g., 120–180 seconds) are typically used for thicker film layers (40 μm) to ensure thorough removal of the underside. Development methods can include immersion, spray, or puddling. The negative photosensitive resin composition of this invention, through optimized resin molecular weight and hydroxyl content, exhibits high contrast even at thicknesses of 30–40 μm, shortens development time, and reduces mechanical stress on the formed pattern.

[0114] Step ⅵ, post-processing (Hard Bake).

[0115] Specifically, after obtaining the high-resolution negative pattern, a hard bake or post-curing process can optionally be performed, such as baking at 140°C–200°C for several minutes. This step aims to further cure and harden the cross-linked structure, improving the glass transition temperature (Tg), etching resistance, and chemical stability of the pattern to meet the challenges of subsequent processes such as electroplating or high-temperature reflow soldering.

[0116] Another specific embodiment of the present invention provides an application of microstructures in semiconductor devices, microelectromechanical systems, and advanced packaging.

[0117] Specifically, the thick film patterns formed using the negative photosensitive resin composition and microstructure preparation method of this invention have wide and critical applications in advanced manufacturing due to their high resolution, high aspect ratio (typically reaching 6:1 to 10:1), and excellent sidewall steepness.

[0118] Redistribution layer (RDL) dielectric layer in advanced packaging: As a permanent insulating layer or stress buffer layer, the pattern formed by this composition has excellent thermomechanical stability and low dielectric constant.

[0119] Passivation and protective layers: used to protect the surface of semiconductor chips from moisture and mechanical damage.

[0120] High aspect ratio plating masks: particularly suitable for manufacturing copper pillar structures or microbumps in advanced packaging. The high-steepness thick-film mask ensures that the copper pillars plated subsequently have uniform tops and sidewalls, which is a prerequisite for ensuring the reliability of high-density interconnects.

[0121] Microelectromechanical systems (MEMS) manufacturing: used to manufacture microfluidic channels, sensor or actuator structures that require high-precision, high-aspect-ratio lithography.

[0122] The present invention will be further described in detail below with reference to specific embodiments.

[0123] Example 1

[0124] The preparation method of the negative photosensitive resin composition in this embodiment is as follows:

[0125] (1) Add p-hydroxystyrene (78g), styrene (15.6g) and methyl methacrylate (16.8g) to a reaction vessel filled with nitrogen, then add 110g of methanol and 5.5g of azobisisobutyronitrile. After stirring evenly, start heating. The heating temperature is set to 75℃. After the reflux in the vessel begins to stabilize, start the reaction for 14 hours and then stop the reaction. Cool the reaction solution to room temperature.

[0126] (2) Add the reaction solution to pure water, precipitate out, filter, and add the filtered solid to an equal mass of tetrahydrofuran and stir until completely dissolved.

[0127] (3) After repeating step (2) three times, a solid precipitate is obtained.

[0128] (4) The solid precipitate was placed in a vacuum oven and dried at low temperature for 48 hours to obtain the desired alkali-soluble resin.

[0129] (5) Take 100g of alkali-soluble resin and add it to PGMEA. Stir at 30°C under a nitrogen atmosphere until the alkali-soluble resin is completely dissolved to form a uniform resin mother liquor.

[0130] (6) Add 5g of divinylbenzene and 0.5g of diphenyliodonium hexafluoroantimonate to the resin mother liquor and stir to dissolve.

[0131] (7) Continue to add 0.01g of 2-phenylbenzimidazole to the resin mother liquor and stir until all solid components are completely dissolved to form a homogeneous solution with a solid content of 20wt%.

[0132] (8) The homogeneous solution is first pre-filtered with 5 μm, then filtered with 1 μm, and finally finely filtered through a 0.2 μm nylon membrane filter to obtain a negative photosensitive resin composition.

[0133] Examples 2-8

[0134] The preparation methods of the negative photosensitive resin compositions in Examples 2-8 are basically the same as those in Example 1, except that the types and amounts of raw materials used are different, as shown in Tables 1 and 2.

[0135] Table 1 Raw materials used in alkali-soluble resins

[0136]

[0137] Table 2 Raw materials used in the negative photosensitive resin compositions of each embodiment

[0138]

[0139] Comparative Example 1

[0140] The preparation method of the negative photosensitive resin composition in this comparative example is as follows:

[0141] (1) Add p-hydroxystyrene (78g) and styrene (15.6g) to a reaction vessel filled with nitrogen, then add 110g of methanol and 5.5g of azobisisobutyronitrile. After stirring evenly, start heating. Set the heating temperature to 75℃. After the reflux in the vessel begins to stabilize, start the reaction for 14 hours and then stop the reaction. Cool the reaction solution to room temperature.

[0142] (2) Add the reaction solution to pure water, precipitate out, filter, and add the filtered solid to an equal mass of tetrahydrofuran and stir until completely dissolved.

[0143] (3) After repeating step (2) three times, a solid precipitate is obtained.

[0144] (4) The solid precipitate was placed in a vacuum oven and dried at low temperature for 48 hours to obtain the desired alkali-soluble resin.

[0145] (5) Take 100g of alkali-soluble resin and add it to PGMEA. Stir at 30°C under a nitrogen atmosphere until the alkali-soluble resin is completely dissolved to form a uniform resin mother liquor.

[0146] (6) Add 20g HMMM and 5g triphenylsulfonium trifluoromethanesulfonate to the resin mother liquor and stir to dissolve.

[0147] (7) Continue to add 1g of 2-phenylbenzimidazole to the resin mother liquor and stir until all solid components are completely dissolved to form a homogeneous solution with a solid content of 30wt%.

[0148] (8) The homogeneous solution is first pre-filtered with 5 μm, then filtered with 1 μm, and finally finely filtered through a 0.2 μm nylon membrane filter to obtain a negative photosensitive resin composition.

[0149] Comparative Examples 2-5

[0150] The preparation methods of the negative photosensitive resin compositions in Comparative Examples 2-5 are basically the same as those in Example 3, except that the types and amounts of raw materials used are different, as shown in Table 3.

[0151] Table 3 Raw materials used in the negative photosensitive resin compositions of Comparative Examples 2-5

[0152]

[0153] Microstructures were prepared using the negative photosensitive resin compositions from each example and comparative example, and the preparation methods are as follows:

[0154] (1) Take a silicon wafer substrate and coat the negative photosensitive resin composition onto the silicon wafer substrate to form a film layer with a thickness of 35 μm.

[0155] (2) Pre-bake the coated substrate at 100°C for 3 minutes.

[0156] (3) Expose the pre-baked film layer with a mask bearing a predetermined precision pattern using KrF (248nm) at an exposure dose of 150mJ·cm⁻¹. -2 .

[0157] (4) After exposure, bake at 120℃ for 3 minutes.

[0158] (5) The microstructure was obtained by developing the microstructure using a 2.38 wt% tetramethylammonium hydroxide (TMAH) aqueous solution for 100 seconds.

[0159] The microstructures obtained using the negative photosensitive resin compositions in each example and comparative example are observed, with the microstructure diagram of Example 1 shown below. Figure 1 As shown, the linewidth of the microstructure meets the requirement of 3μm-5μm, no "T-topping" structure is observed at the top, and no "footing" is generated in the unexposed areas. In the other embodiments, the linewidth of the microstructure obtained also meets the requirement of 3μm-5μm, no "T-topping" structure is observed at the top, and no "footing" is generated in the unexposed areas. The microstructure in Comparative Example 1 is as follows... Figure 2 The example shown has a top T-topping and a bottom footing, and the other comparative examples also have top T-topping and bottom footing, which does not meet the requirements.

[0160] It will be apparent to those skilled in the art that this disclosure is not limited to the details of the exemplary embodiments described above, and that this disclosure can be implemented in other specific forms without departing from the spirit or essential characteristics of this disclosure. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of this disclosure is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within this disclosure.

[0161] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. This narrative style is merely for clarity. Those skilled in the art should consider the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A negative photosensitive resin composition, characterized in that, The negative photosensitive resin composition comprises at least the following components by weight: 100 parts alkali-soluble resin, 5-50 parts crosslinking agent, 0.5-10 parts photoacid-generating agent, 0.01-5 parts acid diffusion control agent, and appropriate amount of organic solvent. The acid diffusion control agent is 2-phenylbenzimidazole.

2. The negative photosensitive resin composition according to claim 1, characterized in that, The molar ratio of the acid diffusion control agent to the photo-induced acid-producing agent is 0.1:1-2:

1.

3. The negative photosensitive resin composition according to claim 1, characterized in that, The alkali-soluble resin is at least one of hydroxystyrene-styrene-acrylate copolymer and hydroxystyrene-styrene-methacrylate copolymer.

4. The negative photosensitive resin composition according to claim 3, characterized in that, The alkali-soluble resin has a weight-average molecular weight of 3,000 g·mol⁻¹. -1 -30,000 g·mol -1 The hydroxyl content is 45 mol%-70 mol%.

5. The negative photosensitive resin composition according to claim 3, characterized in that, The molar percentage of acrylate units or methacrylate units in the alkali-soluble resin is from 5 mol% to 25 mol%.

6. The negative photosensitive resin composition according to claim 1, characterized in that, The crosslinking agent includes at least one of melamine derivatives, urea derivatives, styrene-based crosslinking agents, and epoxy resins; and / or, The photoacid-producing agent includes at least one of sulfonium salt compounds and iodonium salt compounds; and / or, The organic solvent includes at least one of propylene glycol monomethyl ether acetate, propylene glycol monomethyl ether, ethyl lactate, cyclohexanone, and γ-butyrolactone; the solid content of the negative photosensitive resin composition is 20wt%-40wt%.

7. The negative photosensitive resin composition according to claim 1, characterized in that, The negative photosensitive resin composition also includes at least one of a surfactant and an adhesion promoter; The surfactant includes at least one of nonionic fluorocarbon-based surfactants and siloxane-based surfactants; The adhesion promoters include compounds containing silane groups and compounds containing epoxy groups.

8. A method for preparing the negative photosensitive resin composition according to claim 1, characterized in that, The preparation method of the negative photosensitive resin composition includes the following steps: At least the alkali-soluble resin, crosslinking agent, photoacid-generating agent, and acid diffusion control agent are dissolved in an organic solvent to obtain a negative photosensitive resin composition.

9. A microstructure, characterized in that, The raw materials for the microstructure include at least the negative photosensitive resin composition of claim 1.

10. The microstructure according to claim 9, characterized in that, The aspect ratio of the microstructure is greater than or equal to 6:1; and / or, The sidewall steepness of the microstructure is 85°–95°; and / or, The microstructure has a linewidth of 3μm-5μm and a thickness of 30μm-40μm.

11. A method for preparing the microstructure according to claim 9, characterized in that, The method for preparing the microstructure includes the following steps: The negative photosensitive resin composition is coated on a substrate to form a film layer with a thickness of 30μm-40μm; Pre-bake the film layer at 80℃-120℃ for 1-5 minutes; The pre-baked film layer is exposed using a patterned mask; The exposed film layer is baked at 90℃-130℃ for 1min-5min; The microstructure is obtained by developing the microstructure using a developer.

12. The method for preparing the microstructure according to claim 11, characterized in that, In the exposure step, KrF exposure or i-line exposure is used, with an exposure dose of 50 mJ·cm⁻¹. -2 -300 mJ·cm -2 ; and / or, In the development step, a 2 wt%-3 wt% TMAH aqueous solution is used for development for 30s-180s.

13. The method for preparing the microstructure according to claim 11, characterized in that, The method for preparing the microstructure further includes the following steps: After development with a developer, it is cured at 140℃-200℃.

14. The application of the microstructure described in claim 9 in semiconductor devices, microelectromechanical systems, and advanced packaging.

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