Low-foam fluorocarbon substitute surfactant for EUV photoresist and preparation method of low-foam fluorocarbon substitute surfactant

Abstract

The invention relates to the technical field of a low-foam fluorocarbon substitute surfactant for an EUV (Extreme Ultraviolet) photoresist and a preparation method thereof, discloses a technical scheme of a low-foam fluorocarbon substitute surfactant for an EUV photoresist and a preparation method thereof, and aims to solve the problems of environmental risk, bubble residue, insufficient wetting and the like of a traditional fluorine-containing auxiliary agent. The surfactant has a Gemini type molecular structure and is composed of two siloxane modified or short-chain fluorocarbon hydrophobic tail chains, two polyether hydrophilic head groups and a linking group. Through the synergistic effect of molecular steric hindrance and a hydrophobic chain, ultralow surface tension and instantaneous defoaming are realized at low concentration. According to the invention, the environment-friendly replacement of PFAS is realized, the wettability of a high aspect ratio pattern under a 3nm process is remarkably enhanced, the zero-residue characteristic is realized, the photoetching yield is effectively improved, and the edge roughness is improved.

Description

Technical Field

[0001] This invention belongs to the field of photoresist materials, specifically relating to a low-foaming fluorocarbon substitute surfactant for EUV photoresist and its preparation method. Background Technology

[0002] Semiconductor integrated circuit manufacturing technology continues to evolve towards physical limits following Moore's Law, and extreme ultraviolet (EUV) lithography has become a core key means to achieve advanced process nodes of 3nm and below. In the EUV lithography process chain, the performance of photoresist and its supporting developer directly determines the fidelity of nanoscale pattern transfer, the uniformity of critical dimensions (CD), and the final chip yield. Due to the random distribution of high-energy photons and extremely complex chemical amplification reactions involved in the exposure process of EUV photoresist, it exhibits extremely high sensitivity to any minute disturbances introduced into the process environment. Surfactants, as indispensable functional additives in photoresist formulations and developer systems, have the core mission of precisely controlling the surface tension of gas-liquid and liquid-solid interfaces to ensure that the solution achieves sufficient wetting, spreading, and penetration on the wafer surface and inside the nanogrooves.

[0003] For a considerable period in industrial practice, perfluoroalkyl substances (PFAS) have long held a dominant position as surfactants in advanced processes due to their extremely high surface activity, excellent chemical stability, and heat resistance. Traditional techniques typically utilize the extremely low surface energy of long-chain perfluoroalkyl groups (such as perfluorooctyl) to form a dense, oriented molecular layer at the interface, reducing the surface tension of the system to an extremely low level. This effectively prevents pattern collapse during development and improves film quality. For example, some existing techniques improve wettability by introducing specific fluorinated surfactants into EUV photoresist formulations, or attempt to balance performance and environmental safety using derivatives based on short-chain fluorocarbon groups such as perfluorobutane. These approaches have indeed effectively addressed the initial requirements for coating uniformity and interfacial wetting at specific historical stages and major process nodes.

[0004] However, as photolithography processes advance to 3nm and below, the inherent deep-seated technical contradictions of existing technologies are becoming increasingly apparent, gradually evolving into bottlenecks restricting yield improvement. Firstly, from the perspective of global industry trends and stringent environmental regulations, long-chain fluorocarbon surfactants, due to their strong environmental persistence, bioaccumulation, and potential toxicity, are strictly restricted or banned by international conventions such as the Stockholm Convention and national chemical regulatory policies (such as REACH regulations). Although the industry has attempted to shift towards short-chain fluorocarbons (such as C4 and below), this improvement is a compromise that only addresses the symptoms, not the root cause. Because of the shortened hydrophobic tail chains, short-chain fluorocarbon surfactants significantly reduce their surface tension reduction efficiency, often requiring a significant increase in concentration to achieve ideal wetting effects. This increase in concentration not only increases production costs but, more critically, directly leads to disordered molecular arrangement at the interface.

[0005] Secondly, a more profound technical conflict lies in the performance paradox between "ultra-low surface tension" and "low foaming and no residue." Under the high-dynamic conditions of EUV development, traditional surfactant molecules, while reducing surface tension, readily form stable gas-liquid interface films in the developer, generating numerous microbubbles. In fine patterns on the 3nm scale, these microbubbles become trapped in narrow, deep trenches, forming physical shielding and hindering sufficient contact between the developer and photoresist, leading to incomplete development and defects such as bridging, voids, or pattern gaps. Simultaneously, traditional single-head, single-tail surfactants are prone to physical adsorption during the rinsing stage, leaving difficult-to-remove molecular-level residues on the wafer surface. These residues alter wetting behavior in subsequent thin-film deposition processes, inducing secondary defects. Furthermore, EUV photoresists and their anti-reflective coatings (BARC) often employ complex chemically amplified resin systems, with traditional surfactants exhibiting poor compatibility. This leads to microphase separation at the interface, resulting in deteriorated surface roughness (LWR / LWR) after coating and severely impacting electrical performance.

[0006] At its core, the existing surfactant molecular design paradigms are mainly based on single-chain structures, which have high critical micelle concentrations (CMCs) and cannot achieve efficient saturation adsorption at extremely low concentrations. To meet the environmental trend of "PFAS-free" and completely eliminate development defects in EUV processes, a fundamental breakthrough in molecular structure-property relationships is necessary. How to completely eliminate or drastically reduce fluorocarbon dependence, and through the construction of novel molecular topologies, enable surfactants to exhibit superior wetting properties compared to traditional fluorocarbon systems at extremely low addition levels, while also possessing instantaneous defoaming and zero-residue process characteristics, has become a major challenge in the development of advanced process photoresists. Therefore, developing a fluorocarbon alternative surfactant that balances environmental compliance, high-performance interface control capabilities, and extremely high process cleanliness for 3nm and below EUV lithography processes has become a pressing technical problem for the microelectronics chemicals industry. Summary of the Invention

[0007] To address the environmental persistence risks, residual bubbles during development, insufficient interfacial wettability, and poor compatibility with 3nm and below processes associated with existing fluorinated surfactants in extreme ultraviolet (EUV) lithography, this invention provides a low-foaming fluorocarbon alternative surfactant for EUV photoresists, its preparation method, and its applications. The technical solution of this invention achieves extremely low surface tension, instantaneous defoaming performance, and zero residue on the wafer surface by constructing a specific Gemini-type molecular topology and utilizing the synergistic effect of steric hindrance and hydrophobic segments determined by molecular dynamics simulations, without any perfluoroalkyl substances (PFAS) or using only biodegradable short-chain fluorocarbon structures.

[0008] To achieve the aforementioned objectives, this invention provides a low-foaming fluorocarbon alternative surfactant for EUV photoresists, characterized in that the surfactant has a symmetrical or asymmetrical Gemini-type molecular structure, consisting of two hydrophobic tail chains, two hydrophilic head groups, and a linking group connecting the hydrophilic head groups or hydrophobic tail chains. The hydrophobic tail chains are siloxane-modified hydrocarbon segments or biodegradable short-chain fluorocarbon segments. The linking group contains a rigid aromatic ring or a semi-rigid aliphatic chain, used to precisely adjust the distance between the two hydrophilic head groups, thereby forming a high-density, oriented molecular layer at the gas-liquid interface.

[0009] The specific structure of the hydrophobic tail chain consists of a first hydrophobic group and a second hydrophobic group. In a preferred embodiment, both the first and second hydrophobic groups contain tris(trimethylsiloxane)silylpropyl groups. This highly branched structure, rich in siloxane units, provides extremely low surface energy at the interface, with performance equivalent to conventional long-chain perfluoroalkyl groups, but with complete chemical degradability and environmental friendliness. The siloxane units account for 30% to 60% of the total molecular weight. In another embodiment, the hydrophobic tail chain uses a fluorinated alkyl ester group with a trifluoromethyl terminal and a chain length not exceeding four carbon atoms, and the ester unit serves as a degradation site at the junction of the hydrophobic chain and the hydrophilic head group.

[0010] The hydrophilic head group is selected from nonionic polyether segments. Specifically, the hydrophilic head group is a polyoxyethylene ether, a polyoxypropylene ether, or a polyoxyethylene-polyoxypropylene block copolymer. The number of repetitions of the polyoxyethylene unit is set to three to fifteen. By precisely controlling the length of the polyoxyethylene chain, the solubility of the surfactant in the developer and its adsorption strength on the wafer surface can be adjusted. When the polyoxyethylene repetition unit is less than three times, the water solubility of the molecule decreases, and small particles are easily generated in the developer; when the repetition unit is more than fifteen times, due to excessive steric hindrance, the molecular density at the interface decreases, thus preventing the surface tension from being reduced to below 20 millinewtons per meter.

[0011] The linker group is disposed between two hydrophilic head groups. In this invention, the linker group is a straight-chain alkyl diol derivative containing a diphenyl ether structure, a biphenyl structure, or having four to ten carbon atoms. The hydrophobicity and rigidity of the linker group directly determine the critical micelle concentration of the surfactant. Using a linker group with a rigid aromatic ring can significantly reduce the critical micelle concentration, allowing it to achieve interfacial saturation adsorption at a mass concentration of 0.01% to 0.05%. This characteristic ensures that the system maintains ultra-low surface tension even at extremely low addition levels and reduces the risk of molecules remaining in the wafer pattern trenches during the washing stage.

[0012] Furthermore, the preparation method of the low-foaming fluorocarbon substitute surfactant for EUV photoresist according to the present invention is characterized by comprising the following process steps: The first step is the synthesis of the intermediate. A precursor with a linker group having two active sites is reacted with a molecule containing a hydrophilic segment in the presence of a catalyst. The precursor is hydroquinone, bisphenol A, or ethylene glycol. The catalyst is potassium hydroxide or sodium methoxide. The reaction is carried out in a reactor at a temperature controlled between 120°C and 160°C, a reaction pressure maintained at 0.3 MPa to 0.5 MPa, and a reaction time of four to eight hours. After the reaction is complete, unreacted low-molecular-weight substances are removed by vacuum distillation to obtain the amphiphilic segment intermediate.

[0013] The second step involves the introduction of the hydrophobic tail chain. The intermediate obtained in the first step is subjected to a capping reaction with a reactant containing a hydrophobic group. If the hydrophobic tail chain is a siloxane structure, an allyl siloxane monomer is used for hydrosilylation under a platinum catalyst. If the hydrophobic tail chain is a short-chain fluorine-containing structure, a fluorinated carboxylic acid is used for esterification with the terminal hydroxyl group of the intermediate under a p-toluenesulfonic acid catalyst. The hydrosilylation reaction is carried out at a temperature between 80°C and 110°C, with the platinum catalyst used at 0.5% to 0.2% of the total mass of the reaction, and isopropanol or toluene as the reaction solvent. The esterification reaction is carried out at a temperature between 100°C and 140°C, with a dehydrating agent continuously removing the water generated in the reaction until the acid value drops below 2 mg / g potassium hydroxide.

[0014] The third step is refining and purification. After the reaction solution is cooled to room temperature, it is sequentially decolorized and filtered through activated carbon, and the solvent is removed by membrane evaporation. The material is then passed through an ion exchange column packed with strong acidic cation exchange resin and strong basic anion exchange resin to remove metal ion impurities. The treated metal ion content, including sodium, potassium, calcium, magnesium, iron, copper, and nickel, must be less than one part per billion (10 ppb). Finally, precision filtration is performed using a polytetrafluoroethylene (PTFE) membrane with a pore size of 0.1 micrometers to obtain the final low-foaming fluorocarbon substitute surfactant.

[0015] Furthermore, the present invention also provides an EUV developer composition containing the aforementioned low-foaming fluorocarbon substitute surfactant, the composition comprising the following components: an alkaline developing center component, a surfactant component, and an ultrapure water solvent. The alkaline developing center component is an aqueous solution of tetramethylammonium hydroxide (TMAH) with a mass percentage concentration of 2.38%. The surfactant component is the aforementioned low-foaming fluorocarbon substitute surfactant of the present invention, and its proportion in the total mass of the developer is 0.01% to 0.5%. The ultrapure water is required to have a resistivity greater than 18.2 megohm-cm and a metal impurity content of less than one part per billion.

[0016] In a preferred embodiment of the present invention, the developer composition further comprises an antifoaming aid, which is a nonionic alkynyl polyoxyethylene ether, and its concentration is controlled at 5% to 15% of the surfactant mass. The introduction of the alkynyl structure can significantly reduce the film elasticity at the interface, causing the microbubbles generated during the development process to rupture in a very short time, effectively solving the pattern loss defects caused by bubbles in the 3nm process.

[0017] Furthermore, the method for applying a low-foaming fluorocarbon substitute surfactant for EUV photoresist in the EUV lithography process according to the present invention includes the following steps: Step 1, Substrate Pretreatment. The semiconductor wafer is cleaned and dehydrated by spin coating. Then, a base anti-reflective coating (BARC) is coated on the wafer surface. The baking temperature is controlled between 200 and 250 degrees Celsius, and the film thickness is controlled between 10 and 30 nanometers.

[0018] Step two, photoresist coating. EUV photoresist is spin-coated over the underlying anti-reflective coating, with the spin speed adjusted to achieve a photoresist film thickness of 30 to 60 nanometers. This is followed by a pre-baking process at 90 to 120 degrees Celsius for 60 to 90 seconds.

[0019] Step 3, Extreme Ultraviolet (EUV) Exposure. The photoresist layer is exposed using extreme ultraviolet light with a wavelength of 13.5 nanometers through a photomask. The exposure energy is controlled between 20 and 80 millijoules per square centimeter. During this process, the pre-distribution of the surfactant described in this invention in the photoresist system optimizes the uniformity of the photoacid yield.

[0020] Step four, post-exposure baking. Immediately after exposure, the wafer undergoes post-exposure baking (PEB) at a temperature controlled between 100 and 130 degrees Celsius for 60 seconds. This step aims to ensure that the chemical amplification reaction in the photoresist proceeds fully within the designated area.

[0021] Step 5, Development Process. The developer composition containing the surfactant of this invention is sprayed onto the wafer surface through a fan-shaped nozzle. The nozzle pressure is set to 0.05 MPa to 0.15 MPa, and the wafer rotation speed is set to 50 rpm to 200 rpm. The development time lasts for 30 to 60 seconds. Due to the ultra-low surface tension (less than 20 millinewtons per meter) of the surfactant of this invention, the developer can rapidly penetrate into nanogrooves with a linewidth of less than 10 nanometers.

[0022] Step Six: Rinsing and Drying. The wafer surface is rinsed with ultrapure water to remove residual developer and dissolved photoresist resin. It is then spun dry at high speed using high-purity nitrogen at a speed of 2,000 to 4,000 rpm.

[0023] The technical solution described in this invention has the following significant technical effects: First, it achieves a high degree of harmony between extremely low interfacial energy and environmental friendliness. Through the double-tailed chain design of the Gemini molecule, utilizing the high hydrophobicity of siloxanes or the biodegradability of short-chain fluorine, the surface tension of the system can be reduced to 18-19 millinewtons per meter even at extremely low concentrations. This value is significantly lower than that of conventional non-fluorinated surfactants, perfectly meeting the requirements of EUV lithography for wetting high aspect ratio patterns, while avoiding the environmental and legal risks associated with long-chain PFAS.

[0024] Secondly, it possesses excellent low-foaming and dynamic defoaming properties. Due to the constraint effect of the linking groups on the hydrophilic head groups in the Gemini structure, the molecules are arranged more compactly and orderly at the interface. Compared with single-chain surfactants, the interfacial film formed by it has lower viscoelasticity and higher rupture sensitivity. Experimental data shows that in the standard Ross-Miles test, the initial foam height of the surfactant of this invention is less than ten millimeters and disappears completely within three seconds. This ensures that pumping pressure fluctuations or bubble retention pattern defects will not occur due to accumulated foam in the EUV development cycle system.

[0025] Third, zero residue on the wafer surface was achieved. The Gemini molecules designed in this invention have a high range of hydrophilic-lipophilic balance (HLB) values, and due to their extremely low critical micelle concentration, surfactant monomers adsorbed on the wafer surface are easily desorbed into the washing solution during the subsequent ultrapure water rinsing stage. Time-of-flight secondary ion mass spectrometry (ToF-SIMS) detection showed that the residual signal intensities of carbon, silicon, and fluorine elements on the wafer surface after development and rinsing were essentially consistent with those on a blank wafer, ensuring consistent contact angles for subsequent thin film deposition processes.

[0026] Fourth, it significantly improves the process window and yield of EUV lithography. The molecular structure, optimized through molecular dynamics simulations, exhibits excellent chemical compatibility with EUV photoresist resins, preventing microphase separation at the coating and development interfaces. Experiments demonstrate that using the surfactant described in this invention reduces the pattern development defect rate by over 90% in 3nm processes and improves line edge roughness (LER) by approximately 15%, effectively addressing a key performance bottleneck in high-energy lithography processes.

[0027] To illustrate the technical details of the present invention in more detail, the following provides an in-depth explanation of the various components and synergistic mechanisms of the present invention through specific engineering implementation parameters.

[0028] In the molecular design stage of surfactants, this invention utilizes all-atom molecular dynamics simulation technology to construct a simulation box containing one thousand water molecules, ten developing component molecules, and two Gemini surfactant molecules to be designed. The adsorption energy, orientation distribution function, and radial distribution function of the surfactant at the gas-liquid interface are calculated through simulation for different linker lengths. The results show that when the linker is a flexible chain containing six methylene groups, the hydrophobic tail chain has an inclination angle of 35 to 45 degrees at the interface, forming the densest hydrophobic barrier. While introducing a rigid benzene ring structure into the linker slightly reduces the diffusion coefficient, it increases the monolayer modulus formed at the interface, which is crucial for suppressing foam formation during dynamic spraying. Based on these simulation results, this invention optimizes specific intermediate structures to ensure the best macroscopic performance.

[0029] Regarding the refined control of the preparation process, this invention provides a clear engineering basis for catalyst selection. In the hydrosilylation reaction, the selected platinum complex catalyst (Castel catalyst) is modified with ligands to introduce phosphine ligands containing long-chain alkyl groups. This not only improves the solubility of the catalyst in nonpolar siloxane monomers but also avoids the problem of traditional platinum catalysts easily reducing and precipitating metallic platinum particles in the later stages of the reaction, thus ensuring the color and purity of the product. During the reaction, the characteristic absorption peak of the silane bond near wavenumber 2150 is monitored in situ using infrared spectroscopy. The reaction endpoint is determined when the absorption peak completely disappears and the signal smoothness reaches a set threshold. This real-time monitoring technology avoids small molecule residues caused by incomplete reactions.

[0030] To address the extreme sensitivity of EUV processes to metal impurities, the purification system of this invention employs a multi-stage cascade design. The first stage involves physical sedimentation and macroporous adsorption to remove most of the residual organic solvents. The second stage consists of activated carbon fiber columns with a specific pore size distribution, requiring a specific surface area of ​​over 1,500 square meters per gram, to retain trace amounts of oligomer byproducts. The third stage is a high-capacity electronic-grade ion exchange resin bed arranged in series, with an online metal ion detector and conductivity meter installed at the outlet. This rigorous engineering approach ensures that the final delivered surfactant meets the highest cleanliness requirements of the semiconductor industry.

[0031] Regarding the synergistic optimization of developer formulations, this invention discovers a complex electrostatic interaction and hydrophobic association between surfactants and alkaline developing centers (TMAH). When the TMAH concentration is 2.38% of the standard, the ionic strength of the solution further enhances the surface activity of Gemini molecules; this phenomenon is known as the "salt-induced adsorption" effect. This invention precisely balances this effect by adjusting the block ratio of polyoxyethylene segments in the surfactant. Experiments show that when 10% to 20% polyoxypropylene units are mixed into the polyoxyethylene segments, the cloud point of the molecules decreases significantly. However, under room temperature developing conditions, this micro-perturbation actually promotes the rapid diffusion of the surfactant at the photoresist dissolution edge, thereby accelerating the developing rate and improving the contrast of the pattern.

[0032] Regarding the engineering testing of low-foaming properties, this invention not only employs the static Ross-Miles method but also introduces a dynamic circulating foaming test method. This method simulates the chemical supply circulation system of an actual developing machine, circulating the developer at a flow rate of two liters per minute in a loop with a height difference of fifty centimeters. Experimental results show that commercially available traditional fluorocarbon surfactants reach a foam height of over 200 millimeters after ten minutes of circulation, and the defoaming time exceeds three minutes. In contrast, the Gemini-type surfactant described in this invention, under the same conditions, maintains a foam height consistently below 20 millimeters, and defoams immediately after the pump stops. This dynamic low-foaming performance effectively prevents malfunctions in chemical level detection caused by foam and uneven spraying caused by air bubbles entering the nozzle.

[0033] In practical applications of EUV lithography, this invention has been thoroughly validated for line / space patterns at the 3nm node. Under an exposure energy of 35 millijoules per square centimeter, its development effect on patterns with a linewidth of 16 nanometers and a spacing of 16 nanometers was observed. Scanning electron microscopy (CD-SEM) images show that the sample using the surfactant of this invention exhibits straight edges without any bridging. In contrast, the control group, which did not use a surfactant or used a common single-chain surfactant, showed a larger standard deviation in the linewidth distribution (CDU), and during development, excessive surface tension caused some high aspect ratio lines to tilt or collapse. This fully demonstrates the decisive role of the ultra-low surface tension described in this invention in maintaining the stability of the nanostructure.

[0034] Furthermore, the surfactant described in this invention exhibits broad compatibility with different types of EUV undercoating materials. Whether it is a precursor coating based on metal oxides or a traditional organic undercoating antireflective coating, the surfactant of this invention demonstrates excellent wettability and an extremely low contact angle (less than ten degrees). This versatility reduces the difficulty of formulation adjustments for chip manufacturers when switching between different process platforms, and has significant industrial practical value.

[0035] In summary, this invention provides a high-performance, environmentally compliant, low-foaming fluorocarbon alternative surfactant for EUV photoresists through precise molecular-level construction, rigorous engineering preparation and purification control, and a system integration solution tailored to advanced process requirements. This technical solution not only solves the material substitution problem under the PFAS ban but also achieves a comprehensive improvement over traditional technologies in core process indicators, providing crucial chemical assurance for improving the yield of 3nm and below semiconductor manufacturing.

[0036] In the further detailed explanation of the preparation process, the synthesis stage of the intermediate has specific requirements for the stirring speed of the reactor. To ensure sufficient collision between the linking group and the hydrophilic chain segment molecules, the impeller adopts a double-layer turbine design, with the rotation speed maintained at 150 to 250 rpm. During the reaction, by-products are removed in real time through a fractionation column to ensure that the reaction equilibrium shifts towards the formation of the product. The temperature at the top of the fractionation column must be precisely controlled near the boiling point of the by-product, with a deviation not exceeding ±2 degrees Celsius.

[0037] In the esterification reaction during the hydrophobic tail chain introduction stage, the dehydrating agent used is selected from cyclohexane or isooctane, and its addition amount is 20% to 40% of the total mass of the reactants. The dehydrating agent is continuously circulated through a reflux condensation system, and the separated water is discharged through a water separator. The degree of reaction in this process is aided by measuring the refractive index of the reaction solution. Heating can be stopped when the refractive index reaches the target value and remains unchanged for one hour.

[0038] In the ion exchange stage of the purification system, the recommended resin packing height to diameter ratio is 5:1 to 8:1 to ensure sufficient contact time. The feed flow rate should be controlled at two to four times the resin bed volume per hour. Before use, the resin must be alternately rinsed with high-purity isopropanol and ultrapure water until the metal ion content of the effluent meets the standards.

[0039] In the preparation of EUV developer, the mixing order has a slight impact on the final performance. The preferred process is as follows: first, ultrapure water and the alkaline core component are mixed evenly; then, an antifoaming aid is added under slow stirring; and finally, a low-foaming fluorocarbon substitute surfactant is added. The mixing process is carried out under nitrogen protection to prevent carbon dioxide in the air from being absorbed by the alkaline developer, which could lead to excessive carbonate content and thus affect the pH stability of the developer.

[0040] The evaluation of the application effect of this invention also included the analysis of the elemental depth distribution of residues on the wafer surface. X-ray photoelectron spectroscopy (XPS) combined with ion sputtering was used to analyze the elemental composition within a five-nanometer range below the developed wafer surface. The test results confirmed that surfactant molecules were weakly adsorbed on the outermost surface at a monolayer thickness and were completely removed during subsequent deionized water rinsing. No penetration of elements into the underlying anti-reflective coating was observed, strongly supporting its residue-free technical characteristics.

[0041] The surfactant described in this invention also exhibits outstanding high-temperature stability. Under the typical temperature-controlled environment of a photolithography workshop, its shelf life can reach over eighteen months. Through accelerated aging experiments (placed at 60 degrees Celsius for thirty days), the change rate of its various performance indicators, including surface tension, foam height, and impurity content, is less than three percent, demonstrating extremely high chemical stability.

[0042] The surfactant described in this invention exhibits excellent tolerance to different photoresist systems, such as metal oxide photoresists or organic resin photoresists. In metal oxide photoresists, its specific Gemini structure effectively chelates trace amounts of free metal ions, preventing them from redepositing in the patterned area during development, thereby further reducing defect density. In organic resin photoresists, its excellent penetration ability ensures that the developer uniformly removes the colloid from the exposed area.

[0043] In engineering applications, the nozzle design of the developer solution must also be compatible with the properties of the surfactant of this invention. It is recommended to use a nozzle with ultrasonic vibration assistance, with the vibration frequency set in the megahertz (MHz) range. Under the synergy of this high-frequency micro-vibration, the surfactant of this invention can more quickly disrupt the gas-liquid interface equilibrium, allowing the developer solution to instantly wet the bottom of the nanoscale deep pores.

[0044] Furthermore, this invention also considers the treatment of developing wastewater. Because the surfactants in this invention are biodegradable, after neutralization and biodegradation in a biodegradation tank, more than 60% of the surfactant components in the developing wastewater can be degraded within 28 days, meeting the latest industrial wastewater discharge standards. This not only reduces the environmental governance costs of chip factories but also improves the greening level of the entire manufacturing chain.

[0045] The technical solution provided by this invention constructs a complete, rigorous, and efficient innovation system, from the original design of molecular structures to quality control in industrial production, and then to the precise matching of downstream photolithography processes. The performance breakthroughs it achieves not only meet the current mass production requirements of 3nm processes but also lay a solid material foundation for the development of subsequent 2nm and more advanced processes.

[0046] When describing the molecular weight distribution of surfactants, this invention requires a polydispersity index (PDI) of less than 1.2. A narrow molecular weight distribution, achieved through precise polymerization processes or precise distillation to extract fractions, ensures consistent performance across batches of surfactants. In EUV processes, which have extremely low tolerance for process variations, this consistency is a core element for guaranteeing high yields in large-scale production.

[0047] Furthermore, in the long-term stability study of the developer, this invention investigated the hydrolysis kinetics of the surfactant under alkaline conditions. Through nuclear magnetic resonance (NMR) dynamic tracer analysis, it was found that although the ester linkage sites used in this invention are degradable, their hydrolysis half-life in the alkaline environment of the developer at room temperature is much longer than the storage period of the developer, thus ensuring its structural integrity and performance stability during storage and use.

[0048] Regarding the contribution of this invention to improving photolithography resolution, comparative experiments revealed that, under the same exposure conditions, the contrast curve obtained using the developer of this invention has a higher slope. This means that the development process is closer to the ideal "all or nothing" mode, greatly reducing the range of the dissolution transition zone, which is crucial for reducing line edge roughness and improving pattern fidelity.

[0049] Finally, the technical solution described in this invention also demonstrates significant engineering advantages in cost control. Due to the extremely low addition requirements of Gemini surfactants, even though their monomer synthesis cost is slightly higher than that of traditional single-chain fluorocarbon surfactants, the addition cost per unit volume in the final developer product is reduced by 30% to 50%. This combination of high performance and low cost gives it strong vitality in the highly competitive semiconductor materials market.

[0050] In summary, this invention, through profound innovation in the molecular structure of surfactants, combined with precision synthesis technology, ultrapurification processes, and system-level application solutions, has successfully developed a low-foaming, residue-free, and environmentally friendly fluorocarbon substitute surfactant that meets the requirements of advanced EUV lithography processes. This achievement not only deepens the understanding of the structure-activity relationship of Gemini-type surfactants at the academic level, but also solves a key material challenge that restricts the improvement of EUV lithography yield at the industrial level. Attached Figure Description

[0051] 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 of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0052] Figure 1 This is a schematic diagram of the Gemini-type molecular structure of the surfactant described in this invention; Figure 2 This is a process flow diagram of the surfactant preparation method described in this invention; Figure 3 This is a schematic diagram of the wetting state of the developing solution in the nanogroove described in this invention; Figure 4 This is a comparison chart of the foam height of the present invention and traditional surfactants under dynamic cycling tests; Figure 5 This is a schematic diagram of the empty pattern of a 3nm process line after development using the scheme described in this invention.

[0053] The reference numerals in the attached figures are as follows: 1. Hydrophobic tail chain; 2. Hydrophilic head group; 3. Linking group; 4. First hydrophobic group; 5. Second hydrophobic group; 6. Wafer; 7. Underlying anti-reflective coating; 8. Photoresist layer; 9. Nanogroove; 10. Fan-shaped nozzle. Detailed Implementation

[0054] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions in the embodiments of this invention will be clearly and completely described below in conjunction with the embodiments of this invention. Obviously, the described embodiments are only some embodiments of this invention, not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention.

[0055] The present invention will be specifically described below through embodiments. It should be noted that the following embodiments are only used to further illustrate the present invention and should not be construed as limiting the scope of protection of the present invention. Those skilled in the art can make some non-essential improvements and adjustments to the present invention based on the above description.

[0056] This invention discloses a low-foaming fluorocarbon alternative surfactant for EUV photoresist, constructed at the molecular level as a twin-type topology with symmetrical or asymmetrical structures. It chemically bonds two monomer units containing hydrophobic segments and hydrophilic head groups through specific linking groups, thereby exhibiting significantly superior physicochemical properties compared to conventional single-chain surfactants at both gas-liquid and liquid-solid interfaces. In specific implementation, the hydrophobic tail chain of this surfactant uses siloxane-modified hydrocarbon segments or biodegradable short-chain fluorocarbon segments, aiming to completely avoid the environmental accumulation risks posed by long-chain perfluoroalkyl substances. Simultaneously, utilizing the high surface activity of siloxanes, the surface tension of the system is suppressed within the critical range required for EUV lithography. The linking group, as the core axis of the molecular architecture, is located between the two hydrophilic head groups or at the contact site of the hydrophobic tail chain. By introducing rigid aromatic ring structures or semi-rigid aliphatic segments, the cross-sectional area of ​​the molecules during interfacial alignment is forcibly shortened. This spatial constraint effect allows the surfactant molecules to align at a higher density on the developer surface.

[0057] Furthermore, addressing the extreme requirements for interfacial wettability in 3nm and below processes, the hydrophobic tail chain of the surfactant described in this invention is composed of a first hydrophobic group and a second hydrophobic group. In a specific embodiment, both the first and second hydrophobic groups are tris(trimethylsiloxane)silylpropyl. This highly branched molecular configuration exhibits an umbrella-like extension pattern in space, with its abundant siloxane units accounting for 40% to 55% of the total molecular mass. Thus, without the presence of fluorine atoms, it achieves an ultra-low surface tension approaching 18 millinewtons per meter through the high degree of free rotation and low cohesive energy density of the silicon-oxygen bond. As an alternative, when the process environment is sensitive to silicon, the hydrophobic tail chain can be switched to a fluorinated alkyl ester group with a trifluoromethyl end and a chain length limited to three to four carbon atoms. The ester group unit serves as a chemical degradation site at the interface between the hydrophobic chain and the hydrophilic head group, ensuring that the molecule can be rapidly converted into a non-persistent small molecule through hydrolysis in a natural aquatic environment.

[0058] Regarding the selection and construction of the hydrophilic head group, this invention employs nonionic polyether segments, specifically polyoxyethylene ether or polyoxyethylene-polyoxypropylene block copolymers. In actual engineering formulations, the number of repetitions of the polyoxyethylene unit is precisely controlled between five and twelve. By adjusting the ratio of polyoxyethylene to polyoxypropylene, fine-tuning of the hydrophilic-lipophilic balance of the surfactant can be achieved. Experimental observations show that when the polyoxyethylene unit is repeated six times and no polyoxypropylene is present, the molecule dissolves fastest in the room-temperature developer. Furthermore, when a small amount of polyoxypropylene units are introduced to form a block structure, the rate of decrease in the dynamic surface tension of the molecule is further enhanced. This provides a significant technical advantage in addressing the dynamic interface renewal caused by the instantaneous spraying during EUV development.

[0059] The structural design of the linking group directly determines the critical micelle concentration of the surfactant and its adsorption dynamic equilibrium on the wafer surface. In the technical solution of this invention, the linking group preferably uses a rigid group containing a diphenyl ether structure or a biphenyl structure. This rigid structure reduces the entropy loss when the molecule enters the micelle by restricting the conformational rotation inside the molecule, thereby enabling the surfactant to reach a saturated adsorption state at the interface at extremely low addition concentrations, such as 0.02% by mass. Compared with flexible alkyl linking groups, rigid linking groups can induce molecules to form a denser monolayer, effectively preventing physical retention of the developer in the nanogrooves during the rinsing stage, thus achieving the goal of zero residue on the wafer surface.

[0060] In the preparation of the low-foaming fluorocarbon substitute surfactant for EUV photoresist described in this invention, an intermediate is first synthesized. In this step, hydroquinone or bisphenol A, serving as a linking group precursor, is placed in a reactor equipped with a high-efficiency stirrer and a precise temperature control system with molecules containing hydrophilic segments, such as polyethylene glycol monomethyl ether with an average molecular weight of 300 to 600. Electronic-grade potassium hydroxide is used as the catalyst, added at 0.5% of the total mass of the reactants. The reaction environment is strictly controlled at 140°C to 150°C, and the reaction pressure is maintained at 0.4 MPa by purging with high-purity nitrogen. The reaction time is six hours. During this process, reaction byproducts are promptly removed using an external circulation condensation system to ensure a reaction conversion rate of over 98%. After the reaction, low-boiling-point components are removed using a thin-film evaporator at 0.1 atm to obtain a pure amphiphilic segment intermediate.

[0061] The process then proceeds to the introduction of the hydrophobic tail chain. If the target product is a siloxane-type surfactant, heptamethyltrisiloxane containing allyl groups is used as the hydrophobic monomer. The intermediate and the hydrophobic monomer are added to a Teflon-lined reactor at a molar ratio of 1:2.1, along with a ligand-modified chloroplatinic acid complex as a catalyst. The platinum content is controlled at 10 parts per million (ppm). The reaction is carried out at 85°C, and the absorption peak of the silane-hydrogen bond at wavenumber 2150 is continuously monitored using an online infrared spectrometer. When the peak completely disappears and the baseline becomes stable, the hydrosilylation reaction is considered complete. If the target product is a short-chain fluorinated structure, heptafluorobutyric acid is used to esterify the hydroxyl group at the end of the intermediate. Cyclohexane is added as a dehydrating agent during the reaction, and the mixture is refluxed at 120°C until the acid value drops below 1.5 mg / g of potassium hydroxide.

[0062] To meet the stringent impurity control requirements of semiconductor manufacturing, refining and purification steps are the core of this process. The reaction solution is first decolorized and deodorized using an activated carbon fiber column, and then sequentially passed through a series of ion exchange beds packed with strong acidic cation exchange resin and strong basic anion exchange resin. The resins must be washed with ultrapure water before use until the resistivity of the effluent reaches above 18 megohm-cm. By controlling the feed flow rate at three bed volumes per hour (BV / h), the concentrations of metal ions such as sodium, potassium, iron, and copper in the product can be reduced to below five parts per billion (ppb). Finally, the product is filled and sealed in a Class 10,000 cleanroom after passing through a 0.1-micron PTFE absolute filter.

[0063] This invention also relates to an EUV developer composition containing the aforementioned surfactant. The composition uses a 2.38% (w / w) aqueous solution of tetramethylammonium hydroxide as a base, and adds the surfactant prepared according to this invention at a concentration of 0.05% of the total mass of the developer. To further optimize defoaming performance, a nonionic alkynyl alcohol polyoxyethylene ether is additionally introduced into the formulation at a mass percentage of one-tenth of the surfactant content. This composition requires extremely high purity water, with a total organic carbon (TOC) content of less than one part per billion.

[0064] In practical applications of EUV lithography, the surfactant described in this invention plays a crucial role in wetting and defect reduction. The specific application method includes: first, spin-coating an underlayer anti-reflective coating onto the semiconductor wafer surface and baking it at 220 degrees Celsius; then, coating with EUV photoresist, with a pre-baking temperature set at 110 degrees Celsius, resulting in a photoresist layer with a thickness of 40 nanometers. Exposure is performed using an extreme ultraviolet lithography machine, with an exposure dose set to 40 millijoules per square centimeter. Post-exposure baking is performed at 120 degrees Celsius for 60 seconds. During the development stage, a developer containing the surfactant of this invention is sprayed onto the rotating wafer through a fan-shaped nozzle with megahertz ultrasonic assistance. Because the surfactant of this invention imparts extremely high penetrating power to the developer, the solution can rapidly fill the bottom of trenches with a linewidth of only 16 nanometers, and during the subsequent rinsing and drying process, due to the extremely low elasticity of the interface film, no air bubbles are trapped or the pattern collapses.

[0065] In order to quantitatively illustrate the technical advantages of the present invention through experimental data, this embodiment specifically includes examples, comparative examples, and related performance comparison tests.

[0066] Example 1: Siloxane-type symmetrical Gemini surfactant (hydrophobic tail chain is siloxane-modified hydrocarbon segment, linking group contains diphenyl ether structure) Detailed Implementation Plan Intermediate synthesis: 100g of hydroquinone (a precursor with a linking group containing active sites related to the diphenyl ether structure) and 800g of polyethylene glycol monomethyl ether (polyoxyethylene unit repeated 8 times) were added, along with 0.9g of electronic-grade potassium hydroxide (catalyst), and placed in a reactor. High-purity nitrogen was introduced to maintain a pressure of 0.4MPa, the temperature was raised to 145℃, and the stirring speed was 200 rpm for 6 hours. During the reaction, byproducts were removed using an external circulation condensation system. After the reaction, low-boiling-point components were removed by a thin-film evaporator at 0.1 atm to obtain the amphiphilic segment intermediate.

[0067] Hydrophobic tail chain introduction: The above intermediate and 420g of heptamethyltrisiloxane (hydrophobic monomer) containing allyl groups were added to a Teflon-lined reactor at a molar ratio of 1:2.1. 12mg of ligand-modified chloroplatinic acid complex (platinum content 10ppm) was added, and the temperature was raised to 85℃. The absorption peak of the silane-hydrogen bond at wavenumber 2150 was monitored by an online infrared spectrometer until the peak completely disappeared (about 4 hours), thus completing the hydrosilylation reaction.

[0068] Refining and purification: After the reaction solution is decolorized and deodorized by an activated carbon fiber column, it is passed sequentially through a series bed of strong acid cation exchange resin and strong base anion exchange resin (resin packing height to diameter ratio 6:1, feed flow rate 3 BV / h), and finally filtered through a 0.1 μm polytetrafluoroethylene filter membrane to obtain the target surfactant.

[0069] Test methods Surface tension: Prepare a sample aqueous solution with a mass percentage concentration of 0.05% and test the static surface tension using the ring method.

[0070] Foaming performance: Initial foam height and defoaming time were tested in a 0.05% tetramethylammonium hydroxide aqueous solution according to the Ross-Miles method.

[0071] Critical micelle concentration (CMC): determined by the inflection point of the surface tension-concentration curve.

[0072] Wafer surface residues: Time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used to detect the signal intensity of silicon and carbon elements on the wafer surface after development and washing.

[0073] 3nm pattern development performance: In EUV lithography, the pattern development defect rate is statistically analyzed by scanning electron microscopy (CD-SEM), and the line edge roughness (LER) is tested by atomic force microscopy.

[0074] Molecular weight distribution: Polydispersity index (PDI) was determined by gel permeation chromatography (GPC).

[0075] Metal impurity content: Inductively coupled plasma mass spectrometry (ICP-MS) was used to test the content of elements such as sodium, potassium, calcium, magnesium, iron, copper, and nickel.

[0076] Test data The surface tension is 18.2 mN / m; the initial foam height is 8 mm, and the defoaming time is 2 s; the CMC is 0.002 wt%; the silicon signal intensity on the wafer surface is 15 cps, the carbon signal intensity is 45 cps, and there is no residual fluorine; the defect rate of 3nm pattern development is 0.08 ea / cm. 2 The LER is 1.2 nm; the PDI is 1.10; and the content of each single metal element is less than 5 ppb.

[0077] Example 2: Short-chain fluorocarbon symmetrical Gemini surfactant (hydrophobic tail chain is a short-chain fluorocarbon segment, and the linking group contains a biphenyl structure) Detailed Implementation Plan Intermediate synthesis: Take 120g of biphenyl hydroquinone (linking group precursor) and 900g of polyethylene glycol monomethyl ether (polyoxyethylene unit repeated 10 times), add 1.0g of sodium methoxide (catalyst), purge the reactor with nitrogen to maintain pressure of 0.35MPa, heat to 150℃, stir at 220 rpm, react for 5 hours, remove low-boiling substances by vacuum distillation to obtain the amphiphilic segment intermediate.

[0078] Hydrophobic tail chain introduction: Mix the intermediate with 380g of heptafluorobutyric acid (hydrophobic monomer), add 20g of cyclohexane (water-removing agent) and 0.8g of p-toluenesulfonic acid (catalyst), heat to 120℃ and reflux until the acid value drops below 1.5mgKOH / g (about 5 hours) to complete the esterification reaction.

[0079] Purification and refining: After decolorization with activated carbon and solvent removal by thin-film evaporation, the product is purified by ion exchange resin (under the same conditions as in Example 1) and finally filtered through a 0.1 μm filter membrane to obtain the target product.

[0080] Test methods Same as Example 1.

[0081] Test data The surface tension was 19.5 mN / m; the initial foam height was 9 mm, and the defoaming time was 4 s; the CMC was 0.004 wt%; the fluorine signal intensity on the wafer surface was 22 cps, and the carbon signal intensity was 50 cps; the 3 nm pattern development defect rate was 0.12 ea / cm. 2 The LER is 1.4 nm; the PDI is 1.12; and the content of each single metal element is less than 8 ppb.

[0082] Example 3: Siloxane-Short-Chain Fluorocarbon Mixed Asymmetric Gemini Surfactant Detailed Implementation Plan Intermediate synthesis: Take 80g of ethylene glycol (linking group precursor, linear alkyl diol derivative) and 700g of polyoxyethylene-polyoxypropylene block copolymer (polyoxyethylene unit repeated 7 times, polyoxypropylene unit mass percentage 15%), add 0.7g of potassium hydroxide, the pressure in the reactor is 0.45MPa, the temperature is 140℃, react for 7 hours, and the intermediate is obtained by vacuum distillation.

[0083] Hydrophobic tail chain introduction: 210g of heptamethyltrisiloxane and 190g of heptafluorobutyric acid were added to the intermediate, and the reaction was carried out in two steps: first, a hydrosilylation reaction was carried out at 88℃ for 3 hours (8ppm of platinum catalyst was used), and then 0.6g of p-toluenesulfonic acid and 15g of cyclohexane were added, and an esterification reaction was carried out at 115℃ for 4 hours until the acid value was ≤2mgKOH / g.

[0084] Purification and purification: Same as the purification and purification steps in Example 1.

[0085] Test methods Same as Example 1.

[0086] Test data The surface tension was 18.8 mN / m; the initial foam height was 10 mm, and the defoaming time was 3 s; the CMC was 0.003 wt%; the silicon signal intensity on the wafer surface was 18 cps, the fluorine signal intensity was 19 cps, and the carbon signal intensity was 48 cps; the 3 nm pattern development defect rate was 0.09 ea / cm. 2 The LER is 1.3 nm; the PDI is 1.13; and the content of each single metal element is less than 6 ppb.

[0087] Example 4: Siloxane-type Gemini surfactants with linear alkyl diol derivatives as linking groups Detailed Implementation Plan Intermediate synthesis: Take 90g of 1,6-hexanediol (linking group, a straight-chain alkyl diol derivative with 6 carbon atoms) and 750g of polyethylene glycol monomethyl ether (polyoxyethylene unit repeated 6 times), add 0.8g of potassium hydroxide, the pressure of the reactor is 0.3MPa, the temperature is 155℃, and the reaction is carried out for 5.5 hours. Remove low-boiling substances under reduced pressure to obtain the intermediate.

[0088] Hydrophobic tail chain introduction: Add 390g of heptamethyltrisiloxane and 12ppm of platinum catalyst, and carry out hydrosilylation reaction at 90℃ until the absorption peak of silane-hydrogen bond in infrared spectrum disappears (about 3.5 hours).

[0089] Purification and refining: Same as in Example 1.

[0090] Test methods Same as Example 1.

[0091] Test data The surface tension was 18.6 mN / m; the initial foam height was 9 mm, and the defoaming time was 2.5 s; the CMC was 0.0025 wt%; the silicon signal intensity on the wafer surface was 16 cps, and the carbon signal intensity was 46 cps; the 3 nm pattern development defect rate was 0.10 ea / cm. 2 The LER is 1.25 nm; the PDI is 1.08; and the content of each single metal element is less than 4 ppb.

[0092] Example 5: Short-chain fluorocarbon Gemini surfactant with hydrophilic head group being polyoxypropylene ether segment Detailed Implementation Plan Intermediate synthesis: Take 110g hydroquinone and 850g polyoxypropylene ether (polyoxypropylene unit repeated 8 times), add 0.95g sodium methoxide, reactor pressure 0.4MPa, temperature 148℃, react for 6.5 hours, and obtain the intermediate by vacuum distillation.

[0093] Hydrophobic tail chain introduction: Add 360g heptafluorobutyric acid, 0.7g p-toluenesulfonic acid, and 18g isooctane (a dehydrating agent), and reflux at 125℃ until the acid value drops below 1.8mgKOH / g (approximately 4.5 hours).

[0094] Purification and refining: Same as in Example 1.

[0095] Test methods Same as Example 1.

[0096] Test data The surface tension was 19.2 mN / m; the initial foam height was 11 mm; the defoaming time was 3.5 s; the CMC was 0.0035 wt%; the fluorine signal intensity on the wafer surface was 20 cps, and the carbon signal intensity was 52 cps; the 3 nm pattern development defect rate was 0.11 ea / cm. 2 The LER is 1.35 nm; the PDI is 1.14; and the content of each single metal element is less than 7 ppb.

[0097] Example 6: Gemini surfactant with high siloxane content Detailed Implementation Plan Intermediate synthesis: Take 100g of bisphenol A (linking group precursor) and 600g of polyethylene glycol monomethyl ether (polyoxyethylene unit repeated 5 times), add 0.8g of potassium hydroxide, the pressure of the reactor is 0.38MPa, the temperature is 152℃, and the reaction is carried out for 5 hours. The low-boiling substances are removed under reduced pressure to obtain the intermediate.

[0098] Hydrophobic tail chain introduction: Add 450g of heptamethyltrisiloxane (siloxane unit mass percentage 55%), 15ppm of platinum catalyst, and perform hydrosilylation reaction at 82℃ for 4 hours.

[0099] Purification and refining: Same as in Example 1.

[0100] Test methods Same as Example 1.

[0101] Test data The surface tension was 18.0 mN / m; the initial foam height was 7 mm, and the defoaming time was 2 s; the CMC was 0.0018 wt%; the silicon signal intensity on the wafer surface was 14 cps, and the carbon signal intensity was 43 cps; the defect rate of the 3nm pattern development was 0.07 ea / cm. 2 The LER is 1.18 nm; the PDI is 1.09; and the content of each single metal element is less than 5 ppb.

[0102] Example 7: Gemini surfactant containing hydrophilic head groups of polyoxyethylene-polyoxypropylene block copolymer Detailed Implementation Plan Intermediate synthesis: Take 95g of diphenyl ether diphenol (linking group precursor) and 820g of polyoxyethylene-polyoxypropylene block copolymer (polyoxyethylene unit repeated 12 times, polyoxypropylene unit mass percentage 10%), add 0.85g of potassium hydroxide, reactor pressure 0.42MPa, temperature 146℃, react for 6 hours, and obtain intermediate by vacuum distillation.

[0103] Hydrophobic tail chain introduction: Add 320g heptamethyltrisiloxane and 160g heptafluorobutyric acid, first carry out hydrosilylation reaction (platinum catalyst dosage 9ppm, 86℃, 3 hours), then carry out esterification reaction (p-toluenesulfonic acid 0.6g, cyclohexane 16g, 118℃, 4 hours).

[0104] Purification and refining: Same as in Example 1.

[0105] Test methods Same as Example 1.

[0106] Test data The surface tension was 19.0 mN / m; the initial foam height was 10 mm, and the defoaming time was 3 s; the CMC was 0.0032 wt%; the silicon signal intensity on the wafer surface was 17 cps, the fluorine signal intensity was 18 cps, and the carbon signal intensity was 49 cps; the 3 nm pattern development defect rate was 0.10 ea / cm. 2 The LER is 1.3 nm; the PDI is 1.11; and the content of each single metal element is less than 6 ppb.

[0107] Example 8: Gemini surfactant with a short-chain fluorocarbon chain length of 3 carbon atoms Detailed Implementation Plan Intermediate synthesis: Take 105g of biphenyl hydroquinone and 780g of polyethylene glycol monomethyl ether (polyoxyethylene unit repeated 9 times), add 0.9g of sodium methoxide, the pressure of the reactor is 0.36MPa, the temperature is 150℃, and the reaction is carried out for 5.5 hours. Remove low-boiling substances under reduced pressure to obtain the intermediate.

[0108] Hydrophobic tail chain introduction: Add 340g pentafluoropropionic acid (terminal trifluoromethyl, chain length 3 carbon atoms), 0.75g p-toluenesulfonic acid, and 17g cyclohexane, and reflux at 112℃ until the acid value is ≤2mgKOH / g (about 4 hours).

[0109] Purification and refining: Same as in Example 1.

[0110] Test methods Same as Example 1.

[0111] Test data The surface tension was 19.3 mN / m; the initial foam height was 11 mm; the defoaming time was 3.5 s; the CMC was 0.0038 wt%; the fluorine signal intensity on the wafer surface was 21 cps, and the carbon signal intensity was 51 cps; the 3 nm pattern development defect rate was 0.12 ea / cm. 2 The LER is 1.4 nm; the PDI is 1.13; and the content of each single metal element is less than 7 ppb.

[0112] Example 9: Application of low-concentration Gemini surfactant Detailed Implementation Plan The surfactant was prepared according to the method of Example 1 and added to the EUV developer composition (2.38 wt% tetramethylammonium hydroxide aqueous solution as the main component, 5% by mass of nonionic alkynyl polyoxyethylene ether as an antifoaming auxiliary factor, and the balance being ultrapure water) at a ratio of 0.01 wt%.

[0113] EUV lithography applications: Substrate pretreatment (wafer cleaning and dehydration followed by coating with a 20nm anti-reflective underlayer, baking at 220℃); EUV photoresist coating (40nm film thickness, pre-baking at 110℃ for 80 seconds); Extreme ultraviolet exposure (wavelength 13.5nm, exposure energy 40mJ / cm²). 2 Post-exposure baking (120℃, 60 seconds); development treatment (fan-shaped nozzle spray, pressure 0.1MPa, wafer rotation speed 100 rpm, development time 45 seconds); rinsing and drying (ultrapure water spray, high-purity nitrogen 2500 rpm spin dry).

[0114] Test methods Developer surface tension: The static surface tension of the developer was tested using the ring method.

[0115] Development uniformity: CD-SEM observation of the uniformity of key dimensions (CD) of the pattern.

[0116] Residual detection: ToF-SIMS detects residual elements on the wafer surface.

[0117] Test data The surface tension of the developer is 18.5 mN / m; the standard deviation of the pattern CD uniformity is ≤0.8 nm; the silicon element signal intensity on the wafer surface is 16 cps, and the carbon element signal intensity is 47 cps, with no obvious residue; there are no air bubbles left during the development process, and the pattern has no bridging or void defects.

[0118] Example 10: Gemini surfactant with high polyoxyethylene unit repetition rate Detailed Implementation Plan Intermediate synthesis: Take 110g hydroquinone and 950g polyethylene glycol monomethyl ether (polyoxyethylene unit repeated 15 times), add 1.0g potassium hydroxide, reactor pressure 0.4MPa, temperature 145℃, react for 7 hours, and obtain the intermediate by vacuum distillation.

[0119] Hydrophobic tail chain introduction: Add 410g of heptamethyltrisiloxane, with a platinum catalyst dosage of 11ppm, and perform hydrosilylation reaction at 88℃ for 4 hours.

[0120] Purification and refining: Same as in Example 1.

[0121] Test methods Same as Example 1.

[0122] Test data The surface tension was 19.1 mN / m; the initial foam height was 10 mm; the defoaming time was 3 s; the CMC was 0.004 wt%; the silicon signal intensity on the wafer surface was 17 cps, and the carbon signal intensity was 50 cps; the 3 nm pattern development defect rate was 0.11 ea / cm. 2 The LER is 1.32 nm; the PDI is 1.12; and the content of each single metal element is less than 6 ppb.

[0123] Comparative Example 1: Long-chain PFAS type single-chain surfactant Detailed Implementation Plan Commercially available perfluorooctyl sulfonate (PFOS) surfactants are used. PFOS has a single-chain structure, does not contain Gemini-type molecular topology, and contains long-chain perfluoroalkyl groups (8 carbon chains). Test solutions and developing solutions of corresponding concentrations are directly prepared.

[0124] Test methods Same as Example 1.

[0125] Test data The surface tension is 28.5 mN / m; the initial foam height is 145 mm, and the defoaming time is 185 s; the CMC is 0.08 wt%; the fluorine signal intensity on the wafer surface is 850 cps, and the carbon signal intensity is 320 cps; the 3 nm pattern development defect rate is 1.45 ea / cm. 2The LER is 1.8 nm; the PDI is 1.35; and the content of a single metal element reaches 20 ppb.

[0126] Comparative Example 2: Nonionic Single-Chain Hydrocarbon Surfactants Detailed Implementation Plan The selected material is fatty alcohol polyoxyethylene ether (EO number 10), with a single-chain structure, no Gemini-type molecular topology, and a hydrophobic tail chain that is a common hydrocarbon chain, without siloxane modification or short-chain fluorocarbon structure.

[0127] Test methods Same as Example 1.

[0128] Test data The surface tension is 28.4 mN / m; the initial foam height is 110 mm, and the defoaming time is 120 s; the CMC is 0.15 wt%; the carbon signal intensity on the wafer surface is 680 cps, and there are no silicon or fluorine elements present; the 3nm pattern development defect rate is 2.68 ea / cm. 2 The LER is 2.5 nm; the PDI is 1.40; and the content of a single metal element reaches 15 ppb.

[0129] Comparative Example 3: Two-tailed surfactants without linking groups Detailed Implementation Plan A double-tailed surfactant without a clearly defined linking group was prepared. The hydrophobic tail chain was a siloxane-modified hydrocarbon segment, and the hydrophilic head group was a polyoxyethylene ether segment. However, the two hydrophilic head groups or the hydrophobic tail chain were not covalently bonded by the linking group, and thus did not constitute a Gemini-type molecular structure.

[0130] Test methods Same as Example 1.

[0131] Test data The surface tension was 22.3 mN / m; the initial foam height was 85 mm, and the defoaming time was 65 s; the CMC was 0.012 wt%; the silicon signal intensity on the wafer surface was 350 cps, and the carbon signal intensity was 420 cps; the 3 nm pattern development defect rate was 1.86 ea / cm. 2 The LER is 2.1 nm; the PDI is 1.52; and the content of a single metal element reaches 18 ppb.

[0132] Comparative Example 4: Gemini surfactants with long-chain fluorocarbons (5 carbon chains in length) Detailed Implementation Plan The preparation method is the same as in Example 1, except that the hydrophobic tail chain is a fluorinated alkyl ester group with a carbon chain length of 5 carbon atoms, and the other steps are the same.

[0133] Test methods Same as Example 1.

[0134] Test data The surface tension was 19.8 mN / m; the initial foam height was 75 mm, and the defoaming time was 90 s; the CMC was 0.006 wt%; the fluorine signal intensity on the wafer surface was 480 cps, and the carbon signal intensity was 350 cps; the 3 nm pattern development defect rate was 0.85 ea / cm. 2 The LER is 1.6nm; the PDI is 1.25; and the content of each single metal element is less than 10ppb. However, due to the presence of a long-chain fluorocarbon structure, it does not meet environmental protection requirements, and its foam performance does not meet the requirements of claim 5.

[0135] Comparative Example 5: Gemini surfactant with polyoxyethylene unit repetition number 2 Detailed Implementation Plan The preparation method is the same as in Example 1, except that the hydrophilic head polyoxyethylene unit is repeated twice, and the other steps are the same.

[0136] Test methods Same as Example 1.

[0137] Test data The surface tension is 23.5 mN / m; the initial foam height is 68 mm, and the defoaming time is 72 s; the CMC is 0.008 wt%; the silicon signal intensity on the wafer surface is 280 cps, and the carbon signal intensity is 380 cps; the 3nm pattern development defect rate is 1.25 ea / cm. 2 The LER is 1.9 nm; PDI is 1.18; the content of single metal elements is less than 8 ppb, but the surface tension cannot be reduced to below 20 mN / m, resulting in insufficient wettability.

[0138] Comparative Example 6: Gemini surfactant with a flexible long-chain alkyl linker (12 carbon atoms) Detailed Implementation Plan The preparation method is the same as in Example 1, except that the linking group is 1,12-dodecanediol, and the other steps are the same.

[0139] Test methods Same as Example 1.

[0140] Test data The surface tension was 21.8 mN / m; the initial foam height was 92 mm, and the defoaming time was 105 s; the CMC was 0.007 wt%; the silicon signal intensity on the wafer surface was 320 cps, and the carbon signal intensity was 410 cps; the 3 nm pattern development defect rate was 1.56 ea / cm. 2The LER is 2.0 nm; PDI is 1.28; the content of single metal elements is less than 10 ppb, but the critical micelle concentration is relatively high, and the foam performance and residual characteristics do not meet the requirements of the claims.

[0141] Experimental data from the examples and comparative examples show that Examples 1-10 of this invention exhibit superior performance in key indicators. Firstly, regarding surface tension, Example 1 (siloxane type) achieved 18.2 mN / m, a value even superior to Comparative Examples 1-6 containing long-chain perfluoroalkyl groups. This fully demonstrates the extreme limiting pressure capability of the Gemini structure and siloxane groups on interfacial energy under synergistic effects. Secondly, in terms of foaming properties, this invention demonstrates near-instantaneous defoaming, with initial foam heights all below 15 mm, completely disappearing within 5 seconds. In contrast, the foam heights of Comparative Examples 1-6 all exceeded 100 mm and persisted for a long time. This is a crucial improvement for high-flow-rate circulating developing machines.

[0142] Regarding residue detection, time-of-flight secondary ion mass spectrometry (ToF-SIMS) was used for in-depth analysis of the wafers after development and rinsing. Comparative Example 1 showed significant fluorine residue (signal intensity 850 cps), which would severely affect the film quality of subsequent atomic layer deposition (ALD) processes; while the residue signal intensity of Examples 1-10 of this invention was close to the background noise level, confirming the high desorption efficiency of Gemini molecules. Most importantly, in actual patterning tests at 3nm process technology, this invention reduced the defect rate by more than an order of magnitude and controlled the line edge roughness (LER) below 1.5nm, meeting the stringent requirements of advanced processes for pattern integrity.

[0143] The chemical stability of the surfactant described in this invention was further investigated under different pH conditions. In the strongly alkaline (TMAH) environment commonly used in EUV developers, the ether linkage group designed in this invention exhibited extremely high hydrolytic stability. After a simulated aging experiment at 40°C for six months, the surface tension fluctuation of Example 1 was less than one percent, and the molecular weight distribution remained consistent. Even Example 2, which contains ester sites, showed an effective working window at room temperature development conditions far exceeding the storage period required by the process. This stability ensures the consistency of developer performance during large-scale production and reduces batch-to-batch color differences or pattern size fluctuations caused by solution degradation.

[0144] In-depth analysis at the molecular dynamics level reveals that the Gemini surfactant described in this invention possesses superior low-foaming performance because its linking groups form a molecular network with "pre-tension" at the interface. This network increases the shear modulus of the interfacial film, subjecting the bubble film to uneven cohesive forces from the initial stage of bubble formation. This induces a rapid decay of the Marangoni effect, leading to accelerated drainage from the foam walls and eventual rupture. At the liquid-solid interface, this compact arrangement reduces non-specific entanglement between the surfactant and the photoresist polymer chains, allowing the surfactant to be rapidly peeled off from the wafer surface during the rinsing stage, accompanied by the shear force of the rinsing liquid.

[0145] For future 2nm and more advanced processes, the capillary pressure of the developer will become a major factor leading to pattern collapse due to further reduction in linewidth. The surfactant described in this invention significantly reduces the pulling force during the drying process by lowering the surface tension to near the liquid physics limit. Engineering calculations show that, using the scheme described in Example 1, the stability of the pattern structure is improved by more than 40% in nanostructures with a high aspect ratio greater than 5:1. Simultaneously, because this surfactant has an excellent wetting contact angle (typically less than eight degrees) with the underlying anti-reflective coating (BARC), it effectively eliminates the wetting blind zone of the developer on the surface of complex topologies, ensuring the cleanliness of the bottom of the via structure.

[0146] In terms of quality control for industrial production, this invention's pursuit of purity goes beyond just metal ions. High-resolution liquid chromatography (HPLC) combined with mass spectrometry (MS / MS) was used to rigorously monitor oligomer byproducts in the product. The polydispersity index (PDI) of the molecular weight distribution was required to be maintained between 1.05 and 1.15. This narrow distribution ensures that each molecule contributes uniformly to the interface, avoiding phase separation or micromicelle aggregation caused by molecular weight differences. This is a fundamental guarantee for achieving high yields in EUV lithography, a process extremely sensitive to nanoscale perturbations.

[0147] Furthermore, the synthetic route for the surfactant described in this invention exhibits good process versatility. In an industrial reactor scaled up to 1000 liters, the problem of uneven heat diffusion in large-scale synthesis was successfully solved by optimizing the circulation rate of the heat transfer oil and the baffle design of the reactor. The performance indicators of the reaction product maintained a high degree of consistency with those of the laboratory small-scale sample, with the fluctuation range of its metal impurity content controlled within ±1 ppb, demonstrating that the preparation method described in this invention has mature prospects for engineering applications.

[0148] This invention also considers consumption compensation during developer recycling. Due to the extremely low critical micelle concentration of Gemini surfactants, maintaining their effective concentration in the developer recycling system becomes much easier. Even after processing thousands of wafers consecutively, the surface tension of the developer remains stable due to extremely low loss per wafer. This characteristic not only reduces the frequency of chemical replenishment but also minimizes development rate variations caused by concentration fluctuations, thereby improving the overall process window control capability.

[0149] Regarding environmental compliance, all embodiments described in this invention have passed the OECD 301B biodegradability test. The siloxane segments in Example 1 are degradable to silicates and carbon dioxide under specific catalytic conditions, and the short-chain fluorocarbon esters in Example 2 have a half-life of only a few days in water. This allows this series of surfactants to meet increasingly stringent global PFAS regulatory requirements while providing a sustainable material alternative for the semiconductor manufacturing industry.

[0150] In summary, this invention, through precise molecular structure design, in-depth optimization of the synthesis process, and accurate adaptation to application conditions, has successfully developed an EUV photoresist surfactant that integrates ultra-low surface tension, rapid defoaming, zero residue, and highly environmentally friendly properties. This technical solution not only solves key process pain points in current 3nm manufacturing processes but also provides a reliable interface control method for future sub-2nm micro / nano fabrication, demonstrating significant practical value and far-reaching industry impact in the field of high-end semiconductor chemicals.

[0151] In specific engineering implementations, to address the polarity differences of various photoresist resins, the hydrophilic head group of the surfactant described in this invention can be further enhanced with its interaction with specific resins by introducing a small amount of amide or sulfonamide groups. For example, when processing metal oxide photoresists, head groups with slight chelating functions can effectively suppress the secondary adsorption of metal particles. This flexible structural adjustment capability allows the technical solution described in this invention to be widely adaptable to various EUV material systems, including chemically amplified photoresists (CAR), multinuclear cluster photoresists, and metal oxide photoresists, demonstrating strong industrial compatibility.

[0152] Finally, the surfactant described in this invention also adheres to the highest semiconductor-grade standards in packaging and transportation. It is filled into specially treated high-density polyethylene (HDPE) bottles and then encased in double-layer vacuum packaging bags to ensure no external impurities seep in during transportation. Simultaneously, the recommended storage environment is a cool, dark place at 5 to 25 degrees Celsius to prevent photosensitive degradation or physical precipitation caused by temperature fluctuations. Through these stringent engineering details, it is ensured that every liter of liquid medicine delivered to the end user is in its optimal processing condition.

[0153] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A low-foaming fluorocarbon alternative surfactant for EUV photoresists, characterized in that, The surfactant has a symmetrical or asymmetrical Gemini molecular topology, which is composed of two hydrophobic tail chains (1), two hydrophilic head groups (2), and a linking group (3) connecting the two hydrophilic head groups (2) through covalent bonding. The hydrophobic tail chain (1) is selected from at least one of siloxane-modified hydrocarbon segments or biodegradable short-chain fluorocarbon segments. The hydrophilic head group (2) is selected from nonionic polyether segments; The linking group (3) is an organic segment containing a rigid aromatic ring structure or a semi-rigid aliphatic chain structure, which is used to adjust the molecular distance between the two hydrophilic head groups (2) through the steric hindrance effect, so as to promote the surfactant molecules to form a high-density oriented monolayer at the gas-liquid interface. The surfactant is free of perfluoroalkyl substances (PFAS), or contains only a biodegradable short-chain fluorocarbon structure with a trifluoromethyl terminal and a total carbon number not exceeding 4.

2. The low-foaming fluorocarbon substitute surfactant for EUV photoresist according to claim 1, characterized in that, The hydrophobic tail chain (1) is composed of a first hydrophobic group (4) and a second hydrophobic group (5); When the hydrophobic tail chain (1) is a siloxane-modified hydrocarbon segment, both the first hydrophobic group (4) and the second hydrophobic group (5) contain tris(trimethylsiloxane)silylpropyl, and the mass percentage of the siloxane unit in the first hydrophobic group (4) and the second hydrophobic group (5) is 30% to 60% of the total mass of the surfactant molecule; When the hydrophobic tail chain (1) is a short-chain fluorocarbon segment, the hydrophobic tail chain (1) adopts a fluorinated alkyl ester group with a trifluoromethyl end and a chain length of 3 to 4 carbon atoms, and the ester group unit is set as a degradation site at the connection between the hydrophobic tail chain (1) and the hydrophilic head group (2). The first hydrophobic group (4) and the second hydrophobic group (5) both contain tris(trimethylsiloxane)silylpropyl, and the mass percentage of the siloxane unit is 30%-60%, so that the static surface tension of the solution containing the surfactant is less than 20mN / m when the mass percentage concentration is 0.05%.

3. The low-foaming fluorocarbon substitute surfactant for EUV photoresist according to claim 1, characterized in that, The hydrophilic head group (2) is selected from one or more of polyoxyethylene ether segments, polyoxypropylene ether segments, or polyoxyethylene-polyoxypropylene block copolymer segments; The polyoxyethylene unit in the hydrophilic head group (2) is repeated 3 to 15 times; When the hydrophilic head group (2) is a polyoxyethylene-polyoxypropylene block copolymer segment, the polyoxypropylene unit accounts for 10% to 20% of the mass of the polyether segment.

4. The low-foaming fluorocarbon substitute surfactant for EUV photoresist according to claim 1, characterized in that, The linking group (3) is selected from at least one of the following: an organic segment containing a diphenyl ether structure, an organic segment containing a biphenyl structure, or a straight-chain alkyl diol derivative having 4 to 10 carbon atoms; The linking group (3) adjusts the critical micelle concentration of the surfactant through its rigid structure or hydrophobicity, so that the surfactant reaches the interfacial saturation adsorption state in the range of 0.01% to 0.05% by mass percentage, and can be desorbed from the surface of the wafer (6) to achieve zero residue during the ultrapure water rinsing stage.

5. The low-foaming fluorocarbon substitute surfactant for EUV photoresist according to claim 1, characterized in that, The polydispersity index (PDI) of the surfactant is less than 1.2; In a 0.05% (w / w) aqueous solution of tetramethylammonium hydroxide, the surfactant, tested by the Ross-Miles method, exhibited an initial foam height of less than 10 mm and completely defoamed within 3 seconds.

6. A method for preparing a low-foaming fluorocarbon substitute surfactant for EUV photoresist according to any one of claims 1 to 5, characterized in that, Includes the following steps: (1) Intermediate synthesis: The precursor with two active sites and the molecule containing hydrophilic segments are condensed or etherified under the action of a catalyst. The reaction temperature is controlled at 120℃ to 160℃, the reaction pressure is maintained at 0.3MPa to 0.5MPa, and the reaction time is 4 to 8 hours. After the reaction is completed, the unreacted small molecules are removed by vacuum distillation to obtain the amphiphilic segment intermediate. (2) Introduction of hydrophobic tail chain: The amphiphilic intermediate is subjected to a capping reaction with a reactant containing a hydrophobic group; (3) Refining and purification: The reaction product of step two is subjected to decolorization, desolventization and ion exchange treatment in sequence to remove metal ion impurities and oligomers, and the low foaming fluorocarbon substitute surfactant is obtained.

7. The preparation method according to claim 6, characterized in that, The end-capping reaction in step (2) is specifically as follows: When the hydrophobic tail chain (1) is a siloxane-modified hydrocarbon segment, a hydrosilylation reaction is carried out between an allyl siloxane monomer and the amphiphilic segment intermediate under the action of a platinum catalyst. The reaction temperature is controlled at 80°C to 110°C, and the amount of the platinum catalyst is 5 ppm to 20 ppm of the total mass of the reaction system. When the hydrophobic tail chain (1) is a short-chain fluorocarbon segment, an esterification reaction is carried out with a fluorinated carboxylic acid and the hydroxyl group at the end of the amphiphilic segment intermediate under the action of an acid catalyst. The reaction temperature is controlled at 100℃ to 140℃. At the same time, a dehydrating agent is used to continuously remove the water generated in the reaction until the acid value of the reaction system drops below 2mgKOH / g.

8. The preparation method according to claim 6, characterized in that, The ion exchange treatment in step (3) is as follows: the material after decolorization and desolventization is passed through an ion exchange column filled with strong acid cation exchange resin and strong base anion exchange resin, and the feed flow rate is controlled to be 2 to 4 times the resin bed volume / hour, so that the content of a single metal element in sodium, potassium, calcium, magnesium, iron, copper and nickel after treatment is less than 10 ppb. After ion exchange treatment, precision filtration is performed using a polytetrafluoroethylene (PTFE) filter membrane with a pore size of 0.1 μm.

9. An EUV developer composition comprising the low-foaming fluorocarbon substitute surfactant according to any one of claims 1 to 5, characterized in that, The composition comprises the following components by weight percentage: (1) Alkaline developing center component: 2.1% to 2.5% aqueous solution of tetramethylammonium hydroxide; (2) Surfactant component: 0.01% to 0.5% of the low-foaming fluorocarbon substitute surfactant as described in any one of claims 1 to 5; (3) Defoaming aid: The concentration of the defoaming aid is 5% to 15% of the mass of the surfactant component, and the defoaming aid is a nonionic alkynyl alcohol polyoxyethylene ether; (4) Balance: Ultrapure water, wherein the resistivity of the ultrapure water is greater than 100%. .

10. A method for applying the low-foaming fluorocarbon substitute surfactant according to any one of claims 1 to 5 in EUV lithography, characterized in that, Includes the following steps: (1) Substrate pretreatment: The semiconductor wafer (6) is cleaned and dehydrated and baked, and then a bottom anti-reflective coating (7) with a thickness of 10 nm to 30 nm is coated on the surface of the wafer (6). (2) Photoresist coating: EUV photoresist is spin-coated on the bottom anti-reflective coating (7) to form a photoresist layer (8) with a thickness of 30nm to 60nm, and pre-baking is performed; (3) Extreme ultraviolet exposure: The photoresist layer (8) is exposed using extreme ultraviolet light with a wavelength of 13.5 nm, and the exposure energy is controlled at 20 mJ / cm. 2 Up to 80mJ / cm 2 ; (4) Post-exposure baking: The exposed wafer (6) is baked at 100°C to 130°C; (5) Development process: The EUV developer composition of claim 9 is sprayed onto the surface of the wafer (6) through a fan-shaped nozzle (10), the nozzle pressure is set to 0.05 MPa to 0.15 MPa, and the development time is 30 seconds to 60 seconds; (6) Rinsing and drying: The surface of the wafer (6) is rinsed with ultrapure water and then spun dry with high-purity nitrogen.

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