Method for reducing post-etching defects of photoresist and method for manufacturing semiconductor structure

Abstract

The application discloses a method for reducing defects of photoresist after development and a semiconductor structure manufacturing method, and belongs to the semiconductor field. The application brings forward the microwave heating to the evaporation development liquid process, and inert gas is introduced to reduce the pressure difference inside and outside the photoresist pattern. The development liquid on the semiconductor structure is evaporated by microwave heating, and the inert gas is introduced and the air exhaust device of the drying chamber is opened at the same time, so that the development liquid vapor is exhausted. The drying chamber is maintained in a slightly positive pressure state by the inert gas to protect the semiconductor structure. The microwave heating heats the photoresist to further cross-link and solidify at the same time of evaporating the development liquid. The photoresist pattern is cleaned to remove the residues after the evaporation of the development liquid. The application integrates the development liquid cleaning replacement, the development liquid evaporation and the hard baking into one process, so that the hard baking time of the application can be shortened or even the hard baking process can be removed. The obtained photoresist pattern is more compact and firm, and therefore, the photoresist pattern is not easy to collapse in the subsequent cleaning process.

Description

Technical Field

[0001] This invention belongs to the field of semiconductors and relates to a photolithography process technology, specifically a method for reducing defects after photoresist development and a method for fabricating semiconductor structures. Background Technology

[0002] Photolithography is a crucial technology in semiconductor manufacturing. In photolithography, the wafer undergoes a series of processing steps in the coater / developer. Pre-processing involves coating the upper surface of the wafer with photoresist, spin-coating, and baking (often called soft baking). An automated transfer system within the equipment moves the wafers between various operating positions. Another transfer system feeds the coated wafers one at a time into the alignment and exposure system. The photolithography machine directly imprints the pattern of a specific mask onto the coated wafer. After exposure, the wafer is transferred from the exposure system to the wafer track system and undergoes a short post-exposure baking (often called post-bake) to improve photoresist adhesion and reduce standing waves. The wafer then returns to the coater / developer, where the pattern is revealed when developer is sprayed onto the wafer. After development, the developer is replaced with deionized water to terminate the development process. After drying, it is baked again (often called hard baking, at a temperature of 120℃-150℃) to complete the photoresist pattern shaping. Finally, measurements are taken to check whether the line width of the etched pattern is appropriate. If there are major defects, the wafer can be de-resisted and reworked.

[0003] Development involves selectively dissolving the exposed photoresist with a developing solution to form a photoresist pattern. This process is divided into two dissolution modes based on the properties of the photoresist: positive photoresist and negative photoresist. In positive photoresist, the exposed areas are dissolved due to the increased solubility caused by the formation of carboxylic acids, while in negative photoresist, the exposed areas are retained and the unexposed areas are dissolved. In existing technologies, after development, hard baking is used to fully shape the photoresist before deionized water is used to replace the developing solution and drying is performed.

[0004] As semiconductor processes advance to the 40nm node, the specific surface area and aspect ratio of photolithographic patterns increase. During the drying process after cleaning, the likelihood of photoresist patterns collapsing increases. Analysis revealed that the main reason for the collapse is that the photoresist patterns have not yet undergone hard baking during the drying process, resulting in insufficient strength. The surface tension of the solution pulls the flexible structure towards the substrate. Once the drying process is complete, the structure and the substrate will adhere firmly together, which is the main reason for the failure of the photoresist patterns.

[0005] To avoid photoresist pattern collapse, various solutions have been proposed in existing technologies, such as: critical point drying, which uses supercritical carbon dioxide to clean and dry the device; freeze-sublimation; and adding surfactants to water-based solvents. However, when the pattern size reaches 22nm and below, all of these methods inevitably cause the nanopatterns to break, collapse, or stick together.

[0006] The prior art CN102929110A discloses a microwave-excited supercritical drying apparatus and method. A wafer is placed in a quartz device containing developing solution for development. After development, the developing solution in the quartz device is replaced with deionized water. The replaced quartz device containing the wafer is then placed in the chamber of a supercritical drying apparatus, where an alternating electric field is used to heat the wafer. When the water reaches its boiling point and enters a rotating supercritical state, a vacuum pump removes the water from the quartz device, and the alternating electric field in the supercritical drying apparatus continues to heat the wafer. Once the water on the wafer has completely evaporated and drying is complete, the wafer is removed. This technology utilizes microwaves to induce a rotating supercritical state in water, thereby breaking down the water molecule cluster structure and eliminating the surface tension of the water, resulting in a certain anti-collapse effect during the drying process after development. Although this technology rapidly evaporates the water in the gaps between photoresist patterns through microwave heating, reducing surface tension and preventing it from pulling the photoresist patterns toward the substrate, the water inside the photoresist pattern (mainly in the gaps between adjacent lines) boils violently during microwave heating, generating significant pressure. Combined with the fact that a vacuum is typically drawn within the chamber, this creates a huge pressure difference, causing the photoresist pattern to flip upwards. This affects the quality of the photoresist, particularly the hard baking quality, resulting in a low yield rate for forming photoresist patterns. Therefore, it is necessary to conduct relevant research and development to further explore how to improve the quality of photoresist patterns after exposure and development. Summary of the Invention

[0007] One of the objectives of this invention is to provide a method for reducing defects in photoresist after development. By advancing microwave heating to the evaporation process of the developer, the process of replacing the developer with deionized water is eliminated. Furthermore, by combining hard baking and drying, the drying and hard baking can be carried out simultaneously, which greatly reduces the probability of defects in the photoresist pattern obtained after development.

[0008] Another object of the present invention is to provide a method for fabricating a semiconductor structure, wherein the above method is used to develop and dry the photoresist to obtain a high-quality photoresist pattern, thereby obtaining a high-quality semiconductor structure after performing an etching process.

[0009] To solve the above-mentioned technical problems, the present invention employs the following technical means:

[0010] In a first aspect, the present invention provides a method for reducing defects after photoresist development, comprising the following steps:

[0011] A semiconductor structure is provided, wherein photoresist is applied to the semiconductor structure, and the photoresist is developed using a developing solution;

[0012] The semiconductor structure containing the developer is transferred to the drying chamber. The developer on the semiconductor structure is evaporated by microwave heating. At the same time, inert gas is introduced and the vacuum device of the drying chamber is turned on. The developer vapor is removed by the vacuum device. The inert gas is used to maintain the drying chamber in a slightly positive pressure state to protect the semiconductor structure. The microwave heating heats the photoresist pattern while evaporating the developer, so that it is further cross-linked and cured.

[0013] The photoresist pattern is cleaned to remove residues left after evaporating the developer.

[0014] Preferably, the microwave heating frequency is 2-10 GHz.

[0015] Preferably, the power of the microwave heating is 200-1000W.

[0016] Preferably, the microwave heating time is 10-50 seconds.

[0017] Preferably, the pressure of the micro-positive pressure environment in the drying chamber is 100-500 Pa.

[0018] Preferably, the flow rate of the inert gas is 0.3-1 m / s.

[0019] Preferably, the material is dried using a supercritical drying process after cleaning.

[0020] Preferably, the photoresist is a positive photoresist, and a weak alkaline solution is used for cleaning.

[0021] Preferably, the weak alkaline solution is a sodium hydroxide solution, ammonia, or tetramethylammonium hydroxide solution with a pH less than 10.

[0022] Preferably, a surfactant that reduces surface tension is added to the weak alkaline solution.

[0023] Preferably, the photoresist pattern further includes, before development:

[0024] Coating with photoresist;

[0025] Pre-bake the photoresist;

[0026] Expose the photoresist;

[0027] The photoresist is then post-baked.

[0028] In a second aspect, the present invention provides a method for fabricating a semiconductor structure, comprising the following steps:

[0029] A first semiconductor structure is provided, and photoresist is coated on the first semiconductor structure;

[0030] Pre-bake the photoresist;

[0031] Expose the photoresist;

[0032] Post-bake the photoresist;

[0033] The photoresist is developed using a developing solution;

[0034] The developed first semiconductor structure is transferred to the drying chamber, where the developer on the semiconductor structure is evaporated by microwave heating. At the same time, inert gas is introduced and the vacuum device of the drying chamber is turned on. The developer vapor is removed by the vacuum device, and the inert gas is used to maintain the drying chamber in a slightly positive pressure state to protect the semiconductor structure. The microwave heating heats the photoresist pattern while evaporating the developer, causing it to further crosslink and solidify.

[0035] Clean the photoresist pattern to remove residues left after evaporating the developer;

[0036] An etching process is performed to obtain a second semiconductor structure.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] Compared with existing technologies, this invention creatively advances microwave heating to the evaporation and development process, and introduces inert gas to reduce the pressure difference between the inside and outside of the photoresist pattern. The unexpected technical effects are: this invention not only utilizes microwave heating to generate heat through a high-frequency electromagnetic field, causing water molecules in the developer within the photoresist pattern to vibrate rapidly, thus reducing molecular cluster size and lowering the surface tension of water, achieving rapid evaporation and dehydration; but also maintains a slightly positive pressure state within the drying chamber using inert gas, avoiding the pressure imbalance caused by the removal of water vapor in existing technologies, which leads to water vapor rising and generating numerous bubbles that impact the photoresist pattern, causing defects. Furthermore, the inert gas in this invention also provides protection... The invention prevents the photoresist pattern from oxidizing and deteriorating. Furthermore, by microwaving the photoresist pattern before cleaning, it combines drying and hard baking, using microwave heating to achieve a hard baking effect, making the photoresist pattern denser and stronger. Ultimately, for most photoresists, this invention can reduce the hard baking time after drying to one-third of the existing technology. For some special photoresists, the hard baking process can be omitted. Because this invention selects the microwave frequency and power to make the photoresist pattern denser and stronger, it is less likely to cause the photoresist pattern to collapse during subsequent cleaning. This has a significant technical advantage over the existing technology CN102929110A.

[0039] This invention employs microwave direct heating of the developer, meaning the photoresist pattern is rapidly heated to a high temperature while still immersed in the chemical developer. This creates excellent conditions for accelerating the thermal acid catalytic reaction and promoting crosslinking. For chemically amplified resists, the high temperature significantly accelerates the acid deprotection reaction generated by the photoacid catalyst (PAG), making the resin more hydrophobic and structurally more stable. For some photoresists, the high temperature can promote crosslinking reactions between molecular chains, directly and significantly increasing the glass transition temperature (Tg) and mechanical modulus of the photoresist.

[0040] Compared to the existing technology of hard baking after development, cleaning and drying (where there is no developer in the hard baking process, it is simply heating and drying), this invention integrates developer cleaning and replacement, drying and hard baking into one process by heating the developer with microwave. The three processes are completed in the same drying process, which greatly simplifies the process flow. The pattern hardens well before losing liquid support, and its resistance to deformation is far higher than that of photoresist patterns in the traditional process of first replacing the developer with deionized water, then drying and finally hardening.

[0041] This invention eliminates the step of replacing the developer with deionized water. This not only removes a step, but also saves time, reduces defect sources, and lowers chemical consumption. It directly shortens the production cycle and increases equipment capacity. It avoids physical damage to the pattern caused by water flow impact during the replacement process (because the photoresist pattern is not sufficiently hardened without hard baking). Simultaneously, it avoids watermark defects that may be caused by deionized water; it reduces chemical consumption and saves a significant amount of ultrapure water (DIW); furthermore, this invention solves the problems caused by deionized water replacement by removing developer residue through a post-hard baking cleaning process. Moreover, since this cleaning is performed after the photoresist pattern has been thoroughly hard baked, the impact of this process on photoresist collapse is negligible. Attached Figure Description

[0042] Figure 1 This is a flowchart of the method for reducing defects after photoresist development in Embodiment 1 of the present invention.

[0043] Figure 2 This is a schematic diagram of the drying chamber provided in Embodiment 1 of the present invention.

[0044] Figure 3 This is a schematic diagram of the microwave heating and drying principle in Embodiment 1 of the present invention.

[0045] Figure 4 This is a flowchart of the semiconductor structure fabrication method in Embodiment 2 of the present invention.

[0046] 110-Drying chamber, 111-Air inlet, 112-Air outlet, 120-Conveyor belt, 130-Wafer box, 131-Wafer, 150-Microwave heating device, 151-Microwave power supply, 152-Microwave generator, 200-Photoresist pattern. Detailed Implementation

[0047] The embodiments of the present invention will be described in further detail below with reference to the accompanying drawings and examples. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0048] In the description of this invention, it should be noted that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance.

[0049] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "connected" and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0050] The method for reducing defects after photoresist development provided by this invention is applicable to all known photolithography layers in semiconductor manufacturing, including common ion implantation layer photolithography, isolation layer photolithography, gate layer photolithography, wiring layer photolithography, etc. It is also applicable to all known photolithography processes in semiconductor manufacturing, including common single-photoresist processes and photolithography processes based on anti-reflective coatings. Furthermore, it is applicable to all known types of photoresist in semiconductor manufacturing, including positive and negative photoresists, and is particularly suitable for positive photoresists.

[0051] Example 1: As Figure 1 As shown, this embodiment provides a method for reducing defects after photoresist development, including the following steps:

[0052] S100. A semiconductor structure is provided, wherein the semiconductor structure has a photoresist pattern after photoresist has been developed by a developing solution.

[0053] S200: The semiconductor structure is transferred to the drying chamber. The developer on the semiconductor structure is evaporated by microwave heating. At the same time, inert gas is introduced and the vacuum device of the drying chamber is turned on. The developer vapor is removed by the vacuum device. The inert gas is used to maintain the drying chamber in a slightly positive pressure state to protect the semiconductor structure. The microwave heating heats the photoresist pattern while evaporating the developer, so that it is further cross-linked and cured.

[0054] S300: Clean the photoresist pattern to remove residues left after evaporating the developer.

[0055] This invention creatively combines microwave heating with the introduction of inert gas, and advances this process to the evaporation of the developing solution. The unexpected technical effects are: this invention not only utilizes microwave heating to generate heat through a high-frequency electromagnetic field, causing water molecules in the developing solution within the photoresist pattern to vibrate rapidly, thus reducing molecular clusters and lowering the surface tension of water, achieving rapid evaporation and dehydration, but also maintains a slightly positive pressure state within the drying chamber using inert gas. This avoids the pressure imbalance caused by the removal of water vapor in existing technologies, which leads to water vapor forming numerous bubbles that impact the photoresist pattern and cause defects. Furthermore, the inert gas in this invention also provides protection, preventing the photoresist pattern from being damaged. Oxidation and deterioration are prevented. An unexpected benefit is that the invention uses microwave heating to heat the photoresist pattern before cleaning, combining drying and hard baking. Microwave heating achieves the hard baking effect, making the photoresist pattern denser and more robust. Ultimately, for most photoresists, this invention can reduce the hard baking time after drying to one-third of the existing technology. For some special photoresists, the hard baking process can be omitted. Because this invention selects microwave frequency and power to make the photoresist pattern denser and more robust, it is less likely to cause the photoresist pattern to collapse during subsequent cleaning. This has a significant technical advantage over the existing technology CN102929110A.

[0056] This invention employs microwave direct heating of the developer, meaning the photoresist pattern is rapidly heated to a high temperature while still immersed in the chemical developer. This creates excellent conditions for accelerating the thermal acid catalytic reaction and promoting crosslinking. For chemically amplified resists, the high temperature significantly accelerates the acid deprotection reaction generated by the photoacid catalyst (PAG), making the resin more hydrophobic and structurally more stable. For some photoresists, the high temperature can promote crosslinking reactions between molecular chains, directly and significantly increasing the glass transition temperature (Tg) and mechanical modulus of the photoresist.

[0057] Compared to the existing technology of hard baking after development, cleaning and drying (where there is no developer in the hard baking process, it is simply heating and drying), this invention integrates developer cleaning and replacement, drying and hard baking into one process by heating the developer with microwave. The three processes are completed in the same drying process, which greatly simplifies the process flow. The pattern hardens well before losing liquid support, and its resistance to deformation is far higher than that of photoresist patterns in the traditional process of first replacing the developer with deionized water, then drying and finally hardening.

[0058] This invention eliminates the step of replacing the developer with deionized water. This not only removes a step, but also saves time, reduces defect sources, and lowers chemical consumption. It directly shortens the production cycle and increases equipment capacity. It avoids physical damage to the pattern caused by water flow impact during the replacement process (because the photoresist pattern is not sufficiently hardened without hard baking). Simultaneously, it avoids watermark defects that may be caused by deionized water; it reduces chemical consumption and saves a significant amount of ultrapure water (DIW); furthermore, this invention solves the problems caused by deionized water replacement by removing developer residue through a post-hard baking cleaning process. Moreover, since this cleaning is performed after the photoresist pattern has been thoroughly hard baked, the impact of this process on photoresist collapse is negligible.

[0059] In step S100, the provided semiconductor structure can be any semiconductor structure in the prior art that requires photolithography, such as silicon (Si) substrate semiconductor, silicon germanium (SiGe) substrate semiconductor, silicon germanium carbon (SiGeC) substrate semiconductor, silicon carbide (SiC) substrate semiconductor, gallium arsenide (GaAs) substrate semiconductor, indium arsenide (InAs) substrate semiconductor, indium phosphide (InP) substrate semiconductor, or other III / V semiconductor substrates or II / VI semiconductor substrates.

[0060] The following steps are included before developing the photoresist with a developer:

[0061] S110, Coating with photoresist.

[0062] S120, Pre-bake the photoresist.

[0063] S130, Expose the photoresist.

[0064] S140. Post-bake the photoresist to obtain a photoresist pattern after developing the photoresist with a developing solution.

[0065] Existing technologies can be used for steps S110-S140, and the appropriate parameters can be selected according to the specific photolithography process type.

[0066] In some embodiments, the photoresist coating in step S110 is achieved by spin coating, where liquid photoresist is uniformly spin-coated onto the surface of a wafer (semiconductor structure) to form a thin film with precisely controlled thickness. The thickness and uniformity are controlled by rotation speed and acceleration.

[0067] In step S120, pre-baking is the first baking of the wafer after photoresist coating. The purpose of pre-baking is to remove solvent, enhance adhesion, and stabilize film thickness. After spin coating, the photoresist film contains a large amount of solvent (usually propylene glycol methyl ether acetate, PGMEA, etc.). Pre-baking evaporates most of the solvent (about 90-95%) by heating, transforming the photoresist from a viscous liquid to a solid film. The solvent evaporation process helps the photoresist molecules to bond more tightly to the wafer surface, improving adhesion and reducing peeling or undercutting in subsequent processes. Removing the solvent stabilizes the film volume and prevents thickness changes due to solvent evaporation during exposure and development. A uniformly dried photoresist film ensures more uniform absorption and reaction of light during exposure.

[0068] In some embodiments, the pre-baking temperature is typically between 90°C and 120°C. Too low a temperature results in incomplete solvent removal, leading to poor adhesion, pinholes, and pattern distortion after development. Too high a temperature or too long a time can cause partial cross-linking or decomposition of the photoresist, particularly the PAC (photoacid generator) in chemically amplified photoresists, which may react prematurely, reducing photosensitivity. The pre-baking time is typically 60-120 seconds (hot plate) or longer (oven). The time must be sufficient to ensure adequate solvent evaporation, but not too long to avoid over-baking. Pre-baking time and temperature are interrelated parameters and should be adjusted according to actual process requirements.

[0069] In step S130, the exposure uses existing technology processes, selects the appropriate light source according to the level of process advancement, and selects the photomask for exposure operation according to the photoresist image.

[0070] In step S140, post-baking is a second baking process performed on the wafer after exposure. Its purpose is to promote photochemical reactions, smooth standing wave effects, and stabilize latent images. Promoting photochemical reactions is the core objective of post-baking, especially crucial for chemically amplifying photoresists. In DUV / EUV lithography, exposure primarily generates photoacid generators, releasing acid catalysts. Post-baking provides heat energy, driving the acid to diffuse within the photoresist film, catalyzing deprotection reactions (positive resist) or cross-linking reactions (negative resist) in the resin, thus creating solubility differences in the developer. Smoothing the standing wave effect occurs during exposure when reflection and interference of light at the photoresist / wafer interface creates standing wave effects (unevenness) on the photoresist sidewalls. Appropriate post-baking heat can cause slight flow of photoresist polymer molecules, smoothing these standing wave profiles and improving the verticality of the pattern sidewalls. Stabilizing the latent image involves stabilizing the chemical changes generated during exposure before development.

[0071] In step S100, the present invention is particularly applicable to positive photoresist. The principle of positive photoresist development is to generate an acid-catalyzed reaction to obtain carboxylic acid substances soluble in the developer, including but not limited to g-line positive photoresist (436nm), i-line positive photoresist (365nm), deep ultraviolet positive photoresist (DUV), and extreme ultraviolet positive photoresist (EUV, 13.5nm). The residual carboxylic acid substances in the developer are removed by microwave evaporation and subsequent cleaning with a weak alkaline solution.

[0072] In step S100, a corresponding developer needs to be prepared according to the type of photoresist for development. An example parameter is as follows:

[0073] Developing time: 10-90 seconds, developing temperature: 20-25°C; developer concentration: taking tetramethylammonium hydroxide (TMAH) as an example, the mass concentration is 1wt%-10wt%.

[0074] In existing technologies (such as CN102929110A), the developing process is terminated by adding deionized water to replace the developer in the post-developing stage, thus avoiding over-development. The present invention creatively uses microwave heating to directly evaporate the developer to terminate the developing process. The unexpected technical effect is that the present invention not only accurately terminates the developing process, but also combines it with a hard baking process, achieving a simultaneous hard baking effect.

[0075] In step S200, as Figure 2 As shown, the equipment used in this invention includes a drying chamber 110. Two opposite side walls of the drying chamber 110 are respectively provided with an air inlet 111 and an air outlet 112. The drying chamber 110 is equipped with a microwave heating device 150, which includes a microwave power supply 151 and a microwave generator 152 located at the top of the drying chamber 110. The microwave generator 152 is a device already existing in the prior art; in this invention, only the installation location, heating power, and frequency need to be selected, and the structural form of the microwave generator 152 itself will not be described further. A conveyor belt 120 is provided at the bottom of the drying chamber 110 for feeding wafer cassettes 130 into or out of the drying chamber 110. Wafer cassettes 130 contain wafers 131 (i.e., the semiconductor structure in this embodiment). The air inlet 111 is inclined downwards at a certain angle and connected to an inert gas source (which can be a gas cylinder or a pressurization device). Figure 2 (Not shown in the image) By tilting the air inlet 111, the inert gas is blown at a certain angle to the surface of the wafer 131. If the angle θ is too large, the inert gas replacement efficiency will be low, which is not conducive to rapid evaporation. If the angle θ is too small, the inert gas will have too great an impact force on the side of the photoresist pattern, which will increase the risk of collapse.

[0076] In some embodiments, an air extraction device is also provided outside the air extraction port 112. Figure 2(Not shown in the image), the air extraction device can be a common air extraction device such as a vacuum pump or a negative pressure pump. The purpose of air extraction is to quickly remove the water vapor in the drying chamber 110.

[0077] In some embodiments, a gas velocimeter is provided in the drying chamber 110. Figure 2 (Not shown in the image; any mature equipment from existing technology can be used), used to monitor the gas flow rate near wafer 131. A pressure sensor can also be installed at the top of the drying chamber 110. Figure 2 (Not shown in the image), used to monitor the pressure inside the drying chamber 110.

[0078] In some other embodiments, a controller is also provided ( Figure 2 (Not shown in the figure, any mature controller from the existing technology can be used) to adjust the suction speed of the suction device according to the pressure set value in the drying chamber 110, so that the pressure in the drying chamber 110 is near the set value, thereby improving the drying effect.

[0079] The principle of microwave heating: The developer contains a large amount of water as a solvent. Water molecules are polar molecules. As the direction of the alternating electric field changes rapidly, the polarity of the water molecules also changes. When the frequency of the change increases, the water molecules begin to rotate at high speed, their kinetic energy increases, and the molecular clusters constantly rub and collide, increasing heat energy. The chemical bonds between water molecules are broken, the water evaporates, and drying is completed. Figure 3 As shown, this invention creatively combines microwave heating with the introduction of inert gas, and advances this process to the evaporation of the developing solution. The unexpected technical effect is that this invention not only utilizes microwave heating to generate heat through a high-frequency electromagnetic field, causing water molecules in the developing solution inside the photoresist pattern 200 to vibrate rapidly, thus reducing the size of molecular clusters and lowering the surface tension of water, achieving rapid evaporation and dehydration, but also maintains a slightly positive pressure state within the drying chamber using inert gas. This avoids the pressure imbalance caused by the removal of water vapor in existing technologies, which leads to a large number of bubbles rising upwards and impacting the photoresist pattern 200, causing defects in the photoresist pattern. Furthermore, the inert gas in this invention also provides protection, preventing the photoresist pattern 200 from... The 00 is oxidized and deteriorated; at the same time, an unexpected effect is that the present invention microwaves the photoresist pattern 200 before cleaning, which combines drying and hard baking. The microwave heating achieves the hard baking effect, making the photoresist pattern 200 denser and stronger. Ultimately, for most photoresists, the present invention can shorten the hard baking time after drying to one-third of the prior art. For some special photoresists, the hard baking process can be omitted. Since the present invention makes the photoresist pattern denser and stronger by selecting microwave frequency and power, it is less likely to cause the photoresist pattern to collapse during subsequent cleaning. It has obvious technical advantages over the prior art CN102929110A.

[0080] The microwave heating frequency is 2-10 GHz; for example, the frequency of 2.45 GHz has the best heating efficiency. In practice, the frequency needs to be selected according to the semiconductor structure. Taking the frequency of 2.45 GHz as an example, its wavelength is 12.23 cm, which generates a standing wave at half the wavelength. If a part of the wafer under test happens to be located at half the wavelength, it will cause the local temperature of the wafer under test to rise, resulting in the wafer breaking. Therefore, it is necessary to avoid generating standing waves in the semiconductor structure.

[0081] The microwave heating power is 200-1000W. The microwave heating power is selected according to the size of the semiconductor structure (wafer) to enable rapid evaporation of the developer, avoid the collapse of the photoresist pattern caused by the surface tension of water in the developer during the evaporation process, and generate sufficient power for hard baking, so that the photoresist pattern is more dense and firm. If the power is too low, the water cannot be evaporated quickly, and if the power is too high, the photoresist pattern will be overheated or over-dried in some areas.

[0082] In some embodiments, the microwave heating time is 10-50 seconds. If the time is too short, the solvent in the developer cannot be completely evaporated; if the time is too long, the photoresist pattern will be over-baked. 10-50 seconds is a proven reasonable time.

[0083] It should be noted that the main component of photoresist is generally resin (such as phenolic resin), which has a high dipole moment. During the experiment, the applicant found that when the developing solution is heated by microwave, the photoresist can also absorb microwave energy to promote cross-linking. However, the power needs to be controlled well. Excessive power will cause local overheating (hot spot effect), which will cause the pattern to curl or carbonize. Therefore, this invention selected a power range of 200-1000W and a time of about 10-50s, which can meet the requirements of evaporating the developing solution and also harden the photoresist well to obtain a dense photoresist pattern.

[0084] In existing technologies, during the drying process after the developer is replaced with deionized water, the photoresist pattern lacks hard curing, resulting in relatively low strength. Although microwave heating can rapidly vaporize water and reduce its surface tension, it also introduces a problem: rapid vaporization generates bubbles in the developer. These bubbles overflow and impact the sidewalls of the photoresist pattern, causing damage or dark spots and weakening its strength. Furthermore, existing technologies incorporate a vacuum system in the drying chamber to remove vapor and increase drying speed. However, this vacuuming can lead to excessively low pressure above the wafer, further exacerbating the impact of bubbles on the sidewalls of the photoresist pattern and intensifying damage. Therefore, after extensive experimental research, the applicant found that microwave heating promotes the curing of photoresist. During the microwave heating process, an inert gas is introduced into the drying chamber. Considering cost issues, nitrogen is generally introduced to maintain a slight positive pressure in the drying chamber. This ensures that the steam is quickly removed and reduces the pressure difference between the inside and outside of the photoresist pattern, greatly avoiding the impact of a large number of bubbles on the photoresist pattern and significantly reducing photoresist pattern defects. Experiments have shown that the photoresist pattern defect rate is significantly lower than that of the prior art described in the background section.

[0085] For example, the pressure of the micro-positive pressure environment in the drying chamber 110 is 100-500 Pa, which can achieve better results.

[0086] For example, the flow rate of the inert gas is 0.3-1 m / s. If the flow rate is too low, the replacement efficiency is low, resulting in slow vapor removal. If the flow rate is too high, the photoresist pattern is at risk of collapsing.

[0087] It should be noted that the inert gas of this invention is blown at a certain angle θ to the wafer surface, and the angle θ is generally 30-60 degrees. Vertical blowing of the gas will result in low gas circulation efficiency, resulting in low steam extraction efficiency and affecting the evaporation rate. Horizontal blowing will cause excessive force on the sides of the photoresist pattern lines, which may cause the photoresist to collapse.

[0088] It should be noted that since this invention directly evaporates the developer solution by microwave heating, thus achieving a hard baking effect, after drying, it is possible to decide whether to perform a hard baking process according to process requirements. For example, phenolic resin photoresists have a more obvious heating effect and do not require a separate hard baking process. If other photoresists do not have such an obvious microwave heating effect, then an additional hard baking process can be added. However, in this case, the hard baking process requires a lower temperature and shorter time compared to the hard baking in the prior art, thus achieving the purpose of saving energy.

[0089] In step S300, since the present invention directly evaporates the developer by microwave heating, there will inevitably be photoresist residues in the photoresist pattern, which are generally carboxylic acid substances. Therefore, the present invention needs to remove the photoresist residues by weak alkali cleaning. It should be noted that before this cleaning, since the photoresist pattern has been hard baked and has sufficient strength, the probability of photoresist collapse is greatly reduced during this cleaning process.

[0090] For example, the weak alkaline solution is a sodium hydroxide solution, ammonia, or tetramethylammonium hydroxide solution with a pH less than 10; the weak alkaline solution can effectively remove photoresist residues and avoid affecting subsequent etching processes.

[0091] In some embodiments, a surfactant that reduces surface tension is added to the weak alkaline solution, such as 0.005% of a fluorocarbon surfactant (e.g., FS-31).

[0092] Taking a 100nm line photoresist pattern as an example, the technical solution of this invention is compared with the prior art CN102929110A, and the results are shown in the table below:

[0093] Table 1. Comparison of the anti-collapse performance of the present invention and prior art

[0094]

[0095] It should be noted that in order to improve the cleaning efficiency, deionized water needs to be added to replace the photoresist residue in the process of removing the photoresist residue in the weak alkaline solution of the present invention. The subsequent deionized water drying process can refer to the scheme in the prior art CN102929110 A to further reduce the photoresist collapse rate.

[0096] Example 2: As Figure 4 As shown, this embodiment provides a method for fabricating a semiconductor structure, including the following steps:

[0097] M100 provides a first semiconductor structure, and photoresist is coated on the first semiconductor structure.

[0098] M200, pre-baking the photoresist.

[0099] M300 exposes the photoresist.

[0100] M400, perform post-baking of the photoresist.

[0101] M500: The photoresist is developed using a developer.

[0102] M600: The developed first semiconductor structure is transferred to the drying chamber. The developer on the semiconductor structure is evaporated by microwave heating. At the same time, inert gas is introduced and the vacuum device of the drying chamber is turned on. The developer vapor is removed by the vacuum device. The inert gas is used to maintain the drying chamber in a slightly positive pressure state to protect the semiconductor structure. The microwave heating heats the photoresist pattern while evaporating the developer, so that it is further cross-linked and cured.

[0103] M700 is used to clean the photoresist pattern to remove residues left after evaporating the developer.

[0104] M800 performs an etching process to obtain a second semiconductor structure.

[0105] In step M100, the type of the first semiconductor structure is the same as in step S100. The first semiconductor structure that needs to be photolithographically processed can be any semiconductor structure in semiconductor integrated circuit (IC) manufacturing (front-end process FEOL), semiconductor packaging (back-end process BEOL), microelectromechanical system (MEMS) manufacturing, and other micro-nano processing fields.

[0106] Semiconductor integrated circuit (IC) manufacturing (front-end process FEOL) includes, but is not limited to, any one of the following: active area (AA) definition, gate patterning, source / drain implantation, and interconnect formation.

[0107] Semiconductor packaging (back-end process BEOL) includes, but is not limited to, any one of the following: Under Bump Metallization (UBM), Solder Bump, and Redistribution Layer (RDL).

[0108] For example, in the formation of gate lines, the first semiconductor structure is the semiconductor structure to be formed as the gate line. The required size of the photoresist pattern is relatively small, and the technology of this invention has a particularly good effect. For photoresist coating, refer to step S110.

[0109] In M200, the photoresist is pre-baked as per step S120.

[0110] M300, Expose the photoresist according to step S130.

[0111] M400, Post-baking of photoresist (refer to step S140).

[0112] M500, Step S100: Developing the photoresist with a developing solution.

[0113] M600: The developed first semiconductor structure is transferred to the drying chamber. The developer on the semiconductor structure is evaporated by microwave heating. At the same time, inert gas is introduced and the vacuum device of the drying chamber is turned on. The developer vapor is removed by the vacuum device. The inert gas is used to maintain the drying chamber in a slightly positive pressure state to protect the semiconductor structure. The microwave heating heats the photoresist pattern while evaporating the developer, so that it is further cross-linked and cured. The specific process of microwave heating is referred to step S200.

[0114] M700: Clean the photoresist pattern to remove residues left after evaporating the developer. Refer to step S300 for details.

[0115] M800. Perform an etching process to obtain a second semiconductor structure. The etching process can use existing technology. For example, for a gate line formation process, this step is to form a gate groove by dry etching or wet etching. In this embodiment, the second semiconductor structure refers to a semiconductor structure with a gate groove formed.

[0116] After forming the gate groove, the gate material is filled to obtain the gate line; other semiconductor structures will not be described one by one in this invention.

[0117] The above embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Although the invention has been described in detail with reference to the embodiments, those skilled in the art should understand that various combinations, modifications, or equivalent substitutions of the technical solutions of the invention do not depart from the spirit and scope of the invention and should be covered within the scope of the claims of the invention.

Claims

1. A method of reducing post-etching defects in a photoresist, comprising: The method comprises the following steps: providing a semiconductor structure with photoresist on the semiconductor structure, and developing the photoresist by a developing solution; transferring the semiconductor structure with the developing solution into a drying chamber, evaporating the developing solution on the semiconductor structure by microwave heating, introducing inert gas into the drying chamber, and opening an air exhaust device of the drying chamber to exhaust the developing solution vapor, and maintaining the drying chamber in a slightly positive pressure state by the inert gas to protect the semiconductor structure, wherein the microwave heating heats the photoresist pattern to further cross-link and solidify the photoresist pattern while evaporating the developing solution, and the pressure of the slightly positive pressure environment in the drying chamber is 100-500 Pa; cleaning the photoresist pattern to remove residues after evaporating the developing solution.

2. The method of claim 1, wherein the photoresist is exposed to the plasma after the photoresist is developed. The frequency of the microwave heating is 2-10 GHz.

3. The method of claim 1, wherein the photoresist is exposed to the plasma after the photoresist is developed. The power of the microwave heating is 200-1000 W.

4. The method of claim 1, wherein the photoresist is exposed to the plasma after the photoresist is developed. The microwave heating time is 10-50 s.

5. The method of claim 1, wherein the photoresist is exposed to the plasma after the photoresist is developed. The flow rate of the inert gas is 0.3-1 m / s.

6. The method of claim 1, wherein the photoresist is exposed to the plasma after the photoresist is developed. After cleaning, a supercritical drying process is used for drying.

7. The method of claim 1, wherein the photoresist is exposed to the plasma after the photoresist is developed. The photoresist is a positive photoresist, and a weak alkali solution is used for cleaning.

8. The method of claim 7, wherein the photoresist is exposed to the plasma after the photoresist is developed. The weak alkali solution is a sodium hydroxide solution, ammonia water or tetramethylammonium hydroxide solution with a pH less than 10.

9. The method of claim 8, wherein the photoresist is exposed to the plasma after the photoresist is developed. The weak alkali solution is added with a surfactant to reduce surface tension.

10. The method of claim 1, wherein the photoresist is a positive photoresist. The photoresist pattern further comprises the following steps before development: coating photoresist; pre-baking the photoresist; exposing the photoresist; post-baking the photoresist.

11. A method of fabricating a semiconductor structure, the method comprising: The method comprises the following steps: providing a first semiconductor structure, and coating photoresist on the first semiconductor structure; pre-baking the photoresist; exposing the photoresist; post-baking the photoresist; developing the photoresist by a developing solution; transferring the developed first semiconductor structure into a drying chamber, evaporating the developing solution on the semiconductor structure by microwave heating, introducing inert gas into the drying chamber, and opening an air exhaust device of the drying chamber to exhaust the developing solution vapor, and maintaining the drying chamber in a slightly positive pressure state by the inert gas to protect the semiconductor structure, wherein the microwave heating heats the photoresist pattern to further cross-link and solidify the photoresist pattern while evaporating the developing solution, and the pressure of the slightly positive pressure environment in the drying chamber is 100-500 Pa; cleaning the photoresist pattern to remove residues after evaporating the developing solution; performing an etching process to obtain a second semiconductor structure.

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