A cleaning method for removing HK film in wafer regeneration

Abstract

The application discloses a cleaning method for wafer regeneration and HK film removal, which comprises three sequential steps: step 1, using a mixed solution of hydrofluoric acid and hydrogen peroxide to remove dense HK film, and through the synergistic effect of hydrogen peroxide oxidation and hydrofluoric acid dissolution, the HK film is completely peeled off from the silicon substrate; step 2, using aqua regia to remove other metal films, and using the stable complex formed by chloride ions and metal ions to enhance the metal removal effect; step 3, using SC2 cleaning solution for metal control cleaning, and removing trace metal ions; after each chemical treatment, the cleaning process of ultrapure water flushing and spin-drying is adopted. The method also comprises a neutralization treatment process of waste liquid and sodium hydroxide solution. Through the above three-step sequential process, the application can realize the beneficial effects of significantly improving the film removal efficiency, greatly improving the yield, effectively controlling the damage of the silicon substrate and enhancing the environmental friendliness of the process.

Description

Technical Field

[0001] This application belongs to the field of semiconductor manufacturing technology, and specifically relates to a cleaning method for removing HK film during wafer regeneration. Background Technology

[0002] As semiconductor manufacturing processes continue to evolve towards smaller technology nodes, wafer regeneration technology has become a crucial link in the semiconductor industry chain, serving as a key means to reduce production costs and improve material utilization for wafer manufacturers. Wafer regeneration primarily targets and recycles failed wafers such as control wafers and test wafers generated during the manufacturing process, enabling them to be reused on the production line. This effectively reduces the need for new wafer procurement and lowers overall manufacturing costs. In this technological field, the core indicator for measuring the maturity of wafer regeneration technology is how efficiently and stably various failed film layers on the wafer surface can be removed while ensuring that the silicon substrate remains undamaged and restored to a reusable state.

[0003] Among them, HK films, as representatives of high dielectric constant gate dielectric films, play a crucial role in advanced chip manufacturing processes. Their main components are metal oxides such as HfO2. Wafer regeneration of HK films faces more complex technical challenges compared to ordinary film layers. This is because HK films have high surface metal activity, high film density, and may simultaneously contain composite structures of multiple film layers and multiple metal films, significantly increasing the difficulty of film removal. While existing general-purpose wafer regeneration methods have formed relatively mature process systems for processing ordinary dielectric films or simple metal films, a systematic solution is still lacking for the special high-density, multi-layered metal film composite structure of HK films.

[0004] Several wafer regeneration methods exist in the prior art, but none can meet the actual needs of HK film wafer regeneration. Patent CN118335591A uses a stepwise treatment with a mixed solution of aqua regia and hydrofluoric acid to remove the metal film layer. While this method can remove the film layer to some extent, it suffers from the technical drawback of aqua regia severely corroding the silicon substrate, leading to wafer structural damage. Furthermore, it does not optimize the process for the high density and complex structure of HK films, resulting in inconsistent and incomplete film removal. Another patent, CN118380307A, uses a combination of dry etching and polishing to remove the dielectric film layer. However, dry etching has poor selectivity for the high-density, multi-layered metal film composite structure of HK films, making uniform removal difficult. Additionally, dry etching equipment is expensive and may cause additional damage to the wafer. This method also fails to effectively remove the metal film layer in HK films. The aforementioned existing technical solutions demonstrate significant limitations in handling HK films during wafer regeneration: single-solution treatments cannot simultaneously achieve thorough HK film removal and effective silicon substrate protection; the step-by-step process design lacks synergistic optimization tailored to the specific properties of HK films; and improper control of solution parameters leads to low removal efficiency and a high risk of substrate damage. Therefore, there is an urgent need to develop a wafer regeneration cleaning method specifically for HK films to address the technical problems of incomplete removal, low efficiency, and silicon substrate damage in existing technologies. Summary of the Invention

[0005] The purpose of this invention is to provide a cleaning method for removing HK film during wafer regeneration, which can effectively solve the problems mentioned in the background art.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A cleaning method for removing HK film from wafer regeneration includes the following specific steps: Step 1: Removal of dense HK film: The wafer to be treated is placed in a mixed solution of hydrofluoric acid and hydrogen peroxide, wherein the mass concentration of hydrofluoric acid is 49%, the mass concentration of hydrogen peroxide is 30%, the volume ratio of each component is HF:H2O2:H2O=1:2:7, the solution temperature is 32℃, and the processing time is 30min, so that the dense HK film on the wafer surface is peeled off from the silicon substrate in one piece; Step 2: Removal of other metal films: After the treatment in Step 1 is completed, the wafer is placed in an aqua regia solution. The process involves a nitric acid to hydrochloric acid volume ratio of 3:1, a solution temperature of 25°C, and a processing time of 30 minutes to remove residual metal films on the wafer surface. Step 3 involves metal-controlled cleaning: after step 2, the wafer is placed in an SC2 cleaning solution with a hydrochloric acid, hydrogen peroxide, and deionized water volume ratio of HCl:H2O2:H2O=1:1:6, a solution temperature of 60°C, and a processing time of 10 minutes to control residual metal ions on the wafer surface. Each chemical treatment is followed by an ultrapure water rinsing and spin-drying process.

[0008] Preferably, the ultrapure water rinsing equipment includes: a water storage tank (resistivity ≥18MΩ·cm, TOC ≤5ppb), a terminal filter with a filtration accuracy of 0.1μm, and a spray arm (equipped with uniformly distributed nozzles with a nozzle spacing of 50mm); the spin dryer includes: a rotary drive motor (adjustable speed range 100-2000rpm), a vacuum suction system (vacuum degree ≤-0.08MPa), a wafer tray (equipped with elastic claws to fix the wafer edge), and a heating module (optional, temperature control range room temperature-80℃); after ultrapure water rinsing, the wafer is transferred to the spin dryer tray, fixed by the claws, and the spin drying program is started, with a spin drying speed of 600rpm and a spin drying time of 3min.

[0009] Preferably, in the mixed solution of hydrofluoric acid and hydrogen peroxide used in step 1, hydrofluoric acid is used to dissolve the silicon dioxide layer at the interface between the HK film and the silicon substrate, and hydrogen peroxide is used to oxidize hafnium oxide into soluble hafnium oxide. The two work together to peel the HK film off the silicon surface in one piece, and hafnium finally enters the solution in the form of hexafluorohafnium ions.

[0010] Preferably, in step 1, the solution temperature of 32°C is such that the oxygen produced by the decomposition of hydrogen peroxide at this temperature can effectively destroy the dense structure of the HK film, while the etching rate of hydrofluoric acid is at the optimal window, which can ensure that the HK film is completely peeled off within 30 minutes, and avoid excessive damage to the silicon substrate.

[0011] Preferably, in step S2, the aqua regia solution utilizes the property that chloride ions generated by the ionization of hydrochloric acid form stable complexes with metal ions to enhance the reducing ability of the metal; after aqua regia treatment, ultrapure water is used to rinse away the metal chloride complexes. If trace amounts of hafnium residue are present on the wafer surface, the wafer is further removed by step S3, SC2 cleaning.

[0012] Preferably, in step 3, the SC2 cleaning solution is used at a treatment temperature of 60°C to further remove trace metal ions from the wafer surface by utilizing the complexing effect of hydrochloric acid and the oxidation effect of hydrogen peroxide, preventing metal ions from causing contamination in subsequent processes. The 10-minute treatment time meets the time requirements for efficient mass production.

[0013] Preferably, the cleaning process after each chemical treatment includes: rinsing with ultrapure water for 5 minutes at a water temperature of 25°C and a water flow rate of 5L / min; then spin-drying with a spin dryer at a speed of 600rpm; this cleaning process ensures that there is no chemical residue on the wafer surface, providing a clean surface condition for the next step of processing.

[0014] Preferably, the process also includes an alkali neutralization treatment process for discharge: the waste liquid containing hydrofluoric acid, nitric acid and hydrochloric acid used in steps 1 to 3 are respectively neutralized with sodium hydroxide solution to make the waste liquid meet the standards before discharge; wherein hydrofluoric acid reacts with sodium hydroxide to produce sodium fluoride and water, nitric acid reacts with sodium hydroxide to produce sodium nitrate and water, and hydrochloric acid reacts with sodium hydroxide to produce sodium chloride and water.

[0015] Preferably, steps S1 to S3 constitute a three-step sequential process, and there is a clear cooperative relationship between each step. The specific cooperative mechanism is as follows:

[0016] The design principle of step S1, which prioritizes the removal of the HK film: The main component of the HK film is HfO2. If the HK film is not removed beforehand and the process proceeds directly to the aqua regia treatment in step S2, HfO2 may react with HCl in the aqua regia to form insoluble HfCl4. Simultaneously, HfO2 will consume the oxidizing power of the aqua regia, reducing its removal efficiency for other metal films. Step S1 uses an HF-H2O2 mixed solution to convert HfO2 into soluble H2HfF6, thereby achieving complete removal of the HK film and avoiding interference from HfO2 in subsequent aqua regia treatment. The mechanism for improved selectivity and reaction efficiency in step S2: After step S1, the HK film on the wafer surface is completely removed, and the aqua regia solution directly contacts the metal film layer. There is no need to consider the protection of the HK film; therefore, the aqua regia concentration and treatment time can be optimized according to the metal film removal requirements without reserving additional HK film protection margin. The functional positioning of step S3 as the final cleaning step: Step S2 cleaning uses an HCl-H2O2 mixed solution, utilizing Cl... -The complexation and oxidation of H2O2 further remove trace amounts of metal ions such as hafnium, iron, and copper that may remain in steps S1 and S2. At the same time, the O2 bubbles generated by the decomposition of H2O2 have an auxiliary cleaning effect, ensuring that the metal contamination on the wafer surface meets the requirements for regeneration and use.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] 1. Significantly improved film removal efficiency

[0019] This invention employs a three-step sequential process to remove HK film, other metal films, and perform metal-controlled cleaning. The total processing time is significantly shortened compared to the existing process route that first involves aqua regia treatment followed by HF-H2O2 treatment, resulting in a significant improvement in overall process efficiency and meeting the time requirements for large-scale mass production.

[0020] 2. Yield rate significantly improved

[0021] The method of this invention is used to regenerate HK film wafers. The results are verified using a certain number of wafers as a sample. The yield is improved from a certain level of the prior art to the target yield level. This significantly reduces the loss in the wafer regeneration process and improves the wafer regeneration utilization rate and economic benefits.

[0022] 3. Effective control of silicon substrate damage

[0023] In step 1 of this invention, the HK film is peeled off in its entirety through the synergistic effect of hydrogen peroxide oxidation and hydrofluoric acid dissolution. This avoids the severe corrosion of the silicon substrate caused by direct treatment with aqua regia in the prior art. At the same time, the reaction products are soluble in water and will not form secondary pollution on the wafer surface, thus protecting the structural integrity of the silicon substrate and increasing the number of times the regenerated wafer can be recycled.

[0024] 4. Enhanced environmental friendliness of the process

[0025] This invention uses sodium hydroxide to neutralize waste liquid containing hydrofluoric acid, nitric acid, and hydrochloric acid, converting the acidic substances in the waste liquid into their corresponding sodium salts. After reaching the required standards, the waste liquid is discharged, reducing environmental pollution and meeting the environmental protection requirements of semiconductor manufacturing. Attached Figure Description

[0026] Figure 1 This is a schematic diagram of the overall technical solution process architecture of the cleaning method for removing HK film from wafer regeneration according to an embodiment of this application.

[0027] Figure 2 This is a schematic diagram illustrating the core principle framework of the cleaning method for removing HK film in wafer regeneration according to an embodiment of this application, in which hydrofluoric acid and hydrogen peroxide work together to remove HK film.

[0028] Figure 3This is a schematic diagram of the collaborative relationship and data flow framework of the three-step sequential process in the cleaning method for removing HK film from wafer regeneration according to an embodiment of this application.

[0029] Figure 4 This is a schematic diagram of the process flow framework for the waste liquid neutralization treatment and discharge in the cleaning method for removing HK film during wafer regeneration according to an embodiment of this application. Detailed Implementation

[0030] Example 1

[0031] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0032] This invention provides a cleaning method for removing HK film during wafer regeneration. The method employs a three-step sequential chemical wet removal process, including a step to remove the dense HK film, a step to remove other metal films, and a metal-controlled cleaning step. The selection of reagents, mixing parameters, temperature parameters, and time parameters for each of the three steps have been rigorously optimized within the process window. There are clear synergistic relationships between each step. The entire process ensures complete removal of the HK film and metal film layers while effectively protecting the structural integrity of the silicon substrate, achieving high yield and high regeneration rate in wafer regeneration.

[0033] Step 1: Remove the dense HK membrane

[0034] The wafer to be processed was placed in a mixed solution of hydrofluoric acid and hydrogen peroxide. The mass concentration of hydrofluoric acid was 49%, and the mass concentration of hydrogen peroxide was 30%, with a volume ratio of HF:H₂O₂:H₂O = 1:2:7. The solution temperature was controlled at 32℃, and the processing time was 30 minutes. Under these process conditions, the hydrofluoric acid and hydrogen peroxide worked synergistically to peel the dense HK film on the wafer surface entirely off the silicon substrate.

[0035] Specifically, before proceeding to step 1, the wafers undergo pretreatment to ensure their surfaces are in a suitable initial state for the chemical reaction. The purpose of pretreatment is to remove any interfering factors such as particulate matter, organic residues, and natural oxide layers that may be present on the wafer surface, creating a clean chemical reaction interface for subsequent HK film removal. After pretreatment, the wafers are transferred to the chemical bath in step 1. This bath is equipped with a precise temperature control module and a circulating stirring system to ensure the chemical bath temperature is uniformly maintained at the set value of 32°C, and that the chemical components remain evenly distributed during the reaction.

[0036] In step 1, hydrogen peroxide plays a crucial oxidative destructive role. When heated, hydrogen peroxide decomposes to produce oxygen. This oxygen forms tiny bubbles within the dense structure of the HK membrane. The expansion force of these bubbles effectively disrupts the continuity and density of the HK membrane, making the originally compact membrane structure loose and porous. The oxidizing effect of hydrogen peroxide also oxidizes the main component of the HK membrane, hafnium oxide (HfO2), into soluble hafnium oxide, creating favorable conditions for the subsequent dissolution reaction of hydrofluoric acid.

[0037] Meanwhile, hydrofluoric acid plays a selective interfacial dissolving role. Hydrofluoric acid can react violently with the silica layer at the interface between the HK film and the silicon substrate, forming a soluble fluorosilicic acid complex, which significantly weakens the adhesion between the HK film and the silicon substrate. Under the synergistic effect of hydrogen peroxide, hafnium oxide undergoes the following chemical reaction with hydrofluoric acid:

[0038] HfO2 + 6HF → H2HfF4 + 2H2O; In this reaction, H2O2 mainly plays the role of oxidizing and destroying the dense structure of the film, and does not directly participate in the dissolution reaction of HfO2; In the actual reaction process, the active oxygen generated by the decomposition of H2O2 destroys the dense structure of the HK film, allowing HF to fully penetrate and react with HfO2 to generate soluble hexafluorohafnium acid.

[0039] Ultimately, hafnium enters the chemical solution in the form of hafnium hexafluorophosphate (H₂HfF₆), achieving complete peeling of the HK film from the silicon surface. All products generated during the entire reaction process are water-soluble and will not remain on the wafer surface or undergo secondary reactions with the chemical solution to form precipitation contamination.

[0040] The selection of process parameters in Step 1 is based on the following technical considerations: A solution temperature of 32°C represents the optimal balance between the oxygen production efficiency of hydrogen peroxide decomposition and the etching rate of hydrofluoric acid. At this temperature, the decomposition rate of hydrogen peroxide is moderate, enabling a continuous and stable generation of oxygen to disrupt the dense structure of the HK film, while avoiding excessive oxygen escape due to overly rapid decomposition, which would reduce oxidation efficiency. The etching rate of hydrofluoric acid at 32°C is within the optimal process window, ensuring complete removal of the HK film within a 30-minute processing time while minimizing damage to the silicon substrate. The 30-minute processing time has been verified as the optimal duration to ensure complete removal of the HK film without excessive corrosion.

[0041] Step 2: Remove other metal films

[0042] After step 1 is completed, the wafer is removed from the mixed solution of hydrofluoric acid and hydrogen peroxide, undergoes a standard cleaning process, and then transferred to the solution tank in step 2 for further processing. Step 2 uses aqua regia as the treatment solution to remove other metal films. Aqua regia is a mixture of nitric acid and hydrochloric acid, with a volume ratio of 3:1. The solution temperature is controlled at 25°C, and the processing time is 30 minutes.

[0043] In step 2, the technical principle behind aqua regia's removal of other metal films is based on the synergistic effect of the strong oxidizing power of nitric acid and the strong coordinating ability of chloride ions in hydrochloric acid. Its core reaction mechanism is as follows:

[0044] First, hydrochloric acid (HCl) completely ionizes in water, producing a high concentration of chloride ions (Cl-). - Chloride ions, as strong ligands, can bind with a variety of transition metal ions (such as Cu). 2+ Fe 3+ Ni 2+ (etc.) form stable soluble metal chloride complexes, such as [CuCl4] 2- [FeCl4] - This complexation reaction process can be represented as (taking copper as an example):

[0045] Cu 2+ +4Cl - →[CuCl4] 2-

[0046] This complexation reaction has two key functions: first, it significantly reduces the concentration of free metal ions in the solution, which, according to Le Chatelier's principle, strongly promotes the condensation of the metal element (M... 0 ) to metal ions (M n+ Firstly, the oxidation equilibrium shifts to the right; secondly, the formation of complexes alters the redox potential of metals, making metals that are normally difficult to oxidize with nitric acid (such as gold, platinum, and other precious metals) oxidizable.

[0047] Driven by chloride ion complexation, nitric acid (HNO3), acting as a strong oxidizing agent, oxidizes the metallic element into the corresponding metal ions. Taking copper as an example, the overall reaction equation can be summarized as follows:

[0048] 3Cu+6HCl+2HNO3→3H2[CuCl4]+2NO↑+4H2O

[0049] In the actual reaction, the reduction product of nitric acid is mainly NO, which is rapidly oxidized to NO2 in the air, turning brownish-red.

[0050] The metal chloride complex generated by this reaction is highly soluble in water and can be rapidly carried away by the chemical solution, thus achieving complete and residue-free removal of the metal film from the wafer surface. A reaction temperature of 25°C and a processing time of 30 minutes are the optimal window to ensure the full progress of this complexation-oxidation synergistic reaction while balancing process efficiency and safety.

[0051] Step 3: Perform controlled metal cleaning

[0052] After step 2 is completed, the wafer is removed from the aqua regia solution bath, undergoes a standard cleaning process, and then transferred to the solution bath for step 3. Step 3 uses SC2 cleaning solution, which is a mixture of hydrochloric acid, hydrogen peroxide, and deionized water, with a volume ratio of HCl:H2O2:H2O = 1:1:6. The solution temperature is controlled at 60℃, and the processing time is 10 minutes.

[0053] In step 3, the technical principle of SC2 cleaning solution (also known as standard cleaning solution No. 2) in removing trace metal ions is also based on the synergistic chemical action of hydrochloric acid and hydrogen peroxide. Its core lies in the enhanced mechanism of the "oxidation-complexation-dissolution" cycle.

[0054] Specifically, hydrogen peroxide (H2O2) decomposes at 60°C, producing highly reactive oxygen species. These reactive oxygen species can oxidize trace metal contaminants (such as Fe, Cu, Zn, etc.) existing on the wafer surface in low-valence or elemental forms into high-valence metal ions. The oxidation process can be simplified as follows (taking iron as an example):

[0055] 2Fe + 3H₂O₂ → 2Fe 3+ +6OH -

[0056] At the same time, hydrochloric acid provides chloride ions (Cl... - It immediately undergoes a complexation reaction with these newly formed high-valence metal ions to form stable water-soluble metal chloride complexes (such as [FeCl4)). - This complexation reaction not only promptly "captures" the oxidized metal ions, preventing them from redepositing onto the wafer surface, but also continuously propels the oxidation reaction in the positive direction by consuming the reaction products.

[0057] Furthermore, the physical disturbance generated by the rising oxygen bubbles produced during the decomposition of hydrogen peroxide helps to peel off contaminants from microscopic depressions or particles on the wafer surface and carry them into the bulk solution, enhancing the physical cleaning effect. Deionized water, as the reaction medium, ensures the smooth progress of the entire chemical reaction.

[0058] A temperature of 60℃ is the optimal equilibrium point for this reaction system: it ensures that the hydrogen peroxide has sufficiently high oxidizing activity without causing the effective components to be depleted too quickly due to violent decomposition. A treatment time of 10 minutes is sufficient to achieve deep removal of trace metal ions from the surface, making it the preferred solution that balances cleaning effectiveness and mass production efficiency.

[0059] The aqua regia treatment temperature of 25℃ in step 2 is based on the optimal synergistic consideration of the oxidizing power of nitric acid and the complexing power of hydrochloric acid. At this temperature, the metal film layer can be fully removed while the complexing reaction proceeds stably, avoiding excessive temperature that would cause HCl volatilization and affect the complexing effect. The SC2 cleaning temperature of 60℃ in step 3 is a commonly used parameter in standard cleaning processes. At this temperature, the oxidizing activity of hydrogen peroxide and the complexing effect of hydrochloric acid reach the best balance, which can effectively remove trace metal ions without reducing cleaning efficiency due to the violent decomposition of hydrogen peroxide caused by excessive temperature.

[0060] Cleaning process

[0061] After each chemical treatment step (Steps 1, 2, and 3) is completed, a standardized cleaning process is required to ensure that there is no chemical residue on the wafer surface, providing a clean surface condition for the next processing step. The cleaning process includes two steps: an ultrapure water rinsing step and a spin-drying step.

[0062] The specific parameters for the ultrapure water rinsing step are as follows: rinsing water temperature is 25℃, rinsing time is 5 minutes, and water flow rate is 5 L / min. During rinsing, the wafer is fixed on a dedicated wafer chuck, and the water flow evenly covers the wafer surface, rinsing away any residual chemicals and reaction products after chemical treatment. The 25℃ rinsing water temperature effectively dissolves chemical residues without causing thermal stress on the wafer surface due to excessive temperature. The 5-minute rinsing time ensures that chemical residues are fully diluted and removed. The 5 L / min water flow rate ensures rinsing efficiency while avoiding mechanical damage to the thin film structure on the wafer surface due to excessive water flow.

[0063] The specific parameters for the spin-drying step are as follows: A dedicated wafer spin dryer is used for processing, with a spin speed of 600 rpm. During the spin-drying process, under the centrifugal force of high-speed rotation, the residual ultrapure water on the wafer surface is ejected, achieving rapid drying of the wafer surface. The 600 rpm spin speed has been optimized to ensure spin-drying efficiency while avoiding mechanical vibration of the wafer or damage to the thin film structure caused by excessive speed.

[0064] Waste liquid treatment process

[0065] The present invention also includes a waste liquid treatment process, which involves neutralizing the waste liquid containing hydrofluoric acid, nitric acid and hydrochloric acid used in steps 1 to 3 with alkali, and discharging it after it meets the standards.

[0066] The principle of waste liquid neutralization treatment is based on acid-base neutralization reactions. Waste liquid containing hydrofluoric acid reacts with sodium hydroxide solution to produce sodium fluoride and water: HF + NaOH → NaF + H₂O. Waste liquid containing nitric acid reacts with sodium hydroxide solution to produce sodium nitrate and water: HNO₃ + NaOH → NaNO₃ + H₂O. Waste liquid containing hydrochloric acid reacts with sodium hydroxide solution to produce sodium chloride and water: HCl + NaOH → NaCl + H₂O.

[0067] In the process of waste liquid treatment, the waste liquid generated in each step must first be classified and collected, and stored in dedicated waste liquid storage tanks. The waste liquid treatment system includes: waste liquid classification and collection storage tanks (step S1 waste liquid storage tank, step S2 waste liquid storage tank, step S3 waste liquid storage tank, each with a capacity of 50L, made of PTFE corrosion-resistant material, each equipped with a level sensor and an overflow alarm device); a neutralization reactor (made of 316L stainless steel, equipped with a cooling jacket, temperature sensor, and stirrer, with an adjustable speed of 100-500rpm); a sodium hydroxide storage tank (concentration 10-15%, equipped with a level gauge and concentration meter); an online pH monitoring system (including a pH sensor and transmitter, the sensor material is hydrofluoric acid resistant glass electrode, detection range 0-14, response time ≤5 seconds); an automatic dosing system (including a metering pump, with an adjustable flow rate of 0.5-5L / h, equipped with a flow meter); and a waste gas treatment system (including an alkaline scrubbing tower for absorbing nitrogen oxides generated during the neutralization process); the treated waste liquid is filtered and pH checked before being discharged in compliance with standards or entering the next treatment unit.

[0068] Synergistic relationship of the three-step sequential process

[0069] Steps 1 to 3 constitute a complete three-step sequential process. There are clear collaborative logical relationships and functional divisions between each step. The entire process design reflects a deep understanding and systematic optimization of the HK film wafer regeneration process.

[0070] Step 1, prioritizing the removal of the dense hafnium oxide (HK) film, is a key innovation in the entire process design. By treating HK film removal as the first step, direct contact between the HK film and the aqua regia treatment solution is effectively avoided during subsequent treatment. The main component of the HK film, hafnium oxide, undergoes complex chemical reactions in aqua regia, generating insoluble hafnium salt precipitates. These precipitates adhere to the wafer surface, causing secondary contamination and reducing the removal efficiency of aqua regia for other metal films. By removing the HK film first, the subsequent aqua regia treatment solution directly acts on other metal film layers, significantly improving both solution selectivity and reaction efficiency.

[0071] Step 2 involves treating other metal films after the removal of the HK film, allowing for a more direct and efficient reaction between the aqua regia and the metal films. At this point, the HK film on the wafer surface is no longer present, and the aqua regia solution can directly contact various metal film layers without needing to consider protecting the HK film. The oxidizing and complexing abilities of the aqua regia are fully utilized, completely removing all metal film layers within a 30-minute treatment time.

[0072] Step 3, as the final cleaning step, plays a dual role in metal control and quality assurance. SC2 cleaning further removes any trace metal ions that may remain from Steps 1 and 2, ensuring that the metal contamination level on the wafer surface meets the cleanliness standards required for subsequent processes. Simultaneously, the oxidation process during SC2 cleaning provides a final interface cleaning of the wafer surface, removing any remaining organic residues and particulate matter, creating an optimal surface condition for the subsequent use of the reclaimed wafer.

[0073] The sequential design of the three-step process achieves an optimal balance between film removal efficiency and wafer surface condition control. The total processing time is 70 minutes, with step 1 taking 30 minutes, step 2 taking 30 minutes, and step 3 taking 10 minutes. Compared with the existing process route of first treating with aqua regia and then with HF-H2O2, the total processing time is shortened by more than 17 minutes, significantly improving process efficiency and throughput.

[0074] Process effect verification

[0075] The three-step sequential process of this invention was used to regenerate HK film wafers, with a sample size of 5000 wafers for process verification. Under the original process conditions, the wafer regeneration yield was 64%. After adopting the process of this invention, the wafer regeneration yield increased to 90%, an improvement of 26 percentage points. This significant yield improvement is mainly attributed to the following technical factors:

[0076] First, the three-step sequential process effectively avoids backcontamination. The process design of removing the HK film first and then other metal films makes the reaction between the chemical solutions and the film layers in each step more direct and efficient, avoiding interference from HK film residues in subsequent processing steps, and also avoiding substrate damage that may be caused to the HK film wafer by direct treatment with aqua regia.

[0077] Secondly, the scientific setting of key process parameters ensured a win-win situation for both film removal and substrate protection. Step 1 uses a HF:H2O2:H2O ratio of 1:2:7, a temperature of 32°C, and a time of 30 minutes, ensuring complete removal of the HK film while minimizing damage to the silicon substrate. Step 2 uses an HNO3:HCl ratio of 3:1, a temperature of 25°C, and a time of 30 minutes, ensuring complete removal of the metal film while minimizing the impact on the silicon substrate. Step 3 uses an HCl:H2O2:H2O ratio of 1:1:6, a temperature of 60°C, and a time of 10 minutes, ensuring effective metal control while meeting the time requirements for efficient mass production. The 32°C solution temperature was verified through orthogonal experiments as the optimal balance point between hydrogen peroxide decomposition oxygen production efficiency and hydrofluoric acid etching rate. In the example verification, the temperature step was set to ±2°C, and the HK film thickness reduction rate was monitored in real time using an ellipsometry (controlled within 0.8-1.0 nm / min). When the film thickness is reduced to a residual thickness of ≤20nm, a termination command is automatically triggered. If the initial HK film thickness deviation on the wafer exceeds ±5%, the processing time is shortened or extended by 1-2 minutes according to the linear compensation model to ensure that the silicon substrate loss is controlled to <0.1nm while the HK film is peeled off completely. Validated in a continuous batch of 5000 wafers, this dynamic monitoring mechanism can stabilize the yield at 90%±1.5%.

[0078] Third, the standardized cleaning process ensures the cleanliness of the wafer surface. The ultrapure water rinsing and spin-drying process effectively removes residual chemicals from each step of the process, providing a clean surface for the next step and avoiding adverse effects of chemical residues on subsequent processes.

[0079] Fourth, the alkali neutralization wastewater treatment process ensures environmental protection and process safety. By neutralizing wastewater containing hydrofluoric acid, nitric acid, and hydrochloric acid, the acidic substances in the wastewater are converted into their corresponding sodium salts, which are then discharged after meeting emission standards. This reduces environmental pollution and prevents the wastewater from corroding equipment and the environment.

[0080] The three-step sequential process of this invention not only improves yield but also significantly increases the number of reusable wafers. Because the damage to the silicon substrate during processing is effectively controlled, the number of reusable wafers is greatly increased, further reducing the production costs of FAB plants and improving economic efficiency.

[0081] Specific application examples

[0082] A semiconductor manufacturing company's FAB plant generates a large number of control wafers and test wafers with HK film during daily production. These wafers require regeneration before they can be reused. The company uses the three-step sequential process of this invention to regenerate the HK film wafers. The specific operation process is as follows:

[0083] First, the wafers to be processed enter the pre-processing section. The pre-processing section includes three stages: megasonic cleaning, SC1 cleaning, and SC2 cleaning. The megasonic cleaning tank is equipped with a 950kHz megasonic transducer array, with transducers evenly distributed along the bottom of the tank at a spacing of 30mm. The output power is 500W, ultrapure water is used as the medium, and the cleaning time is 5 minutes. The wafer is fixed on a wafer holder with a positioning groove at the bottom. The holder enters the megasonic field area along with the cleaning basket. The SC1 cleaning tank contains an alkaline solution of NH4OH:H2O2:H2O = 1:1:5, with the solution temperature controlled at 60±2℃. The cleaning time is 10 minutes. The tank is equipped with a circulation pump with a circulation rate of 10L / min, and the tank itself is equipped with a temperature-controlled heater and a level sensor. The SC2 cleaning tank contains a solution of HCl:H2O2:H2O = 1:1:6, the temperature of which is controlled at 30±2℃, and the cleaning time is 10 minutes.

[0084] In step 1, the chemical solution tank contains a mixed solution of HF:H₂O₂:H₂O = 1:2:7, and the solution temperature is controlled at 32℃. The wafer to be treated is placed on a wafer rack in the chemical solution tank, ensuring the wafer is completely immersed in the solution. The circulation and stirring system of the chemical solution tank is started to ensure uniform flow of the solution. After 30 minutes of treatment, the dense HK film on the wafer surface has been completely peeled off. The wafer is removed from the chemical solution tank, rinsed with ultrapure water for 5 minutes (water temperature 25℃, water flow rate 5L / min), and then centrifuged at 600rpm. The wafer is then transferred to the chemical solution tank in step 2.

[0085] In step 2, the reagent bath contains aqua regia solution with an HNO3:HCl ratio of 3:1, and the solution temperature is controlled at 25°C. The wafer is placed in the aqua regia solution for 30 minutes to remove any residual metal film on the wafer surface. After treatment, the wafer is removed from the aqua regia solution bath, rinsed with ultrapure water for 5 minutes, and then spun dry at 600 rpm. The wafer is then transferred to the reagent bath in step 3.

[0086] In step 3, the cleaning solution tank contains SC2 cleaning solution with an HCl:H2O2:H2O ratio of 1:1:6, and the solution temperature is controlled at 60℃. The wafer is placed in the SC2 cleaning solution for 10 minutes for final metal control cleaning. After treatment, the wafer is removed from the SC2 cleaning solution tank, rinsed with ultrapure water for 5 minutes, and then spun dry at 600 rpm to complete the entire chemical wet film removal process.

[0087] After the chemical wet stripping process, the wafers enter the post-processing stage for quality inspection and grading. The post-processing stage includes three steps: surface roughness inspection, metal contamination inspection, and film thickness inspection. Surface roughness inspection uses atomic force microscopy (AFM) to measure the surface roughness of the wafers, ensuring that the surface roughness meets the requirements for regeneration. Metal contamination inspection uses inductively coupled plasma mass spectrometry (ICP-MS) to quantitatively analyze residual metal ions on the wafer surface, ensuring that the metal contamination level is within acceptable limits. Film thickness inspection uses elliptic polarization spectroscopy to measure the film thickness on the wafer surface, confirming that the HK film and metal film layers have been completely removed.

[0088] Based on the test results, the wafers are divided into three grades: superior, qualified, and unqualified. Superior grade wafers have the best surface condition and can be directly used in production; qualified wafers have minor surface defects and can be used in production after minor polishing; unqualified wafers have serious surface defects and require rework or scrapping. After sorting, the superior and qualified wafers are packaged and stored for future use.

[0089] After adopting the three-step sequential process of this invention, the company increased the yield of HK film wafer regeneration from 64% to 90%, significantly increasing the number of reusable wafers per month and effectively reducing wafer procurement costs. Simultaneously, due to the optimization of process parameters and the improvement of the cleaning process, the quality stability of regenerated wafers was significantly improved, and the number of times regenerated wafers could be reused also increased significantly, further reducing production costs.

[0090] Example 2

[0091] In another specific embodiment of the present invention, the chemical parameters of the three-step sequential process are optimized and adjusted within a certain range to adapt to the regeneration needs of different types of HK film wafers.

[0092] For HK film wafers with high hafnium oxide content (hafnium content > 15 wt%), the processing parameters in step S1 are adjusted as follows: the HF mass concentration is increased to 51%, the H2O2 mass concentration remains unchanged at 30%, the volume ratio of the mixed solution is adjusted to HF:H2O2:H2O = 1.1:2:6.9, the solution temperature is controlled at 33℃, and the processing time is extended to 32 min. The basis for parameter adjustment is that an increased hafnium content means an increase in HK film thickness or density, requiring stronger etching ability (increased HF concentration) and a faster oxidation rate (increased temperature) to ensure that the HK film is completely peeled off within 30 min. The verification method of the adjustment scheme is as follows: the HK film thickness is measured using an elliptic polarization spectrometer, the basic processing time is calculated based on the thickness value at a removal rate of 0.8 nm / min, and then corrected according to the hafnium content.

[0093] For wafers with a thin HK film, the processing parameters in step 1 can be adjusted as follows: the HF mass concentration is reduced to 47%, the H2O2 mass concentration remains unchanged at 30%, the volume ratio of the mixed solution is adjusted to HF:H2O2:H2O=0.9:2:7.1, the solution temperature is controlled at 31℃, and the processing time is shortened to 28 minutes. This parameter adjustment can reduce the etching rate on the silicon substrate, ensuring the removal of the HK film while maximizing the protection of the structural integrity of the silicon substrate, making it suitable for precision applications with higher requirements for surface finish.

[0094] For wafers with a variety of metal films or thicker metal films, the processing parameters in step 2 can be adjusted as follows: the volume ratio of nitric acid to hydrochloric acid is adjusted to 3.2:1, the solution temperature is increased to 27°C, and the processing time is extended to 32 minutes. This parameter adjustment can enhance the oxidizing power of aqua regia, ensuring that various metal films can be completely removed within the extended processing time.

[0095] For wafers with particularly stringent requirements for metal contamination control, the processing parameters in step 3 can be adjusted as follows: the volume ratio of hydrochloric acid, hydrogen peroxide, and deionized water is adjusted to 1:1.1:5.9, the solution temperature is increased to 62℃, and the processing time is extended to 12 minutes. This parameter adjustment enhances the complexing and oxidizing capabilities of SC2 cleaning, ensuring that trace metal ions are thoroughly removed, thus meeting the requirements of applications with particularly stringent metal contamination control.

[0096] All the above parameter adjustment schemes are carried out within the basic framework of the three-step sequential process of this invention. The range of parameter adjustment has been rigorously verified by the process window to ensure that the synergistic relationship between each step is not disrupted and the overall process effect is maintained at the optimal level.

[0097] The foregoing has shown and described the basic principles, main features, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments. The embodiments and descriptions in the specification are merely illustrative of the principles of the invention. Various changes and modifications can be made to the invention without departing from its spirit and scope, and all such changes and modifications fall within the scope of the present invention as claimed. The scope of protection of this invention is defined by the appended claims and their equivalents.

Claims

1. A cleaning method for removing HK film during wafer regeneration, characterized in that, Includes the following steps: Step S1: Remove the dense HK film: Place the wafer to be processed in a mixed solution of hydrofluoric acid and hydrogen peroxide, wherein the mass concentration of hydrofluoric acid is 49%, the mass concentration of hydrogen peroxide is 30%, the volume ratio between the components is HF:H2O2:H2O=1:2:7, the temperature of the solution is 32℃, and the processing time is 30min, so that the dense HK film on the surface of the wafer is peeled off from the silicon substrate in one piece. Step S2: Removal of other metal films: After the processing in Step S1 is completed, the wafer is placed in aqua regia solution for treatment, wherein the volume ratio of nitric acid to hydrochloric acid is 3:1, the solution temperature is 25°C, and the processing time is 30 minutes, to remove the residual metal film layer on the wafer surface; in the aqua regia solution, hafnium oxide has been pre-converted into soluble hafnium hexafluorophosphate by the HF-H2O2 mixed solution in Step S1, so it will not react with the hydrochloric acid in the aqua regia to form insoluble hafnium tetrachloride precipitate; after the processing in Step S1 is completed, the wafer surface is rinsed with ultrapure water to remove the residual hafnium hexafluorophosphate, and then the aqua regia treatment in Step S2 is performed; Step S3 is to perform metal control cleaning: After the processing in step S2 is completed, the wafer is placed in the SC2 cleaning solution for treatment, wherein the volume ratio of hydrochloric acid, hydrogen peroxide and deionized water is HCl:H2O2:H2O=1:1:6, the solution temperature is 60℃, the processing time is 10min, and the residual metal ions on the wafer surface are controlled.

2. The cleaning method according to claim 1, characterized in that, In step S1, the mixed solution of hydrofluoric acid and hydrogen peroxide is used to dissolve the silicon dioxide layer at the interface between the HK film and the silicon substrate. Hydrofluoric acid is used to oxidize hafnium oxide into soluble hafnium oxide. The two work together to peel the HK film off the silicon surface in one piece. Hafnium finally enters the solution in the form of hexafluorohafnium ions.

3. The cleaning method according to claim 1 or 2, characterized in that, In step S1, the solution temperature of 32°C is such that the oxygen produced by the decomposition of hydrogen peroxide at this temperature can effectively destroy the dense structure of the HK film. At the same time, the etching rate of hydrofluoric acid is at the optimal window, which can ensure that the HK film is completely peeled off within 30 minutes and avoid excessive damage to the silicon substrate.

4. The cleaning method according to claim 1, characterized in that, In step S2, the aqua regia solution utilizes the property that chloride ions generated by the ionization of hydrochloric acid form stable complexes with metal ions, thereby enhancing the reducing power of the metal and enabling nitric acid to oxidize and remove the metal. The gas generated by the reaction is nitric oxide, and the 30-minute treatment time ensures that the metal film is completely removed.

5. The cleaning method according to claim 1, characterized in that, In step S3, the SC2 cleaning solution, at a treatment temperature of 60°C, utilizes the complexing effect of hydrochloric acid and the oxidizing effect of hydrogen peroxide to further remove trace metal ions from the wafer surface, preventing metal ions from causing contamination in subsequent processes. The 10-minute treatment time meets the time requirements for efficient mass production.

6. The cleaning method according to claim 1, characterized in that, The cleaning process after each chemical treatment includes: rinsing with ultrapure water for 5 minutes at a temperature of 25°C and a flow rate of 5L / min; then spin-drying with a spin dryer at a speed of 600rpm; this cleaning process ensures that there is no chemical residue on the wafer surface, providing a clean surface condition for the next step of processing.

7. The cleaning method according to claim 1, characterized in that, It also includes an alkaline neutralization treatment process for discharge: the waste liquid containing hydrofluoric acid, nitric acid and hydrochloric acid used in steps S1 to S3 are respectively neutralized with sodium hydroxide solution to make the waste liquid meet the standards before discharge; wherein hydrofluoric acid reacts with sodium hydroxide to produce sodium fluoride and water, nitric acid reacts with sodium hydroxide to produce sodium nitrate and water, and hydrochloric acid reacts with sodium hydroxide to produce sodium chloride and water.

8. The cleaning method according to claim 1, characterized in that, Steps S1 to S3 constitute a three-step sequential process, with a clear synergistic relationship between each step: Step S1 prioritizes the removal of the dense HK film, eliminating the potential backcontamination problem that may occur when the chemical solution in subsequent steps comes into direct contact with the HK film; Step S2 processes other metal films after the HK film removal, resulting in higher chemical selectivity and reaction efficiency; Step S3, as the final cleaning step, further removes any trace metal ions that may remain in Steps S1 and S2. The sequential design of the three-step process achieves an optimal balance between film removal efficiency and wafer surface condition control.

9. The cleaning method according to claim 1, characterized in that, For HK film wafers with a high hafnium oxide content, the processing parameters in step S1 are adjusted as follows: the HF mass concentration is increased to 51%, the H2O2 mass concentration remains unchanged at 30%, the volume ratio of the mixed solution is adjusted to HF:H2O2:H2O = 1.1:2:6.9, the solution temperature is controlled at 33℃, and the processing time is extended to 32 min. For wafers with a thinner HK film, the processing parameters in step S1 are adjusted as follows: the HF mass concentration is reduced to 47%, the H2O2 mass concentration remains unchanged at 30%, and the volume ratio of the mixed solution is adjusted to HF:H2O2:H2O. For wafers with a metal film layer ratio of O=0.9:2:7.1 and a solution temperature controlled at 31℃, the processing time is shortened to 28 min. For wafers with a variety of metal film layers or a large thickness, the processing parameters in step S2 are adjusted as follows: the volume ratio of nitric acid to hydrochloric acid is adjusted to 3.2:1, the solution temperature is increased to 27℃, and the processing time is extended to 32 min. For wafers with strict requirements for metal contamination control, the processing parameters in step S3 are adjusted as follows: the volume ratio of hydrochloric acid, hydrogen peroxide, and deionized water is adjusted to 1:1.1:5.9, the solution temperature is increased to 62℃, and the processing time is extended to 12 min.

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