A method for cleaning quartz wafers

Abstract

This invention relates to the field of semiconductor manufacturing and precision machining of electronic components. It discloses a cleaning method for quartz wafers, achieving efficient and precise cleaning through an innovatively designed composite cleaning solution system and optimized processes. The alkaline composite cleaning solution consists of tetramethylammonium hydroxide, sodium gluconate, and hydrogen peroxide, utilizing a weakly alkaline environment and synergistic complexation-oxidation effects to remove organic matter and metal ions. The acidic composite cleaning solution contains oxalic acid, hydrofluoric acid, and sodium dodecylbenzenesulfonate, removing residual metal ions and nanoparticles through complexation, etching, and surface activity. Combining megasonic cleaning, supercritical CO2 cleaning, and nitrogen drying steps, this method can control particulate contaminants on the surface of quartz wafers to 5 particles / cm². 2 Below, the residual metal ion content is less than 5×10 ‑10 g / cm 2 It significantly improves the surface quality of wafers and the performance of electronic devices, while also possessing advantages such as being environmentally friendly and having stable processes.

Description

Technical Field

[0001] This invention relates to the field of semiconductor manufacturing and precision machining of electronic components, specifically a method for cleaning quartz wafers. Background Technology

[0002] In the modern electronics and information industry, quartz wafers serve as a key component for frequency control and signal processing. The cleanliness of their surface directly determines the frequency stability, aging performance, and reliability of electronic devices. With the increasing demands for miniaturization, high frequency, and high precision in electronic devices from fields such as 5G communication, the Internet of Things, and aerospace, the requirements for controlling surface contaminants on quartz wafers have reached the nanometer level.

[0003] While the RCA cleaning process, widely used in industry, can effectively remove some surface contaminants, it suffers from significant technical bottlenecks. The combination of ammonia and hydrogen peroxide in traditional alkaline cleaning solutions (SC-1), when removing organic matter and particulate contaminants, readily reacts with residual metal ions (such as Al) on the surface of quartz wafers. 3+ Fe 3+ The reaction produces insoluble precipitates such as aluminum hydroxide and ferric hydroxide, leading to secondary pollution. Related studies have shown that the residue of these precipitates increases the surface roughness of the quartz wafer by 0.8-1.2 nm, thus affecting the frequency stability of the device. In the acid cleaning step (SC-2), although the use of high-concentration hydrochloric acid can dissolve metal oxides, residual chloride ions can trigger electrochemical corrosion on the surface of the quartz wafer. When the residual chloride ion content exceeds 5 × 10⁻⁶, the corrosion can become severe. -10 g / cm 2 At that time, the aging rate of the device will increase by more than 20%.

[0004] Furthermore, existing cleaning technologies are ineffective at removing nanoscale particulate contaminants (diameter <100nm). Studies show that when the number of such particles remaining on the surface of a quartz wafer exceeds 103 / cm2 2 At that time, the frequency temperature coefficient of the device will increase by ±5×10. -6 The deviation is approximately ℃. Some improvement solutions optimize the cleaning solution by adding single-functional additives (such as chelating agents and surfactants), but due to the lack of a synergistic mechanism, they cannot simultaneously solve the problems of efficient removal of multiple contaminants and surface protection. Therefore, developing a new cleaning method that can achieve synergistic removal of multiple contaminants, avoid surface damage, and is environmentally friendly has become a key technical challenge that urgently needs to be overcome in the quartz wafer manufacturing industry. Summary of the Invention

[0005] The core objective of this invention is to provide a quartz wafer cleaning method that, through an innovatively designed composite cleaning solution formula and optimized cleaning process, achieves efficient removal of various contaminants such as organic matter, metal ions, and nanoparticles, while ensuring the surface integrity of the quartz wafer and improving device performance.

[0006] The technical solution adopted by this invention to solve its technical problem is: a method for cleaning quartz wafers, comprising the following steps:

[0007] The quartz wafer was ultrasonically cleaned for 10-15 minutes at 50-60°C using an alkaline composite cleaning solution consisting of 0.3-0.5 mol / L tetramethylammonium hydroxide, 0.05-0.1 mol / L sodium gluconate, 0.1-0.2 mol / L hydrogen peroxide and deionized water.

[0008] Use an acidic composite cleaning solution consisting of 0.2-0.3 mol / L oxalic acid, 0.01-0.03 mol / L hydrofluoric acid, 0.05-0.1 mol / L sodium dodecylbenzenesulfonate, and deionized water to ultrasonically clean the quartz wafer for 8-12 minutes at room temperature. After cleaning, rinse three times with deionized water with a resistivity ≥18.2 MΩ·cm, each rinse lasting 30-60 seconds, to remove residual cleaning solution from the surface.

[0009] The acid-cleaned quartz wafer was placed in deionized water and subjected to a 1MHz megasonic wave with a power density of 0.2W / cm². 2 Clean for 5-8 minutes. After cleaning, rinse 3 times with deionized water with a resistivity ≥18.2MΩ·cm, each rinse lasting 30-60 seconds, to ensure that acidic residues are completely removed.

[0010] The quartz crystal after megason cleaning was placed in a supercritical CO2 cleaning device and cleaned for 10 minutes at a temperature of 35℃ and a pressure of 8MPa.

[0011] Nitrogen gas is used for drying, with a flow rate of 15-20 L / min and a temperature of 40-50℃.

[0012] Specifically, the alkaline composite cleaning solution contains 0.4 mol / L tetramethylammonium hydroxide, 0.08 mol / L sodium gluconate, and 0.15 mol / L hydrogen peroxide. Tetramethylammonium hydroxide, as a weakly alkaline medium, can effectively decompose organic pollutants while controlling the etching rate of the quartz wafer surface to below 0.05 nm / min at this concentration. Sodium gluconate, through multiple coordinating groups in its molecular structure, interacts with metal ions (such as Fe). 3+ Cu 2+It forms stable five- or six-membered cyclic complexes with a complexation stability constant lgK > 10, ensuring that the removal efficiency of metal ions reaches more than 98%; at this concentration, hydrogen peroxide can continuously release hydroxyl radicals (·OH) in an alkaline environment, with a redox potential as high as 2.8V, which can completely decompose organic pollutants into CO2 and H2O.

[0013] Specifically, the acidic composite cleaning solution contains 0.25 mol / L oxalic acid, 0.02 mol / L hydrofluoric acid, and 0.08 mol / L sodium dodecylbenzenesulfonate. At this concentration, oxalic acid can react with various metal ions (such as Al). 3+ Zn 2+ A stable oxalate complex is formed. By controlling the pH of the solution at 2-3, the complexation reaction proceeds in the forward direction, increasing the metal ion removal rate to 99%. Trace amounts of hydrofluoric acid in an acidic environment can precisely control the removal rate of the oxide layer on the surface of the quartz wafer, forming a smooth surface with a roughness Ra≤0.3nm. The hydrofluoric acid etching rate is controlled below 0.02nm / min. Sodium dodecylbenzenesulfonate, as an anionic surfactant, forms a micelle structure in the solution. Its critical micelle concentration (CMC) is 0.001-0.002mol / L. At a concentration of 0.08mol / L, it can significantly reduce the adhesion between nanoparticles and the wafer surface, improving the particle removal efficiency by 40%.

[0014] Specifically, in the alkaline composite cleaning solution cleaning step, the ultrasonic frequency is 40kHz and the ultrasonic power is 80W. The 40kHz ultrasonic frequency can generate cavitation bubbles with a diameter of about 100-500μm. In the alkaline composite cleaning solution, the instantaneous high temperature (about 5000K) and high pressure (about 100MPa) generated by the collapse of cavitation bubbles can effectively destroy the molecular structure of organic matter and promote the complexation reaction. The 80W ultrasonic power ensures that the cavitation effect is evenly distributed in the cleaning solution, so that the consistency deviation of the cleaning effect of each part of the quartz wafer is <5%.

[0015] Specifically, in the acidic composite cleaning solution cleaning step, the ultrasonic frequency is 40kHz and the ultrasonic power is 80W. In the acidic system, the cavitation effect generated by these ultrasonic parameters can accelerate the complexation reaction rate of oxalic acid and metal ions, shortening the reaction time by 30%. At the same time, the vigorous movement of cavitation bubbles helps SDBS micelles to encapsulate and disperse nanoparticles, and in conjunction with the surface activity of SDBS, achieves efficient removal of nanoparticles.

[0016] Specifically, in the megason cleaning step, the resistivity of the deionized water is not less than 18.2 MΩ·cm; high-purity deionized water can avoid introducing additional ionic impurities, and the acoustic flow effect generated by the 1 MHz megason can form a microflow field with a speed of about 0.1-0.3 m / s. This microflow field can effectively flush away the nanoparticles remaining on the surface of the quartz wafer, and combined with the acoustic radiation force it generates, it can achieve precise removal of submicron particles.

[0017] The calculation formula is as follows: ,in Where is the particle radius, Medium density, For the speed of sound, For nonlinear parameters, This represents the sound pressure level.

[0018] Specifically, in the supercritical CO2 cleaning step, the purity of the CO2 is not less than 99.99%; the CO2 in the supercritical state has a density of approximately 0.4-0.9 g / cm³. 3 It has excellent solubility (viscosity approximately 0.02-0.09 mPa·s), capable of dissolving residual chemical reagents and moisture; at 35℃ and 8 MPa, the diffusion coefficient of CO2 is approximately 10. -4 cm 2 / s, it can quickly penetrate into the tiny pores of quartz wafers, carrying away residual impurities. After cleaning, the detection limit for residual chemical reagents is <1×10 -12 g / cm 2 .

[0019] Specifically, in the nitrogen drying step, the water content of the nitrogen is no higher than 1 ppm; during the drying process, nitrogen at 40-50°C at a flow rate of 15-20 L / min can form forced convection on the wafer surface, accelerating the rate of moisture evaporation; the low water content of the nitrogen can prevent water vapor from condensing on the wafer surface and forming watermarks, while preventing the adsorption of airborne impurity particles on the quartz wafer surface, ensuring that the cleanliness of the wafer surface is not affected after drying.

[0020] Specifically, before the alkaline composite cleaning solution cleaning step, the quartz wafer is visually inspected and its dimensions are measured. The visual inspection uses a 10-20x magnifying glass to detect whether there are defects such as cracks or scratches on the wafer surface. The dimensional measurement uses an optical measuring instrument with an accuracy of 0.1μm to ensure that the wafer size meets the design requirements (the dimensional deviation is controlled within ±0.5μm). Only wafers that pass the inspection will enter the subsequent cleaning process to avoid wasting cleaning resources on unqualified products.

[0021] Specifically, after the nitrogen drying step, the process includes surface cleanliness testing and frequency characteristic testing of the cleaned quartz wafer. Surface cleanliness testing uses a scanning electron microscope (SEM) and an energy dispersive spectroscopy (EDS) instrument to detect the number of particulate contaminants and the presence of residual metal ions. Frequency characteristic testing uses a high-precision frequency meter to test parameters such as the resonant frequency and frequency stability of the quartz wafer under constant temperature (25±0.5℃) and constant humidity (45±5%RH) conditions, ensuring that the cleaned wafer meets the requirements for use in high-precision electronic devices.

[0022] The beneficial effects of this invention are:

[0023] 1. Highly Efficient Synergistic Removal of Multiple Pollutants: Through the synergistic effect of alkaline and acidic composite cleaning solutions, organic matter, metal ions, and nanoparticles are removed simultaneously and efficiently. Testing shows that the number of particulate pollutants on the surface of the quartz wafer can be controlled to 5 particles / cm² after cleaning. 2 Below, the residual metal ion content is less than 5×10 -10 g / cm 2 The residual carbon content of organic matter is <0.1 μg / cm³. 2 .

[0024] 2. Non-destructive surface protection: Weak alkaline TMAH is used to replace traditional strong alkali, oxalic acid is used to replace hydrochloric acid, and the HF concentration is precisely controlled. Combined with optimized ultrasonic and mega-sonic parameters, the etching amount on the quartz wafer surface is controlled within 0.1nm, effectively avoiding surface damage and maintaining the inherent frequency characteristics of the wafer.

[0025] 3. Green, environmentally friendly, and energy-saving: The additives in the new composite cleaning solution (such as sodium gluconate and SDBS) all have good biodegradability, reducing the amount of chemical reagents used by 35% compared to traditional processes and lowering wastewater treatment costs by 45%. Supercritical CO2 cleaning enables the recycling of the cleaning medium, further reducing resource consumption.

[0026] 4. Significantly Improved Device Performance: When quartz wafers cleaned using this method are used in quartz crystal resonators, frequency stability is improved by 32%, aging rate is reduced by 28%, and the frequency temperature coefficient is improved to ±2×10⁻⁶. -6 / ℃, effectively improving the reliability and lifespan of electronic devices.

[0027] 5. High process stability: By precisely controlling the parameters of each cleaning step (such as cleaning solution concentration, temperature, ultrasonic power, etc.), the cleaning process is highly repeatable, and the consistency deviation of cleaning effect between different batches of wafers is <3%. Attached Figure Description

[0028] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0029] Figure 1 A flowchart of a quartz wafer cleaning method provided by the present invention. Detailed Implementation

[0030] To make the technical means, creative features, objectives and effects of this invention easier to understand, the invention will be further described below in conjunction with specific embodiments.

[0031] like Figure 1 As shown, the cleaning method for quartz wafers according to the present invention specifically includes the following steps:

[0032] Alkaline composite cleaning solution cleaning: The quartz wafer is immersed in an alkaline composite cleaning solution composed of 0.3-0.5 mol / L tetramethylammonium hydroxide (TMAH), 0.05-0.1 mol / L sodium gluconate, 0.1-0.2 mol / L hydrogen peroxide (H2O2), and deionized water. TMAH, as a weakly alkaline medium, is used to clean the quartz wafer for 10-15 minutes under ultrasonic conditions of 40 kHz and 80 W at 50-60℃. The weakly alkaline properties of TMAH (pH≈11.5-12.5) effectively decompose organic contaminants and control the etching rate of the wafer surface below 0.05 nm / min. Sodium gluconate, through multiple coordinating groups (such as hydroxyl and carboxyl groups) in its molecular structure, interacts with metal ions (such as Fe). 3+ Cu 2+ It forms stable five- or six-membered cyclic complexes with a complexation stability constant lgK > 10, ensuring that the metal ion removal efficiency reaches more than 98%; H2O2 continuously releases hydroxyl radicals (·OH) in an alkaline environment, with a redox potential as high as 2.8V, which can completely mineralize organic pollutants into CO2 and H2O.

[0033] Acidic composite cleaning solution cleaning: Transfer the alkaline-cleaned quartz wafers to an acidic composite cleaning solution composed of 0.2-0.3 mol / L oxalic acid, 0.01-0.03 mol / L hydrofluoric acid (HF), 0.05-0.1 mol / L sodium dodecylbenzenesulfonate (SDBS), and deionized water. Clean with ultrasound at 40 kHz and 80 W for 8-12 min at room temperature. Oxalic acid reacts with Al through complexation (lgK≈4-6). 3+ Zn 2+Once metal ions form stable complexes, the complexation reaction is fully carried out by controlling the solution pH at 2-3, increasing the metal ion removal rate to 99%. Trace amounts of HF (0.01-0.03 mol / L) in an acidic environment can precisely control the removal rate of the oxide layer on the quartz wafer surface, forming a smooth surface with a roughness Ra≤0.3 nm. SDBS, as an anionic surfactant, forms micelle structures in solution (critical micelle concentration CMC≈0.001-0.002 mol / L), and at a concentration of 0.05-0.1 mol / L, it can significantly reduce the adhesion between nanoparticles and the wafer surface, improving particle removal efficiency by 40%.

[0034] Megasonic cleaning: The acid-cleaned quartz wafer is placed in deionized water with a resistivity of not less than 18.2 MΩ·cm, and a 1 MHz megasonic wave is used at a frequency of 0.2 W / cm. 2 Power density cleaning for 5-8 minutes. The acoustic flow effect generated by 1MHz megahertz waves forms a microflow field with a velocity of approximately 0.1-0.3m / s, combined with acoustic radiation force ( ,in Where is the particle radius, Medium density, For the speed of sound, For nonlinear parameters, (The sound pressure amplitude) enables precise removal of submicron particles.

[0035] Supercritical CO2 cleaning: Quartz wafers cleaned using megasonic waves are placed in a supercritical CO2 cleaning device with a purity of not less than 99.99% and cleaned for 10 minutes at a temperature of 35℃ and a pressure of 8MPa. Supercritical CO2 has a density of 0.4-0.9 g / cm³. 3 Viscosity 0.02-0.09 mPa·s, diffusion coefficient approximately 10⁻⁶. -4 cm 2 It exhibits excellent dissolving properties, enabling it to rapidly penetrate into the micropores of the wafer, completely dissolving and carrying away residual chemical reagents and moisture. The detection limit for residual chemical reagents after cleaning is <1×10⁻⁶. -12 g / cm 2 .

[0036] Drying: Use nitrogen gas with a water content of no more than 1 ppm to dry the quartz wafer at a flow rate of 15-20 L / min and a temperature of 40-50℃ to ensure that there is no moisture residue on the wafer surface and to avoid secondary contamination.

[0037] Example 1

[0038] Pre-treatment: Before cleaning, the quartz wafers are visually inspected using a 10x magnifying glass to carefully observe whether there are obvious cracks, scratches or other defects on the surface of the wafers; at the same time, the length, width and thickness of the wafers are measured using an optical measuring instrument with an accuracy of 0.1μm to ensure that their dimensions meet the design requirements (length 10.00±0.05mm, width 8.00±0.05mm, thickness 0.50±0.02mm). After testing, all wafers in this batch meet the standards and can proceed to the subsequent cleaning process.

[0039] Alkaline composite cleaning solution: Prepare 500 mL of alkaline composite cleaning solution using deionized water with a resistivity of not less than 18.2 MΩ·cm, according to the ratio of 0.3 mol / L tetramethylammonium hydroxide (TMAH), 0.05 mol / L sodium gluconate, and 0.1 mol / L hydrogen peroxide (H2O2). Arrange the quartz wafers neatly in a PTFE cleaning basket, slowly immerse them in the cleaning solution, and place them in a constant temperature water bath ultrasonic cleaner. Set the ultrasonic frequency to 40 kHz, ultrasonic power to 80 W, temperature to 50 °C, and cleaning time to 10 min. During this process, the weakly alkaline environment of TMAH (pH approximately 11.8) effectively decomposes photoresist, grease, and other organic contaminants on the wafer surface; sodium gluconate rapidly reacts with residual Fe... 3+ Cu 2+ Metal ions undergo a complexation reaction to form a stable five-membered ring complex; H2O2 continuously releases hydroxyl radicals (·OH), oxidizing complex organic matter into CO2 and H2O. After cleaning, the wafer is removed and immediately rinsed three times with deionized water, each rinse lasting 30 seconds, to remove any residual alkaline cleaning solution from the surface.

[0040] Acidic composite cleaning solution: Prepare 500 mL of an acidic composite cleaning solution containing 0.2 mol / L oxalic acid, 0.01 mol / L hydrofluoric acid (HF), and 0.05 mol / L sodium dodecylbenzene sulfonate (SDBS). Transfer the rinsed quartz wafer to this acidic cleaning solution and place it in an ultrasonic cleaner at room temperature (25°C). Set the ultrasonic frequency to 40 kHz and the power to 80 W, and clean for 8 minutes. Oxalic acid reacts with residual Al... 3+ Zn 2+ Metal ions form stable complexes; trace amounts of HF precisely remove the oxide layer on the wafer surface at a rate of approximately 0.02 nm / min; SDBS forms micelle structures in the solution, reducing the adhesion between nanoparticles and the wafer surface; and ultrasonic cavitation accelerates the removal of contaminants. After cleaning, the wafer is rinsed three times with deionized water, with each rinse lasting 45 seconds to ensure thorough removal of the acidic cleaning solution.

[0041] Megasonic Cleaning: Prepare 1000 mL of fresh deionized water with a resistivity of 18.2 MΩ·cm and pour it into the megasonic cleaning tank. Place the acid-cleaned quartz wafer into the cleaning tank, turn on the megasonic cleaning equipment, and set the frequency to 1 MHz and the power density to 0.2 W / cm². 2 The cleaning process lasted 5 minutes. A 1MHz megasonic wave generated a strong acoustic flow effect and microfluidic field, which, combined with the acoustic radiation force, effectively removed submicron-sized particulate contaminants remaining on the wafer surface. During the cleaning process, the resistivity change of the deionized water was monitored in real time to ensure the purity of the cleaning environment.

[0042] Supercritical CO2 Cleaning: The quartz wafers, after megasonic cleaning, are carefully transferred to the autoclave of a supercritical CO2 cleaning system. The system is pre-filled with 99.99% pure CO2 gas. The temperature inside the autoclave is raised to 35°C and the pressure is adjusted to 8 MPa using a temperature control system, and maintained for 10 minutes. Due to its excellent solubility and high diffusion coefficient, supercritical CO2 rapidly penetrates into the tiny pores and surface depressions of the wafer, completely dissolving and carrying away any residual chemical reagents and moisture. After cleaning, the pressure is slowly released, and the wafers are removed once the pressure drops to atmospheric pressure.

[0043] Drying: The quartz wafers, cleaned with supercritical CO2, were placed on a clean drying table and dried using high-purity nitrogen gas with a moisture content of less than 1 ppm, a flow rate of 15 L / min, and a temperature of 40°C. The nitrogen gas was blown at a uniform speed and angle of 45° from a distance of 10 cm from the wafer surface to ensure rapid evaporation of moisture while avoiding the introduction of new contaminants. After the drying process lasted for 5 minutes, an infrared humidity detector was used to check the wafer surface to confirm that no moisture remained.

[0044] Testing and Performance Evaluation: The surface of the cleaned quartz wafer was observed using a scanning electron microscope (SEM) at a magnification of 5000x. The results showed that the number of surface particulate contaminants was 4 particles / cm². 2 Elemental analysis was performed using energy-dispersive X-ray spectroscopy (EDS), and the residual metal ion concentration was detected to be 4 × 10⁻⁶. -10 g / cm 2 The surface roughness of the wafer was measured using an atomic force microscope (AFM), with an Ra value of 0.28 nm. The wafer was then fabricated into a quartz crystal resonator, and its frequency stability was tested using a high-precision frequency analyzer under constant temperature (25℃) and constant humidity (45%RH) conditions. The results showed that the frequency stability was improved by 28%, achieving the expected effect.

[0045] Example 2

[0046] Pre-processing: Similar to Example 1, the quartz wafers are subjected to rigorous visual inspection and dimensional measurement to ensure that the wafers are defect-free and that their dimensions meet the standards (length 12.00±0.05mm, width 10.00±0.05mm, thickness 0.60±0.02mm).

[0047] Alkaline composite cleaning solution: Prepare 800 mL of an alkaline composite cleaning solution containing 0.4 mol / L TMAH, 0.08 mol / L sodium gluconate, and 0.15 mol / L H2O2. Place the wafer in a cleaning basket and immerse it in the cleaning solution. Clean in a constant temperature water bath ultrasonic cleaner at a frequency of 40 kHz, power of 80 W, and temperature of 55 °C for 12 minutes. During this process, monitor the pH of the cleaning solution in real time (approximately 12.0) using a pH meter to ensure a stable alkaline environment. After cleaning, rinse three times with deionized water, each rinse lasting 40 seconds.

[0048] Acidic composite cleaning solution: Prepare 800 mL of an acidic composite cleaning solution containing 0.25 mol / L oxalic acid, 0.02 mol / L HF, and 0.08 mol / L LDBS. Transfer the alkaline-cleaned wafer to the acidic cleaning solution and sonicate at room temperature for 10 min. During the cleaning process, the solution color was observed to gradually darken due to the metal ion complexation reaction. After cleaning, rinse three times with deionized water, each rinse lasting 50 s.

[0049] Megasonic cleaning: Prepare 1500mL of high-purity deionized water, place the acid-cleaned wafer into the megasonic cleaning tank, and set the frequency to 1MHz and the power density to 0.2W / cm². 2 The water was rinsed for 6 minutes. During the rinsing process, a laser particle size analyzer was used to monitor changes in particle concentration in the water to ensure effective removal of particulate contaminants.

[0050] Supercritical CO2 cleaning: Place the wafer in a supercritical CO2 cleaning device, adjust the temperature to 35℃ and the pressure to 8MPa, and clean for 10 minutes. After cleaning, depressurize and remove the wafer according to the standard procedure.

[0051] Drying: The wafers were dried using nitrogen gas at a flow rate of 18 L / min, a temperature of 45°C, and a moisture content of less than 1 ppm for 6 minutes. During the drying process, an infrared thermal imager was used to monitor the temperature distribution on the wafer surface to ensure uniform drying.

[0052] Detection and performance evaluation: SEM analysis showed that the number of particulate contaminants on the wafer surface was 3 particles / cm. 2 EDS analysis revealed a residual metal ion content of 3 × 10⁻⁶. -10 g / cm 2The surface roughness Ra value measured by AFM is 0.25 nm. When this wafer was applied to a quartz crystal oscillator, testing showed a 33% improvement in frequency stability and a 26% reduction in aging rate, meeting the requirements for high-precision electronic devices.

[0053] Example 3

[0054] Pre-processing: A comprehensive quality inspection is carried out on the quartz wafers, including visual inspection and dimensional measurement (length 8.00±0.05mm, width 6.00±0.05mm, thickness 0.40±0.02mm) to ensure that the wafers are qualified.

[0055] Alkaline composite cleaning solution: Prepare 400 mL of an alkaline composite cleaning solution containing 0.5 mol / L TMAH, 0.1 mol / L sodium gluconate, and 0.2 mol / L H2O2. After immersing the wafer in the cleaning solution, clean it in an ultrasonic cleaner at a frequency of 40 kHz, power of 80 W, and temperature of 60 °C for 15 min. During the cleaning process, tiny bubbles were observed to be generated in the solution, indicating that the organic matter was being oxidized and decomposed. After cleaning, rinse three times with deionized water, each rinse lasting 45 s.

[0056] Acidic composite cleaning solution: Prepare 400 mL of an acidic composite cleaning solution containing 0.3 mol / L oxalic acid, 0.03 mol / L HF, and 0.1 mol / L LDBS. Immerse the alkaline-cleaned wafer in the acidic cleaning solution and sonicate at room temperature for 12 min. After cleaning, rinse thoroughly three times with deionized water, each rinse lasting 60 s.

[0057] Megasonic cleaning: Pour 1000mL of deionized water into the megasonic cleaning tank, place the acid-cleaned wafer inside, and set the frequency to 1MHz and the power density to 0.2W / cm². 2 Cleaning time is 8 minutes. During the cleaning process, the operating parameters of the megasonic equipment are recorded to ensure stable cleaning conditions.

[0058] Supercritical CO2 cleaning: The wafer is placed in a supercritical CO2 cleaning device and cleaned for 10 minutes at a temperature of 35°C and a pressure of 8 MPa. After cleaning, the pressure is slowly released and the wafer is removed.

[0059] Drying: The wafer is dried using nitrogen gas at a flow rate of 20 L / min, a temperature of 50°C, and a moisture content of less than 1 ppm for 7 minutes. After drying, the wafer is subjected to electrostatic protection to prevent dust adsorption.

[0060] Detection and performance evaluation: SEM analysis showed that the number of particulate contaminants on the wafer surface was 2 particles / cm². 2 EDS analysis showed that the residual metal ions were 2 × 10⁻⁶. -10 g / cm 2The surface roughness Ra value measured by AFM is 0.22 nm. This chip was used in the frequency control module of high-end communication equipment, and test results show that frequency stability is improved by 35%, aging rate is reduced by 29%, and performance is excellent.

[0061] Example 4

[0062] Pre-treatment: Quartz wafers are strictly screened. Unqualified products are rejected by visual inspection and dimensional measurement (length 15.00±0.05mm, width 12.00±0.05mm, thickness 0.70±0.02mm).

[0063] Alkaline composite cleaning solution: Prepare 1000 mL of an alkaline composite cleaning solution containing 0.35 mol / L TMAH, 0.06 mol / L sodium gluconate, and 0.12 mol / L H₂O₂. Immerse the wafer in the cleaning solution and clean in an ultrasonic cleaner at a frequency of 40 kHz, a power of 80 W, and a temperature of 52 °C for 11 minutes. During the cleaning process, stir the cleaning solution periodically to ensure uniform cleaning. After cleaning, rinse three times with deionized water, each rinse lasting 35 seconds.

[0064] Acidic composite cleaning solution: Prepare 1000 mL of an acidic composite cleaning solution containing 0.22 mol / L oxalic acid, 0.015 mol / L HF, and 0.06 mol / L LDBS. Transfer the alkaline-cleaned wafer to the acidic cleaning solution and sonicate at room temperature for 9 min. During the cleaning process, monitor the pH value of the solution using pH test paper to ensure it remains within the appropriate range. After cleaning, rinse three times with deionized water, each rinse lasting 45 s.

[0065] Megasonic cleaning: Prepare 1800mL of deionized water, place the acid-cleaned wafer into the megasonic cleaning tank, and set the frequency to 1MHz and the power density to 0.2W / cm². 2 Rinse for 5 minutes. Observe the change in the clarity of the deionized water during the rinsing process.

[0066] Supercritical CO2 cleaning: Place the wafer in a supercritical CO2 cleaning device, adjust the temperature to 35℃ and the pressure to 8MPa, and clean for 10 minutes. After cleaning, remove the wafer according to the operating procedures.

[0067] Drying: The wafers were dried using nitrogen gas at a flow rate of 16 L / min, a temperature of 42°C, and a moisture content of less than 1 ppm for 5 minutes. After drying, the wafers were stored in a clean, sealed container.

[0068] Detection and performance evaluation: SEM analysis showed that the number of particulate contaminants on the wafer surface was 4 / cm. 2 EDS analysis revealed a residual metal ion content of 4 × 10⁻⁶. -10 g / cm2 The surface roughness Ra value measured by AFM was 0.26 nm. This wafer was fabricated into a quartz crystal resonator for performance testing, showing a 29% improvement in frequency stability and a frequency temperature coefficient of ±2.1 × 10⁻⁶. -6 / ℃, meeting relevant technical specifications.

[0069] Example 5

[0070] Pre-treatment: The quartz wafers are inspected for appearance and size (length 10.00±0.05mm, width 8.00±0.05mm, thickness 0.55±0.02mm) to ensure they meet the requirements before proceeding to the cleaning process.

[0071] Alkaline composite cleaning solution: Prepare 600 mL of an alkaline composite cleaning solution containing 0.45 mol / L LMAH, 0.09 mol / L sodium gluconate, and 0.18 mol / L H₂O₂. Immerse the wafer in the cleaning solution and clean for 14 minutes in an ultrasonic cleaner with an ultrasonic frequency of 40 kHz, power of 80 W, and temperature of 58 °C. During the cleaning process, observe the color change of the cleaning solution to determine the removal of contaminants. After cleaning, rinse three times with deionized water, each rinse lasting 40 seconds.

[0072] Acidic composite cleaning solution: Prepare 600 mL of an acidic composite cleaning solution containing 0.28 mol / L oxalic acid, 0.025 mol / L HF, and 0.09 mol / L LDBS. Immerse the alkaline-cleaned wafer in the acidic cleaning solution and sonicate at room temperature for 11 min. During the cleaning process, carefully control the ultrasonic intensity to avoid damaging the wafer. After cleaning, rinse three times with deionized water, each rinse lasting 50 s.

[0073] Megasonic cleaning: Prepare 1200mL of deionized water, place the acid-cleaned wafer into the megasonic cleaning tank, and set the frequency to 1MHz and the power density to 0.2W / cm². 2 Cleaning time is 7 minutes. During the cleaning process, the actual power output of the megasonic wave is monitored to ensure the cleaning effect.

[0074] Supercritical CO2 cleaning: The wafer is placed in a supercritical CO2 cleaning device and cleaned for 10 minutes at a temperature of 35°C and a pressure of 8 MPa. After cleaning, the pressure is slowly released and the wafer is removed.

[0075] Drying: The wafer was dried using nitrogen gas at a flow rate of 19 L / min, a temperature of 48°C, and a moisture content of less than 1 ppm for 6 minutes. After drying, the surface resistance of the wafer was tested to ensure that there was no electrostatic residue.

[0076] Detection and performance evaluation: SEM analysis showed that the number of particulate contaminants on the wafer surface was 3 particles / cm. 2EDS analysis showed that the residual metal ions were 3 × 10⁻⁶. -10 g / cm 2 The surface roughness Ra value measured by AFM is 0.24 nm. When this chip was applied to electronic devices in the aerospace field, tests showed a 32% improvement in frequency stability and a 27% reduction in aging rate, demonstrating excellent performance.

[0077] Example 6

[0078] Pre-processing: The quartz wafers undergo meticulous visual inspection and precise dimensional measurement (9.00±0.05mm in length, 7.00±0.05mm in width, and 0.45±0.02mm in thickness) to ensure wafer quality.

[0079] Alkaline composite cleaning solution: Prepare 500 mL of an alkaline composite cleaning solution containing 0.38 mol / L TMAH, 0.07 mol / L sodium gluconate, and 0.13 mol / L H₂O₂. Immerse the wafer in the cleaning solution and clean in an ultrasonic cleaner at a frequency of 40 kHz, a power of 80 W, and a temperature of 53 °C for 13 min. Monitor the temperature fluctuation of the cleaning solution during the cleaning process to ensure stability. After cleaning, rinse three times with deionized water, each rinse lasting 35 s.

[0080] Acidic composite cleaning solution: Prepare 500 mL of an acidic composite cleaning solution containing 0.23 mol / L oxalic acid, 0.018 mol / L HF, and 0.07 mol / L SDBS. Immerse the alkaline-cleaned wafer in the acidic cleaning solution and sonicate at room temperature for 10 min. During the cleaning process, observe the encapsulation of particulate contaminants by SDBS micelles. After cleaning, rinse three times with deionized water, each rinse lasting 45 s.

[0081] Megasonic cleaning: Prepare 1000mL of deionized water, place the acid-cleaned wafer into the megasonic cleaning tank, and set the frequency to 1MHz and the power density to 0.2W / cm². 2 Clean for 6 minutes. During the cleaning process, record the water flow in the cleaning tank to ensure even cleaning.

[0082] Supercritical CO2 cleaning: Place the wafer in a supercritical CO2 cleaning device, adjust the temperature to 35℃ and the pressure to 8MPa, and clean for 10 minutes. After cleaning, remove the wafer according to the prescribed procedure.

[0083] Drying: The wafer was dried using nitrogen gas at a flow rate of 17 L / min, a temperature of 43°C, and a moisture content of less than 1 ppm for 5 minutes. After drying, the wafer was placed in a clean environment to await testing.

[0084] Detection and performance evaluation: SEM analysis showed that the number of particulate contaminants on the wafer surface was 4 / cm.2 EDS analysis revealed a residual metal ion content of 4 × 10⁻⁶. -10 g / cm 2 The surface roughness Ra value measured by AFM is 0.27 nm. When this chip was used in the clock module of an IoT device, test results showed a 30% improvement in frequency stability and minimal frequency fluctuation under different ambient temperatures, meeting practical application requirements.

[0085] 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 protection claimed by the present invention. The scope of protection of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method of cleaning a quartz wafer, characterized by, The method comprises the following steps: ultrasonic cleaning of the quartz wafer at 50-60 DEG C for 10-15 min using an alkaline composite cleaning solution composed of 0.3-0.5 mol / L tetramethylammonium hydroxide, 0.05-0.1 mol / L sodium gluconate, 0.1-0.2 mol / L hydrogen peroxide and deionized water; ultrasonic cleaning of the quartz wafer at room temperature for 8-12 min using an acidic composite cleaning solution composed of 0.2-0.3 mol / L oxalic acid, 0.01-0.03 mol / L hydrofluoric acid, 0.05-0.1 mol / L sodium dodecyl benzene sulfonate and deionized water, and rinsing and megasonic cleaning with deionized water after the cleaning; placing the quartz wafer cleaned by megasonic cleaning into a supercritical CO2 cleaning device for cleaning and drying with nitrogen; in the alkaline composite cleaning solution cleaning step, the ultrasonic frequency is 40 kHz and the ultrasonic power is 80 W; in the acidic composite cleaning solution cleaning step, the ultrasonic frequency is 40 kHz and the ultrasonic power is 80 W; in the megasonic cleaning step, the resistivity of the deionized water is not less than 18.2 MΩ·cm; The number of surface particle contaminants on the quartz wafer after cleaning can be controlled to 5 / cm 2 The following metal ion residual amount is less than 5 x 10 -10 g / cm 2 The residual carbon content of organic matter is < 0.1 μg / cm 2 .

2. The method of claim 1, wherein: in the alkaline composite cleaning solution, the concentration of tetramethylammonium hydroxide is 0.4 mol / L, the concentration of sodium gluconate is 0.08 mol / L and the concentration of hydrogen peroxide is 0.15 mol / L.

3. The method of claim 1, wherein: in the acidic composite cleaning solution, the concentration of oxalic acid is 0.25 mol / L, the concentration of hydrofluoric acid is 0.02 mol / L and the concentration of sodium dodecyl benzene sulfonate is 0.08 mol / L.

4. The method of claim 1, wherein: in the supercritical CO2 cleaning step, the purity of CO2 is not less than 99.99%.

5. The method of claim 1, wherein: in the nitrogen drying step, the water content of the nitrogen is not higher than 1 ppm.

6. The method of claim 1, wherein: before the alkaline composite cleaning solution cleaning step, visual inspection and size measurement of the quartz wafer are further included; the visual inspection uses a 10-20 times magnifying glass and the size measurement uses an optical measuring instrument with a precision of 0.1 μm.

7. The method of claim 1, wherein: after the nitrogen drying step, surface cleanliness detection and frequency characteristic test of the cleaned quartz wafer are further included.

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