Centralized supply system for silicon oxide polishing solution of SiC substrate

Abstract

The invention relates to the technical field of silicon oxide polishing solution centralized supply systems for SiC substrates, discloses a silicon oxide polishing solution centralized supply system for SiC substrates, and aims to solve the problems of unstable process and wafer defects caused by abrasive particle sedimentation and chemical component drifting of an existing polishing solution centralized supply system. The system is characterized by comprising a first stock solution storage and pretreatment unit, a second polishing solution precise mixing unit, a third centralized conveying and terminal supply unit and a central control unit, and physical stability is maintained through a periodic pulse disturbance control method. And closed-loop chemical compensation is realized by a distributed online sensing network and an active trace dosing system. By adopting the technical scheme, the consistency, the yield and the reliability of the chemical mechanical polishing process of the silicon carbide substrate can be improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of semiconductor manufacturing, and in particular relates to a system for centrally supplying silicon oxide polishing liquid for SiC substrates. Background Art

[0002] As third-generation semiconductor material technology, represented by silicon carbide (SiC), matures, its exceptional physical properties, including wide bandgap, high thermal conductivity, and high breakdown field strength, demonstrate tremendous application potential in cutting-edge fields such as power electronics, high-frequency radio frequency devices, and optoelectronics. The surface quality of wafer substrates is a prerequisite for the performance, reliability, and yield of semiconductor devices. Chemical mechanical polishing (CMP), a critical final step in achieving global planarization and eliminating surface and subsurface damage, directly impacts the final quality of SiC substrates. The extremely high hardness and excellent chemical inertness of SiC materials place extremely stringent requirements on the performance of polishing slurries during the polishing process. Currently, the industry generally uses alkaline polishing slurries containing nano-silicon dioxide (SiO2) particles as abrasives, achieving efficient, low-damage removal of SiC surfaces through the synergistic effects of chemical etching and mechanical grinding. In order to meet the stringent standards for process consistency and cost control in large-scale production, the use of a centralized dispenser system (CDS) to uniformly mix and deliver polishing liquid has become the mainstream technical path in the industry.

[0003] Against this backdrop, researchers in related fields have made a series of valuable discoveries. For example, Chinese patent CN109571227B discloses a polishing liquid supply system. Its core design concept is to construct functionally separate subsystems to efficiently supply and precisely mix the stock solution. Specifically, this solution deconstructs the complex liquid supply process into a stock solution supply subsystem and an equipment-side supply subsystem. The stock solution supply subsystem is responsible for high-volume, high-throughput delivery from raw material barrels to a central storage tank, while the equipment-side supply subsystem performs dilution and mixing of the stock solution near the point of use, based on the real-time needs of each polishing machine. This layered, divide-and-conquer architecture effectively achieved logical decoupling of the liquid supply tasks under the prevailing process conditions. On the one hand, it separated high-frequency, small-batch mixing operations from low-frequency, large-volume replenishment operations, significantly mitigating pressure and flow fluctuations in the main supply pipeline. On the other hand, centralized mixing at the equipment-side facilitates unified management and control of polishing liquid formulations for different machines, thereby improving the overall stability and quality of the polishing process. The design concept of this solution reflects a positive attempt to improve the response speed and management efficiency of the liquid supply system.

[0004] However, with the continuous improvement of the processing precision and production scale of silicon carbide substrates, the stability and precision control ability of the polishing liquid supply system in the whole process are unprecedentedly challenged. The above technical scheme solves the problem of flow allocation, but its design principle inherently leads to a series of more hidden and profound technical contradictions. The root cause lies in that the scheme mainly focuses on the macro management of the fluid in the "dynamic delivery" process, but relatively ignores the micro physical and chemical behavior of the silicon oxide polishing liquid as a complex colloidal suspension in the "quasi-static" and "static" states. Specifically, the silicon oxide polishing liquid is not a true solution, but a metastable suspension system composed of nano-sized abrasive particles, pH stabilizers, dispersants and other components. In the centralized supply system, since the terminal polishing equipment is not always in full load operation state, there must be some sections of the pipeline system in a low flow rate or even completely static state for a long time. In the system described in CN109571227B, once the device end supply subsystem suspends the liquid supply, the polishing liquid in the long delivery pipeline at the front end will lose the support of fluid kinetic energy, and the suspended silicon dioxide abrasive particles will inevitably settle, agglomerate, and even form hard lumps that are difficult to disperse again at the bottom of the pipeline. When the system starts to supply liquid again, the initial delivery of the polishing liquid abrasive concentration will deviate significantly from the set value, directly causing a sharp fluctuation in the polishing rate, and destroying the process consistency within and between batches. More seriously, the deposited agglomerated particles will form serious scratch defects on the wafer surface once they are brought up by the fluid and delivered to the polishing pad, causing irreversible damage to the expensive silicon carbide substrate. In addition, the scheme lacks an online monitoring and adjustment mechanism for the stability of the chemical components. The SiC polishing process is extremely sensitive to the pH value of the polishing liquid, and an accurate and stable alkaline environment is a prerequisite for achieving an ideal chemical corrosion rate. In actual operation, the pH value of the polishing liquid may drift during storage and transportation due to factors such as contact with the environment air (such as absorption of carbon dioxide). The existing system only guarantees the initial pH value when mixing at the front end, but cannot real-time confirm and compensate the pH value when delivered to the terminal use point, which greatly reduces the control accuracy of the process window.

[0005] Therefore, the core limitation of the existing centralized polishing liquid supply system has evolved from a simple flow rate and ratio control problem to a systematic problem of how to achieve efficient centralized supply while maintaining the physical suspension stability and chemical environment constancy of the complex multiphase system of polishing liquid in the entire time domain and all paths. How to build an integrated liquid supply system that can not only accurately mix and deliver, but also effectively inhibit particle sedimentation through an active circulation disturbance mechanism, and achieve closed-loop precision control of key chemical parameters (such as pH value) through online sensing and feedback control technology, thereby fundamentally eliminating the process uncertainty caused by pipeline static and chemical composition drift, has become a key challenge currently faced by technical personnel in this field and a technical problem that needs to be solved urgently. Summary of the Invention

[0006] The present invention aims to overcome the technical issues of abrasive particle settling, chemical composition drift, and the resulting process instability and wafer defects associated with existing centralized silicon oxide polishing slurry supply systems. This system provides a centralized silicon oxide polishing slurry supply system for SiC substrates. By constructing a precision fluid management architecture that integrates multimodal cyclic perturbations, distributed online sensing, and closed-loop feedback control, this system aims to actively maintain the physical suspension stability and chemical environment constancy of the polishing slurry throughout the entire time domain and along the entire path, thereby fundamentally improving the consistency, yield, and reliability of the chemical mechanical polishing process for silicon carbide substrates.

[0007] To achieve the above-mentioned purpose of the invention, the present invention provides a system for centralized supply of silicon oxide polishing liquid for SiC substrates, characterized in that the system includes: a first stock liquid storage and pretreatment unit, a second polishing liquid precision mixing unit, a third centralized transportation and terminal supply unit, and a central control unit for data exchange and command control with the aforementioned units.

[0008] Specifically, the first stock solution storage and pretreatment unit is configured to receive, store, and preliminarily process high-concentration silicon oxide polishing liquid stock solution and pH regulator stock solution. This unit includes a first stock solution storage tank, a second stock solution storage tank, a first stock solution delivery pump assembly, a first gas pipeline system, and a first circulation pipeline. The first stock solution storage tank, used to store high-concentration silicon oxide polishing liquid stock solution, has a tank structure constructed of 316L stainless steel lined with perfluoroalkoxy plastic (PFA). The bottom is designed with a conical angle of no less than 15 degrees to eliminate fluid dead zones, and a drain port is provided at the center of the cone bottom. The inner wall of the tank is electropolished to a surface roughness Ra value of no more than 0.4 microns. A magnetically driven stirring device is provided within the tank, comprising an external driving magnet, an internal driven magnet encapsulated in a polytetrafluoroethylene (PTFE) shell, and a stirring blade. The speed of the stirring device is steplessly adjusted within a range of 0 to 300 RPM via an analog output signal from a central control unit. The second stock solution storage tank is used to store a pH adjuster stock solution, such as sodium hydroxide (NaOH) solution. Its structure and materials are the same as those of the first stock solution storage tank, but it lacks a stirring mechanism. The first stock solution delivery pump assembly consists of a first stock solution pump and a second stock solution pump, both of which are magnetically driven centrifugal pumps with flow-through components made of high-purity PTFE. The inlet of the first stock solution pump is connected to the discharge port of the first stock solution storage tank, and its outlet is connected to the subsequent second polishing liquid precision mixing unit. The inlet of the second stock solution pump is connected to the discharge port of the second stock solution storage tank, and its outlet is also connected to the second polishing liquid precision mixing unit. The first gas pipeline system is used to deliver high-purity (no less than 99.999%) nitrogen gas to the headspaces of the first and second stock solution storage tanks, creating a positive pressure seal to prevent carbon dioxide from the ambient air from dissolving into the polishing liquid and causing a drop in pH. The system includes a nitrogen source, a precision pressure reducing valve, a mass flow controller, and branch pipes and electronically controlled pneumatic valves leading to the tops of the two storage tanks. The first circulation pipeline is connected at one end to the outlet main line of the first raw liquid pump and at the other end to the top of the first raw liquid storage tank, forming a local circulation loop. A first circulation control valve is installed in this loop. When the first raw liquid pump suspends supply to subsequent units, the central control unit instructs the first circulation control valve to open, allowing the first raw liquid pump to continue operating at a low flow rate, maintaining the flow of raw liquid in this section of the pipeline and preventing sedimentation.

[0009] Furthermore, the function of the second polishing liquid precision mixing unit is to accurately mix, mature and verify the silicon oxide stock solution, pH regulator and ultrapure water (DIWater) from the first stock solution storage and pretreatment unit according to a preset process formula. The unit includes a mixing tank, a weighing module, a multi-channel feed valve group, a mixing and stirring device, a mixing delivery pump and a set of built-in integrated sensing modules. The structure and material of the mixing tank are the same as those of the first stock solution storage tank, with a conical bottom and polished inner wall. The weighing module is composed of three to four high-precision shear beam weighing sensors arranged at the bottom of the mixing tank. Its comprehensive measurement accuracy reaches 0.05% of the full scale or higher. Its real-time weight data is transmitted to the central control unit through a signal transmitter in the form of a 4-20mA current signal or an industrial Ethernet protocol (such as EtherNet / IP). The multi-channel feed valve assembly, integrated into the top of the mixing tank, comprises three pneumatic diaphragm valves connected to the outlet pipelines of the first and second stock liquid pumps, as well as the external ultrapure water supply line. A central control unit sequentially opens and closes the corresponding valves based on real-time feedback from the weighing module, achieving high-precision addition of the silica stock solution, pH adjuster, and ultrapure water by weight. The mixing and stirring device, identical in structure to the stirring device within the first stock liquid storage tank, is controlled by the central control unit for start, stop, and speed, ensuring thorough mixing of the tank contents during and after material addition. The built-in integrated sensing module, fixedly mounted at a specific depth within the mixing tank, integrates a composite pH electrode, a four-electrode conductivity sensor, and a temperature sensor. The composite pH electrode features automatic temperature compensation, a measurement range of 0-14°C, and a resolution of 0.01 pH. The conductivity sensor assists in determining ion concentration, and the temperature sensor monitors temperature changes during mixing and compensates for other sensors. Signals from all sensors are connected to the central control unit for real-time monitoring of key chemical parameters of the mixed liquid. The mixing and delivery pump is a low shear volumetric pump, such as a peristaltic pump or a diaphragm pump, with its inlet connected to the discharge port of the mixing tank and its outlet connected to the third centralized delivery and terminal supply unit.

[0010] As a preferred embodiment of the present invention, the operation logic of the second polishing liquid precision mixing unit is strictly executed by the central control unit. A typical mixing process is as follows: first, the central control unit instructs to open the ultrapure water feed valve and inject a preset weight of ultrapure water according to the reading of the weighing module; secondly, the central control unit instructs to open the first stock solution feed valve, injects a preset weight of silicon oxide stock solution, and starts the mixing and stirring device at the same time; thirdly, under the continuous stirring state, the central control unit instructs to open the second stock solution feed valve, drips the pH regulator in batches at a small flow rate, and monitors the pH reading of the built-in integrated sensor module in real time until the pH value stabilizes at the center value of the process setting window; finally, all feed valves are closed and stirring is continued for a preset aging time (for example, 30 minutes). During this period, the central control unit continuously records the pH, conductivity and temperature data. If the fluctuation of all parameters within the specified time (for example, the last 10 minutes) is less than the preset threshold, the batch of polishing liquid is determined to be mixed and qualified and ready for delivery; otherwise, the system alarms and prompts manual intervention.

[0011] Furthermore, the third centralized delivery and terminal supply unit is a key part for achieving the core function of the present invention - maintaining full-path physical and chemical stability. The unit includes a main circulation supply pipeline, multiple terminal point of use (POU) supply modules, a distributed online sensor network, an active micro-dosing system, and a pipeline maintenance system. The main circulation supply pipeline constitutes a closed loop (Loop), the starting point of which is connected to the outlet of the mixing and delivery pump. The pipeline surrounds the polishing area of ​​the entire clean room, and finally its end point returns to the top inlet of the mixing tank to form a global cycle. The entire pipeline is made of PFA material with a smooth inner wall, and all connection points are made of hot-melt welding or flared (Flare) joints to eliminate the source of particle generation. The multiple terminal point use supply modules are arranged along the main circulation supply pipeline, and each module corresponds to a chemical mechanical polishing machine. Each module includes a three-way sampling valve leading from the main circulation supply pipeline, a branch pipeline leading to the polishing machine buffer tank (TK barrel), a supply control valve arranged on the branch pipeline and a flow meter.

[0012] A key innovation of this invention lies in the operating mode of the primary circulation supply line. During system operation, regardless of whether polishing fluid is needed at the terminal, the mixing and delivery pump maintains a constant, low-speed circulation of polishing fluid throughout the primary circulation supply line at a base flow rate (e.g., 10% to 20% of the rated flow rate). This design fundamentally eliminates prolonged periods of stagnant polishing fluid within the line, initially suppressing the tendency of abrasive particles to settle.

[0013] On this basis, the present invention sets up a more sophisticated physical stability maintenance mechanism. The central control unit implements a periodic pulse disturbance control method. Specifically, when the central control unit determines that the system enters the global standby mode (that is, all polishing machines have not requested liquid supply for more than a preset time, such as 5 minutes) by monitoring the status of the supply modules of all terminal use points, it will automatically switch the operation mode of the mixing and delivery pump. At this time, on top of the basic low-speed cycle, the central control unit will perform periodic, high-frequency pulse modulation on the speed of the mixing and delivery pump through its analog output or pulse width modulation (PWM) signal. For example, with a cycle of 1 minute, within the first 5 seconds of the cycle, the pump flow rate is instantly increased to 80% of the rated flow rate, generating a high-flow pressure wave, and then restored to the basic cycle flow rate in 55 seconds. This periodic high-energy fluid pulse can generate strong turbulence and shear force in the pipeline, and its energy is sufficient to re-suspend any particles that have begun to attach or settle weakly. Its effect is far better than a single constant low-speed flow, and the total energy consumption is lower. Parameters such as the frequency, amplitude and duty cycle of the pulse can be configured on the human-machine interface (HMI) of the central control unit according to the batch characteristics of the polishing liquid (such as viscosity and density) and the total length of the pipeline.

[0014] Another key innovation of the present invention lies in its closed-loop active control mechanism for chemical stability. The distributed online sensing network is composed of a plurality of online sensing nodes, which are strategically installed in key positions of the main circulation supply pipeline, such as after the outlet of the mixing and delivery pump, the farthest end of the loop, and before the loop returns to the mixing tank. Each sensing node is integrated with a composite pH electrode and conductivity sensor of the same specifications as those in the mixing tank. The data of these sensors are transmitted to the central control unit in real time. The active micro-dosing system includes a micro-dosing storage tank (for storing diluted pH regulator), a high-precision micro-metering pump (such as a piezoelectric ceramic-driven micro-pump with a discharge accuracy of up to nanoliters) and a dosing injection point connected to the main circulation supply pipeline. The injection point is set at a position after the outlet of the mixing and delivery pump and before the first online sensing node.

[0015] The closed-loop control system for chemical stability operates as follows: A central control unit continuously collects and analyzes pH data from all distributed online sensing nodes. It uses an averaging algorithm to calculate the average pH value for the entire circulation system and compares it with the target pH value set for the process. If the average pH value falls below the set control limit (e.g., -0.05 of the target value), the central control unit initiates a PID (proportional-integral-derivative) control algorithm. The output of this algorithm precisely controls the on-time and frequency of a micro-metering pump, injecting a very small amount of pH adjuster into the main circulation supply line in a pulsed manner. The newly injected adjuster is rapidly and evenly distributed throughout the system as it circulates. Thanks to distributed sensing and closed-loop feedback, the system accurately compensates for small, slow pH drifts caused by factors such as carbon dioxide absorption in real time, ensuring that the pH value of the polishing slurry is maintained within a very narrow process window at all times and locations within the pipeline.

[0016] In addition, the pipeline maintenance system includes ultrapure water pipelines and high-purity nitrogen pipelines connected to the main circulation supply pipeline, each branch pipeline and all functional units. The central control unit has a built-in automatic cleaning and purging program. Before changing the polishing liquid of different formulas or the system is scheduled to be shut down for maintenance, the automatic cleaning program can be started. The program will open and close the relevant valves in a preset order. First, the polishing liquid remaining in the pipeline will be purged back to the mixing tank with high-purity nitrogen, and then ultrapure water will be injected for multiple pulse flushing. Finally, the pipeline will be thoroughly dried with high-purity nitrogen to prevent moisture residue and crystal precipitation. The branch pipelines that supply the module at each terminal use point will also automatically perform a short nitrogen purging program by the central control unit after each supply is completed to ensure that there is no liquid residue in this section of "blind pipe".

[0017] Finally, the central control unit, as the command center of the entire system, has an industrial-grade programmable logic controller (PLC) as its hardware body, equipped with a sufficient number of digital I / O modules, analog I / O modules and industrial Ethernet communication modules. Its software runs a control program based on a state machine model, which defines various working states of the system, such as "standby", "mixing", "circulation supply", "pulse maintenance", "cleaning" and "fault", and strictly stipulates the switching conditions and execution actions between states. The speed of all pumps, the opening and closing of valves, the readings of sensors, the data of weighing modules and the operating status of each subsystem are all centrally monitored, parameterized and data traced through the human-machine interface (HMI), realizing highly automated, intelligent and precise control of the entire process of polishing liquid supply.

[0018] The present invention offers the following benefits: By integrating multimodal pulse cycling, distributed online sensing, closed-loop chemical compensation, and fully automated process control, this system creates a centralized supply system capable of proactively maintaining the physical and chemical stability of complex colloidal suspensions. Rather than passively addressing the sedimentation and deterioration of polishing fluids, this system proactively, continuously, and precisely intervenes to fundamentally ensure that the polishing fluid delivered to each polishing station maintains high consistency and stability across key quality indicators such as abrasive concentration, particle size distribution, and pH, providing a solid process foundation for the production of high-quality, highly reliable silicon carbide substrates. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a block diagram of the overall structure of a system for centralized supply of silicon oxide polishing liquid for SiC substrates according to the present invention.

[0020] Figure 2 It is a structural schematic diagram of the connection relationship between the first stock solution storage and pretreatment unit and the second polishing liquid precision mixing unit in the present invention.

[0021] Figure 3 It is a structural schematic diagram of the third centralized transportation and terminal supply unit in the present invention.

[0022] Figure 4 Schematic diagram of the process of the closed-loop control method of chemical stability in the present invention.

[0023] The accompanying drawings are marked as follows: 10, first stock solution storage and pretreatment unit; 11, first stock solution storage tank; 111, stirring device; 12, second stock solution storage tank; 13, first stock solution delivery pump group; 131, first stock solution pump; 132, second stock solution pump; 14, first gas pipeline system; 15, first circulation pipeline; 151, first circulation control valve; 20, second polishing liquid precision mixing unit; 21, mixing tank; 22, weighing module; 23, multi-channel feeding Valve group; 24. Mixing and stirring device; 25. Mixing and conveying pump; 26. Built-in integrated sensor module; 30. Third centralized conveying and terminal supply unit; 31. Main circulation supply pipeline; 32. Terminal use point supply module; 33. Distributed online sensor network; 331. Online sensor node; 34. Active micro-dosing system; 341. Micro-dosing storage tank; 342. High-precision micro-metering pump; 35. Pipeline maintenance system; 40. Central control unit. DETAILED DESCRIPTION

[0024] In order to make the purpose, technical solutions and advantages of the present invention clearer and more complete, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, rather than to limit the scope of protection of the present invention. In the description of the present invention, it should be noted that the orientation or positional relationship indicated by the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. is based on the orientation or positional relationship shown in the accompanying drawings, and is only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore cannot be understood as a limitation on the present invention.

[0025] Reference Figures 1 to 4 The present invention discloses a system for centralized supply of silicon oxide polishing liquid for SiC substrates, which aims to achieve full-time and full-path active maintenance of the physical suspension stability and chemical environment constancy of the polishing liquid by constructing a precision fluid management architecture that integrates multi-modal cyclic disturbance, distributed online sensing and closed-loop feedback control. From a macroscopic perspective, the system consists of a first stock solution storage and pretreatment unit 10, a second polishing liquid precision mixing unit 20, a third centralized transportation and terminal supply unit 30, and a central control unit 40 that serves as the nerve center of the entire system. The central control unit 40 establishes a stable and high-speed data interaction and command control link with the aforementioned physical units through industrial Ethernet, hard-wired signals, etc., to ensure the precise coordination of the actions of various parts of the system and the orderly execution of programs.

[0026] Specifically, refer to Figure 2 In the structure shown, the first stock solution storage and pretreatment unit 10 is the source of the entire supply system. Its core function is to safely and stably receive, store, and perform preliminary treatment on the high-concentration silicon oxide polishing solution and pH adjuster solution to maintain their initial state. This unit comprises a first stock solution storage tank 11, a second stock solution storage tank 12, a first stock solution delivery pump assembly 13, a first gas pipeline system 14, and a first circulation pipeline 15.

[0027] The first stock solution tank 11 is dedicated to store high-concentration silica polishing solution stock solution as the core material. Considering the sensitivity of colloidal silica particles to metal ions in a specific chemical environment and the weak adsorption trend of the particles to the inner wall of the tank, the selection of the material and the structural design of the tank are crucial. The main structure adopts high-purity 316L stainless steel material to ensure sufficient mechanical strength and pressure-bearing capacity; and all the inner surfaces in contact with the stock solution are integrally lined with perfluoroalkoxy plastic (PFA) with a thickness of not less than 3 mm. PFA material has extremely low surface energy and extremely low chemical inertness, which can effectively prevent metal ion dissolution pollution and abrasive particle adhesion on the inner wall. In order to completely eliminate the static area of the fluid at the bottom of the tank, prevent the initial sedimentation of particles at this point, the bottom of the tank is designed to have a taper angle of not less than 15 degrees. The conical bottom can guide the fluid to naturally converge to the center, and a drain port is provided at the center of the conical bottom. In order to further reduce the possibility of particle adhesion, the PFA lining surface of the inner wall of the tank is also subjected to precise mechanical or chemical polishing treatment, so that the surface roughness Ra value is controlled at a level of not greater than 0.4 microns, thereby reducing the pits available for particle parking at the micro level. A magnetic force driven stirring device 111 is provided in the tank. The power source of the device, i.e. the external driving magnet, is installed outside the tank and drives the internal driven magnet and the stirring paddle connected thereto to rotate through non-contact magnetic field coupling. This magnetic force driven design completely eliminates the need for a stirring shaft penetrating through the tank and the corresponding dynamic seal structure of the traditional stirrer, thereby eliminating the risk of particle contamination caused by shaft seal wear. The rotational speed of the stirring device 111 is precisely controlled by the central control unit 40 through a 4-20 mA analog output signal, which can realize continuous stepless adjustment from 0 to 300 RPM, so as to apply gentle and effective stirring according to the storage time, viscosity and other characteristics of the stock solution, and maintain its uniform suspension.

[0028] The second stock solution tank 12 is provided side by side with the first stock solution tank 11, and its function is to store the pH adjuster stock solution for subsequent precise mixing. In a typical embodiment, the adjuster is sodium hydroxide (NaOH) solution or potassium hydroxide (KOH) solution. Considering that the adjuster solution is also sensitive to metal ion contamination, the second stock solution tank 12 adopts the same standards as the first stock solution tank 11 in terms of structure and material, i.e. 316L stainless steel tank body shell and PFA integral lining, also with a conical bottom and a high-finish inner wall. Since the pH adjuster is a true solution, there is no particle sedimentation problem, so the tank is not provided with a stirring device.

[0029] The first stock liquid delivery pump group 13 is the power core for realizing the precise delivery of stock liquid from the storage area to the mixing area. It is composed of two pumps, the first stock liquid pump 131 and the second stock liquid pump 132. The inlet of the first stock liquid pump 131 is connected to the bottom discharge port of the first stock liquid storage tank 11 through a clean pipeline, and its outlet is connected to the subsequent second polishing liquid precision mixing unit 20. Similarly, the inlet of the second stock liquid pump 132 is connected to the discharge port of the second stock liquid storage tank 12, and its outlet also leads to the second polishing liquid precision mixing unit 20. In order to ensure that no new pollution is introduced during the transportation process, both pumps use magnetically driven centrifugal pumps. Their working principle is similar to that of the aforementioned magnetic agitator. The impeller is driven to rotate by magnetic coupling, and there are no dynamic seals in the pump chamber. All its flow-through components that come into contact with the liquid, such as the pump head, impeller, etc., are made of high-purity PTFE or PFA materials, ensuring the chemical purity of the fluid during the transportation process.

[0030] The first gas piping system 14 provides a protective layer of inert gas for the top gas phase space of the first and second stock liquid storage tanks 11, 12. The system draws gas from a high-purity nitrogen source (whose purity is strictly required to be above 99.999% to minimize oxygen and moisture content). The system then passes through a precision pressure reducing valve to reduce the pressure to a stable operating pressure (e.g., 0.2 MPa). The nitrogen flow rate is then precisely controlled by a mass flow controller (MFC). The pipeline then bifurcates into two branches, each connected to the top gas phase inlet of the first and second stock liquid storage tanks 11, 12 via an independent electrically controlled pneumatic valve. During system operation, the central control unit 40 controls the continuous flow of a small amount of high-purity nitrogen into the two tanks, forming a positive pressure seal slightly above atmospheric pressure (e.g., 5-10 kPa) within their internal gas phase spaces. The core purpose of this design is to isolate the surrounding air, specifically to prevent carbon dioxide (CO2) in the air from dissolving into the alkaline silicon oxide polishing liquid and pH adjuster. CO2 dissolves in water to form carbonic acid, which reacts with alkaline substances in the polishing liquid, causing an uncontrollable drop in pH value, thereby seriously affecting the chemical stability of the polishing liquid and subsequent polishing performance.

[0031] In addition, a first circulation pipeline 15 is also creatively provided in the first stock solution storage and pretreatment unit 10. One end of the pipeline is led out from the main pipeline at the outlet of the first stock solution pump 131 through a three-way joint, and the other end is connected back to the top of the first stock solution storage tank 11. On this circulation loop, a first circulation control valve 151 controlled by the central control unit 40 is installed. The application scenario of this design is that when the system is in standby state, i.e. the second polishing solution precision mixing unit 20 does not request the supply of silicon oxide stock solution for a long time (e.g. more than 15 minutes), in order to prevent the stock solution in the pipeline between the first stock solution pump 131 and the outlet to the mixing unit valve from settling due to complete stillness, the central control unit 40 will automatically execute a local keep-alive program: it will instruct to open the first circulation control valve 151, and at the same time, let the first stock solution pump 131 run continuously at a lower speed (e.g. 10% of the rated speed). In this way, the stock solution will maintain low-speed flow in this local loop consisting of the pump, the outlet pipeline, the first circulation pipeline 15 and the storage tank 11, effectively preventing the problem of particle settlement in the dead zone of the pipeline.

[0032] Then, when the stock solution needs to be prepared into finished polishing solution that meets the process requirements, the process enters the second polishing solution precision mixing unit 20. Referring to Figure 2 , the function of this unit is to mix the silicon oxide stock solution from the first unit, the pH adjuster and the externally supplied ultrapure water (DI water) by high-precision gravimetric metering according to the process formula previously set in the central control unit 40, and to perform maturation treatment and online verification of key parameters after mixing. This unit mainly consists of a mixing tank 21, a weighing module 22, a multi-channel feed valve group 23, a mixing stirring device 24, a mixing delivery pump 25 and an integrated internal sensing module 26.

[0033] The mixing tank 21 is the main container for mixing operation. Its structure design, material selection and inner wall treatment all follow the same highest cleanliness standard as the first stock solution storage tank 11, i.e. PFA-lined 316L stainless steel structure, more than 15-degree conical bottom and Ra value not greater than 0.4 microns of inner wall surface roughness, to ensure the cleanliness of the mixing process and facilitate subsequent emptying and cleaning.

[0034] In order to achieve high-precision dosing of various components, the entire tank body of the mixing tank 21 is installed on a weighing module 22. The module is usually composed of three to four high-precision shear beam weighing sensors evenly distributed under the tank support legs. These sensors are designed to withstand the total weight of the tank body and the liquid. The output signals of all sensors are aggregated into a dedicated signal transmitter, which processes and digitizes the signals. The overall measurement accuracy that can be achieved is better than 0.05% of the full scale (for example, 3000kg). This means that for a 1000kg batch of ingredients, the weight measurement error can be controlled within 0.5kg. The transmitter transmits real-time, high-resolution weight data to the central control unit 40 through an industrial fieldbus protocol, such as a stable 4-20mA analog current signal or a higher-speed EtherNet / IP digital protocol, as the core basis for closed-loop control of the batching process.

[0035] A multi-channel feed valve assembly 23 is integrated at the top of the mixing tank 21. This valve assembly consists of three independently controlled pneumatic diaphragm valves. The inlets of these three valves are connected to the outlet pipeline of the first raw liquid pump 131, the outlet pipeline of the second raw liquid pump 132, and the external ultrapure water supply main line from the plant system. Their outlets are collectively connected to the top feed port of the mixing tank 21. Pneumatic diaphragm valves are selected because only the diaphragm and valve body are in contact with the fluid, with no other moving parts. The diaphragm can be made of PTFE, which ensures clean switching operation.

[0036] The tank is also equipped with a magnetically driven mixing and stirring device 24 with the same structure as that in the first raw liquid storage tank 11. The central control unit 40 controls its start and stop and the speed within the range of 0-300RPM. It is used to quickly and evenly mix the various liquids in the tank at the macro and micro levels during and after the addition of materials.

[0037] As an important technical feature of the present invention, a set of built-in integrated sensing modules 26 is also fixedly installed in the mixing tank 21. The module is carefully designed and installed in a specific depth position in the tank that can represent the state of the main fluid, usually in the lower middle part of the liquid surface and away from the center of the stirring vortex. The module integrates at least one high-precision composite pH electrode, a four-electrode conductivity sensor and a PT1000 or similar temperature sensor on an integrated probe bracket. Among them, the composite pH electrode has a built-in temperature compensation element, which can automatically correct the pH reading according to the real-time temperature. Its measurement range covers 0-14 and the resolution is as high as 0.01pH. Compared with the traditional two-electrode type, the four-electrode conductivity sensor has a wider range and better anti-pollution ability. It is used to assist in judging the total ion concentration in the mixed liquid and indirectly reflect the stability of the chemical components. The temperature sensor is used to accurately monitor the exothermic or endothermic effects during the mixing process and provide accurate temperature compensation values ​​for the measurement of pH and conductivity. The signals of these three sensors are converted into standard signals through dedicated transmitters and connected to the analog input module of the central control unit 40, thereby realizing real-time, in-situ and continuous monitoring of key chemical parameters of the mixed liquid.

[0038] The mixed polishing liquid is sent to the next unit through the mixing and delivery pump 25. Considering that the silicon oxide polishing liquid is a colloidal suspension, the three-dimensional network structure formed by the weak interaction between its particles is more sensitive to shear force. Excessive shear force may destroy its colloidal stability and cause particle agglomeration. Therefore, the mixing and delivery pump 25 specifically uses a low-shear volumetric pump, such as a peristaltic pump or a double-diaphragm pneumatic pump. The peristaltic pump transports fluid by alternating squeezing of the hose, without valves throughout the process and with extremely low shear force; the double-diaphragm pump transports fluid volumetrically by driving the diaphragm to move back and forth through air pressure, and also has less disturbance to the fluid. The inlet of the pump is connected to the bottom drain port of the mixing tank 21, and its outlet serves as the total outlet of the entire system, connected to the main circulation pipeline of the third centralized delivery and terminal supply unit 30.

[0039] As a preferred embodiment of the present invention, the entire operating logic of the second polishing liquid precision mixing unit 20 is strictly automatically executed by the central control unit 40 according to a preset program, eliminating the arbitrariness and errors of manual operation. A typical fully automatic mixing process is as follows: First, the central control unit 40 checks whether the mixing tank 21 is empty (judged by the weighing module 22 reading being zero or the tare value). After confirmation, the central control unit 40 instructs to open the valve connected to the ultrapure water pipeline in the multi-channel feed valve group 23 and start injecting ultrapure water. The central control unit 40 monitors the reading of the weighing module 22 in real time. When the weight of the injected ultrapure water reaches the preset target value (for example, 500.0 kg), it immediately instructs to close the valve. Secondly, the central control unit 40 instructs to open the valve connected to the first stock liquid pump 131, and starts the first stock liquid pump 131 to start injecting high-concentration silicon oxide stock solution. During this process, the mixing and stirring device 24 is started at the same time and stirred at a medium speed (for example, 150 RPM) to promote the initial dispersion of the stock solution and water. When the increment displayed by the weighing module 22 reaches the preset weight of the stock solution (for example, 500.0 kg, to prepare a polishing liquid with half the solid content), the valve is closed and the first stock solution pump 131 is stopped. Once again, the most critical pH value precision adjustment stage is entered. Under continuous stirring, the central control unit 40 instructs to open the valve connected to the second stock solution pump 132, and drips the pH regulator in batches and pulses at an extremely low flow rate (achieved by controlling the start and stop frequency or speed of the pump). At the same time, the central control unit 40 collects the pH readings of the built-in integrated sensor module 26 at a high frequency (for example, 10 times per second). After each dripping of the regulator, the dripping will be paused for a short period of time (for example, 10 seconds), and the stable pH value will be read after stirring evenly. This "drip-wait-read" cycle will continue until the pH value stabilizes at the center value of the process setting window (for example, the target value is 10.50). Finally, all feed valves are closed and the maturation stage is entered. The mixing and stirring device 24 continues to stir at a relatively low speed (e.g. 60RPM) for a preset aging time (e.g. 30 minutes) to ensure that all chemical components react fully and the system reaches equilibrium. During this period, the central control unit 40 continuously records pH, conductivity and temperature data. In the last 10 minutes of the aging process, if the central control unit 40 analyzes that the fluctuation of the pH value is less than a preset threshold (e.g. ±0.02), the drift rate of the conductivity is less than a specific value, and the temperature is stable, the system determines that the batch of polishing liquid is mixed and qualified, and the status of the mixing tank 21 is switched to "ready for delivery". On the contrary, if any parameter continues to fluctuate significantly within the specified time, the system will determine that the mixing has failed, immediately issue an alarm on the human-machine interface (HMI), lock the batch of liquid, and prompt the process engineer to perform manual inspection and intervention.

[0040] Next, the process enters the third centralized transport and terminal supply unit 30 that realizes the core innovative value of the present invention.Figure 3 This unit constructs a closed, dynamically managed delivery network from the mixing tank to all polishing machines. Its core design focuses on maintaining the physical and chemical stability of the polishing fluid throughout the entire delivery path through a variety of active interventions. The unit includes a main circulation supply pipeline 31 that runs throughout the entire system, multiple point-of-use (POU) supply modules 32 located along the route, a strategically deployed distributed online sensor network 33, an active micro-dosing system for fine-grained control 34, and a pipeline maintenance system 35 for routine maintenance.

[0041] The main circulation supply line 31 is the artery of the entire delivery system. It forms a physically closed loop. The starting point of the line is connected to the outlet of the mixing and delivery pump 25 of the second unit. Then, starting from the functional area where the supply system is located, the line follows the optimal path planning, encircling all areas in the clean room where the chemical mechanical polishing machines that need to use the polishing liquid are located. Finally, the end of the line returns and connects to the return port at the top of the mixing tank 21, thus forming a complete fluid circuit that can circulate globally. To eliminate particulate contamination at the source, the entire line uses PFA pipes with specially treated inner walls to achieve a mirror effect. All connection points between the pipes do not use traditional ferrule joints, but instead use more advanced hot-melt welding technology or flare joints. Hot-melt welding heats and melts the end faces of two sections of PFA pipe, then butts them together, forming a seamless, step-free whole after cooling. Flare joints use a special tool to turn the pipe ends outward to form a sealing surface, and the connection is also smooth. These connection methods minimize the potential for particle loss or fluid disturbances due to joint gaps, steps, or material mismatches.

[0042] Along the main circulation supply line 31, multiple terminal point supply modules 32 are arranged according to the layout of the polishing machines, each of which precisely corresponds to a chemical mechanical polisher. The structure of each supply module 32 includes: a liquid collection point connected to the main circulation supply line 31 through a specially designed low dead volume three-way sampling valve, a branch pipe connecting the sampling valve to the daily buffer tank (or TK barrel) of the corresponding polishing machine, a supply control valve (usually a pneumatic diaphragm valve) that accurately controls the supply of liquid to the branch, and an online flow meter for measuring the current supply volume. When a polishing machine needs to be replenished with polishing liquid, it will send a request signal to the central control unit 40, which will then open the supply control valve corresponding to the machine, and the polishing liquid will be diverted from the main circulation line to the buffer tank of the machine. The flow meter measures the flow in real time. When the set amount is reached, the valve closes, completing the supply.

[0043] A key innovation of the present invention lies in the active management of the fluid state in the main circulation supply pipeline 31. During the operation of the entire system, regardless of whether there is a terminal requesting liquid supply, the mixing and delivery pump 25 always runs continuously at a basic flow rate (for example, 10% to 20% of its rated flow rate, the specific value is calculated based on the total length of the pipeline, the diameter of the pipeline and the viscosity of the polishing liquid to ensure that the flow rate in the pipe is always in the laminar flow or transition flow zone, for example, the Reynolds number is maintained between 1800-2100). This makes the polishing liquid in the entire main circulation supply pipeline 31 always in a low-speed, uninterrupted circulating flow state. This design fundamentally eliminates the problem of severe sedimentation and agglomeration of abrasive particles under the action of gravity due to long-term stagnation of the polishing liquid in the pipeline in the traditional "supply on demand" mode, and preliminarily ensures the macroscopic uniformity of the fluid.

[0044] However, relying solely on constant low-speed flow, its ability to remove weak particle attachment and initial sedimentation that may occur at locations such as the bottom of the pipeline or elbows is limited. To this end, the present invention further provides a more precise and efficient physical stability maintenance mechanism, namely a periodic pulse disturbance control method, which is automatically triggered and executed by the central control unit 40 under specific conditions. Specifically, the central control unit 40 will continuously monitor the status of all terminal use point supply modules 32. When it detects that the system has entered global standby mode, that is, all polishing machines have not issued a liquid supply request within a preset period of time (for example, 5 minutes), it will determine that the entire system is in a low-energy idle state, and this is the best time to perform a strong disturbance. The central control unit 40 will automatically switch the operating mode of the mixing and delivery pump 25. At this time, on top of the original basic low-speed cycle, the central control unit 40 will perform periodic, high-frequency pulse speed modulation on the driver of the mixing and delivery pump 25 through its high-speed analog output module or pulse width modulation (PWM) signal output module. For example, the central control unit 40 can be programmed with a 60-second pulse program: within the first 5 seconds of each cycle, a ramp function is used to rapidly increase the pump flow rate from the base flow rate (e.g., 20 L / min) to 80% of the rated flow rate (e.g., 160 L / min), and this high flow rate is maintained for 5 seconds. This instantaneous high flow rate generates a traveling, high-energy pressure wave and fluid shear wave throughout the closed piping system. The generated turbulent energy is sufficient to flush out any particle clusters that have begun to weakly adhere to the pipe walls or settle at the bottom of the pipe, and resuspend them evenly in the main fluid. Subsequently, over the remaining 55 seconds of the cycle, the pump flow rate is gradually restored to the base circulation flow rate. This periodic high-energy fluid pulse is far more effective in resuspending settled particles than simply increasing the constant flow rate (which would result in significant energy consumption and continuous wear on the pump), and the increase in overall energy consumption is very limited. A series of key parameters such as pulse trigger conditions, basic flow, pulse amplitude (peak flow), pulse width (high flow duration) and pulse period can be flexibly configured and optimized by process engineers on the human-machine interface (HMI) of the central control unit 40 based on factors such as the specific batch characteristics of the polishing liquid used (such as particle density, viscosity), the total length and complexity of the pipeline system, etc.

[0045] Another key innovation of the present invention lies in its full-path, closed-loop active control mechanism for the chemical stability of the polishing liquid, which is mainly achieved through the coordinated operation of a distributed online sensor network 33 and an active micro-dosing system 34. The distributed online sensor network 33 is composed of multiple online sensor nodes 331. These sensor nodes are strategically installed at several key locations in the main circulation supply pipeline 31 to obtain a panoramic view of the chemical parameters in the entire pipeline system. Typical installation locations include: not far from the outlet of the mixing and delivery pump 25 (representing the "freshest" polishing liquid state), the point at the farthest physical distance of the entire loop (representing the "end" state where the greatest chemical changes may occur), and the return pipe section before the loop returns to the mixing tank 21 (representing the "comprehensive" state after completing a cycle). The hardware structure of each online sensor node 331 is exactly the same as the built-in integrated sensor module 26 in the mixing tank 21, that is, it integrates a high-precision composite pH electrode and a four-electrode conductivity sensor. The real-time data collected by these sensors throughout the pipeline network are continuously transmitted to the central control unit 40, providing a basis for it to make accurate chemical status judgments and decisions.

[0046] Accompanying it is an active micro-dosing system 34. The system includes a small-volume micro-dosing storage tank 341 for storing a precisely diluted pH regulator (for example, a dilute solution after the original solution is diluted 100 times); a high-precision micro-metering pump 342 that can achieve nanoliter-level discharge accuracy, such as a micro-pump based on the piezoelectric ceramic drive principle; and a dosing injection point that connects the pump outlet to the main circulation supply pipeline 31. The injection point is cleverly set after the outlet of the mixing and delivery pump 25 and before the first online sensor node 331. This design ensures that the injected micro-regulator can be immediately preliminarily mixed by the fluid disturbance at the pump outlet and quickly detected by the first downstream sensor, forming a fast-response control loop.

[0047] The workflow of this chemical stability closed-loop control system is as follows: Figure 4As shown, the system demonstrates a high degree of intelligence. The central control unit 40 continuously and in parallel collects pH data from all nodes in the distributed online sensor network 33. It runs an averaging algorithm internally, calculating a real-time, dynamic, and representative average pH value for the entire circulation system based on the location and representativeness of each node in the pipeline. This average pH value is then continuously compared with the target pH value (e.g., 10.50) and the upper and lower control limits (e.g., ±0.05) specified in the process recipe. When the central control unit 40 detects that the calculated average pH value is slowly decreasing due to factors such as CO2 absorption and reaches the lower control limit (e.g., 10.45), it automatically activates an internal PID (proportional-integral-derivative) control algorithm. The input to this PID algorithm is the error between the current pH value and the target pH value, and its output is a precisely calculated control signal that directly controls the start-up time and pumping frequency of the high-precision micro-metering pump 342. For example, the algorithm might calculate that 50 microliters of regulator are needed to adjust the pH back to 0.01. The central control unit 40 then precisely drives the micro pump 342 to complete this pulsed injection of a very small dose. The newly injected regulator, along with the continued flow of the main circulation pipeline, can be quickly and evenly dispersed throughout the thousands of liters system within a few minutes. Thanks to the use of distributed sensing, the system can capture subtle differences throughout the pipeline; thanks to the use of high-precision micro-dosing and PID closed-loop feedback, the system can compensate for small, slow pH drifts caused by various unavoidable factors in real time, accurately, and smoothly, avoiding the drastic pH fluctuations and overshoots caused by traditional manual large-scale additions to the main tank, ensuring that the pH value of the polishing liquid at any time and anywhere in the pipeline is "locked" and strictly maintained within an extremely narrow process window.

[0048] In addition, in order to ensure the long-term stable operation of the system and the cleanliness when changing polishing fluids with different formulas, the system also integrates a complete pipeline maintenance system 35. Physically, the system is manifested as a network of ultrapure water (DIW) pipelines and high-purity nitrogen (N2) pipelines connected to the main circulation supply pipeline 31, the branch pipelines of each terminal supply module 32, and all functional units (such as storage tanks and mixing tanks), as well as the corresponding control valves. In terms of software, it is manifested as a series of automated cleaning and purging programs built into the central control unit 40. For example, before planning to change to a polishing fluid with a different solid content or pH value, the operator only needs to select and start the "full system automatic cleaning" program on the HMI. This program automatically controls the opening and closing of relevant valves in a strict, pre-set logical sequence. First, high-pressure, high-purity nitrogen is used to purge any remaining polishing liquid from the main circulation pipeline 31 and each branch pipeline back into the mixing tank 21 or a designated waste liquid collection tank. Ultrapure water is then injected and the mixing pump 25 performs multiple high-speed, pulsed flushes to thoroughly remove any residue from the pipe walls. Finally, all pipes are thoroughly dried again with high-purity nitrogen filtered through a 0.003-micron filter to prevent residual moisture from diluting the subsequent polishing liquid or causing crystallization within the pipes. For each terminal point supply module 32, the branch pipeline from the main circulation pipeline to the polishing machine is a "blind leg" when not supplying liquid, making it prone to sedimentation. Therefore, the central control unit 40 has designed a separate maintenance procedure for this branch pipeline. After each branch pipeline completes its supply mission to the machine, the system automatically performs a brief nitrogen backflush to flush the liquid in this blind leg back into the main circulation pipeline, ensuring that no liquid remains stagnant in this section of the pipeline for an extended period.

[0049] Finally, as the command center of the whole system, the hardware body of the central control unit 40 is selected as a powerful and reliable industrial programmable logic controller (PLC), such as Siemens S7-1500 series or Rockwell ControlLogix series. It is equipped with a sufficient number of digital input / output (DI / DO) modules for controlling valves, pumps and other on-off devices; high-speed analog input / output (AI / AO) modules for reading sensor signals and controlling pump speed; and communication modules supporting industrial Ethernet (such as PROFINET or EtherNet / IP) for high-speed data exchange with weighing modules, HMI, and upper-layer manufacturing execution system (MES). Its software core is a control program designed based on a rigorous state machine model. The program clearly defines the complex operation logic of the entire supply system as a number of mutually exclusive and explicit working states, such as "system standby", "raw liquid pretreatment", "automatic mixing", "constant flow circulation supply", "pulse disturbance maintenance", "automatic cleaning", "system failure", etc. It also strictly specifies the trigger conditions that must be met for switching between states, as well as a series of precise actions to be performed after entering each state. All system operating parameters (such as formula, flow rate, pressure, temperature, pH target value), real-time state (such as pump speed, valve position, sensor readings), historical data curves, and alarm records are visualized, monitored, parameterized, and data-traced through a large-size touch screen human-machine interface (HMI), thereby achieving full-process, highly automated, intelligent, and precise closed-loop control of the silicon oxide polishing liquid from raw liquid entering the factory to terminal use.

[0050] Embodiment

[0051] To verify the actual effect of the technical solutions described in the present application, a complete "system for centralized supply of silicon oxide polishing liquid for SiC substrates" was built and a 72-hour continuous simulation production test was conducted.

[0052] The test conditions are set as follows:

[0053] 1. Polishing liquid: a commercial colloidal silicon oxide polishing liquid raw liquid with nominal parameters of 50wt% solid content, 70nm original particle size (D50), and pH value of 9.5.

[0054] 2. Process target: to prepare a finished polishing liquid with a solid content of 25wt% and a pH value of 10.80±0.05 for use in 10 SiC chemical mechanical polishing machines.

[0055] 3. System parameters: The total length of the main circulation supply pipeline 31 is 200 meters, and the inner diameter of the pipeline is DN40 (PFA material). The single liquid dispensing volume of the mixing tank 21 is 1000 kg. The basic circulation flow rate is set to 40 L / min. The pulse disturbance maintenance mode parameters are set as follows: global standby exceeds 5 minutes, the pulse period is 60 seconds, the pulse width is 4 seconds, and the pulse peak flow rate is 200 L / min. The chemical stability closed-loop control PID parameters are set as follows: proportional coefficient Kp = 0.7, integral coefficient Ki = 0.15, differential coefficient Kd = 0.03; the pH control lower limit is 10.75.

[0056] 4. Monitoring point: At the sampling port of the terminal use point supply module 32 at the farthest end of the main circulation supply pipeline (about 100 meters away from the mixing and delivery pump 25), samples are taken every hour, and the median particle size (D50) and the number of large particles (LPC) larger than 500 nm are detected using a laser particle size analyzer. At the same time, the real-time pH reading of the online sensor node 331 at this location is recorded.

[0057] Operational Process: The system first executed an automated mixing procedure, precisely adding 500.0 kg of ultrapure water and 500.0 kg of stock solution. The pH was then precisely adjusted to 10.80 by adding a 1 M dilute KOH solution. After 30 minutes of aging, the system determined the solution was qualified and began supplying the solution to the main circulation supply line 31, initiating continuous circulation. During the 72-hour operation, random terminal supply requests were simulated.

[0058] Comparative Example

[0059] For comparison, a traditional centralized liquid supply system was used. This system consists of a main storage tank with agitation, connected to 10 polishing machines via a pump and a loop pipeline. However, this system lacks the following features: 1) continuous low-speed circulation, with the pump only energized when a terminal requests liquid supply; 2) pulse perturbation capability; and 3) distributed online pH sensing and closed-loop micro-dosing. pH adjustment relies solely on manual addition of KOH solution by operators sampling the main storage tank every four hours.

[0060] The same polishing liquid, process target and monitoring method as in the embodiment were used and the same 72-hour operation test was carried out.

[0061] Test results and data comparison

[0062] After 72 hours of continuous operation, the key performance indicators of the embodiments and comparative examples were statistically analyzed and the results are summarized in the following table:

[0063]

[0064]

[0065] The data comparison in the table above clearly demonstrates that the proposed "centralized supply system for silicon oxide polishing slurry for SiC substrates" successfully minimizes fluctuations in the median particle size (D50) of the polishing slurry at the farthest end (standard deviation 0.6nm vs. 4.5nm) through its unique multimodal pulse perturbation design to maintain physical stability. It also suppresses the number of large particles (LPCs), which are highly susceptible to scratch defects during the process, to an extremely low level (12 particles / mL vs. 185 particles / mL). More importantly, its innovative distributed sensing and closed-loop micro-dosing system achieves unparalleled precision in-line pH control, with a standard deviation of only 0.018 at the farthest end, compared to 0.42 and a wide range of fluctuations in conventional systems. This high degree of physical and chemical stability directly translates into significantly improved process results: the number of scratch defects on simulated wafers was reduced by nearly an order of magnitude, and the consistency (relative standard deviation) of polishing removal rate was significantly improved from 6.8% to 1.2%.

[0066] In summary, the embodiments of the present invention fully demonstrate that this system can effectively overcome the challenges of polishing liquid sedimentation and chemical drift in the prior art, fundamentally ensuring that the polishing liquid delivered to each process terminal has unprecedented consistency and stability in key quality indicators, providing a solid and reliable process guarantee for large-scale, high-quality, and high-reliability semiconductor substrate manufacturing. Those skilled in the art will understand that the above embodiments are merely illustrative and that various modifications and variations are possible without departing from the spirit and scope of the present invention.

Claims

1. A system for centralized supply of silicon oxide polishing liquid for SiC substrates, characterized in that: The system comprises: A first stock solution storage and pretreatment unit (10) is configured to receive, store and preliminarily treat a high-concentration silicon oxide polishing liquid stock solution and a pH regulator stock solution; a second polishing liquid precision mixing unit (20), which is in fluid communication with the first stock solution storage and pretreatment unit (10) and is configured to precisely mix and mature the stock solution with ultrapure water according to a preset process formula to prepare a finished polishing liquid; The third centralized transport and terminal supply unit (30) is in fluid communication with the second polishing liquid precision mixing unit (20) and is configured to circulate and transport the finished polishing liquid to one or more terminal use points. The third unit comprises a closed main circulation supply pipeline (31), a distributed online sensor network (33) arranged along the pipeline, an active micro-dosing system (34), and a central control unit (40). The central control unit (40) performs data exchange and command control with the first stock solution storage and pretreatment unit (10), the second polishing liquid precision mixing unit (20) and the third centralized transport and terminal supply unit (30). The configuration is as follows: a) when the system is in standby mode, periodically pulse-modulating a pump for circulating the polishing liquid to generate fluid pulses in the main circulation supply line (31) to maintain the physical stability of the polishing liquid; as well as b) Based on the feedback from the distributed online sensor network (33), the chemical parameters of the polishing liquid are closed-loop regulated by the active micro-dosing system (34) to maintain its chemical stability.

2. The system according to claim 1, wherein: The first stock solution storage and pretreatment unit (10) comprises: A first stock solution storage tank (11) is used to store the high-concentration silicon oxide polishing liquid stock solution, and a stirring device (111) is provided inside the first stock solution storage tank (11); A second stock solution storage tank (12) is used to store the pH adjuster stock solution; a first stock liquid delivery pump group (13), comprising a first stock liquid pump (131) and a second stock liquid pump (132) respectively connected to the discharge ports of the first stock liquid storage tank (11) and the second stock liquid storage tank (12), for delivering the stock liquid to the second polishing liquid precision mixing unit (20); a first gas pipeline system (14) for delivering high-purity nitrogen to the headspace of the first raw liquid storage tank (11) and the second raw liquid storage tank (12) to form a positive pressure gas seal to prevent carbon dioxide in the ambient air from dissolving into the headspace; and A first circulation pipeline (15) has one end connected to the outlet pipeline of the first raw liquid pump (131) and the other end connected back to the top of the first raw liquid storage tank (11). A first circulation control valve (151) is provided on the loop for forming a local circulation by opening the first circulation control valve (151) when the supply of the first raw liquid pump (131) to the subsequent unit is suspended, so as to maintain the flow state of the raw liquid in this section of the pipeline.

3. The system according to claim 2, characterized in that The tank structure of the first raw liquid storage tank (11) is made of 316L stainless steel lined with perfluoroalkoxy plastic, and its bottom is designed as a cone-shaped structure to eliminate the fluid dead zone, and the inner wall of the tank is electrolytically polished, and the surface roughness Ra value is not greater than 0.4 microns; the stirring device (111) is a magnetically driven stirring device, including an external driving magnet and an internal driven magnet and stirring blades encapsulated in a polytetrafluoroethylene shell, and the rotation speed of the stirring device (111) is steplessly adjusted by the central control unit (40).

4. The system according to claim 1, wherein: The second polishing liquid precision mixing unit (20) comprises: A mixing tank (21) for containing and mixing the component liquids; a weighing module (22), disposed at the bottom of the mixing tank (21), for measuring the total weight of the liquid in the mixing tank (21) in real time and transmitting the weight data to the central control unit (40); A multi-channel feed valve group (23) is integrated on the top of the mixing tank (21), comprising a plurality of feed valves respectively connected to the first raw liquid delivery pump group (13) and an external ultrapure water supply pipeline, wherein the central control unit (40) controls the opening and closing of the feed valves according to the real-time feedback of the weighing module (22), thereby achieving high-precision mixing of each component by weight measurement; A mixing and stirring device (24) is provided in the mixing tank (21) for mixing liquids; A built-in integrated sensing module (26) is fixedly installed in the mixing tank (21), the module integrating a composite pH electrode, a conductivity sensor and a temperature sensor for real-time monitoring of key chemical parameters of the mixed liquid; and The mixing and delivery pump (25) is a low shear force positive displacement pump, the inlet of which is connected to the discharge port of the mixing tank (21), and the outlet of which is connected to the third centralized delivery and terminal supply unit (30).

5. The system according to claim 4, characterized in that The central control unit (40) is configured to execute a preset mixing process based on feedback from the weighing module (22) and the built-in integrated sensor module (26), the process comprising the following steps: Instructing to open the feed valve corresponding to the ultrapure water and injecting a preset weight of ultrapure water according to the reading of the weighing module (22); Instructing to open the feed valve corresponding to the silicon oxide stock solution, injecting a preset weight of the silicon oxide stock solution according to the reading of the weighing module (22), and starting the mixing and stirring device (24); Under continuous stirring, the feed valve corresponding to the pH regulator is opened, and the pH regulator is added dropwise in batches at a small flow rate, while the pH reading of the built-in integrated sensor module (26) is monitored in real time until the pH value is stabilized within the process setting window; and Close all feed valves, continue stirring for the preset aging time, and continuously record chemical parameters. If the fluctuation of the parameters within the specified time is less than the preset threshold, the batch of polishing liquid is judged to be mixed qualified.

6. The system according to claim 1, wherein: The third centralized transportation and terminal supply unit (30) comprises: a main circulation supply pipeline (31), which forms a closed loop, with a starting point connected to the outlet of the mixing and delivery pump (25) of the second polishing liquid precision mixing unit (20) and an end point returning to the top of the mixing tank (21) of the second polishing liquid precision mixing unit (20); and A plurality of terminal point-of-use supply modules (32) are arranged along the main circulation supply pipeline (31), each module corresponding to a chemical mechanical polishing machine; The central control unit (40) is configured to control the mixing and delivery pump (25) to maintain a continuous low-speed circulation flow of the polishing liquid in the main circulation supply pipeline (31) at a basic flow rate during system operation, regardless of whether the terminal use point supply module (32) requests liquid supply, so as to eliminate the long-term static state of the polishing liquid in the pipeline.

7. The system according to claim 6, characterized in that The central control unit (40) is further configured to execute a periodic pulse disturbance control method for active maintenance of physical stability; The central control unit (40) monitors the status of all terminal point-of-use supply modules (32). When it is determined that the system enters a global standby mode, it automatically performs periodic pulse modulation on the operation of the mixing and delivery pump (25) above the basic flow rate to generate a high-flow rate fluid pulse in the main circulation supply pipeline (31). The energy of the fluid pulse is sufficient to re-suspend any particles that have begun to weakly adhere or settle. The frequency, amplitude and duty cycle parameters of the pulse modulation can be configured on the human-machine interface of the central control unit (40).

8. The system according to claim 6, wherein: In order to realize closed-loop active regulation of chemical stability, the third centralized transportation and terminal supply unit (30) further comprises: a distributed online sensing network (33) consisting of a plurality of online sensing nodes (331), the online sensing nodes (331) being strategically installed at key locations of the main circulation supply pipeline (31), including locations after the outlet of the mixing and delivery pump (25), at the farthest end of the loop, and before the loop returns to the mixing tank (21), each sensing node being integrated with a composite pH electrode and a conductivity sensor for collecting real-time chemical parameters at various points in the pipeline; and An active micro-dosing system (34) includes a micro-dosing storage tank (341) for storing a diluted pH regulator, and a high-precision micro-metering pump (342) connected to the main circulation supply pipeline (31). The dosing injection point of the high-precision micro-metering pump (342) is set after the outlet of the mixing and delivery pump (25) and before the first online sensing node (331).

9. The system according to claim 8, characterized in that The central control unit (40) is configured to execute a chemical stability closed-loop control workflow, the workflow comprising: Continuously collecting and analyzing pH value data from all distributed online sensor nodes of the distributed online sensor network (33), and calculating an average pH value in the entire circulation pipeline system through an averaging algorithm; comparing the average pH value to a target pH value set by the process; and When the average pH value is lower than the set control lower limit, a PID control algorithm is started. The output of the algorithm accurately controls the opening time and frequency of the high-precision micro-metering pump (342), and a very small amount of pH regulator is pulsed into the main circulation supply pipeline (31) to compensate for the drift of the pH value in real time and accurately.

10. The system according to claim 1, wherein: The system further comprises a pipeline maintenance system (35), wherein the pipeline maintenance system (35) comprises an ultrapure water pipeline and a high-purity nitrogen pipeline connected to the main circulation supply pipeline (31), branch pipelines of each terminal point supply module (32), and all functional units; The central control unit (40) is equipped with an automatic cleaning and purging program, which controls the relevant valves in a preset sequence to realize the automated maintenance operation of using high-purity nitrogen to purge the polishing liquid remaining in the pipeline, injecting ultrapure water for multiple pulse flushing, and finally using high-purity nitrogen to completely dry the pipeline; After the branch pipeline of each terminal point supply module (32) completes one supply, the central control unit (40) automatically performs a nitrogen purge procedure to ensure that no liquid remains in the blind pipe.

Images