Preparation method of high-purity hafnium tetrachloride

Abstract

The application belongs to the technical field of inorganic chemical industry, and discloses a preparation method of high-purity hafnium tetrachloride, which comprises the following steps: vacuum degassing pretreatment of mixed hafnium dioxide and high-purity carbon source; continuously feeding the pretreated material into a horizontal rotary chlorination reactor, and reacting with chlorine at 950 DEG C to 1050 DEG C to generate a crude product mixture; filtering the crude product mixture through a high-temperature ceramic filter, removing iron and aluminum impurities through a chemical interception reaction column, and separating zirconium and hafnium through a multi-stage gradient sublimation rectification system, wherein the sublimation rectification system is integrated with a dynamic mass transfer separation control system, and the operation conditions are dynamically adjusted through a mass transfer-heat coupling model based on real-time collected process parameters; and finally collecting and packaging under a fully-closed condition. The obtained hafnium tetrachloride is a high-purity rare metal compound, and can realize deep removal of zirconium impurities and process self-adaptive optimization.

Description

Technical Field

[0001] This invention belongs to the field of inorganic chemical technology, specifically relating to a method for preparing high-purity hafnium tetrachloride. Background Technology

[0002] As integrated circuit manufacturing processes continue to advance towards sub-10 nanometer and even more advanced process nodes, the research and application of high-dielectric-constant gate oxide stack materials in the semiconductor industry has become a core driving force for technological evolution. Hafnium tetrachloride, as a key precursor for preparing hafnium dioxide thin films in atomic layer deposition (ALD) processes, directly determines the electrical performance, leakage current control, and long-term reliability of the final semiconductor device in terms of purity. In modern semiconductor manufacturing systems, hafnium tetrachloride not only requires strict control over the content of common transition metals and main group elements such as iron, aluminum, and titanium, but also, because hafnium and zirconium belong to Group IVB in the periodic table and have extremely similar chemical properties, atomic radii, and ionic radii, deep removal of zirconium tetrachloride has become a core indicator for evaluating the level of high-purity hafnium tetrachloride preparation technology.

[0003] In existing technologies, the preparation of high-purity hafnium tetrachloride typically faces the following technical bottlenecks: Gaseous impurities generated during the chlorination reaction (such as ferric chloride and aluminum chloride) are difficult to completely remove through physical sedimentation and are prone to secondary volatilization and contamination of products in subsequent processes. Hafnium tetrachloride and zirconium tetrachloride have very small differences in saturated vapor pressure, and traditional single-stage condensation or intermittent sublimation processes have low separation efficiency and small throughput, making it difficult to achieve continuous production. The entire process is not sufficiently sealed, and materials are prone to contact with trace amounts of oxygen and moisture in the environment during transfer and packaging, leading to the formation of hydrolysis products and affecting the quality of thin film deposition. Fourth, batch fluctuations in raw materials have a significant impact on the stability of the final product quality, and existing processes lack adaptive adjustment capabilities. Summary of the Invention

[0004] The purpose of this invention is to provide a method for preparing high-purity hafnium tetrachloride, which solves the technical problems in existing high-purity hafnium tetrachloride preparation methods, such as difficulty in deeply removing impurities, low zirconium-hafnium separation efficiency, insufficient process sealing, and poor adaptability to raw material fluctuations, resulting in unsatisfactory product purity and stability.

[0005] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is as follows: This invention provides a method for preparing high-purity hafnium tetrachloride, characterized by comprising the following steps: Step 1: Pretreatment and activation of the reaction raw materials. Hafnium dioxide powder and a high-purity carbon source are physically mixed at a mass ratio of 1:0.25 to 1:0.35, wherein the purity of hafnium dioxide is not less than 99.9% and the median particle size D50 is 5 μm to 10 μm; the high-purity carbon source is high-purity graphite powder or acetylene black, with a fixed carbon content greater than 99.99% and a median particle size D50 of 2 μm to 5 μm. The mixed material is placed in a vacuum drying oven and degassed for 4 to 8 hours under conditions of absolute pressure below 10 Pa and temperature of 250 ℃ to 350 ℃ to remove physically adsorbed water and surface hydroxyl groups, obtaining the pretreated material.

[0006] Step Two: Dynamic Rotary Chlorination Reaction. The pretreated material from Step One is continuously and quantitatively fed into a horizontal rotary chlorination reactor. The inner wall of the horizontal rotary chlorination reactor is equipped with lifting plates. A variable frequency motor drives the reactor to rotate at 5 rpm to 15 rpm, causing the material to fall in a uniform waterfall-like manner under the action of the lifting plates, thereby increasing the solid-gas contact area. A mixed gas consisting of chlorine and a high-purity inert carrier gas, selected from argon or helium, is introduced into the reactor. The high-purity inert carrier gas has a purity of not less than 99.9999% and a moisture content of less than 0.1 ppmv (volume fraction). The volume fraction of chlorine in the mixed gas is controlled at 60% to 80%, and the gas phase empty tower velocity is controlled at 0.05 m / s to 0.15 m / s. The internal temperature of the reactor is controlled at 950 ℃ to 1050 ℃, and the absolute pressure is controlled at 0.12 MPa to 0.15 MPa. Hafnium dioxide undergoes a chlorination reaction to produce a crude product mixture containing hafnium tetrachloride vapor, zirconium tetrachloride vapor, ferric chloride vapor, aluminum trichloride vapor, residual chlorine, and carbon monoxide.

[0007] The transition section between step two and step three: A high-temperature gas cooling section is set between the outlet of the horizontal rotary chlorination reactor and the inlet of the high-temperature ceramic filter unit. The high-temperature gas cooling section adopts a jacketed water-cooling structure with a cooling water flow rate of 0.5 m³ / h to 1.5 m³ / h, which uniformly reduces the temperature of the crude product mixed gas from 950 ℃ to 1050 ℃ to 450 ℃ to 550 ℃, and the cooling rate is controlled at 30 ℃ / min to 50 ℃ / min.

[0008] Step 3: High-Temperature Gas-Solid Separation and Dust Retention. The cooled crude product mixture is introduced into a high-temperature ceramic filter unit. This unit uses a silicon carbide or alumina ceramic membrane filter element with a pore size of 0.5 μm to 2.0 μm. The operating temperature of the filter unit is controlled between 450 ℃ and 550 ℃ to remove unreacted raw material powder, carbon powder, and non-volatile metal oxide particles entrained in the mixture through physical interception. The high-temperature ceramic filter unit has an online pulse backflushing function. The backflushing gas is a high-purity inert gas preheated to above 500 ℃, and the backflushing pressure is 0.3 MPa to 0.5 MPa. The backflushing operation is triggered when the pressure difference across the high-temperature ceramic filter unit reaches 5 kPa.

[0009] Step 4: Chemical Vapor Retention and Deep Iron and Aluminum Removal. The filtered mixed gas enters a chemical retention reaction column, which is filled with a supported composite reagent. This supported composite reagent uses anhydrous activated alumina spheres with a specific surface area of ​​200 m² / g to 300 m² / g and a pore volume of 0.4 cm³ / g to 0.6 cm³ / g as a carrier, and loads a 1:1 molar ratio of sodium chloride and potassium chloride mixed salt through a vacuum melt impregnation process. The reaction column temperature is controlled at 280 ℃ to 320 ℃. Ferric chloride and aluminum chloride in the mixed gas undergo a solid-gas surface coordination reaction with the solid sodium chloride on the surface of the packing material, forming a low-volatility complex that is retained.

[0010] Transition section between steps four and five: A heat-insulating transition pipe is installed between the outlet of the chemical retention reaction column and the inlet of the first temperature zone of the horizontal multi-stage sublimation distillation system. The outer layer of the heat-insulating transition pipe is covered with electric heating tape and heat-insulating cotton to maintain the temperature inside the pipe at no less than 280 ℃.

[0011] Step 5: Multi-stage gradient sublimation and zirconium-hafnium separation. The mixed gas, after deep iron and aluminum removal, sequentially passes through a horizontal multi-stage sublimation distillation system with three independent temperature zones. Inside the system, a variable frequency vacuum unit, composed of a multi-stage dry screw pump and a Roots pump, maintains a negative pressure. This variable frequency vacuum unit is located after the outlet of the third temperature zone of the horizontal multi-stage sublimation distillation system. The back pressure is controlled by adjusting the speed of the variable frequency vacuum unit, and simultaneously, a pressure balancing pipe located between the horizontal rotary chlorination reactor and the high-temperature gas cooling section ensures that the reactor pressure is stable between 0.12 MPa and 0.15 MPa. The first temperature zone is a pre-condensation zone, with a controlled temperature of 180 ℃ to 220 ℃, causing selective condensation of high-boiling-point heavy metal chlorides in the mixed gas. The second temperature zone is the core sublimation distillation zone, equipped with spiral guide vanes. The pipe wall temperature is controlled between 315 ℃ and 325 ℃, and the system back pressure is adjusted to 0.01 MPa to 0.03 MPa (absolute pressure). Within this temperature zone, the preferential vaporization of hafnium tetrachloride and zirconium tetrachloride under specific partial pressures is utilized to achieve the enrichment and separation of zirconium tetrachloride. The third temperature zone is the refining condensation zone, which adopts an internally cooled jacket structure. The cooling medium is heat transfer oil, and the temperature gradient is controlled to linearly decrease from 150 °C to room temperature, causing high-purity hafnium tetrachloride to precipitate in the form of dense crystals on the inner wall of the collector.

[0012] Step Six: Fully Enclosed Collection and Packaging. The collector is connected to an automatic weighing system via a magnetohydrodynamic sealing device. When the collected volume reaches a preset threshold, the system automatically switches to a vacuum replacement program, using 99.9999% pure argon gas to perform at least five vacuum-gas-filling cycles on the collection space to ensure that both oxygen and water content are below 0.1 ppmv (volume fraction). Subsequently, the material is unloaded into a packaging container by gravity under fully enclosed conditions, completing the preparation process.

[0013] As a further improvement of the present invention, the anhydrous activated alumina balls loaded with sodium chloride and potassium chloride, which fill the chemical retention reaction column in step four, are arranged with an axial gradient load distribution along the flow direction of the mixed gas. Specifically, the reaction column is divided into three equal regions along the flow direction of the mixed gas: an inlet section, a transition section, and an outlet section. The mixed salt impregnation rate of the inlet section is 5% to 10%, the mixed salt impregnation rate of the transition section is 15% to 20%, and the mixed salt impregnation rate of the outlet section is 25% to 35%.

[0014] As a further improvement of the present invention, in step five, the pitch of the spiral guide vane... With the inner diameter of the distillation zone pipe The ratio interval satisfies: ,in The pitch of the helical guide vanes, in mm. The inner diameter of the pipeline in the core sublimation distillation zone is in mm.

[0015] As a further improvement of the present invention, in step five, the high-purity hafnium tetrachloride crystallization process in the third temperature zone is controlled by adjusting the flow rate of high-purity nitrogen and the temperature of the cooling medium to control the supersaturation of crystallization. satisfy: ,in The degree of crystallization supersaturation is dimensionless; the degree of crystallization supersaturation Defined by the following formula:

[0016] in, This represents the actual gas-phase partial pressure of hafnium tetrachloride in the gas mixture, expressed in Pa. This represents the saturated vapor pressure of hafnium tetrachloride at the condensation interface temperature, expressed in Pa.

[0017] As a core technological improvement of this invention, the horizontal multi-stage sublimation distillation system in step five also integrates a dynamic mass transfer separation control system. The dynamic mass transfer separation control system performs the following operations: S1: A first online gas chromatograph is installed at the inlet of the second temperature zone, with a sampling frequency of once every 30 seconds. The sampled gas is pre-treated to 150 °C before entering the chromatograph. The real-time concentration ratio of hafnium tetrachloride to zirconium tetrachloride in the mixed gas is collected and recorded as the real-time feed ratio. Dimensionless; a second online gas chromatograph is installed at the outlet of the third temperature zone, sampling once every 30 seconds, to collect the real-time concentration ratio of hafnium tetrachloride to zirconium tetrachloride in the product, which is recorded as the real-time yield ratio. , dimensionless.

[0018] S2: Three K-type armored thermocouples are equidistantly arranged along the airflow direction within the second temperature zone, located at the inlet, middle, and outlet of the second temperature zone, respectively. The sampling frequency is 1 Hz, and the temperature distribution along the flow path within the second temperature zone is collected in real time. , , The unit is ℃; a Pitot tube flow meter is installed at the inlet of the second temperature zone, with a sampling frequency of 1 Hz, to collect the gas phase flow velocity in real time. The unit is m / s.

[0019] S3: The real-time feed ratio Real-time yield ratio Temperature distribution along the route , , and gas phase flow rate The input is fed into a dynamic mass transfer separation model, which is based on the Helmholtz free energy minimization principle and the Maxwell-Stephen diffusion equation, and calculates in real time the maximum separation coefficient under the current operating conditions in the second temperature range. Required optimal pipe wall temperature Optimal system back pressure and optimal carrier gas velocity The separation coefficient It is a dimensionless parameter.

[0020] S4: The dynamic mass transfer separation model will calculate the optimal pipe wall temperature. Optimal system back pressure and optimal carrier gas velocity The outputs are respectively sent to a high-precision proportional-integral-derivative temperature controller, a variable frequency vacuum unit controller, and a mass flow controller to adjust the pipe wall temperature, system back pressure, and carrier gas flow rate in the second temperature zone in real time. This allows the actual operating state of the system to track the optimal working condition in real time, thereby increasing the real-time yield ratio. Stable control within the preset target value above, It is a dimensionless parameter, with a value range of 0.95 to 0.99.

[0021] The dynamic mass transfer separation model is constructed and run through the following steps: S3-1: Construct a mass transfer-heat transfer coupled model, equating the second temperature region to... A packed tower with theoretical trays connected in series, wherein The geometric parameters of the spiral guide vanes determine the following:

[0022] in, This is the axial length of the second temperature zone, in meters. The pitch of the guide vanes is in meters (m). The empirical correction coefficient has a value ranging from 0.8 to 1.2, is dimensionless, and is obtained by fitting experimental data at at least three different flow rates.

[0023] S3-2: For the first A theoretical plate was used to establish the composition based on the Maxwell-Stephen diffusion equation. Mass transfer flux between gas and solid phases With temperature ,pressure and concentration gradient Relationship:

[0024] in, and For component indexing, Represents hafnium tetrachloride. Represents zirconium tetrachloride; For the first Components on plate The mole fraction of , dimensionless; Components In the The mass transfer flux on the plate is expressed in mol / (m²·s). For the first Total molar concentration on the plate, in mol / m³; Components With components At temperature and pressure The binary diffusion coefficient, expressed in m² / s, is calculated using the following formula:

[0025] in, The diffusion coefficient reference value under standard conditions is taken as... m² / s; The standard temperature is 273.15 K. The standard pressure is 101325 Pa. For the first The temperature of the plate is expressed in Kelvin (K). For the first The absolute pressure of the plate, measured in Pa.

[0026] S3-3: Calculate the first equation based on Antoni's equation. Components on plate saturated vapor pressure :

[0027] in, The unit is mmHg; For the first The temperature of the plate is expressed in °C. , , Components The Antoin constant, obtained through experimental calibration, for hafnium tetrachloride, , , For zirconium tetrachloride, , , .

[0028] S3-4: Establish the first Components on plate The gas-solid phase equilibrium relationship, where the separation coefficient With temperature and pressure The relationship is given by the modified Clausius-Clapeyron equation:

[0029] in, For the first The separation coefficient of the plate is dimensionless. Components The molar enthalpy of vaporization, in J / mol, for hafnium tetrachloride. J / mol, for zirconium tetrachloride J / mol; The ideal gas constant is 8.314 J / (mol·K); These are the boiling points under standard pressure, expressed in K. Hafnium tetrachloride is 590 K, and zirconium tetrachloride is 604 K. For the first Components on plate The saturated vapor pressure is expressed in Pa. It should be noted that the saturated vapor pressure calculated by the Antoine equation in step S3-3 is in mmHg. Before substituting it into this formula, it needs to be converted to Pa according to the formula 1 mmHg = 133.322Pa. For the first The absolute pressure of the plate, measured in Pa; The Reynolds number correction factor is dimensionless and is obtained by fitting experimental data at at least three different flow rates, with a value ranging from 0.01 to 0.05. For the first The Reynolds number of a plate is dimensionless and is calculated using the following formula:

[0030] in, For the first Density of the mixed gas at the plate, in kg / m³; For the first Gas velocity at the plate, in m / s; For the first The characteristic dimensions of the pipe at the plate are in meters, and are taken as the inner diameter of the pipe in the second temperature zone. For the first The dynamic viscosity of the gas at the plate is expressed in Pa·s. For a hafnium tetrachloride-zirconium tetrachloride mixture, the dynamic viscosity is obtained by referring to a table or experimentally determining the value within the range of 300 °C to 330 °C. Pa·s to Pa·s.

[0031] S3-5: Construct the material and energy balance equations for the entire column, and calculate the mass transfer flux of each theoretical tray. Phase equilibrium relationship and separation coefficient Combined, with the aforementioned real-time feed ratio As boundary conditions, to maximize the overall separation coefficient of the entire tower. The objective function is the temperature distribution along the path. , , Using the initial values, the nonlinear equation system is solved using the Newton-Raphson iterative method. The convergence criterion for the iteration is the sum of the values ​​of two consecutive iterations. The absolute value of the change is less than The maximum number of iterations was set to 500, thereby calculating the optimal tube wall temperature distribution under the constraints of material and energy conservation throughout the tower. and its corresponding optimal system back pressure and optimal carrier gas velocity , It is a dimensionless parameter.

[0032] Compared with the prior art, the present invention has the following beneficial effects: This invention removes physically adsorbed water and surface hydroxyl groups through high-temperature vacuum degassing during the raw material pretreatment stage. A slightly positive pressure inert atmosphere is maintained throughout the reaction, filtration, distillation, and packaging processes. Furthermore, multiple vacuuming-gas-purging procedures are introduced during the collection stage. This effectively blocks the contact pathway between hafnium tetrachloride and trace amounts of oxygen and moisture in the environment, preventing the formation of hydrolysis products and ensuring that the product purity does not undergo secondary degradation during material transfer and packaging.

[0033] This invention breaks through the traditional single approach of physical sedimentation for impurity removal. In the high-temperature gas-solid separation stage, ceramic membrane filtration removes particulate matter. In the chemical retention stage, a supported composite agent undergoes a solid-gas surface coordination reaction with ferric chloride and aluminum trichloride to form a low-volatility complex, achieving deep removal. By combining physical interception with chemical adsorption, a tiered capture capability for impurities of different types and volatility characteristics is formed, significantly reducing the residual amounts of key impurities such as iron and aluminum in the product.

[0034] This invention addresses the technical challenge of the minimal difference in saturated vapor pressure between hafnium tetrachloride and zirconium tetrachloride. It employs a multi-temperature gradient sublimation distillation structure, introducing spiral guide vanes in the core separation zone to optimize gas-solid contact efficiency. Furthermore, through the coordinated control of pipe wall temperature, system back pressure, and carrier gas flow rate, it leverages the vapor pressure difference between the two substances at specific partial pressures to achieve efficient separation. This design elevates the separation process from empirical control to a calculable and predictable level based on first-principles calculations.

[0035] This invention incorporates online monitoring instruments at key process nodes to collect real-time data on feed composition, temperature distribution along the process path, and gas flow rate. Based on the Helmholtz free energy minimization principle and the Maxwell-Stephen diffusion equation, a dynamic mass transfer and separation model is constructed. Optimal operating parameters under current conditions are calculated using Newton-Raphson iteration or sequential quadratic programming algorithms, and a high-precision controller performs closed-loop regulation. This control system enables the process to adapt to fluctuations in raw material parameters, stabilizing product quality within a preset target range.

[0036] This invention further links the state monitoring of the chemical retention reaction column with the operation control of the sublimation distillation unit. A health index model is used to assess the performance degradation of upstream units in real time, triggering response strategies such as feedforward pre-regulation or bypass switching. This cross-unit collaborative mechanism enhances the anti-interference capability of the entire process chain, ensuring the stability of the final product quality even under local unit performance fluctuations. Attached Figure Description

[0037] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation of the scope. For those skilled in the art, other related drawings can be obtained from these drawings without creative effort.

[0038] Figure 1 This is an overall flowchart of the method described in this invention.

[0039] Figure 2 This is a simplified flowchart of the method described in this invention. Detailed Implementation

[0040] In the following description, only certain exemplary embodiments are briefly described. As those skilled in the art will recognize, the described embodiments can be modified in various ways without departing from the spirit or scope of the embodiments of the invention. Therefore, the drawings and description are considered to be exemplary in nature and not restrictive.

[0041] The following is in conjunction with the appendix Figure 1 and Figure 2 The embodiments of the present invention will be described in detail below.

[0042] Example 1: The preparation method of high-purity hafnium tetrachloride according to the present invention is as follows: The raw materials used were hafnium dioxide (99.92% purity) with a median particle size D50 of 8.2 μm and high-purity graphite powder with a median particle size D50 of 3.5 μm. The physical mixing ratio was 1:0.3.

[0043] The pretreatment conditions were: absolute pressure 5 Pa, temperature 300 ℃, duration 6 hours. The horizontal rotary chlorination reactor had a rotation speed of 10 rpm, a reaction section temperature of 1000 ℃, a chlorine concentration of 70%, and an empty tower flow rate of 0.1 m / s.

[0044] A high-temperature gas cooling section is set between steps two and three, with a cooling water flow rate of 1.0 m³ / h and a cooling rate of 40℃ / min. The high-temperature ceramic filter unit operates at 500℃, using a silicon carbide ceramic membrane filter element with a membrane pore size of 1.0 μm. The chemical retention reaction column is at 300℃, and the packing material is alumina balls loaded with a 25% sodium chloride-potassium chloride mixed salt, using a uniform loading method.

[0045] A thermally insulated transition pipe is installed between steps four and five to maintain a temperature of 300 ℃. The second temperature zone of the horizontal multi-stage sublimation distillation system is 320±0.15 ℃, and the system back pressure (absolute pressure) is 0.02 MPa. The third temperature zone does not have precise supersaturation control and lacks a dynamic mass transfer separation control system. The refining condensation rate is controlled at 10 kg / h.

[0046] Example 2: This example improves upon Example 1 by modifying the chemically intercepted reaction column in step four with a gradient loading. The reaction column is divided into three equal regions along the gas flow direction: an inlet section, a transition section, and an outlet section. The mixed salt impregnation rate is 8% in the inlet section, 18% in the transition section, and 30% in the outlet section. All other parameters remain the same as in Example 1.

[0047] Example 3: Based on Example 1, this example makes two improvements to step five: First, the pitch of the spiral guide vanes is limited. With the inner diameter of the distillation zone pipe The ratio is Second, precise control of supersaturation is introduced in the third temperature zone. This is achieved by adjusting the flow rate of high-purity nitrogen and the temperature of the cooling medium to control the supersaturation of crystallization. The value was controlled within 1.10 ± 0.02. The remaining parameters were the same as in Example 1.

[0048] Example 4: This example further integrates a dynamic mass transfer separation control system based on Example 3.

[0049] The system configuration is as follows: A first online gas chromatograph is installed before the inlet of the second temperature zone of the horizontal multi-stage sublimation distillation system. The sampling frequency is once every 30 seconds. The sampled gas is pretreated to 150 °C before entering the chromatograph, and the real-time feed ratio is measured. ; A second online gas chromatograph is installed at the connection between the outlet of the third temperature zone and the collector, sampling every 30 seconds to determine the real-time yield ratio. ; Three K-type armored thermocouples are axially and equidistantly installed inside the second temperature zone, located at the inlet, middle and outlet of the temperature zone, respectively, with a sampling frequency of 1 Hz; A Pitot tube flow meter was installed at the inlet of the second temperature zone, with a sampling frequency of 1 Hz, to monitor the gas phase velocity in real time. .

[0050] The dynamic mass transfer separation model maximizes the overall separation coefficient of the entire column based on real-time acquired data. To achieve the desired effect, the pipe wall temperature in the second temperature zone, system back pressure, and carrier gas flow rate are dynamically adjusted. The PID controller parameters are: proportional coefficient... Integral time Second, differential time Seconds. The remaining parameters are the same as in Example 3.

[0051] Example 5: Based on Example 4, this example upgrades the architecture of the dynamic mass transfer separation control system and introduces a self-optimizing control strategy based on the principle of minimizing separation work.

[0052] This embodiment upgrades the dynamic mass transfer separation control system from a single-stage feedback control to a composite control system that includes a feedforward compensator and a feedback regulator.

[0053] The specific improvements are as follows: A miniature online gas sampling branch was added between the inlet of the second temperature zone of the horizontal multi-stage sublimation distillation system and the outlet of the chemical retention reaction column. This branch switches the sampling gas flow every 60 seconds via an electric three-way valve to collect mixed gas samples from the outlet of the chemical retention reaction column. After being pre-treated to 150°C, the samples are sent to the first online gas chromatograph to obtain the real-time retention efficiency of the chemical retention reaction column for ferric chloride and aluminum chloride. and Dimensionless, defined as follows:

[0054] in, and These are the concentrations of ferric chloride in the mixed gas at the inlet and outlet of the chemically intercepted reaction column, respectively, in volume fractions (ppmv). and This represents the corresponding concentration of aluminum trichloride.

[0055] In this embodiment, the objective function of the dynamic mass transfer separation model is changed from maximizing the overall separation coefficient of the entire tower. Reconstruction to minimize the separation work per unit mole of product The work of separation is defined based on the second law of thermodynamics as follows:

[0056] in, The ideal gas constant is taken as 8.314 J / (mol·K); This represents the average temperature of the second temperature zone, in Kelvin (K). and These are the mole fractions of hafnium tetrachloride and zirconium tetrachloride in the inlet mixed gas of the second temperature zone, respectively, and are dimensionless. and These are the mole fractions of hafnium tetrachloride and zirconium tetrachloride in the outlet mixed gas of the second temperature zone, respectively, and are dimensionless. This is the irreversible loss term, which includes flow resistance loss and heat loss, and is expressed in J / mol. It is calculated using the following formula:

[0057] in, For the first Pressure drop on each theoretical plate, in Pa; For the first Gas velocity at the plate, in m / s; The sampling time interval is set to 30 seconds. For the first Density of the mixed gas at the plate, in kg / m³; The efficiency of the variable frequency vacuum unit is dimensionless and is taken as 0.65. The heat dissipation coefficient, measured in W / K, is obtained through equipment thermal balance calibration. The ambient temperature is expressed in Kelvin (K).

[0058] The dynamic mass transfer separation model executes the following self-optimizing control logic: S5-1: The real-time feed ratio measured at the current moment. Temperature distribution along the route , , and gas phase flow rate Given the initial conditions, a sequential quadratic programming algorithm is used to search within the following constraint space to achieve the separation work. Minimal optimal combination of operating parameters: Constraints: ; ; ; ,in Pick ; ; ; S5-2: The iterative convergence criterion for the sequential quadratic programming algorithm is that the absolute value of the change in the objective function between two adjacent iterations is less than 1. J / mol, with an upper limit of 100 iterations. In each iteration, the dynamic mass transfer separation model calls the mass transfer-heat transfer coupling model as described above to solve the overall material balance, energy balance, and separation coefficient distribution under the current candidate parameter combination.

[0059] S5-3: Retention efficiency of the chemical retention reaction column or When the value is below a preset threshold, the dynamic mass transfer separation model automatically triggers feedforward compensation: When solving for the optimal operating parameters, the weights of the objective function in the second temperature region are shifted towards increasing the separation coefficient. The shift amount is... The decay rate is linearly related to the retention efficiency: ,when hour; ,when hour; in, The feedforward compensation coefficient is dimensionless and ranges from 0.2 to 0.5. It is obtained by fitting experimental data under at least 5 different retention efficiencies.

[0060] S5-4: Calculated optimal pipe wall temperature Optimal system back pressure and optimal carrier gas velocity The outputs are respectively sent to a high-precision PID temperature controller, a variable frequency vacuum unit controller, and a mass flow controller.

[0061] The PID controller uses an incremental algorithm, and its control law is as follows:

[0062] in, To control the increment; The deviation between the set value and the measured value; , , The PID parameters were obtained by combining the Ziegler-Nichols tuning method with on-site step response testing.

[0063] S5-5: The system executes a complete optimal parameter calculation and adjustment cycle every 60 seconds, with real-time yield ratio. The sampling frequency is increased to once every 15 seconds for faster response in PID control. The dynamic mass transfer separation model calculates the optimal parameters and corresponding separation work for each iteration. Recorded in the historical database for online correction of model parameters.

[0064] High-purity hafnium tetrachloride was prepared using the method described in this embodiment. Except for the improvements mentioned above, the process parameters were the same as in Example 4.

[0065] In a validation test that ran continuously for 120 hours, three batches of raw materials with different zirconium contents (150 ppm, 220 ppm and 180 ppm) were processed. The test results are shown in Table 1 below: Table 1:

[0066] Compared to Example 4, this example reduces the average zirconium content of the product from 11 ppm to 6.3 ppm under fluctuating raw material conditions, reduces energy consumption by approximately 8%, and shortens the control response time to less than 15 seconds. By introducing a separation work minimization objective function, the system automatically selects the optimal combination of operating parameters for energy consumption while ensuring the yield ratio meets the target, achieving synergistic optimization of product quality and operating costs.

[0067] Example 6: Based on Example 5, this embodiment adds a bypass feedback control loop between the chemical retention reaction column and the horizontal multi-stage sublimation distillation system to construct a cross-unit collaborative control system for chemical retention-sublimation distillation.

[0068] A three-way diverter valve is added between the outlet of the chemical retention reaction column and the inlet of the insulated transition tube. The bypass outlet of this three-way diverter valve is connected to a micro online analysis unit. The micro online analysis unit includes: The first bypass branch, after being cooled to 150°C, is connected to the first online gas chromatograph for continuous monitoring of the residual concentrations of ferric chloride and aluminum chloride in the mixed gas at the outlet of the chemical retention reaction column. The second bypass branch is connected to a surface acoustic wave sensor array for real-time detection of particulate matter concentration and particle size distribution in the mixed gas. The sampling frequency is 10 Hz, and the detection particle size range is 0.1 μm to 10 μm.

[0069] The surface acoustic wave sensor array consists of three sensors with different center frequencies, corresponding to particle size ranges of 0.1-1 μm, 1-5 μm and 5-10 μm respectively. The particle concentration is inverted by the amplitude change of the sensor response signal.

[0070] When the concentration of particulate matter in any particle size range exceeds a preset threshold, the system determines that the chemical retention reaction column has experienced penetration or pulverization.

[0071] The dynamic mass transfer separation control system is expanded into a collaborative controller that includes monitoring the state of the chemically trapped reaction column and pre-adjusting the parameters of the sublimation distillation unit, and performs the following operations: S6-1: Real-time monitoring of residual ferric chloride concentration at the outlet of the chemical retention reaction column. Residual aluminum trichloride concentration and particulate matter concentration in each particle size range , It corresponds to three particle size ranges.

[0072] S6-2: Construct a state assessment model for chemically cut-off reaction columns and output the health index of the chemically cut-off reaction columns. Dimensionless, defined as follows:

[0073] in, The warning threshold for ferric chloride concentration is set at 0.1 ppmv. The warning threshold for aluminum trichloride concentration is set at 0.1 ppmv. The warning thresholds for particulate matter concentration in each particle size range are set at 0.5 mg / m³, 0.3 mg / m³, and 0.1 mg / m³, respectively. , , The weighting coefficients are determined using the analytic hierarchy process (AHP). , , , , .

[0074] S6-3: Health Index of Chemical Retention Column When the value is below 0.85, the collaborative controller triggers the feedforward pre-adjustment mode. In this mode, the dynamic mass transfer separation model introduces a correction coefficient when solving for the optimal operating parameters in the second temperature range, causing the operating parameters to shift towards improving separation robustness.

[0075] in, , , The basic optimal value calculated by the method described in Example 5 for the dynamic mass transfer separation model; This is the temperature feedforward correction factor, taken as 5℃; The pressure feedforward correction factor is set to 0.002 MPa. The velocity feedforward correction factor is set to 0.02 m / s.

[0076] S6-4: The co-controller simultaneously sends a command to the online pulse backflush system of the chemical retention reaction column, adjusting the backflush frequency from the original "differential pressure trigger" mode to a parallel mode of "health index trigger" and "differential pressure trigger": when Backflushing is triggered when the pressure drops below 0.85 or the pressure difference across the reaction column exceeds 5 kPa. The backflushing gas flow rate is increased by 20% compared to the standard backflushing, and the backflushing duration is extended to 5 seconds.

[0077] S6-5: Health Index of Chemical Retention Column When three consecutive samples are below 0.70, the co-controller determines that the chemical retention reaction column needs regeneration and automatically switches the process to bypass operation mode. Close the inlet valve of the chemical retention reaction column and open the bypass valve to allow the mixed gas to bypass the chemical retention reaction column and directly enter the insulated transition pipe. Simultaneously, send a regeneration request signal to the central control system and record the cumulative operating time and penetration characteristics of the chemical retention reaction column for predictive maintenance.

[0078] S6-6: In bypass operation mode, the co-controller activates the emergency control strategy of the sublimation distillation unit: temporarily raises the upper limit of the temperature setpoint of the second temperature zone to 330℃ and temporarily lowers the lower limit of the back pressure setpoint to 0.008 MPa to compensate for the impact of trace amounts of ferric chloride and aluminum chloride impurities that may enter the system after the chemical retention function is lost on the separation efficiency.

[0079] The emergency control strategy lasts for no more than 60 minutes. If the regeneration and switching of the chemical retention reaction column is not completed within 60 minutes, the system will automatically execute the safety shutdown procedure.

[0080] The cross-unit collaboration model built into the collaborative controller is constructed through the following steps: S6-3-1: Establish the correlation function between the concentration of impurities at the outlet of the chemically intercepted reaction column and the separation efficiency of sublimation distillation. Response surface methodology was used to design the experiment, with ferric chloride concentration (0-5 ppmv), aluminum chloride concentration (0-5 ppmv), and particulate matter concentration (0-2 mg / m³) as input factors, and the separation coefficient in the second temperature zone as the parameter. To determine the response value, a second-order polynomial regression model is established:

[0081] in, As input factors; The regression coefficients are obtained by fitting at least 20 sets of orthogonal experimental data, and the goodness of fit is... .

[0082] S6-3-2: Constructing a feedforward compensation matrix based on correlation functions Matrix elements Indicates the first The change of the input factor affects the first Influence coefficient of each operating parameter:

[0083] S6-3-3: The feedforward compensation matrix is ​​integrated into the dynamic mass transfer separation model, so that in each iteration of the model, the compensation amount is first calculated based on the current state of the chemically cut-off reaction column, and then the optimized search is performed using the compensated operating parameters as the initial values, forming a feedforward-feedback composite control architecture.

[0084] High-purity hafnium tetrachloride was prepared using the method described in this embodiment and continuously operated for 240 hours. During this period, at the 72nd and 168th hours, the partial breakthrough condition of the chemically intercepted reaction column was simulated (by introducing trace amounts of ferric chloride and aluminum chloride through online mixing). The test results are shown in Table 2 below: Table 2:

[0085] In this embodiment, when impurities tend to penetrate through the chemical retention reaction column, the operating parameters of the sublimation distillation unit are adjusted in advance through a feedforward pre-adjustment mechanism, successfully controlling the zirconium content of the product in the penetration stage to below 11 ppm, and the iron and aluminum impurities to below 3 ppb.

[0086] It should be noted that during the simulated breakthrough stage, although the chemical retention reaction column reduced its retention efficiency for iron and aluminum impurities, the feedforward pre-regulation mechanism adjusted the operating parameters of the sublimation distillation unit in advance (increasing the temperature of the second temperature zone and decreasing the system back pressure), which enabled the sublimation distillation unit to also have a certain physical retention effect on the residual trace iron and aluminum impurities. At the same time, the simulated breakthrough was set to a mild breakthrough (the concentrations of ferric chloride and aluminum chloride were controlled below 0.5 ppmv), so the iron and aluminum impurities could still be maintained at a low level.

[0087] The above results verify the effectiveness of the cross-unit collaborative control strategy in addressing the performance degradation of the trapping unit. Compared to Example 4, which did not employ cross-unit collaborative control, this example maintains a 100% product yield even under conditions of trapping unit performance degradation, improving process robustness and anti-interference capability. The bypass operation mode was not triggered in this round of testing, indicating that the feedforward pre-regulation mechanism effectively slows down the breakthrough process of the chemical trapping reaction column.

[0088] Comparative Example 1: Except for not using the chemically trapped reaction column in step four and not using the spiral guide vanes and precise back pressure control in step five, the other process parameters were the same as in Example 1. That is, the crude product was directly fed into a conventional single-stage condenser after ceramic filtration, and the condensation process was carried out at atmospheric pressure.

[0089] Comparative Example 2: A traditional intermittent high-vacuum sublimation method was used. Hafnium dioxide and carbon powder were mixed and subjected to conventional chlorination. The resulting crude product was cooled and solidified, then placed in a sublimation tank. Sublimation purification is carried out under a vacuum of Pa, at a sublimation temperature of 320 °C, and a single operation cycle is 48 hours.

[0090] Comparative Example 3: It is basically the same as Example 3, except that: high-purity nitrogen was not introduced into the third temperature zone for precise control of supersaturation, and traditional natural cooling condensation and crystallization were used.

[0091] Comparative Example 4: It is basically the same as Example 2, except that the composite agent in the chemical retention reaction column is uniformly loaded and the overall impregnation rate is set to a uniform 20%.

[0092] Table 1 below shows the analytical results of the products obtained in the above examples and comparative examples by inductively coupled plasma mass spectrometry (ICP-MS) and infrared absorption spectrometry. The ICP-MS detection conditions were: Agilent 7900 model, and the standard curve linear correlation coefficient was... The detection limits for each element are ≤0.001 ppb.

[0093] Table 3: Comparison of product purity data for different preparation processes (Unit: unless otherwise specified, all values ​​are by weight ppm).

[0094] Table 4: Comparison of process effects between static parameter control and dynamic mass transfer separation control;

[0095] Analysis of the data in Tables 3 and 4 shows that the embodiments of the present invention exhibit superiority in all key impurity indicators. Example 2 demonstrates that the gradient load design effectively extends the lifespan of the retained bed while maintaining a low bed pressure drop; Example 3 demonstrates the precise control of supersaturation and the effectiveness of helical guide vanes. Ratio optimization further reduced zirconium content and improved crystal morphology; Example 4 demonstrated that the dynamic mass transfer separation control system can effectively offset the impact of raw material fluctuations on product quality, reducing the product zirconium content fluctuation rate (maximum deviation rate) from ±26.7% to ±4.3%, while also reducing energy consumption; Example 5 further reduced the average product zirconium content and unit energy consumption by introducing a separation work minimization objective function, while ensuring the yield ratio meets the target; Example 6 improved the robustness of the process under the condition of performance degradation of the cut-off unit by constructing a cross-unit collaborative control system.

[0096] In summary, this invention solves the problems of incomplete impurity removal, low zirconium-hafnium separation efficiency, poor raw material adaptability, and susceptibility to environmental pollution in traditional preparation processes by deeply coupling multiple process units, including dynamic rotary chlorination, high-temperature gas cooling transition, high-temperature ceramic fine filtration, gradient loading chemical coordination retention, heat preservation transition, multi-stage gradient sublimation distillation, dynamic mass transfer separation control, and fully enclosed intelligent packaging. It provides a process route for the large-scale production of high-purity semiconductor precursor materials.

[0097] Preferred embodiments of the invention have been described, but those skilled in the art, upon learning the basic inventive concept, can make other changes and modifications to these embodiments. Therefore, the appended claims are intended to be interpreted as including the preferred embodiments as well as all changes and modifications falling within the scope of the invention.

[0098] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. It should be noted that any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing high-purity hafnium tetrachloride, characterized in that, Includes the following steps: Step 1: Physically mix hafnium dioxide powder and high-purity carbon source at a mass ratio of 1:0.25 to 1:0.

35. Place the mixed material in a vacuum drying oven and degas it for 4 to 8 hours under conditions of absolute pressure below 10 Pa and temperature of 250 ℃ to 350 ℃ to obtain pretreated material. Step 2: The pretreated material described in Step 1 is continuously and quantitatively fed into a horizontal rotary chlorination reactor. A mixed gas consisting of chlorine and high-purity inert carrier gas is introduced into the horizontal rotary chlorination reactor. The volume fraction of chlorine in the mixed gas is controlled to be 60% to 80%, the gas phase empty tower flow rate is 0.05 m / s to 0.15 m / s, the internal temperature of the reactor is controlled to be 950℃ to 1050℃, and the absolute pressure is 0.12 MPa to 0.15 MPa, so that hafnium dioxide undergoes a chlorination reaction to generate a crude product mixed gas containing hafnium tetrachloride vapor. Step 3: Introduce the crude product mixture generated in Step 2 into a high-temperature ceramic filter unit. The high-temperature ceramic filter unit uses a silicon carbide or alumina ceramic membrane filter element with a membrane pore size of 0.5 μm to 2.0 μm. Control the operating temperature of the filter unit to 450 ℃ to 550 ℃ to remove solid particles entrained in the mixture through physical interception. Step 4: The filtered mixed gas enters the chemical retention reaction column, which is filled with a supported composite agent. The supported composite agent uses anhydrous activated alumina balls as a carrier and supports a mixed salt of sodium chloride and potassium chloride. The temperature of the reaction column is controlled at 280 ℃ to 320 ℃. Ferric chloride and aluminum chloride in the mixed gas undergo a solid-gas surface coordination reaction with the supported composite agent to generate a low-volatility complex, which is then retained. Step 5: The mixed gas after deep iron and aluminum removal passes through a horizontal multi-stage sublimation distillation system with three independent temperature zones. The first temperature zone controls the temperature from 180 ℃ to 220 ℃, the second temperature zone controls the tube wall temperature from 315 ℃ to 325 ℃, the system back pressure is from 0.01 MPa to 0.03 MPa, and the third temperature zone controls the temperature gradient to linearly decrease from 150 ℃ to room temperature, causing high-purity hafnium tetrachloride to precipitate on the inner wall of the collector. Step Six: Unload the hafnium tetrachloride from the collector into a packaging drum under a completely sealed condition to complete the preparation; In step four, the anhydrous activated alumina balls loaded with sodium chloride and potassium chloride, which fill the chemical retention reaction column, are arranged with an axial gradient load distribution along the flow direction of the mixed gas. The reaction column is divided into three equal regions along the flow direction of the mixed gas: an inlet section, a transition section, and an outlet section. The mixed salt impregnation rate of the inlet section is 5% to 10%, the mixed salt impregnation rate of the transition section is 15% to 20%, and the mixed salt impregnation rate of the outlet section is 25% to 35%. In step five, the second temperature zone of the horizontal multi-stage sublimation distillation system is equipped with spiral guide vanes, and the temperature fluctuation deviation in the second temperature zone is controlled within ±0.2 ℃. In the third temperature zone, the high-purity hafnium tetrachloride crystallization process controls the supersaturation of crystallization by adjusting the flow rate of high-purity nitrogen and the temperature of the cooling medium. satisfy: ,in The degree of crystallization supersaturation is dimensionless. Defined by the following formula: ； in, This represents the actual gas-phase partial pressure of hafnium tetrachloride in the gas mixture, expressed in Pa. This represents the saturated vapor pressure of hafnium tetrachloride at the condensation interface temperature, expressed in Pa.

2. The method for preparing high-purity hafnium tetrachloride according to claim 1, characterized in that, In step two, the rotation speed of the horizontal rotary chlorination reactor is 5 rpm to 15 rpm. The inner wall of the horizontal rotary chlorination reactor is equipped with lifting plates to make the material fall in a uniform waterfall-like manner.

3. The method for preparing high-purity hafnium tetrachloride according to claim 1, characterized in that, The high-temperature ceramic filter unit described in step three has an online pulse backflushing function. The backflushing gas is a high-purity inert gas preheated to above 500 ℃, and the backflushing pressure is 0.3 MPa to 0.5 MPa. The backflushing operation is triggered when the pressure difference before and after the high-temperature ceramic filter unit reaches 5 kPa.

4. The method for preparing high-purity hafnium tetrachloride according to claim 1, characterized in that, The pitch of the spiral guide vanes in step five With the inner diameter of the distillation zone pipe The ratio interval satisfies: ,in The pitch of the helical guide vanes, in mm. The inner diameter of the pipeline in the core sublimation distillation zone is in mm.

5. The method for preparing high-purity hafnium tetrachloride according to claim 1, characterized in that, The third temperature zone described in step five adopts an internal cooling sleeve structure, and the cooling medium is heat transfer oil. By adjusting the flow rate and inlet temperature of the heat transfer oil, the subcooling of the condensation interface is controlled between 10 ℃ and 20 ℃.

6. The method for preparing high-purity hafnium tetrachloride according to claim 1, characterized in that, In step six, the collector is connected to the automatic weighing system via a magnetic fluid sealing device. When the collected amount reaches a preset threshold, the system automatically switches to a vacuum replacement program and uses argon gas with a purity of 99.9999% to perform at least five vacuum-filling cycles on the collection space to ensure that the oxygen content and water content are both below 0.1 ppmv volume fraction.

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