A method for silicon-28 alane isotopic enrichment
The selective enrichment of silicon-28 isotopes through a one-step chemical reaction solves the problems of complex processes and high energy consumption in existing technologies, and provides an efficient and low-cost method for preparing silicon-28 materials, which is suitable for quantum computing and semiconductor devices.
Patent Information
- Application Number
- CN202610250939.6
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-03-03
- Publication Date
- 2026-06-16
AI Technical Summary
Existing physical separation technologies are complex, energy-intensive, and expensive, making it difficult to efficiently prepare high-purity silicon-28 materials.
A one-step chemical reaction is employed, utilizing the selective reduction reaction of sodium aluminum hydride and silicon tetrafluoride to generate silane gas rich in silicon-28 at low temperature. The selective enrichment of silicon-28 isotopes is achieved by controlling the reaction conditions.
The process was simplified, energy consumption and costs were reduced, the direct product was silane, it was compatible with the existing vapor deposition process in the semiconductor industry, and the abundance of silicon-28 isotopes was increased.
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Figure CN122212148A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of isotope separation and special gas material preparation technology, specifically relating to a method for enriching silane-28 alkyl isotopes. Background Technology
[0002] High-purity silicon-28 (28Si, isotopic abundance >99.99%) is a core material for next-generation quantum computing, high-precision metrological standards (such as Avogadro's constant determination), and future semiconductor devices. Currently, the mainstream technologies for silicon isotope separation internationally are all physical methods, mainly including: 1. Gas centrifugation: This method separates gas molecules of different masses (such as SiF4) by utilizing the difference in centrifugal force experienced by the molecules in a high-speed centrifuge. Although this method can be scaled up, the equipment is extremely complex, the investment is huge, and the energy consumption is high (see: PG Sennikov, AV Vodopyanov et al, Towards 0.99999 28Si, SolidState Communications, Volume 152, Issue 6, 2012, Pages 455-457).
[0003] 2. Low-temperature distillation: This method utilizes the weak "reverse" gas-liquid phase equilibrium isotope effect of SiF4 at low temperatures (approximately -90°C) for multi-stage distillation separation. However, this method also suffers from problems such as large equipment requirements, extremely high energy consumption, long separation cycles, and poor economic efficiency (see reference: Mills, TR (1990). Silicon Isotope Separation by Distillation of Silicon Tetrafluoride. Separation Science and Technology, 25(3), 335–345.).
[0004] The common technical bottleneck of the above physical methods lies in the fact that "isotope separation" and "chemical synthesis of the target product (SiH4 or elemental Si)" are two completely separate unit operations. Typically, a large amount of energy is required first to enrich the target product. 28 SiF4 gas undergoes complex chemical reactions (such as reduction with metal hydrides) to convert it into the desired precursor silane (SiH4), which is then deposited as elemental silicon via chemical vapor deposition. This process is lengthy, has a low overall yield, and is extremely costly, severely limiting the development of high-purity silicon. 28 The application and promotion of Si materials are crucial. Therefore, developing a silicon isotope separation technology with a short process, low energy consumption, and novel principle is of great strategic significance and urgent industrial demand. Summary of the Invention
[0005] The purpose of this invention is to overcome the shortcomings of existing physical separation technologies, such as complex processes, high energy consumption, and high costs, and to provide a novel method and system for silicon-28 isotope separation based on the kinetic isotope effect (KIE). This method aims to achieve selective enrichment of silicon-28 isotopes simultaneously with the synthesis of the target product silane (SiH4) through a one-step chemical reaction, thereby shortening the process and reducing energy consumption and costs.
[0006] A method for enriching silane-28 isotopes includes the following steps: (1) Construction of reaction system: Using silicon tetrafluoride (SiF4) as silicon source and sodium aluminum hydride (NaAlH4) as reducing agent, a multiphase reaction system containing gaseous silicon tetrafluoride and solid or dissolved and dispersed sodium aluminum hydride in an inert solvent is constructed. The silicon tetrafluoride contains different silicon isotopes, and the different silicon isotopes are silicon-28, silicon-29 and at least one of silicon-30. (2) Selective reduction reaction: At a reaction temperature of -100℃ to -50℃, silicon tetrafluoride in step (1) reacts with sodium aluminum hydride to generate silane gas rich in silicon-28. (3) Separation and collection of products: Separate the gaseous products generated in step (2) and collect silane rich in silicon-28.
[0007] The main chemical reaction is: SiF4 + NaAlH4 → SiH4 + NaAlF4.
[0008] Selective reaction: A reaction that takes place under controlled reaction conditions, because... 28 The reaction transition state energy barrier of SiF4 molecules is lower than that of SiF4 molecules. 29 SiF4 and 30 SiF4 molecules exhibit a faster reaction rate kinetically. By precisely controlling the reaction conditions, [the following can be achieved]... 28 SiF4 preferentially reacts with NaAlH4 to produce 28 SiH4.
[0009] Product separation and collection: The gas mixture produced by the reaction is separated, mainly collecting products rich in... 28 The product of Si is SiH4, while the unreacted SiF4 is enriched in the tail gas, which contains heavier SiH4. 29 Si and 30 Si isotopes. Silicon-28 enrichment means that the abundance of silicon-28 isotopes in the product is higher than in the reactants.
[0010] Preferably, in step (1), the inert solvent is at least one of the ether solvents.
[0011] More preferably, in step (1), the inert solvent is at least one of ethylene glycol dimethyl ether (DME) and tetrahydrofuran (THF). The concentration of sodium aluminum hydride in DME can reach about 17.96 wt%, while the concentration of NaAlH in THF is about 10.8 wt%.
[0012] Preferably, in step (2), the reaction temperature is -80℃ to -70℃.
[0013] Preferably, in step (2), the reaction pressure is from atmospheric pressure to 1 MPa. In this application, the reaction pressure is gauge pressure, that is, the reaction pressure is a value exceeding the external ambient air pressure, and atmospheric pressure is 0 MPa.
[0014] More preferably, in step (2), the reaction pressure is 0.1~0.5 MPa.
[0015] Preferably, in step (2), silicon tetrafluoride is introduced into the reaction system at a flow rate of 1 to 5 sccm during the reaction process.
[0016] Preferably, silicon tetrafluoride contains silicon isotopes of different natural abundances. The concentrations of each silicon isotope of natural abundance in silicon tetrafluoride are as follows: 28 Si: 92.23%, 29 Si: 4.67%, 30 Si: 3.10% (Reference: André, L., Cardinal, D. (2011). Silicon Isotopes. In: Gargaud, M., et al. Encyclopedia ofAstrobiology. Springer, Berlin, Heidelberg. https: / / doi.org / 10.1007 / 978-3-642-11274-4_1448).
[0017] Compared with the prior art, the technical solution provided by the present invention has the following significant advantages: 1. Shortened process flow: The process integrates multiple independent unit operations such as separation, transformation and purification in traditional processes into a one-step chemical reaction, realizing "separation as synthesis", which greatly simplifies the process flow.
[0018] 2. Reduced energy consumption and costs: The reaction is carried out at low temperature and at atmospheric to medium pressure, eliminating the need for the massive amounts of electricity and extreme-condition equipment required for gas centrifugation or deep cryogenic distillation, which is expected to significantly reduce equipment investment and operating costs.
[0019] 3. High product value and good compatibility: The direct product is silane (SiH4), which is a standard precursor for the preparation of high-purity single crystal silicon. It is fully compatible with the existing vapor deposition process of the semiconductor industry and has a short application chain. Attached Figure Description
[0020] Figure 1 This is a flowchart illustrating the principle of the separation process of the present invention.
[0021] Figure 2 Obtained from theoretical calculations 28 Si, 29 Si, 30 A schematic diagram of the energy barrier difference of Si in the key transition state during the reaction (exemplary).
[0022] Figure labels: Reactor 1, Temperature control jacket 2, SiF4 gas cylinder 3, Solvent port 4, NaAlH4 feed port 5, Glove box 6, Vacuum pump 7, Gas collection cylinder 8, Pressure gauge 9. Detailed Implementation
[0023] Example 1: Basic Verification Experiment (1) System setup: Refer to Figure 1 A micro-scale reaction system was constructed. Reactor 1 is a corrosion-resistant high-pressure reactor with an internal stirring paddle. Reactor 1 is equipped with a temperature-controlled jacket 2 to control the reaction temperature. Reactor 1 is connected to three inlet pipes and one outlet pipe. The three inlet pipes are used to introduce SiF4 gas, solvent, and NaAlH4, respectively. The first inlet pipe is connected to a SiF4 gas cylinder 3; the second inlet pipe has a solvent port 4 for introducing inert solvent; the third inlet pipe has a feed port 5, which is located inside a glove box 6, where NaAlH4 is fed. A vacuum pump 7 is installed on the outlet pipe to create negative pressure inside reactor 1. The outlet of the outlet pipe is used to discharge the gas extracted from reactor 1 by the vacuum pump 7 and also to collect the product. When product collection is required, the other end of the outlet pipe is connected to a gas collection cylinder 8. A pressure gauge 9 is also installed on reactor 1 to monitor the internal pressure. Valves can be installed on each inlet and outlet pipe to control the opening and closing of the pipelines. The natural abundance of SiF4 gas from SiF4 cylinder 3 is precisely controlled by a mass flow controller. 28 Si: 92.23%, 29 Si: 4.67%, 30 Si: 3.10%) flow rate.
[0024] (2) Experimental procedure: First, add inert solvent to reactor 1 through solvent port 4. Then, in glove box 6, place NaAlH4 powder into reactor 1 through NaAlH4 inlet 5 and seal it. Evacuate the system using vacuum pump 7 and replace it three times with inert gas (the gas cylinder providing the inert gas can be connected to one of the two inlet pipes not connected to glove box 6, and the extracted gas can be collected by connecting a waste gas cylinder to the outlet pipe). Cool the temperature inside reactor 1 to -100℃ to -50℃ using temperature control jacket 2. Introduce SiF4 gas at a flow rate of 1 to 5 sccm while starting stirring.
[0025] (3) Product collection and analysis: After three hours of reaction, SiH4 product was collected by vacuum pump 7. The collected SiH4 was sent to a high-precision gas isotope ratio mass spectrometer (Gas-IRMS) for analysis.
[0026] Example 2: Figure 2 Obtained from theoretical calculations 28 Si, 29 Si, 30 A schematic diagram illustrating the differences in the key transition state energy barriers of Si in the reaction (exemplary). The diagram shows the energy changes for different silicon isotopes (Si-28, Si-29, Si-30) in the reaction SiF4 + NaAlH4 → SiH4 + NaAlF4. The initial energy barrier of Si-28 (0.05382) is much lower than that of Si-29 (0.3666) and Si-30 (0.14377). Utilizing the extremely low initial energy barrier of Si-28, the reaction can be carried out under certain low-temperature conditions, preferentially converting Si-28 into SiH4 gas and separating it, achieving the effect of enriching Si-28 alkane.
[0027] Example 3: Effects at different temperatures To verify the technical effectiveness of the method of the present invention (Example 1), comparative experiments were conducted at different temperatures. Temperature control was achieved by the temperature control jacket of the reactor, with the following temperatures set: room temperature (25℃), -50℃, -70℃, -80℃, and -100℃. Reactor 1 was a corrosion-resistant high-pressure reactor with a volume of approximately 50 mL.
[0028] Experimental Procedure: First, add 30 ml of inert solvent tetrachlorofuran to reactor 1 through solvent port 4. Then, in glove box 6, place 0.5 g of NaAlH4 powder into reactor 1 through NaAlH4 inlet 5 and seal. Evacuate the system using vacuum pump 7 and purge three times with inert gas. Cool the temperature inside reactor 1 to the appropriate temperature using temperature control jacket 2. Introduce SiF4 gas at a flow rate of 2 sccm while simultaneously starting stirring and maintaining the pressure at 0.2 MPa.
[0029] As a result, the reaction at room temperature (25°C) produced... 28 Si abundance was only 92.25%, with no obvious separation effect; reaction at -50℃, 28 Si abundance increased to 92.85%, enriched by 0.62%, and the isotope effect began to appear; reaction at -70℃, 28 Si abundance reached 93.52%, enrichment was 1.29%, and the separation effect was significant; reaction at -80℃, 28 The Si abundance was 93.40%, with an enrichment of 1.17%, slightly below -70℃; the reaction occurred at -100℃. 28 The Si abundance was 93.30%, with an enrichment of 1.07%, indicating a further decrease in separation efficiency.
[0030] Example 4: Effects under different pressures To verify the technical effectiveness of the method of the present invention (Example 1), comparative experiments were conducted under different pressures. The pressure inside the reactor was controlled by the amount of SiF4 gas introduced. At atmospheric pressure, 0 MPa indicated no SiF4 gas was introduced; lower pressure indicated a smaller amount of SiF4 gas introduced, and higher pressure indicated a larger amount of SiF4 gas introduced. The temperature was controlled at -70℃, and the rest was the same as in Example 2. The pressure experiments showed that the pressure in the range of 0.1~1.0 MPa had no significant effect on selectivity.
[0031] In summary, low temperature is a necessary condition for isotope separation, and the temperature range of -100℃ to -50℃ is suitable for achieving this separation. 28 The increase in Si abundance is helpful; the low temperature range of -80℃ to -70℃ is the preferred temperature range that balances separation efficiency and production efficiency. 28 Si abundance can be increased by more than 1.2% while maintaining a reasonable reaction yield.
Claims
1. A method for enriching silane-28 alkyl isotopes, characterized in that, Includes the following steps: (1) Construction of reaction system: Using silicon tetrafluoride as silicon source and sodium aluminum hydride as reducing agent, a multiphase reaction system containing gaseous silicon tetrafluoride and solid or dissolved and dispersed sodium aluminum hydride in an inert solvent is constructed. The silicon tetrafluoride contains different silicon isotopes, and the different silicon isotopes are silicon-28, silicon-29 and at least one of silicon-30. (2) Selective reduction reaction: At a reaction temperature of -100℃ to -50℃, silicon tetrafluoride in step (1) reacts with sodium aluminum hydride to generate silane gas rich in silicon-28. (3) Separation and collection of products: Separate the gaseous products generated in step (2) and collect silane rich in silicon-28.
2. The method for enriching silane-28 alkyl isotopes according to claim 1, characterized in that, In step (1), the inert solvent is at least one of the ether solvents.
3. The method for enriching silane-28 alkyl isotopes according to claim 2, characterized in that, In step (1), the inert solvent is at least one of ethylene glycol dimethyl ether and tetrahydrofuran.
4. The method for enriching silane-28 alkyl isotopes according to claim 1, characterized in that, In step (2), the reaction temperature is -80℃ to -70℃.
5. The method for enriching silane-28 alkyl isotopes according to claim 1, characterized in that, In step (2), the reaction pressure is from atmospheric pressure to 1 MPa.
6. The method for enriching silane-28 alkyl isotopes according to claim 5, characterized in that, In step (2), the reaction pressure is 0.1~0.5 MPa.
7. The method for enriching silane-28 alkyl isotopes according to claim 1, characterized in that, In step (2), silicon tetrafluoride is introduced into the reaction system at a flow rate of 1 to 5 sccm during the reaction process.
8. The method for enriching silane-28 alkyl isotopes according to claim 1, characterized in that, Silicon tetrafluoride contains different silicon isotopes in natural abundance.