Research on the Production of ²⁸Si Isotope with SiH₄ by Gas Diffusion Method

Stable isotopes are currently widely used in medical, biological, agricultural, environmental, industrial manufacturing, scientific research and other fields. There are three isotopes of silicon in nature, namely ²⁸Si, ²⁹Si, and ³⁰Si, with natural abundances of 92.22%, 4.69%, and 3.09%, respectively. ²⁸Si isotopes are mainly used in the semiconductor field and also have certain applications in quantum computing and metrology. Silicon crystals made from pure ²⁸Si isotope with an abundance of over 99% have a perfect lattice structure, which can reduce phonon scattering, improve thermal conductivity, lower gate voltage, increase switching speed, and increase chip frequency. ²⁸Si can be used to manufacture high-speed CPUs, high-power devices, high-performance sensors, and more. Different experimental studies have shown that using ²⁸Si materials with an abundance of over 99.85% to prepare semiconductor components can increase their thermal conductivity by 10%-60% compared to Si materials of natural abundance at room temperature. High abundance ²⁸Si is a key material for preparing long spin coherent time devices in the field of quantum information, which can remove interference from ²⁹Si. Silicon quantum bit is a promising quantum computing platform with advantages such as long coherence time, small device size, and compatibility with industrial manufacturing technology. In addition, ²⁸Si isotope can also be applied in metrology to define the exact values of the Avogadro constant and kilogram units. With SiH₄ as the medium, the separation of ²⁸Si isotope was studied by gas diffusion method in this paper. At present, research on the separation of silicon isotopes using cryogenic distillation methods (SiH₄, SiCl₄, or SiH₃CH₃ systems), gas centrifugation methods (SiF₄ or SiHCl₃), chemical exchange methods (systems of SiF₄ and different complexing agents), laser methods (Si₂F₆, SiF₄), and electromagnetic methods (SiH₄) has achieved certain results both domestically and internationally. However, industrial production of silicon isotopes has not yet achieved breakthroughs. The cryogenic distillation method for silicon isotopes has a smaller separation coefficient, while the gas centrifugation method has a lower efficiency in separating light gases. The laser separation method has a low yield and high cost, and its economic viability for industrial production is poor. Nowadays, low-cost and high-quality polymer organic membranes have been widely applied in industry. A high-speed maglev compressor used under negative pressure conditions can effectively compress SiH₄ gas. Compared to other potential separation media, SiH₄ has a relatively small molecular weight and a relatively large gas diffusion separation coefficient. The overall separation factor of SiH₄ can reach 1.010 measured through a 4-stage diffusion cascade experiment. Using multicomponent separation theory for cascade analysis and calculation, with natural SiH₄ as raw material, the ²⁸Si isotope abundance in light fractions can be concentrated to over 99% through a matched abundance ratio cascade (MARC) of no more than 300 stages. This study verifies the feasibility of diffusion separation of ²⁸Si isotope with SiH₄ as the medium.