Isotopically Enriched Layers for Quantum Computers Formed by ²⁸Si Implantation and Layer Exchange

High Resolution Image Download MS PowerPoint Slide 28 Si enrichment is crucial for production of group IV semiconductor-based quantum computers. Cryogenically cooled, monocrystalline 28 Si is a spin-free, vacuum-like environment where qubits are protected from sources of decoherence that cause loss of quantum information. Currently, 28 Si enrichment techniques rely on deposition of centrifuged SiF 4 gas, the source of which is not widely available, or bespoke ion implantation methods. Previously, conventional ion implantation into natural Si substrates has produced heavily oxidized 28 Si layers. Here we report on a novel enrichment process involving ion implantation of 28 Si into Al films deposited on native-oxide free Si substrates followed by layer exchange crystallization. We measured continuous, oxygen-free epitaxial 28 Si enriched to 99.7%. Increases in isotopic enrichment are possible, and improvements in crystal quality, aluminum content, and thickness uniformity are required before the process can be considered viable. TRIDYN models, used to model 30 keV 28 Si implants into Al to understand the observed post-implant layers and to investigate the implanted layer exchange process window over different energy and vacuum conditions, showed that the implanted layer exchange process is insensitive to implantation energy and would increase in efficiency with oxygen concentrations in the implanter end-station by reducing sputtering. Required implant fluences are an order of magnitude lower than those required for enrichment by direct 28 Si implants into Si and can be chosen to control the final thickness of the enriched layer. We show that implanted layer exchange could potentially produce quantum grade 28 Si using conventional semiconductor foundry equipment within production-worthy time scales.