Exfoliation of β-Ga2O3 Along a Non-Cleavage Plane Using Helium Ion Implantation

Abstract

An important step in the successful transfer of controlled thickness, wafer-scale β-Ga2O3 layers is demonstrated through exfoliation via helium ion implantation. He+ ions were implanted into epi-ready (010) β-Ga2O3 substrates at room temperature with an ion energy of 160 keV and a dose of 5 × 1016 cm−2. The implanted substrate was then annealed at 200°C followed by 500°C. The lower temperature step initiated He bubble nucleation while the higher temperature step promoted He bubble growth at the projected range beneath the substrate surface. No surface blistering was observed after the 200°C anneal. After the 500°C anneal step, micron-sized surface blistering covering the entire implanted area was observed, confirming exfoliation of β-Ga2O3 along a non-cleavage plane. Triple-axis X-ray diffraction ω:2θ measurements showed that after annealing at 500°C, the implantation-induced strain was removed. The ω scans showed some peak broadening after the low temperature step and more extensive broadening after the high temperature step; this observation corresponds to an increase in lattice plane tilt due to the formation of He bubbles at the projected range. Prior to annealing, scanning transmission electron microscopy images showed a dark contrast at the projected range due to the implantation of a high concentration of He ions. After the 500°C anneal, large cracks at the projected range were observed. These observations match early reports of silicon blistering which, when combined with established direct wafer bonding practices, is expected to lead to large-scale transfer of controlled thickness β-Ga2O3 layers along non-cleavage-plane orientations.