Exfoliation of β-Ga₂O₃Along 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.

Thermal Transport across Ion-Cut Monocrystalline β-Ga2O3 Thin Films and Bonded β-Ga2O3–SiC Interfaces

“…To evaluate the strain variation before and after annealing in N 2 , we performed triple-axis X-ray diffraction (XRD) measurements on Samp1 and Samp2, as shown in Figure a,b. The hydrogen implantation elastically distorts the lattice through the introduction of point defects (lattice vacancies, knocked-on Ga and O, intercalated H) and can introduce measurable strain. − Figure a shows the triple-axis diffraction, and the peaks are relative to the (0004) 4H–SiC. The peaks near ∼−30,000 arcsec are from the β-Ga 2 O 3 layers; this large offset shows the angular difference between the ( 2 01) β-Ga 2 O 3 peak and the (0004) 4H–SiC peak.…”

“…The thin-film exfoliation can be achieved by either hydrogen or helium ion implantation. 29 In the present study, the β-Ga 2 O 3 wafers were implanted by hydrogen ions (H + ) with an energy of 35 keV and an implantation dose of around 1 × 10 17 cm −2 at room temperature. The ion implantation was carried out with a 7°tilt to minimize the ion-channeling effect.…”

Thermodynamics of Ion-Cutting of β-Ga2O3 and Wafer-Scale Heterogeneous Integration of a β-Ga2O3 Thin Film onto a Highly Thermal Conductive SiC Substrate

“…A convenient method to investigate the thermodynamics of the ion-cutting of β-Ga 2 O 3 is to inspect the blistering on the β-Ga 2 O 3 surface after post-implantation annealing without bonding the implanted Ga 2 O 3 samples to a handle wafer. Liao et al 27 investigated the blistering of β-Ga 2 O 3 bulk wafer by He implantation with an energy of 150 keV and fluence of 5 × 10 16 cm −2 , while the exfoliation of β-Ga 2 O 3 thin film was not demonstrated. Generally, due to the larger atomic radius, He ion implantation induces more defects in the materials in comparison with H ion implantation.…”

“…Xu et al 25 and Lin et al 26 reported the wafer bonding of β-Ga 2 O 3 wafer onto n-type 4H-SiC and polycrystalline SiC, respectively. Liao et al 27…”

Ion implantation in β-Ga2O3: Physics and technology

“…In Ref. 71 , the formation of bubbles in β-Ga 2 O 3 (010) upon implantation of He + ions with Е = 160 keV and D = 5×10 16 cm -2 , followed by annealing at 200 °С and then at 500 °С was studied using XRD, TEM, and AFM methods. The growth of bubbles known as blistering and the formation of cracks were the main processes leading to the exfoliation of implanted Ga 2 O 3 layer.…”