Towards Controlled Transfer of (001) β-Ga2O3 to (0001) 4H-SiC Substrates

Abstract

We demonstrate successful blistering of He-implanted (001) β-Ga2O3, bonding to (0001) 4H-SiC, and initial results towards large-area transfer of (001) β-Ga2O3 to 4H-SiC. Compatible with large-scale processing, exfoliation is an important step in controlled-thickness transfer of films for heterogeneous integration. Furthermore, integration of β-Ga2O3 to high thermal conductivity materials will be crucial for thermal management of β-Ga2O3-based power devices. Two-inch (001) β-Ga2O3 wafers were implanted with He+ at an energy of 160 keV and a dose of 5×1016 cm-2, which are the same implant parameters used previously to successfully exfoliate (010) β-Ga2O3.1 Strain fringes were observed after the implant which corresponded to a maximum strain of ~1.7%, which is higher than the ~1% strain when implanting (010) β-Ga2O31 likely due to the larger Poisson’s ratio of (001) β-Ga2O3.2 The implanted substrates were then bonded to (0001) 4H-SiC at room temperature using a ~5 nm thin Ti interlayer to assist with the bond. Both unbonded implanted substrates and the bonded structures were first annealed at 200 °C for 10 hours to simultaneously initiate He bubble nucleation at the implanted projected range (~0.68 μm) and strengthen the bond. Then, even after annealing at 500 °C for 10 hours to initiate He bubble growth, the (001) β-Ga2O3 did not transfer to the (0001) 4H-SiC. Unlike what was observed for (010) β-Ga2O3,1 blistering did not even occur at this temperature. Annealing at 800 °C for up to 12 hours resulted in ~10 μm blisters for the unbonded substrates, which is typically an indication that large wafer-area transfer can be achieved if bonding was done prior to annealing.3 However, the β-Ga2O3 substrate did not wafer split from the bonded structure, and instead only small area transfers up to ~200 μm were achieved. Only ~7% of the total bonded area transferred while the entire structure remained bonded. Strategies to improve transfer will be presented, including initiating a cold split prior to exfoliation and refined annealing strategies to improve He bubble nucleation and larger bubble growth at the projected range. These are promising results towards achieving large wafer-scale (001) β-Ga2O3 composite wafers, and when combined with subsurface damage-free chemical mechanical polishing,4 these composite wafers would be suitable for subsequent devices and/or epitaxial growth.The authors would like to acknowledge the support from the Office of Naval Research through a MURI program, grant No. N00014-18-1-2429. This research was performed while M.E.L. and J.S.L. held an NRC Research Associateship award at the U.S. Naval Research Laboratory.References M.E. Liao, et al., ECS J. Solid State Sci. Technol., 8(11), P673 (2019).K. Adachi, et al., J. Appl. Phys., 124, 085102 (2018).M. Bruel, et al., Jpn. J. Appl. Phys., 36, 1636 (1997).M.E. Liao, et al., J. Vac. Sci. Technol. A, 41, 013205 (2023). Figure 1