Towards Controlled Transfer of (001) β-Ga2O3 to (0001) 4H-SiC Substrates
Authors: Liao Michael Evan , Huynh Kenny , Carson Brandon , Matto Lezli , Pan Kaicheng , Lundh James Spencer , Tadjer Marko , Hobart Karl D. , Goorsky Mark S. 
Published: February 2024

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

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M.E. Liao, et al., J. Vac. Sci. Technol. A, 41, 013205 (2023).

Figure 1