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【Device Papers】Formation of High-Quality SiO₂/β-Ga₂O₃ Mos Structures by Combination of Post-Deposition and Post-Metallization Annealing
日期：2025-12-08阅读：55
Researchers from the The University of Osaka have published a dissertation titled "Formation of High-Quality SiO2/Β-Ga2O3 Mos Structures by Combination of Post-Deposition and Post-Metallization Annealing" in ECS Meeting Abstracts.
Abstract
Gallium oxide (Ga2O3), with its ultra-wide bandgap and high breakdown electric field, is well-suited for power semiconductor devices. Although SiO2 offers superior thermal stability and a larger band offset with Ga2O3, its application as a gate dielectric remains less explored compared to Al2O3, which is more commonly reported. In particular, the effect of annealing treatment on the performance and reliability of MOS devices constitutes a highly significant area of investigation. In the present study, the impact of post-deposition annealing (PDA) and post-metallization annealing (PMA) on SiO2/β-Ga2O3 MOS devices was thoroughly investigated.
N-type β-Ga2O3(001) epilayers (effective donor concentration (ND): 1×1016 cm-3) were wet-cleaned, and approximately 30–50 nm of SiO2 films were deposited by plasma-enhanced chemical vapor deposition. Subsequently, PDA was performed in O2, N2, or sequentially in O2 followed by N2 (O2-, N2-, or O2→N2-PDA) at temperatures of 600–1000°C. After that, nickel electrodes were deposited onto the samples, followed by PMA in a H2(3%)/N2 ambient at 200–400ºC. Finally, aluminum electrodes were deposited on the backside of the samples to form MOS capacitors.
First, the effects of PDA under various conditions were investigated without performing PMA. While the 1-MHz capacitance–voltage (C–V) characteristics of as-deposited samples exhibited large stretch-out and hysteresis due to electron traps, the samples after O2-, N2- or O2→N2-PDA treatments at 1000ºC showed improved characteristics. The interface state density evaluated by the high (1 MHz)–low method for the as-deposited, O2-PDA, N2-PDA, and O2→N2-PDA samples were 7.0 × 1011, 4.0 × 1011, 3.0 × 1011, and 1.0 × 1011 eV−1cm−2, respectively, near the conduction band edge of Ga2O3 (i.e., EC − E = 0.2 eV). While O2- and N2-PDA individually improved the interface properties, the combined treatment yielded even better results. Moreover, applying O2- or N2-PDA separately was found to introduce certain drawbacks. When O2-PDA was performed alone, an order-of-magnitude reduction in the ND in near-interface region of Ga2O3 epilayers was observed, as revealed by the 1/C2-V plots. The plausible origins of ND reduction are oxygen interstitials and/or gallium vacancies, which are preferentially formed under oxygen-rich conditions and act as acceptor-type defects in Ga2O3, as suggested by previous theoretical studies. N2-PDA did not induce a similar reduction in ND; moreover, it was found to effectively mitigate the carrier compensation caused by O2-PDA and restore ND to its initial value. However, when N2-PDA was carried out alone, the onset oxide field for gate leakage current was as low as approximately 4 MVcm-1. On the contrary, the O2- and O2→N2-PDA samples showed improved dielectric properties with an onset field for leakage of approximately 6 MVcm-1. This result indicates the necessity of O2-PDA in improving the quality of SiO2 dielectric. Overall, the combination of O2- and N2-PDA (O2→N2-PDA) offers a practical approach in improving both the interface and dielectric properties while preserving the initial ND profile in Ga2O3.
Then, H2/N2-PMA was additionally performed to the sample subjected to combined O2- and N2-PDA treatment. A steep 1-MHz C–V characteristics with a negligible hysteresis of about 0.03 V was observed after the additional PMA treatment at 400ºC. The resulting Dit value at EC − E = 0.2 eV was 4.0 × 1010 eV−1cm−2, indicating a substantial improvement in the interface properties. Since the H2/N2-PMA was found to be effective even at a low temperature of 200ºC, the defects remaining after high-temperature PDA treatments are likely dangling-bond-type defects, which can be passivated by hydrogen atoms with a low reaction energy barrier. Finally, we investigated the reliability of MOS devices subjected to H2/N2-PMA. In the reliability tests, a constant positive gate voltage stress corresponding to an oxide field of 4 MV/cm was applied up to 2000 s to monitor the change in the C–V characteristics. While the as-deposited sample exhibited a large flatband voltage drift (ΔVFB) of about 8 V after 2000 s of stress, the ΔVFB was remarkably reduced to about 1 V after O2→N2-PDA and H2/N2-PMA treatments.
In summary, the present study systematically investigated the effect of PDA and PMA treatments to SiO2/Ga2O3 MOS structures and revealed that the combination of O2→N2-PDA and H2/N2-PMA enables to form MOS devices with improved interface properties and reliability.
DOI：
https://doi.org/10.1149/MA2025-02373522mtgabs
