A Tantalum Nitride (TaNx) metal gate complementary metal oxide semiconductor (CMOS) technology using low-resistivity (∼ 15 μΩcm), bcc(body-centered-cubic)-phase tantalum metal layer has been developed, featuring low-temperature processing below 550°C except for gate oxide formation. It was found for the first time that TaNx works not only as a buffer layer which prevents tantalum metal film and gate oxide film from reaction with each other, but also as a seed layer which helps self-growth of bcc-phase tantalum films by hetero-epitaxy. Furthermore, we have demonstrated that the work function of TaNx gate is close to midgap of silicon, hence similar to Titanium Nitride (TiNx) gate. We have also demonstrated that MOS capacitors on bulk and fully-depleted silicon-on-insulator(FDSOI) CMOS with TaNx/bcc-Ta/TaNx stacked metal gate structure have excellent electrical characteristics and that the ring-oscillator fabricated using the stacked metal gate CMOS can be operated successfully with 3.8 nm-thickness gate oxide.
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