Capacitive effective thickness of a few nanometers by atomic layer deposition and device performance in Ge gate-all-around fin field effect transistors

Ge gate-all-around fin field-effect transistors (Ge FinFETs) with a capacitive effective thickness of a few nanometers have been successfully achieved via atomic-layer-deposited (ALD) high-dielectric Al₂O₃ on GeO₂/Ge and by adopting low-cost thermo ALD equipment. The MOS interface properties of the ZrO₂ or Al₂O₃/GeO₂/Ge structures have been studied systematically. It has been found that a GeO₂ interfacial layer that is greater than approximately 2.5 nm results in a significant degradation of the MOS interfaces, while an equivalent oxide thickness of <3 nm is still possible while maintaining good GeO₂/Ge interface quality. The Ge FinFET's value has been demonstrated with the Al₂O₃/GeO₂/Ge gate stack prepared using a thermal ALD layer of Al₂O₃. The experimental results indicate that the MOS interface quality obtained with the technique developed for high-permittivity/Ge gate stacks is also extremely useful for the fabrication of triangle-fin complementary metal oxide semiconductor devices. An I_on/I_off ratio of 3.2×10⁴ and a subthreshold swing of 103 mV/dec were obtained for the triangular n-type Ge gate-all-around FET with (111) sidewalls. The drain current at V_GS-V_T=V_DS=-1.5 V is 88 mA/mm.