Epitaxial strontium oxide layers on silicon for gate-first and gate-last TiN/HfO₂ gate stack scaling

We show that a thin epitaxial strontium oxide (SrO) interfacial layer enables scaling of titanium nitride/hafnium oxide high-permittivity (high-k) gate stacks for field-effect transistors on silicon. In a low-temperature gate-last process, SrO passivates Si against SiO2 formation and silicidation and equivalent oxide thickness (EOT) of 5 is achieved, with competitive leakage current and interface trap density. In a gate-first process, Sr triggers HfO2-SiO2 intermixing, forming interfacial high-k silicate containing both Sr and Hf. Combined with oxygen control techniques, we demonstrate an EOT of 6 with further scaling potential. In both cases, Sr incorporation results in an effective workfunction that is suitable for n-channel transistors. © 2011 Elsevier B.V. All rights reserved.