Epitaxial SrO interfacial layers for HfO2–Si gate stack scaling

We discuss the structural and electrical properties of scaled 2 nm HfO2/SrO gate stacks. Thin SrO layers are deposited by molecular beam epitaxy onto (001) p-Si substrates as alternative passivating interfacial layers (ILs) to SiO2. X-ray photoelectron spectroscopy and transmission electron microscopy show that, despite some HfO2–SrO intermixing, the SrO IL acts as a barrier against HfxSiy and SiO2 formation during high-κ deposition. Electrical measurements on metal-oxide-semiconductor capacitors with TiN metal gates integrated in a low-temperature process flow reveal an equivalent oxide thickness of 5 Å with competitive leakage current and hysteresis and a negative flat band voltage shift, suitable for n-channel transistors.