Rare-earth oxide/TiN gate stacks on high mobility strained silicon on insulator for fully depleted metal-oxide-semiconductor field-effect transistors

Abstract

We demonstrate the integration of TbScO3, LaScO3, and LaLuO3 as alternative gate oxides for fully depleted silicon on insulator (SOI) and strained SOI metal-oxide-semiconductor field-effect transistors (MOSFETs) with equivalent oxide thicknesses of 2.8, 2.4, and 1.55 nm, respectively. Silicate formation at the high-κ/Si interface was studied by x-ray photoelectron spectroscopy. Electrical investigations revealed good transistor performance with these novel gate oxides with permittivities in the range of 26–32 and TiN as a metal gate. Steep inverse subthreshold slopes of 72 mV/dec, high Ion/Ioff ratios over 108, and a low density of interface states of ≈5×1011 (eV cm2)−1 were achieved. MOSFETs on SOI substrates show good low field electron mobilities of 180, 183, and 188 cm2/V s for all investigated oxides. For devices on strained SOI the electron mobility was improved by a factor of 2. The measured mobilities are close to those of devices with HfO2 as gate dielectric, while offering better electrostatic control due to their higher permittivities.