Process Conditions for Low Interface State Density in Si-passivated Ge Devices with TmSiO Interfacial Layer

Abstract

In this work we study the epitaxial Si growth with Si2H6 for Ge surface passivation in CMOS devices. The Si-caps are grown on Ge in the hydrogen desorption limited regime at a nominal temperature of 400 °C. We evaluate the process window for the interface state density and show that there is an optimal Si-cap thickness between 8 and 9 monolayers for Dit < 5·1011 cm−2 eV−1. Moreover, we discuss the strong impact of the Si-cap growth time and temperature on the interface state density, which arises from the Si thickness dependence on these growth parameters. Furthermore, we successfully transfer a TmSiO/Tm2O3/HfO2 gate stack process from Si to Ge devices with optimized Si-cap, yielding interface state density of 3·1011 eV−1 cm−2 and a significant improvement in oxide trap density compared to GeOx passivation.