Optimisation and scaling of interfacial GeO2 layers for high-k gate stacks on germanium and extraction of dielectric constant of GeO2

Germanium is an attractive channel material for MOSFETs because of its higher mobility than silicon. In this paper, GeO₂ has been investigated as an interfacial layer for high-k gate stacks. Thermally grown GeO₂ layers have been prepared at 550 °C to minimize GeO volatilization. GeO₂ growth has been performed in both pure O₂ ambient and O₂ diluted with N₂. GeO₂ thickness has been scaled down to 3.15 nm. MOS capacitors have been fabricated using different GeO₂ thicknesses with a standard high-K dielectric on top. Electrical properties and thermal stability have been tested up to at least 350°C. The k value of GeO₂ was calculated as 4.5. Interface state densities (D_it) of less than 10¹² cm^-2 eV¹ have been extracted for all devices using the conductance method.