Optimisation and scaling of interfacial GeO2 layers for high-κ 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-κ gate stacks on germanium. Thermally grown GeO2 layers have been prepared at 550 °C to minimise GeO volatilisation. GeO2 growth has been performed in both pure O2 ambient and O2 diluted with N2. GeO2 thickness has been scaled down to approximately 3 nm. MOS capacitors have been fabricated using different GeO2 thicknesses with a standard high-κ dielectric on top. Electrical properties and thermal stability have been tested up to at least 350 °C. The κ value of GeO2 was experimentally determined to be 4.5. Interface state densities (Dit) of less than 1012 cm−2 eV−1 have been extracted for all devices using the conductance method.

► Scaling of thermal GeO2 thickness at 550 °C using N2 dilution.
► Physical characterisation of scaled GeO2 layers.
► Fabrication and testing of high-κ gate stacks on germanium using scaled interfacial GeO2.