Optimisation and scaling of interfacial GeO_2 layers for high-K: gate stacks on germanium and extraction of dielectric constant of GeO_2

摘要

Germanium is an attractive channel material for MOSFETs because of its higher mobility than silicon. In this paper, GeO_2 has been investigated as an interfacial layer for high-κ gate stacks on germanium. Thermally grown GeO_2 layers have been prepared at 550 ℃ to minimise GeO volatilisation. GeO_2 growth has been performed in both pure O_2 ambient and O_2 diluted with N_2. GeO_2 thickness has been scaled down to approximately 3 nm. MOS capacitors have been fabricated using different GeO_2 thicknesses with a standard high-κ dielectric on top. Electrical properties and thermal stability have been tested up to at least 350 ℃. The κ value of GeO_2 was experimentally determined to be 4.5. Interface state densities (D_it) of less than 10~(12) cm~(-2) eV~(-1) have been extracted for all devices using the conductance method.