High-κ/metal gate for advanced transistor applications

Abstract

Advanced HfO2 high-κ materials have been developed to replace SiO2 as the gate dielectrics. The Electronic structures consisting of various HfO2/SiO2/Si-substrate gate stacks have been characterized. The hafnium silicate formed at the HfO2/SiO2 interface is found to play a key role in generating an internal electric field established by interface dipoles. It is found that the variation of the interface dipole with the applied gate voltage results in hysteresis between the forward and reverse CV curves. The magnitude of this hysteresis is observed to be dependent on the viscosity of the local oxide network, the dipole elasticity, the gate-oxide thickness, and the pulse ramp rate. GaN has attracted much attention in replacing silicon in high-power transistors. However, an unavoidable formation of GaOx is the source of charged states which degrade the performance of transistors. It is found that the application of trimethylaluminum-only cycles could convert GaOx into Al2O3. However, a lower limit on the thickness of the resultant Al2O3 layer is necessary to block oxidizing agents during subsequent Al2O3 deposition. Further, it is observed that GaOx layer undergoes a structural change after an elevated-temperature annealing, resulting in a reduction in the Al2O3/GaN-interface defect density.