High dielectric constant oxides

TLDR

The scaling of CMOS transistors has thinned the SiO₂ gate dielectric to ~1.4 nm, causing excessive leakage, and little was known about high‑K oxides, which often crystallise and contain many electronic defects. The goal is to replace SiO₂ with thicker high‑K oxides such as hafnium oxide and hafnium silicate, and intensive research is underway to develop these materials into high‑quality electronic components. This review surveys the selection, structural and metallurgical properties, deposition processes, interface reactions, electronic structure, band offsets, defect behaviour, and performance of high‑K oxides, including their application in DRAM capacitors.

Abstract

The scaling of complementary metal oxide semiconductor (CMOS) transistors has led to the silicon dioxide layer used as a gate dielectric becoming so thin (1.4 nm) that its leakage current is too large. It is necessary to replace the SiO2 with a physically thicker layer of oxides of higher dielectric constant (κ) or ‘high K’ gate oxides such as hafnium oxide and hafnium silicate. Little was known about such oxides, and it was soon found that in many respects they have inferior electronic properties to SiO2, such as a tendency to crystallise and a high concentration of electronic defects. Intensive research is underway to develop these oxides into new high quality electronic materials. This review covers the choice of oxides, their structural and metallurgical behaviour, atomic diffusion, their deposition, interface structure and reactions, their electronic structure, bonding, band offsets, mobility degradation, flat band voltage shifts and electronic defects. The use of high K oxides in capacitors of dynamic random access memories is also covered.