Narrowing the field of high-k gate dielectrics: intrinsic electronically-active bonding defects in nanocrystalline transition metal oxides

Abstract

Gate dielectrics comprised of nanocrystalline HfO2 in gate stacks with thin SiO2/SiON interfacial transition regions display significant asymmetries with respect to trapping of Si substrate injected holes and electrons. Based on spectroscopic studies, and guided by ab initio theory, electron and hole traps in HfO2 and other transition metal elemental oxides are assigned to O-atom vacancies and possibly interstitials as well. These may be clustered at internal grain boundaries. Three potential engineering solutions for defect reduction are identified: i) deposition of ultra-thin, Lt 2 nm, HfO2 dielectric layers, in which grain boundary formation is suppressed by effectively eliminating inter-primitive unit cell-bonding interactions, ii) chemically phase-separated high HfO2 content silicates in which inter-primitive unit cell pi-bonding interactions are suppressed by nanocrystalline grain size limitations resulting from SiO2 inclusions and/or film thickness, and iii) non-crystalline Ti/Zr/Hf Si oxynitrides without grain boundary defects. However, each of these potential engineering solution dielectrics displays pre-existing as well as stress- induced defects.