The conventional theory of work functions (Schottky barriers) does not work at pure-metal/high-k-dielectrics interfaces. This occurs due to the selective interface atom bonding reflecting the large ionicity of high-k materials and the characteristic density of pmetal electronic states. Taking into accounts these features, we have constructed a new theory of work functions based on a concept of generalized charge neutrality levels. This theory systematically explains work functions of various gate materials on high-k dielectrics, in particular the unusual behavior of p-metal work functions, and naturally reproduces band offsets at various semiconductor/semiconductor interfaces.

No abstract

Recent development of VLSI technique requires wide variety of controlled interfaces especially in high-k metal gate technologies. As for metal/dielectric interfaces, they have been intensively studied for a long time, and a lot of knowledge and concepts have been proposed so far. In this paper, we point out the breakdown of the two Schottky barrier limits (Bardeen and Schottky limits) which have been believed for a long time as the essential limits of Schottky barrier heights, by considering the electronic and the atomistic structures of metal/insulator interfaces. Moreover, we have experimentally confirmed the breakdown of the Schottky limit.

We have theoretically investigated poly-Si and metal gates on Hf-related high-k gate dielectrics. First, we have investigated the cause of the substantial threshold voltage (V th ) shifts observed in Hf-related high-k gate stacks with p+poly-Si gates. The oxygen vacancy (Vo) level in ionic HfO 2 is located in a relatively higher part of the band gap. If the p+poly-Si-gate is in contact with HfO 2 , Vo formation in the HfO 2 induces a subsequent electron transfer across the interface because of the higher energy level position of Vo, causing a substantial V th shifts in p+poly-Si gate MISFETs. Next, we also investigate the microscopic electronic structures at metal gates/HfO 2 interfaces. We have found that the wave functions of metal induced gap states (MIGS) have large amplitudes both around Hf and O atoms, which may be the cause of unusual work function behaviors of p-like metals.

No abstract