DG: NBTI mechanisms

NBTI remains one of the critical reliability issues for the devices with the advanced gate stacks, both ultra-thin SiON and metal/high-k. While the leading NBTI mechanism in SiON is still a subject of intense debates, high-k stack introduces additional complexity to the instability evaluation. Since a silicon dioxide layer is a common component in both types of gate stacks, understanding instability processes in SiON may provide clues to the research on the degradation mechanisms in high-k dielectrics.

This discussion is intended to facilitate exchange of ideas on feasibility of certain processes, which potentially may contribute to NBTI. We may focus on several important questions:

· Bulk charges and interface traps generation/relaxation in SiON

- Under what conditions (stress voltage, precursor defects, etc.) one may expect bulk charge generation? What is the process?

- Can the bulk charges and interface traps generation (relaxation) processes correlate or they are independent processes?

- What might be a possible mechanism for the observed ultra-fast relaxation component? Same mechanism covers the total relaxation time range (about 10 orders of magnitude) or different processes are responsible for relaxation within a specific time interval?

· Instability in high-k gate stacks

- How might high-k layer contribute to bulk charging, interface trap generation, H diffusion? Hole trapping in the high-k layer? High-k –induced precursor defects near the interface with the substrate?

- Any high-k-related specifics in NBTI or the processes are very similar to those in SiON?

Gennadi Bersuker