Universal Correlation Between Mobility and NBTI on Advanced High-K/Metal Gate Stacks

Negative Bias Temperature Instabilities (NBTI) and mobility were extensively studied on a wide range of technological options for advanced CMOS gate stack technologies including pure HfO2, silicates, nitrided silicates, HfZr compounds; metal gates included TiN, TaN, TaC, WN with various deposition modes and thicknesses; bottom oxide was pure SiO2 or SiON. The effect of Nitrogen on the two main components of NBTI, fast reversible and slow, is first investigated. Then we show that NBTI and mobility show extensive process variations leading in worst case to bad drivability and reliability. The cause was clearly identified as the Nitrogen incorporated in the stack with cumulative effects with the various process steps. The importance of metal gate is particularly emphasized. By controlling the amount of N in the layers, it is possible to obtain a mobility close to 100% of the universal SiO2 mobility as well as a good reliability.