Microscopic Understanding of PBTI and NBTI Mechanisms in High-k / Metal Gate Stacks

Abstract

We have established a comprehensive understanding of the PBTI and NBTI reliability of high-k/metal gate stacks. PBTI is found to exhibit a universal relationship, in terms of fast transient carrier traps and stress voltage, due to the formation of positive oxygen vacancies near cathode. The use of metal gates for T inv scaling is promising for the improvement of drain current without PBTI lifetime degradation. However, in the case of NBTI, interface state degradation becomes more serious with T inv scaling. Thus, the use of a high quality interfacial layer, such as a wet oxide interface, is a promising solution for the improvement of NBTI lifetime.

Correlation of Negative Bias Temperature Instability and Breakdown in HfO2/TiN Gate Stacks

“…Figure 4(a) shows the activation energy (E a ) extracted from NBTI measurements performed on various samples with different high-k thickness and IL. The defects generated are typical of the Frenkel-pair with Vo ++ (18). Gate stacks with 3 nm and 5 nm HfO 2 and identical chemical oxide IL have demonstrated almost same E a (around 0.07 eV).…”

“…This lower E a of chemical oxide IL (0.07 eV) compared to ISSG IL (0.09 eV) indicates higher concentration of defects in the interfacial layer because the quality of IL plays an important role. In addition, suppression of electron current during gate injection towards silicon substrate beyond the SiO 2 interface layer by a high quality interfacial layer is considered for NBTI improvement (18). The inferior quality of the chemical oxide also tends to dominate the defect generation process in the gate stack.…”