Effects of Al2O3 Dielectric Cap and Nitridation on Device Performance, Scalability, and Reliability for Advanced High-k/Mëtal Gate pMOSFET Applications.

A pFET threshold-voltage (V_t) reduction of about 200 mV is demonstrated by inserting a thin Al₂O₃ layer between the high-K dielectric and the TiN gate without noticeable degradation of other electrical properties. HfSiO_x capped with 9 Å of Al₂O₃ obtains a low long-channel V_t of —0.37 V (the lowest among those with TiN gate), a high mobility of 59 cm² ⁄V · s at 0.8 MV/cm (92% of universal value), a negligible equivalent. oxide-thickness (EOT) increase of 0.1 Å (compared to the uncapped reference), and a low V_t instability of 4.8 mV at 7 MV/cm. It also passes the ten-year negative-bias-temperature-instability (NBTI) lifetime specification with a gate overdrive of —0.7 V. This indicates that Al₂O₃ caps are beneficial to the pFET applications. In contrast, nitrogen incorporation in the Al₂O₃-capped HfSiO_x is not favorable because it increases the V_t by 50—140 mV, degrades the mobility by 10%-22%, increases the EOT by 0.5—0.8 Å and the V_t instability by 5–13 mV, and reduces the NBTI lifetime by four to five orders of magnitude. Compared to postcap nitridation, posthigh-k nitridation results in more severe degradation of these properties by incorporating nitrogen closer to the Si/SiO₂ interface. [ABSTRACT FROM AUTHOR]