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A pFET threshold-voltage (Vt) 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. HfSiOpropcapped with 9 Aring of thin Al2O3obtains a low long-channel Vt of -0.37 V (the lowest among those with TiN gate), a high mobility of 59 cm2 /V ldr s at 0.8 MV/cm (92% of universal value), a negligible equivalent- oxide-thickness (EOT) increase of 0.1 Aring (compared to the uncapped reference), and a low Vt 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 thin Al2O3obtains caps are beneficial to the pFET applications. In contrast, nitrogen incorporation in the Al2O3-capped HfSiOprop is not favorable because it increases the Vt by 50-140 mV, degrades the mobility by 10%-22%, increases the EOT by 0.5-0.8 Aring and the Vt instability by 5-13 mV, and reduces the NBTI lifetime by four to five orders of magnitude. Compared to postcap nitridation, high-k nitridation results in more severe degradation of these properties by incorporating nitrogen closer to the Si/SiO2 interface.
Date of Publication: Oct. 2007