On the formation of positive charges in ultrathin silicon-oxynitride p-MOSFETs subjected to negative bias temperature stress

p-MOSFET negative bias temperature instability (NBTI) has become the most important reliability issue for the CMOS industry. This letter investigates the formation of oxide positive charges (PCs) and its effects on the NBTI. Evidence shows that PC dominates NBTI at stress temperature lower than 373 K, whereas interface-state generation has an obvious contribution above 373 K. Two kinds of PC are distinguished as follows: The trapped holes are the main origin of NBTI at lower temperatures, and the generated PC plays a role at higher temperatures. The physical mechanisms of the two kinds of PC are also discussed in this letter.