Effect of nitrogen at SiO2/Si interface on reliability issues—negative-bias-temperature instability and Fowler–Nordheim-stress degradation

Degradation process of a metal–oxide–semiconductor (MOS) structure with NO-nitrided SiO2 under negative-bias-temperature (NBT) and Fowler–Nordheim (FN) stresses has been investigated. The FN stress immunity improves with increasing nitrogen concentration at the SiO2/Si interface, while the incorporation of excess nitrogen (more than 3 at. %) at the SiO2/Si interface accelerates NBT instability (NBTI). This stronger immunity of NO-nitrided SiO2 under FN stress is due to the stronger Si–N bonds formed by NO nitridation at the interface. Without hydrogen annealing to form Si–H bonds, the MOS capacitors do not show NBTI. This indicates that the Si–N bonds are not broken under NBT stress and the main cause of the NBTI is the breaking of the Si–H bonds. The NO nitridation decreases the number of Si–H bonds and thus suppresses NBTI. However, nitrogen provides hole-trap centers. Hydrogen at the interface is dissociated and bonds to the hole-trapping nitrogen, so interface traps are left behind. An excess amount o...