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 of nitrogen thus accelerates NBTI. (C) 2002 American Institute of Physics.