Improved memory performance of metal–oxide–nitride–oxide–silicon by annealing the SiO_2 tunnel layer in different nitridation atmospheres

摘要

Metal–oxide–nitride–oxide–silicon (MONOS) capacitors with thermally grown SiO_2 as the tunnel layer are fabricated, and the effects of different ambient nitridation (NH_3, NO and N_2O) on the characteristics of the memory capacitors are investigated. The experimental results indicate that the device with tunnel oxide annealed in NO ambient exhibits excellent memory characteristics, i.e. a large memory window, high program/erase speed, and good endurance and retention performance (the charge loss rate is 14.5% after 10 years). The mechanism involved is that much more nitrogen is incorporated into the tunnel oxide during NO annealing, resulting in a lower tunneling barrier height and smaller interface state density. Thus, there is a higher tunneling rate under a high electric field and a lower probability of trap-assisted tunneling during retention, as compared to N_2O annealing. Furthermore, compared with the NH3-annealed device, no weak Si–H bonds and electron traps related to the hydrogen are introduced for the NO-annealed devices, giving a high-quality and high-reliability SiON tunneling layer and SiON/Si interface due to the suitable nitridation and oxidation roles of NO.