Charge trapping properties in thin oxynitride gate dielectrics prepared by rapid thermal processing

Abstract

In this letter, effects of post-nitridation anneals on charge trapping properties and charge-to-breakdown (Qbd) of thin (∼8.6 nm) rapidly thermal nitrided (RTN) gate SiO2 have been studied. Post-nitridation anneals consist of either rapid thermal reoxidation (RTO) in pure O2 or rapid thermal anneal (RTA) in pure N2 ambient. Both the gate voltage shift (ΔVg) and flatband voltage shift (ΔVfb) have been used to characterize the charge trapping properties under Fowler–Nordheim electron injection. It is found that both RTO and RTA reduce ΔVfb and/or ΔVg resulting from the reduction of trapped electrons as well as high-field stress-induced positive charge generation. Positive charge generation resulting from either donor-type interface state generation or trapped holes is discussed. Qbd of RTN SiO2 has been improved after RTO, and can be even larger than that of the thermal SiO2. RTA of RTN SiO2 in N2 also improves Qbd; however, the charge trapping behavior is different from that of RTO/RTN SiO2. The physical mechanism is discussed to account for the observation.