Positive charge generation in thin SiO2 films during nitridation process

Abstract

Thin SiO2 films, ranging from 5 to 15 nm in thickness, were annealed in NH3 (99.999%) in a polycrystalline silicon reactor. Generation of positive charge during the initial period of nitridation was found. Large negative flatband (ΔVfb) shift (∼0.56 V) was found for films annealed in NH3 for short periods of time (10 min). The amount of capacitor-voltage (C-V) shift decreased sharply as the annealing time increased from 10 to 30 min and then decreased very slowly for annealing time >30 min. The value of the initial negative flatband shift (10 min annealing) increased with increasing SiO2 film thickness. Generation of positive charge near the SiO2/Si interface during the initial period of nitridation is proposed. From the amount of C-V and current-voltage (I-V) shifts, a charge density of 2×1011 cm−2 and a charge center ∼2.4 nm away from the SiO2/Si interface were estimated for the 10-nm SiO2 films annealed in NH3 for 10 min.