Spatial Charge Distribution in As-Deposited and UV-Illuminated Gate-Quality Nitrogen-Rich Silicon Nitride

Gate-quality N-rich silicon nitride films have been prepared by means of plasma-enhanced chemical vapor deposition (PECVD) at substrate temperatures of 250 and 400°C. Films of different thicknesses t, ranging from 20 to 1100 nm, were obtained by varying the deposition time. The flat-band voltage shift was found to be proportional to t and t2before and after UV illumination, respectively. The linear dependence before illumination suggests a centroid of the positive charge located close to (within a region narrower than 20 nm) the silicon/nitride interface. After UV illumination the distribution of positive charge throughout the film is uniform. The bulk value of the positive photoinduced fixed charges is around 9 × 1016 and 4 × 1016 cm-3 for N-rich films deposited at 250 and 400°C, respectively. © 1989 IEEE