Spatial charge distribution in as-deposited and UV-illuminated gate-quality nitrogen-rich silicon nitride

Gate-quality N-rich amorphous SiN/sub 1.6/:H films prepared by plasma-enhanced chemical vapor deposition (PECVD) at substrate temperatures of 250 and 400 degrees C are discussed. 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 t/sup 2/ before 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 of) the silicon/nitride interface. After UV illumination the distribution of the positive charge throughout the film is uniform. The bulk value of the positive photoinduced fixed charges is around 9*10/sup 16/ and 3*10/sup 16/cm/sup -3/ for N-rich films deposited at 250 and 400 degrees C, respectively.<
>