The degradation of TDDB characteristics of Si0/sub 2//Si/sub 3/N/sub 4//Si0/sub 2/ stacked films caused by surface roughness of Si/sub 3/N/sub 4/ films (DRAMs)

The effect of surface roughness of Si/sub 3/N/sub 4/ films on time-dependent dielectric breakdown (TDDB) characteristics of SiO/sub 2//Si/sub 3/N/sub 4//SiO/sub 2/ (ONO) stacked films was investigated. The surface roughness of Si/sub 3/N/sub 4/ films-was found to become higher with increasing deposition temperature and to cause the degradation of TDDB characteristics of ONO films in DRAMs. A local thinning of ONO films, evaluated from the TDDB characteristics, agreed with the surface roughness measured by atomic force microscopy (AFM) and cross-sectional transmission electron microscopy (XTEM). Dependence of time to breakdown of ONO films on the deposition conditions was interpreted by electric field intensification due to the surface roughness of Si/sub 3/N/sub 4/ films.<
>