High Temperature Oxide for NVM Interpoly Dielectric Applications

High quality interpoly dielectrics are required for non-volatile memories (NVM) in order to achieve long term data retention and endurance over many program/erase cycles. LPCVD high temperature oxide (HTO) deposited at 800°C-900°C is investigated for use in oxide-nitride-oxide (ONO) interpoly dielectric stacks. HTO allows for reduced thermal budgets, improved conformal coverage at edge features and more flexibility in scaling the ONO stack compared to thermal oxide layers. SIMS and atomic force microscopy results indicate that smooth, high quality films are deposited with a rms roughness of 0.12nm. Etch rates of as-deposited films are lowered 35% following several densification anneals. Field strengths (at 1μA) of 7-8MV/cm and leakage currents in the pA range are measured. Centroid measurements on sressed oxides show traps to be located at the HTO/polysilicon interfaces. Finally, double poly flash memory cells fabricated with ONO stacks containing HTO top oxide show improved field strength and data retention.