High-k Materials in Flash Memories

The scaling down of Flash memories can be pursued using theconventional stacked gate architecture only with major changesof the active dielectrics, mainly the inter-poly dielectric(IPD).The required 4-6 nm EOT thickness for the IPD cannot beachieved by the conventional ONO (Oxide-Nitride-Oxide)technology which starts failing in the 10-12 nm range in termsof charge retention properties. Therefore high-k materials arecurrently investigated for IPD formation in future Flashmemories. It is worth noticing that the requirements for IPD arevery different from those of the gate dielectrics used inlogics. Alumina and alumina based materials (like hafniumaluminates) are among the possible candidates. Promising andtunable electrical and structural properties are achieved forthese materials by varying the high-k stack chemicalcompositions and post- deposition thermal treatments. Differentmaterial combinations have been selected as potential solutionsfor the replacement of the conventional ONO(Oxide-Nitride-Oxide) stack.