RELIABILITY AND CHARACTERIZATION OF COMPOSITE OXIDE/NITRIDE DIELECTRICS FOR MULTIMEGABIT DYNAMIC RANDOM-ACCESS MEMORY STACKED CAPACITORS

The reliability and electrical properties of planar and 3D interpoly oxide/nitride films stacked on multi-megabit dynamic random access memory (DRAM) array topography are reported to determine their thinning and capacitance limits. A compromise between reliability, leakage current, and storage capacity is proposed for oxidized low-pressure chemical vapor deposited nitride layers with different nitride thicknesses, oxidation conditions, and top/bottom polysilicon doping levels. Capacitance, leakage current, and time-dependent dielectric breakdown measurements show that thinner nitride layers with longer oxidation times provide the maximum lifetime and capacitance. However, the nitride thinning is limited when leakage current by Poole-Frenkel or Fowler-Nordheim emission occurs. For 5 V operated high-density DRAMs, nitride layers as thin as 7 nm, giving a capacitance of 6 fF/mu-m2 present the optimum conditions. For 3.3 V operations, films as thin as 4-5 nm, giving a capacitance of 9 fF/mu-m2, can be expected.