Equivalent oxide thickness reduction of interpoly dielectric using ALD-Al2O3 for flash device application

An interpoly dielectric stack consisting of silicon dioxide, aluminum oxide, and silicon dioxide (OAO stack) has been proposed to replace the oxide-nitride-oxide (ONO) stack in flash memory. Atomic layer deposition and annealing conditions of Al2O3 films were studied to achieve low equivalent oxide thickness (EOT) and leakage current. Aluminum oxide films were deposited from alternating pulses of trimethylaluminum and ozone. The within-wafer nonuniformity and wafer-to-wafer thickness repeatability were both typically below 1.0% (1σ). The OAO interpoly dielectric exhibited leakage current density below 0.1μA∕cm2 at an electric field of 5MV∕cm while an 11% reduction in EOT to 12.5nm was achieved as compared with an ONO stack. The OAO stack has higher breakdown field and greater charge to breakdown than the ONO stack.