NON-VOLATILE MEMORY CELLS WITH SELECTIVELY FORMED FLOATING GATE

摘要

PURPOSE: A non-volatile memory cell with a selectively formed floating gate is provided to reduce the spacing between floating gates of the cells without being limited by a photolithography process. CONSTITUTION: A hemispherical grained polysilicon layer(61) is formed on a polysilicon layer(42) by using processing steps called the seeding method designed to modify the morphology and topography of the polysilicon layer(42). The seeding method involves irradiating the surface of the polysilicon layer(42) with Si2H6 molecules at a high temperature to create amorphous silicon seeds over the surface of polysilicon layer(42), and then annealing the wafer in a high vacuum at the same temperature. CVD is then used to form hemispherical grains of polysilicon on the surface of regions. Subsequently, polysilicon is selectively deposited on top of floating gate layer to form a third polysilicon layer that has a non-flat, non-uniform surface. The third polysilicon layer comprises, for example, hemispherical grains of polysilicon that are formed using the seeding method or He-diluted SiH4.