Method for making a double-cylinder-capacitor structure for dynamic random access memory (DRAM)

摘要

A method using a single masking step for making double-cylinder stacked capacitors for DRAMs which increases capacitance while eliminating erosion of an underlying oxide insulating layer when the masking step is misaligned is described. A planar silicon oxide (SiO2) first insulating layer is formed over device areas, and a first silicon nitride (Si3N4) etch-stop layer is deposited, and openings are etched for capacitor node contacts. A first polysilicon layer is deposited to a thickness sufficient to fill the openings and to form an essentially planar surface. A second insulating layer is deposited and patterned to form portions with vertical sidewalls over the node contacts. A conformal second Si3N4 layer is deposited and etched back to form spacers on the vertical sidewalls, and the first polysilicon layer is etched to the first Si3N4 layer. The second insulating layer is selectively removed using HF acid while the first polysilicon and first Si3N4 layers prevent etching of the underlying first SiO2 layer. A second polysilicon layer is deposited and etched back to form double-cylinder sidewalls for the capacitor bottom electrodes. The first and second Si3N4 layers are removed in hot phosphoric acid. The capacitors are completed by forming an interelectrode dielectric layer on the bottom electrodes, and depositing a third polysilicon layer for top electrodes.