Increasing capacitance for high density dram by microlithography

Abstract

A method is disclosed for increasing the capacitance of high-density DRAM devices by microlithographic patterning. A semiconductor substrate having a MOS transistor comprising a gate and source/drain regions, and a word line and a bit line is provided. A layer of inter-poly oxide is deposited over the substrate and planarized. Contact holes are etched in the oxide layer until the substrate is exposed. A layer of photoresist is next blanket deposited over the substrate. Using microlithographic methods, the photoresist is then patterned with in-line or staggered micron size features and the underlying inter-poly oxide layer is etched using the photoresist as a mask. The resulting inter-poly oxide surface, therefore, acquires the shape of a micro-folded topography having a roughened surface area of many folds larger than the original flat surface. A first conductive layer such as polysilicon is conformally deposited over the microlithoqraphically roughened surface forming the storage electrode of the capacitor which is completed by forming a high dielectric oxide such as ONO over the first polysilicon and then depositing a second polysilicon to form the upper electrode of the capacitor.