Importance

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Abstract

A method for fabricating a type of Trench Mask ROM cell comprises steps including: providing a substrate doped lightly with p-type dopant, sequentially forming a pad oxide layer and a nitride layer on the substrate; etching back the pad oxide layer, the nitride layer and the substrate to form plural trenches; a gate oxide layer being formed on surfaces of each trench; then, implanting n.sup.+ -type ions into the substrate beneath the pad oxide layer and between each two adjacent trenches; and, forming a polysilicon layer on the gate oxide and pad oxide; finally, implanting n.sup.+ -type ions into the substrate beneath the gate oxide layer on bottoms of selected trenches. And, it is appreciated that the sequence of the formation of plural trenches and implanting n.sup.+ -type ions into substrate between each trench can be reversed in the embodiment without affecting subsequent steps.

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First Claim