US 6,303,436 B1 · Method for fabricating a type of trench mask ROM cell

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+-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+-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+-type ions into substrate between each trench can be reversed in the embodiment without affecting subsequent steps.

Claims12

Dependent claims

A method for fabricating a type of Trench Mask ROM cell on a substrate, wherein said method comprises the steps in the following sequence:

forming a pad oxide layer on said substrate;
forming a nitride layer on said pad oxide layer;
forming plural trenches on said substrate by etching back said pad oxide layer, said nitride layer and said substrate;
removing said nitride layer;
forming a gate oxide layer on an outer surface of each said trench;
forming plural first doped regions in said substrate, wherein said first doped regions are beneath said pad oxide layer and between two adjacent trenches, with said first doped regions acting as bit lines of said Trench Mask ROM cell;
forming a polysilicon layer on an outer surface of said pad oxide layer and said gate oxide layer, wherein said polysilicon layer is a word line of said Trench Mask ROM cell;
and
forming plural second doped regions in said substrate beneath said gate oxide layer and beneath said gate oxide layer on bottoms of selected trenches to form coding regions of said Trench Mask ROM cell.

6 more elements

Dependencies are inferred from the claim text.

Method for fabricating a type of trench mask ROM cell

Life of this patent

Method for fabricating a type of trench mask ROM cell

Life of this patent

Abstract

Claims12