Shallow trench air gaps and their formation

摘要

A method of forming a NAND flash memory includes etching between word lines to expose isolation material in shallow trench isolation (STI) trenches while active areas between word lines remain covered, then forming protective sleeves at locations over exposed isolation material. Subsequently, with the protective sleeves in place, isotropic etching of isolation material forms an air gap extending continuously between the protective sleeves along an individual STI trench.

主权项

1. A NAND flash memory comprising:
a plurality of active areas extending along a first direction in a substrate; a plurality of shallow trench isolation (STI) trenches extending along the first direction in the substrate between the plurality of active areas; a plurality of word lines extending over the plurality of active areas and over the plurality of STI trenches along a second direction that is perpendicular to the first direction, the plurality of word lines separated from the plurality of STI trenches by a plurality of dielectric strips that extend under the plurality of word lines; an air gap extending under the plurality of word lines along an individual STI trench of the plurality of STI trenches; a plurality of portions of an isolating material located along undersides of the plurality of dielectric strips where the plurality of dielectric strips overlie the individual STI trench, the isolating material filling a remaining portion of the individual STI trench that extends from the air gap to the bottom of the trench; and wherein the air gap has a profile along a word line direction at a location under an individual word line that has a first width at a first height above a bottom surface of the individual STI trench and has a second width at a second height above the bottom surface that is greater than the first height, the second width being less than the first width.