Memory device and method of forming the same

A method of forming a memory device, comprising:

• (a) forming a word-line structure on a substrate;
• (b) conformally forming a nitride layer on the word-line structure;
• (c) forming a sacrificial pattern on the nitride layer to expose an upper portion of the nitride layer;
• (d) performing a nitridation treatment to nitride the upper portion of the nitride layer into a first cap layer;
• (e) removing the sacrificial pattern to expose a lower portion of the nitride layer;
• (f) performing an etching process to thin the lower portion of the nitride layer;
• (g) performing an oxidation process to oxidize a thinned lower portion of the nitride layer to an oxide layer;
• and
• (h) removing the oxide layer to expose a lower portion of the word-line structure, while the first cap layer covers an upper portion of the word-line structure.

A memory device, comprising:

• a plurality of word-line structures, disposed on a substrate;
• a plurality of cap structures, respectively disposed on the plurality of word-line structures, wherein a material of the plurality of cap structures includes a nitride, and the nitride has a nitrogen concentration decreasing along a direction near to a corresponding word-line structure toward far away from the corresponding word-line structure;
• and
• a dielectric layer, disposed on the plurality of cap structures and extending to cover sidewalls of the plurality of word-line structures, so as to form a plurality of air gaps between the plurality of word-line structures.