Semiconductor device and method of fabricating the same

A method of fabricating a semiconductor device, comprising:

• forming a conductive structure on a substrate;
• forming a first dielectric layer, the first dielectric layer covering the conductive structure and the substrate;
• removing an upper part of the first dielectric layer to form a trench over the conductive structure;
• performing a widening treatment to the trench to partially widen the upper part of the first dielectric layer, and forming a liner layer on a sidewall of the widened upper part of the first dielectric layer;
• removing a middle part of the first dielectric layer to deepen and widen the trench;
• and
• forming a second dielectric layer on the first dielectric layer to seal the trench and therefore form an air gap.