Semiconductor device with air gap and method of fabricating the same

A method for fabricating a semiconductor device, the method comprising:

• forming, over a substrate, a plurality of bit line structures, each including a stacked bit line and a hard mask pattern;
• forming an inter-layer insulation layer over the plurality of bit line structures;
• forming, by etching the inter-layer insulation layer, a contact hole between the plurality of bit line structures;
• forming a carbon-containing spacer on sidewalls, of the plurality of bit line structures, that define the contact hole;
• forming a first plug in the contact hole to form a recess plug structure, including the carbon-containing spacer, wherein the carbon-containing spacer is located between the first plug and the sidewalls of the contact hole;
• removing the carbon-containing spacer to expose sidewalls of the hard mask pattern;
• reducing a thickness of the exposed sidewalls of the hard mask pattern;
• forming a capping spacer to cap the carbon-containing spacer and the reduced thickness sidewalls of the hard mask pattern;
• and
• forming an air gap between the bit line and the first plug by converting the carbon-containing spacer to a volatile form.