Fin field effect transistor (finfet) device structure with air gap and method for forming the same

A method for forming a fin field effect transistor (FinFET) device structure, comprising:

• forming a fin structure over a substrate;
• forming a gate structure across the fin structure;
• forming a first spacer over a sidewall of the gate structure;
• forming a second spacer over a sidewall of the first spacer;
• removing a first portion of the gate structure to form a first opening;
• partially removing the first spacer and the second spacer through the first opening;
• removing a second portion of the gate structure to form a second opening below the first opening;
• etching the second spacer to form a gap after the second opening is formed;
• and
• forming a mask layer covering the gate structure, the first spacer and the gap such that an air gap is formed in the gap.

A fin field effect transistor (FinFET) device structure, comprising:

• a fin structure formed over a substrate;
• a gate structure formed across the fin structure;
• a first spacer formed on a sidewall of the gate structure;
• a contact formed over the fin structure and adjacent to the gate structure, wherein the contact and the first spacer have an air gap therebetween;
• and
• a mask layer formed over the gate structure, the first spacer and the air gap, wherein a top surface of the first spacer is higher than an interface between the mask layer and the air gap.