Fin field effect transistor (FinFET) device structure and method for forming the same

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

• a fin structure formed over a substrate;
• a first inter-layer dielectric (ILD) layer formed over the fin structure;
• a first gate structure formed in the first ILD layer;
• a first S/D contact structure formed in the first ILD layer and adjacent to the first gate structure;
• a second ILD layer formed over the first ILD layer;
• a second S/D contact structure formed over the first S/D contact structure;
• a first air gap formed on a sidewall of the first S/D contact structure;
• and
• a second air gap formed on a sidewall of the second S/D contact structure, wherein a bottom surface of the second air gap is in direct contact with the first air gap, the first S/D contact structure or the second ILD layer.

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

• forming a gate structure over a fin structure;
• forming an S/D structure adjacent to the gate structure;
• forming a first ILD layer over the S/D structure;
• forming a second ILD layer over the first ILD layer;
• forming a first trench in the first ILD layer and the second ILD layer to expose the top surface of the S/D structure;
• forming a first sacrificial layer in the first trench, wherein a bottommost surface of the first sacrificial layer is lower than a top surface of the S/D structure;
• forming a first S/D contact structure in the first trench and over the first sacrificial layer;
• removing the first sacrificial layer to form a first air gap on a sidewall of the first S/D contact structure;
• and
• forming a sealing layer over the second ILD layer, wherein a portion of the sealing layer is formed in the first air gap.