Semiconductor device structure with air gap and method for preparing the same

A method for preparing a semiconductor device structure, comprising:

• forming a first fin structure and a second fin structure over a semiconductor substrate;
• forming an isolation structure over the semiconductor substrate, wherein the first fin structure and the second fin structure protrude from the isolation structure;
• partially removing the first fin structure and the second fin structure to form a first recessed portion of the first fin structure and a second recessed portion of the second fin structure;
• epitaxially growing a first source/drain (S/D) structure over the first recessed portion and a second S/D structure over the second recessed portion, wherein the first S/D structure is separated from the second S/D structure by a first opening;
• partially removing the isolation structure through the first opening to form a second opening, wherein the first opening and the second opening are a continuous space;
• forming a contact etch stop layer (CESL) over the first S/D structure and the second S/D structure such that an air gap is formed and sealed in the first opening and the second opening;
• forming an interlayer dielectric (ILD) structure over the CESL;
• removing a portion of the ILD structure and a portion of the CESL over the first S/D structure to form a third opening, wherein the third opening exposes the first S/D structure;
• performing an anisotropic deposition process to deposit a barrier layer in the third opening, wherein the barrier layer comprises a bottom portion in contact with the first S/D structure and a side portion in contact with the ILD structure;
• and
• forming a conductive layer over the barrier layer, wherein the barrier layer and the conductive layer are configured to be a bit line contact.