Method for forming semiconductor structure and semiconductor structure

A method for forming a semiconductor structure, comprising:

• providing a substrate, wherein separate bit line structures are formed on the substrate;
• forming a first sacrificial layer on a side wall of each of the bit line structures;
• forming a first dielectric layer filling each gap between the bit line structures;
• patterning the first dielectric layer and the first sacrificial layer to form through holes, wherein along an extension direction of the bit line structures, the through holes and a remaining portion of the first dielectric layer and the first sacrificial layer are alternately arranged, and the through holes expose active regions in the substrate and the side wall of each of the bit line structures;
• forming a second sacrificial layer on a side wall of each of the through holes, and filling each of the through holes to form a contact plug surrounded with an isolation layer;
• forming a contact structure on the contact plug;
• and
• removing the remaining portion of the first sacrificial layer to form a first air gap, and removing the second sacrificial layer to form a second air gap;
• wherein the first air gaps located only between the dielectric layers and the bit line structures, a part of each of the second air gaps is located between a corresponding bit line structure and a corresponding contact plug of the contact plugs and expose a side wall of the corresponding bit line structure, the second air gap surrounds the contact structure and the isolation layer, and the second air gap is located on the substrate.