Semiconductor structure, method for forming semiconductor strucutre, and memory

A method for forming a semiconductor structure, comprising:

• providing a base, wherein the base comprises a substrate and an insulating dielectric layer, the substrate comprises a plurality of first trenches spaced apart from each other in a first direction, and the insulating dielectric layer is filled in each of the plurality of first trenches;
• patterning and etching the base to form a plurality of second trenches spaced apart from each other in a second direction, wherein the second direction intersects with the first direction;
• forming a word line structure in each of the plurality of second trenches;
• forming an air gap between each two adjacent word line structures of a plurality of word line structures;
• and
• sealing the air gap;
• forming an insulating layer between said each two adjacent word line structures of the plurality of word line structures, wherein the air gap is located within the insulating layer;
• wherein forming the insulating layer comprises:
• forming a protective layer adaptively attached to a sidewall of each of the plurality of second trenches;
• forming a first insulating material layer on a surface of a structure collectively formed by the base and the protective layer;
• forming a first insulating layer within each of the plurality of second trenches provided with the first insulating material layer, wherein a top portion of the first insulating layer is lower than a top portion of the first insulating material layer;
• forming a second insulating material layer on the top portion of the first insulating layer;
• planarizing a surface of the second insulating material layer to allow a top portion of the second insulating material layer to be flush with a surface of the substrate, wherein a remaining portion of the second insulating material layer and the first insulating material layer collectively form a second insulating layer;
• etching back the protective layer and the insulating dielectric layer to form an insulating gap;
• filling an insulating material in the insulating gap, wherein the insulating material and the second insulating layer collectively form a passivation layer;
• and
• removing a preset thickness of the protective layer in a direction perpendicular to the substrate to form a plurality of word line filling trenches, wherein a bottom portion of each of the plurality of second trenches is unexposed by a respective one of the plurality of word line filling trenches.