Semiconductor structure and fabrication method thereof

A semiconductor structure, comprising:

• a substrate having a plurality parallel first regions, a plurality of parallel second regions and a plurality of parallel third regions, wherein a first region of the plurality of parallel first regions is adjacent to a second region of the plurality of parallel second regions and a third region of the plurality of parallel third regions at two sides, respectively;
• and
• a conductive layer in each of the plurality of parallel first regions, the plurality of parallel second regions and the plurality of parallel third regions,
• wherein the semiconductor structure is formed by:
• providing a to-be-etched layer having the substrate and a first hard mask layer on the substrate, wherein the to-be-etched layer includes the plurality of first regions, the plurality of second regions and the plurality of third regions;
• forming a first core layer on the first region of the plurality of first regions, wherein the first core layer extends along a second direction perpendicular to the first direction;
• forming a first sidewall spacer on sidewall surfaces of the first core layer;
• forming a sacrificial layer covering a portion of the first sidewall spacer on the to-be-etched layer, wherein the sacrificial layer includes a plurality of initial first openings, an initial first opening of the plurality of initial first openings is on the second region, the initial first opening extends along the second direction, and a portion of the initial first opening exposes a portion of the first sidewall spacer on the second region;
• removing the portion of the first sidewall spacer exposed by the portion of the initial first opening to form a first opening;
• forming a second sidewall spacer in the first opening;
• forming a plurality of second openings in the sacrificial layer, wherein a second opening of the plurality of second openings exposes one of or both the portion of the first sidewall spacer and a portion of the second sidewall spacer;
• removing the first core layer to form a plurality of third openings in the sacrificial layer;
• etching the first mask layer using the sacrificial layer, the first sidewall spacer and the second sidewall spacer as a mask to form a plurality of transitional trenches in the first mask layer;
• etching the substrate using the first mask layer as a mask to form a plurality of target trenches in the substrate;
• and
• forming the conductive layer in each of the plurality of target trenches, respectively.