Semiconductor structure and its formation method

A semiconductor structure formation method, comprising:

• providing a substrate, the substrate being provided with a groove, a sidewall of the groove comprising a first sub-sidewall and a second sub-sidewall that extend upwards from a bottom of the groove, the first sub-sidewall being located between the second sub-sidewall and the bottom of the groove;
• blowing a first precursor to a surface of the substrate at a flow rate less than a preset value, so that the first precursor is attached both to a top surface of the substrate and the second sub-sidewall;
• blowing a second precursor to the surface of the substrate, so that the second precursor reacts with the first precursor to form a dielectric layer;
• and
• alternately blowing the first precursor and the second precursor to the surface of the substrate to form a plurality of dielectric layers until a top opening of the groove is blocked, a region enclosed by the first sub-sidewall, the plurality of dielectric layers and the bottom of the groove forming a void.