US Patent 12087616 Air gap formation method

A method of forming a semiconductor device includes forming a plurality of non-insulator structures on a substrate, the plurality of non-insulator structures being spaced apart by trenches, forming a sacrificial layer overfilling the trenches, reflowing the sacrificial layer at an elevated temperature, wherein a top surface of the sacrificial layer after the reflowing is lower than a top surface of the sacrificial layer before the reflowing, etching back the sacrificial layer to lower the top surface of the sacrificial layer to fall below top surfaces of the plurality of non-insulator structures, forming a dielectric layer on the sacrificial layer, and removing the sacrificial layer to form air gaps below the dielectric layer.