The present disclosure provides a method for preparing a semiconductor device structure. The method includes forming a capacitor contact over a semiconductor substrate, and forming a base layer over the capacitor contact. The method also includes forming a dielectric layer over the base layer, and performing a first doping process to form a first doped region in the dielectric layer. The method further includes etching the dielectric layer such that a sidewall of the dielectric layer is aligned with a sidewall of the first doped region, and removing the first doped region to form a first gap structure in the dielectric layer after the dielectric layer is etched. In addition, the method includes forming a surrounding portion along sidewalls of the dielectric layer and a first interconnect portion in the first gap structure by a deposition process.