Semiconductor device and forming method thereof

The invention discloses a semiconductor device and a forming method thereof. The forming method comprises the steps: forming a sacrifice side wall on the side wall of a conductive connection structure, and then forming an external side wall material layer on the surface of the sacrifice side wall; performing perforation treatment on the external side wall material layer, and forming pinholes exposing the surface of the sacrificial side wall in the external side wall material layer; removing the sacrificial side wall through the pinholes to form air gaps; and forming a cover layer for sealing the pinholes. According to the invention, due to the fact that the pinholes formed in the external side wall material layer can be located at a plurality of positions in the external side wall material layer, the sacrificial side wall can be removed from the plurality of positions by an etching solution through the plurality of pinholes, so that the sacrificial side wall can be removed cleanly, the residue of the sacrific