Interconnect structure and method for preparing the same

A method for preparing an interconnect structure, comprising:

• providing a first dielectric layer over a first connecting line, wherein the first dielectric layer is substantially horizontally disposed over the first connecting layer and the first dielectric layer includes SiO, SiN, phosphosilicate glass (PSG), borophosphosilicate glass (BPSG), fluorosilicate glass (FSG), organosilicate glass (OSG) or a combination thereof, wherein the first connecting line is a metal line to form a lower level of the interconnect structure;
• forming a first upper via opening in the first dielectric layer, wherein the first upper via opening has a first width, the first upper via opening includes an upper sidewall and a bottom wall connected to the upper sidewall, and the bottom wall is substantially parallel to a top surface of the first dielectric layer;
• forming a first lower via opening in the first dielectric layer to expose the first connecting line, wherein the first lower via opening is formed under and coupled to the first upper via opening, the first lower via opening has a second width less than the first width of the first upper via opening, and the first lower via opening includes a lower sidewall connected to the bottom wall of the first upper via opening;
• forming a connecting via in the first upper via opening and the first lower via opening;
• and
• forming a second connecting line over the connecting via, wherein the second connecting line is a metal line to form a higher level of the interconnect structure,
• wherein the first connecting line is covered by the first dielectric layer after the formation of the first upper via opening.