Semiconductor device with composite dielectric and method for fabricating the same

A semiconductor device, comprising:

• a pattern-sparse region;
• a pattern-dense region;
• a semiconductor substrate formed at the pattern-sparse region and the pattern-dense region;
• a first interconnect structure disposed in the semiconductor substrate, wherein the first interconnect structure comprises:
• a first conductive line;
• and
• a first manganese-containing layer disposed over the first conductive line;
• a first dielectric layer disposed over the semiconductor substrate;
• a second dielectric layer disposed over the first dielectric layer;
• a second interconnect structure disposed in the first dielectric layer and the second dielectric layer, and electrically connected to the first interconnect structure, wherein the second interconnect structure comprises:
• a second conductive line;
• and
• a second manganese-containing layer disposed between the second conductive line and the first dielectric layer, and between the second conductive line and the second dielectric layer;
• and
• a third interconnect structure disposed in the semiconductor substrate, wherein the third interconnect structure comprises:
• a third conductive line;
• and
• a third manganese-containing layer disposed over the third conductive line, wherein the third manganese-containing layer of the third interconnect structure and the first manganese-containing layer of the first interconnect structure are made of a same material;
• wherein the first interconnect structure and the second interconnect structure are disposed in the pattern-sparse region and the third interconnect structure is disposed in the pattern-dense region;
• wherein the first dielectric layer comprises a bottom porous dielectric layer disposed on the semiconductor substrate, a middle porous dielectric layer disposed on the bottom porous dielectric layer and a top porous dielectric layer disposed on the middle porous dielectric layer.