Semiconductor device and manufacturing method thereof

A semiconductor device, comprising:

• a semiconductor substrate;
• an interlayer insulating layer formed above said semiconductor substrate;
• a first metal interconnection embedded in said interlayer insulating layer with a surface thereof exposed to substantially the same plane as a surface of said interlayer insulating layer;
• a diffusion preventive layer formed on at least said metal interconnection to prevent diffusion of a metal included in said first metal interconnection;
• a first nitrogen-doped silicon oxide layer formed on said diffusion preventive layer and having a substantially constant first refractive index falling in a range between 1.50 (inclusive) and 1.55 (inclusive) throughout said first nitrogen-doped silicon oxide layer;
• a fluorine-doped silicon oxide layer formed on said first nitrogen-doped silicon oxide layer;
• a second nitrogen-doped silicon oxide layer formed on said fluorine-doped silicon oxide layer and having a substantially constant second refractive index falling in a range between 1.50 (inclusive) and 1.55 (inclusive) throughout said second nitrogen-doped silicon oxide layer;
• and
• a second metal interconnection embedded in said fluorine-doped silicon oxide layer with a surface thereof exposed to substantially the same plane as a surface of said second nitrogen-doped silicon oxide layer, penetrating through said second nitrogen-doped silicon oxide layer, and electrically connected to said first metal interconnection.