Deposition and CMP of sub 100 nm silver damascene lines

Silver (Ag) is a promising material for interconnect metallization with improved electromigration properties which reduces the resistivity increase due to size effect that becomes substantial for metallization structures below 100 nm. In this work a method for the fabrication of thin silver lines is presented. Very narrow damascene trenches in SiO₂ down to 70 nm line width were completely filled with Ag at a maximum aspect ratio of 2:1 using sputter deposition and chemical mechanical polishing. These are the thinnest silver lines published so far. The measured resistivity of as-deposited samples was not much higher than that of equally sized, highly optimized Cu damascene lines. An improvement in resistivity is expected by annealing, so that the resistivity of comparable Cu lines can be reached or even undercut.