Porous Low-k Materials and Effective K

摘要

By driving interconnect dimen-sions to ever-smaller sizes, the RC delay becomes the domi-nant factor to impact IC per-formance. The RC delay time is controlled by the re-sistance of the metal lines in the interconnect structure of an IC, and the capacitance between the metal lines. To reduce RC delay, copper interconnects were introduced to replace aluminum at the 175 nm generation for metal linewidths of 0.25 μm, utilizing copper's 37% lower resistivity than aluminum. The reduction of capacitance is still ongoing, and has happened in stages so far. SiO_2 (relative permeability k=4.1) was replaced by fluorinated silica (FSG, k=3.7) in the mid-90s. Currently, IC manufacturers are pushing the implementation of dense CVD SiCOH materials (k=2.7-3.0).