Air gap uses air as an insulator to reduce the capacitance at advanced process nodes. IBM introduced the concept in 2007 and it is considered the only fundamental improvement in dielectrics in decades.
At one time, logic vendors hoped to use air or a vacuum gap for the ILD, which could bring the k-value down to its theoretical limit of 1.0. But air gap technology was more difficult and expensive than previously thought, forcing logic vendors to delay the idea.
Intel has introduced air gap with its 14nm finFET process. That process includes 9 to 12 metal layers, and air gaps are used on two layers, MT4 and MT6. Intel said the use of air gap technology resulted in a 17% improvement in capacitance.