This work focuses on the formation of residues that grow on a metallic-hard mask after etching of porous low-k materials in fluorocarbon-based plasmas. The residue growth, which is dependent on the air exposure time after etching, causes line and via opens that strongly impact the yield performance. The different elements which could play a role in the chemical reactions have been clarified. The authors have demonstrated that in their experimental conditions, after fluorocarbon etching and air exposure, the oxidized titanium nitride reacts with fluorhydric acid to form metallic salts. This is a reaction between fluorine from the reactive layer formed on titanium nitride and hydrogen coming from the atmosphere. This reaction is all the more fast because the titanium nitride is oxidized.