The effect of He/H-2 downstream plasma on chemical vapor deposition (CVD) low-k films with different porosities was studied. The results show that this plasma does not reduce the concentration of Si-CH3 bonds in the low-k matrix and that the films remain hydrophobic. However, mass loss and reduction in bulk C concentration were observed. The latter phenomena are related to the removal of porogen residue formed during the UV curing of the low-k films. It is demonstrated that the porogen residue removal changes the films' porosity and mechanical properties. The depth of the modification is limited by the penetration of H radicals into the porous low-k films.