A method of depositing a SiNxCy liner on a porous low thermal conductivity (low-k) substrate by plasma-enhanced atomic layer deposition (PE-ALD), which includes forming a SiNxCy liner on a surface of a low-k substrate having pores on a surface thereon, in which the low-k substrate is repeatedly exposed to a aminosilane-based precursor and a plasma selected from nitrogen, hydrogen, oxygen, helium, and combinations thereof until a thickness of the liner is obtained, and wherein the liner is prevented from penetrating inside the pores of a surface of the substrate. A porous low thermal conductivity substrate having a SiNxCy liner formed thereon by the method is also disclosed.