UV curing effects on mechanical and electrical performances of a PECVD non-porogen porous SiOC: H films (in k [2.2-2.4] range) for 45nm node and below

A challenge for semiconductor industry is to reach low permittivity required by ITRS (k<2.4) integrating porous interconnect insulator for the sub-65nm technology nodes keeping high mechanical performances as close as possible to dense a-SiOC:H material (H=[1.5-1.8GPa], E=[8-11GPa]). Thus, UV post-deposition treatments were carried out on single PECVD non-porogen porous methylsilsesquioxane (MSQ) films, proposed for 45nm node and below. UV curing is able to enhance stiffness revealing a 50% increase in reduced modulus without degrading k-value. The paper reveals that UV efficiency is actually limited by a top SiO"2-like dense layer. Indeed, without this capping, 8min of UV cure exposure enable to reach a 300% increase in reduced modulus and a 600% increase in hardness maintaining k at 2.27. Finally, UV curing on 300nm porous MSQ film stacks is investigated. The study correlates the limited UV effect by the capping layer and demonstrates that the best stack mechanical properties improvement with limited k degradation is achieved performing UV curing on each layer combined with interfacial hydrogen plasma treatment.