We have computationally explored chemical structures of SiOCH low-k films that have appropriate mechanical and dielectric properties for the application to the future interconnect technology. We have focused on the carbon-rich SiOCH films where the hydrocarbon components are involved in the polymer network. It has been found that film structures of this type can have substantially smaller k-values (by ~0.5) than a typical PECVD films of 90nm technology node, with the mechanical strengths being comparable to that of the PECVD film. These structures may give films of k~2.1 if they are created experimentally