Methods of preparing low-k carbon-doped oxide (CDO) films having high mechanical strength are provided. The methods involve contacting the substrate with a CDO precursor to deposit the film typically using a plasma-enhanced chemical vapor deposition (PECVD) method. After the film is deposited, it is exposed to ultraviolet radiation in a manner that increases cross-linking and/or lowers the dielectric constant of the film. The resulting films have ultra-low dielectric constants, e.g., about 2.5, but also high mechanical strength, e.g., a modulus of at least about 7.5 GPa. In certain embodiments, a single hydrocarbon precursor is used, resulting in an improved process for obtaining ULK films that does not require dual (porogen and backbone) precursors.