In this work, the authors report an investigation of the effects of cesium (Cs) ion implantation on both porogen-embedded and ultraviolet (UV)-cured (porous) SiCOH films. For porogen-embedded SiCOH, it was found that Cs ion implantation can greatly improve the elastic modulus. It can also increase the time-zero dielectric breakdown (TZDB) strength. It also leads to an increase in the k-value for medium and high Cs doses, but for low Cs doses, the k-value decreased compared with its pristine counterpart. For UV-cured SiCOH, it was found that Cs-ion implantation does not improve the elastic modulus. It also leads to lower TZDB field strength and much higher k-values than its pristine counterpart. These effects can be understood by examining the changes in chemical bonds. This treatment is shown to have the potential to help solve the problem of the demand for lower k-values and the concomitant weak mechanical strength of SiCOH.