We have fabricated porous plasma polymerized SiCOH (ppSiCOH) films with low-dielectric constants (low-k, less than 2.9), by applying dual radio frequency plasma in inductively coupled plasma chemical vapor deposition (ICP-CVD) system. We varied the power of the low radio frequency (LF) of 370 kHz from 0 to 65 W, while fixing the power of the radio frequency (RF) of 13.56 MHz. Although the ppSiCOH thin film without LF had the lowest k value, its mechanical strength is not high to stand the subsequent semiconductor processing. As the power of the LF was increased, the densities of ppSiCOH films became high, accordingly high in the hardness and elastic modulus, with quite satisfactory low-k value of 2.87. Especially, the ppSiCOH film, deposited at 35 W, exhibited the highest mechanical strength (hardness: 1.7 GPa, and elastic modulus: 9.7 GPa), which was explained by Fourier transform infrared spectroscopy. Since the low-k material is widely used as an inter-layer dielectric insulator, good mechanical properties are required to withstand chemical mechanical polishing damage. Therefore, we suggest that plasma polymerized process based on the dual frequency can be a good candidate for the deposition of low-k ppSiCOH films with enhanced mechanical strength.