For precise measurements of the electron density and temperature in bis-trimethylsilymethane (BTMSM) and argon plasma, the authors adapted a wave cutoff method that use the plasma frequency and floating type probe that use nonlinear characteristics. The films were deposited on a p-type Si(100) substrate by means of UV-assisted inductively coupled plasma-enhanced chemical vapor deposition. Fourier transform infrared spectroscopy was used to investigate the bonding configuration of the SiCH films. With UV illumination, the electron density was found to increase in the low power region and decrease in the high power region. The peak intensity of Si-CH3 decreases with UV illumination under all conditions. When the RF power is lower, the electron energy is not high enough to dissociate the BTMSM molecular state fully. Furthermore, given the large number of organic monomers, polymerization becomes the predominant mechanism. The effect of the UV illumination is the dissociation of the Si-CH3 monomer. Moreover, when the UV source illuminates the plasma, the peak intensity of CH2 increases whereas the peak intensity of CH3 decreases. As the RF power increases, the BTMSM becomes nearly dissociated into more reactive ions and radicals such as Si* and -CH3*. Thus, at a high power, the film deposition process depends more on reactive ions and radicals. Floating probe results show that the electron temperature is not affected by UV illumination. In other words, UV illumination is generally related to the dissociation, but cannot affect plasma heating. According to the electron data, the difference in the electron density with UV illumination and without UV illumination decreases as the pressure increases. The dissociation rate of the BTMSM molecules decreases as the pressure increases. And the UV photons are absorbed to other vibration or transition channels that are not contributing to the dissociation process as the pressure increase.