Dielectric permittivity of organosilicate glass thin films on a sapphire substrate determined using time-domain THz and Fourier IR spectroscopy

The engineering of dielectrics such that they have low dielectric constants is an important challenge in the semiconductor industry. The IR absorption and THz relaxation make a significant contribution to the low-frequency dielectric constant of porous organosilicate glass (OSG) thin films used in the interconnects of integrated circuits as low-k dielectrics. Determination of the dielectric contributions with the aid of the electric dipole absorption bands in the THz region has certain methodological limitations owing to the effect of the substrate. To overcome this problem, we used a c-cut sapphire plate as a substrate, which is optically isotropic and transparent in the THz range. The parameters of both the IR and THz absorption bands in the OSG films were measured using Fourier IR and pulsed THz spectroscopy and analysed using the classical oscillator model. The contribution of the THz relaxation is responsible for approximately 15%-17% of the value of the low-frequency dielectric constant.