Low dielectric constant films prepared by plasma-enhanced chemical vapor deposition from trimethylsilane

Dielectric materials with lower permittivity (low k) are required for isolation to reduce the interconnect RC delay in deep submicron integrated circuit. In this work, carbon-doped silicon oxide films are investigated as a potential low k material. The films were prepared by the radio frequency plasma-enhanced chemical vapor deposition (PECVD) technique from trimethylsilane (3MS) in an oxygen (O2) environment. The O2/3MS flow ratio (in sccm) was varied from 50:600 to 900:600 to investigate its effects on the properties of the films. The films were also annealed at 400 °C in an N2 atmosphere for 30 min to determine the thermal stability of their properties. Thickness and refractive index were measured by opti-probe. Chemical structures were characterized by Fourier transform infrared spectroscopy (FTIR). Dielectric constants were measured using a Si/insulator/mercury probe structure. It was found that the deposition rate increased almost three times while the refractive index decreased from 1.46 to 1.39 with increasing oxygen concentration in the gas feed. Dielectric constants as low as 2.9 have been obtained for the as-prepared film with a O2/3MS flow ratio of 100:600. FTIR spectra revealed that more Si–CH and Si–CH3 groups were introduced into the silicon dioxide backbone of the films at this flow ratio, and the low dielectric constant obtained is attributed to the increased incorporation of carbon in the form Si–CH3 bond, which has lower polarizability compared to the Si–O bonds that were replaced. The annealing has been found to lower the dielectric constant of the films, but has no effect on their composition and chemical structure.