Plasma characteristics of low-k SiOC(–H) films prepared by using plasma enhanced chemical vapor deposition from DMDMS/O2 precursors

We report in-situ plasma diagnostics during the deposition of low dielectric constant SiOC(–H) thin films on p-Si(100) substrates by using plasma enhanced chemical vapor deposition with dimethyldimethoxysilane (DMDMS, C4H12O2Si) and oxygen gas as precursors. The bulk plasma was characterized by using Langmuir probe and optical emission spectroscopy as a function of radio frequency (rf) power. The electron density and electron temperature were found to increase with increasing rf power. As the applied rf power increases the –CH3 groups present in the DMDMS precursor first dissociated into CH, C and O, without forming CH2 and CH3 radicals and then the CH radical further dissociated into C, Hα, and Hβ related radicals, respectively. The SiO2–C2 and SiO3–C, SiO–C3 and C–C/C–H bonding configurations of the SiOC(–H) film were increased with increasing rf power whereas Si–O2 bond decreased. These bonding structures help to reduce the k value of SiOC(–H) films. The lowest dielectric constant of 2.04 was obtained for the film with an rf power of 700 W.