Creation of SiOF films with SiF4/O2 plasmas: From gas-surface interactions to film formation

Fluorinated SiO2 (SiOF) films have been studied because of their relatively low dielectric constant and their potential as a replacement for SiO2 in the microelectronics industry. Despite the intense scrutiny, many of the details of the mechanisms for SiOF film deposition remain unclear. Here, we examined the macroscopic and molecular level chemistry of SiOF film deposition using SiF4/O2 plasmas. In the film formation studies, the plasma parameters of SiF4 fraction in the feed gases, F, defined as SiF4/(SiF4+O2), and applied rf power (P) were examined as well as the effects of ion bombardment and substrate temperature on film deposition. Fluorine incorporation in the film increases with both F and P. Film-deposition rate also increases with P, whereas its dependence on F is more complex. Ion bombardment decreases the film deposition rate and affects film composition significantly. On the molecular level, we examined the surface reactivity of SiF and SiF2 during SiOF film deposition using the imaging of radicals interacting with surfaces technique. SiF2 shows significant surface production during film deposition. The scattering coefficient S varies from 1.63±0.07 to 2.01±0.07. In contrast, SiF shows high surface reactivity R (defined as 1−S for S⩽1), which varies from 0.96±0.13 to 0.73±0.09, depending on plasma parameters. The surface interactions of SiF and SiF2, along with plasma gas-phase composition, were correlated with film characteristics to reveal possible film-deposition mechanisms.