Fourier transform infrared characterization of moisture absorption in SiOF films

In this paper, the water absorption characteristics of as-deposited and annealed liquid-phase-deposited fluorinated silicon oxide (LPD-SiOF) films were investigated to clarify the film properties. The stability of moisture absorption was characterized under an air-exposure environment of 23°C and 65% humidity. The as-deposited LPD-SiOF film was found to easily absorb moisture from air and therefore to become unstable in terms of the dielectric property. To obtain a highly stable dielectric film, a hydrofluosilicic acid concentration of 2.2 M (with the corresponding fluorine content of 4.9 at.%) is suggested because it has a minimum water absorption change (<3%). The related OH concentration was comparable (or even smaller) to those of other SiOF films grown by chemical vapor deposition. Moreover, high-temperature annealing in nitrogen ambient was utilized to drive out the moisture absorbed in an LPD-SiOF film. The annealing process after deposition tends to render the film surface hydrophobic. The resulting OH bonds were found to disappear after annealing and did not reappear even after long time of air exposure.