Fluorine-modified low-k a-SiOC:H composite films prepared by plasma enhanced chemical vapor deposition

In situ fluorine-modified organosilicate glass (OSG, F-SiOC:H) composite thin films and OSG (SiOC:H) thin films were deposited on p-type (100) substrates at various temperatures (200-400°C) by the plasma enhanced chemical vapor deposition method using tetrafluorosilane (SiF₄) with trimethelysilane (3MS) and oxygen as precursors. Fluorine content in the composite films was adjusted by varying the SiF₄/3MS gas flow ratio of 0.5-2. The films were investigated by examining the bonding configuration, index of refraction, surface composition, hardness, leakage current density and breakdown field strength. The composition analysis and water contact angle measurements suggest that the surface of the films is defluorinated progressively with increasing deposition temperature. The absorbance spectrum of Fourier transform infrared spectroscopy shows that the frequency of the Si-O stretching vibration mode in the F-SiOC:H film shifts to a lower wave number (red shift) at higher temperature, and that shifts to a higher wave number (blue shift) with increasing amount of fluorine incorporation. Meanwhile, the refractive index of the F-SiOC:H films increases slightly with increasing fluorine content, and decreases with increasing deposition temperature. Although the film density increases with deposition temperature and fluorine content, the dielectric constant of the F-SiOC:H remains in the range between 2.8 and 3.2, which is still slightly lower than that of the OSG films (k=2.9-3.3). The F-SiOC:H films deposited at higher temperatures contain higher fluorine content as well as higher mechanical hardness and higher dielectric breakdown voltage. Higher mechanical strength of the F-SiOC:H films relative to that of the OSG films is realized by the structural change associated with fluorine incorporation.