Instability of Si-F bonds in fluorinated silicon oxide (SiOF) films formed by various techniques

Instability of Si-F bonds in fluorinated silicon oxide (SiOF) films is studied. Al wiring corrosion and underlayer SiO₂ etching problems are the major issues for the use of SiOF interlayer dielectric films. To clarify the mechanism, three kinds of SiOF films have been used for this study. They are: (i) a fluorinated silicon oxide (SiOF) film prepared by room-temperature chemical vapour deposition (RTCVD) using fluorotriethoxysilane and pure water as gas sources; (ii) a fluorinated spin-on-glass (SOG) film prepared by fluorotrialkoxysilane vapor treatment (FAST); and (iii) a room-temperature liquid phase deposition (LPD) SiOF film. The initial refractive indices for the RTCVD-SiOF, FAST-SOG and LPD-SiOF films are 1.400, 1.398 and 1.433, respectively. After conducting a pressure cooker test (PCT) at 125°C for 520 h, the refractive indices for the RTCVD-SiOF, FAST-SOG and LPD-SiOF films increase to 1.450,1.440 and 1.436, respectively. The Si-O bond peak absorption coefficient for the LPD-SiOF film decreases at the early stage of PCT, but those for the RTCVD-SiOF and FAST-SOG films increase at the early stage of PCT. The initial Si-F bond peak absorption coefficient for the RTCVD-SiOF film is much higher than those for the LPD-SiOF and FAST-SOG films. It decreases drastically in the PCT time ranging from 0 to 140 h. The Si-F bond peak absorption coefficients for the FAST-SOG and LPD-SiOF films show a slow reduction, as compared with that for the RTCVD-SiOF film at the early stage of PCT. Although the OH peak absorption coefficients for the RTCVD-SiOF and FAST-SOG films increase at the early stage of PCT and level off at 50 h, that for the LPD-SiOF film increases at 306 h. After conducting 520 h PCT, concentrations of fluorine atoms for the RTCVD-SiOF and FAST-SOG films decrease by three orders and two orders of magnitudes, respectively. However, the LPD-SiOF film has a limited change in the fluorine concentration, as compared with those for the RTCVD-SiOF and FAST-SOG films. The thicknesses for all of the films remain almost unchanged after PCT for 520 h.