Surface modified spin-on xerogel films as interlayer dielectrics

SiO2-based xerogels are highly porous materials that may enhance the perfor mance of microelectronic devices due to their extremely low dielectric cons tants (epsilon=1.36-2.2). Conventional xerogel and aerogel manufacturing te chniques include an expensive and hazardous supercritical drying step to de posit crack free, high porosity films. Ambient drying techniques have recen tly been developed and in this article, we discuss how the process paramete rs in the ambient drying process affect the properties of a spin-coated fil m. Successful spin-on deposition of highly porous (>70%), thick (>1 mu m), crack-free, xerogel films was accomplished using a solvent saturated atmosp here during spinning and aging. The saturated atmosphere allowed for the is olation of each processing step and a better understanding of the effects o f process variable changes. The film porosity was controlled by varying the extent of silylation (surface modification), the aging time, or the initia l water/silane ratio. Fourier transform infrared spectra demonstrated that silylation of xerogel films helps eliminate bound moisture in these films a nd renders them hydrophobic. Finally, the dielectric constants extrapolated from refractive index measurements were in good agreement with those obtai ned from our conventional electrical measurements. (C) 1999 American Vacuum Society. [S0734-211X(99)01701-1].