Thermal Conductivity Measurement of Low-k Dielectric Films: Effect of Porosity and Density
M. T. Alam, R. A. Pulavarthy, J. Bielefeld, S.W. King and M. A. Haque
The thermal conductivity of low dielectric constant (low-k) SiOC:H and SiC:H thin films was measured as a function of porosity using a heat transfer model based on a micro-fin geometry and infrared thermometry. Microscale specimens were patterned from blanket films, released from the substrate, and subsequently integrated with the experimental setup. Results show that thermal conductivity of a dense specimen, 0.7 W/mK, can be reduced to as low as 0.1 W/mK by introducing 30% porosity in it. The measured thermal conductivity shows a nonlinear decrease with increased porosity that approximately follows the porosity-weighted simple medium model for porous materials. Neither the diﬀerential eﬀective medium nor the coherent potential model could predict the density dependence of thermal conductivity. These results suggest that more careful consideration is required for application of generic porous materials modeling to the low-k dielectrics.
(a) Low k dielectric specimens are patterned from blanket films then manipulated around a heater (b) infrared thermography is used to measure the spatial temperature profile and the free convective heat transfer and (c) thermal conductivity as function of porosity.