Increases in RC delay times in interconnect wiring for microelectronics as feature sizes decrease have motivated investigations into the use of low-dielectric constant insulators, and in particular, porous silicon-dioxide (PS). Profile evolution and maintenance of critical dimensions during plasma etching of PS are problematic due to the exposure of open pores. To investigate these issues, reaction mechanisms for fluorocarbon plasma etching of SiO2 in C2F6, CHF3, and C4F8 chemistries have been developed and incorporated into the Monte Carlo Feature Profile Model which was modified to address these two-phase systems. The reaction mechanism was validated by comparison to experiments by others for etching of PS and solid SiO2 (SS). We found that the etch rates for PS are generally higher than that of SS due to the inherently lower mass fraction. Mass corrected etch rates of PS can be larger or smaller than those for SS depending on the degree of pore filling by polymer and the degree of ion activated chemical sputtering. Pore filling is particularly important for PS having open networks with large pores and high porosities. We found little dependence of the taper of high aspect ratio profiles on the average pore radius and porosity. However, the profile changes from tapered to bowed as the interconnectivity of the porous network increases. Scaling laws for profile shapes are otherwise similar for both SS and PS. (C) 2004 American Vacuum Society.