The need for reliable low-k/Cu interconnect technologies is increasing, and many kinds of low-k materials have been proposed. We need a process design for etching that will correspond to a change in the film densities and compositions of low-k materials for 90 and 65-nm node devices. Using many different in-situ plasma-measuring tools, such as IRLAS, OES, surface wave probes, and QMS, we counted the absolute number of incident species (CF@sub x@, O, N, H, F, radicals and ions) that were dissociated and/or ionized in fluorocarbon plasmas. Next, we evaluated the surfaces of the various SiOCH films (k = 2.9-2.2) that had different film compositions and densities, and that had been exposed to various fluorocarbon plasmas. The etch rates, selectivity, and thicknesses of the surface polymers were analyzed. We found that the etch rates of the SiOCH films depended on both the "total number of F atoms in all of the incident CF@sub x@ reactive species", and "the surface reaction probability, which depends on ion energy". Lower oxygen concentrations in SiOCH film induce a narrower process window because the fluorocarbon polymer became thicker, even during lower incident CF@sub x@ flux conditions.@footnote 1@ As a result, the etch rate became very sensitive to changes in the incident CF@sub x@ fluxes, resulting a narrow process window for etching SiOCH and porous SiOCH materials. To ensure reliable interconnects for 45 nm and beyond, we require new technologies to realize both "quantitative control" and "instant stabilization" of the plasma parameters. Furthermore, we also need to develop a model to control the atomic layer modification (etching and/or degradation) of the actual etched surface for various materials. Cooperation between etching and other unit process engineers must be promoted in order to create a more reliable process module. @FootnoteText@ @footnote 1@ T.Tatsumi et al, Proceedings of the 2003 IITC (2003) 239.