The first 5 layers are typically 0.8um and the top metal 1.2um (thicker top metal for bonding efficiency. These thicknesses include the barrier metals (Ti/TiN at the bottom oif the stack and TiN on the top). For 0.18um, where all the interlevel dielectrics between the metals are planarised using chemical mechanical polishing and tungsten plugs are used to connect between layers, the elcromigration performance of these backend processes often out perform older technologies. This is because the older processes did not planarise the inter metal dielectrics and so the thicker metal thinned over steps or sharp discontinuities especially at contacts or vias. So although the process sepcifies 2.0um metal, it might actually thin down below 0.5um in places.