The interface formation of copper and low dielectric constant fluoro-polymer: Plasma surface modification and its effect on copper diffusion

The bulk and surface diffusion of Cu deposited on a treated low dielectric constant fluoropolymer (FLARE(TM) 1.0, AlliedSignal) was studied using x-ray photoelectron spectroscopy. Copper was found to be relatively unreactive on untreated, N-2 and O-2 plasma treated, and Ar+ sputtered surfaces. Shifts in the Cu 2p(3/2) binding energy showed that larger Cu islands formed when Cu was evaporated on the untreated surface. Because sputter deposition of Cu damaged the fluoropolymer and formed nucleation sites for Cu islands, many smaller islands were found for Cu sputter deposited on untreated polymer. The competition between bulk and surface diffusion also plays a role in Cu island size: Plasma treatments and sputtering limit diffusion of Cu into the bulk of the polymer below the glass transition temperature T-g. The plasma treatments increase the surface reactivity and the plasma treatments and sputtering increase the cross linking in the surface region. Above T-g, no treatment was found to effectively limit diffusion into the bulk. Bulk diffusion during Cu deposition, however, is found to limit island size. (C) 1999 American Institute of Physics. [S0021-8979(99)01003-8].