Diffusion barrier integrity evaluation by ellipsometric porosimetry

Abstract

In order to reduce resistance and capacitance copper wiring is used along with materials possessing a low dielectric constant (low-k materials). A diffusion barrier is used in Cu/low-k integration scheme to prevent Cu diffusion into low-k materials. A film integrity evaluation method is needed for barrier characterization. The method should be able not only to test the barrier integrity but also to find low-density defects (so called “killer defects”). We propose fast, simple, and accurate evaluation of diffusion barriers by ellipsometric porosimetry (EP). This method can be used for testing barriers with respect to solvent penetration. When a barrier contains pores, an adsorptive (toluene) penetrates through these pores and condenses in the low-k dielectric film (e.g., porous glass or organic polymer). The condensation changes optical characteristics of the low-k film that is measured by EP. Low-density killer defects are visualized by toluene trapped around the defect beneath the barrier. We have evaluated a Ta(N) barrier on a porous glass and a WCN barrier on an organic polymer low-k films. Our experiments show that EP is able to test barrier integrity and find killer defects. If a barrier deposited on a porous film is noncontinuos, then EP is able to determine barrier optical constants and thickness as well as to estimate barrier porous structure.