Characterization of silicon metallization systems using energetic ion backscattering

Silicon metallization systems have become increasingly sophisticated in order to tailor contact properties such as adhesion, electrical conductivity, barrier height, and long-term reliability. These contact properties are highly susceptible to solid-solid reactions, typically involving atom migration over distances less than 1 µm. Analysis by monoenergetic ion beam irradiation is a valuable new materials characterization technique to optimize process parameters and contact lifetime. Energy analysis of the backscattered ions allows nondestructive determination of the depth distribution of the atomic composition of thin multilayered systems. Recent application of this technique has provided extensive data on the energetics and kinetics of interdiffusion and compound formation for thin-film metallizations on silicon, particularly those used in silicon device technology. After a brief introduction to the technique, the results of these studies are reviewed and systematized. Interdiffusion results are treated for silicon-metal and metal-metal reactions. Distinction is made between cases where internal surface transport effects dominate and cases where compound formation dominates. Examples are taken from each of these areas and are discussed in terms of metallurgical properties.