Surface characterization of a low dielectric constant polymer–SiLK* polymer, and investigation of its interface with Cu

The integration of copper and new low dielectric constant materials is a fundamental challenge to be met for further miniaturization of high speed integrated circuits. In this preliminary work, core level x-ray photoelectron spectroscopy (XPS) has been used for the first characterization of the surface composition of Dow Chemical’s SiLK* semiconductor dielectric (*trademark of the Dow Chemical Company), its behavior during annealing in vacuo, and its interface formation with thermally evaporated copper in situ. The fully conjugated SiLK* resin shows a C 1s spectrum with intense shake-up structures, quite similar to those of polystyrene; a small amount of oxygen is detected. Upon annealing in ultrahigh vacuum (7.10−9 Pa) no significant outgassing is observed; no noticeable change in intensity, width, position of the C 1s and O 1s core level peaks or satellite structures is measured. After annealing, the interface formation between SiLK* dielectric and copper has been characterized as a function of incremental coverages from 0.5 to 10 Å of Cu. While the XPS C 1s spectrum shows only a normal intensity decrease, the Cu 2p3/2 levels shift from a high binding energy to a purely metallic value: this is interpreted as the formation of small Cu clusters, evolving to a more continuous layer for higher Cu coverage. Annealing in vacuo of the as-prepared Cu(10 Å)–SiLK* interface at 400 °C for 1 h does induce an increase of the carbon signal, attributed to further coalescence of copper in metallic clusters.