Picosecond sonar used to characterize copper processes

In an industry where process control has always been critical in maximizing yield, the switch to copper interconnects makes process control even more challenging. Proven aluminum processes must be abandoned in favor of the pr ocesses required by copper, and the dual move to smaller design rules and l arger wafers brings challenges of its own. To facilitate the transition, ac curate and detailed characterization is necessary. This article discusses p icosecond sonar, a noncontact optical technology used to characterize indiv idual layer thicknesses of multilayer stacks in the range from 40 Angstrom to 5 mum.