Line and via voiding measurements in damascene copper lines using metal illumination

New methods for monitoring via and line voiding in metal interconnect structures are described. A focused laser beam injects heat into a structure such as a line or via chain, which may have width considerably smaller than the spot size. Conduction of heat, and therefore temperature under the spot, is a function of via or line integrity. Probing the temperature using laser reflection provides a direct nondestructive measure of via continuity or line voiding.