Ultrasound holography for noninvasive imaging of buried defects and interfaces for advanced interconnect architectures

Imaging high resolution subsurface defects nondestructively in advanced interconnect structures and devices is a challenge and no known metrology tools are available to identify such defects in a nondestructive way at nanometer level. Monitoring these defects necessitate the understanding of their growth mechanism of these interconnects as well as defect formation. We report here the application of scanning near field ultrasound holography by imaging buried defects in copper interconnects and low-K dielectric materials. Defects in these copper lines such as voids and delaminations appear as regions of dark contrast in ultrasound holography imaging due to large acoustic impedance mismatch at the voids. Identification of these buried defects in these interconnect architectures in a nondestructive way will open up unique opportunities in using this technique to detect subsurface defects and material imperfections.