Diffraction Metrology Measures Overlays Down to 45 nm

摘要

Aerial imaging overlay technology has been a reassuringly familiar feature of semiconductor manufacturing for years, experiencing little change. The wafers are loaded, special box-in-box targets are examined using a white-light microscope, and the images are then processed to determine overlay error. Although this has worked well, as we move toward implementing deep nanometer process levels there are several issues with image overlay tools. One of these has to do with the box-in-box structures that have been traditionally used, which tend to have large geometries and typically consist of bars microns in size that do not correspond to circuit feature sizes.