An inspection area on a semiconductor wafer can be examined using a
photonic nanojet. The photonic nanojet, an optical intensity pattern
induced at a shadow-side surface of a dielectric microsphere, is
generated. The inspection area is scanned with the photonic nanojet. A
measurement is obtained of the retroreflected light from the dielectric
microsphere as the photonic nanojet scans the inspection area. The
existence of a structure in the inspection area is determined with the
obtained measurement of the retroreflected light.