1. A method of controlling a fabrication cluster using optical metrology, the method comprising: performing a fabricating process on a wafer using a first fabrication cluster; generating a photonic nanojet, wherein the photonic nanojet is an optical intensity pattern induced at a shadow-side surface of a dielectric microsphere; scanning an inspection area on the wafer with the photonic nanojet; obtaining a measurement of retroreflected light from the dielectric microsphere as the inspection area is scanned with the photonic nanojet; determining the existence of a structure in the inspection area with the obtained measurement of the retroreflected light; and adjusting one or more process parameters of the first fabrication cluster based on the determination of the existence of the structure in the inspection area.