Measuring the thickness profiles of wafers to subnanometer resolution using Fabry-Perot interferometry

The resolution of an angle-scanning technique for measuring transparent optical wafers is analyzed, and it is shown both theoretically and experimentally that subnanometer resolution can be readily achieved. Data are acquired simultaneously over the whole area of the wafer, producing two-dimensional thickness variation maps in as little as 10 s. Repeatabilities of 0.07 nm have been demonstrated, and wafers of up to 100 mm diameter have been measured, with 1 mm or better spatial resolution. A technique for compensating wafer and system aberrations is incorporated and analyzed.