Inspecting a multilayer sample

A system for inspecting a multilayer sample, the system comprising:

• a broadband light source configured to emit light;
• a beam splitter configured to receive the light from the broadband light source and split the light into first and second portions, direct the first portion of the light toward an outer surface of a first layer of a multilayer sample in which the first layer is oriented proximal to the beam splitter and the outer surface of the first layer is positioned a first optical distance from the beam splitter, direct the second portion of the light onto a reflector positioned a second optical distance from the beam splitter, combine the first portion of the light after being reflected from the multilayer sample and the second portion of the light after being reflected from the reflector, and direct the combined light toward a system for analyzing Fabry-Perot fringes;
• the system for analyzing Fabry-Perot fringes configured to receive, at a computer-controlled etalon filter, the combined light, filter the combined light at the computer-controlled etalon filter, direct, from the computer controlled-etalon filter, the filtered light over a single-mode optical fiber, receive at a computer-controlled spectrograph included in the system for analyzing Fabry-Perot fringes, the filtered light over the single-mode optical fiber, and spectrally analyze the filtered light, using the computer-controlled spectrograph, to determine at least a first peak of a Fourier transform of the filtered light, the first peak created by an optical path difference (OPD) between an optical path of the first portion of the light and an optical path of the second portion of the light;
• a motion stage configured to change a frequency of at least the first peak to a new frequency by changing one or both of the first optical distance and the second optical distance;
• and
• a computer configured to control the system for analyzing Fabry-Perot fringes, determine the OPD between the optical path of the first portion of the light and the optical path of the second portion of the light, control the motion stage between measurements to change the OPD to a different OPD, and determine thicknesses and order of the layers of the multilayer sample based on the different OPD and the new frequency of at least the first peak.