A Michelson Interferometer with a low coherence light source is used to determine distances: L2 is the beam path length from the light source LS to a surface or interface on the wafer w and back to the detector D. L1 is the beam path from LS to the reference mirror and back to D. If L1 = L2 interference is observed.
Substrate Thickness, Warp, and TTV Measurement - with or without Tape - for Wafer Backgrind and Etch Thinning processes. Non-contact Echoprobe Technology. Thin film and surface roughness options.