Plurality layer thickness measuring device and method with fast fourier transform

Abstract

A thickness measuring device includes: a light source circuit including: a light source which irradiates light to a surface of a substrate including a plurality of thin films and a lens which magnifies light emitted from the light source or reflected from the surface of the substrate, a detector circuit including a spectrometer which measures a reflectance for each wavelength of light reflected from the surface of the substrate and passed through the lens to generate reflectance values and which derives reflectance spectrum data for each wavelength from the reflectance values, and a control circuit which converts the reflectance spectrum data for each wavelength into a digital signal and calculates a thickness of at least one thin film among the plurality of thin films by performing fast Fourier transform on the digital signal.