Synthetic wavelength scanning interferometry for 3D surface profilometry with extended range of height measurement using multi-colour LED light sources

Abstract

We report three-dimensional surface profilometry with extended range of height measurements using synthetic wavelength scanning interferometry without tunable filters, wavelength-tuning lasers, grating elements. We have used inexpensive multiple colour light emitting diodes (LEDs) and operate them sequentially one by one or combination of two or more colours simultaneously to visualize synthetic wavelength light source. Multiple colour LED light source was synthesized and entire visible range from violet to deep red colour was covered. A wide range of synthetic wavelengths were obtained. Five step phase shifting algorithm was used to recover phase maps with Mirau type interferometer which can be further utilized for 3D height measurements. A simple phase subtraction method was used to reconstruct the phase map at synthetic wavelength. The present system provides extended range of height measurements from sub-wavelength to tens of wavelengths. Experimental results of 3D-surface profile measurements of Si-IC chip and standard step object are presented.