Phase Extracting and Phase Unwrapping in Differential Interferometry System for Wafer Surface Topography
|School||Harbin Institute of Technology|
|Keywords||Topography Differential interference Phase extracting Phase unwrapping Digital image processing|
With the high density and high performance development on electronic products, non-trau-matic superficial surface and subsurface are expected more and more. Online testing of wafer surface quality is becoming extremely important in semiconductor manufacturing process.In this dissertation, with a thorough research of the developments of surface topography testing technology, a wafer micro-surface topography measuring system has been constructed, which combines polarization interference and phase-shifting technology. Phase-shifting interferograms can be obtained with the help of this system. Then by phase extraction algorithm, reconstruction surface algorithm, and phase unwrapping algorithm we can finally achieve wafer surface topography.In this dissertation, we first present basic principles of differential phase-shifting interferometry system, including phase-shifting interference principle and phase-shifting method. The overall design of measuring system is completed as well. Then thoroughly introduced phase extracting and phase unwrapping algorithm in this dissertation.Finally, denoise preprocessing algorithm, five-step phase-extraction algorithm of insensitive to linear phase-shifting error and complex integral reconstruction surface algorithm were implemented and the sample surface topography was obtained. With phase unwrapping analysis the real surface topography can be obtained.Phase unwrapping algorithm plays very important role in noncontract optical profilometry, because the phase map acquired is limited from ?πtoπ, which is called wrapped phase. It must be unwrapped to retrieve the nature phase employing suitable phase unwrapping algorithm.Research and experimental results indicate that the designed differential interference system for wafer surface topography works correctly; testing equipment is feasible; the system has characteristics of working at general experimental conditions.