Design And Experimental Study Of Differential Interferometry System For Wafer Surface Topography

Wafer is the basic material of the production of Integrated Circuit, and surface roughness is an important parameter for evaluating surface quality. Online testing of wafer surface quality is becoming an extremely important part in semiconductor manufacturing process.In this thesis, with a thorough research of the developments of surface topography testing technology , a wafer micro-surface topography measuring system based on optical differential phase-shifting interference principle has been constructed, which combines polarization interference, lateral shearing and phase-shifting technology. While polarized incident light is reflected on the sample surface, the polarized light is deflected into lateral shearing device and goes through the phase-shifter; the light is divided into double-beam polarized rays, which take interference. Changing phase-delay between two beams by phase-shifter, some pieces of phase-shifting interferograms can be obtained. Then by phase extraction algorithm and reconstruction surface algorithm, we can achieve wafer surface topography.In this dissertation, we first presents basic principles of differential phase-shifting interferometry system, including differential shearing principle, phase-shifting interference principle and phase-shifting method, and completes the overall design of measuring system. Differential-shearing exploits uniaxial birefringence parallel crystal (uniaxial parallel crystal), and phase-shifting exploits polarization phase-shifter, constructed from a quarter wave plate and an analyzer.The dissertation makes specific study with shearing properties of uniaxial parallel crystal, the polarization relations and the experimental adjustment method. According to system solutions and measuring requirements, we have completed design structure parameters of uniaxial parallel crystal, the polarization angle, CCD parameters, micro-lens magnification and numerical aperture, illumination method and so on. And based on that, experimental apparatus was constructed and debugged. Finally, collection five experimental interferograms, denoising preprocessing algorithm, five-step phase-extraction algorithm of insensitive to linear phase-shifting error, complex integral reconstruction surface algorithm were implemented and the sample surface topography was obtained.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, anti-jamming, in nm magnitude accuracy.