Optimization of global accuracy on specular surfaces with a "Dual Core" 3D sensor (SIM + µPMD)

SIM has been proven as an incoherent microscopic 3D technology on technical surfaces that may even compete with white light interferometry[1]. Height measuring uncertainties can be achieved down to 10nm by choosing the optimal system parameters. However, as we extend SIM to a larger field of view, the aberrations of the objective will introduce large space variant systematic errors, which are dependent on the surface normal and cannot be easily calibrated. This phenomenon is due to the coma and spherical aberration and critical on strongly curved specular surfaces. In order to compensate for these systematic errors, we have carried out a modelfree calibration strategy, measuring the relationship between focus shift(Δx,Δy,Δz), pixel position(i,j) and surface normal(θ,φ) for the given system. During realistic measurement, μPMD(micro Phase Measuring Deflectometry) was incorporated into SIM to obtain the unknown surface normals enabling us to calculate the corrective vectors. In this presentation we will show how the focus shift depends on the third order aberrations and introduce the novel calibration strategy with a "Dual Core" 3D sensor (SIM+µPMD). [1]Kranitzky,DGaO,A12,2009