3D analysis of buried interfaces using interference microscopy

The use of white light interference microscopy for the non-destructive 3D measurement of an interface buried under a transparent layer has been investigated. Test samples consisting of step structures (< 2 mu m) etched in silicon and then covered by a thick (> 1 mum) layer of resin have been studied. The 3D morphology of the buried step was successfully measured through the transparent layer. Comparison of the step heights measured before and after the deposition of the resin layer shows a reduction in the estimated measurement precision from 4% in air to 9% through the transparent layer. The additional errors arise from optical aberrations due to the roughness and the geometry of the air/resin surface, the thickness of the layer and possibly from inhomogeneities in the refractive index of the layer that contribute to a degradation of the wavefront reflected from the interface.