Non-contact measurement of silicon thin wafer warpage by THz tomography and laser triangulation

This paper investigates contact-less sensing concepts for measuring the three-dimensional deformation of (silicon) thin wafers. The deformation shape under different load conditions is a vital measurand, as it directly correlates to internal mechanical stresses in the wafer and is of importance for in-line process control of manufacturing processes involving thin wafer handling. Both time-domain THz tomography and laser triangulation were investigated and the results successfully used to validate FEM simulation models used to predict the deformation shapes of wafers of different thicknesses, layer structures and processing histories.