Investigating the optical response of a through silicon via (TSV) for measuring the conic geometry

A popular method to combine different layers in the advanced packaging processes is the use of Through Silicon Vias (TSVs). These interconnects are predicted to reach aspect ratios (AR) of up to 20:1 and a top critical dimension (CD) down to 1 μm. To understand the optical effects caused by the Via it is vital to simulate the interaction of the electromagnetic wave and the material. The optical waves can be simulated with the Finite Difference Time Domain (FDTD) method. A spectrum compatible with an optical sensor based on reflectometric white light interference can be calculated from the FDTD simulation in which the information of Via geometry is decoded. This paper presents an initial investigation into a novel method for measuring the conical shape of the Via with an approach based on operations in the Fourier-spectrum of TSVs with varying shapes and a comparative analysis with a white light interferometric measurement.