Experimental study and modelling of high aspect ratio through silicon vias (TSVs)

Abstract

As the semiconductor industry moves forward towards advanced packaging, through silicon vias (TSVs) with a top Critical Dimension (CD) down to 1 µm and aspect ratio 1:15 or higher are being projected. This poses a major challenge to optical metrology as the dimensions of the lattice get close to the wavelength of the visible light. White-light interferometry is commonly used to measure the depth of the vias, but suffers from decreasing signal-to-noise ratio depending on aspect ratio and diameter. To understand the limitations and develop new approaches for sensing these structures, modelling has proved to be a valuable tool. In this paper, we present results from electromagnetic wave propagation analysis compared to experimental interferometry data from high aspect ratio samples. Effects of via shape, spacing and dimension as well as simulation parameters on the resulting spectra are shown. Simulation can thus be used to predict for which type of vias a successful measurement can be expected.