Dimensional Analysis of Through Silicon Vias Using the TSOM Method
Ravikiran Attota, Andrew Rudack
There is a great need for accurate, truly-3D metrology solutions that can be used for analysis of high aspect ratio features such as through-silicon-vias (TSVs). Through-focus scanning optical microscopy (TSOM) is an optical metrology method that provides three-dimensional information (i.e. the size, shape and location) about micro- and nanometer-scale structures[1-4]. TSOM, based on a conventional optical microscope, achieves this by acquiring and analyzing a set of optical images collected at various focus positions going through focus (from above-focus to under-focus). The measurement resolution is comparable to what is possible with typical light scatterometry, scanning electron microscopy (SEM) and atomic force microscopy (AFM). However, TSOM is capable of analyzing target dimensions from under 20 m to over 50 m both in the lateral and the vertical dimensions and is ideally suited for 3D targets such as TSVs. One of the unique characteristics of the TSOM method is its ability to separate different dimensional differences (i.e., the ability to distinguish, for example, linewidth difference from line height difference) and hence it is expected to reduce measurement uncertainty. In the current paper we present experimental TSOM dimensional analysis of TSVs with different types of dimensional variations generated using through focus-exposure-matrix (FEM). Figure 1 shows a preliminary TSOM experimental comparison of one micrometer and five micrometer diameter TSVs in three different FEM dies. TSOM holds the promise of high-throughput comparative measurements for a wide variety of application areas with potentially significant savings and yield improvements.