Practical WLRC methodology & applications in a wafer foundry

As the product life cycle shrinks, qualification needs to be completed in a much shorter time. This makes wafer level reliability (WLR) an important tool, enabling results to be obtained in a much shorter time. The two key issues for WLR are to guarantee the same failure mechanisms as conventional package-level reliability (PLR) and to maintain a statistically acceptable correlation (in terms of parameter estimation, lifetime projections and trend). We report the correlation of WLR and PLR tests and present WLR control (WLRC) methodology to ensure in-line reliability/process stability and to assist new technology development. We also present WLRC cases/plots/models, which show the benefits of a special control chart and principal component analysis (PCA). Apart from its use for in-line monitoring, by suitably designing the test structures and choosing the fail criteria, we also apply WLRC as a quick assessment of process/tool change qualification. WLRC can be embedded in the wafer acceptance test (WAT). We show how to use WLRC data to formulate reliability-WAT-yield models to facilitate yield improvement and reliability optimization.