Virtual metrology for TSV etch depth measurement using optical emission spectroscopy

In TSV fabrication process, TSV depth measurement of all wafers is essential to maintain high yield and wafer quality. However, there are limits such as high cost and (low throughput using an actual metrology, i.e. scanning electron microscope (SEM), and only few wafers in a lot are monitored in practice. In this research, we presented a virtual metrology (VM) system for TSV depth measurement after etching process. The proposed VM system is based on PLS regression (PLSR) and neural networks (NN) using OES data to predict TSV depth. Real operational data taken during TSVs etching process along with 80 and 25 μm diameter TSVs are used in order to verify the quality of the prediction accuracy of the proposed VM model.