Frontside analysis with photon emission techniques is facing severe limitations with the growing use of multi-level metals which prevents photon emission of the defects from reaching the detector.

For instance, Figure 4868 shows PEM mapping depending on the local levels of the defects in the wafer. For this vertical MOSFET structure, some defects are analyzed by using frontside PEM (since the defect locates at the top side of the wafer), while some by backside PEM (since the defect locates at the bottom side of the wafer). The electrically conductive layers in the gates, and drain and source contacts are TiN/Ti(TiSix) metal layers.

Figure 4868. PEM mapping depending on the local levels of the defects in the wafer. [1]

[1] Abul Khair Yahya, Nik Tajuddin Yusof, and Yusnani Mohamad Yusof, Noble Failure Analysis Procedure for Trench MOSFET Technology Devices Through Detail Electrical Parameter Characterization and Unique Fault Isolation Technique, 2012 19th IEEE International Symposium on the Physical and Failure Analysis of Integrated Circuits, DOI: 10.1109/IPFA.2012.6306269, (2012).