As device dimensions continued to shrink and semiconductor architectures evolved into increasingly complex 3D structures, single‑tool metrology approaches began to encounter fundamental limitations in accuracy and precision. This challenge led to the development of holistic metrology, which enhanced scatterometry performance by incorporating multiple information channels, azimuth angles, and measurement targets. The concept of holistic metrology later expanded into hybrid metrology, enabling complementary use of OCD, CD‑SEM, AFM, XPS, and other metrology techniques to further strengthen measurement robustness. More recently, AI‑enabled hybrid approaches have extended these capabilities. Alok Vaid played a central role in pioneering all these innovations, and this article serves both as a technical review of these developments and as a tribute to his lasting contributions to the metrology community.
Keywords: Holistic metrology, Hybrid metrology, Scatterometry, OCD, CD-SEM, AFM, XPS, XRF, Machine Learning, Virtual Metrology, AI, TMU
