The emergence of three-dimensional (3D) semiconductor devices has increased the importance of thermal imaging techniques. This paper presents a dual-capability system combining thermo-reflectance and thermal lock-in imaging (LIT) for high-speed, highly sensitive thermal analysis. We evaluate the hotspot detection capabilities of two-wavelength thermo-reflectance compared to LIT, including results from actual failure analysis cases. Our findings demonstrate the effectiveness of thermo-reflectance detection (TD) imaging for 3D devices where direct optical access to active layers is limited, such as 3D NAND flash memory and BSP-DN structured devices. This approach offers a promising solution for the thermal characterization of complex 3D semiconductor architectures.

The growing demand for flash memory in the artificial intelligence and big data industries has driven the development of Negative AND (NAND) gates. To increase yield and cost competitiveness, NAND has evolved to stack gates vertically, resulting in vertical NAND (VNAND) technology. However, this advancement has led to challenges, such as high aspect ratio-related difficulties and word line (WL) metal Tungsten (W) substitution process defects. In this study, we investigated Voltage Blocking Oxide Barrier (VBB) defects in VNAND cells under high-temperature conditions using in-situ heating TEM. By artificially creating VBB defect environments within VNAND cells and analyzing structural and chemical changes, we identified VBB defects expression phenomenon caused by residual HF(g) in metal voids during post-metal replacement processes. Our findings offer insights into defect-inducing heat treatment conditions affecting VBB in VNAND devices and propose directions for next-generation NAND flash processes.