edfas.org 13 ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 28 NO. 2 capable of inducing reliability failures such as copper diffusion, dielectric separation, or interfacial cracking. The objective of this study is to identify and analyze the inspection and metrology challenges inherent to hybrid bonding across all process stages. The discussion focuses on defect sources related to planarization, alignment, and thermal bonding, and evaluates the performance limits of current nondestructive inspection technologies. In addition, this article explores emerging AI-assisted frameworks that integrate multiple imaging modalities to improve defect coverage and process insight. Through this analysis, the work aims to outline existing bottlenecks and propose a pathway toward scalable and adaptive inspection methodologies suitable for next-generation chiplet-based integration. OVERVIEW OF THE HYBRID BONDING PROCESS Hybrid bonding represents a sophisticated interconnect technology that enables the direct joining of two surfaces, each patterned with copper pads embedded within dielectric layers, through the synergistic application of mechanical, chemical, and thermal processes. In contrast to conventional solder bump-based methods, hybrid bonding eliminates solder connections, which allows significantly higher interconnect densities, a critical requirement for contemporary 3D integration and chiplet-based architectures. By simultaneously combining dielectric-to-dielectric and metal-to-metal bonding mechanisms within a single interface, the process establishes a mechanically robust and electrically stable connection between stacked components that supports structural integrity. An illustration of an advanced package structure with hybrid bonding interconnects and their key manufacturing-induced defect locations is shown in Fig. 2. The wafer-to-wafer (W2W) and chip/die-to-wafer (C2W/D2W) hybrid bonding process can be systematically partitioned into four fundamental stages: surface planarization, surface activation, precision alignment, and thermal bonding. Each stage exerts a pivotal influence on the overall reliability and functional performance of the bonded interface. Surface planarization establishes a high degree of topographical uniformity, enabling intimate contact between opposing wafers or Fig. 2 (a) Advanced package interconnected with hybrid bonding technology. (b) Critical hybrid bonding manufacturing-induced defects highlighted in an advanced package. (a) (b)
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