High-Resolution Nanoscale X-ray Imaging for Non-Destructive Inspection of Copper Grains in Fine-Pitch Pads for Hybrid Bonding

The rapid evolution of three -dimensional heterogeneous integration (3D -HI) is transforming semiconductor packaging by enabling higher performance, increased functionality, and reduced power consumption. As interconnect features such as copper (Cu) micro -bumps and hybrid bonding pads shrink to sub-micrometer dimensions, device reliability becomes increasingly sensitive to local morphology, grain structure, and residual strain. Conventional X-ray inspection techniques, however, lack the spatial resolution and strain sensitivity required to probe these nanoscale crystalline features and to detect process-induced defects non-destructively. In this work, we demonstrate the application of Bragg Coherent Diffractive Imaging (BCDI) as a high-resolution, non-destructive X -ray metrology technique for three -dimensional characterization of individual Cu grains in fine -pitch hybrid bonding pads. BCDI employs a highly coherent synchrotron X-ray beam to interrogate a single crystalline grain near a Bragg reflection, recording coherent diffraction patterns that are inverted using iterative phase -retrieval algorithms. The recon-structed amplitude provides grain morphology, while the phase encodes lattice displacements, enabling quantitative mapping of internal strain fields and identification of defects such as dislocations, stacking faults, and twin boundaries. BCDI measurements were performed on Cu grains extracted from advanced 3D-HI test wafers fabricated by IBM at the NY Creates Albany, NY 300-mm facility. Experiments were conducted at the ID01 beamline of the European Synchrotron Radiation Facility (ESRF), targeting the Cu (111) Bragg reflection. Three -dimensional reciprocal -space maps were acquired using a highly coherent incident beam and high-sensitivity area detectors, followed by rigorous data preprocessing and advanced phase-retrieval reconstruction. The resulting ∼6 nm-resolution reconstructions reveal individual grain sizes on the order of 150 nm and non -uniform compressive strain distributions ranging from 0.1% to 0.5%. The observed strain heterogeneity is indicative of residual plastic deformation and stress localization introduced during chemical–mechanical planarization (CMP) and thermal annealing. Coherent diffraction analysis further confirms that the dominant grain orientations are along the (111) and (001) crystallographic directions. These results demonstrate that BCDI overcomes the resolution and sensitivity limitations of conventional X -ray inspection techniques for 3D-HI interconnects, providing quantitative, three-dimensional insight into nanoscale strain and defect states without destroying the sample. Looking forward, BCDI enables operando investigations of grain growth, strain relaxation, and defect evolution during hybrid bonding, thermal cycling, and electrical stressing. Such measurements will provide critical insight into electromigration, void formation, and interfacial degradation mechanisms. When combined with complementary techniques such as electron backscatter diffraction (EBSD), transmission electron microscopy (TEM),