Interfacial structural modification in Cu/low- k interconnects revealed by atomic force microscopy infrared spectroscopy

Process-induced modification confined to the immediate vicinity of Cu/low-k interfaces is a key issue in advanced interconnects, yet direct vibrational-band-specific characterization of this region on the tens-of-nanometers scale remains difficult. Here, resonance-enhanced atomic force microscopy (AFM) infrared spectroscopy has been applied from the upper surface of a practical damascene Cu/low-k interconnect structure comprising 330 nm wide Cu lines separated by 270 nm in a 200 nm thick, porous SiOC-based dielectric film, enabling direct comparison of the central low-k region and the interface-adjacent region. Local spectroscopy together with a 15-point line scan at an 18 nm step interval revealed reduced Si–CH3-related and Si–H-related vibrational responses and an enhanced OH-related response, including possible contributions from Si–OH, hydrogen-bonded hydroxyl species, and adsorbed water, near the Cu/low-k interface, with the most pronounced methyl-related change observed at the first low-k measurement point adjacent to the boundary. This direct nanoscale identification of interfacial structural modification has been enabled by resonance-enhanced photothermal detection and AFM-based positional control and has been demonstrated directly on a practical top-surface device structure without preparing a special cross-sectional specimen. The observed interfacial chemistry is consistent with localized demethylation, modification of Si–H-related environments, and increased hydroxyl/water-related character and is, therefore, consistent with the formation of a locally higher-k interfacial zone, which is expected to contribute to increased capacitance, leakage risk, and breakdown susceptibility in practical low-k interconnects.