Nanoscale Chemical-Mechanical Characterization of Nanoelectronic Low-k Dielectric/Cu Interconnects

Combined nanoscale chemical and mechanical property characterization has largely been limited by the inability to extend chemical structure identification techniques such as infrared (IR) absorption spectroscopy into the nanometer regime due to diffraction limitations. The recent development of atomic force microscope (AFM) based IR spectroscopy (AFM-IR) has now enabled infrared chemical spectroscopy with resolution well below the diffraction limit. However, the combination of AFM-IR with other AFM based techniques to achieve nanoscale chemical structure-mechanical property characterization has yet to be demonstrated. In this regard, we have combined AFM-IR chemical and contact resonance AFM (CR-AFM) mechanical measurements in the investigation of low dielectric constant (low- k ) / Cu damascene structures fabricated using a 90 nm interconnect process technology. We show that the combined AFM-IR and CR-AFM results can be utilized to perform nanoscale chemical-mechanical characterization of both the nano-patterned metal and the low- k dielectric whose mechanical properties are sensitive to chemical modification by the interconnect fabrication process. chemical structure and Lorentz contact resonance AFM (LCR-AFM) 32 mechanical property measurements of nanoelectronic interconnects. The specific circuitry investigated was comprised of Cu damascene wiring embedded in an insulating low dielectric constant (i.e. low- k ) a-SiOC:H dielectric. Low- k a-SiOC:H/Cu interconnects were chosen for this demon- stration due to the large disparity in chemical and mechanical properties between low- k dielectrics and Cu, and the extreme sensitivity a-SiOC:H dielectrics deposited on a thick Si substrate. AFM-IR spec- tra from the unpatterned a-SiOC:H dielectric were found to closely resemble those obtained from the same dielectric using conventional T-FTIR spectroscopy and thus reflect the true chemical make-up of the low- k dielectric. AFM-IR spectra of the ∼ 1.65 μ m wide patterned regions of the a-SiOC:H dielectric were also found to resemble those obtained using T-FTIR, but exhibited subtle differences relative to the ∼ 330 nm regions that were attributed to chemical modification by the Cu interconnect fabrication process. The latter demonstrates the ability of AFM-IR to perform IR spectroscopy well below the diffraction limit and detect chemical structure differences not likely resolved in traditional T-FTIR measurements. The AFM-IR chemical measurements were complemented by LCR-AFM mechanical measurements performed in tandem on the same a-SiOC:H/Cu structures. The LCR-AFM measurements showed clear differences in the mechanical properties between the a-SiOC:H dielectric, TNT barrier layer, and Cu wiring. The combination of AFM-IR and LCR-AFM has significant potential for providing high spatial resolution chemical and mechanical analysis of low- k a-SiOC:H/Cu interconnect and related nanoelectronic structures