Modification and Characterization of Interfacial Bonding for Thermal Management of Ruthenium Interconnects in Next-Generation Very-Large-Scale Integration Circuits

Ruthenium may replace copper interconnects in next-generation very-large-scale integration (VLSI) circuits. However, interfacial bonding between Ru interconnect wires and surrounding dielectrics must be optimized to reduce thermal boundary resistance (TBR) for thermal management. In this study, various adhesion layers are employed to modify bonding at the Ru/SiO2 interface. The TBRs of film stacks are measured using the frequency-domain thermoreflectance technique. TiN and TaN with high nitrogen contents significantly reduce the TBR of the Ru/SiO2 interface compared to common Ti and Ta adhesion layers. The adhesion layer thickness, on the other hand, has only minor effect on TBR when the thickness is within 2-10 nm. Hard X-ray photoelectron spectroscopy of deeply buried layers and interfaces quantitatively reveals that the decrease in TBR is attributed to the enhanced bonding of interfaces adjacent to the TaN adhesion layer, probably due to the electron transfer between the atoms at two sides of the interface. Simulations by a three-dimensional electrothermal finite element method demonstrate that decreasing the TBR leads to a significantly smaller temperature increase in the Ru interconnects. Our findings highlight the importance of TBR in the thermal management of VLSI circuits and pave the way for Ru interconnects to replace the current Cu-based ones.