Thermal Conductivityand Thermal Boundary Resistanceof Low–Dielectric Constant Interlayer Dielectrics in AdvancedVery Large Scale Integration Interconnects

Low–dielectric constant (low-<i>k</i>) interlayer dielectrics (ILDs) are necessary to reduce signal propagation delay and electronic crosstalk in advanced very large–scale integration (VLSI) circuits. The thermal conductivity of low-<i>k</i> ILDs substantially influences the temperature rise of VLSI interconnects, which in turn affects the performance and reliability of VLSI circuits. Furthermore, as the technology node is scaled, the thermal boundary resistance (TBR) between wires and low-<i>k</i> ILDs becomes increasingly critical for thermal management in VLSI interconnects. In this study, we experimentally investigated the thermal conductivities and TBRs of methylpolysiloxane-based low-<i>k</i> ILDs. The results showed that although a 5% increase in the methyl content minimally affected the thermal conductivity, it substantially increased the TBR, while curing enhanced both the thermal conductivity and TBR. Persistent homology analysis was performed on the transmission electron microscopy images of the low-<i>k</i> ILDs to extract hidden structural features and quantify the medium-range order, which further elucidated the mechanisms underlying the thermal conductivity modification. The enhanced thermal conductivities of the cured ILDs were attributed to both enhanced phonon group velocities and effective mean free paths of delocalized vibration modes owing to film densification. Fourier-transform infrared spectra revealed that variations in TBR were primarily attributed to modifications of the hydrophilic and hydrophobic functional groups. In the low-<i>k</i> ILDs, more hydrophobic methyl or fewer hydrophilic hydroxyl and silanol groups reduced interfacial bonding between the low-<i>k</i> ILD and its adjacent layers, thereby enhancing the TBR. Contact angle measurements revealed a linear relationship between the interfacial bonding strength and TBR. Our findings offer insights into thermal transport in low-<i>k</i> ILDs and at interfaces, which are both essential for developing next-generation thermally conductive low-<i>k</i> ILDs and composite thermal interface materials for thermal management in VLSI circuits.