Grain-Size Engineering in Vapor-Deposited ZIF-8 MOF: Low-Leakage Low-k Films with Enhanced Breakdown Field

The integration of low-k dielectrics into advanced logic and memory technologies requires materials that combine low permittivity with high electrical reliability and plasma robustness. Zeolitic imidazolate framework-8 (ZIF-8) has emerged as a promising candidate for back-end interlayer dielectrics due to its vapor phase deposition, thermal stability, and low dielectric constant. However, vapor-deposited ZIF-8 films reported to date exhibit relatively large grains and limited dielectric breakdown strength (∼0.5-0.7 MV cm^-1), constraining their application in advanced packaging. In this study, grain-size engineering is demonstrated as an effective route to overcome this limitation. By kinetically controlling the oxide-to-MOF conversion during vapor-phase synthesis, we obtained fine-grained ZIF-8 films with reduced surface roughness and minimized defect percolation pathways. The resulting small-grain ZIF-8 exhibits a 3-fold enhancement in breakdown strength (2.1 MV cm^-1) while maintaining a low dielectric constant (k ≈ 2.5-2.6) and a leakage current at 1 MV cm^-1 > 1000× lower than large-grain ZIF-8. Both small-grain and large-grain ZIF-8 films show high fluorocarbon-plasma resistance, with etch rates >5× slower than SiCOH, the common commercial low-k dielectric. These results establish microstructural control as a powerful design lever for improving electrical robustness in vapor-deposited MOFs and position ZIF-8 as a viable low-k dielectric for future backend and 3D heterogeneous-integration platforms.