Recommendations of IRDS require low-κ materials to possess dielectric (κ ≤ 2 by 2028), be mechanically robust, and serve as diffusion barriers against interconnect-atom migration into semiconductors. However, typical non-polar low-κ materials exhibit κ values exceeding 2 and poor thermo-mechanical properties. Here, I will demonstrate realisation of ultra-low κ values of 1.89 and 1.29 at 100 kHz and 1 MHz, respectively, in amorphous boron nitride (a-BN) via complementary metal-oxide semiconductor-compatible deposition at 400 °C. The resulting structure is mechanically robust, with excellent diffusion-barrier characteristics. Detailed structural characterisation indicates that a-BN is sp2-hybridised, with no measurable crystallinity. The breakdown strength of a 3-nm thick a-BN sample was 7.3 MV/cm. Cross-sectional transmission electron micrographs revealed no diffusion of metal atoms across a-BN under harsh conditions when compared against TiN barriers considered as reference.