Ultralow-dielectric-constant amorphous boron nitride

Miniaturisation of electronic devices has resulted in increased interconnect resistance–capacitance delay and high power dissipation. Integration of low-k dielectrics—insulating materials that exhibit weak polarisation under applied electric fields—which also serve as diffusion barriers, facilitates miniaturisation beyond the current state-of-the-art. Recommendations of the International Roadmap for Devices and Systems require low-k materials to possess dielectric (k values ≤ 2 by 2028, be mechanically robust, and serve as diffusion barriers against interconnect-atom (typically Cu) migration into semiconductors. However, typical non-polar low-k materials, such as oxide derivatives (SiCOH), organic compounds, and aerogels, exhibit k values exceeding 2 and poor thermo-mechanical properties. In this talk, I will demonstrate realisation of ultra-low k 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 (CMOS)-compatible deposition at 400 °C.[1] 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 – high enough for contemporary applications. 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. Hence, our results suggest that the amorphous counterpart of two-dimensional hexagonal boron nitride possesses ideal characteristics for use in next-generation low-k dielectrics for high-performance electronic applications.

[1] S. Hong et al., Nature 582, 511-514 (2020).