Porous Ultralow-κ sp²-Bonded Boron Nitride Thin Films as Copper Diffusion Barriers

Dielectric materials with low dielectric constant (κ < 2) are highly needed to overcome a series of problems caused by the decreasing size of microelectronics. An effective way to reduce dielectric constant is introducing void structure in dielectric materials, however challenging in mechanical strength and wetting properties. Herein, porous sp²-bonded boron nitride (BN) films are directly grown on Si substrates via radio frequency magnetron sputtering. The Guinier plot analysis of grazing incidence small-angle X-ray scattering spectra and electron microscopy confirms the pore size of ∼1.85 nm. The porous BN (p-BN) films show a band gap of ∼5.88 eV and a hydrophobic surface, ensuring the stability of dielectric properties. P-BN films exhibit an ultralow-κ of 1.77 at 100 kHz. These porous ultralow-κ BN films are electrically robust and mechanically stable superior to the previously reported porous dielectrics and close to the referent dense amorphous BN and hexagonal BN. Additionally, the p-BN films demonstrate notable diffusion barrier capability, effectively blocking Cu diffusion even with a thickness as low as 3 nm. This work provides a viable approach towards the controlled synthesis of porous ultralow-κ BN films as versatile dielectrics for transistor gate barriers, passivation layers, and capacitor spacers in high-performance electronics.