A method of forming features in a dielectric layer is described. A via, trench or a dual-damascene structure may be present in the dielectric layer prior to depositing a conformal aluminum nitride layer. The conformal aluminum nitride layer is configured to serve as a barrier to prevent diffusion across the barrier. The methods of forming the aluminum nitride layer involve the alternating exposure to two precursor treatments (like ALD) to achieve high conformality. The high conformality of the aluminum nitride barrier layer enables the thickness to be reduced and the effective conductivity of the subsequent gapfill metal layer to be increased.