Cubic HfN (B1-NaCl) thin films were grown epitaxially on Si(001) substrates by using a TiN (B1-NaCl) buffer layer as thin as similar to 10 nm. The HfN/TiN stacks were deposited by pulsed laser deposition with an overall thickness below 60 nm. Detailed microstructural characterizations include x-ray diffraction, transmission electron microscopy (TEM), and high resolution TEM. The electrical resistivity measured by four-point probe is as low as 70 mu Omega cm at room temperature. Preliminary Cu diffusion tests show a good diffusion barrier property with a diffusion depth (2D tau) of 2-3 nm after annealing at 500 degrees C for 30 min in vacuum.