Growth, structural and mechanical properties of magnetron-sputtered ZrN/SiNx nanolaminated coatings

Coatings with nanoscale architectures, such as nanocomposites or nanolaminates, offer improved mechanical properties and resistance to radiation environments due to their increased interface area per unit volume. Here, we present a systematic study of the evolution of structure, stress state and mechanical properties of nanoscale ZrN/SiNx multilayers with different thickness of elementary layers, grown at Ts=300°C by reactive magnetron sputter-deposition from Zr and Si3N4 targets. Both the multilayer period Λ (7–41nm range) and ZrN thickness ratio, fMe, (0.24–0.95 range) were varied. X-ray reflectivity and transmission electron microscopy revealed the presence of planar interfaces, with roughness lower than 1nm, yielding to the formation of a highly periodic layer stacking throughout the entire film thickness. X-ray diffraction (XRD) show that the presence of amorphous SiNx layer (for elementary thickness ha≥1nm) induces a change in the preferred orientation of the cubic (B1-type) ZrN layers from (111) to (002), while the ZrN layer becomes X-ray amorphous at thickness hMe lower than 2nm. Using in situ wafer curvature measurements we show that both SiNx and ZrN layers are growing under an intrinsic compressive stress state, of a constant value of −1GPa for SiNx and varying from −5.7 to −4GPa with increasing ZrN layer thickness. Nanoindentation tests revealed a gradual increase of the elastic modulus from 200 to 265GPa with fMe, while the hardness showed a maximum (H=24.1GPa) for the ZrN(8nm)/SiNx(0.4nm) multilayer, corresponding to an 3–4GPa increase compared to monolithic ZrN (21.0GPa) and Si3N4 (19.2GPa) films. We ascribe this enhancement of mechanical properties to local epitaxy and stronger bonding at (001) ZrN/SiNx interfaces when the SiNx thickness reduces down to 0.4nm, as confirmed by XRD results obtained from ZrN/SiNx superlattices grown on MgO (001) substrate. •ZrN/SiNx nanolaminates were deposited by reactive magnetron sputtering.•Highly periodic multilayer with planar interfaces are formed.•Maximum hardness (24GPa) obtained at the thinnest SiNx layer (0.4nm)•Strengthening not related to Hall-Petch mechanism nor correlated to residual stress•Local epitaxy and stronger interfacial bonding are the main causes of hardening.