The Structure And Physical Properties Of Rock-salt Hafnium Nitride Films

The excellent electrical properties,optical performances and mechanicalproperties of hafnium nitride (-HfNx) thin films make them widely used in electronicdevices,the mechanical system and the protective coating of cutting tools and so on.All these excellent properties are strongly dependent on its structure. Although thescientists have got many important achievements on the study of-HfNxfilms, thereare still two insufficiencies in these investigations. Firstly, the influence ofcomposition for the microstructure and optical electrical and mechanical properties ofrocksalt-HfNxthin films are still lack of systematic and detailed discussion.Secondly, the influence rules of bombarding ions on the structure, mechanicalproperties, optical properties and electrical properties of rocksalt-HfNxthin films arenot clear at present.In this paper,-HfNxthin films have been prepared via magnetron sputtering inthe discharge of N2/Ar, the N/Hf ratio in-HfNxthin films is controlled by changingthe nitrogen flow rate. The microstructure, mechanical properties and electricalproperties have been explored by XRD, HRTEM, XPS, Nanoindentation, Raman,AFMresistivity test experiment and the theoretical calculation. The conclusions aresummarized as follows:(1) When we only change the N/Hf ratio in the-HfNxfilms, the XRD and TEMresults proved that all the-HfNxfilms keep the rocksalt structure unchanged, but notthe perfect cubic NaCl structure. All the films have been elongated along (111)direction and distorted from cubic to orthorhombic structure. It is attributed to the allfilms are present (111) preferred orientation and in a compressive stress state and (111)plane is more likely to accommodate interstitial atom due to its larger gap space.Compared with the-HfNxfilm, the substoichiometric and overstoichiometric filmsdistort more intensely, this is attributed to Hf and N which lead to the latticecontraction. In particular, all the other surface spacing decreases faster than (111),aggravating the lattice distortion. In addition, Hf atom is bigger than N atom, so Hfvacancies create a larger lattice distortion than N vacancies do.(2) The structure, hardness and resistivity of-HfNxthin films are influenced byion bombardment, with the substrate bias changing from floating to200V, the latticeconstant of-HfNxincreases first and then decreases, this is due to the increase of thenegative substrate bias increases the energy of bombarding ions, and then the vacancydefect density of the films decreases first and then increases, leading to the latticecontraction degree and the hardness and resistance to plastic deformation ability firstdecrease and then increase. The reduce of the vacancy defect density reduces the mainelectron scattering centers within the film, increase the free electron relaxation time,increase the film conductivity and reduce the resistivity of the films. We also find thatthe appropriate negative substrate bias will reduce the surface roughness of the filmsbut when the substrate negative bias voltage is too high, it will increase thesurface roughness of the films again.