Phase composition of polycrystalline HfNx (0.45 ≤ x ≤ 1.60) and effects of low-energy ion irradiation on microstructure, texture, and physical properties

We have investigated the phase composition of HfNx as a function of x and the effects of low-energy ion irradiation on the microstructure and physical properties of polycrystalline layers grown on SiO2 at 350 degrees C by ultrahigh vacuum reactive dc magnetron sputtering of Hf in mixed N-2/Ar discharges. X-ray diffraction and Rutherford backscattering spectrometry results show that the phases obtained in polycrystalline HfNx layers with increasing x are hcp-structure alpha-Hf:N (x less than or similar to 0.6); multiphase mixtures consisting of alpha-Hf, NaCl-structure delta-HfN, rhombohedral epsilon-Hf3N2, and/or zeta-Hf4N3 (0.6 less than or similar to x less than or similar to 0.9); delta-HfN single phase (0.9 less than or similar to x less than or similar to 1.3); and mixtures of delta-HfN and higher nitrides (x greater than or similar to 1.3). HfNx layers with 0.9 less than or similar to x less than or similar to 1.2 grown under mild ion irradiation (incident ion energy E-i similar or equal to 7 eV and ion-to-Hf flux ratios J(i)/J(Hf) = 1-3) are underdense with mixed orientation, low in-plane stress, and rough surface morphology due to limited adatom mobilities resulting in kinetic roughening and atomic shadowing during film growth. However, the use of intense ion irradiation (E-i = 25 eV and J(i)/J(Hf) = 4-20) results in HfNx layers, which are fully dense with strongly 111-oriented texture, compressive in-plane stress, and smooth surfaces due to ion irradiation enhanced adatom surface mobilities. In addition, the latter films have lower resistivity and higher hardness. For stoichiometric delta-HfN layers, rho decreases from 69.7 to 35.2 mu Omega cm and H increases from 22.1 to 27.4 GPa, with increasing ion-irradiation intensity. However, for HfNx layers with 1.2 less than or similar to x less than or similar to 1.6, the correspondingly higher steady state atomic N surface coverages during deposition alter growth kinetics in favor of 001 texture with a fully dense structure and compressive in-plane stress.

Automated summary

We investigated the phase composition of HfNx and the effects of low-energy ion irradiation on the microstructure of polycrystalline layers. The results show that the phases in the layers change with increasing x, and the properties of the layers are influenced by ion irradiation.