In situ scanning tunneling microscopy studies of the evolution of surface morphology and microstructure in epitaxial TiN(001) grown by ultra-high-vacuum reactive magnetron sputtering

The group IV-B transition metal nitride TiN is widely employed as a wear-resistant coating on mechanical components and as a diffusion barrier in microelectronic devices. We use the epitaxial growth of TiN as a model system for insight on the evolution of surface morphology and microstructure in more complex polycrystalline films. Atomically-flat MgO(001) substrates, prepared by air annealing at 950 degrees C for 12 h, are verified by atomic force microscopy (AFM). Epitaxial TiN layers are grown by reactive magnetron sputter deposition in pure N-2 at 650 less than or equal to T-s less than or equal to 750 degrees C. Scanning tunneling microscopy (STM) results show that the development of surface morphology is dominated by growth mounds with an aspect-ratio of approximate to 0.006; both the roughness amplitude and average separation between mounds follow an approximate power law dependence on film thickness, t(gamma), with gamma = 0.25 +/- 0.07. The films grow in a two-dimensional multilayer mode in which island edges exhibit dendritic geometries characteristic of limited step-edge mobility. Transmission electron microscopy (TEM) shows that the films are epitaxial with dislocation loops on {111} planes and [001] misfit dislocations at the interface. Low-energy N-2(+) ion irradiation during film growth leads to surface smoothing with the smoothest layers, having a surface width of congruent to 0.22 nm, obtained with V-s = 43 V. Increasing V-s greater than or equal to 43 V leads to surface roughening with decreased in-plane length scales. (C) 1997 Elsevier Science S.A.