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 we ar-resistant coating on mechanical components and as a diffusion barri er in microelectronic devices. We use the epitaxial growth of TiN as a model system for insight on the evolution of surface morphology and m icrostructure in more complex polycrystalline films. Atomically-flat M gO(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. Scanni ng tunneling microscopy (STM) results show that the development of sur face morphology is dominated by growth mounds with an aspect-ratio of approximate to 0.006; both the roughness amplitude and average separat ion between mounds follow an approximate power law dependence on film thickness, t(gamma), with gamma = 0.25 +/- 0.07. The films grow in a t wo-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 dis location loops on {111} planes and [001] misfit dislocations at the in terface. Low-energy N-2(+) ion irradiation during film growth leads to surface smoothing with the smoothest layers, having a surface width o f congruent to 0.22 nm, obtained with V-s = 43 V. Increasing V-s great er than or equal to 43 V leads to surface roughening with decreased in -plane length scales. (C) 1997 Elsevier Science S.A.