Surface Morphology Evolution of Epitaxial TiN(001) Layers Grown by Reactive Magnetron Sputtering

Abstract

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. I use the epitaxial growth of single crystal TiN as a model system for insight on the evolution of surface morphology and microstructure in more complex polycrystalline films. Atomically-flat MgO substrates, prepared by air annealing at 950$\sp\circ$C for 12 hours, are verified by atomic force microscopy (AFM). Epitaxial TiN layers are grown on MgO(001) by reactive magnetron sputter deposition in pure N$\sb2$ at $\rm650<T\sb{s}<750\sp\circ$C. Without energetic ion bombardment, scanning tunneling microscopy (STM) results show that the development of surface morphology is dominated by growth mounds with an aspect-ratio of approximately 0.003; both the roughness amplitude and average separation between mounds follow an approximate power law dependence on film thickness, $t\sp{\gamma},$ with $\gamma=0.25\pm0.07.$ The island edges exhibit dendritic geometries characteristic of limited step-edge mobility. Low-energy N$\sb2\sp+$ ion irradiation during film growth at $\rm T\sb{s}=650\sp\circ$C leads to both surface smoothing and a decrease in the in-plane length scale, by a factor of $\approx$1.4, when V$\rm\sb{s}$ is increased from 3 to 43 V. However, the exponent which describes the roughening and coarsening is unchanged by the ion bombardment. Increasing T$\rm\sb{s}$ to 750$\sp\circ$C reduces the effects of N$\sb2\sp+$ ion bombardment between 3 and 48 V, but increasing $\rm V\sb{s}>48$ V leads to enhanced surface roughening with decreased in-plane length scales resulting from bulk defect production.