chapter  9
60 Pages

Chapter 9

Abstract ............................................................................... 432 9.1 Introduction ................................................................ 432 9.2 Atomistic Processes in the Growth of Transition-Metal

Nitrides ....................................................................... 435 9.2.1 Texture Evolution ............................................ 437 9.2.2 Role of Ion Irradiation ................................... 441

9.3 Nanopipes ................................................................... 447 9.3.1 Surface Morphological Evolution ................... 453 9.3.2 Ion-Irradiation Effects on Surface Morphology

and Nanopipe Development ........................... 465 9.3.3 Atomic Shadowing Theory .............................. 471 9.3.4 Glancing-Angle Deposition Modeling ............ 475 9.3.5 Glancing-Angle Deposition ............................. 478 9.3.6 Future Directions for Nanopipe Design ........ 481

References ............................................................................ 484

ABSTRACT

This chapter describes the current atomic-level understanding of the growth of transition-metal nitride layers by physical vapor deposition, presents a summary of the growth of 1-nm-wide nanopipes, and describes the effect of atomic shadowing on surface morphological evolution and nanostructure formation. Transition-metal nitrides exhibit a highly anisotropic surface diffusion, which is several orders of magnitude higher on (001) versus (111) surfaces and favors 〈111〉-oriented grains during the kinetically limited competitive growth of polycrystalline layers. The texture evolution toward 〈111〉 is reversed under the influence of high-flux low-energy N+2 -ion irradiation that results in a steady-state atomic N coverage on (001) surfaces, increasing the effective adatom binding energy on 002-grains, and leading to a 002-oriented texture. Epitaxial single-crystal layers exhibit self-organized arrays of 1-nm-wide nanopipes that extend through the layers and form due to a combination of anisotropic adatom mobilities and atomic shadowing from periodic surface mound structures. The nanopipe density is controlled by the ion-irradiation flux during deposition. Ion irradiation increases the surface diffusion by a simple momentum transfer process, resulting in smoother surfaces, less atomic shadowing, and the suppression of nanopipe formation. Atomic shadowing causes strong surface roughening and leads to separated columns. The degree of shadowing can be increased by deposition from oblique angles. This is illustrated by the glancing-angle deposition (GLAD) technique that leads to well-separated nanopillars, which themselves exhibit complex engineered shapes, obtained by controlling both azimuthal and polar angles of the deposition flux. Such angular control will in the future allow the creation of complex interconnected nanochannel arrays in epitaxial transitionmetal nitrides.