AVS 51st International Symposium
    Advanced Surface Engineering Monday Sessions
       Session SE-MoA

Paper SE-MoA6
Surface Morphological Evolution of Epitaxial CrN(001) Layers

Monday, November 15, 2004, 3:40 pm, Room 303D

Session: Structure Control of Hard Coatings in Sputtering Processes
Presenter: D. Gall, Rensselaer Polytechnic Institute
Authors: J.R. Lynch, Rensselaer Polytechnic Institute
J. D'Arcy-Gall, Rensselaer Polytechnic Institute
S.V. Kesapragada, Rensselaer Polytechnic Institute
D. Gall, Rensselaer Polytechnic Institute
Correspondent: Click to Email
CrN layers, 7 to 300 nm thick, were grown on MgO(001) at 600-800 @degree@C by ultra-high-vacuum magnetron sputter deposition in pure N@sub 2@ discharges at 20 mTorr. Microstructural and surface morphological evolution were found to depend strongly on the growth temperature T@sub s@. Layers grown at 600 @degree@C nucleate as single crystals with a cube-on-cube epitaxial relationship with the substrate. However, above a critical thickness of ~50 nm, misoriented CrN grains nucleate and develop into cone-shaped grains that protrude out of the epitaxial matrix to form triangular faceted surface mounds. These mounds lead to a dramatic increase in the root-mean-square surface roughness, from 3 to 19 nm, for a 300-nm-thick layer. CrN grown at T@sub s@ = 700 and 800 @degree@C are complete single crystals. Their surfaces exhibit dendritic mounds with fingers extending along orthogonal <110> directions. In addition, the T@sub s@ = 700 @degree@C layer also shows square shaped "super"-mounds which protrude out of the underlying matrix and are attributed to a growth instability related to atomic shadowing effects which were purposely enhanced by non-normal deposition. For all layers, the surface roughness follows a power law with t. The exponent @beta@ is 1@+-@0.2 for the matrix-part of the surfaces, that is, the surfaces excluding the triangular and square shaped mounds for the T@sub s@ = 600 and 700 @degree@C layers, respectively. In contrast, @beta@ increases to 1.8@+-@0.3 when including the protruding grains. The two distinct @beta@-values are related to two roughening mechanisms: kinetic roughening, which is associated with an adatom motion towards ascending step edges due to a kinetic barrier for diffusion over descending steps, and atomic shadowing roughening, which is due to an increased local growth rate of surface protrusions caused by a higher capture rate of the incoming deposition flux.