Abnormal Grain Growth in AlScN Thin Films Induced by Complexion Formation at Crystallite Interfaces

Sputter deposited Al(1–x)ScxN thin films with a Sc content from x = 0 to 43 at% are investigated by electron microscopy in order to study and explain the formation and growth of abnormally oriented grains (AOG). It is found that the latter did not nucleate at the interface with the substrate, but at...

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Published inPhysica status solidi. A, Applications and materials science Vol. 216; no. 2
Main Authors Sandu, Cosmin Silviu, Parsapour, Fazel, Mertin, Stefan, Pashchenko, Vladimir, Matloub, Ramin, LaGrange, Thomas, Heinz, Bernd, Muralt, Paul
Format Journal Article
LanguageEnglish
Published Weinheim Wiley Subscription Services, Inc 23.01.2019
Subjects
abnormal grain growth
aluminum nitride
Crystallites
Film thickness
Grain boundaries
grain boundary
Grain growth
Nucleation
Scandium
Substrates
Surface diffusion
Thin films
Wurtzite
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Summary:Sputter deposited Al(1–x)ScxN thin films with a Sc content from x = 0 to 43 at% are investigated by electron microscopy in order to study and explain the formation and growth of abnormally oriented grains (AOG). It is found that the latter did not nucleate at the interface with the substrate, but at high energy grain boundaries, at which systematically higher Sc concentrations are detected. The AOGs are thus formed during the growth of c‐textured grains. They grow faster than those, and finally protrude from the c‐textured film surface, having at their end a pyramidal shape with three facets of a hexagonal wurtzite crystal: one (0001) and two (112¯0) facets. Process conditions favoring less compact grain boundaries, and lower surface diffusion across grain boundaries are thought to promote nucleation of AOGs. Finally, a 4‐step growth mechanism explaining the nucleation from a Sc‐rich complexion and proliferation of AOGs with increasing film thickness is proposed. Characterization with hyper‐map STEM‐EDX and automated crystal orientation mapping prove that the growth and proliferation of abnormally oriented grains in (0001)‐oriented AlScN films initiate by the segregation of Sc atoms to grain boundaries, forming a Sc‐rich complexion layer. Secondary nucleation from the latter leads to the growth of heavily tilted, faster growing wurtzite grains.
ISSN:1862-6300
1862-6319
DOI:10.1002/pssa.201800569