Atomic-scale mechanisms for diffusion of impurities in transition-metal nitrides

Copper diffusion into single-crystalline TiN studied by transmission electron microscopy and atom probe tomography

“…Similar interactions with native point defects have been proposed by first-principles calculations for Cu atoms in TiN [12,14].…”

“…With these values the diffusion coefficient at 1000 °C was calculated to be about 8×10 -18 cm 2 s -1 . A comparison to theoretical studies [11][12][13][14][15] based on densityfunctional theory shows that the likely diffusion mechanism in the present substoichiometric TiN films is Cu migration from one N vacancy site to another with an activation energy of 2.8 eV and a pre-exponential factor of about 9.7×10 -7 cm 2 s -1 .…”

“…The present paper shows how the two complementary methods can be used to provide both structural and chemical information of high resolution at buried interfaces. Experimental findings are correlated with results of first-principles studies [11][12][13][14][15]. Ultimately, this information will on the one hand contribute to the understanding of complex segregation and diffusion phenomena; on the other hand this combined experimental approach could become the basis for innovations in materials for microelectronics such as ultrathin and highly effective diffusion and oxidation barrier layers, or -more generally -reliable and degradation-resistant layered materials.…”

“…Extensive theoretical studies illustrating diffusion of Cu and other species in TiN are available by Tsetseris et al [11][12][13][14][15], where especially the importance of the defect structure in the TiN film is analyzed based on density-functional theory. In a perfectly stoichiometric, defect-free TiN film the activation energy E a for diffusion of an can be obtained from the Arrhenius-relation…”

“…This may be partly due to the fact that during the early stages of lattice diffusion the diffusion length is so small and the concentration of the diffusing species so low, that it is often below the detection threshold of conventional techniques for chemical analyses. Furthermore, theoretical studies of bulk TiN suggest that point defects present in the TiN barrier layer strongly affect the migration of impurity atoms [11][12][13][14][15]. TiN retains its stable rocksalt structure for a wide stoichiometry range, often resulting in high numbers of native point defects such as vacancies or interstitials that interact with impurity species.…”