Nitrogen self-diffusion in magnetron sputtered Si-C-N films

Abstract

Self-diffusion was studied in magnetron sputtered nitrogen-rich amorphous compounds of the system Si-C-N by using nitrogen as a model tracer. As shown by infra-red spectroscopy a transient metastable region exists, where the structure of the material can be visualized as silicon nitride tetrahedra which are connected by carbo-diimide (-N¼C¼N-) bonds to a three dimensional amorphous network. In this region diffusion studies are carried out by neutron reflectometry and isotope multilayers as a function of annealing time, temperature and chemical composition. Low diffusivities between 10 À20 and 10 À24 m 2 /s were found. In the metastable region, diffusion is faster than diffusion in amorphous silicon nitride by 1 to 2 orders of magnitude, while the activation enthalpies of diffusion between 3.1 and 3.4 eV are the same within error limits. This can be explained by the fact that the diffusion mechanism along SiN 4 tetrahedra is identical to that in amorphous silicon nitride, however, the carbo-diimide bonds seem to widen the structure, allowing faster diffusion. A correlation between diffusivities and the number of carbo-diimid bonds present in the material is found, where the highest diffusivities are observed for materials with the highest number of carbo-diimid bonds, close to the composition Si 2 CN 4. V

Diffusivity determination in bulk materials on nanometric length scales using neutron reflectometry

“…Figure 2 compares experimental reflectivity patterns of a bare nat LiNbO 3 single crystal and a single crystal with a sputtered nat LiNbO 3 layer on top in the as-deposited and annealed state together with PARRATT32 simulations. The bare nat LiNbO 3 single crystal can be perfectly fitted by PARRATT32 using a neutron scattering length density (SLD) of 4.25 × 10 −6Å−2 that corresponds to a mass density of 4.6 g/cm 3 and a surface roughness of 0.6 nm. For the sample with the nat LiNbO 3 layer on top we observe the formation of characteristic fringes in the pattern, which are due to the interference of neutrons reflected at the surface and the film/ single-crystal interface, respectively.…”

“…Self-diffusion is a fundamental matter transport process in solids, playing a dominant role in the preparation, processing, and application of various materials. 1 The determination of self-diffusivities on very short length scales of ∼1 nm is important to understand the transport properties of nanostructured 2 and metastable materials 3,4 as well as of thin films, 5,6 especially at low temperatures. 7 Neutron reflectometry (NR) is a reliable method to measure diffusion length on the (sub)nanometer scale, as demonstrated for metallic, 2,6 intermetallic, 10,11 semiconducting, 7,9 and ceramic [3][4][5] thin films.…”

“…In order to carry out NR-based experiments, so-called isotope heterostructures of the material under investigation are used, [2][3][4][5][6][7] which are deposited by sputtering or molecular beam epitaxy on appropriate substrates [see Fig. 1(a)].…”

“…Here, characteristic Bragg peaks are formed in the reflectivity pattern and the decrease of this peak during annealing is analyzed. [2][3][4][5][6][7][9][10][11] This efficient approach has the drawback that it only works for as-deposited thin films of a certain material with a thickness between 10 and 500 nm and not for bulk materials. Such thin films are often in a nonequilibrium state after deposition, and equilibrium properties can hardly be determined.…”

Effect of dopants on thermal stability and self-diffusion in iron-nitride thin films

“…Since scattering length density (SLD) of neutrons is [43], B self-diffusion in amorphous boron [44], and N self-diffusion in Si 3 N 4 [45], Si-C-N [46], and iron monontrides (Nat. % ∼ 50) [47] compounds.…”