Berlin 2008 – wissenschaftliches Programm

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MM: Fachverband Metall- und Materialphysik

MM 23: Poster session

MM 23.3: Poster

Dienstag, 26. Februar 2008, 14:45–18:00, Poster B

Nitrogen Diffusion in Amorphous Silicon (Carbo)Nitride Probed by Neutron Reflectometry — •Erwin Hüger¹, Thomas Gutberlet², Jochen Stahn², Michael Bruns³, and Harald Schmidt¹ — ¹Institut für Metallurgie, AG Materialphysik, TU Clausthal, Germany — ²Laboratorium für Neutronstreuung, ETH Zuerich & PSI, Villigen, Switzerland — ³Institut für Materialforschung III, Forschungszentrum Karlsruhe GmbH, Germany

Covalently bound amorphous solids are distinguished by extremely low self-diffusivities, which necessitates the detection of extremely short diffusion lengths in order to prevent an overlapping of crystallization and diffusion processes during annealing. We present nitrogen diffusion studies on amorphous SiN_x and SiC_xN_y materials, which were carried out by neutron reflectometry on isotope heterostructures. Here, a sequence of 14-N and 15-N enriched layers are deposited by magnetron sputtering on silicon substrates. Due to the different coherent neutron scattering lengths of 14-N (9.37 fm) and 15-N (6.44 fm) a scattering contrast for neutrons occurs between chemically identical layers. Self-diffusivities are determined from the modification of the reflectivity due to interdiffusion of the two nitrogen isotopes after annealing at elevated temperatures. We present a systematic study on samples with 3, 5, 12 and 40 single layers and demonstrate that it is possible to detect miniumum diffusion lengths of 0.7 nm and self-diffusivities of 5 x 10⁻²⁵ m²/s. The temperature and annealing time dependence of the diffusivities is analyzed and explained in the framework of structural relaxation processes.