The diffusion of silver in 6H–SiC and polycrystalline CVD-SiC was investigated using α-particle channelling spectroscopy and electron microscopy. The 360keV 109Ag+ were implanted to a fluence of 2 x 1016/cm2 at room temperature, 350C or 600C; producing an atomic density of about 2% at the projected range of some 110nm. The broadening of the implantation profile, and the loss of silver through the front surface during vacuum annealing at up to 1600C, were determined. Appreciable silver diffusion was observed, after an initial 10h annealing period at 1300C, in both polycrystalline and monocrystalline SiC. This was due mainly to implantation-induced damage. After further annealing at this temperature, no additional diffusion took place in 6H–SiC samples, but it was considerably reduced in CVD-SiC. The latter was attributed to grain-boundary diffusion, and could be described by Fick’s diffusion equation. Isochronal annealing of CVD-SiC at up to 1400C revealed an Arrhenius-type temperature dependence, with a frequency-factor of about 4 x 10−12m2/s and an activation energy of some 4 x 10−19J. Annealing of the 6H–SiC at above 1400C shifted the silver profile, without any broadening, towards the surface; where most of the silver was released at 1600C. Electron microscopy revealed that this process was accompanied by significant re-structuring of the surface region. A maximum diffusivity of less than 10−21m2/s was estimated for 6H–SiC at 1300C.

Study of Silver Diffusion in Silicon Carbide. E.Friedland, J.B.Malherbe, N.G.van der Berg, T.Hlatshwayo, A.J.Botha, E.Wendler, W.Wesch: Journal of Nuclear Materials, 2009, 389[2], 326-31