Surface roughness and resonant scattering effects in soft X-ray speckle from random semiconductor interfaces

We report the use of coherent soft X-ray scattering, or speckle, to study t he morphology of random surfaces on single crystal semiconductor substrates . The experiments were carried out with photon energies in the 266-290 eV r ange. The effect of the magnitude of the roughness on the scattering was ob served by measuring speckle patterns at various angles of incidence from tw o different surfaces with InP islands in the nanometer size range and in th e micron range. The effect of element-specific resonant scattering was expl ored with a PMMA-coated textured silicon sample by tuning the wavelength to the carbon K-edge. Two dimensional numerical simulations of the coherent s cattering have been carried out in the Fraunhofer approximation, using AFM data for the sample surface morphology. Good agreement with the observed sp eckle patterns was obtained, taking into account the 20 mu m lateral cohere nce length of the source.