Thin film structural analysis using variable-period x-ray standing waves

摘要

Variable-period x-ray standing wave (VPXSW) studies have been carried out using 3 keV x rays and photoelectron detection. Two model surfaces have been used, a native SiO2 layer (20 angstrom thick) on bulk silicon, and a purpose-built multilayer surface comprising a chloroform/water marker layer (12 angstrom thick) on an ionic liquid spacer layer (211 angstrom thick) deposited on a SiO2/Si substrate at 90 K. By using photoelectron detection, both chemical and elemental sensitivity were achieved. The surfaces were modeled using dynamic x-ray scattering for x-ray intensity, and attenuation of photoelectrons transmitted through the layers, to produce simulations which accurately reproduced the experimental VPXSW measurements. VPXSW measurements made using the substrate, spacer layer, and marker layer photoelectron signatures produced consistent structural values. This work demonstrates that VPXSW can be used to determine chemically specific layer thicknesses within thick (less than or similar to 300 angstrom) surface structures composed of the light elements B, C, N, O, F, and C1 with an accuracy of 10 to 15 angstrom, perpendicular to the surface.