Surface roughness of thin layers - a comparison of XRR and SFM measurements

X-ray reflectivity (XRR) studies of thin layers (3 to 120 nm thick) were pe rformed for the determination of layer thickness, density and roughness. Th e simulations of X-ray reflectivity measurements were performed using Parra t's recursive algorithm, while those of the reflection of X-rays from inter faces were performed using Fresnel formulae. Using this approach, the rough ness of the interface was described by intensity damping by gaussian type f unctions. This allowed for the determination of layer thickness and density and average interface roughness. As an extension of this simple model, an enhanced theoretical description of rough interfaces proposed by Sinha was applied, where the X-ray reflection from interfaces was separated into a di rect fraction and a diffuse scattered one with the use of the first Born ap proximation. A simulation procedure, calculating both fractions of the refl ection was developed, that enabled the detailed characterisation of layers and inner layers. The complementary information required for proper adjusti ng of input simulation parameters was obtained from SFM measurements of the investigated surfaces. Surface roughness was described using fractal surfa ce functions instead of simple gaussian peaks. A comparison between this me thod and SFM measurement shows a reasonable agreement, particularly in the estimation of shapes of interface structures. (C) 1999 Published by Elsevie r Science B.V. All rights reserved.