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

• Published in: Applied surface science Vol. 141; no. 3-4; pp. 357 - 365
• Main Authors: Lekki, J, Filies, O, Boling, O, Grewer, K, Lekka, M, Stachura, Z, Cleff, B
• Format: Journal Article
• Language: English
• Published: 28-05-1998
• ISSN: 0169-4332

X-ray reflectivity (XRR) studies of thin layers (3 to 120 nm thick) were performed for the determination of layer thickness, density and roughness. The simulations of x-ray reflectivity measurements were performed using Parrat's recursive algorithm, while those of the reflection of x-rays from interfaces were performed using Fresnel formulae. Using this approach, the roughness of the interface was described by intensity damping by gaussian type functions. 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 direct fraction and a diffuse scattered one with the use of the first Born approximation. A simulation procedure, calculating both fractions of the reflection was developed, that enabled the detailed characterisation of layers and inner layers. The complementary information required for proper adjusting of input simulation parameters was obtained from SFM measurements of the investigated surfaces. Surface roughness was described using fractal surface functions instead of simple gaussian peaks. A comparison between this method and SFM measurement shows a reasonable agreement, particularly in the estimation of shapes of interface structures. Materials discussed include Co/Ag and Al/Ti bilayers and Ti and Sn layers on Si.