Determining sample alignment in X-ray Reflectometry using thickness and density from GaAs/AlAs multilayer certified reference materials

Published

September 8, 2014

Author(s)

Donald Windover, David L. Gil, Yasushi Azuma, Toshiyuki Fujimoto

Abstract

X-ray reflectometry (XRR) provides researchers and manufacturers with a non-destructive way to determine thickness, roughness, and density of thin films deposited on smooth substrates. Due to the nested nature of equations modeling this phenomenon, the inter-relation between instrument alignment and parameter estimation accuracy is somewhat opaque. In this study, we intentionally shift incident angle information contained in a high-quality XRR data set and refine this shifted data using an identical structural model to assess the effect angle misalignment has on parameter estimation. We develop a series of calibration curves relating data misalignment to variation with layer thickness and density for a multilayer GaAs/AlAs Certified Reference Material on a GaAs substrate. We then test the validity and robustness of several approaches of using known thickness and density parameters from this structure to calibrate instrument alignment. We find the highest sensitivity and stability to measurement misalignment from buried AlAs and GaAs layers, in contrast to the surface layers, which show the most instability. This is a fortuitous result, as buried AlAs and GaAs have shown the highest long-term stability in thickness. Therefore, it is indeed possible to use thickness estimates to validate XRR angle alignment accuracy. Buried layer mass density information also shows promise as a robust calibration approach. This is suprising, as electron density of buried layers is both a highly-correlated phenomenon, and a subtle component in the XRR model.

Citation

Measurement Science & Technology

Volume

25

Pub Type

Journals

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DOI Link

Keywords

X-ray reflectometry, thickness, density, sample alignment, calibration, certified reference material, genetic algorithm

Citation

Windover, D. , Gil, D. , Azuma, Y. and Fujimoto, T. (2014), Determining sample alignment in X-ray Reflectometry using thickness and density from GaAs/AlAs multilayer certified reference materials, Measurement Science & Technology, [online], https://doi.org/10.1088/0957-0233/25/10/105007 (Accessed May 2, 2025)