Development of x-ray reflectivity measurement system under N₂ to prevent surface contamination

In this study, a method to prevent surface contamination on an SiO₂ film/Si substrate system was used to improve thickness determination by x-ray reflectometry (XRR). XRR profiles can be significantly affected by the growth of a surface contamination layer, originating from the organic matter present in the measurement environment. An N₂ spray method that enables XRR measurement under high-purity N₂ has been developed to keep the surface free of contaminants. The method was adopted due to its high applicability to an existing XRR instrument and the ease of system construction. The system mainly consists of an outlet for N₂ spray that is positioned in front of the sample and an N₂ gas purifier. The high-purity N₂ is sprayed on the sample until the measurements are complete. It was revealed that the measured XRR profiles were stable for 115 h, and the evaluated thicknesses were obtained with high reproducibility (±0.05 nm for 10 nm thickness) by adopting the analysis model for clean surfaces.