Investigating Stability of Si Sphere Surface Layer in Ambient–Vacuum Cyclic Measurements Using Ellipsometry

Abstract

This paper reports an investigation conducted to evaluate the stability of surface layers on a Si sphere in ambient–vacuum cyclic measurements. An ellipsometer equipped with a vacuum chamber and a vapor-controlling system was developed to characterize the surface layers on the Si spheres. To investigate the stability and reproducibility of the surface layer, particularly for realizing and disseminating the kilogram, surface layer thickness measurements by ellipsometry were repeatedly conducted in air and vacuum for 1.5 months on a Si sphere with natural isotopic abundance. The surface layers of the Si sphere were relatively stable throughout the cyclic measurements, and no significant contamination was observed. We also conducted ellipsometry on the Si sphere after introducing water vapor into the vacuum chamber. The adsorbed water layer thickness in the air–vacuum and water vapor–vacuum measurements were almost identical, showing that gas components other than water vapor, such as carbonaceous materials stemming from the environment, had little effect on surface layer thickness in the air-vacuum cyclic measurements.