X-Ray Reflectometry Analysis of Platinum Thin Film Properties deposited in E-beam Deposition Systems

Abstract:

X-ray reflectometry (XRR) is a powerful, non-destructive technique where coherent x-rays are impinged at small incidence angles (<5°) onto the surface of a material in order to characterize specific properties of the material (i.e. density, thickness, and roughness) in the near-surface region. The measurements generate a plot of intensity versus the incidence angle (rocking curve), which shows periodic oscillations versus incidence angle, based on which the vertical (layer thickness and density) and lateral (roughness) properties can be extracted. The purpose of this study is to compare the measured properties of platinum (Pt) thin films deposited by three separate and nominally identical electron beam evaporators (EBEs). Nominal 9 nm Pt thin films were deposited on top of three-inch silicon (Si) wafers using the three EBEs. Since no de-oxidation steps were taken before deposition, an SiO2 layer also formed on top of the substrate. A RIGAKU Smartlab X-Ray Diffractometer then performed 9 sets of XRR measurements consisting of three sites on the wafer: the center, as well as 20 mm above and below the center. The measurements were then modeled with the Rigaku Globalfit simulation software to calculate the properties of the thin films and SiO2 layer on each wafer. The simulation revealed that the measurements of the wafers from different EBEs generated different rocking curves, meaning the best-fit Pt density profiles differ from system to system. In addition, the density profile of the Pt thin film is not constant, and contains three layers of varying densities. The density also varies linearly with depth in the first two layers from bottom to top (11.08 g/cm³ to 16.52 g/cm³ in the first layer, 16.33 g/cm³ to 5.68 g/cm³ in the second), likely due to the structural transient in these layers. The density of the third Pt layer approaches that of the bulk density (21.45 g/cm³) as the deposited thickness increases. The simulation also revealed that an SiO2 layer is needed for the rocking curve to have a good fit with the model. Finally, the measurements showed solid uniformity across the wafer in each system. The calculated values of the density, thickness, and roughness of the Pt films and Si substrate were similar across all points on the wafer, with standard deviation values of less than 0.10 between the measured values and the theoretical.