Limitations in critical angle determination with grazing incidence x-ray reflectivity

Abstract

X-ray reflectivity (XRR) is an effective non-destructive characterization method that has recently gained interest in the semiconductor industry for routine quality control. XRR is capable of measuring thin film properties such as density, thickness and interfacial characteristics. In particular, this method is being studied to determine its usefulness in characterizing porous SiO₂, one possible replacement for standard SiO₂ as a low-k dielectric for device miniaturization. A necessary component to evaluating these porous materials is to understand the level of porosity as determined by the overall density of the material. The density information can be obtained from the critical angle observed in XRR data, hence the necessity of accurate measurements. In this work, the authors explore the limitations of XRR for determining the overall density of a layer using a simulation and fitting program, SimulReflec, designed for x-ray and neutron reflectivity studies. This fitting program is applied to both experimental and simulated data. Various versions of noise have been added to simulated data and then re-fit to determine the sensitivity of the technique.