Lawrence O. Anderson, Dehua Yang, Ebatco, Eden Prairie, MN
Characterizing thin films, especially those with 100 nm thicknesses and less, provides challenges that largely arise from the small sample volume that is available for analysis. Many analytical techniques can be less than ideal, often requiring careful, and possibly destructive, sample preparation, and they may not be able to fully isolate film composition from the substrate influences. X-ray methods, like x-ray diffraction (XRD) and x-ray reflectivity (XRR), require very little sample preparation, are nondestructive, and can differentiate film and substrate contributions within the measured signals.
In this presentation, XRD is used to determine thin film phases and residual stress, and XRR is used to determine film thickness, density, and surface/interface roughness on several industrially-significant film on substrate systems, such as a low-k dielectric film on Si wafer, TiN film on metal substrate, nitride film on Si substrate, and Au film on glass. Thin film properties like crystalline phase and residual stress can be heavily influenced by lattice mismatch with the underlaying substrate, and this can significantly influence the desired mechanical, electrical, and thermal properties. One common difference between thin films and bulk materials is the emergence of significant anisotropy in material properties for thin films that result from crystallographic distortions. Thickness, density, and roughness can also influence end-product performance, with potential changes to optical properties, adhesion strengths, and other functional properties. Understanding how a substrate influences film structure, stress states, and morphology can be critical to product development, and ensuring fabrication consistency can help to maintain product quality and functionality.