Characterization of Barrier Layer Phase and Morphology As a Function of Differing Dielectric Substrate Conditions by AFM and Grazing Angle XRD

Abstract

Tantalum (Ta) metal has emerged as one of the leading materials of choice for diffusion barrier applications in Cu-damascene interconnects. For successful implementation, the microstructure, the electrical property and the surface roughness of the barrier layer have to be controlled. To satisfy such needs, atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques have been employed to monitor the surface roughness and crystal phase of the PVD Ta thin film deposited on low-£ dielectrics. XRD results show that the population of the two different Ta crystal phases, a and p, depends on substrate material, surface pretreatment prior to thin film deposition and deposition conditions. AFM results reveal that surface roughness of the thin barrier layer is mainly determined by the starting substrate surface roughness. Also, AFM surface imaging discovered that each Ta crystal phase possesses a unique surface morphology. Therefore, the population of the Ta crystal phases can be crudely quantified by performing image analysis on the AFM images. The Ta phase population obtained from AFM images correlates very well with the XRD results.