The Role of a Ta2O5 Seed Layer on Phase Evolution and Epitaxial Growth of Ta3N5 Thin Films on Al2O3(0001)

Abstract

The present work investigates the growth, microstructure, and phase evolution of reactively sputtered Ta–N thin films deposited on Al₂O₃(0001) substrates with and without a Ta₂O₅ seed layer using complementary experimental techniques and theoretical calculations. X-ray diffraction (XRD) patterns reveal that without a seed layer, the films predominantly consist of the (111)-oriented cubic δ-TaN phase. In contrast, Ta₂O₅ seed layers promote the formation of an orthorhombic Ta₃N₅ phase with preferred orientation along the c-axis. Scanning transmission electron microscopy (STEM) results show the presence of large epitaxial Ta₃N₅ domains. Thickness-dependent XRD patterns and STEM images, together with fast Fourier transform studies, reveal that the transformations from β-Ta₂O₅ to a Ta–N mixed phase and finally to Ta₃N₅ take place during film growth. This observed phase transformation depicts that the seed layer serves not only as a structural template for the epitaxial growth of Ta₃N₅ but also as an active participant in the nitridation process during growth. Energy calculations suggest that the Ta–N species play a crucial role in stabilizing Ta₃N₅ growth. This work elucidates the complex interplay among seed layers, deposition conditions, and precursor energetics, offering a comprehensive understanding of Ta₃N₅ thin film epitaxial growth mechanisms.