Interfacial reactions in epitaxial Al/TiN(111) model diffusion barriers: Formation of an impervious self-limited wurtzite-structure AIN(0001) blocking layer

Abstract

Single-crystal TiN(111) layers, 45 nm thick, were grown on MgO(111) by ultrahigh vacuum reactive magnetron sputter deposition in pure N2 discharges at Ts=700 °C. Epitaxial Al(111) overlayers, 160 nm thick, were then deposited at Ts=100 °C in Ar without breaking vacuum. Interfacial reactions and changes in bilayer microstructure due to annealing at 620 and 650 °C were investigated using x-ray diffraction and transmission electron microscopy (TEM). The interfacial regions of samples annealed at 620 °C consist of continuous ≃7-nm-thick epitaxial wurtzite-structure AlN(0001) layers containing a high density of stacking faults, with ≃22 nm thick tetragonal Al3Ti(112) overlayers. Surprisingly, samples annealed at the higher temperature are more stable against Al3Ti formation. TEM analyses of bilayers annealed at 650 °C (10 °C below the Al melting point!) reveal only the self-limited growth of an ≃3-nm-thick interfacial layer of perfect smooth epitaxial wurtzite-structure AlN(0001) which serves as an extremely effective deterrent for preventing further interlayer reactions.