Effects of high-flux low-energy ion bombardment on the low-temperature growth morphology of TiN(001) epitaxial layers

Ultrahigh vacuum scanning tunneling microscopy (STM) is used to characterize the surface morphology of TiN(001) epitaxial layers grown by dc reactive magnetron sputtering at growth temperatures of Tₛ=650 and Tₛ=750^∘C. An auxiliary anode is used to bias the N₂ plasma and produce a large flux of low-energy N₂⁺ ions that bombard the film surface during growth: the ratio of the N₂⁺ flux to the Ti growth flux is ≈25. At ion energies Eᵢ near the threshold for the production of bulk defects (Eᵢ=43eV and Tₛ=650^∘C), ion bombardment decreases the amplitude of the roughness, decreases the average distance between growth mounds, and reduces the sharpness of grooves between growth mounds. The critical island radius for second layer nucleation Rc is approximately 12 and 17 nm at growth temperatures of 650 and 750^∘C respectively; at 650^∘C, Rc is reduced to ≈10nm by ion bombardment.