Evaluation of radio-frequency sputter-deposited textured TiN thin films as diffusion barriers between copper and silicon

Abstract

Thin textured titanium nitride (TiN) films with thicknesses under 100 nm were grown on (100) silicon wafers by employing a radio-frequency generator to sputter reactively a Ti target under poisoned modes in mixtures of fixed Ar (3.6×10−1 Pa) and N2 at various partial pressures. The texture of the TiN films can be tailored by appropriately controlling the partial pressure of the reactive nitrogen. (111) textured films can be deposited over a broad range of lower N2 partial pressures from 2.9×10−2 to 1.8×10−1 Pa, while (100) textured films can be deposited in a narrow range of higher nitrogen partial pressures (2.3×10−1 to 3.3×10−1 Pa). The texturing effect is accounted for by a previously described thin film deposition mechanism. Scanning electron and atomic force microscopies demonstrate that the two textured TiN films both exhibit a column-grained structure; the columnar size of the (111) oriented TiN (⩾30 nm) is coarser than that of the (100) oriented TiN (10–20 nm). Evaluations of the textured TiN barriers, based on differences in sheet resistance, surface morphology, and phase transformation induced by annealing Si/TiN(40 nm)/Cu(200 nm) samples, suggest that the (111) TiN is a superior diffusion barrier material for copper than (100) TiN. The difference in barrier effectiveness is attributed to variations in crystallographic packing and microstructure of the textured diffusion barrier.