Improved properties of atomic layer deposited ruthenium via postdeposition annealing

Abstract

The resistivity, morphology, and effective work function of thin film ruthenium deposited by thermal atomic layer deposition (ALD) using η4-2,3-dimethylbutadiene ruthenium tricarbonyl [Ru(DMBD)(CO)3] and O2 are investigated before and after annealing at temperatures up to 500 °C. Annealing at 500 °C in either N2 or H2/N2 reduces the average resistivity of as-deposited 30 nm thick Ru films from 16.2 to as low as 13.7 or 9.1 μΩ cm, respectively, approaching the bulk value of Ru. X-ray diffraction shows that as-deposited films are polycrystalline hexagonal Ru. Annealing at 500 °C in either N2 or H2/N2 results in crystallite growth accompanied by a roughening of the surface from approximately 0.7 to 2.2 nm RMS, as shown by atomic force microscopy. Secondary ion mass spectroscopy shows low residual carbon and oxygen in as-deposited films. Annealing in N2 at 500 °C reduces only the carbon content, whereas annealing in H2/N2 at 500 °C results in a further reduction of carbon combined with reduction in oxygen as well. Using series of metal/oxide/silicon capacitors with varying oxide thickness, the effective work function of 500 °C H2/N2 annealed Ru films on ALD Al2O3 and HfO2 was determined to be approximately 4.9 and 5.3 eV, respectively. Using internal photoemission spectroscopy, the Ru/Al2O3 and Ru/HfO2 electron energy barrier heights were determined to be 3.4 ± 0.1 and 3.8 ± 0.1 eV, respectively.