Improved properties of atomic layer deposited ruthenium via postdeposition annealing

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.