Electroless Plating of Ru Using Hydrazine Hydrate as a Reducing Agent

Ruthenium (Ru)-a high-melting-point precious metal-has attracted attention for use as ultrafine interconnections in large-scale integrations. This is because the resistivity of Ru interconnects is not expected to increase with a reduction in the interconnect width owing to their short mean free path for electrons. In this study, we investigated electroless plating of Ru using hydrazine hydrate as a reducing agent to obtain low-resistivity Ru films. We obtained polycrystalline Ru films on a thin (10-nm) catalytic chemical-vapor-deposited Ru underlayer. The electroless Ru films exhibited significant grain growth upon annealing at 600 & DEG;C in a forming gas (N-2:H-2 = 9:1). The Ru (101) and (100) crystalline orientations were strengthened by annealing, and the resistivity decreased from 160 & mu;& omega; cm to 22 & mu;& omega; cm concomitantly. Thermal desorption spectroscopy showed that the electroless Ru films contained impurities, such as CO, CO2, NH3, O, C, and H-2. Desorption of C, CO, CO2, and NH3 showed peak maxima at approximately 450-500 K. These impurity molecules likely came from the inclusion of the complexing agents (tartaric acid: C-4(OH)(4)O-2, and ammonium chloride: NH4Cl) and reducing agent (hydrazine: N2H2) into the Ru film. Desorption of these molecules during annealing may improve the grain growth of polycrystalline Ru and reduce its resistivity.