Low temperature crystallization of high permittivity Ta oxide using an Nb oxide thin film for metal/insulator/metal capacitors in dynamic random access memory applications

(Ta1-xNbx)(2)O-5 as the dielectric for metal/insulator/metal capacitors with Ru electrodes were investigated. Deposition was performed by ALD using tantalum ethoxide, niobium ethoxide, and ozone as source materials. The high-kappa dielectric layer was synthesized from a binary layer (Ta2O5/Nb2O5) with self-diffusion of the seed layer, Nb2O5. The seed layer becomes effective at a thickness of over 60 Angstrom. The dielectric deposited with 60 Angstrom Nb2O5 crystallized at 575 degreesC, the lowest processing temperature required to achieve good step-coverage (86%) for future generation dynamic random access memory. A capacitance density of about 23.0 fF/mum(2) was observed for seed layers of 20 and 35 Angstrom. Capacitors with a Nb2O5 seed layer of 60 Angstrom achieved a capacitance density as high as 44.2 fF/mum(2). The reason for this disparity is that the thicker insulator crystallizes at a post-annealing temperature of 575 degreesC. The leakage current measured at 1 V Was moderately low, near 1 x 10(-7) A/cm(2). (C) 2005 American Vacuum Society.