Investigation Of Intermetallic Barrier Layer For Integration Of Si–based Ferroelectric Capacitors

Ni–Al, Ti₃Al films with different crystallinities and orientations have been used as conductive diffusion barrier layers for integrating La_0.5Sr_0.5CoO₃/Pb(Zr_0.4Ti_0.6)O₃/ La_0.5Sr_0.5CoO₃ (LSCO/PZT/LSCO) ferroelectric capacitors on silicon substrates, in which Ni–Al or Ti₃Al film is prepared using RF magnetron sputtering, and PZT film by sol–gel method. Various techniques, including X–ray diffraction (XRD), atomic force microscopy (AFM), transmission electron microscope (TEM), ferroelectric tester (Precision LC unit) and LCR meter, were used for investigating the microstructure, morphology, interface, physical properties of the ferroelectric capacitors and the impacts of annealing conditions.No reaction/ or interdiffusion occur between Ni–Al and LSCO, but there exists epitaxial NiSi locally at the interface of Ni–Al and Si after high temperature anneal. NiSi has a low resistance and an excellent chemical and thermal stability, which lead to a good barrier property. The resistance of Ni–Al film annealed in oxygen increases with the increase of the depth. LSCO/PZT/LSCO ferroelectric capacitors fabricated on conducting silicon with Ni–Al film thicker than 60 nm, vertically characterized as the memory cells at 5 V, demonstrate very good physical properties, e.g. large remnant polarization 16～22μC/cm2, relatively small leakage current density of 2×10–5 A/cm2. But ultra–thin polycrystalline Ni–Al cannot be used as a diffusion barrier layer.Highly oriented (0001) Ti₃Al films is deposited on Si(111) substrate, and shows a well oxidation resistance and barrier property during the high temperature treatment. The ferroelectric capacitors fabricated on oriented (0001) Ti₃Al films have very good ferroelectric properties. LSCO/PZT/LSCO capacitor on Ti₃Al, compared with that on amorphous Ti–Al, shows a higher remnant polarization, lower coercive electric field and larger dielectric constant of 23μC/cm2, 1.9 kV/cm and 590, respectively.Amorphous Ti–Al film is still amorphous after high temperature annealing, and RTA for 6 min can yield the best physical results for the LSCO/PZT/LSCO capacitor, whose remnant polarization and coercive electric field are 22μC/cm² and 83 kV/cm, respectively. Moreover, it is also found that leakage mechanism of LSCO/PZT/LSCO capacitor does not depend on the annealing conditions. It is Ohmic conduction at applied fields smaller than 46.7 kV/cm, and Schottky conduction at fields higher than 46.7 kV/cm.