Characteristics of Amorphous Bi2Ti2O7 Thin Films Grown by Atomic Layer Deposition for Memory Capacitor Applications

Bi 2 Ti 2 O 7 films were deposited on sputtered Ru/SiO 2 /Si substrates by atomic layer deposition using tris(l-methoxy-2-methyl-2-propoxy)bismuth [Bi(mmp) 3 ], titanium tetraisopropoxide as Bi and Ti precursors, and H 2 O as oxidant, respectively. The wafer temperature was varied from 225 to 300°C. The growth rates decreased from 0.075 nm/cycle at 225°C to 0.055 nm/cycle at 300°C. The Bi concentration in the film decreased with increasing growth temperature and it could be controlled within a certain range by changing the Bi feeding at a given temperature. The as-grown Bi 2 Ti 2 O 7 films were amorphous but contained metallic Bi at high growth temperatures and high Bi concentrations. Bi and Ti piled-up on the film surface and the Ru interface, respectively. The electrical leakage property of the Bi 2 Ti 2 O 7 thin film became worse with increasing deposition temperature and Bi concentration due to the metallic Bi formation. The dielectric constant at the optimum deposition condition (225°C) was ∼40, and the leakage current level was < 10 - 7 A/cm 2 at 1.0 MV/cm at a film thickness of ∼15 nm. Reasonable conformal film thickness and cation composition over contact holes with a diameter of 0.15 μm and a depth of 1.1 μm were obtained.