Plasma-assisted atomic layer deposition of TiN/Al2O3 stacks for metal-oxide-semiconductor capacitor applications

Abstract

By employing plasma-assisted atomic layer deposition, thin films of ${\text{Al}}_2{\text{O}}_3$ and TiN are subsequently deposited in a single reactor at a single substrate temperature with the objective of fabricating high-quality $\text{TiN}/{\text{Al}}_2{\text{O}}_3/p\text{-Si}$ metal-oxide-semiconductor capacitors. Transmission electron microscopy and Rutherford backscattering spectroscopy analyses show well-defined interfaces and good ${\text{Al}}_2{\text{O}}_3$ stoichiometry, respectively. Electrical investigation of as-deposited test structures demonstrates leakage current densities as low as $\sim 1\text{nA}/{\text{cm}}^2$ . Current-voltage $\left(I\text{-}V\right)$ measurements demonstrate clear Fowler–Nordheim tunneling with an average $\text{TiN}/{\text{Al}}_2{\text{O}}_3$ barrier height of 3.3 eV. Steep Weibull distributions of the breakdown electric field around 7.5 MV/cm indicate good reliability of these devices. Time-dependent dielectric breakdown measurements demonstrate that the devices can sustain high operating electric fields of 3–4 MV/cm for the 10 year lifetime criterion. From capacitance-voltage $\left(C\text{-}V\right)$ measurements, a dielectric constant $\left(k\right)$ of $8.7\pm 0.1$ was extracted for the ${\text{Al}}_2{\text{O}}_3$ . No direct dependence on the deposition temperature was found in the range $350–400°\text{C}$ , although the stack deposited at $400°\text{C}$ demonstrates significantly lower $C\text{-}V$ hysteresis of $\sim 50\text{mV}$ . A negative fixed oxide charge density of $\left(9.6\pm 0.2\right)\times {10}^{12}{\text{cm}}^{-2}$ was found to be present at the ${\text{Al}}_2{\text{O}}_3/p\text{-Si}$ interface.