Oxygen Vacancies in High Dielectric Constant Oxide-Semiconductor Films

We provide evidence that the oxygen vacancy is a dominant intrinsic electronic defect in nanometer scaled hafnium oxide dielectric films on silicon, relevant to microelectronics technology. We demonstrate this by developing a general model for the kinetics of oxygen vacancy formation in metal-ultrathin oxide-semiconductor heterostructures, calculating its effect upon the band bending and interfacial oxidation rates and showing good experimental agreement with the predictions.

Figure 1

(a) Schematic of the silicon-metal oxide-metal gate stack, showing the mechanism of transport of oxygen from the ambient to the silicon interface; (b) experimental capacitance vs voltage curves obtained across this stack after anneals (6 h at $400°\mathrm{C}$) at different partial pressures of oxygen. Note the parallel shift along the voltage axis (indicated by the line with arrows) of $\sim 0.33\mathrm{V}$ with increasing oxygen pressure. This shift is tracked by noting the voltage ${\varphi }^{*}$ at a fixed capacitance of $5\times {10}^{-3}\mathrm{F}/{\mathrm{cm}}^2$.

Figure 2

(a) The translation of the capacitance voltage curves as a function of oxygen partial pressure ($p_{{\mathrm{O}}_2}$) during anneals at different temperatures is shown by plotting the voltage ${\varphi }^{*}$ versus $p_{{\mathrm{O}}_2}$, where ${\varphi }^{*}$ is measured at a fixed capacitance of $5\times {10}^{-3}\mathrm{F}/{\mathrm{cm}}^2$ from the different CV traces; (b) the variation of the electrical thickness ($t_{\mathrm{el}}$) as a function of $p_{{\mathrm{O}}_2}$ during anneals at different temperatures. Anneal temperatures are 450 (solid circles), 400 (open circles), 260 (solid squares), and $220°\mathrm{C}$ (open squares). The drawn curves are for guiding the eyes only.

Figure 3

The translation in the capacitance voltage curves ($\Delta \varphi$), plotted in (a) as a function of the oxygen partial pressure ($p_{{\mathrm{O}}_2}$) for the samples annealed at 450 (triangles) and $400°\mathrm{C}$ (squares), (b) versus $(p_{{\mathrm{O}}_2}{)}^{0.5}$ for the samples annealed at 260 (circles) and $220°\mathrm{C}$ (open squares), and (c) versus the electrical thickness of the stack ($t_{\mathrm{el}}$) for samples annealed at 400 (solid circles) and $450°\mathrm{C}$ (open circles).