Stabilization of TetragonalHfO2underLow Active Oxygen Source Environment in Atomic Layer Deposition.

The structural and electronic properties of HfO2thinfilms grown by atomic layer deposition (ALD) under various ozone concentrationswere investigated using X-ray diffraction (XRD), photoemission (XPS),reflectometry (XRR), and absorption spectroscopy (XAS) and their finestructure (XAFS) analysis. It was found that in the as-grown states,the oxygen stoichiometry and local atomic structure in amorphous HfO2domains are maintained nearly as constants even when thefilm is grown without external ozone supply, while some C–Obonds remain between the almost stoichiometric HfO2domainsdue to incomplete oxidation of the precursors. After a postdepositionannealing (PDA), the films crystallize with a monoclinic structure(P21/c), except for thecase of the no-ozone supply in which the film possesses a tetragonalcrystal structure (P42/nmc). It is demonstrated that the carbonate bonds play a major rolein stabilizing the tetragonal structure through nanoscale separationof the HfO2domains. Accordingly, the roles of the oxygensource and the PDA are also newly addressed as being related to thecarbonate bonds. The ozone gas acts as an oxygen supplier, and moreimportantly, it reduces the residual carbonates to stabilize the bulkcrystal structure in the thin films. The PDA not only delivers thethermal energy to induce the crystallization but also eliminates Catoms to increase the size of the HfO2domains leadingto the densification of the films. [ABSTRACT FROM AUTHOR]