Structural and electrical properties of Ge-doped ZrO₂ thin films grown by atomic layer deposition for high-k dielectrics

Enhancing the dielectric constant (k) of conventional gate dielectric materials such as HfO₂ and ZrO₂ is one of the important requirements for further scaling down of devices in future years. One promising approach for achieving this is to incorporate a specific element in the high-k host material for stabilizing a particular higher-k crystalline phase. Although Ge has been theoretically suggested as a stabilizer for ZrO₂, there are no experimental studies correlating the structure of ZrO₂ films fabricated by atomic layer deposition (ALD) with their electrical properties. In this work, we systematically investigated the structural and electrical properties of Ge-doped ZrO₂ films prepared by ALD. We used germanium butoxide (Ge(OⁿBu)₄) and Zr tris(dimethylamino)cyclopentadienyl zirconium as the Ge and Zr precursors, respectively, with O₃ as a reactant. We controlled the ALD cycle ratio using a supercycle process (GeO₂/ZrO₂ = 1:128, 1:64, 1:32, 1:16, 1:8, 1:4, and 1:2) to produce the alloy films. Electrical properties of these samples were evaluated by measuring the electrical characteristics of metal-oxide-semiconductor (MOS) capacitors based on them, and the results are discussed together with crystallographic analysis. The results revealed that Ge incorporation into ZrO₂ induced the stabilization of the cubic/tetragonal phase of the ZrO₂ film at low temperatures and improved its dielectric properties. Consequently, this is a systematic and facile method to optimize the dielectric properties of Ge-doped ZrO₂ prepared by varying the ALD cycle ratio, and these films could be applied in future nanoscale devices.