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.