Stability of La2O3 and GeO2 passivated Ge surfaces during ALD of ZrO2 high-k dielectric

La2O3 grown by atomic layer deposition (ALD) and thermally grown GeO2 are used to establish effective electrical surface passivations on n-type (1 0 0)-Ge substrates for high-k ZrO2 dielectrics, grown by ALD at 250 °C substrate temperature. The electrical characterization of MOS capacitors indicates an impact of the Ge-surface passivation on the interfacial trap density and the frequency dependent capacitance in the inversion regime. Lower interface trap densities can be obtained for GeO2 based passivation even though a chemical decomposition of the oxidation states occur during the ALD of ZrO2. As a consequence the formation of a ZrGeOx compound inside the ZrO2 matrix and a decline of the interfacial GeO2 are observed. The La2O3 passivation provides a stable amorphous lanthanum germanate phase at the Ge interface but also traces of Zr germanate are indicated by X-ray-Photoelectron-Spectroscopy and Transmission-Electron-Microscopy.

► Comparative XPS analysis of the chemical stability of La2O3 and GeO2 Ge surface passivation during ALD of ZrO2. ► Comparative electrical characterization of La2O3 and GeO2 Ge surface passivations in MOS capacitors. ► Decomposition of the 1.5 nm thick initial GeO2 interface layer during ALD of 6.5 nm ZrO2 indicated by TEM and XPS. ► Changing of the Ge oxidation states during ALD of ZrO2 on interfacial GeO2 indicated by XPS. ► Detection of zirconia germanate inside the ZrO2 matrix by XPS independently from surface passivation.