In this work, an in-situ ozone treatment is carried out to improve the interface thermal stability of HfO_2/Al_2O_3 gate stack on germanium(Ge) substrate. The micrometer scale level of HfO_2/Al_2O_3 gate stack on Ge is studied using conductive atomic force microscopy(AFM) with a conductive tip. The initial results indicate that comparing with a non insitu ozone treated sample, the interface thermal stability of the sample with an in-situ ozone treatment can be substantially improved after annealing. As a result, void-free surface, low conductive spots, low leakage current density, and relative high breakdown voltage high-κ/Ge are obtained. A detailed analysis is performed to confirm the origins of the changes.All results indicate that in-situ ozone treatment is a promising method to improve the interface properties of Ge-based three-dimensional(3D) devices in future technology nodes. In this work, an in-situ ozone treatment is carried out to improve the interface thermal stability of HfO 2 / Al 2 O 3 gate stack on germanium (Ge) substrate. The micrometer scale level of HfO 2 / Al 2 O 3 gate stack on Ge is studied using conductive atomic force microscopy (AFM) with a conductive tip. The initial results that comparing with a non insitu ozone treated sample, the interface thermal stability of the sample with an in situ ozone treatment can be substantially improved after annealing. As a result, void- free surface, low conductive spots, low leakage current density, and relative high breakdown voltage high-κ / Ge are obtained. A detailed analysis is performed to confirm the origins of the changes. All results indicated that in-situ ozone treatment is promising method to improve the interface properties of Ge-based three-dimensional (3D) devices in future technology nodes.