CEA, LETI, MINATEC Campus, Grenoble, France, Université de Grenoble, Lab. SIMaP-CNRS, BP 75 Cedex, St Martin d'Hères, France

Thin amorphous alumina layers (10 to 40 nm thick) are processed on sputtered aluminum thin film (500 nm) by atomic layer deposition (ALD) at low temperature (85 °C). Global methodology combining quantitative experimental observations of fracture and numerical modeling is proposed to obtain the fracture strength of ALD thin film on Al layer. First, mechanical properties of the multilayer specimen are characterized by Berkovich nanoindentation, then fracture of ALD alumina is studied through spherical indentation with various tip radius. Spherical indentation load driven-displacement curves display a plateau (pop-in) at a critical load and critical indentation depth. A statistical approach is used to determine pertinent/fracture parameters from pop-in displacement. Careful SEM and AFM observations of indentation imprint exhibit circumferential cracking in agreement with the assumption that the pop-in event is predominantly controlled by the fracture of the oxide layer on the soft Al film. Finally, a numerical model calibrated with experimental results is used in order to predict both the mechanical response prior to the oxide fracture and a value of fracture strength for ALD alumina thin films. © 2017 Elsevier B.V.

ALD alumina, Cracks, Finite element modeling, Fracture strength, Nanoindentation, Pop-in, Thin hard film, Weibull statistical analysis

Alumina, Aluminum coatings, Amorphous films, Atomic layer deposition, Cracks, Deposition, Film preparation, Finite element method, Fracture toughness, Nanoindentation, Numerical models, Optical films, Oxide films, Spheres, Thin films, Alumina thin films, Aluminum thin films, Berkovich nanoindentation, Hard films, Mechanical response, Spherical indentations, Statistical approach, Weibull statistical analysis, Fracture