Impact of morphological defects on the electrical breakdown of ultra thin atomic layer deposition processed Al2O3 layers

•Defects in atomic layer deposited Al2O3 films detected by Cu electroplating•Defect density rises as layer thickness decreases.•Relative permittivity decreases at lower layer thicknesses.•Despite of increasing defect density, breakdown electric field increases.•Defect density not correlated to those defects supporting electrical breakdown

We report on the continuous increase of the breakdown electric field, also known as disruptive strength, of an ultra thin layer based on Al2O3 prepared by low temperature atomic layer deposition (ALD) by reducing its thickness down to 3 nm. By measuring the disruptive strength for lower thicknesses, we demonstrate that these observations are in agreement with recent reports. Furthermore we detected an increase within the disruptive strength towards lower thicknesses together with a rise of the pin hole density. The pin holes, originating from an inhomogeneous growth of the dielectric and referred to as morphological defects and current conducting paths, are detected by Cu electroplating and result in a lower permittivity of the dielectric. As a conclusion, the dielectric breakdown of thin, low temperature ALD processed Al2O3 layers does not seem to be negatively influenced by the increase of the pin hole density. Thus, the increase of the disruptive strength is either due to the morphological defects in the form of pin holes or a material phenomenon that is not affected by its nanoporous structure.