Quality control of grain boundaries in copper thin films used for 3D interconnections

In this study, the quality of grain boundaries was evaluated by measuring their strength. In order to evaluate the strength of grain boundaries quantitatively, a micro-tensile test method that can measure the strength of a grain boundary has been developed. A focused ion beam was used for making a fine columnar sample which consisted of two grains in series. The sample was jointed to a small both ends fixed beam made of single-crystalline silicon. A tensile load was applied and the deformation of the sample and the beam was monitored by a scanning electron microscope to measure the load-displacement relationship of the sample. The relationship between the factors of controlling strength and the mechanical properties of the copper thin films was clarified quantitatively by using the micro-tensile test.