Study of nano-mechanical properties for thin porous films through instrumented indentation: SiO2 low dielectric constant films as an example

Much research has been focused on the mechanical properties of porous materials such as films of silica xerogels because of their potential for application to microelectronic interconnects. To accurately probe the film properties, one has to challenge with the porosity as well as the large differences between film and substrate properties. In this paper, a study is presented for the investigation of Young's modulus and yield stress of these porous films by instrumented indentation under complete consideration of the substrate influence by using the approach of the 'effectively shaped indenter concept'. This concept provides the basis of a more appropriate analysis for thin films in case of elastic-plastic contact situations as given for porous low-k films. It was found that the ratio of yield stress to Young's modulus, which equals the yield strain of the stress-strain curve, is not constant and changes with porosity