Void detection in copper interconnects using energy dispersive x-ray spectroscopy

The formation of small voids in narrow sub-50 nm Cu interconnect lines during their fabrication is a major challenge for the development of integrated circuits. Focused ion beam sectioning and scanning electron microscopy imaging are being used for void detection during process development, but as they are destructive, they are less suited for in-line metrology. Therefore, the authors developed a nondestructive method based on energy dispersive x-ray spectroscopy where voids can be detected as changes in x-ray intensity due to the direct proportionality of the generated characteristic x-ray intensity with the amount of copper atoms contained in the interaction volume. The procedure allows the detection of small voids down to 15 nm in a fast and nondestructive way. This is possible for thin and chemically mechanically polished Cu interconnects where intensity variations due to thickness variations can be ignored.