Application of high-resolution X-ray microscopy to image backend-of-line structures

One of the challenges to process control and failure analysis in semiconductor industry is the nondestructive visualization of sub-50nm features and defects. The availability of high-brilliance X-ray sources, high-precision X-ray focusing optics and very efficient CCD area detectors have contributed essentially to the development of transmission X-ray microscopy (TXM) and X-ray computed tomography (XCT) to reach a spatial resolution of 50nm and below. High-resolution X-ray microscopes with rotating anode X-ray sources that can be installed in an analytical lab next to a semiconductor fab have been developed recently. These unique TXM/XCT systems provide an important new capability of nondestructive 3D imaging of internal circuit structures without destructive sample preparation such as crosssectioning. In this paper, the potential of TXM/XCT lab systems for failure localization in micro- and nanoelectronic structures and devices is discussed. Applications to backend-of-Iine structures seem to be realistic in near future, e. g., to visualize voids and residuals in on-chip metal interconnects without physical modification of the chip.