Defect Localization and Nanofabrication for Conductive Structures with Voltage Contrast in Helium Ion Microscopy.

ABSTRACT

As the dimensions of feature sizes in electronic devices decrease to nanoscale, an easy method for failure analysis and evaluation of processing steps is required. Gallium-focused ion beam (Ga-FIB) or scanning electron microscope is an efficient approach to detect voltage contrast for addressing failure analysis in semiconductor devices and processing. However, Ga-FIB may cause damage or implantation to the surface of the analyzed area, and its resolution is low. Helium ion microscopy (HIM) uses a light ion beam (helium or neon) for imaging and fabrication at nanoscale. With passive voltage contrast (PVC) in HIM images, the defect localization for failure of conductive structures can be rapidly and easily detected with a sufficient voltage contrast. Furthermore, a defect gap as narrow as sub-10 nm can be investigated with HIM imaging. PVC with HIM is an efficient method for defect localization at nanoscale with a minimal damage to the analyzed area. For circuit edit and failure analysis, it may be necessary to intentionally cut the conductive connection. In this circumstance, final results can be easily verified using PVC imaging with HIM. With XeF2 gas assistance, both helium and neon ion beams can be used to perform nanofabrication for metal disconnection. XeF2 gas plays an important role in preventing deposition of conductive materials on etching region and enhancing material removal rates to achieve electrically isolated structures. The etching rate with a neon ion beam is much faster than that of a helium ion beam. PVC in HIM images with controllable operation and dimensions using a helium ion beam with XeF2 gas assistance could also be used to localize a hidden defect for a single-location-defect situation. With neon ion beam irradiation on a defective location, PVC can be used to find the defect locations in the case of a series of defects.