Proceedings Article | 12 July 2002
KEYWORDS: Metals, Scanning electron microscopy, Discrete inspection, Etching, Chemical mechanical planarization, Inspection, Microelectronics, Semiconducting wafers, Contamination, Manufacturing
Timely detection and prevention of defect excursions is the primary goal of any yield enhancement methodology in a wafer processing fab. Contamination killer defects are traditionally at the focus of such efforts. However, systematic process-induced defects are increasingly impacting the yield in the contemporary manufacturing environment, which is characterized by rapid modifications, constantly decreasing design rules and narrowing process windows. While the treatment of killer random defects remains important, the emphasis on yield-limiting problems is shifting to subtle treatment of killer random defects remains important, the emphasis on yield-limiting problems is shifting to subtle precursor phenomena, before the tool yield is severally damaged. Common light-scattering inspection is limited when applied to early symptoms of process deterioration, such as defects below 100nm or those lying in trenches. Electrical defects are even more challenging, since in most cases they are entirely undetectable by optical means. Disconnected metal plugs, under-etch of contact and via holes, implant variations undetectable by optical means. Disconnected metal plugs, under-etch of contact and via holes, implant variations on active area, gate to active area shorts, junction leakage - all of them can produce an electrical signature that can be detected with electron beam microscopy using Voltage Contrast imaging. In this paper, we describe a methodology implemented at the STMicroelectronics fab in Crolles, France, that addresses the above issues. SEM reviews and discrete inspections with a SEMVision cX were used for characterization of a variety of optically invisible defects on several critical inspection steps: Shallow Trench Isolation after etch and CMP, Polysilicon after etch, Via after etch, Tungsten plugs after CMP, Aluminum metal lines after etch and Copper metal lines after CMP.
