Integration of FIB (focused ion beam) into an automatic defect review SEM provide new dimension to defect root cause analysis. It brings out defect cross-section application from failure analysis lab to the clean room process, providing sub-surface information of the defect in addition to defect surface information, therefore closing the defect analysis loop on the same platform. Sub-surface defects such as embedded defects and electrical defects are often yield limiting nature and require cross-section information to determine failure mode and the root cause. The main advantage of integrated SEM-FIB is it provides much shorter root cause analysis cycle time and thus improve yield and fab productivity. Feedback time can be cut from typically 1-2 days to several hours, saving valuable time for process trouble-shooting. It eliminates the risk of damaging the samples due to handling and the need to re-localize the defect of interest prior to cross-section. Moreover, the cross-sectioned wafer can be returned to production by excluding the affected die instead of scrapping the whole wafer which is often desirable especially for 300mm wafer. FIB milling principle of operation is displacement of surface materials through atom sputtering effect by bombardment of the surface with high energy gallium ions. Defect analysis flow begins with wafer inspection which generates defect map followed by defect review on SEM-FIB tool. Defect of interest was identified and can be located easily when switching to FIB microscope since the exact defect location has been established during SEM review, which is sometimes very challenging for offline FIB tool especially for electrical defects and tiny defects. Defect surface area usually coated with a thin layer of platinum or tungsten to protect the surface from milling damage. Defect cross-sectioning by FIB milling are then performed. Decoration effect by XeF<sub>2</sub> gas etching is often required to enhance the contrast between the layers. Cross-section SEM image are then taken at 45 degree tilt angle.
This paper provides case studies on how the tool was effectively use to solve process issues through defect cross section examination. Identifying electrical defects root cause are challenging as it may involve few process steps upstream and often require cross sectioning. With integrated SEM-FIB, possible root causes of various electrical defects on copper CMP layers were determined easily within shortest amount of time.