Abstract
This paper introduces a technique to reveal a small feature defect of an SRAM cell via utilizing a 200kV dedicated field emission STEM on a FIB prepared sample. The initial TEM sample contains the entire defective cell; one side of the sample has n-type transistors and the other p-type. Both sides of the sample were observed using STEM bright field and dark field (HAADF) detectors (transmitted beam – inner information) and SEM mode (surface and sub-surface information). With deep beam penetration of STEM, one contact was found to be very close to the poly gate. Further FIB cuts were performed to remove the rest of the bulk away from the defect, thinning down to the area of interest. When the sample was thinned to a final thickness of less than ~100nm, a final image was taken of the exposed defect. The failing root cause was that the upper corner of the poly had touched the adjacent contact. Such an approach offers many unique advantages for site specific failure analysis over conventional SEM and/or TEM techniques.
