August_EDFA_Digital

edfas.org 5 ELECTRONIC DEVICE FAILURE ANALYSIS | VOLUME 22 NO. 3 attempted on the failing bit. Figure 1 shows the FIB cross section image on a suspected failing bit. With the tool resolution limitations, it is not possible to conclusively determine from the SEM image alone whether there is a defect there that can cause a fail. To confirm the suspected defect, the team selected a newsample andperformed top-down sample preparation to facilitate nanoprobing. Electrical data confirmed there is a voltage threshold ( V t ) shift on the pull down transis- tor, which is enough to cause a fail. Figure 2 shows I drain V gate (drain current vs. gate voltage) results from nanoprobing. Later, the sample was submitted for TEM cross-section analysis and the defect was confirmed. Figure 3 shows the defect found in the gate by TEM cross-section showing abnormal gate material. CASE STUDY #2: METAL LINE SIDE-TO-SIDE SHORT This case study illustrates another ex- ampleof hownanoprobing isused toconfirm a defect. During top-down SEM inspection, a particle was observed on a failing memory wordline (WL), but no final conclusion could be drawn without first determining whether the particle was an actual defect or an artifact introduced during deprocessing. To validate whether the particle was a defect, two-point IV testing was done using the nanoprobing technique. Figure 4 shows two-point IV testing on the failingWL, confirming a short (left IV curve). On the right is a reference curve (passing WL). Figure 5 shows the defect that was initially in question. After confirming the defect was real and not a polishing artifact, the samplewas submitted for TEManalysis. Figure 6 shows TEMcross-section results. TEMconfirmed there is a metal-to-metal line short causing the WL fail. CASE STUDY #3: GATE DEFECT This case study showed how a defect found in a FIB cross-section along with traditional TEM analysis was not sufficient to understand the failure. Figure 7 shows the defect captured from a FIB cross-section. The SEM image shows a gate tapered at the bottomand a defective active Fig. 3 TEM was submitted based on electrical character- ization fromnanoprobing and showed abnormal gate material. Fig 4 Two-point IV tests from nanoprobing confirmed a linear short on the failing WL (fail site on the left; reference site on the right). Fig. 5 TopdownSEM image of themetal-to-metal line short. Fig. 6 TEMconfirmed the defect as a particle causingmetal- to-metal line short.