15.1
A Case Study: Improving FIB Passive Voltage Contrast Imaging for Deep N-well Circuits
A Case Study: Improving FIB Passive Voltage Contrast Imaging for Deep N-well Circuits
Wednesday, November 4, 2015: 4:45 PM
Meeting Room D139 & 140 (Oregon Convention Center )
Summary:
This paper presents a case study of a customer return that failed functional testing on the production tester. Investigation by applications and design engineering identified several circuit blocks where a possible failure mechanism could be located causing the functional failure mode seen at test. These circuit blocks all resided in deep n-well preventing regular PVC from being used to isolate the fault location (Figure 2). Neither functional probing nor active voltage contrast imaging to isolate the failure mechanism to a specific location was available to the analyst. The analyst, being alert and looking for an alternative as well as having a good understanding of the principles of PVC and the issues in regards to PVC imaging of deep n-well circuits, identified and took advantage of a design feature in the device to restore the ability to perform passive voltage contrast imaging on these circuits. When PVC capability was restored, two polysilicon capacitors with damage oxides resulting in leakage to the substrate were easily identified (Figure 3). The capacitor leakage was then verified by means of nanoprobe analysis. Without identifying and taking advantage of a design feature not intended for failure analysis, locating these damage poly capacitors would have been extremely difficult due to the number of circuit blocks indicated as possible failure locations. This paper will present a brief detailed over-view of PVC imaging, the issues with PVC imaging of deep n-well circuits, followed by this case study, and conclude with recommendations for design for failure analysis (DFA).
This paper presents a case study of a customer return that failed functional testing on the production tester. Investigation by applications and design engineering identified several circuit blocks where a possible failure mechanism could be located causing the functional failure mode seen at test. These circuit blocks all resided in deep n-well preventing regular PVC from being used to isolate the fault location (Figure 2). Neither functional probing nor active voltage contrast imaging to isolate the failure mechanism to a specific location was available to the analyst. The analyst, being alert and looking for an alternative as well as having a good understanding of the principles of PVC and the issues in regards to PVC imaging of deep n-well circuits, identified and took advantage of a design feature in the device to restore the ability to perform passive voltage contrast imaging on these circuits. When PVC capability was restored, two polysilicon capacitors with damage oxides resulting in leakage to the substrate were easily identified (Figure 3). The capacitor leakage was then verified by means of nanoprobe analysis. Without identifying and taking advantage of a design feature not intended for failure analysis, locating these damage poly capacitors would have been extremely difficult due to the number of circuit blocks indicated as possible failure locations. This paper will present a brief detailed over-view of PVC imaging, the issues with PVC imaging of deep n-well circuits, followed by this case study, and conclude with recommendations for design for failure analysis (DFA).