Focused ion beam technology and application in failure analysis

Focused ion beam, also known as FIB, is a technique widely used in semiconductor field, such as circuit modification, layout verification, microcircuit failure analysis, mask repair and transmission electron microscope (TEM) specimen preparation of site specific locations. Among these applications, microcircuit failure analysis is a very important one. In the paper, after an introduction to the FIB technology and the operating principles, several applications of FIB for microcircuit failure analysis were described and discussed. First, Using FIB system milling for cross-section enable the engineer to review and verify the defect of specific locations. Secondly, FIB systems could be used to remove of the local passivation layer to expose underlying metal lines for mechanical or electron beam probing, emission microscopy, or liquid crystal analysis. Thirdly, local circuit test for defect localization sometimes need FIB system to form probe pads or cut metallization and polysilicon lines to isolate interconnections. Finally, locating shorts and opens in circuitry by utilizing passive voltage contrast (PVC) in FIB system is also a common usage in IC failure analysis. Furthermore, two successful cases for FIB technique analyzing failed integrated circuits were described. Case 1: gold aluminum bonding failure. The connection resistance of Vdd pin of the sample was increasing. With the function of FIB precise micro-cutting, the cross-section of the gold aluminum bonding area was performed and analyzed. The cross-section view showed that gold diffused to aluminum. Combining with EDS analysis, the bonding failure mechanism was attributed to Kirkendall effect. Case 2: dielectric breakdown. The failed sample was a dual 8-bit monolithic analog-to-digital converter. Dielectric breakdown usually occurs between multi-layer metal. First, using passive voltage contrast in FIB, short failure was easily detected by contrast between contacted and non-contacted interconnects. Then cross-section of the FIB milling was performed to verify the localized fail within the previously determined area. The cross-section view showed that the defect was caused by dielectric breakdown between metal 1 and metal 2. According to the cases, FIB system is particularly effective for analyzing invisible defect from the surface.