Current leakage fault localization using backside OBIRCH

Localization of current leakage faults in modern ICs is a major challenge in failure analysis. To deal with this issue, several techniques such as liquid crystal thermography and emission microscopy can be used. However, traditional front-side failure analysis techniques are unable to localize faults obscured by several metal layers. This trend, as well as the appearance of new packaging technologies, has driven alternative approaches from the backside of the die. Of the infrared light optical techniques, the optical beam induced resistance change (OBIRCH) technique has shown to be very promising for locating current leakage type faults (Barton et al, 1999; Nikawa et al, 1999). In this paper, a backside failure analysis case study on four-level interconnection BICMOS ICs is presented. Different front side defect localization approaches such as liquid crystal were tried, but none worked since interconnection layers obscured the fault. Backside emission microscopy also failed due to the resistive nature of the defect. Only the OBIRCH technique could quickly and precisely localize the defect causing current leakage from the backside of the die.