Contact resistance from wafer acceptance test (WAT) data is one of the critical parameter to significantly affect fabrication process. While WAT data shows open/short fail, high resistance fail and leakage fail in contact chain structure, the first job in failure analysis (FA) field is to localize failure site. For example, High resistance failure and leakage failure sites can be localized by Infrared Ray Optical Beam Induced Resistance Change (IR-OBIRCH) detection. Most of open failure modes could be isolated by front side passive voltage contrast (PVC) technique. However, there is still a limitation to this technique while contacts are still connected to substrate in metal-1/contact/active chain structure. Active Voltage Contrast (AVC) [1, 2] is a good method to overcome this problem, but the major concern is how to mark the failure location in SEM based probing system. In this paper, we provide a novel backside passive voltage contrast method to improve the failure analysis technique. By thinning down silicon substrate to the active area, a new contact chain from active area is created. Therefore, novel backside PVC is applied to locate the failed site.

The oxide-nitride-oxide (ONO) is one of the critical layers in the deep trench (DT) capacitor of the modern DRAM structure. This paper highlights a ONO inspection methodology, which used the silicon wet etching to enhance the ONO leakage point. First, a hole was milled nearby the leakage ONO, which was localized by using focused ion beam (FIB). Then, silicon was removed by an etching solution from the opening. When the poly of DT is etched through the ONO weak point, the leakage site will be enhanced. With the silicon wet etching enhancement, the ONO leakage point is easy to be observed by X-S FIB inspection. The real ONO leakage point is useful information for the root cause finding and the process improvement.

IR-OBIRCH (Infrared Ray – Optical Beam Induced Resistance Change) is one of the main failure analysis techniques [1] [2] [3] [4]. It is a useful tool to do fault localization on leakage failure cases such as poor Via or contact connection, FEoL or BEoL pattern bridge, and etc. But the real failure sites associated with the above failure mechanisms are not always found at the OBIRCH spot locations. Sometimes the real failure site is far away from the OBIRCH spot and it will result in inconclusive PFA Analysis. Finding the real failure site is what matters the most for fault localization detection. In this paper, we will introduce one case using deep sub-micron process generation which suffers serious high Isb current at wafer donut region. In this case study a BEoL Via poor connection is found far away from the OBIRCH spots. This implies that layout tracing skill and relation investigation among OBIRCH spots are needed for successful failure analysis.