Failure analysis technique of backside focused ion beam on decapsulated device

Abstract

Focused Ion Beam, also known as FIB, is a technique that widely used in semiconductor field. The common purpose is to do circuit modification, layout verification, micro-circuit failure analysis, mask repair and Transmission Electron Microscope (TEM) specimen preparation of site specific locations [1]. Backside fault isolation is a method to get optimum transmission and localized failure site. Fault site isolation is the step in which various techniques are employed to localize the defect area on the failed die. It is the most critical step in the failure analysis process because it greatly reduces the area required for failure analysis [2]. Having of topside fault isolation sometimes may lead to in-accurate of determining the failure site. The reason is emission site can be underneath of wire or blocking by thicker metallization and causing in-accurate of emission spot. As example, after decapsulation, the superimposed image between top side and backside revealed an emission site which located underneath wire bond. However, if the failing device is recover after removing the wire, then it is difficult to identify the defect since the fault isolation process can no longer be repeated. Hence, the wire should be remained. That analysis with leakage recovery cases is being known as a challenge in Failure Analysis (FA) process and resulted in a low success rate of determining the mechanism. It is hard for a FA engineer to find the failure root cause after recovering [3]. The conventional method next is by remove the wire upon revealed the emission site located underneath aluminum wire. Another new-approach technique is by performing Focused Ion Beam, FIB analysis from backside. The challenge is the device has been decapsulated for a die surface inspection. As for backside FIB milling approach, the sample must be in package form. Remolding the sample can be one of the method towards backside fault isolation analysis. In order to increase the accuracy of FIB milling, we are reducing the length of measurement into less than 200um × 200um length. Figure 1 showed the illustration diagram of the theory. While biasing the sample with similar parameter setup, the emitting emission site area should be same as previous backside fault isolation. This paper aims to describe and compare conventional technique which is by removing wire to reveal the defect underneath aluminum wire versus new approaches technique which is backside FIB Milling after decapsulate device.