MOFM: Magneto-Optical Frequency Mapping system for very low resistance short circuit failure imaging

摘要

Magnetic field imaging (MFI) has been an excellent tool for a low resistance failure localization in LSI devices. A Superconducting Quantum Interference Device (SQUID) and a Giant Magneto Resistive (GMR) sensor are well known in this field. A SQUID has extremely high magnetic sensitivity (500 nA, <40 pT/√Hz)[1], but the spatial resolution is somewhat problematic due to the clearance that is needed for cooling and vacuuming mechanism. A GMR sensor has higher resolution but lower sensitivity (50 μA, <10 nT/√Hz)[1] and, they have less flexibility because the sensor/stage has to be scanned during operation. In this paper, we present a new current imaging method called Magneto-Optical (MO) Frequency Mapping (MOFM). The imaging is based on a laser beam scanning, which allows flexibility and ease of use. The MO signal intensity is inversely proportional to the distance between the sensor and the current path to be detected. Since it can be 10 μm or less, i.e., one half of the MO crystal thickness, it practically makes the MOFM's system sensitivity is 10 μA, it only 20 times lower than a SQUID method, even though the intrinsic sensitivity may be about 250 times or so lower. It can also achieve high special resolution as with the GMR sensor because of the short distance or clearance needed to sense the current. These characteristics are verified with a TEG sample and we present a case in which it is applied for the short circuit failure localization.