Detecting small defects in conductive thin metallic layers using injected AC current and GMR magnetic sensor

In this paper, injected current technique and giant magneto-resistance (GMR) sensor were used to detect small defects in the order of few hundred micrometers in thin layers. This technique is based on injecting AC currents through the thin film using two connectors and detecting the perturbation of the magnetic field due to a defect using a GMR sensor. A sample of silicon wafer with copper metallization of few micrometers in thickness was used. On the conductive surface a 2.5 mm long scratch was created where the width of the scratch was 0.2 mm. Two measurements were conducted to detect this defect. The first measurement was performed when the sensitive axis of GMR sensor was perpendicular to scratch. The second measurement was performed when the sensitive axis of the sensor was parallel to scratch. By comparing the voltage output amplitude for both measurements, it was found that the scratch was successfully detected. It was verified that the signal-to-noise ratio (SNR) is much more than 3 (minimum for detection) in both measurements. Applications of injecting current technique include detecting defects in thin metallic layers (5-10 micrometers in thickness) and quality control of metallization layers on silicon wafers for IC manufacturing.