Structure Analysis of Tungsten Contact Failure in Silicon on Insulator Device

We analyzed the leakage current failure in the silicon (Si) on insulator devices. The failure sites were detected by light emission microscopy, and they were found to be tungsten (W) contacts. The cross section of the failed W contact was processed by focused ion beam, and it was observed by scanning ion and transmission electron microscopes. The defect goes the through active Si and buried SiO2 layer from the buried W and arrives at the Si substrate. Our Auger electron spectroscopy analysis and energy-dispersive x-ray spectroscopy analysis identified that the defect included W, and that the active Si layer included a slight crystal defect. Our analysis suggests that the failure mechanism is over-etching of reactive ion etching (RIE) and a crystal defect of active Si layer. If the etching speed of the defective crystal is faster than the normal Si, a void is formed in the SiO2 layer. Currently, the RIE process was improved, the crystal defect decreased, and the leakage current failure mode in the W contact decreased.