Detecting Defects in Cu Metallization Structures by Electron-Beam Wafer Inspection

A technique using an electron-beam to inspect wafers with Cu interconnects was developed. It can detect defects such as voids or incomplete contact failures with resistances of more than by utilizing the voltage contrast of a secondary electron image. The technique is performed by controlling the charging voltage of the interconnect while the electron-beam is irradiating the wafer. The charging voltage was found to depend on the conditions of the incident electron-beam, including the incident energy. To investigate the generation of voltage contrast in a Cu via chain, the electronic characteristics of detected defects were measured with probes. It was found that the resistance of a defect measured during electron irradiation and that measured with probes agree well. The contrast of a secondary electron image depends on the resistance of the differential voltage between the ends of a defect during electron-beam irradiation. To detect voids with high sensitivity, the differential voltage between the ends of a defect should be kept between 1 and 2 V, because the resistance of the defect suddenly decreases when the differential voltage is increased beyond a certain point. © 2004 The Electrochemical Society. All rights reserved.