(Invited) Non-Visual Defect Monitoring with Surface Photovoltage Mapping

Abstract

Non-Visual Defects (NVD) is a category of semiconductor material and process induced defects that cause electrical failures, but are not detected with visual wafer inspection tools. This paper gives an overview of our non-contact electrical NVD metrology that uses fast whole wafer inspection with standard mm resolution Kelvin probe surface voltage mapping. In an advanced approach the detected NVD regions are imaged in high resolution (mm range) using Force Kelvin Probe Microscopy. In depth NVD characterization is done with the corona-Kelvin method that quantifies dielectric and interfacial properties in the defect sites. This characterization is performed in a non-invasive fluence range of corona charging and all measurements are non-contact, and do not require fabrication of test devices. Principles of non-contact surface voltage are explained for whole wafer mapping using a high throughput dual Kelvin-probe approach, and for high-resolution micro-Kelvin Force Probe mapping of defect sites. Application examples are discussed in chronological order of the metrology development, starting with monitoring of plasma damage first introduced about 20 years ago. Further examples include surface voltage mapping of surface alkali-metals including novel high resolution micro-Kelvin Force Probe results. Recent trends in monitoring are illustrated with patterned wafer mapping and micro-scale intra die NVD’s. Finally an extension of the technique to defect mapping in SiC is presented together with in-depth corona-Kelvin characterization of defect sites. A broad application range is demonstrated with examples relevant to silicon IC, silicon photovoltaics and to wide bandgap epitaxial SiC.