Investigation of Scanning Electron Microscope Overlay Metrology

Abstract

Compared with optics-based measurement, overlay measurement using scanning electron microscope (SEM) is more suitable for small overlay marks. Small overlay marks can be located freely in a chip. This method realizes highly accurate measurement. SEM overlay metrology has been studied in recent years. It has been reported that SEM-based overlay metrology is capable of making accurate measurements. Overlay marks of grooves were used in that case and signals were obtained easily from marks with topographic structure. We have investigated SEM overlay metrology using marks covered with flat oxide film and anti+reflection coating. Using voltage contrast images, we demonstrated that SEM is also capable of making accurate measurements in such a case. In this work, we examine the accuracy and precision of SEM-based overlay metrology using a mark covered with thick resist film. In addition, we investigated the effect of small overlay marks.