In order to realize high productivity and reliability of modern semiconductor fabrication, defects inspection techniques for layers of SOI (Silicon On Insulator) wafer become more essential. The layers on SOI wafer have only about 100∼200nm thickness, therefore, technique for evaluating appropriately the defects in such thin layers has not been developed until now.
Novel optical defect measurement method is proposed, which enables to detect and classify the nano-defects that exist in the layers of SOI wafers by using evanescent field. In this method, evanescent field is generated by total internal reflection of infrared laser propagating in the top silicon layer. To execute light coupling into the layer, novel silicon prism coupler was developed.
In this paper, first electromagnetic field of the wafer surface vicinity was analyzed by using FDTD (Finite Difference Time Domain) simulation tool. The results show this method can detect and classify the nano-meter scale defects on the surface and in the layers. Next fundamental experiment was carried out to detect defects like sub-micrometer diameter hole that was fabricated on SOI wafer using FIB (Focused Ion Beam) machining. The experimental result also shows this method can detect sensitively the defects on the surface of SOI wafers.