Improved Image Resolution for Wafer Inspection Tool Using Sub-200-nm Wavelength Light Optical System

摘要

In order to extend bright field imaging systems to the 65 nm design rule and beyond, we evaluated inspection imaging characteristics with deep UV (DUV) light with a sub-200 nm wavelength, which is the shortest wavelength in practical use, by reflectivity simulations and with experiments using a pilot proof of concept (POC) tool. The results have confirmed that DUV light has enough reflectivity to enable the inspection of defects in principal semiconductor materials. Furthermore, DUV light shows up to 7 times greater image contrast than UV light (365 nm) for test pattern whose spatial frequency is near the resolution limit of UV optics. When pixel size is reduced, light contrast produced by DUV light is further enhanced to such an extent that it is up to 12 times greater than that produced by UV light. Our evaluation has also confirmed that contrast depends not only on resolving power, but also on coat thickness and reflectivity. Based on optical considerations and current UV inspection technology, it can be concluded that our DUV optical inspection system has the possibility of being used in the design rule of half-pitch 65 nm (hp65 nm) and beyond.