Uv Inspection Of Euv And Scalpel Reticles

A UV inspection tool has been used to image and inspect Next Generation Lithography (NGL) reticles. Inspection images acid simulations have been used to provide feedback to mask makers so that inspectability of NGL masks can be optimized. SCALPEL masks have high optical contrast and look much the same in reflection as conventional chrome on glass masks do in transmission. EPL stencil masks can be imaged well in reflection, but defects below the top surface, in the cutouts, may not be detectable optically. EUV masks that have been made to date tend to have relatively low contrast, with line edge profiles that are complex due to interference effects. Simulation results show that improved EUV inspection images can be obtained with a low reflectivity absorbing layer and proper choice of buffer layer thickness.