Aerial Image Metrology for OPC Modeling and Mask Qualification

As nodes become smaller and smaller, the OPC applied to enable these nodes becomes more and more sophisticated. This trend peaks today in curve-linear OPC approaches that are currently starting to appear on the roadmap. With this sophistication of OPC, the mask pattern complexity increases. CD-SEM based mask qualification strategies as they are used today are starting to struggle to provide a precise forecast of the printing behavior of a mask on wafer. An aerial image CD measurement performed on ZEISS Wafer-Level CD system (WLCD) is a complementary approach to mask CD-SEMs to judge the lithographical performance of the mask and its critical production features. The advantage of the aerial image is that it includes all optical effects of the mask such as OPC, SRAF, 3D mask effects, once the image is taken under scanner equivalent illumination conditions. Additionally, it reduces the feature complexity and analyzes the printing relevant CD. [GRAPHICS] . In the first part, this paper will present different approaches to use the aerial image for a printing-aware mask qualification complementary to the mask CD-SEM. In the second part of the paper, the usage of the aerial image as an additional input for OPC model calibration will be discussed. The last part will describe how an OPC resist model can be tuned to forecast the printing CD based in measured aerial images.