High-NA optical CD metrology on small ln-cell targets, enabling improved higher order dose control and process control for logic

The logic manufacturing process requires small in-device metrology targets to exploit the full dose correction potential of the modern scanners and process tools. A high-NA angular resolved scatterometer (YieldStar (TM) S-1250D) was modified to demonstrate the possibility of OCD measurements on 5x5 mu m(2) targets. The results obtained on test wafers in a logic manufacturing environment, measured after litho and after core etch, showed a good correlation to larger reference targets and AEI to ADI intra-field CDU correlation, thereby demonstrating the feasibility of OCD on such small targets. The data was used to determine a reduction potential of 55% for the intra-field CD variation, using 145 points per field on a few inner fields, and 33% of the process induced across wafer CD variation using 16 points per field full wafer. In addition, the OCD measurements reveal valuable information on wafer-to-wafer layer height variations within a lot.