As the industry transitions to 90 and 65nm photolithography, the increased complexity and costs of advanced photomask remain an industry focus. Mask makers and wafer fabs must develop new techniques in photomask inspection and quality control to improve turnaround time and ultimately the mask and wafer production yield. Specific to wafer fabs, this requires an increased focus on the incoming quality control techniques combined with improved communication with the mask shop.
For incoming mask inspection "mask-level" defect inspection and dispositioning is no longer adequate. Aggressive OPC on PSM masks, combined with tighter CD requirements increases the burden on both machine and operator increasing the risk of mission a killer defect. For 90nm and beyond, simulation-based defect disposition techniques will be required to predict the wafer-level printing behavior and disposition the defects appropriately.
A simulation-based defect disposition flow using Synopsys's i-Virtual Stepper System (iVSS) for incoming mask quality assurance is presented in this study. This paper will examine the feasibility of implementing such a flow from a wafer-fab operation point of view. What kind of benefits can be achieved and how it works will be also presented.
Mask manufacturers and mask users continue to pursue improvements in mask inspection and qualification processes driving standards to guarantee the highest performance of advanced photomasks while maintaining a high degree of predictability of turn-around-time.
Simulation-based defect analysis and dispositioning has become an area of much interest for both mask manufacturers and mask users. Repairing only the defects that impact wafer level performance (lithographically significant) improves both mask cycle time and eliminates unnecessary and costly repairs. Mask maker and mask users can utilize defect simulation as a common standard by which to benchmark the quality of results. We report in this paper the results of a joint evaluation of the i-Virtual Stepper system (i-VSS) the automated simulation based defect dispositioning software solution in an advanced photomask qualification flow. Results discussed include the optimization and automation of the mask inspection flow using i-VSS, simulation accuracy comparisons of i-VSS versus AIMS versus wafer printability for binary and phase shifting masks at 130nm, 90nm, and 65nm technology nodes, and a comparison of the iVirtual Stepper system's automated defect severity scoring (ADSS) versus manual defect dispositioning.