Study of high-transmission PSM for lithographic performance and defect control

ArF lithography is still applied to the majority of critical layers, even with increasing of extreme ultraviolet lithography in leading-edge production. As wafer design shrinks, conventional 6% phase shift mask (PSM) becomes hard to meet the ArF lithography requirements especially for array dot on mask (hole on wafer). Therefore, transmission dependency was evaluated by mask 3D simulation, and it was found that 30% transmission has the best lithographic performances for array dot. Based on these results, mask blank and mask making process for new 30% PSM were developed. Wafer printability test using negative tone development demonstrated that new 30% PSM has better process window and mask error enhancement factor (MEEF) than conventional 6% PSM for array dot (hole on wafer). To investigate further application of new 30% PSM, lithography performances of various patterns were evaluated by mask 3D simulation and aerial image measurement system (AIMSTM). The results indicated that new 30% PSM has larger lithography margin than 6% PSM for iso dot, iso line and logic pattern. Additionally, wafer printability test demonstrated that new 30% PSM has better process window than 6% PSM for iso dot. Defect control is also an important factor in high volume manufacturing. Therefore, it is necessary to evaluate the repairability and printability of the defects on new 30% PSM. We repaired various types of defects by electron-beam repair tool and confirmed the repairability by AIMS. And the defect printability of new 30% PSM and 6% PSM to critical dimension (CD) on wafer was evaluated by program defect mask that has pin dot, extrusion and intrusion defects.