Solution for Pond Shape Defect Near Wafer Edge

Defect reduction is one of the key factors to improve the process stability and yield in lithography process. This paper discusses defects in pond shape around wafer edge. These defects have mild surface topography difference on photoresist. Majority of the defects exist on the wafer edge area where there is Wafer Edge Exposure (WEE). This paper discusses the defect mechanism and potential solution for this defect type. ASML I-line Scanner and TEL track were used in this test. Investigation was carried out on the defect formation on same type of photoresist with different recipe content. Results indicated that recipe with small WEE size and without chemical EBR tends to induce this pond defects; total defect quantity is related to softbake & WEE condition. Based on the elemental analysis and Design of experiment (DOE), we can conclude that pond defect is generated where nitrogen popping or foaming as a side product of the photoreaction of DNQ-based resists during exposure. By optimizing softbake, WEE and recipe structure this pond defect could be eliminated.