The Inline Detection of Tiny Bubble Defect and Solution for 14NM Photolithography Process

The research aims at the very tiny bubble defect found during the process development of 14nm technology node. A special shape of middle-ring distribution defect was found at wafer center, which was caused by the imperfect litho process and the source can be traced back to the prior litho process. The defect quantity is low but its kill ratio is very high. It turns out the end of the line chip yield showed exact the same shape of failure map. The defect location is specific, and the stack map of multiple wafers revealed a circular distribution of 55 mm radius. The defect couldn't be caught effectively by the low failure rate and counts, and the inline sampling inspection rarely capture it. In this paper, an alternative way of using bare wafers to do print down without pre-layer interference achieved purified defect signature and caught low count cases. Besides, bare wafers instead of product ones quickly accomplished massive quantity of inspections and figured out the path of defect transformation. Since the defect could be detected, an inline monitoring index was set up. The following process evaluation and corresponding experiments were carried out and instantly examined. Finally, the tiny bubble defect was fixed by an optimized combination of litho conditions.