Use of wafer backside inspection and SPR to address systemic tool and process issues

Defects on the backside of wafers can be either tool or process induced and can cause lithography-related issues such as focus deviation or chuck contamination. Tool induced scratches, process induced contamination, or residues on the back of wafers often have unique signatures, such as a repeatable scratch caused by wafer handling equipment or a chuck imprint on the backside of a wafer. Certain backside defect signatures such as large scratches or divots can contribute to wafer breakage or reliability issues. Spatial Pattern Recognition (SPR) is a method of comparing defect patterns at the wafer level with known defect signatures stored in a library that is created from process data. These defect signatures can represent systemic issues with process tools, handling equipment, or the process itself. This paper describes a backside inspection method for identifying wafers with both known and new spatial pattern signatures. By reporting the frequency of each signature category, process partitioning can efficiently trace the source of these problems. In addition, new defect signatures can be automatically learned and added to the library. The paper also includes examples of how this method was used to identify backside defect patterns caused by process and tool excursions in a 300mm fabricator.