In semiconductor manufacturing, the control of defects at the edge of the wafer is a key factor to keep the number of
yielding die on a wafer as high as possible. Using dry lithography, this control is typically done by an edge bead
removal (EBR) process, which is understood well. Immersion lithography however changes this situation significantly.
During this exposure, the wafer edge is locally in contact with water from the immersion hood, and particles can then be
transported back and forth from the wafer edge area to the scanner wafer stage. Materiel in the EBR region can also
potentially be damaged by the dynamic force of the immersion hood movement.
In this paper, we have investigated the impact of immersion lithography on wafer edge defectivity. In the past, such work
has been limited to the inspection of the flat top part of the wafer edge, due to the inspection challenges at the curved
wafer edge and lack of a comprehensive defect inspection solution. This study utilized KLA-Tencor's VisEdge, a new
automated edge inspection system, that provides full wafer edge imaging (top, side, bottom) using laser-based optics and
multi-sensor detection, and where defects of interest can be classified with Automated Defect Classification (ADC)
Using the VisEdge technology, the impact from the immersion lithography towards wafer edge defectivity is
investigated. The work revealed several key challenges to keep the wafer edge related defectivity under control : choice
of resist, optimization of EBR recipes, scanner pollution and related memory effects, wafer handling, device processing,
etc... Contributing to the understanding of the mechanisms of wafer edge related immersion defects and to the
optimization the die yield level, this technology is believed to be important when the immersion processes are introduced
in semiconductor manufacturing.