Wafer edge dies yield improvements

Abstract

As the technology shrink to smaller Critical Dimension (CD) geometry, Spin On Glass (SOG) and Chemical Mechanical Polishing (CMP) techniques are employed. For 0.30/0.35micrometers processes that uses these techniques, wafer edge dies were having zero yield. These zero yielding wafer edge dies were found to be caused by topography difference between wafer edge and center due to coating, etching and polishing non-uniformity. The use of Wafer Edge Exposure (WEE) using ultraviolet light to create the Edge Bead Removal (EBR) on selected layers provide a more consistent and sharper EBR ring as compared to liquid EBR. This will also result in more complete dies at the wafer edge. The stepper is only able to provide either or no leveling information for the partial wafer edge fields due to the location of the field being too close to wafer edge. In this paper, we present an approach to resolve this problem which addresses the shortcomings of the stepper. We employ a manual top down CD Sem measurements on these non yielding wafer edge dies to check on the CD and profile, a different exposure and/or focus is/are than applied to these non yielding wafer edge field. KLA scan and sort yield are than used to confirm the effectiveness of the changes.