Target recovery process optimization to improve image based overlay performance for critical recording head manufacturing processes

Overlay and alignment target recovery process is often required in recording head fabrication where targets are covered by opaque materials. In this study, we have investigated the recovery process impact on the image based overlay (IBO) measurement performance in critical stages of the recording head fabrication. The trench topography created by the target recovery process can result in the asymmetric resist coating uniformity across the wafer and result in errors in the measured overlay values and modeled correctable wafer terms such as the scale and rotation. These errors become significant at critical pattering layers when there is a large z-spacing between the current resist overlay mark and the previous overlay reference mark layer. The recovery pattern size and the recovery depth impact on the measured overlay performance are evaluated. The overlay mark needs to be optimized to reduce the overlay measurement variation. Overlay mark designs, including box-in-box, AIMid and multi AIMid overlay marks, are investigated. Self-referencing marks (SRM) are used to evaluate recovery process and overlay mark impacts on overlay measurement accuracy.