Comparative study on MEEF and dose latitude between attenuated PSM and Cr binary mask

摘要

As the feature size shrinks dramatically, it is essential to use low-k1 factor for minimum resolution under present optical technology. However, low k1 causes the increase of the mask error enhancement factor(MEEF), which means that the wafer CD error transferred from mask CD error will be amplified non-linearly. This MEEF becomes one of the most critical issues in depth of focus(DOF) and an exposure latitude. This paper confirms that a small MEEF and better dose latitude is achievable if an attenuated phase shift mask (att.PSM) is combined with an optimal off axis illumination(OAI) condition because the image contrast on wafer can be improved by reducing the magnitude difference between the zeroth order and te first order. This improvement is more noticeable especially in contact hole patterns. And it is confirmed that the choice of optimal intensity threshold is critical to MEEF, according to the dose error enhancement factor(DEEF) results for various resist thresholds. In conclusion, a smaller MEEF is obtained by combination of OAI and att.PSM and by choosing optimal intensity threshold on this low K1 lithography regime.