CDP - Application of focus drilling

Inhalt:
In this paper, we investigate Nikon’s CDP (continuous depth of focus expansion procedure) used for focus drilling. The method is based on tilting the wafer stage along the scanning direction, with the stage moving upor downwards. This averages the aerial images in the resist and increases the achievable depth of focus. The application of CDP (or tilted stage approach) would enlarge the depth of focus (DOF) for patterning of contact holes, especially in backend of line processes with increased topographical complexity. For CDP to be applied in mass production, it is necessary to understand the relation between CDP values, numerical aperture (NA), the coherence parameter σ and the depth of focus. The influence of CDP on patterning of isolated and dense contact holes needs to be considered. We show that CDP could enlarge the depth of focus and thus improve the process stability for patterning of contact holes.