The design rules for advanced image sensor applications are requiring continuous CD shrinkage, and increasing aspect
ratios which resulting in major challenges associated with using KrF technology. For the implant photo layers in
particular, the need to block high-energy boron implants (well above 2 MeV) with extremely localized implant profiles
requires an aspect ratio of deep well structures greater than 10:1. Other desirable attributes of a good photoresist for such
demanding applications are high transparency, a steep wall profile consistent throughout the entire film, good adhesion
with no structure collapse, and a wide process window.
In this paper, we will discuss the role of a chemically amplified, ESCAP-type of resist in meeting these design criteria
using a double focal plane exposure technique.