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.
Line-edge roughness (LER) continues to be one of the biggest challenges as the CD size shrinks down to sub 100 nm. It is shown that resist components as well as illumination conditions play a big role. Influence of resist components in both 248 and 193nm chemically amplified resist formulations has been reported but the root cause is not fully understood and may be platform or even specific formulation dependent. This paper attempts to tackle the issue from the processing side. Effects of a simple hard bake process on the LER were studied. In the hard bake process, a given resist pattern was typically baked close to the glass-transition temperature after the development process. LER improved dramatically due to melting down of the rough surface. However, the wall angle of the edge lines also started to degrade at the optimum hard bake temperature. Studies on the effects of polymer Tg, hard bake temperature and time and the issues of the process are discussed.
Keeping post exposure bake (PEB) sensitivity low has become one of the most crucial factors for implementing the 193nm resist process into mass production. In a previous report, we have demonstrated that the nature of the photo acid generator (PAG) has a strong effect on the PEB sensitivity of 193 resists. Based on our findings, we decided to extend our studies to the other important resist components, such as polymers prepared with various monomer compositions, and casting solvents. Also, in an effort to investigate whether PEB sensitivity can be reduced by process optimization, the influence of soft bake and post exposure bake conditions was studied. This paper describes our new findings on some of the important factors that affect the PEB sensitivity of 193 resists.