193 immersion lithography has reached its maximal achievable resolution. There are mainly two lithographic
strategies that will enable continued increase in resolution. Those are being pursued in parallel. The first is extreme
ultraviolet (EUV) lithography and the second is double patterning (exposure) lithography. EUV lithography is counted
on to be available in 2013 time frame for 22 nm node. Unfortunately, this technology has suffered several delays due to
fundamental problems with source power, mask infrastructure, metrology and overall reliability. The implementation
of EUV lithography in the next five years is unlikely due to economic factors. Double patterning lithography (DPL) is a
technology that has been implemented by the industry and has already shown the proof of concept for the 22nm node.
This technique while expensive is the only current path forward for scaling with no fundamental showstoppers for the
32nm and 22nm nodes. Double exposure lithography (DEL) is being proposed as a cost mitigating approach to advanced
lithography. Compared to DPL, DEL offers advantages in overlay and process time, thus reducing the cost-of-ownership
(CoO). However, DEL requires new materials that have a non-linear photoresponse. So far, several approaches were
proposed for double exposure lithography, from which Optical Threshold Layer (OTL) was found to give the best
lithography performance according to the results of the simulation. This paper details the principle of the OTL
approach. A photochromic polymer was designed and synthesized. The feasibility of the material for application of DEL
was explored by a series of evaluations.
Intermediate state two-photon (ISTP) photoacid generator (PAG) and optical threshold layer (OTL) approaches to
double exposure lithography have been explored. We have synthesized "transparent" PAG and sensitizer compounds for
use in ISTP systems and have demonstrated the possibility of utilizing such energy transfer systems to generate acid.
We have also synthesized side chain liquid crystalline polymers and small molecule azobenzene compounds for use in
OTL applications and have begun photoswitching studies.