Pitch division lithography (PDL) with a photobase generator (PBG) allows printing of grating images with twice
the pitch of a mask. The proof-of-concept has been published in the previous paper and demonstrated by
others. Forty five nm half-pitch (HP) patterns were produced using a 90nm HP mask, but the image had line
edge roughness (LER) that does not meet requirements. Efforts have been made to understand and improve the
LER in this process. Challenges were summarized toward low LER and good performing pitch division.
Simulations and analysis showed the necessity for an optical image that is uniform in the z direction in order for
pitch division to be successful. Two-stage PBGs were designed for enhancement of resist chemical contrast. New
pitch division resists with polymer-bound PAGs and PBGs, and various PBGs were tested. This paper focuses on
analysis of the LER problems and efforts to improve patterning performance in pitch division lithography.
The semiconductor industry is pursuing several process options that provide pathways to printing images smaller
than the theoretical resolution limit of 193 nm projection scanners. These processes include double patterning, side
wall deposition and pitch division. Pitch doubling lithography (PDL), the achievement of pitch division by addition
of a photobase generator (PBG) to typical 193 nm resist formulations was recently presented.<sup>1</sup> Controlling the net
acid concentration as a function of dose by incorporating both a photoacid generator (PAG) and a PBG in the resist
formulation imparts a resist dissolution rate response modulation at twice the frequency of the aerial image.
Simulation and patterning of 45 nm half pitch L/S patterns produced using a 90 nm half pitch mask were reported.<sup>2</sup>
Pitch division was achieved, but the line edge roughness of the resulting images did not meet the current standard.
To reduce line edge roughness, polymer bound PBGs and polymer bound PAGs were investigated in the PDL resist
formulations. The synthesis, purification, analysis, and functional performance of various polymers containing PBG
or PAG monomers are described herein. Both polymer bound PBG with monomeric PAG and polymer bound PAG
with monomeric PBG showed a PDL response. The performance of the polymer bound formulations is compared to
the same formulations with small molecule analogs of PAG and PBG.
The drive to sustain the improvements in productivity that derive from following Moore's law has
led the semiconductor industry to explore new technologies that enable production of smaller and
smaller features on semiconductor device. Pitch division techniques and double exposure lithography
are approaches that print features beyond the fundamental resolution limit of state-of-art lenses by
modifying the lithographic process. This paper presents a new technique that enables pitch division in
the printing of gratings using only a single exposure that is fully compatible with the current
manufacturing tools. This technique employs a classical photoresist polymer together with a
photoactive system that incorporates both a photoacid generator (PAG) and a photobase generator
(PBG). The PBG is added to the resist formulation in higher molar concentration than the PAG, but has
a base production rate that is slower than the acid production rate of the PAG. The PBG functions as a
dose-dependent base quencher, which neutralizes the acid in high dose exposure regions but not in the
low dose regions. This photoactive system can be exploited in the design of both positive tone and
negative tone resist formulations that provide a developed image of a grating that is twice the
frequency of the grating on the mask. A simulation of this process was performed for a 52 nm line and
space pattern using PROLITH and customized codes. The results showed generation of a 26 nm half
pitch relief image after development. Through this new technique, a 45 nm half pitch line and space
pattern was experimentally achieved with a mask that produces a 90 nm half pitch aerial image. This
corresponds to a k1 factor of 0.13. The principles, the materials design and the first lithographic
evaluations of this system are reported.
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.