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.1 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.2
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.
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 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.
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.
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.
Polymers with methyl acetal ester moiety in the side chain as acid labile protecting group were synthesized and their thermal property, plasma stability and chemical amplification (CA) positive-tone resist characteristics were investigated. 2-Admantyloxymethyl (AdOM) groups in the copolymer indicated lower glass transition temperatures and higher thermal decomposition temperatures than those of 2-methyl-2-admantyl (MAd) groups in the copolymer. AdOM polymer film showed smooth surface roughness after Ar plasma exposure compared with MAd polymer film due to the high thermal stability. The activation energies (Ea) of these deprotection reactions were calculated from Arrhenius plots of these deprotection reaction rate constants. In the low post exposure bake (PEB) temperature region, the Ea of these resists decreased in the order MAd > AdOM. The low Ea methyl acetal resists displayed good thermal flow resist characteristics for contact holes printing. In addition, the low Ea methyl acetal resist achieved a wide exposure latitude of 8.1 % and depth of focus of 400 nm for printing 80 nm 1:1 dense line pattern using NSR-306C (NA 0.78, 2/3 annular). Furthermore, the 65 nm 1:1 dense lines using ASML XT1400 (NA 0.93, C-Quad) for low Ea methyl acetal resist pattern showed no tapered and no footing profiles and small roughness on the lines pattern sidewall was observed.
We have investigated the possibility of amorphous low molecular weight polyphenols as a chemically amplified positive-tone electron-beam (EB) resist. Low molecular weight polyphenol, 4'4-methylenebis{2-[di(2-methyl-4-hydroxy-5-cyclohexylphenyl)]methyl} phenol (3M6C-MBSA) as a base matrix, was protected by 1-ethoxyethyl (EE) groups to control the dissolution rate in 0.26 N tetramethylammonium hydroxide aq. developer. The film distribution in the depth direction for resist components with a Time-of-Flight Secondary Ion Mass Spectrometry (TOF-SIMS) and the Fourier amplitude spectra of line-edge roughness (LER) have been investigated to understand the relationship between them for the resists formulated with 3M6C-MBSA and two types of photo acid generator (PAG), triphenylsulfonium perfluoro-1-butanesulfonate (TPS-PFBS) and triphenylsulfonium n-octanesulfonate (TPS-nOS). From these results, it was found that the resist film consisting of TPS-nOS showed more homogeneous in the depth film distribution than that with TPS-PFBS, and the resist with TPS-nOS also indicated the suppressed LER value of 5.1 nm in the wide frequency range. Therefore, the homogeneity of the resist film may affect the pattern LER.
We are reporting on the development of acryl polymer based on novel methacrylate and acrylate monomers with various trifluoromethyl groups for the application to 157nm chemically amplified positive-tone resists. The (alpha) - trifluoromethylation of the alkyl ester in methacrylate or acrylate could employ the reduction of acrylpolymer absorbance at 157nm by spectra analysis with the VUV-200 spectrophotometer by JASCO. Although the trifluoromethyl groups could employ the reduction of base polymer absorbance at 157nm, the homopolymers have issued weak etch resistance as a photoresist base polymer. To take account of this issue, we have developed a novel monomer, trifluoromethyl- iso-adamantylmethacrylate (TFIAdMA) and a new co-polymer system with the combination of fluorinated methacrylate derivatives and substituted p-hydroxystyrene. The absorption coefficient of poly(p-tert-butoxystyren-co- hexafluoro-tert-butyl methacrylate-co-methacrylic acid) incicated to be less than 3 micrometers -1 at 157nm. Patterning results were obtained with a 157nm contact exposure system of VUVES-4500 by LTJ. One of the experimental resists, based on a particular polymer ratio and photo acid generator, has clearly achieved 180nm line and space pattern resolution. At 140nm resist film thickness, the sensitivity was 31 mJ/cm2 when using 0,26N tetrametylammonium hydroxide surfactant type developer.
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