A novel series of stable, acid amplifiers (AAs) has been designed and tested for use in Extreme Ultraviolet
(EUV) lithography, that generate strong, fluorinated polymer bound sulfonic acids. Novel polymer bound and
blended AAs were prepared in moderate to good yields and characterized by NMR. We demonstrated by EUV
lithography that the polymer bound AA resist has line-edge roughness (LER) values of 3.8 nm and the
polymer blended AA resist has LER values of 2.1 nm while the control resist has LER values of 4.6 nm.
Although sensitivity comparisons have yet to be made, these new resists using bound and blended AAs are
showing remarkable improvements in LER when compared with the control resist without AAs.
This paper presents two new concepts that together provide a 100,000X improvement in stability
for AAs that produce highly-fluorinated, strong sulfonic acids. These two new design concepts are
based on (1) an olefin-trigger structure and (2) a trifluoromethyl group <i>alpha</i> to the sulfonic ester.
These new concepts led to the synthesis of the first stable acid amplifier that generates triflate acid
and for the synthesis of AAs that are stable enough to be used as monomers in free-radical
polymerization reactions yet produce very strong, fluorinated acids. Lastly, we present preliminary
results where one new AA is able to improve the LER of a control resist from 4.6 ± 0.5 nm to 2.1 ±
The development of resists that meet the requirements for resolution, line edge roughness and sensitivity remains one of
the challenges for extreme ultraviolet (EUV) lithography. Two important processes that contribute to the lithographic
performance of EUV resists involve the efficient decomposition of a photoacid generator (PAG) to yield a catalytic acid
and the subsequent deprotection of the polymer in the resist film. We investigate these processes by monitoring the
trends produced by specific masses outgassing from resists following EUV exposure and present our initial results. The
resists tested are based on ESCAP polymer and either bis(4-tert-butylphenyl)iodonium perfluoro-1-butanesulfonate or
bis(4-tert-butylphenyl)iodonium triflate. The components originating from the PAG were monitored at various EUV
exposure doses while the deprotection of the polymer was monitored by baking the resist in vacuum and detecting the
cleaved by-product from the polymer with an Extrel quadruple mass spectrometer.
This paper describes the lithographic properties of fifteen acid amplifiers (AAs) and the chemical modeling
approach used to predict their thermal stability in an ESCAP polymer resist system at 70 and 110 °C. Specifically, we
show how added AAs affect the sensitivity (Eo and Esize), resolution, line edge roughness (LER), exposure latitude, and
Z-parameter of ESCAP resists. We find that acid amplifiers that generate fluorinated sulfonic acids give the best
combination of sensitivity, LER, and exposure latitude. Additionally, we show that these compounds are not
photochemically active. Combining thermodynamic and kinetic modeling has allowed us to predict the relative enthalpies of activation for catalyzed and uncatalyzed decomposition pathways and compare the results to experimental
thermal stability tests.
Successful fluids for use in 3rd generation 193 nm immersion lithography must have refractive indices of ≥ 1.80 at
193 nm, ≤ 0.15/cm absorbance at 193 nm, and be photochemically inert to 193 nm radiation. Various classes of organic
compounds were prepared and evaluated for use as 3rd generation 193 nm immersion fluids. Functional groups that were
evaluated included: sulfones, sulfoxides, sulfonic acids, ammonium sulfonate salts, alkanes, alkyl chlorides, alkynes,
and nitriles. Several compounds were synthesized including three sulfone and three sulfonic acid compounds. Other
commercially available compounds of interest underwent extensive purification prior to evaluation. Although this work
did not lead to any specific solutions to the challenge of identifying 3rd generation 193 nm immersion fluids, it can be
concluded that high density hydrocarbons based on cubane may have the best chance of meeting these goals.
A method to evaluate the sensitivity of photoresists used for extreme ultraviolet (EUV) lithography has been developed.
EUV sources produce out-of-band radiation and the reflective optics used in EUV tools reflect some of this out-of-band
light on the wafer plane. The effect of exposing these photoresists to this unwanted light can reduce the image contrast
on the wafer, and thereby reduce the image quality of the printed images. To examine the wavelengths of light that may
have an adverse effect on these resists, a deuterium light source mounted with a monochromator has been designed to
determine how sensitive these photoresists are to light at selected wavelengths in the range 190-650 nm.
A simple empirical model is presented that predicts the index of refraction at 589 nm (D-line) and 193 nm for molecules based solely on chemical structure. The model was built by comparing literature values of refractive indices (sodium D-line 589 nm) of compounds with representative functionalities and has 18 adjustable parameters. Published values for n<sub>D</sub> and n<sub>193</sub> were used to extrapolate the predictions from values of n<sub>D</sub> to values of n<sub>193</sub>. These simple, accessible models can be run using only Excel software on a laptop computer.