Given the current need for resist
materials for patterning transistors
with ultralow nodes, there has been a quest for developing resists
with improved performance for nanoscale patterning with good contrast.
The present work demonstrates polymeric resists (MAPDST-TIPMA) developed
through the integration of a radiation-sensitive monomer (MAPDST)
with an organoiodine functionality (TIPMA) for sub-16 nm patterning
using electron-beam and helium ion beam lithography. The structural
integrity was established by several spectroscopic techniques particularly
NMR, FTIR, XPS, and GPC. These polymeric resists possess weight-average
molecular weight (M
w) in the range of
10000–12000 with low PDI. While the resists 3a and 3b were synthesized with feed ratios of 80:20 and
70:30 of the monomers MAPDST and TIPMA, respectively, the actual microstructure
compositions were calculated, using XPS and GPC data, to be ∼94:6
and 91:9, respectively. The present resists have the potential for
patterning 16 nm line/space features when exposed to e-beam. Also,
15 nm features were successfully patterned using MAPDST-TIPMA resists.
The line edge roughness (LER) and line width roughness (LWR) of the
20 nm L/3S features were calculated to be 2.48 and 3.6 nm, respectively.
Moreover, complex nanofeatures of different shapes were successfully
patterned using 3b. A critical analysis of nanofeatures
using AFM revealed that the patterns are very well developed with
a sharp wall profile. The normalized resist thickness (NRT) curve
was established to evaluate the sensitivity of the present resist
which was calculated to be 341 μC/cm2 at 20 keV.
The nature and slope of the NRT curve indicated that MAPDST-TIPMA
is a negative tone resist with good contrast. Finally, the resist
was found to be highly sensitive to He+ beam (sensitivity
∼6.21 μC/cm2) resulting in 20 nm L/S as well
as 15 nm features with a good wall profile.
Extending the resolution limit of next-generation lithography down to 15 nm or below requires the resist to attain small features, high irradiation sensitivity, and low line edge/width roughness. To meet this prerequisite, an increase of irradiation absorption in resists is an important strategy. A negative tone, deep ultraviolet, electron beam, and helium ion beam active resist formulation has been realized comprising a hydroxystyrene-based polymer tert-butyl 2-ethyl-6-(4-hydroxyphenyl)-4-phenylheptanoate (Terpolymer). Further, the resist performance was enhanced by doping of a microemulsion-based Ag nanoparticle (size distribution ∼2 nm) irradiation sensitizer. As a result, a tenfold decrease in the critical dose (E o ) was observed by increasing Ag nanoparticle contents from 0.1 to 1.0 wt %. The developed resist patterns exhibit significantly higher sensitivities and resolutions of 50 and 34.12 μC/cm 2 and ∼12 and ∼11 nm line patterns, respectively, for e-beam (E e ) and helium ion beam (E He ) irradiations. The line edge/width roughness of well-developed e-beam exposed patterns was found to be 1.5 ± 0.1/2.8 ± 0.3 nm, respectively. These e-beam/resist interactions were modeled by the Monte-Carlo trajectory, and the results were in line with the experimentally observed one. These simulations suggest the enhanced irradiation absorption inside the resist matrix with the addition of a high-electron-density Ag entity. These investigations reveal that one of the best ways to simultaneously improve the sensitivity and resolution of the resist is the optimum incorporation of higher-atomic-number nanoparticles in the polymeric matrix, which enhances the absorption cross section (σ) without altering the resist properties.
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