Current minimum feature sizes in the microelectronics industry dictate that molecular interactions affect process fidelity
and produce stochastic excursions like line edge roughness (LER). The composition of future resists is still unknown at
this point, and so simulation of various resist platforms should provide useful information about resist design that
minimizes LER. In the past, researchers developed a mesoscale model for exploring representative 248 nm resist
systems through dynamic Monte Carlo methods and adaptation of critical ionization theory. This molecular modeling
uses fundamental interaction energies combined with a Metropolis algorithm to model the full lithographic process (spin
coat, PAB, exposure, PEB, and development). Application of this model to 193 nm platforms allows for comparison
between 248 and 193 nm resist systems based on molecular interactions. This paper discusses the fundamental
modifications involved in adapting the mesoscale model to a 193 nm platform and investigates how this new model
predicts well-understood lithographic phenomena including the relationship between LER and aerial image, the
relationship between LER and resist components, and the impact of non-uniform PAG distribution in the resist film.
Limited comparisons between the 193 nm system and an analogous 248 nm platform will be discussed.
In an effort to improve on the sensitivity of commercial nonchemically amplified e-beam resists, four polyacrylates functionalized with -CF3 and/or CH2CF3 alkoxy substituents were studied. The -CF3 substituent is known to increase backbone-scission efficiency while simultaneously eliminating acidic outgassing and cross-linking known to occur in -halogen substituted polyacrylates. Contrast curves for the polymeric -CF3 acrylates, generated through e-beam exposure, showed that the resists required an order of magnitude less dose than the current industry standards, poly(methyl methacrylate) (PMMA) and ZEP. The fundamental sensitivity of these materials to backbone scissioning was determined via 60Co -ray irradiation. The chain scissioning, G(s), and cross-linking, G(x), values calculated from the resulting change in molecular weight demonstrated that all fluorinated resists possess higher G(s) values than either PMMA or ZEP and have no detectable G(x) values. Utilizing e-beam and EUV interference lithographies, the photospeed of poly(methyl -trifluoromethacrylate) (PMTFMA) was found to be 2.8× and 4.0× faster, respectively, than PMMA.
The challenge in obtaining good resist performance in terms of resolution, line width roughness and sensitivity at EUV
wavelength forces to make more efficient use of photons that reach the wafer plane than has been the case for traditional
optical lithography. Theory demonstrates that the current absorbance levels of EUV resists are quite far from optimal and
absorbance should be increased. The most attractive pathway to achieve this is by increasing the fluorine content of EUV
resists. The viability of this approach has been demonstrated using non-chemically amplified PMMA as model resist and
comparing its photospeed with a fluorinated analogue. It has been demonstrated that the photospeed increases due to
improved resist absorbance by ~1.5X, which is close to 1.7X that is predicted by the difference in absorbance.
Further modeling studies support the experimental results and indicate an optimum for total film absorbance of ~0.20-
0.25. Compared to current platforms this would correspond to an increase in photospeed by ~1.7X which is accompanied with an improvement in LWR of ~1.14X. Combining this approach with the trends in EUV resists to increase PAG loading and include sensitizer in order to improve photospeed will likely provide a path for EUV resists that will meet the specifications that are required for the 32nm and 22nm node.
In an effort to improve upon the sensitivity of commercial non-chemically amplified e-beam resists, four polyacrylates
functionalized with α-CF3 and/or CH<sub>2</sub>CF<sub>3</sub> alkoxy substituents were studied. The α-CF<sub>3</sub> substituent is known to increase
backbone-scission efficiency while simultaneously eliminating acidic out-gassing and cross-linking known to occur in α-
halogen substituted polyacrylates. Contrast curves for the polymeric α-CF3 acrylates, generated through e-beam
exposure, showed the resists required an order of magnitude less dose than the current industry-standards, PMMA and
ZEP. The fundamental sensitivity of these materials to backbone scissioning was determined via <sup>60</sup>Co γ-ray irradiation. The chain scissioning, G(s), and cross-linking, G(x), values calculated from the resulting change in molecular weight
demonstrated that all fluorinated resists possess higher G(s) values than either PMMA or ZEP and have no detectable
G(x) values. Utilizing e-beam and EUV interference lithographies, the photospeed of PMTFMA was found to be 2.8x
and 4.0x faster, respectively, than PMMA.