The main challenge in ArF lithography is to reduce cost of ownership (CoO) because increase in multi-patterning process is generally required to obtain a fine pattern. As a consequence, industry strongly requires ArF lithography process with a fast scan speed scanner and low defectivity material for CoO. The breakthrough technology to improve defectivity and resolution simultaneously was the polarity-change property of film surface from hydrophobic to hydrophilic after alkaline development process because a property after development process should be only associated with defectivity, not fast scan speed. The materials with high polarity change function were explored to EUV process to achieve low defectivity with good lithography performances.
Blurs, swelling properties and lithographic performance for polymer bound PAG and polymer PAG blended type resists
were studied. A Blur strongly depends on PAG size and the polymer bound PAG type resist reduces the Blur. The Blur
for the polymer bound PAG type resist is smaller than that for ZEP (non CAR). That indicates that polymer bound PAG
should reduce secondary electron diffusion. The polymer bound PAG type resist acquires very small Blur with higher
sensitivity and suppresses swelling very well, therefore polymer bound PAG is one of the promising technologies that
improve Resolution, LWR and sensitivity (RLS) property. RLS property on EUV exposure tool is significantly
improved by using the polymer bound PAG type resist. Resolution reaches 24nmhp and is limited by pattern collapse
and line breaking. Further lithographic experiments on EB exposure tool which has higher NILS than EUV exposure
tool were carried out in order to make clear relation between Blur and resolution. The resolution of the polymer bound
PAG type resist reaches 17.5nmhp with 35nm thickness and there is possibility that the resolution of an optimized
polymer bound PAG type resist reaches under 15nmhp. The resolution of the resist with lower capillary force (C.F.)
given and lower swelling and on higher NILS exposure tool strongly depends on the Blur.
Fundamental studies on polymer bounded PAG and polymer - PAG blend type were carried out with the viewpoint of
dissolution property, lithographic performance, and blur. These materials were prepared to be able to directly compare
and to discuss the difference between blend and bounded PAG, with different PAG loading amount. Dissolution
property revealed the clear difference of these materials tendency to the PAG loading amount variation. Lithographic
performance difference corresponds to the dissolution property difference, and there found the strategy to improve
lithographic performance with polymer bounded PAG type resist. Blur study suggests the advantage in polymer bounded PAG in resolution.
Several methods to improve sensitivity of EUV resist, with a couple of key points of acid generation efficiency and deprotection
reaction efficiency. Larger loading of PAG to increase the secondary electron absorption possibility, cation
unit design to lower the lowest unoccupied molecular orbital of cation, and lowering ionization potential of polymer to
enable efficient secondary electron generation, were discussed in the viewpoint of acid generation efficiency. Larger
size of anion structure design on PAG was applied to special formulation of small loading of quencher to minimize
necessary generated acid concentration to give enough de-protection reaction amount, and to higher PEB temperature
resist process to maximize de-protection reaction efficiency.
EUV lithography performances of resist materials with different molecular weight of polymer were investigated. EUV
exposure experiment using a SFET at Selete clearly showed that line-width roughness (LWR) and 1:1 half-pitch (hp)
resolution were each improved using the polymers with middle and low molecular weights. These polymers showed high
dissolution contrast relative to polymer with high molecular weight. Mask linearity data also showed that the polymer
with low molecular weight gave a linear dependence on critical dimension (CD) against mask size down to hp 26 nm.
Thermal analysis of resist film revealed that thermal glass transition temperature (Tg) was dramatically decreased from
190 °C to 110 °C with decreasing molecular weight from high to low. In contrast with Tg which directly reflects
mobility of polymer, exposure latitude (EL) was increased from 12.3% to 14.5% at hp 32 nm by decreasing molecular
weight of polymer. Similarly, iso-dense bias was also improved by utilizing the low molecular weight polymer.
Combination of PAG-B with the low molecular weight polymer caused further improvement in mask linearity, EL, and
iso-dense bias at hp 32 nm, although LWR was rather increased.