Design considerations for ultraviolet-nanoimprint lithography resists were investigated focusing on the major issues of ink-jetting performance, pattern formability, release property, and dry etching resistance. Regarding ink-jetting performance, small droplet ink-jetting of 0.7 pl was successfully demonstrated by adjusting the resist fluid property to the ink-jet coater and controlling the resist volatilization. Regarding pattern formability, a resist pattern was imprinted from a mold pattern of 28 nm in width and 60 nm in depth without pattern dimension change. It was thought that modulus control of the resist was more important than resist shrinkage in achieving excellent pattern formability. As for release property, resist with fluorine monomer and with nonreactive fluorine antisticking agent were compared. The results indicated that resist design has the capability to both reduce separation force and maintain a clear mold surface. The mold release agent decomposed with an increasing number of imprint shots, but the low release-force resist with nonreactive antisticking agent was able to control degradation of the mold release agent and thus improve release property endurance. Regarding etching resistance, it was found that increasing the ring parameter of resist is essential for high etching resistance, and resulted in improved etched pattern features of the substrate.
Design considerations for UV-NIL resists were investigated focusing on the major issues of ink-jetting performance,
pattern formability, release property, and dry etching resistance. Regarding ink-jetting performance, small droplet inkjetting
of 0.7pl was successfully demonstrated by adjusting the resist fluid property to the ink-jet coater and controlling
the resist volatilization. Regarding pattern formability, a resist pattern was imprinted from a mold pattern of 28nm in
width and 60nm in depth without pattern dimension change. It was thought that modulus control of the resist was more
important than resist shrinkage in achieving excellent pattern formability. As for release property, resist with fluorine
monomer and with non-reactive fluorine anti-sticking agent were compared. The results indicated that resist design has
the capability to both reduce separation force and maintain a clear mold surface. The mold release agent decomposed
with increasing number of imprint shots, but the low release force resist with non-reactive anti-sticking agent was able to
control degradation of the mold release agent and thus improve release property endurance. Regarding etching
resistance, it was found that increasing the ring parameter of resist is essential for high etching resistance, and resulted in
improved etched pattern features of the substrate.
We have been developing nanoimprint templates for the next-generation sub-20nm nanofabrication technology, with
particular emphasis on duplicate fabrication of quartz templates created from Si masters. In general, the narrowing of
pattern line widths is accompanied by concerns about whether resist will sufficiently fill such lines. Our development has
concentrated on the filling property of resist in narrow lines and on pattern shape after release from the mold. Our
findings indicated that pattern formability differs according to the type of resist monomer. We inferred that these
differences are manifested in such behaviors as resist shrinkage after or during release of the mold. Using a novel resist
that has good formability, we pursued quartz template duplication that employs UV-NIL. As a result, we demonstrated
HP20nm quartz pattern formation using the duplication process. We were also verified NIL resist pattern resolution of
HP17.5nm.
Reduction of resist filling time was investigated with the aim of improving UV-nanoimprint lithography (UV-NIL)
throughput. A novel low volatility, low viscosity resist was developed to enable ink-jetting with minute resist droplets
and imprinting under reduced air atmosphere. Direct observation of resist spreading showed that the resist filling process
is composed of three steps: A) capillary bridge formation, B) resist spreading, and C) air bubble dissolution. Resist
filling time was drastically decreased by changing the atmosphere from helium to a reduced air atmosphere of 0.02MPa.
A comparison of 0.7pl and 6pl resist droplets showed that reducing resist droplet size while increasing area density also
reduces resist filling time. Improved bubble dissolution speed is thought to result from imprinting under reduced air
atmosphere. Moreover, ink-jetting smaller size resist droplets with higher density is thought to have an effect on
reducing the time of each of the three steps, particularly bubble dissolution time. Combining dispensing-NIL with
imprinting in vacuum is expected to improve UV-NIL throughput.
The immersionspecific watermark defect is discussed in its formation mechanism and in the influence of materials and exposure process. The non-topcoat approach was the basis of the work, where the properties of resist surface itself played the key role. Water droplets left on the resist surface were considered to induce the watermark defect in two possible ways; (1) the droplet is carried over to PEB process and impact the resist properties under the heat, (2) the droplet already evaporates before the PEB leaving some residue on the surface. A notable reduction in the resist dissolution rate was observed in the former case, which could be due to either physical or chemical change in the resist materials triggered by the water, and thereby would result in an unavoidable patterning failure. Therefore it is essential not to leave any water droplets on the surface in preventing the watermark formation. A very much hydrophobic materials design was proven effective in achieving this. The watermark formation was correlated to the scanning speed of immersion showerhead and the defectivity was evaluated in this perspective. The receding contact angle of the resist surface was found to well correlate to the "allowable" scanning speed, and was concluded that the higher was the better. A resist material was newly designed by using a hydrophobic polymer on this basis and the resist demonstrated a promising results not only in the watermark defectivity but also in lithographic performance.
Transparency of the resist film at exposure wavelength affects lithographic performances, such as sensitivity, profile and resolution. Not only binder polymer, but also photo acid generator (PAG) itself has a significant impact on transparency of the formulated resist. Triphenylsulfonium salt (TPS) or Diphenyliodonium salt (DPI) have been widely used as PAGs in DUV chemically amplified (CA) resists, however, aromatic groups there have strong absorption at 193nm and thereby these PAGs have to suffer from low transparency. In this paper, we will report a novel class of transparent enone sulfonium salt PAGs(ENS-PAG), which we believe useful for 193nm resist. The ENS-PAGs do not have any aromatic groups but have an α,β-unsaturated ketone structure for the absorbing moiety in the backbone. These PAGs showed excellent transparency, thermal stability, and demonstrated an advantage in the line edge roughness (LER).
Synthesis of new alicyclic (meth)acrylate polymers containing androstane moieties, especially cholic acid derivatives, and their characteristics were investigated for 193nm single layer resists. Among the derivatives, a work of adhesion, Ohnishi and ring parameters were used as measures for the adhesion and the dry-etching resistance in this study. In the synthesis of the polymers, the use of 3- (beta) -methacryloyoxy-deoxycholic acid, which is the inverse configuration against the original 3-(alpha) -structure, was effective as a monomer, because the steric hindrance at 3- (alpha) -position degraded its polymerization ability. The polymers partially protected by acid labile groups showed a satisfactory adhesion, which was probably due to the hydrophilic hydroxyl group at the 12-position and the carboxyl group linked at the 17-position, and a good dry- etching resistance. On the lithographic imaging with these polymers, the reduction of the side reaction on the acid decomposition and also the control of the flexibility on the polymers largely affected their performance. THe adjustment of the Tg values of the polymers by the co-polymerization and the change of the polymer backbone from the methacrylate to acrylate structure performed well on imaging under 193nm exposure.
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