As Extreme Ultraviolet Lithography (EUVL) gets closer to production, an increasing interest is devoted to Deep Ultraviolet Out-of-Band (DUV OoB). In fact, EUV sources are known to emit a broad spectrum of wavelengths, among which DUV could potentially contribute to the exposure and degrade imaging performance. In this paper, the DUV/EUV ratio in pre-production (ASML NXE:3100) and alpha (ASML ADT) EUVL scanners is investigated. The OoB is quantified using a previously proposed methodology  based on the use of an aluminum-coated mask capable to provide quantitative in situ information on DUV/EUV ratio without disrupting the tool. The OoB sensitivity of an extensive set of resists is estimated in order to properly guide material development. The impact of OoB on imaging and on Intra-Field Critical Dimension Uniformity (IF CDU) is quantified using resists with large differences in OoB sensitivity. In addition, the impact of mask design on OoB is also investigated. The results indicated that it is in fact possible to reduce the OoB sensitivity of a resist (from 2.5 down to 0.3%) without compromising imaging performance and that tool OoB qualification and monitoring are critical in a production environment.
Out of band (OoB) radiation has been regarded as one of the key issues on Extreme Ultra Violet
Lithography (EUVL). OoB light especially in the deep ultraviolet (DUV) region have a negative
impact on image contrast and resist profile, since general photo acid generator (PAG) used in chemically
amplified EUV resist are also sensitive for DUV. It is reported that a Spectral Purify Filter (SPF) would
eliminate OoB radiation. However it expense a large reduction in EUV power and hence throughput, so
it is reported that HVM EUV exposure tool would not employ SPF.
Therefore, both EUV sensitive and DUV insensitive are required property to overcome OoB radiation
issue by resist material itself. Consideration of PAG cation structure was proceeded to control
absorption for DUV. Based on the concept, OoB insensitivity was investigated both on blend resist
platform and Polymer Bound PAG (PBP) platform. OoB insensitive concept was confirmed with UV
spectrum and sensitivity for KrF and ArF. The OoB insensitive PAG cation worked well on PBP, while
dark loss are seen on blend resist platform due to lack of inhibition effect. Lithographic performance
would be exhibited using Alpha Demo Tool (ADT) and NXE3100. Outgassing property on witness
sample (WS) and Residual Gas Analysis (RGA ) will be also discussed.
The concept of nonlinear acid diffusion coefficient would be emphasized to achieve better latent image
quality, resulting in better lithographic performance. Focusing on realizing the concept, we
previously reported about a main chain decomposable star shaped polymer (STAR polymer).STAR polymer consists of a core unit and several arm units which connect to the core unit with easily
acid cleavable bonding. (Fig.1) The main chain decomposition system is ideal to achieve promoted acid
diffusion at exposed area because it accompanies great molecular weight reduction at exposed area. The
significance of the STAR system had been confirmed for partially protected poly(p-hydroxystyrene)
(PHS) considering arm length and core structure.
Employing p-hydroxy-α-methylstylene (PHOMS) for arm structure, novel STAR polymer with
appropriate glass transition temperature (T<sub>g</sub>) could be realized. (Fig.2) Poly PHOMS is known to
undergo acid-catalyzed decomposition from the polymer end. Lithographic performance comparison
between the STAR polymer and the linear polymer as a control using a Micro Exposure Tool (MET)
would be exhibited.
Thermal property change with exposure and dissolution charactersitic will be also discussed. Moreover
main chain decomposition mechanism was investigated with flood EB irradiation.
We prepared three different kinds of polymers. The first was the STAR polymers having various length of the arms
connected to the single core which could be decomposed by the acid. The second was the Linear polymers based on
p-hydroxystylene (HS) which was also used for the arms of the STAR polymer. The other was the non-decomposable
STAR polymer which had a quite similar shape to the STAR polymer and of which core structure could not be
Using those materials, lithographic performance obtained using a Micro Exposure Tool (MET) was compared with
thermal property, and it was found that STAR-9mer-H having the 9 HS unit arms provided best overall performance,
24 nm of ultimate resolution, 4.3 nm of line width roughness and 4.6x10<sup>-8</sup> mJ•nm<sup>3</sup> of Z factor on MET evaluation. In
addition to this, the specific resist based on the STAR polymer could achieve 26 nm resolution with quite wider
process window capability that the control resist consisting of partially protected poly(p-hydroxystyrene) on the Alpha
Demo Tool evaluation with conventional illumination.
We report the development and applications of ArF negative tone resist for ArF immersion lithography. New developed
topcoat-free ArF negative tone resists has sufficient water repellent capability that is applicable to over 700mm/s scan
speed water immersion exposure tool and suitable leaching suppression capability within reaching specification of
exposure tool. We demonstrated lithographic performance of topcoat-free negative tone resist utilizing 1.07NA
immersion tool and confirmed the lithographic window of 55nm 1L1S and 50nm 1L1S. And 27.4nm of isolated space
pattern at over dose condition of 55nm 1L1S patterning. This result shows the possibility of topcoat free negative tone
resist for dual trench based litho-etch-litho-etch double patterning. Additionally we have demonstrated contact hole
patterning utilizing double exposure and generated 65nm gridded contact hole patterns utilizing 0.92NA ArF scanner
with applicable pattern profiles.
The Extreme Ultra Violet lithography (EUVL) is expected to be the most promising semiconductor
fabrication technology for 22 nm node and beyond. Kozawa and his colleagues have documented that
non-constant acid diffusion coefficient have a significant impact on the latent image quality of 22 nm
We prepared a novel main chain decomposable star shaped polymer (STAR polymer) to examine the
concept. STAR polymer consists of a core unit and several arm units which connect to the core unit as
shown in Fig.1. The arm units are partially protected poly (<i>p</i>-hydroxystyrene) (PHS) base linear
polymer. The core unit that attached on the arm units employs easily acid cleavable group. The
adoption of living anion polymerization for the arm units of the STAR polymer makes the controlled
polymerization of one monomer unit possible.
Based on this material design concept, the protecting group on the arm unit is de-protected by the acid
generated during exposure and continues its reaction at the Post Exposure Bake (PEB) step and the acid
will also cleave the bonding of the core unit which would then result in a lower molecular weight
polymer of lower <i>T</i><i><sub>g</sub></i>.
The concept of the novel polymer, which is the decomposition of the core and protecting group of arm
units of the STAR polymer, was confirmed with a gel-permeation-chromatography (GPC) study.
The thermal property of the exposed and unexposed area was also investigated through a thermal flow
method. The <i>T</i><i><sub>g</sub></i> decrease of the exposed area was observed with the STAR polymer, regardless of increase
in <i>T</i><i><sub>g</sub></i> of the linear polymer.
General lithographic performance on EUV exposure for STAR polymer was also discussed.
Double patterning based on existing ArF immersion lithography is considered the most viable option for 32nm and below CMOS node. Most of double patterning approaches previously described require intermediate process steps like as hard mask etching, spacer material deposition, and resist freezing. These additional steps can significantly add to the cost of production applied the double patterning. In this paper, pattern freezing free litho-litho-etch double patterning process is investigated to achieve a narrow pitch imaging without the intermediate processing steps. Pattern freezing free litho-litho-etch double patterning utilizing positive-positive resist combination demonstrated composite pattern generation.