We demonstrated an enhancement of light-extraction efficiency (LEE) in an AlGaN UVC light-emitting diode (LED) using photonic-crystal (PhC)-reflector fabricated on a p-GaN contact layer, which was introduced to realize both of low resistivity and high-reflectivity in p-contact layer. We fabricated an AlGaN UVC-LED with PhC-reflector on p-GaN contact layer, and confirmed that the external quantum efficiency (EQE) was increased by 1.7 times by introducing PhC-reflector. We also fabricated flip-chip UVC LED with PhC-reflector on p-contact layer and obtained more than 50 mW output power.
AlGaN UV-C light-emitting diodes (LEDs) are attracting a great deal of attentions for applications of sterilization, water purification, in the medical fields, and so on. The increase in wall-plug efficiency (WPE) is a recent main subject for an AlGaN UVC-LED. The main cause for reducing WPE is a significant reduction in light-extraction efficiency (LEE) owing to a heavy light absorption by p-GaN contact layer. If we introduce transparent p-AlGaN contact layer for increasing LEE, the contact resistance is increased, resulting in the significant increase of operating voltage. In order to achieve both of low contact resistance and high-reflectivity in a p-contact layer, we introduced a photonic crystal (PhC) reflector on a p-contact layer. We predicted by a simulation analysis that an LEE of UVC-LED can be increased by 2.8 times by introducing a PhC reflector on p-GaN contact layer.
Previously, we fabricated a 283nm AlGaN DUV-LED with PhC reflector on a p-AlGaN transparent contact layer, and obtained an increase of external quantum efficiency (EQE) from 8 to 10 % by introducing PhC reflector. However, the contact resistance was increased. In this work, we fabricated a 273nm AlGaN UVC-LED with PhC reflector on p-GaN contact layer. The EQE was increased by about 1.7 times by introducing PhC reflector. The operating voltage was not changed even when introducing PhC and remained low value. We confirmed that it is possible to realize high WPE by introducing PhC reflector on the p-GaN contact layer of UVC-LED.
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
decomposed.
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 4.6x10-8 mJ•nm3 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.
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
patterns.
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 (p-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 Tg.
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 Tg decrease of the exposed area was observed with the STAR polymer, regardless of increase
in Tg of the linear polymer.
General lithographic performance on EUV exposure for STAR polymer was also discussed.
Polymer structure effects on the dissolution kinetics and deprotection reaction were investigated to understand inherent
extreme ultraviolet (EUV) resist characteristics because it is important for EUV lithography to select appropriate
protecting group and protecting ratio. The difference of activation energy caused by protecting groups and protecting
ratio was observed. For small protecting group such as tert-butoxy carbonyl group and ethoxy ethyl group, dependence
of activation energy on protecting ratio was small. On the other hands, for bulky protecting group such as naphtoxy
group protecting ratio significantly affect the activation energy probably due to the effect of steric hindrance. Also, the
deterioration of resist sensitivity was observed with increase of protecting ratio while the dissolution slope increase with
increase of protecting ratio. A slight difference in Rmax was observed due to the difference of resulting products because
it is not chemically identical to polyhydroxystyrene (PHS) because of side reaction occurred during post exposure bake
(PEB). Also, Rmin decreased with increase of protecting ratio. Thus, the dissolution rates and sensitivity were more
affected by changing the protection ratio of polymer than the type of protecting group.
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.
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.
This report will introduce novel resist materials including specific photo acid generator (PAG) to improve flare
issue from the resist standpoint. We have developed a method to control the acid diffusion length from the PAG. It
previously reported that acid diffusion length can be altered by the PAG anion size. In this report, we focused on the
effect of the Tg of a resist film. The thermal flow rate of a resist film can suggest the approximate resist Tg.
Therefore, we measured the thermal flow rate of the resist. And we found out passivity of acid diffusion control by
changing PAG species and volume.
Moreover, newly designed PAG tested was confirmed to have uniform distribution in the resist film with no PAG
clustering at the resist surface at compared to our conventional PAG. This new positive tone resist formulation
shows good performance under flare condition.
In addition, we focused on the pattern density variation as one of the key parameters for flare value. Low
pattern density indicated less flare value. It is considered that negative tone resist to have advantage for isolated line
type features. Novel positive and negative tone type resists were compared side-by-side and discussed for its
advantages at varying pattern densities.
193nm immersion lithography is the most promising lithography candidate for 45nm node technology and beyond. However, immersion specific issue, such as the immersion specific defect and the leaching of resists compound into immersion fluid, still exists without any effective countermeasure. To realize a productive 193nm immersion lithography process, we have to develop a cost effective material that might be immersion dedicated resist. In this paper, we investigated the leaching with different polymer protective agents and hydrophobicity. It was found that the leaching amount was strongly related to the activation energy of the protective agent and hydrophobicity of the polymer. Higher activation energy of protective agents and higher hydrophobicity of polymer showed less amount of leaching. In this paper, newly developed developable type topcoat TILCTM-031 demonstrated the excellent ability of immersion defect prevention.
Changes in chemical nature of an ArF photoresist caused by various plasmas were analyzed, and it was found that the HBr plasma treatment induces a selective detachment of a heterocyclic unit of the photoresist, and the detached unit remains in the photoresist film. Thermomechanical analyses were performed, which showed that the softening temperature of the photoresist decreases by the HBr treatment, indicating that the detached heterocyclic unit acts as a plasticizer in the photoresist film. These results showed that the HBr treatment can be regarded as a softening process of the photoresist. This HBr treatment was applied to the fabrication of line patterns and it was shown that the treatment remarkably improves LWR (line width roughness) after etching. This improvement was more pronounced for the case of an isolated pattern than the case of a dense pattern. Further investigations on the HBr treatment were performed by changing the copolymerization ratio of a monomer containing the heterocyclic unit. It was shown that the reduction of LWR by the HBr treatment becomes more enhanced when the copolymerization ratio increases. However, an intensive HBr treatment was found to deteriorate LWR, showing that there is an optimum condition of the HBr treatment in terms of improving LWR.
Various resists, which consisted of polymer systems, such as methacrylate, acrylate and cycloolefin/maleic anhydride (COMA), were investigated in the viewpoint of etching resistance, lithographic performance and shelf life. The oxide etching rate was in order of acrylate < methacrylate << COMA. The surface roughness of the acrylate type resist after oxide etching was the smallest among all samples. The methacrylate type resist showed high resolution capability as a line and space resist. On the other hand, pattern collapse was observed in the acrylate type resist, and low resolution was shown in the COMA type resist because of the large resist thickness loss. In the case of contacts, the acrylate type resist showed better linearity. The sensitivity of the acrylate and methacrylate type resists kept at room temperature did not changed in 20 days, while the sensitivity of the COMA type resist changed. It was found that the methacrylate type resist was the most suitable as a line and space resist and the acrylate type resist was the most promising as a contact hole resist.
We report the development of a novel acryl polymer with an (alpha) -hydroxymethyl acrylate in the application to 193nm chemically amplified negative-tone resist. This new polymer structure consists of ((alpha) -hydroxymethyl)acrylate and MAA. The ester and alcohol group in the polymer contribute to an intramolecule and/or intermolecular hybrid crosslinking reactions without crosslinker and in the presence of a photo generated acid as a catalysis. In an intramolecular crosslink reaction, the ester group reacts to a neighboring hydroxymethyl group within the polymer chain. As a result, a lactone group is made in the main polymer chain. On the other hand, in an intermolecular crosslink reaction, the ester group reacts to a hydroxymethyl group of another polymer chain to make an ester chain. In this reaction, the new polymer is densely crosslinked and fine resist pattern is obtained without having any swelling problem. Consequently, the resist is optimized and contains the new polymer, photoacid generator and a small amount of crosslinker. Under conventional illumination condition, 180nm line and space pattern are achieved without any kind of swelling problem. The sensitivity is 40 mJ/cm2 with the standard developer, NMD-3 2.38 percent.
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