EUV lithography (EUVL) is the most promising solution for 16nm HP node semiconductor device manufacturing and
beyond. The fabrication of defect free EUV mask is one of the most challenging roadblocks to insert EUVL into high
volume manufacturing (HVM). To fabricate and assure the defect free EUV masks, electron beam inspection (EBI) tool
will be likely the necessary tool since optical mask inspection systems using 193nm and 199nm light are reaching a
practical resolution limit around 16nm HP node EUV mask. For production use of EBI, several challenges and potential
issues are expected. Firstly, required defect detection sensitivity is quite high. According to ITRS roadmap updated in
2011, the smallest defect size needed to detect is about 18nm for 15nm NAND Flash HP node EUV mask. Secondly,
small pixel size is likely required to obtain the high sensitivity. Thus, it might damage Ru capped Mo/Si multilayer due
to accumulated high density electron beam bombardments. It also has potential of elevation of nuisance defects and
reduction of throughput. These challenges must be solved before inserting EBI system into EUV mask HVM line.
In this paper, we share our initial inspection results for 16nm HP node EUV mask (64nm HP absorber pattern on the
EUV mask) using an EBI system eXplore® 5400 developed by Hermes Microvision, Inc. (HMI). In particularly, defect
detection sensitivity, inspectability and damage to EUV mask were assessed. As conclusions, we found that the EBI
system has capability to capture 16nm defects on 64nm absorber pattern EUV mask, satisfying the sensitivity
requirement of 15nm NAND Flash HP node EUV mask. Furthermore, we confirmed there is no significant damage to
susceptible Ru capped Mo/Si multilayer. We also identified that low throughput and high nuisance defect rate are critical
challenges needed to address for the 16nm HP node EUV mask inspection. The high nuisance defect rate could be
generated by poor LWR and stitching errors during EB writing of 64nm HP resist pattern. This result suggests we need
further improvements not only in the EBI inspection system but also the patterning processes for 16nm HP node EUV
EUV lithography is considered the most promising lithography solution for the 16 nm node and beyond. As EUV
light is strongly absorbed by all known materials, reflective optics are used instead of conventional transmittance optics
applied to ArF and KrF lithography. The EUV mask must also need be reflective. It typically consists of a Ta-based
absorber layer, Ru capping layer, Si/Mo multilayer on a low thermal expansion material (LTEM) substrate with a
backside Cr-based metal coating. Because of the strong absorbance of the EUV light, a pellicle is not practical. Therefore,
EUV masks must be cleaned more frequently to maintain the necessary cleanliness. This poses numerous unique
challenges in cleaning processes. For example, the EUV mask integrity, including critical dimension (CD), EUV
reflectivity, and absorber thickness must be kept intact during multiple cleanings throughout the mask's lifetime.
Requirements of defect size for the cleaning, furthermore, are becoming tighter as semiconductor circuit design rules get
smaller. According to the International Technology Roadmap For Semiconductors (ITRS), the smallest defect size that
must be removed is 23 nm for the 18 nm NAND Flash node in 2013. In addition to defects on the frontside, defects
on a backside also need to be minimized since they might lead overlay error due to local distortions of EUV masks on an
This paper focuses on evaluations of cleaning performances using the Lasertec M1350 and M7360 blank
inspection system, which has a 71 nm and 43 nm sensitivity. The 43nm is the current best sensitivity while keeping a
>90% defect capture rate. First, the cleaning performance using the standard process has been investigated. We found a
mitigation of adders was a key challenge for the EUV mask cleaning. The primary source of the adders was also
identified as pits. Secondly, the megasonic cleaning process has been optimized to mitigate the adders. We could
successfully reduce the adders by 30%. Thirdly, to confirm the entire cleaning process, a backside cleaning process
combined with frontside cleaning was investigated, demonstrating that the backsides of the EUV mask blanks could be
cleaned without additional impact on frontside defectivity.
EUV masks include many different layers of various materials rarely used in optical masks, and each layer of material has a
particular role in enhancing the performance of EUV lithography. Therefore, it is crucial to understand how the mask quality and
patterning performance can change during mask fabrication, EUV exposure, maintenance cleaning, shipping, or storage. The fact that
a pellicle is not used to protect the mask surface in EUV lithography suggests that EUV masks may have to undergo more cleaning
cycles during their lifetime. More frequent cleaning, combined with the adoption of new materials for EUV masks, necessitates that
mask manufacturers closely examine the performance change of EUV masks during cleaning process. We have investigated EUV
mask quality and patterning performance during 30 cycles of Samsung's EUV mask SPM-based cleaning and 20 cycles of
SEMATECH ADT exposure. We have observed that the quality and patterning performance of EUV masks does not significantly
change during these processes except mask pattern CD change. To resolve this issue, we have developed an acid-free cleaning POR
and substantially improved EUV mask film loss compared to the SPM-based cleaning POR.
EUV lithography (EUVL) is considered the most attractive solution for semiconductor device manufacturing
beyond the 22nm half-pitch node. In EUVL, one of the greatest challenges is the lack of a pellicle, which makes EUV
masks prone to particle contamination. Therefore, mask cleaning plays an important role in keeping masks clean during
both fabrication in the mask shop and usage in the wafer fab. According to the International Technology Roadmap for
Semiconductors (ITRS), in 2013 mask cleaning processes should remove all defects larger than 25nm without damaging
78nm and smaller patterns for the 23nm Flash half-pitch node . In addition to contamination concerns, EUV masks
introduce new materials and a multilayer structure that is different from the Cr on glass used in traditional optical masks.
Physical forces applied by megasonic cleaning to remove particles on an optical mask could damage EUV mask patterns.
Thus, it is important to determine the magnitude of the physical forces that can break absorber patterns (TaN or TaBN)
from the surface of a Ru-capped MoSi multilayer film. The adhesion of particles of interest to the Ru-capped multilayer
should also be measured. In the complex structure of an EUV mask, adhesion forces of particles on the top surface are
modified by the different layers beneath the Ru. Hence, it is crucial to directly measure the force required to remove
particles and break absorber patterns on EUV mask surfaces to determine the process window for applicable cleaning
We used scanning probe microscopy (SPM) to quantify these forces. The SPM probe was precisely controlled to
remove particles and break patterns on Ru-capped EUV mask blanks. While being manipulated, the deflection signals of
the probe were monitored and then converted to forces using a simple beam model.
In this paper, we present the measured breakage forces for absorber patterns as a function of their size and
compare them with removal forces for 50nm and 100nm SiO2 and polystyrenelatex (PSL) particles. Based on these data
and our analysis, we will demonstrate a process window for physical force that can successfully clean EUV masks
beyond the 16nm half-pitch node.
Fabrication of defect free EUV masks including their inspection is the most critical challenge for implementing EUV
lithography into semiconductor high volume manufacturing (HVM) beyond 22nm half-pitch (HP) node. The contact to
bit-line (CB) layers of NAND flash devices are the most likely the first lithography layers that EUV will be employed for
manufacturing due to the aggressive scaling and the difficulty for making the pattern with the current ArF lithography.
To assure the defect free EUV mask, we have evaluated electron beam inspection (EBI) system eXplore™ 5200
developed by Hermes Microvision, Inc. (HMI) . As one knows, the main issue of EBI system is the low throughput.
To solve this challenge, a function called Lightning Scan™ mode has been recently developed and installed in the system,
which allows the system to only inspect the pattern areas while ignoring blanket areas, thus dramatically reduced the
overhead time and enable us to inspect CB layers of NAND Flash device with much higher throughput.
In this present work, we compared the Lightning scan mode with Normal scan mode on sensitivity and throughput. We
found out the Lightning scan mode can improve throughput by a factor of 10 without any sacrifices of sensitivity.
Furthermore, using the Lightning scan mode, we demonstrated the possibility to fabricate the defect free EUV masks
with moderate inspection time.
Semiconductor lithography candidates toward 2xnm node and beyond include wide variety of options, such as
extension of 193i, EUVL, NIL, and ML2. Most of those candidates, except ML2, need critical mask feature to realize
effective high volume manufacturing. In this presentation, EUVL mask technology update and future issues will be
Fabrication of defect free EUV mask is one of the most critical roadblocks for implementing EUV lithography into
semiconductor high volume manufacturing for 22nm half-pitch (HP) node and beyond. At the same time, development
of quality assurance process for the defect free EUV mask is also another critical challenge we need to address before the
mass production. Inspection tools act important role in quality assurance process to ensure the defect free EUV mask. We
are currently evaluating two types of inspection system: optical inspection (OPI) system and electron beam inspection
(EBI) system [1, 2]. While OPI system is sophisticated technology and has an advantage in throughput, EBI system is
superior in sensitivity and extendability to even small pattern.
We evaluated sensitivity of EBI system and found it could detect 25 nm defects on 88nm L/S pattern which is as small
as target defect size for 23 nm Flash HP pattern in 2013 in 2009 ITRS lithography roadmap [2, 3]. EBI system is
effective inspection tool even at this moment to detect such small defects on 88nm HP pattern, though there are still
some challenges such as the slow throughput and the reliability. Therefore, EBI system can be used as bridge tool to
compensate insufficient sensitivity of current inspection tools and improve EUV mask fabrication process to achieve the
defect free EUV mask. In this paper, we will present the results of native pattern defects founded on large field 88nm HP
pattern using advance EBI system. We will also classify those defects and propose some ideas to mitigate them and
realize the defect free EUV mask, demonstrating the capability of EBI as bridge tool.
Achieving the specifications of resolution, sensitivity and line width roughness (LWR) of wafer resist is one of the top
challenges of bringing extreme ultraviolet lithography (EUVL) into high volume manufacturing. Contributions to the
resist LWR on wafer can be divided into two categories; chemical properties of the resist and aerial image. Chemical
properties of the resist are complicated and many factors contribute to LWR, such as polymer size, sensitivity, surface
reaction etc. Aerial image LWR is much simply determined by the optical properties of a mask and a scanner. Since
very small LWR value of the resist is needed, EUV mask LWR is also set very severely from ITRS <sup></sup>.
In our previous work <sup></sup>, we demonstrated current mask LWR as comparing them with mask resist LWR and absorber
LWR. As a result, we found that the absorber's LWR almost depends on resist patterning.
In this paper, we will present the influence of resist patterning on absorber LWR comparing resist materials and EB
tools. From the results, LWR has been reduced by 10-20% by improving EB tool. However, the LWR value at line and
space pattern for 22nm-hp case have not met target of ITRS' roadmap while, by using Non-CAR, the LWR value has
met the target. In particularly, the value at isolated line is dramatically improved using Non-CAR.
Readiness of defect-free mask is one of the biggest challenges to insert extreme ultraviolet (EUV) lithography into
semiconductor high volume manufacturing for 22nm half pitch (HP) node and beyond. According to ITRS roadmap
updated in 2008, minimum size of defect needed to be removed is 25nm for 22nm HP node in 2013 . It is necessary,
therefore, to develop EUV mask pattern inspection tool being capable of detecting 25nm defect. Electron beam
inspection (EBI) is one of promising tools which will be able to meet such a tight defect requirement.
In this paper, we evaluated defect detection sensitivity of electron beam inspection (EBI) system developed by
Hermes Microvision, Inc. (HMI) using 88nm half-pitch (HP) line-and-space (L/S) pattern and 128nm HP contact-hole
(C/H) pattern EUV mask. We found the EBI system can detect 25nm defects. We, furthermore, fabricated 4 types of
EUV mask structures: 1) w/ anti-reflective (AR) layer and w/ buffer layer, 2) w/ AR layer and w/o buffer layer, 3) w/o
AR layer and w/ buffer layer, 4) w/o AR layer and w/o buffer layer. And the sensitivity and inspectability for the EBI
were compared. It was observed that w/o AR layer structure introduce higher image contrast and lead to better
inspectability, although there is no significant different in sensitivity.
Readiness of defect free mask supply is one of the critical challenges for the insertion of extreme ultra violet
lithography (EUVL) into high volume semiconductor manufacturing for 32 nm half pitch (HP) and beyond. According to
ITRS updated in 2008, the defect size which is needed to remove is 25 nm for 32 nm HP . On the other hand, in the
presentation published in 2008, critical defect size for absorber defect on EUV mask was described around 24 nm for 32
nm HP line and space patterns, meaning that the particles having the equivalent size are necessary to be removed . In
such a stringent defect requirement, cleaning process must play critical role to remove such tiny particulate defects.
However, EUV mask cleaning faces unique challenges related to the reflective mask structure, new material such as
ruthenium (Ru) capping layer and more frequent cleaning due to the lack of pellicle protection. Consequently, it must be
gentle enough not to damage fragile patterns and surfaces on EUV mask, particularly the very thin Ru capping layer. The
competing demand makes the EUV mask cleaning more challenging.
We have reported comprehensive evaluation of cleaning related issues using the blank inspection tool M1350 with
80 nm sensitivity [3, 4]. In this paper we extend our effort to much smaller defects using the new blank inspection tool
M7360 with 50 nm sensitivity.
Surface cleaning has become one of the most critical processes in photomask manufacturing in the last few years
because of the demands for high cleaning efficiency with no film loss and no damage to fragile patterns. The requirement
is getting tighter as the feature-size shrinks. In addition, EUV masks pose further unique challenges in the cleaning
process, because of the reflective multilayer (ML) mask structure, which is sensitive to surface damage, and a more
frequent cleaning requirement due to the lack of pellicle protection during handing and usage. To address the challenge
of ML surface damage from EUV mask cleaning processes, this paper presents the chemical durability of Ru-capped ML
blanks against two types of chemistries: a mixture of sulfuric acid and hydrogen peroxide (SPM) and ozonated water
(DIO3). The authors found that SPM slightly oxidized the Ru capping layer, but with minimal effect to EUV reflectivity.
It was observed that DIO3 damaged the Ru capping layer and resulted in a significant EUV reflectivity drop. An alloyed
Ru-capping layer showed improved durability against DIO3 damage. The changes to the Ru-surface were characterized
with atomic force microscopy (AFM) and X-ray photo electron spectroscopy (XPS).
A scanning probe microscopy is applied to measure high adhesive energy between Cr or MoSi patterns and quartz
substrates by using probes with high stiffness cantilevers. Line patterns with the widths of ~100 nm are peeled from the
interface by strain energy stored in the probe, and no residue was observed after peeling. The strain amount has good
linear relationship with sensor outputs, and is quantified as a displacement of cantilevers. As a measurement result,
adhesive energy of MoSi patterns on the substrate is larger than that of Cr patterns. In addition, adhesive energy of line
patterns is sensitive to the pattern width which is parallel side to scan direction, and decreases with pattern width
reduction. The method is effective to measure strong adhesion, like chemical bonds, of micro patterns, and will
contribute process development for micro fabrication in photomask and wafer fields.
Currently a few hundreds nm dimension is employed to achieve visible and infrared light optical elements for optics field as nano-optics. On the other hand there are a lot of reports of nano-imprint experiment including under 50 nm for storage, bio-technology or semiconductor application. And one of the biggest advantages of nano-imprint is three dimensional fabrications at one imprint procedure. However already introduced two or three dimensional imprinted optical elements are either just confirming replication of conventional Fresnel optics or defect negligible lattice structure.
Three dimensional nano-imprint mold (3D-mold) must have great potential for optics fabrication. The combination of 3D-mold and three dimensional nano-imprint method can create flexible optical behavior. Here practical fabrication trials for three dimensional photonic crystal waveguide with 3D-mold and nano-imprint technology are discussed. Particularly fabrication 3D-mold with quarts, nano-imprint methodology and waveguide structure with evaluation and simulation are focused.