EUV lithography has been delayed due to well-known issues such as source power, debris, pellicle, etc. for high volume
manufacturing. For this reason, conventional optical lithography has been developed to cover more generations with
various kinds of Resolution Enhancement Techniques (RETs) and new process technology like Multiple Patterning
Technology (MPT). Presently, industry lithographers have been adopting two similar techniques of the computational
OPC scheme such as Inverse Lithography Technology (ILT) and Source Mask Optimization (SMO) . Sub-20 nm node
masks including these technologies are very difficult to fabricate due to many small features which are near the limits of
mask patterning process. Therefore, these masks require the unseen level of difficulty for inspection. In other words,
from the viewpoint of mask inspection, it is very challenging to maintain maximum sensitivities on main features and
minimum detection rates on the Sub-Resolution Assist Features (SRAFs). This paper describes the proper technique as
the alternative solution to overcome these critical issues with Aerial Imaging (AI) inspection and High Resolution (HR)
Advanced 193nm DUV optical inspection tools that can cover 2Xnm HP node become more important and they are being tested to estimate their extendibility. We report DUV based inspection results evaluated and compared to wafer prints, as well as mask CD-SEM images in order to determine the size of printable defects that must be detected in each device node. Applied Materials® advanced Aera™ optical mask inspection tool that adapted a new optical technology enhancement was utilized to evaluate its inspection capability. The illumination conditions and pixel size were optimized to increase inspection sensitivity and reach detection requirements for not only critical defects that print on the wafer but also non-printing defects that indicate to a mask issue. Simulation was used to study suitable optical illumination conditions analyzing results to achieve the best performance for high-end EUV mask inspection toward next generation lithography.
Extreme Ultra Violet Lithography (EUVL) is one of the most advanced patterning technologies to overcome the critical
resolution limits of current ArF lithography for 30nm generation node and beyond. Since EUVL mask manufacturing
process has not been fully stabilized yet, it is still suffering from many defect issues such as blank defects, defects inside
multilayer causing phase defects, CD defects, LERs (Line Edge Roughness), and so on. One of the most important
roles in mask manufacturing process belongs to mask inspection tools, which monitor and visualize mask features,
defects and process quality for the EUVL process development. Moreover, as the portion of EUV mask production has
been increased due to the EUV Pre-Production Tool (PPT) development, mask inspection technologies for EUVL
become highly urgent and critical to guarantee mask quality. This paper presents a promising inspection technique for
increasing the contrast of pattern imaging and defects capture rate using configurable illumination conditions in 193nm
wavelength inspection tool.
Extreme Ultra Violet Lithography (EUVL) is a major patterning solution candidate being
considered for the ITRS (International Technology Roadmap for Semiconductors)
advanced technology nodes commencing with the 22nm Half Pitch (HP) nodes.
Achieving defect free EUVL masks is a critical issue in the wafer manufacturing process
and thus the importance for mask inspection technology to be ready to support pilot line
EUV mask inspection presents additional challenges with smaller line width, multilayer
defects and no pellicle to protect the mask. In addition, Line Edge Roughness on the
mask can limit the detection sensitivity. Configurable inspection illumination conditions
were considered to enhance the contrast of the mask image and improve the detection
Here we present experimental results of evaluating the defects detecting capability on
several EUVL masks of different technology nodes. EUVL mask inspections were done
using Material's Aera3TM DUV (193nm) reflected illumination optical inspection system
employing configurable inspection illumination conditions and magnifications.
OPC (Optical Proximity Correction) technique is inevitable and getting more complex to resolve finer features on
wafer with existing optical lithography technology. Some SRAFs generated with special model-based OPC engines
are so sophisticated that we can hardly imagine final patterns on wafer simply by seeing patterns on reticle. These
model-based OPCs consist of many kinds of assist features since they are designed differently according to various
target features on wafer and lithographic conditions. Not only small main features but also even smaller and
aggressive SRAFs (Sub Resolution Assist Features) may cause too many false counts and/or nuisance defects during the
reticle inspection, which makes inspection TAT (Turn Around Time) longer and inspection process more laborconsuming.
To improve the inspectability of this sort of complex OPC patterns, appropriate MRC (Mask Rule Check)
rules should be considered. As far as the inspection methods are concerned, several approaches have been
developed, such as TLD (Thin Line Desense), LPI (Lithographic Plane Inspection), and Aerial Image Based
Inspection to relax MRC rules. In this paper, we've compared and analyzed the functionalities of enhanced
inspection methods for complex OPC features of 4x nodes and beyond.
In the ever-changing semi-conductor industry, new innovations and technical advances constantly bring new
challenges to fabs, mask-shops and vendors. One of such advances is an aggressive optical proximity
correction (OPC) method, sub-resolution assist features (SRAF). On one hand, SRAFs bring a leap forward
in resolution improvement during wafer printing; on the other hand they bring new challenges to many
processes in mask making. KLA-Tencor Corp. working together with Samsung Electronics Co. developed an
additional function to the current HiRes 1 detector to increase inspectability and usable sensitivity during the
inspection step of the mask making process. SRAFs bring an unique challenge to the mask inspection process,
which mask shops had not experienced before. SRAF by nature do not resolve on wafer and thus have a
higher tolerance in the CD (critical dimension) uniformity, edge roughness and pattern defects.
This new function, Thin-Line De-sense (TLD), increase the inspectability and usable sensitivity by generating
different regions of sensitivity and thus will match the defect requirement on a particular photomask with
SRAFs better. The value of TLD was proven in a production setting with more than 30 masks inspected, and
resulted in higher sensitivity on main features and a sharp decrease in the amount of defects that needed to be
As design rules continue to shrink towards 4x nm, there are increase usage of aggressive Optical Proximity Correction
(OPC) in reticle manufacturing. One of the most challenging aggressive OPCs is Sub Resolution Assist Feature (SRAF)
such as scattering and anti-scattering bars typically used to overlap isolated and dense feature process windows. These
SRAF features are sub-resolution in that these features intentionally do not resolve on the printed wafer. Many reticle
manufacturers struggle to write these SRAFs with consistent edge quality even the most advanced E-Beam writers and
processes due to resolution limitations. Consequently, this inconsistent writing gives reticle inspection
challenges. Large numbers of such nuisance defects can dominate the inspection and impose an extraordinarily high
burden on the operator reviewing these defects. One method to work around inconsistent assist feature edge quality or
line-end shortening is to adjust the mask inspection system so that there is a substantial sensitivity decrease in order to
achieve good inspectability, which then compromises the sensitivity for the defects on main geometries.
Modern defect inspection tools offer multiple modes of operation that can be effectively applied to optimize defect
sensitivity in the presence of SRAF feature variability. This paper presents the results of an evaluation of advance
inspection methods and modes such as die to database selective thinline desense, transmitted & reflected light
inspections, review system and die to die selective desense to increase inspectability and usable sensitivity using
challenging production and R&D masks.
Key learnings are discussed.