As optical lithography progresses towards 32nm node and beyond, shrinking feature size on photomasks and growing
database size provides new challenges for reticle manufacture and inspection. The new TeraScanXR extends the
inspection capability and sensitivity of the TeraScanHR to meet these challenges. TeraScanXR launches a new function
that can dynamically adjust defect sensitivities based on the image contrast (MEEF) -- applying higher sensitivity to
dense pattern regions, and lower sensitivity to sparse regions which are lithographically less significant. The defect
sensitivity of TeraScanXR for Die-to-Die (DD) and Die-to-Database (DDB) inspection mode is improved by 20-30%,
compared with TeraScanHR. In addition, a new capability is introduced to increase sensitivity specifically to long CD
defects. Without sacrificing the inspection performance, the new TeraScanXR boosts the inspection throughput by 35%-
75% (depending upon the inspection mode) and the dataprep speed by 6X, as well as the capability to process 0.5-1
Terabyte preps for DDB inspection.
Non-uniformity in reticle CDs can cause yield loss and/or performance degradation during chip manufacturing. As a
result, CD Uniformity (CDU) across a reticle is a very important specification for photomask manufacturing. In addition
the photomask CDU data can be used in a feedback loop to improve and optimize the mask manufacturing process. A
typical application is utilizing CDU data to adjust the mask writer dose and compensate for non-uniformity in the CDs,
resulting in improved quality of subsequent masks.
Mask makers are currently using the CD-SEM for data collection. While the resolution of SEM data ensures its position
as the industry standard, an output map of CDU using the reticle inspection tool has the advantage of denser sampling
over larger areas on the mask. High NA reticle inspection systems scan the entire reticle at high throughput, and are
ideally suited for collecting CDU data on a dense grid.
In this paper, we describe the basic theory of a prototype reticle inspection-based CDU tool, and results on advanced
memory masks. We discuss possible applications of CDU maps for optimizing the mask manufacturing process or in
adjusting scanner dose to improve wafer CD uniformity.
A prototype die-to-database high-resolution reticle defect inspection system has been developed for 32nm and below
logic reticles, and 4X Half Pitch (HP) production and 3X HP development memory reticles. These nodes will use
predominantly 193nm immersion lithography (with some layers double patterned), although EUV may also be used.
Many different reticle types may be used for these generations including: binary (COG, EAPSM), simple tritone,
complex tritone, high transmission, dark field alternating (APSM), mask enhancer, CPL, and EUV. Finally, aggressive
model based OPC is typically used, which includes many small structures such as jogs, serifs, and SRAF (sub-resolution
assist features), accompanied by very small gaps between adjacent structures. The architecture and performance of the
prototype inspection system is described. This system is designed to inspect the aforementioned reticle types in die-todatabase
mode. Die-to-database inspection results are shown on standard programmed defect test reticles, as well as
advanced 32nm logic, and 4X HP and 3X HP memory reticles from industry sources. Direct comparisons with currentgeneration
inspection systems show measurable sensitivity improvement and a reduction in false detections.
In the ever-changing semiconductor industry, wafer fabs and mask shops alike are adding low
cost of ownership (CoO) to the list of requirements for inspections tools. KLA-Tencor has
developed and introduced STARlight2+ (SL2+) to satisfy this need. This new software
algorithm is available on all TeraScanHR and TeraFab models. KLA-Tencor has cooperated
with United Microelectronics Corporation (UMC) to demonstrate and improve SL2+, including
its ability to lower CoO, on 65nm and below photomasks.
These improvements are built on the rich history of STARlight. Over the years, STARlight has
become one of the industry standards for reticle inspection. Like its predecessors, SL2+ uses
only transmitted and reflected light images from a reticle to identify defects on the reticle. These
images along with plate-specific information are then processed by SL2+ to generate reference
images of how the patterns on the reticle should appear. These reference images are then
compared with the initial optical images to identify the defects.
The new and improved SL2+ generates more accurate reference images. These images reduce
background noise and increase the usable sensitivity. With the results from controlled
engineering tests, a fab or mask shop can then decide to inspect reticles at a given technology
node with a large pixel; this is sometimes referred to as pixel migration. The larger pixel with
SL2+ can then perform the inspections at similar sensitivity settings and higher throughput, thus
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 the design rule continues to shrink towards 3x nm and below, lithographers are searching for new and
advanced methods of mask lithography such as immersion, double patterning and extreme ultraviolet
lithography (EUVL). EUV lithography is one of the leading candidates for the next generation lithography
technologies after 193 nm immersion and many mask makers and equipment makers have focused on
stabilizing the process. With EUV lithography just around the corner, it is crucial for advanced mask makers
to develop and stabilize EUV mask processes. As a result, an inspection tool is required to monitor and
provide quick feedback to each process step.
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.
As the photomask design rules continue to shrink towards 45nm and below, the defect classification criteria is
becoming more challenging to be set accurately. Pattern fidelity issues and masks defects that were once considered
insignificant or merely nuisances are now yield-limiting. On the other hand, there are still cases of small defects
captured during reticle inspection but will not print on the wafer. In addition, in a production setting environment it is
critical to ascertain quickly and efficiently the true lithographic effect of reticle defects in order to avoid yield and cycle
As a starting point, it is best to inspect the reticle at the highest sensitivity to find all defects and anomalies. From there,
fast and efficient means to sort and prioritize defects are necessary for inspection operators' and engineers' convenience.
Then, it is critical to model all the defects accurately for their lithographic impact. Finally, an accurate lithography-based
set of reticle defect disposition criteria can be developed for the manufacturing process flow.
The focus of this study is on contact or hole patterns since the issues regarding capture of defects on such patterns are
typically more complex than the ones on line and space patterns. The intent is to assess and devise defect disposition
criteria for contact hole layers utilizing KLA-Tencor's 5X6 DUV inspection system with both standard die-to-die and
Litho2 algorithms and the Automated Mask Defect Disposition (AMDD) system. AMDD lithographic printability
results will be compared to AIMS results and printed results on wafer.