Photomask contamination inspections, whether performed at maskshops as an outgoing
inspection or at wafer fabs for incoming shipping and handling or progressive defect monitoring,
have been performed by KLA-Tencor STARlight systems for a number of design nodes.
STARlight has evolved since it first appeared on the 3xx generation of KLA-Tencor mask
inspection tools. It was improved with the TeraStar (also known as SLF) based tools with the
SL1 algorithm. SL2 first appeared on the TeraScan systems (also known as 5xx) and has been
widely adopted in both mask shops and wafer fabs.
Design rules continue to advance as do inspection challenges. Advances in computer processing
power have enabled more complex and powerful algorithms to be developed and applied to the
STARlight technology. The current generation of STARlight, which is known as SL2+,
implements improved modeling fidelity as well as a completely new paradigm to the existing
STARlight technology known as HiRes5, or simply "H5". H5 is integrated seamlessly within
SL2+ and provides die-to-die-like performance in both transmitted and reflected light, in addition
to the STARlight detection, in unit time. It achieves this by automatically identifying repeating
structures in both X and Y directions and applying image alignment and difference threshold.
A leading mask shop partnered with KLA-Tencor in order to evaluate SL2+ at its facility. SL2+
demonstrated a high level of sensitivity on all test reticles, with good inspectability on advanced
production reticles. High sensitivity settings were used for 45 nm HP and smaller design rule
masks and low false detections were achieved. H5 provided additional sensitivity on production
plates, demonstrating the ability to extend the use of SL2+ to cover 32 nm DR plate inspections.
This paper reports the findings and results of this evaluation.
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
lowering CoO.
Results from the recently available TeraScanHR reticle inspection system were published in early 2007. These
results showed excellent inspection capability for 45nm logic and 5xnm half-pitch memory advanced production
reticles, thus meeting the industry need for the mid-2007 start of production. The system has been in production use
since that time. In early 2007, some evidence was shown of capability to inspect reticles for 32nm logic and sub-50nm half-pitch memory, but the results were incomplete due to the limited availability of such reticles. However,
more of these advanced reticles have become available since that time. In this paper, inspection results of these
advanced reticles from various leading-edge reticle manufacturers using the TeraScanHR are shown. These results
indicate that the system has the capability to provide the needed inspection sensitivity for continued development
work to support the industry roadmap.
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.
Results from the recently available TeraScanHR reticle inspection system were published in early 2007. These
results showed excellent inspection capability for 45nm logic and 5xnm half-pitch memory advanced production
reticles, thus meeting the industry need for the mid-2007 start of production. The system has been in production use
since that time. In early 2007, some evidence was shown of capability to inspect reticles for the next nodes, 32nm
logic and sub-50nm half-pitch memory, but the results were incomplete due to the limited availability of such
reticles. However, more of these advanced reticles have become available since that time. Inspection results of
these advanced reticles from various leading edge reticle manufacturers using the TeraScanHR are shown. These
results indicate that the system has the capability to provide the needed inspection sensitivity for continued
development work to support the industry roadmap.
A new die-to-database high-resolution reticle defect inspection platform, TeraScanHR, has been developed for
advanced production use with the 45nm logic node, and extendable for development use with the 32nm node (also the
comparable memory nodes). These nodes will use predominantly ArF immersion lithography although EUV may also
be used. According to recent surveys, the predominant reticle types for the 45nm node are 6% simple tri-tone and COG.
Other advanced reticle types may also be used for these nodes including: dark field alternating, Mask Enhancer,
complex tri-tone, high transmission, CPL, etc. Finally, aggressive model based OPC will typically be used which will
include many small structures such as jogs, serifs, and SRAF (sub-resolution assist features) with accompanying very
small gaps between adjacent structures. The current generation of inspection systems is inadequate to meet these
requirements. The architecture and performance of the new TeraScanHR reticle inspection platform is described. This
new platform is designed to inspect the aforementioned reticle types in die-to-database and die-to-die modes using both
transmitted and reflected illumination. Recent results from field testing at two of the three beta sites are shown (Toppan
Printing in Japan and the Advanced Mask Technology Center in Germany). The results include applicable programmed
defect test reticles and advanced 45nm product reticles (also comparable memory reticles). The results show high
sensitivity and low false detections being achieved. The platform can also be configured for the current 65nm, 90nm,
and 130nm nodes.
Chrome-less Phase Lithography (CPL) was introduced as a potential strong Resolution Enhancement Technology (RET) for 90nm to 65nm node critical layers. One of the important issue with trench type chrome-less mask manufacturing for post structure is quartz defect detection capability. This study will focus on half pitch 80nm (1X) design node and apply different trench sizes and programmed defect sizes. All test patterns will be inspected on KLA-Tencor TeraScan576 inspection tool with both standard Die-to-Die (DD) and TeraPhase DD inspection modes to determine defect detection capability. All programmed defects will also be simulated on the Zeiss AIMS Fab-193 to determine wafer CD error. Finally, we will establish the relationship between trench size, defect detection capability and printability, and summarize the chrome-less mask quartz defect detection capability for 80nm post structure application.
The standard inspection flow typically consists of transmitted light pattern inspection (die-to-die or die-to-database) and STARlightTM (Simultaneous Transmitted And Reflective Light) contamination inspection. The initial introduction of TeraScan (DUV) inspection system was limited to transmitted pattern inspection modes. Hence, complete inspections of critical mask layers required utilizing TeraScan for maximized pattern defect sensitivity and the previous generation TeraStar (UV) for STARlightTM contamination inspection.
Recently, the reflective light die-to-database (dbR) inspection mode was introduced on the DUV tool to compliment transmitted light die-to-database (dbT) inspection. The dbR inspection mode provides not only pattern inspection but also contamination inspection capabilities.
The intent of this evaluation is to characterize the dbR inspection capability on pattern defects and contaminations. A series of standard programmed defect test plates will be used to evaluate pattern inspection capability and a PSL test plate will be used to determine the contamination performance. Inspection results will be compared to the current inspection process of record (dbT + STARlightTM).
Lastly, the learning will be used to develop and implement an optimal dbR inspection flow for selected critical layers of the 65-nm node to meet the inspection criteria and minimize the cycle time.
As the lithography design rule of IC manufacturing continues to migrate toward more advanced technology nodes, the mask error enhancement factor (MEEF) increases and necessitates the use of aggressive OPC features. These aggressive OPC features pose challenges to reticle inspection due to high false detection, which is time-consuming for defect classification and impacts the throughput of mask manufacturing. Moreover, higher MEEF leads to stricter mask defect capture criteria so that new generation reticle inspection tool is equipped with better detection capability. Hence, mask process induced defects, which were once undetectable, are now detected and results in the increase of total defect count. Therefore, how to review and characterize reticle defects efficiently is becoming more significant.
A new defect review system called ReviewSmart has been developed based on the concept of defect grouping disposition. The review system intelligently bins repeating or similar defects into defect groups and thus allows operators to review massive defects more efficiently. Compared to the conventional defect review method, ReviewSmart not only reduces defect classification time and human judgment error, but also eliminates desensitization that is formerly inevitable. In this study, we attempt to explore the most efficient use of ReviewSmart by evaluating various defect binning conditions. The optimal binning conditions are obtained and have been verified for fidelity qualification through inspection reports (IRs) of production masks. The experiment results help to achieve the best defect classification efficiency when using ReviewSmart in the mask manufacturing and development.
As design rule continues to shrink towards ITRS roadmap requirements, reticle defect capture criteria are becoming ever more challenging. Pattern fidelity and reticle defects that were once perceived as insignificant or nuisance are now becoming a significant considerable yield impacting factor. More defects are also detectable and presented with increase in implementation of new generation reticle inspection systems. Therefore, how to review and characterize defects accurately and efficiently is becoming more significant. In particular, defect classification time often corresponds directly to the cost and the cycle time of mask manufacturing or new technology development.
In this study we introduce a new mask defect review tool called ReviewSmart, which retrieves and processes defect images reported from KLA-Tencor's high sensitivity TeraScan inspection tool. Compared to the traditional defect review method, ReviewSmart provides a much better method to manage defects efficiently by utilizing the concept of defect grouping disposition.
Through the application and qualification results with respectable reticle production cases, the implementation of ReviewSmart has been proven to be effective for reducing defect classification loading and improving defect characterizing efficiency. Moreover, the new review tool is helpful to categorically identify tool or process variations thus allowing users to expedite the learning process for developing production worthy leading node processes.
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