Microelectronics industry leaders routinely name the cost and cycle time of mask technology and mask supply as top
critical issues. A survey was created with support from SEMATECH and administered by SEMI North America to
gather information about the mask industry as an objective assessment of its overall condition. This year's survey
data were presented in detail at BACUS and the detailed trend analysis presented at EMLC. The survey is designed
with the input of semiconductor company mask technologists, merchant mask suppliers, and industry equipment
makers. This year's assessment is the sixth in the current series of annual reports. With continued industry support,
the report can be used as a baseline to gain perspective on the technical and business status of the mask and
microelectronics industries. The report will continue to serve as a valuable reference to identify the strengths and
opportunities of the mask industry. The results will be used to guide future investments on critical path issues. This
year's survey is basically the same as the 2005 and 2006 surveys. Questions are grouped into eight categories:
General Business Profile Information, Data Processing, Yields and Yield Loss, Mechanisms, Delivery Times,
Returns and Services, Operating Cost Factors, and Equipment Utilization. Within each category is a multitude of
questions that creates a detailed profile of both the business and technical status of the critical mask industry. Note:
the questions covering operating cost factors and equipment utilization were added to the survey only in 2005;
therefore, meaningful trend analysis is not available.
Defects are still one of the main challenges of extreme ultraviolet (EUV) mask blanks. In particular, a majority(~75%) of
substrate defects are nanometer size pits. These pits are usually created during final surface polishing of the synthetic,
quartz glass substrates. This study presents data that indicates cleaning may also induce pits in the substrate surface.
These pits are typically 20 nm and larger, and are contained in a circular area on the surface, which is scanned by a
megasonic nozzle during cleaning. Concentrated collapse of cavitation bubbles in the areas scanned by megasonic is
expected to be one of the main mechanisms of pit creation. The data indicates the existence of a hard surface layer with
an estimated thickness of approximately 30 to 60 nm, which is resistive to pit creation. After this layer is removed, the
number of pit defects present on the substrate increases dramatically with megasonic cleaning. It is also demonstrated
that, within the detection limits of the atomic force microscope (AFM), the size of a pit does not change due to cleaning.
Extreme ultraviolet lithography (EUVL) is a strong contender for the 32 nm generation and beyond. A defect-free mask
substrate is an absolute necessity for manufacturing EUV mask blanks. The mask blank substrates are, therefore,
cleaned with different cleaning processes to remove all defects down to 30 nm. However, cleaning suffers from the
defects added by various sources such as the fab environment, chemicals, ultra pure water, and the cleaning process
itself. The charge state of the substrate during and after cleaning also contributes to the number of adder defects on the
substrate. The zeta potentials on the substrate surface and the defect particles generated during the cleaning process
determine whether the particles get deposited on the surface. The zeta potential of particle or substrate surfaces depends
on the pH of the cleaning fluids. Therefore, in this work, pH-zeta potential maps are generated for quartz substrates
during the various steps of mask cleaning processes. The pH-zeta potential maps for defect particles commonly seen on
mask substrates are measured separately. The zeta potential maps of substrate and contaminant particle surfaces are
used to determine whether particles are attracted to or repulsed from the substrate. In practice, this technique is
especially powerful for deriving information about the origin of particles added during a cleaning process. For example,
for a known adder with a negative zeta potential, all cleaning steps with a positive zeta potential substrate could be the
source of added particles.
Microelectronics industry leaders routinely name the cost and cycle time of mask technology and mask supply as top
critical issues. A survey was created with support from SEMATECH and administered by SEMI North America to
gather information about the mask industry as an objective assessment of its overall condition. The survey is
designed with the input of semiconductor company mask technologists, merchant mask suppliers, and industry
equipment makers. This year's assessment is the sixth in the current series of annual reports. With ongoing industry
support, the report can be used as a baseline to gain perspective on the technical and business status of the mask and
microelectronics industries. The report will continue to serve as a valuable reference to identify the strengths and
opportunities of the mask industry. The results will be used to guide future investments pertaining to critical path
issues. This year's survey is basically the same as the 2005 and 2006 surveys. Questions are grouped into categories:
General Business Profile Information, Data Processing, Yields and Yield Loss Mechanisms, Delivery Times,
Returns and Services, Operating Cost Factors, and Equipment Utilization. Within each category is a multitude of
questions that create a detailed profile of both the business and technical status of the critical mask industry.
Microelectronics industry leaders routinely name the cost and cycle time of mask technology and mask supply as top
critical issues. A survey was created with support from SEMATECH and administered by SEMI North America to
gather information about the mask industry as an objective assessment of its overall condition. This year's survey
data was presented at BACUS and a detailed trend analysis is presented here. The annual survey is designed with the
input of semiconductor company mask technologists, merchant mask suppliers and industry equipment makers. This
year's assessment is the fifth in the current series of annual reports. With continued industry support the report can
be used as a baseline to gain perspective on the technical and business status of the mask and microelectronics
industries. The report will continue to serve as a valuable reference to identify trends in the mask industry. The
results will be used to guide future investments on critical path issues. This year's survey is basically the same as the
2005 survey. Questions are grouped into categories: General Business Profile Information, Data Processing, Yields
and Yield Loss, Mechanisms, Delivery Times, Returns and Services, Operating Cost Factors, and Equipment
Utilization. Within each category is a multitude of questions that create a detailed profile of both the business and
technical status of the critical mask industry. Note: the questions covering operating cost factors and equipment
utilization were only added to the survey in 2005; therefore meaningful trend analysis is not yet available.
The capability of hydrogenated water to clean EUV blank substrates was examined. The hydrogenated water cleaning
process was compared with an H2O2/NH4OH/H2O mixture (SC1) and ozonated water cleaning processes. A small
amount ammonia added to the hydrogenated water improved the particle removal efficiency. The concentration of
hydrogen and the method used to dispense the water had little effect. The use of ozonated and hydrogenated water
together gave high particle removal efficiencies, which were similar to those obtained using SC1. Additionally, the use
of ozonated water with hydrogenated water further reduced the amount ammonia required to achieve high particle
removal efficiencies. With further process optimization hydrogenated and ozonated water has the potential to replace
SC1 in cleaning EUV substrates.
Extreme ultraviolet (EUV) substrates have stringent defect requirements. For the 32 nm node, all particles larger than 26
nm must be removed from the substrate. However, real defects are irregularly shaped and there is no clear dimension for
an irregular particle corresponding to 26 nm. Therefore, the sphere equivalent volume diameter (SEVD) for a native
defect is used. Using this definition and defect detection measurements, all particles larger than 20 nm must be removed
from the substrate. Atomic force microscopy (AFM) imaging and multiple cleaning cycles were used to examine the
removal of particles smaller than 50 nm SEVD. Removal of all particles larger than 30 nm was demonstrated. Particles
that required multiple cleaning processes for removal were found to be partially embedded. The best cleaning yield can
be obtained if the cleaning history of the substrate is known and one can choose the proper cleaning processes that will
remove the remaining particles without adding particles. Ag, Au, Al2O3, Fe2O3, and CuO particles from 30 nm to 200 nm
were deposited on quartz surface. It was shown that these deposited defects are much easier to remove than native
defects.
Extreme ultraviolet lithography (EUVL) is being considered as the enabler technology for the manufacturing of future
technology nodes (30 nm and beyond). EUV mask blanks are Bragg mirrors made of Mo and Si bilayers and tuned for
reflectivity at a wavelength λ ~13 nm. Implementation of EUVL requires that the mask blanks be free of defects at 30
nm or above. However, during the deposition of MoSi multilayers and later during the handling of blanks, defects are
added to the blank. Therefore, the cleaning of EUV mask blanks is a critical step in the manufacturing of future devices.
The particulate defects on the multilayer-coated mask blanks can either be embedded in or under the MoSi layers or
adhered to the top capping layer during the deposition process. The defects can also be added during the handling of
photomasks. Our previous studies have shown successful removal of the handling-related defects at SEMATECH's
Mask Blank Development Center (MBDC) in Albany, NY. However, cleaning embedded and adhered defects presents
new challenges. The cleaning method should not only be able to remove the particles, but also be compatible with the
mask blank materials. This precludes the use of any aggressive chemistry that may change the surface condition leading
to diminished mask blank reflectivity. The present work discusses the recent progress made at SEMATECH's MBDC in
cleaning backside Cr-coated mask blanks with a MoSi multilayer and a Si cap layer on the top surface. Here we present
our data that demonstrates successful removal of sub-100 nm particles added by the deposition process. Surface
morphology and defect composition on the surface of the MoSi multilayer are discussed. EUV reflectivity measurements
and atomic force microscopy (AFM) images of the mask blank before and after cleaning are presented. The present data
shows that no measurable damage to the EUV mask blank is caused by the cleaning processes developed at the MBDC.
Microelectronics industry leaders routinely name the cost and cycle time of mask technology and mask supply as top critical issues. A survey was created with support from SEMATECH and administered by SEMI North America to gather information about the mask industry as an objective assessment of its overall condition. The survey is designed with the input of semiconductor company mask technologists, merchant mask suppliers, and industry equipment makers. This year's assessment is the fifth in the current series of annual reports. With continued industry support, the report can be used as a baseline to gain perspective on the technical and business status of the mask and microelectronics industries. The report will continue to serve as a valuable reference to identify the strengths and opportunities of the mask industry. The results will be used to guide future investments pertaining to critical path issues. This year's survey is basically the same as the 2005 survey. Questions are grouped into categories: General Business Profile Information, Data Processing, Yields and Yield Loss Mechanisms, Delivery Times, Returns and Services, Operating Cost Factors, and Equipment Utilization. Within each category is a multitude of questions that create a detailed profile of both the business and technical status of the critical mask industry.
Extreme ultraviolet (EUV) mask blanks must have nearly zero defects larger than 30 nm. Mask blank defects are an accumulation of defects present on the substrate, defects added during the multilayer (ML) deposition process, and defects added by handling the mask blank. A majority of the detectable defects are already present on the substrate before the ML deposition. However, very few of the defects present on the substrate before the ML deposition are detectable. This raises the question of whether the substrate's surface condition contributes to the total number of defects on the mask blank. Here the results of investigations on the relation between the total number of defects on the multilayer and the substrate surface condition are presented. The final surface condition is determined by the mask cleaning process. Correlation studies between defect maps before and after multilayer deposition are presented, and the relation between final defect size on the multilayer and substrate are discussed. SEMATECH's Mask Blank Development Center (MBDC) has a unique capability to characterize the surface of EUV glass substrates by atomic force microscopy (AFM), scanning electron microscopy (SEM), surface energy measurement, and zeta potential metrology. A series of experiments were performed in which different cleaning processes were used to modify the substrate surface condition before multilayer deposition. The effect of the cleaning process on the number of pits and particles after ML deposition was examined. The results indicate that although there is a direct relationship between the number of defects remaining on the substrate and mask blank defects after multilayer deposition, the variation in the total number of defects on the mask blank mainly corresponds to pits and particles already present on the substrate before cleaning and are not the result of the cleaning processes that were used before multilayer deposition.
The feasibility of removing defects from the surface of extreme ultraviolet (EUV) substrates by nanomachining is being
investigated. A commercially available atomic force microscope (AFM) based photomask repair tool was used. A
specific class of defects which has resisted all other removal techniques was targeted. Three AFM probes of varying
sharpness were evaluated. All of the probes removed the majority of each but fell short of achieving the desired 2006
high spatial frequency roughness specification of 0.2nm. Results reported are preliminary; future work will focus on
optimization of scanning parameters and tip geometry targeting specific residual defects reported in the text.
Microelectronics industry leaders routinely name mask cost and cycle time as top issues of concern. In 2002, a
survey was created with support from SEMATECH and administered by SEMI North America to gather information
about the mask industry as an objective assessment of its overall condition. The survey is designed with the input of
mask technologists from semiconductor manufacturers, merchant mask suppliers, and makers of mask equipment.
The 2005 survey was the fourth in the current series of annual surveys. The survey data can be used as a baseline for
the mask industry and the microelectronics industry to gain a perspective on the technical and business status of the
mask industry. The results may be used to guide future investments on critical path issues. Questions are grouped
into categories: general business profile information, data processing, yields and yield loss mechanisms, delivery
times, returns and services, operating cost factors, and equipment utilization. Because the questions covering
operating cost factors and equipment utilization were just added to the survey, no trend analysis is possible. Within
each category are many questions that together create a detailed profile of both the business and technical status of
the mask industry. The assessment participation has changed from year to year. The 2005 survey, for example,
includes inputs from eight major global merchant and captive mask manufacturers whose revenue represents
approximately 85% of the global mask market.
Defects on an extreme ultraviolet (EUV) mask blank strongly depend on the defects on the mask blank substrate. Any imperfection on the substrate surface in the form of a particle, pit, and scratch will appear on the EUV mask blank. In this article, we study the effect of the cleaning process on the creation of defects on the EUV substrate and mask blank. Added particles could be removed by improving the cleaning tool and the cleaning process. Pits are generally created when many large defects, particularly glass-like materials, are present on the surface and the substrate is exposed to a high energy cleaning step. Comparison of different high energy steps in a typical cleaning process suggests that the megasonic step most likely creates pits. Current cleaning processes developed in the Mask Blank Development Center (MBDC) have been optimized so that no added pits or particles are observed after using them.
Low thermal expansion material (LTEM) substrates were cleaned with recipes developed to clean blank quartz substrates. These recipes were capable of cleaning the LTEM without damaging the LTEM substrate. No effect of etching doped metals in LTEM was observed in these experiments. However, LTEM substrates currently require multiple cleaning cycles to obtain the same removal or cleaning efficiencies as quartz substrates. In addition, no change in the surface roughness or degradation of the backside choromium layer was observed.
Mask cleaning has been a significant challenge. Advanced PhotoMasks have proven to be even more difficult. The experimental work on 157nm systems uncovered an issue of particle growth under the pellicle. Since the mask blank had a different composition from existing production mask blanks, there was not a concern about current production impact. Investigations were started after a few incidents occurred on 193nm masks. The investigations demonstrated that the masks have a consistent family of contaminants that are on all chrome absorber masks. The initial work provided clues to the nature of the particle growth and some indication of the potential sources. The issues seemed to evolve from the total system and not a single contaminant source. Currently, hard defects due to particle growth under the pellicle occur industry wide. This paper will provide the methodology employed for a recent cleaning evaluation and identify some of the culprits that cause particle growth. The issue has grown to a major problem and needs to be quickly addressed.
As new technologies are developed for smaller linewidths, the specifications for mask cleanliness become much stricter. Not only must the particle removal efficiency increase, but the largest allowable particle size decreases. Specifications for film thickness and surface roughness are becoming tighter and consequently the integrity of these films must be maintained in order to preserve the functionality of the masks. Residual contamination remaining on the surface of the mask after cleaning processes can lead to subpellicle defect growth once the mask is exposed in a stepper environment. Only during the last several years, has an increased focus been put on improving mask cleaning. Over the years, considerably more effort has been put into developing advanced wafer cleaning technologies. However, because of the small market involved with mask cleaning, wafer cleaning equipment vendors have been reluctant to invest time and effort into developing cleaning processes and adapting their toolset to accommodate masks. With the advent of 300 mm processing, wafer cleaning tools are now more easily adapted to processing masks. These wafer cleaning technologies may offer a solution to the difficulties of mask cleaning and need to be investigated to determine whether or not they warrant continued investigation. This paper focuses on benchmarking advanced wafer cleaning technologies applied to mask cleaning. Ozonated water, hydrogenated water, super critical fluids, and cryogenic cleaning have been investigated with regards to stripping resist and cleaning particles from masks. Results that include film thickness changes, surface contamination, and particle removal efficiency will be discussed.
Phase shift techniques introduced in photolithography to further improve resolution produce a new set of challenges for inspection. Unlike the high contrast provided by patterned and unpatterned areas on a binary mask, phase errors do not provide significant contrast changes, since the phase change is imparted by a difference in material thickness. Surface topology measurements can be used to identify phase defects, but methods for surface topology inspection are typically slow or can damage the surface to be measured. In this study, Spatial Heterodyne Interferometry (SHI) has been considered as a possible method for high-speed non-contact phase defect detection. SHI is an imaging technique developed at Oak Ridge National Laboratory that acquires both phase and amplitude information from an optical wavefront with a single high-speed image capture. Using a reflective SHI system, testing has been performed with a mask containing programmed phase defects of various sizes and depths. In this paper, we present an overview of the SHI measurement technique, discuss issues such as phase wrapping associated with using SHI for phase defect detection on photolithographic masks, and present phase defect detection results from die-to-die comparisons on a 248 nm alternating aperture phase shift mask with intentional phase defects.
Spatial heterodyne interferometry (SHI) is an imaging technique that captures both the phase and amplitude of a complex wavefront in a single high-speed image. This technology was developed at the Oak Ridge National Laboratory (ORNL) and is currently being implemented for semiconductor wafer inspection by nLine Corporation. As with any system that measures phase, metrology and inspection of surface structures is possible by capturing a wavefront reflected from the surface. The interpretation of surface structure heights for metrology applications can become very difficult with the many layers of various materials used on semiconductor wafers, so inspection (defect detection) has been the primary focus for semiconductor wafers. However, masks used for photolithography typically only contain a couple well-defined materials opening the doors to high-speed mask metrology in 3 dimensions in addition to inspection. Phase shift masks often contain structures etched out of the transparent substrate material for phase shifting. While these structures are difficult to inspect using only intensity, the phase and amplitude images captured with SHI can produce very good resolution of these structures. The phase images also provide depth information that is crucial for these phase shift regions.
Preliminary testing has been performed to determine the feasibility of SHI for high-speed non-contact mask metrology using a prototype SHI system with 532 nm wavelength illumination named the Visible Alpha Tool (VAT). These results show that prototype SHI system is capable of performing critical dimension measurements on 400nm lines with a repeatability of 1.4nm and line height measurements with a repeatability of 0.26nm. Additionally initial imaging of an alternating aperture phase shift mask has shown the ability of SHI to discriminate between typical phase shift heights.
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