Image placement (IP) and overlay error specifications in the International Technology Roadmap for
Semiconductors (ITRS) continue to get tighter with each successive technology node. One of the
significant contributors to IP error is the non-flatness of the reticle substrate. In this paper, we will discuss
in detail the effect of reticle substrate shape on the overlay performance in extreme ultraviolet (EUV) tools.
Substrate shape-induced overlay effects are important when multiple device levels are printed using EUV
lithography. We present an analysis of 20 blanks with different flatness specifications for overlay
signatures when used for printing multiple device levels. A comprehensive analysis of scanner correctable
and non-correctable errors for different substrate shapes will also be presented. Non-flatness specifications
for EUV blanks will be reviewed based on these reticle-matching results. We will discuss results from
flatness measurements and the effect on overlay budget due to mismatched substrates using several
substrates with different flatness specifications.
Defect free masks are a critical component to enable extreme ultraviolet lithography (EUVL). It is projected EUVL will
be inserted for the 22nm hp node with a timeframe of 2012-2013 for leading IC manufacturers. To meet the goal of
defect free masks, a concerted effort is required with emphasis on mask blank development and mask infrastructure
readiness. With this in mind, SEMATECH mask program has been uniquely positioned to make important contributions
to these areas. Together with several partners, an overall strategy has been defined focused on meeting EUVL mask
requirements including setting mask standards and enabling the mask-making infrastructure. This paper will highlight
the overview of key projects and accomplishments from the mask blank development program. It is critical that
SEMATECH and its partners be ready to meet the overall pilot line defect density requirement of 0.04 defects/cm<sup>2</sup> at
18nm defect sensitivity by the end of 2010. Although important progress has been made, much work remains to meet
these challenging goals.
As we approach the 22nm half-pitch (hp) technology node, the industry is rapidly running out of patterning options. Of
the several lithography techniques highlighted in the International Technology Roadmap for Semiconductors (ITRS), the
leading contender for the 22nm hp insertion is extreme ultraviolet lithography (EUVL). Despite recent advances with
EUV resist and improvements in source power, achieving defect free EUV mask blank and enabling the EUV mask
infrastructure still remain critical issues. To meet the desired EUV high volume manufacturing (HVM) insertion target
date of 2013, these obstacles must be resolved on a timely bases. Many of the EUV mask related challenges remain in
the pre-competitive stage and a collaborative industry based consortia, such as SEMATECH can play an important role
to enable the EUVL landscape. SEMATECH based in Albany, NY is an international consortium representing several of
the largest manufacturers in the semiconductor market. Full members include Intel, Samsung, AMD, IBM, Panasonic,
HP, TI, UMC, CNSE (College of Nanoscience and Engineering), and Fuller Road Management. Within the
SEMATECH lithography division a major thrust is centered on enabling the EUVL ecosystem from mask development,
EUV resist development and addressing EUV manufacturability concerns. An important area of focus for the
SEMATECH mask program has been the Mask Blank Development Center (MBDC). At the MBDC key issues in EUV
blank development such as defect reduction and inspection capabilities are actively pursued together with research
partners, key suppliers and member companies. In addition the mask program continues a successful track record of
working with the mask community to manage and fund critical mask tools programs. This paper will highlight recent
status of mask projects and longer term strategic direction at the MBDC. It is important that mask technology be ready to
support pilot line development HVM by 2013. In several areas progress has been made but a continued collaborative
effort will be needed along with timely infrastructure investments to meet these challenging goals.
In extreme ultraviolet lithography (EUVL), mask non-flatness contributes to overlay errors in EUVL scanners. Tight
non-flatness targets are required to meet future overlay; for example, the International Technology Roadmap for
Semiconductors (ITRS) requires that substrate non-flatness will need to decrease to 36 nm peak-to-valley in 2013. To
meet these tight non-flatness values, suppliers must use aggressive polishing steps, adversely impacting substrate yield
and mask blank cost of ownership. An alternative option is to use image placement corrections at the writing step of the
reticle to compensate for the predicted impact of the non-flatness pattern placement errors, which would allow the
specifications to be relaxed.
In this paper, we will present the results of using e-beam image placement corrections during mask writing to
compensate for mask non-flatness. A low thermal expansion material (LTEM) substrate with about 500 nm of nonflatness
was employed. Three different compensation methods were used to calculate the predicted image placement
errors based upon the mask non-flatness, including the expected errors from scanner chucking. The mask was designed
to use a repeating set of four ASML alignment marks (XPA marks) across the mask. During e-beam writin, one mark
was left uncompensated, and the three different compensation methods were applied to the remaining marks. The masks
were exposed using the ASML alpha demo tool (ADT). An overview of the viability of e-beam correction
methodologies to compensate for mask non-flatness is presented based upon the wafer overlay results.
For successful implementation of extreme ultraviolet lithography (EUVL) technology for late cycle insertion at 32 nm
half-pitch (hp) and full introduction for 22 nm hp high volume production, the mask development infrastructure must be
in place by 2010. The central element of the mask infrastructure is contamination-free reticle handling and protection.
Today, the industry has already developed and balloted an EUV pod standard for shipping, transporting, transferring,
and storing EUV masks. We have previously demonstrated that the EUV pod reticle handling method represents the best
approach in meeting EUVL high volume production requirements, based on then state-of-the-art inspection capability at
~53nm polystyrene latex (PSL) equivalent sensitivity. In this paper, we will present our latest data to show defect-free
reticle handling is achievable down to 40 nm particle sizes, using the same EUV pod carriers as in the previous study
and the recently established world's most advanced defect inspection capability of ~40 nm SiO<sub>2</sub> equivalent sensitivity.
The EUV pod is a worthy solution to meet EUVL pilot line and pre-production exposure tool development requirements.
We will also discuss the technical challenges facing the industry in refining the EUV pod solution to meet 22 nm hp
EUVL production requirements and beyond.
Extreme Ultraviolet Lithography (EUVL) is one of the leading candidates for Next-Generation Lithography in the sub-45-nm regime. Successful implementation of this technology will depend upon advancements in many areas,
including the quality of the mask system to control image placement errors. For EUVL, the nonflatness of both the
mask and chuck is critical, due to the nontelecentric illumination during exposure. The industry is proposing to use an
electrostatic chuck to support and flatten the mask in the exposure tool. The focus of this research is to investigate the
clamping ability of a pin-type chuck, both experimentally and with the use of numerical simulation tools, i.e., finite
element modeling. A status report on electrostatic chucking is presented, including the results obtained during
repeatability studies and long-term chucking experiments.
Extreme ultraviolet (EUV) photoresists are known to outgas during exposure to EUV radiation in the vacuum
environment. This is of particular concern since some of the outgassed species may contaminate the nearby EUV optics
and cause a loss of reflectivity and therefore throughput of the EUV exposure tools. Due to this issue, work has been
performed to measure the species and quantities that outgas from EUV resists. Additionally, since the goal of these
measurements is to determine the relative safety of various resists near EUV optics, work has been performed to measure
the deposition rate of the outgassed molecules on Mo/Si-coated witness plate samples. The results for various species
and tests show little measurable effect from resist components on optics contamination with modest EUV exposure
Significant progress has been made over the past several years in developing extreme ultraviolet (EUV) mask
infrastructure, especially in EUV reticle handling and protection. Today, the industry has converged to standardize the
dual pod reticle carrier approach in developing EUV reticle handling solutions. SEMATECH has already established
reticle handling infrastructure compliant with industry's draft standard, including carrier, robotic carrier handling,
automated carrier cleaning, vacuum protection, and state-of-the-art particulate contamination testing capabilities. It
proves to be one of the key enablers in developing EUV reticle protection solutions, through broad collaboration with
industry stakeholders and suppliers. In this paper, we discuss our in-house reticle handling infrastructure and provide
insights on how to apply it in EUV lithography pilot line development and future production line. We present particulate
contamination free baseline results of state-of-the-art EUV reticle carriers, i.e., sPod, throughout lifecycle uses. We will
also compare the results against requirements for 32 nm half-pitch (HP) EUV lithography, to identify the remaining
challenges ahead of the industry.
The photon-stimulated emission of organic molecules from the photoresist during exposure is a serious problem for
extreme-ultraviolet lithography (EUVL) because the adsorption of the outgassing products on the EUV optics can lead
to carbonization and subsequent reflectivity loss. In order to accurately quantify the total amount of outgassing for a
given resist during an exposure, we have constructed a compact, portable chamber that is instrumented with a spinning
rotor gauge and a capacitance diaphragm gauge that, unlike the more commonly used ionization gauge or quadrupole
mass spectrometer, provides a direct and accurate measurement of the total pressure that is largely independent of the
composition of the outgas products. We have also developed a method to perform compositional analysis on the outgas
products and, more generally, on any contaminants that might be present in the stepper vacuum. The method involves
collecting the vacuum contaminants in a trap cooled to liquid-nitrogen temperature. Once collected, the products from
the trap are transferred to a system for analysis with gas chromatography with mass spectrometry. We will describe the
workings of the instruments in detail as well as results of initial tests.
In extreme ultraviolet lithography (EUVL), the lack of a suitable material to build conventional pellicles calls for
industry standardization of new techniques for protection and handling throughout the reticle's lifetime. This includes
reticle shipping, robotic handling, in-fab transport, storage, and uses in atmospheric environments for metrology and
vacuum environments for EUV exposure. In this paper, we review the status of the industry-wide progress in developing
EUVL reticle-handling solutions. We show the industry's leading reticle carrier approaches for particle-free protection,
such as improvements in conventional single carrier designs and new EUVL-specific carrier concepts, including
variations on a removable pellicle. Our test indicates dual pod approach of the removable pellicle led to nearly particle-free
use during a simulated life cycle, at ~50nm inspection sensitivity. We will provide an assessment of the remaining
technical challenges facing EUVL reticle-handling technology. Finally, we will review the progress of the SEMI EUVL
Reticle-handling Task Force in its efforts to standardize a final EUV reticle protection and handling solution.
As semiconductor technology nodes continue shrinking down to 45nm and below, the requirements for number of particle adders and their size during optical mask blank shipment are getting tighter and tighter. In the case of extreme ultra-violet lithography (EUVL) for 32nm and below technology nodes, the requirements for shipping the final mask product are even more stringent. It virtually requires zero particle adders or single digit particle adders (if local mask clean tool is equipped at wafer fab) at 30nm size for 32nm technology node and even smaller size for the 22nm technology node. This EUVL mask handling specific issue is due to the lack of pellicle material available at EUV wavelength, because of strong EUV light absorption by all solid materials. In the past few years, several benchmarking studies on mask handling and shipping without pellicles have been conducted by different companies. The results indicated that many improvements are needed to bring down the handling and shipping induced particle adders at the required 30nm size for the 32nm technology node.
In this study, we have evaluated particle generation at ≥60nm PSL equivalent size during mask shipment. We have demonstrated zero particle adders in shipping by using mask carriers with simple design. Our study included different commercially available carriers and non-commercially available carrier with designs to further minimize the particle generation and deposition onto the mask critical surface. The study has also shown that both the carrier design and the shipping packaging are responsible for clean mask transportation. The smallest particle size (60nm) evaluated in this study is limited by the metrology capability. Further evaluation for particle adders at size ≤60nm requires new development for higher sensitivity inspection capability.
Fluoropolymers were/are successfully used for pellicle manufacturing in 248 and 193 nm lithography. However, all known fluoropolymers rapidly degrade when exposed to high-energy 157 nm irradiation. Lack of suitable polymer “soft” pellicle has become one of the major obstacles for implementing 157 nm lithography. The goal of this research was to investigate the photodegradation mechanisms in fluoropolymers under 157 nm irradiation using various analytical techniques, and establish correlation between polymer structure and transparency/durability. Various polymer platforms, developed by Asahi Glass Corporation, as well as model polymer based on industrially available materials, have been employed in this study. Polymer structures have been analyzed using solution NMR, FTIR, Raman spectroscopy, TOF-SIMS, nanoindentation, outgassing, contact angle, ellipsometry, refractometry, n and k measurements. Transparency and durability of polymer membranes under 157 nm irradiation were established using an F<sub>2</sub> 157 nm laser as a source of irradiation, and an environmentally controlled chamber. As the result of this study, photodegradation mechanism for some of the tested polymers was tentatively suggested as cleavage of carbonyl, CO, and/or CFO bonds. Additionally, the following general conclusions have been made: environmental moisture, gas environment, and polymer/adhesive solvents affect structure and durability of the exposed polymers; “skin” surface layer can be formed on the surface of the irradiated polymer; polymer membranes are thinning under 157 nm irradiation; polar groups are formed on the irradiated surface. Effects of gas environment, exposure conditions, technology of the sample preparation on the photodegradation mechanism and kinetics were studied. Possible photodegradation pathways have been derived and assessed. Dependence of polymer durability and transparency on such structural features as number of carbon atoms within the ring, oxygen content, type and number of substituents in the Oxygen containing perfluorinated rings, number and location of carbon-oxygen bonds, structure symmetry, relative ratio of cyclic and linear chains, content and type of the hydrogen bonds, were analyzed. Semi-empirical rules to optimize transparency, durability, and mechanical properties of polymer membranes for 157nm exposure, will be discussed.
We present the methodology and recent results on the long-term evaluation of optical materials for 157-nm lithographic applications. We review the unique metrology capabilities that have been developed for accurately assessing optical properties of samples both online and offline, utilizing VUV spectrophotometry with in situ lamp-based cleaning. We describe ultraclean marathon testing chambers that have been designed to decouple effects of intrinsic material degradation from extrinsic ambient effects. We review our experience with lithography-grade 157-nm lasers and detector durability. We review the current status of bulk materials for lenses, such as CaF2 and BaF2, and durability results of antireflectance coatings. Finally, we discuss the current state of laser durability of organic pellicles.
In this work we present progress on the long-term evaluation of optical materials for 157-nm lithographic applications. We review the unique metrology capabilities that have been developed for accurately assessing optical properties of samples both online and offline, utilizing VUV spectrophotometry with in-situ lamp-based cleaning. We review the current status of bulk materials for lenses, such as CaF<SUB>2</SUB> and BaF<SUB>2</SUB>, and durability results of antireflectance coatings. Finally, we describe progress on materials testing of organic pellicles, both with 172-nm lamps as well as under 157-nm laser irradiation.
157-nm lithography has gained significant momentum and worldwide support as the post-193 nm technology. Due to higher absorption at shorter wavelength, however, there are several critical issues including materials and reticle handling at 157-nm. These key technical areas are being studied at Intel in collaboration with worldwide industrial and academic partners. In this paper, we will report the progress on 157-nm specific mask technology development.
Photolithography utilizing 157-nm excimer lasers is a leading candidate technology for the post-193-nm generation. A key element required for successful insertion of this technology is the near-term performance and long-term reliability of the components of the optical train, including transparent bulk materials for lenses, optical coatings, photomask substrates, and pellicles. For instance, after 100 billion pulses at an incident fluence of 0.5 mJ/cm<SUP>2</SUP>/pulse optical materials, of which the primary candidate is calcium fluoride, should have an absorption coefficient of less than 0.002 cm<SUP>-1</SUP>, and antireflective layers should enable transmission of 98.5 percent for a two-sided coated substrate. Modified fused silica has emerged as a viable option as a transparent photomask substrate, and several approaches are being explored for transmissive membranes to be used as pellicles.
Intel is aggressively pursuing the use of 157 nm lithography for the 0.1 mm patterning node. Two areas of concentration have been in photoresist and reticle materials development. Over the six months, we have seen considerable progress in new materials development in both areas. In the photoresist area, the use of ultra-thin resists of currently used chemistries appear to be capable of providing short-term layer development and tool testing patterning capability. We have obtained imaging results using a 0.5 NA Schwartzchild optics system. Our best result to data show 70-80 nm lines printed on a pitch of 180 nm. While this small field system has considerably immature optics, it can be used effectively to do basic resist development. In the area of reticle materials development, we have seen considerable improvement in the reduction of OH in blank materials, resulting in higher transmission. We expect to see substrates with greater than 80 percent transmission within the next year at the current rate of accelerated progress. Furthermore, we are not seeing any major processing differences with these new blank materials. Overall, we have seen an accelerated pace of learning in materials development for both resist and new blank materials. Overall, we have seen an accelerated pace of learning in materials development for both resist and reticle materials for 157 nm lithography.
There are many commercially available deep-UV resists today that show performance gains above Apex, which has been used in 0.35 micrometers production for some time. In addition there are inorganic antireflection layer (ARL) schemes that can now be used with these newer resists, which were difficult to use with Apex due to substrate sensitivity problems leading to footing. We will require the benefits that these newer deep-UV resists and inorganic antireflection coatings can provide as critical gate dimensions fall below the 0.25 micrometers regime. A key benefit of the use of inorganic layers for antireflection control is the ability to maintain conformality, thus avoiding critical dimension (CD) changes that occur as organic antireflection layers are coated over topography. In this paper we evaluated two of the leading edge positive results in a 0.25 micrometers pilot process on ASML 5500/90 and 5500/300 steppers. We examined basic process characteristics such as depth-of-focus (DOF), exposure latitude, dense/isolated bias, post-exposure delay stability, CD swing effects, and substrate sensitivity. This study shows that the benefits of a new resist on an inorganic ARL are reduced swing effects, decreased post- exposure-bake sensitivity, and improved delay stability, all of which result in improved CD control. A slight decrease in DOF and exposure latitude is observed, however the resultant process latitude is sufficient for sub 0.25 micrometers lithography. Results of other tests as well as data off of the ASML PAS5500/300 are also presented.
Experimental data from the current 0.35micrometers deep-UV process was used in conjunction with simulations of future 0.25micrometers lithography to provide a means of evaluating the possibility of meeting the National Lithography Roadmap goals for CD and overlay. This study found that the CD control issue has too many components to be captured by the single number listed in the Roadmap. The current magnitude of many of these components looks too large to justify their shrinking down to values consistent with the general 30 percent shrinks characteristic of our industry. For overlay, the Roadmap value is clearly attainable for matched steppers in controlled tests, however unlikely for daily product results on random- matched steppers in a production environment. This study also examined the impact of pushing deep-UV technology to the 0.25micrometers regime on the process latitudes of dense/isolated lines and upon the poly endcap.
An experimental comparison of i-line lithography and deep-UV lithography was performed for 0.35 micrometers patterning of isolation level, polysilicon level, and the contact level. Both techniques used standard illumination and standard masks. The i-line process used conventional single level DNQ resists. The deep-UV work used a commercially available single level chemically amplified positive resist, with additional use of bottom-layer organic anti-reflective layers on some levels. The results highlighted the problems of pushing i-line lithography to the 0.35 micrometers regime and demonstrated the manufacturable process latitudes available with deep-UV lithography.
A comparison of SEM measurements vs. electrical measurements of contact holes is presented. In-line SEM measurements on a Hitachi S6000 and measurements of micrographs from an off-line JEOL 845 SEM are compared to electrical measurements on a Prometrix LithoMapR system for metrology of contacts down to 0.25 micrometers size. The electrical measurements of contacts through focus/exposure variations on the stepper are shown to correlate very well with SEM measurements. Electrical measurement of contact holes in conductive films is shown to reflect actual process latitudes on oxide wafers, allowing electrical metrology to be used in optimizing lithography processes.