Defects within the multilayer mirrors of EUV photomasks have been a leading challenge for EUV lithography for quite some time. By creating non-planar surfaces, they distort both the amplitude and phase of reflected light. Amplitude errors generally create a CD error on wafer, whereas phase errors tend to cause asymmetric printing through focus. Since defect-free mask blanks are not expected to be available for initial high volume EUV manufacturing, defect mitigation, compensation, and repair strategies are essential. This paper describes a technique to repair both the amplitude and phase effects of multilayer defects. For a bump defect, the phase effect (i.e. tilted Bossung curve behavior) is corrected by removing multilayer material in the vicinity of the defect. This creates a phase effect opposite to that of the defect and the two effects cancel. The amplitude error (i.e. CD error) caused by both the defect and by the phase repair is then corrected by modifying the surrounding absorber pattern. The repairs in this paper are performed by nanomachining with an AFM repair tool. The concept is validated by a combination of simulation and experimental studies with data from the Actinic Inspection Tool (AIT) at the Lawrence Berkeley National Laboratories, the EUV Alpha Demo Tool (ADT) in Albany, New York, and an AFM repair tool. The process for a complete multilayer repair is described using an example native defect repair. Encouraging results indicate that nanomachining is capable of creating the complex nano-scale three dimensional topographies required for the repair. Repair strategies for both bump and pit defects are addressed. Multiple simulation studies are used to understand the requirements for such a repair and what type of repairs may be possible.
Mask defectivity is often cited as a barrier to EUVL manufacturing, falling just behind low source power. Mask
defectivity is a combination of intrinsic blank defects, defects introduced during the mask fabrication and defects
introduced during the use of the mask in the EUV exposure tool. This paper works towards minimizing the printing
impact of blank defects so that the final EUVL mask can achieve a lower defectivity. Multilayer defects can be created by a step or scratch as shallow as 1nm in the substrate. These small defects create coherent disruptions in the multilayer that can generate significant variations in mask reflectivity and induce clearly-defined, printable defects. If the optical properties of the defect can be well understood, nanomachining repair processes can be deployed to fix these defects. The purpose of this work is to develop new nanomachining repair processes and approaches that can repair complex EUVL mask defects by targeted removal of the EUVL mask materials. The first phase of this work uses nanomachining to create artificial phase defects of different types and sizes for both printability evaluation and benchmarking with simulation. Experimental results validate the concept, showing a reasonable match between imaging with the LBNL Actinic Inspection Tool (AIT) and simulation of the mask topography measured by AFM. Once the printability of various nanomachined structures is understood, the second phase of the work aims to optimize the process to repair real EUVL mask defects with surrounding absorber patterns.
The technology to selectively remove nanoparticles from a photomask surface by adhering it to an AFM tip
(BitClean) first introduced with the Merlin® nanomachining mask repair platform has been successfully integrated
in numerous mask house production centers across the globe over the last two years. One outstanding request for
development from customers has been to develop the capability to not only selectively remove nanoparticles from a
target surface, but to also redeposit in another target region. This paper reviews the preliminary work done to
develop this capability with particular emphasis on its potential applications in creating realistic nanoparticle
inspection sites for KLA systems at critical pattern print locations as well as the accumulation of trace amounts of
contaminates for better compositional and print-impact analysis. There is also a feasibility study of new ultra-high
aspect ratio (AR > 1.5) NanoBits for future BitClean process applications. The potential for these capabilities to be
adapted for new applications will be examined for future work as well as a detailed parametric process analysis
with the goal of showing how to make significant improvements in BitClean PRE.
The haze nucleation and growth phenomenon on critical photomask surfaces has periodically gained
attention as it has significantly impacted wafer printability for different technology nodes over the
years. A number of process solutions have been shown to suppress or minimize the propensity for
haze formation, but none of these technologies has stopped every instance of haze. Additionally, the
management of photo-induced defects during lithography exposure is expensive, so some capability
will always be needed to remove haze on photomasks for long term maintenance over a mask's
lifetime.
A novel technology is reviewed here which uses a dry (no chemical effluents) removal system to
safely sweep the entire printable region of a pelliclized photomask to eliminate all removable haze.
This process is safe regardless of the mask substrate materials or the presence of small critical
patterns such as SRAF's that may represent damage problems for traditional cleaning methods.
Operational process techniques for this system and performance in removal will be shown for haze
located on the mask pattern surface. This paper will also discuss the theory of operation for the
system, including expected chemical reactions and address the reformation rate of haze crystals.
Data from tool acceptance and preliminary production use will also be reviewed including analysis
of process window through a focus-exposure matrix, repair durability, CD performance, and sort
yield.
A number of new technologies and processes have been developed for deep ultraviolet (DUV) wavelength
and femtosecond pulsed laser repair of photomasks. These advances have been shown to improve and extend the
repair of both pelliclized and non-pellicilized photomasks for both hard and soft (or nano-particle) in exhaustive
testing at the factory and the end-user site. However, even the best testing is only a simulation of what a repair
tool will see when brought into full production. The purpose of this work is to review some of the knowledge and
experience gained in bringing the repair processes defined with manufactured defects to the more variable defects
encountered in the real world. The impact of the repair technology on increases in mask house throughput and
decrease in costs will also be compared to other (another laser and an advanced FIB) repair tools.
A number of new RET's have come to significant adoption in advanced lithography recently, extending technology
trends that have allowed the use of 193 nm wavelengths for nodes well beyond their intended limits. These
enhancement technologies include Computational Lithography (CL) techniques such as Source-Mask Optimization
(SMO), and use of innovative materials such as Opaque MoSi on Glass (OMOG). These new techniques are of particular
focus for examination of their applicability to nanomachining photomask repair. Historically comparative repair results
are shown for the OMOG absorbers which can contain a multi-layer potentially in combination with quartz over-etching
for phase correction. The implementation of nanomachining for CL/SMO photomasks encompasses a larger set of new
technologies introduced in a nanomachining repair tool. These include tip shape de-convolution for improved accuracy
and reproducibility of large complex patterns - many of which are non-orthogonal, and automated import of mask design
data to seed the repair polygon for a pattern which may be unique on the entire mask area (i.e. no pattern reference).
Regardless at what technology node it will be implemented, extreme ultraviolet (EUV) lithography appears to be the
most likely candidate to succeed 193 nm wavelength lithography. However, EUV photomasks present new and different
challenges for both repair and clean processes. Among these are different and more complex materials, greater
sensitivity to smaller topography differences, and lack of pelliclization to protect critical pattern areas. Solutions
developed and recently refined to meet these challenges are reviewed as an integrated solution to make the manufacture
and maintenance of this mask type feasible. This proven, integrated solution includes nanomachining, BitClean® and
cryogenic clean processes applied for hard (missing pattern) and soft (nanoparticle) defect removals with no damage to
underlying multilayers.
Contrary to the prior assumptions of its technical demise, deep UV (DUV) femtosecond pulsed laser repair of
photomasks is continuing to mature and improve as a technology. Similar to the optical enhancements that allow
for 193 nm wavelength light to continue being used down to the 32, or even in some cases 22 nm, node, the process
regimes for this type of laser repair continue to expand as new processes are discovered. This work reviews the
qualification of repair performance for production at a major wafer foundry site. In addition advances are shown in
the area of through-pellicle repair (TRP) process development. These advances include the preferential (versus
surrounding reference mask structures) removal of soft defects and the capability to remove or manipulate particles
on top of a flat absorber region with no detectable removal of the absorber. These developments will further
demonstrate the progressive decoupling of the laser repair spot size from the minimum technology node for laser
repair.
Makers and users of advanced technology photomasks have seen increased difficulties with the removal of persistent, or
stubborn, nano-particle contamination. Shrinking pattern geometries, and new mask clean technologies to minimize
haze, have both increased the number of problems and loss of mask yield due to these non-removable nano-particles.
A novel technique (BitCleanTM) has been developed using the MerlinTM platform, a scanning probe microscope system
originally designed for nanomachining photomask defect repair. Progress in the technical development of this
approach into a manufacture-able solution is reviewed and its effectiveness is shown in selectively removing adherent
particles without touching surrounding sensitive structures. Results will also be reviewed that were generated in the
qualification and acceptance of this new technology in a photomask production environment. These results will be
discussed in their relation to the minimum particle size allowed on a given design, particle removal efficiency per pass
of the NanoBitTM (PREPP), and the resultant average removal throughput of particles unaffected by any other available
mask clean process.
Patterns which are not aligned to standard orthogonal (x and y ordinate) directions have recently been developed
for advanced lithography nodes. Efforts have been successful in developing single pass nanomachining repair
processes to meet the printability requirements for these patterns. This development makes use of the latest
improvements made to the COBRA repair process (the Enhanced COBRA process typically completed in less than
2 minutes of repair time) with symmetric NanoBits to repair opposing critical edges of bridging defects. It also
required fundamental changes in the software tools to allow automated detection of the angle of the edges and the
application of pre-programmed repair edge biases normal (90°) to the detected angled edges. Additionally, some
other new improvements (hardware, software, and process) are reviewed in light of more traditional nanomachining
repairs.
A developing reality with advancing DUV femto-second pulsed laser repair of advanced photomasks after
pelliclization is a significant operational cost savings. This economic advantage comes from the elimination of a
previously critical inspection step before mounting the pellicle on the mask. The laser repair processes developed
allow reduce the number of times masks are cycled through mask inspection tools and prevent recontamination of
the mask surface due to handling during and after the inspection before pelliclization. The latter would require,
without effective through-pellicle repair, removal of the pellicle, repair and/or reclean, then re-inspection and
re-pelliclization of the mask (assuming success with the first cycle of repair and/or reclean). Meanwhile, the cost
and lack of feasibility for this additional process both increase the investment in the mask while at the same time
bringing it closer to being completely scrapped. Recently developed processes that allow for effective
through-pellicle laser repair on advanced photomask technologies (sub 65 nm node) are reviewed, that have
economic advantages and also make the repair of lower-end (and higher volume) photomasks significantly more
profitable to the typical mask maker.
A persistent industry problem impacting photomask yield and costs has been haze formation. The haze nucleation
and growth phenomenon on critical photomask surfaces has periodically gained attention as it has significantly
impacted wafer printability for different technology nodes over the years. A number of process solutions have
been promoted in the semiconductor industry which has been shown to suppress or minimize the propensity for
haze formation, but none of these technologies can stop every instance of haze. Thus some capability will always
be needed to remove haze on photomasks with their final pellicles mounted both at the manufacture and long term
maintenance stages of a mask's lifetime. A novel technology is reviewed here which uses a dry (no chemical
effluents) removal system to sweep the entire printable region of a pelliclized photomask to eliminate all removable
haze regardless of the mask substrate materials or the presence of critical patterns. An operational process
technique for this system and performance in removal is shown for haze located on the mask pattern surface.
Finally, preliminary data from tool acceptance and preliminary use in a production environment will also be reviewed.
The AFM-technology based technique of nanomachining has been well-proven in the area photomask repair since
its introduction a decade ago. However, the problems and challenges facing the mask repair operator have
changed significantly in this period, and ongoing engineering platform development has reflected these shifts, as
well as refinements based on specialized experience with nanomachining repair technology. Improvements from
this technical development include improved monitoring and control of the internal tool environment (to minimize
AFM scan noise and thermal drift), and automation to easily and reliably clean and characterize the 3-dimensional
shape of the NanoBitTM apex. For repair applications, improvements will be shown for the automated and
operator-intuitive reconstruction of 3-dimensional nanometer-scale patterns on the photomask with referenced
z-depth and xy alignment regardless of pattern orthogonality. Multiple pattern repair capability is also reviewed
due to a greater diversity of available process options and multi-repair box capability with a common quartz-level
z-reference point. Finally, it will be shown how all of these individual improvements work together to provide
extended repair capability down to the 32 nm technology node.
Makers and users of advanced technology photomasks have seen increased difficulties with the removal of
persistent, or stubborn, nano-particle contamination. Shrinking pattern geometries, and new mask clean technologies
to minimize haze, have both increased the number of problems and loss of mask yield due to these non-removable
nano-particles. A novel technique (BitCleanTM) has been developed using a scanning probe microscope system
originally designed for nanomachining photomask defect repair. Progress in the technical development of this
approach into a manufacture-able solution is reviewed and its effectiveness is shown in selectively removing adherent
particles without touching surrounding sensitive structures. Methods for generating targeted edge test particles along
with considerations for removal of particles in various pattern geometries and materials are also discussed.
Improvements in repair process, software, and AFM tip technology have brought about an overall 2D shape
reconstruction capability to nanomachining that has not been previously imagined. Repair results are shown
for various processes to highlight their relative strengths and weaknesses. The impact of technical
improvements is shown in the advances in repair dimensional precision and overall imaging performance. The
greater technical potential of nanomachining is realized in this examination for mask repair scaled to smaller
repair geometries while repairing larger defects that may span these critical patterns.
It has been found that the femtosecond DUV laser mask repair tool has significant utility in the repair of unknown
foreign material (FM) contamination of sizes ranging from 50 nm to 30 μm with highly variable z-heights both
isolated and within critical complex patterns. Another significant ROI is the repair of masks which have already
been pelliclized (through pellicle repair or TPR) where the laser repair tool may work in conjunction with existing
through-pellicle inspection hardware to detect and remove FM and correct pattern errors. The capability of the tool
is also explored for repairs in patterns including the 45 nm technology node.
Reduced design rules demand higher sensitivity of inspection, and thus small defects which did not affect printability
before require repair now. The trend is expected to be similar in extreme ultraviolet lithography (EUVL) which is a
promising candidate for sub 32 nm node devices due to high printing resolution. The appropriate repair tool for the small
defects is a nanomachining system. An area which remains to be studied is the nano-machining system performance
regarding repair of the defects without causing multilayer damage. Currently, nanomachining Z-depth controllability is 3
nm while the Ru-capping layer is 2.5 nm thick in a Buffer-less Ru-capped EUV mask. For this report, new repair
processes are studied in conjunction with the machining behavior of the different EUVL mask layers. Repair applications
to achieve the Edge Placement(EP) and Z-depth controllability for an optimal printability process window are discussed.
Repair feasibility was determined using a EUV micro exposure tool (MET) and Actinic Imaging Tool (AIT) to evaluate
repairs the 30 nm and 40 nm nodes. Finally, we will report the process margin of the repair through Slitho-EUVTM
simulation by controlling side wall angle, Z-depth, and EP (Edge Placement) on the base of 3-dimensional experimental
result.
The transition to sub 45 nm technology nodes presents a significant technical challenge for mask repair due to a number of
previously lesser known physical phenomena. Nanomachining technology, which has a history of equally successful repair
of all photomask types-including Cr binary masks, has not been immune to these challenges. This has led to the
development of a number of distinctly new processes to meet these technical requirements. In one of the two new processes
reviewed in this work, the bulk of the defect is removed by applying compressive instead of tangential stresses to the
NanoBitTM during repair. This allows for 45 nm and smaller repairs, with sidewall angles and aspect ratios greater than 70°
and 2:1 respectively, in open mask structures. For repair in closed-or missing defect-structures, a process was developed to
minimize tip deflection away from the designated repair box boundaries for accurate two dimensional shape reconstructions
of deep and complex patterns. The successful application of this technique is shown for actinic phase-correct missing and
partial CPL, EAPSM, and Cr-absorber square contacts at these nodes. Additionally, the potential of these new processes to
enable higher aspect advanced NanoBitTM designs for robust mask repair, and the new processes developed to effectively
clean nanomachining debris from these advanced mask structures are discussed to provide a complete review of these
solutions and their supporting technologies.
The majority of trends in lithography technology necessitate the use of smaller, higher aspect, patterns on
photomasks which are increasingly sensitive to traditional cleaning processes. Particle defects are of increasing
concern since, in deep and even overhanging structures, they can become fixed to the surface with such strength
that any traditional cleaning technique would destroy any small, high-aspect, mask structures. A series of
advanced new solutions are presented here which have been shown to remove these types of problem particles as
applied to 45 nm node nanomachining mask repair with a RAVE nm450 system. In the first method, a cryogenic
cleaning system is modified to greatly enhance selective removal of nanoparticles from high aspect structures. In
the second method, the nm450 repair tool itself is applied to selectively remove targeted particles from a nanoscale
area of the mask surface thus only affecting the region of interest and not touching any sensitive surrounding
surfaces or structures.
As mask complexity has increased and design rules continued to shrink, the manufacturing cost per mask has steadily
increased as well. Studies also show that defects are the number one issue for mask yield. Smaller defects are typically
addressed through process development, or through photomask repair. The occurrence of large defects often may only
be further reduced through use of expensive clean room improvements, like SMIF handling systems. The impact of each
large defect therefore increases while the feasibility in their repair decreases as they can span a large number of adjoining
densely packed patterns. The presence of sub-resolution features such as scatter bars and the increasing use of embedded
phase-shifting masks also complicates the timely repair of such defects.
Existing mask repair techniques such as nanomachining, electron beam, or focused ion beam are challenged to produce
high yield repairs on such large defects within a reasonable timeframe. Often very complex repairs may in fact take
longer than a rewrite of the mask! Deep UV (DUV) femtosecond pulse laser mask repair provides a unique solution to
this defect repair need.
Methods and results are discussed for the process optimization for the removal of large (5μm) area repair on both Cr and
MoSi absorber films on quartz. Additionally, high repair throughput results are shown for unknown contamination
removal, and reproduction of ≥1 μm complex unconnected patterns in a single repair run lasting a matter of minutes.
Closed-loop CD feedback in-situ with the iterative repair process for such structures can readily result in an edge
placement control within ±15 nm. Prior iterative CD closed-loop repairs on specific structures have reliably yielded
results within ±10 nm, as confirmed by AIMS CD error, even after aggressive mask wet clean. The nanometer scale
dimensional resolution and repeatability of such repairs is shown with the use of sub-pixel resolution automated pattern
reconstruction using integrated high-NA DUV microscope imaging.
This work represents one in a series of ongoing papers demonstrating the potential utility of integrating advanced photolithographic simulation software into a mask repair tool to provide immediate defect or repair printability feedback. The equipment used here is an AFM-technology based nanomachining photomask repair tool where the high-accuracy AFM surface topography data is fed directly into software applying rigorous solutions to Maxwell's equations. The nature of these systems allows for process endpoint printability evaluation, not restricted by the optical limitations of any given apparatus, of any micro to nano-scale region of the mask in-situ with the defect repair process. In prior work, the capability of this approach was shown in good correlations to AIMSTM at 248 and 193 nm wavelengths, for binary mask repairs of varying dimensions, with no applied optical aberrations to the simulation. In this examination, the development of this system is taken to its next step by introducing it to a real photomask production environment, using production masks, for performance substantiation. Methodologies are shown for the best use of this system in streamlining the mask production process.
Deep ultraviolet (DUV) femtosecond-pulsed laser ablation has numerous highly desirable properties for subtractive photomask defect repair. These qualities include high removal rates, resolution better than the focused spot size, minimized redeposition of the ablated material (rollup and splatter), and a negligible heat affected zone. The optical properties of the photomask result in a broad repair process window because the absorber film (whether Cr or MoSi) and the transmissive substrate allow for a high degree of material removal selectivity. Repair results and process parameters from such a system are examined in light of theoretical considerations. In addition, the practical aspects of the operation of this system in a production mask house environment are reviewed from the standpoint of repair quality, capability, availability, and throughput. Focus is given to the benefit received by the mask shop, and to the technical performance of the system.
Photomask repair has been acknowledged as a value creation step in the mask process flow. As technology pushes forward, the need for more advanced mask repair is apparent. This paper introduces a new mask repair tool directed at the 65 nm node and extendable to the 45 nm node, the nm650de (digital extendible). The system provides high throughput, advanced imaging capabilities, tight control in X, Y, and minimal Z drift with very low noise. Results are shown for the repair of edge defects in tight lines and spaces on both Cr binary and MoSi (EPSM) masks. Statistical analysis is conducted with respect to edge placement, surface damage, and 193 nm AIMSTM, "transmission" (relative normalized peak intensity). This analysis is then compared to specifications for each technology node.
In prior work, the capability of mask-topography (AFM) based photolithographic simulation (SOLID-CTM) to minimize the number of aerial image microscope simulation (AIMSTM) evaluation related mask load/unload cycles in a repair tool was demonstrated for programmed binary edge defects at 248 nm wavelengths and various stages of defect repair. The next stage is to bring the concept of photolithographic mask simulation concurrent with defect repair closer to a production-level system. This was done by comparing SOLID-CTM simulations generated directly from uploaded AFM topography data with 193 nm AIMSTM results for a set of patterns and defect repairs. The results have been successfully compared in both best and through-focus evaluations. With this increased knowledge and experience, it becomes possible to not only increase the efficiency and yield of the repair of any mask defect, but to also further optimize each individual repair with feedback as to the potential impact on the lithography process.
Current generation photomasks use optical enhancements such as phase shifting and aggressive OPC in an effort to maintain image contrast as CDs shrink. The result is non-intuitive complex shapes with jogs and multiple levels with different materials. The mask repair engineer is challenged to work with defects that occur in ever tightening spaces on these complex masks. Prior established nanomachining technology allows nanometer level control of material removal. To date, the challenge in developing repair strategies that will meet transmission specifications as well as maintaining aerial image contrast through focus has been mainly an empirical exercise where the mask repair is attempted and aerial image measurement among other tests are used to verify the result. This approach can be streamlined by the use of lithography simulation which rigorously models the effects of mask defects on the aerial image at the wafer. Once the topography of the defect is measured by the nanomachining mask repair tool, lithography simulation can be proactively used to develop a repair strategy for the nanomachining process. Following this repair, the simulation software can then provide immediate feedback to confirm the post repair 3-D topology from AFM surface measurements for either approval or immediate rework. This integration is initially validated using a significant set of repairs with subsequent aerial image measurements compared to some of the more common evaluative analyses.
Nanomachining has become a mainstream process for repairing photomasks. The advantages of nanomachining versus other repair techniques are improved edge placement, reliable depth control, and minimized substrate damage. This technique can be applied to any defect that requires a subtractive repair process. The process can be equally well applied to defects of any material including unknown materials. This paper evaluates the correlation of different inspection methods in characterizing nanomachined photomask repairs. The repairs were made using an nm650 mask repair tool manufactured by RAVE LLC. The repairs were inspected using a 248nm Aerial Image Measurement System (AIMS) and the Atomic Force Microscope (AFM) image produced by the nanomachining tool itself. These repairs were performed on 248nm MoSi photomasks. Results were compared to measurements by SEM and optical edge placement measurement techniques.
Nanomachining is a new technique for repairing photomask defects. The advantages of this technique are no substrate damage, precise edge placement position and Z height accuracy when compared with current Laser zapper or FIB GAE repair techniques. We have reported that this technique can be applied to any type of opaque film material defects, quartz bump defects on Alternating Aperture Phase Sifting Masks (AAPSM) and complex pattern defect repairs. In this report, we have evaluated about the optimization of Nanomachining condition for repairing most advanced photomasks for 193nm lithography on the materials of binary chrome and MoSi HT-PSM. Evaluation items are adequate edge position and Z height for targeting to achieve better printing performance when analyzed with an AIMS 193nm tool.
Nanomachining is a new technique for repairing photomask defects. The advantages of this technique are no substrate damage, precise edge placement position and Z height accuracy when compared with current Laser zapper or FIB GAE repair techniques. This technique can be applied to any type of opaque defects at any type of film materials and quartz bump defects on Alternating Aperture Phase Sifting Masks (AAPSM). Furthermore, these characteristics enable complex pattern repairs of most advanced photomasks for 193nm lithography and enables iterative repair to achieve improved printing performance when analyzed with an AIMS 193nm tool. Dai Nippon Printing Co., Ltd. (DNP) has been producing AAPSMs in mass production for quite some time. The standard type of AAPSMs manufactured has been etched quartz, single trench with an undercut structure. On this structure, there is a potential for quartz defects underneath the chrome overhang based on the combination of dry and wet etching to create the undercut. For this study, we fabricated this kind of designed quartz defects and repaired them using the nanomachining system. These types of defects are particularly difficult to repair perfectly because they exist underneath the chrome overhang. We will show some options to achieve better printing results through the repair of these kinds of defects.
In this report, we confirmed basic performance of this technique such as edge placement accuracy, Z height accuracy and AIMS printability. Additionally, we also tried to repair some complex defects such as quartz defects of AAPSM, quartz defects of CPL mask and oversized Serifs for application options. We will show these nanomachining repairs with evaluation results of printing performance simulated by the AIMS 193nm tool.
Nanomachining is a relatively new technique to the semiconductor industry. This technique utilizes the positional control of an atomic force microscope coupled with RAVE LLC's nanomachining head to perform material removal with nanometer level precision. This paper discusses the benefits of that technology as applied to photomask repair. Specifically, we will show the capability of the RAVE nm1300 to reconstruct completely missing contacts on 193 nm - 6% MoSi phase shift material utilizing both symmetric and asymmetric NanoBit tips. Wafer print test data confirmed the MSM-193 (AIMS)TM data that symmetric NanoBit tips have the ability to consistently produce contacts with through focus critical dimensions within 15 nm (1x) of unrepaired contacts. Experiments show that in order to reproduce the correct through focus behavior, the nanomachined depth into the quartz substrate must be controlled to within 5 nm on the photomask. In addition, 193 nm AIMS data show that placement errors of the reconstructed contacts are less than 15 nm (1x). Throughput and tip lifetime for both tip types on these repairs will also be examined.
This paper introduces nanomachining with the RAVE LLC nm1300 as an effective alternative for subtractive mask repair on a variety of materials. Because the Rave LLC nm 1300 employs a nanomachining strategy for subtractive removals there is essentially no limitation on the types of materials that may be removed. This unique capability makes the RAVE LLC nm 1300 adaptable to performing repairs on EUV, carbon depositions, and contamination that cannot be removed by standard cleaning processes. EUV is widely regarded as the leading candidate for NGL, with beta systems scheduled for delivery in 2005. This technology still faces several critical challenges, some of which relate to defects and Cost of Ownership. In fact, in industry-wide projections, process defects are listed as one of the largest contributors to yield loss (and yield loss is one of the primary drivers of Cost of Ownership). Because the EUV technology utilizes a reflective mask, it presents several challenges to conventional mask repair techniques which to date have not been overcome. This paper introduces nanomachining with the RAVE LLC nm1300 as an effective alternative for subtractive mask repair of EUV mask defects. In addition, this paper will demonstrate how the Rave LLC nm 1300 nanomachining process can be utilized to repair masks that do not meet specification due to misplaced carbon depositions or 'non-removable' contamination covering critical geometries.
Nanomachining is a new technique to the semiconductor industry. This technique combines the positional control of an AFM and RAVE LLC's proprietary nanomachining head to perform material removal at nanometer levels. This is the first commercial application of this technology. Benefits of this technology as applied to photomask repair are discussed. Specifically, we address the use of this technique for removal of defects in quartz, chrome, MoSi, and various exotic materials. Emphasis is given to materials that provide significant challenges for the current industry standard repair techniques. Specifically, quartz bumps on alternating phase shift masks, trimming of carbon patches, and repairs within tight lines and spaces. Several advantages of the technique are illustrated, including the abilities to machine in tight geometries, approximate line edge slope for both wet and dry etched material, image with resolution exceeding today's needs, extend to future mask sizes and technologies NGL, develop custom repair processes and tips quickly, image and repair quartz bumps of nearly any size and shape, minimize surface damage, and achieve superior edge control and transmission. Statistical analysis is conducted on performance of the technique with respect to edge placement, transmission, and surface damage performance to specifications.
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