As extreme ultraviolet lithographic (EUVL) photomask technology continues to advance to meet the requirements of future technology nodes, significant changes need to be made to the mask that can impact defect repair processes. These changes are different absorber stack materials and thickness (for example, low-n absorbers), anamorphic projection, larger mask substrates, and non-repeating curvilinear patterns. In this work, rigorous simulation studies are performed and analyzed to determine possible solutions for hard defect repair and particle cleaning of the most advanced next-generation proposed mask technologies and the challenges they present. It is believed this will allow for backwards-optimization of repair processes and strategies starting from aerial image printability requirements.
With all the attention and excitement surrounding the development of EUVL into HVM, the ongoing needs of necessary legacy photomasks (193 nm wavelength and longer) have been less in the spotlight. Many layers in semiconductor lithography are still formed using masks at these technologies due to economic, and other, considerations. An aspect of legacy mask production and maintenance that has received even less attention of late has been the availability of toolsets optimized to provide defect repair and particle cleaning. Advanced laser repair and clean processes have been shown in the past several years to be an effective replacement for, not only aging less-advanced laser systems, but also obsolete focused ion beam (FIB) tools. More recently, additional processes have been developed which can even further extend the capabilities of advanced laser processing of these legacy masks. The improvements reviewed here include, but are not limited to, extremely fast removal of multi-micron hard opaque defects with mitigated ablation particle production, removal of softer defects in extremely large areas and sub-resolution patterns. The recent development of an advanced laser deposition repair to clear defects is also introduced for optical mask applications.
In prior work, the capability of novel nanomachining processes to repair TaN EUV absorber materials was shown using 1.8 aspect ratio (AR) AFM tips in line and space patterns down to 90 nm half-pitch. While these repair results were well within the requirements for EUV printability, they only demonstrated the capability to repair an absorber material which has become obsolete with the rapid development of EUVL technology. The introduction of boron into the absorber chemistry indicates a significant increase in the hardness of this material which can be a significant factor in tip deflection in nanomachining. In this work, test repair results are shown for an advanced EUV absorber stack containing a TaBN formulation. The repair dimensional accuracy and repeatability are analyzed along with the throughput and tip wear rates for this nanomachining process. The capability of the BitClean process to clean and finish these repairs will also be shown for this absorber type.
In prior work, the capability of novel nanomachining processes to repair TaN EUV absorber materials was shown using 1.8 aspect ratio (AR) AFM tips in line and space patterns down to 90 nm half-pitch. While these repair results were well within the requirements for EUV printability, they only demonstrated the capability to repair an absorber material which has become obsolete with the rapid development of EUVL technology. The introduction of boron into the absorber chemistry indicates a significant increase in the hardness of this material which can be a significant factor in tip deflection in nanomachining. In this work, test repair results are shown for an advanced EUV absorber stack containing a TaBN formulation. The repair dimensional accuracy and repeatability are analyzed along with the throughput and tip wear rates for this nanomachining process. The capability of the BitClean process to clean and finish these repairs will also be shown for this absorber type.
Photomask technological innovation has entered a new renaissance at the cutting edge due to the transition from 193 nm to extreme ultraviolet (EUV) in high volume production. EUV has allowed the manufacture of smaller and smaller features on the mask with more complex multilayer material stacks that allow for little dimensional error in both patterning and defect repair. To meet these, and other challenges, work has continued to develop material independent AFM nanomachining processes that enable next-generation tips with increasing aspect ratios. Repair results from the current best of breed process, a novel and advanced nanomachining technique, will be analyzed on the latest platforms for production. Data will be reviewed to show the process capability for single pass repair on EUV patterns using 1.8 aspect ratio (AR) NanoBits® while also looking forward to implementation to higher AR NanoBits. The process will be evaluated for dimensional control to target, cleanliness, tip wear, and throughput in defect repair in single-digit nanometer technology node patterns.
Photomask technological innovation has entered a new renaissance at the cutting edge due to the transition from 193 nm to extreme ultraviolet (EUV) in high volume production. EUV has allowed the manufacture of smaller and smaller features on the mask with more complex multilayer material stacks that allow for little dimensional error in both patterning and defect repair. To meet these, and other challenges, work has continued to develop material independent AFM nanomachining processes that enable next-generation tips with increasing aspect ratios. Repair results from the current best of breed process, a novel and advanced nanomachining technique, will be analyzed on the latest platforms for production. Data will be reviewed to show the process capability for single pass repair on EUV patterns using 1.8 aspect ratio (AR) NanoBits® while also looking forward to implementation to higher AR NanoBits. The process will be evaluated for dimensional control to target, cleanliness, tip wear, and throughput in defect repair in single-digit nanometer technology node patterns.
In prior work, progress was shown in the systematic characterization of the process space for efficient and effective repair of extreme ultraviolet (EUV) photomasks using an ultrafast (femtosecond) pulsed deep ultraviolet (DUV) laser apparatus. In this work, the full analysis and conclusions, along with any additional test results are shown. This includes an analysis of the impact of laser repair on the phase shift of the multilayer using multiple processes.
Progress is aggressively being made to advance nanomachining photomask repair technology to the next level of performance. This next level would allow for the dimensional modification of surfaces using diamond AFM tips (NanoBits) with nominal aspect ratios (AR’s) greater than or equal to 1.3 (including 1.8) in the smallest features in production. Prior work along these lines will be presented with new results from a novel process with comparison to established nanomachining processes. These results will evaluate test repairs on the most advanced photomasks currently in production including OMOG and EUV.
Nanomachining is typically described as being a material-independent subtractive mask repair process. This is a correct statement, for the most part, since it does not require a material end-stop nor chemistries targeted to remove only a specific material. However, it is not true when considering the effect of materials being removed on the integrity of the nanomachining tip (also referred to here as NanoBitsTM). While many advanced absorber materials such as OMOG are easier to nanomachine than earlier absorber materials such as chrome and MoSi, the absorbers used in EUV have proven to be much harder and tougher (in a nanomechanical sense) while sitting atop a very fragile multilayer substrate. This work shows results from advancements on the latest nanomachining platform, nm-VI to minimize tip wear during the repair process. Consequently, this improves defect repair capability for smaller dimensions, decreases overhead from tip changeouts, decreases the cost of consumables by increasing NanoBit lifetime, and increases repair tool return-on-investment.
Nanomachining is one of the primary repair processes for leading-edge technology photomasks. Many hardware improvements have been made in successive nanomachining-tool generations to improve repair performance specifications (stability, drift, and z-depth control). However, improvement to the repair processes are still needed to address the use of the latest generation of high aspect-ratio (HAR) NanoBitsTM (1.8 AR and above). Although beneficial for repair of leading-edge photomasks, HAR NanoBitsTM exhibit greater degrees of nonlinear deflection, wear, and even breakage during traditional repair processes. In this work, the authors chronicle investigations into new nanomachining process options to enable subtractive hard defect repair with HAR NanoBitsTM down to the most advanced technology node with topographic z-depth control within ±0.5 nm and no detectable line edge, or multilayer capping layer, roughness.
This publication is a continuation of a prior work on the process space available for the repair and localized cleaning of extreme ultraviolet lithography (EUVL) photomasks with the fpIII femto-pulsed deep ultraviolet (UV) repair tool. This next phase of work was done in partnership with the Paul Scherrer Institute (PSI) to provide a more systematic examination of the process space. In these tests, specialized cells were produced to systematically test the effect of variations in the fpIII laser parameters with both carbon and HSQ (hydrogen silsesquioxane) absorber material pin dots on multilayer fields, according to design of experiments (DOE) methodology. Blank (no pin dot) test cells and pin dots were inspected both with nmVI AFM and PSI RESCAN EUV-actinic lensless metrology before and after laser processing. This data was then analyzed with full-factorial DOE, and less structured techniques, to provide insights into the capability of a modelled optimal fpIII laser process.
In the last year, initial feasibility study results were published which showed that simulated fall-on particles and TEOS deposited pindot features could be removed with low-fluence femtosecond-pulsed laser repair processes with no detectable multi-layer damage as seen in AFM scans. At the time, actinic EUV inspection metrology was not available. In this work, this metrology is used with both process testing and removal of a more diverse range of different defect types both isolated (on multilayer and on absorber) and in patterns of various types and densities. In addition, follow-up work is shown to complete full factorial design of experiments tests for TEOS pindots in OMOG line and space patterns. These results are then parametrically analyzed and compared to simulation results and theoretical first-principles to better understand the mechanisms for defect removal from the EUV mask surface.
Deep ultraviolet (DUV) femtosecond laser repair of Cr binary and phase-shift photomasks is routine and well established over decades of practice. As Moore’s law progresses into sub-10 nm nodes, there is a necessary diversification of lithography technologies which can similarly benefit from the high-throughput, non-contact, contaminate-selective capabilities of ultrashort pulsed laser repair. These alternative lithography masks include extreme ultraviolet (EUV) TaN reflective and DUV SiN-based photomasks. Additionally, parametrically systematic studies are shown with intent to find the limits of selective, sub-resolution, removal of simulated soft defects in various patterns on DUV photomasks.
The specifications performance data for the latest generation system are compared to prior generations. These results are shown for both missing pattern (or hard) and unknown contamination (or soft) defects of various classifications in different patterns. For hard defects, capability will be demonstrated down to the 65 nm node, with soft defect repair and clean significantly exceeding to even smaller nodes down to 14 nm. The latter is of particular note, especially in the application of the cleaning of fall-on unknown contaminates on pelliclized photomasks. Finally, there will be a discussion of future work to further develop soft repair/clean process and laser processes for other mask technologies.
Mask defectivity is a serious problem for all lithographic masks, but especially for EUV masks. Defects in the EUV
blank are particularly challenging because their elimination is beyond control of the mask fab. If defects have been
identified on a mask blank, patterns can be shifted to place as many blank defects as possible in regions where printing
impact will be eliminated or become unimportant. For those defects that cannot be mitigated through pattern shift, repair
strategies must be developed. Repairing defects that occur naturally in the EUV blank is challenging because the
printability of these defects varies widely. This paper describes some types of native defects commonly found and begins
to outline a triage strategy for defects that are identified on the blank. Sample defects best suited to nanomachining
repair are treated in detail: repairs are attempted, characterized using mask metrology and then tested for printability.
Based on the initial results, the viability of repairing EUV blank native defects is discussed.
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.
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).
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.
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.
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.
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.
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.
Recently questions have been raised about whether high aspect ratio (HAR) NanoBitsTM can be effectively utilized to
repair extension defects in 45 nm node and beyond. The primary concern has been how the effect of NanoBitTM
deflection impacts edge placement, sidewall angle and z-depth control repeatability. Higher aspect ratio bits are required
for defects that arise as mask feature sizes become smaller. As the aspect ratio of the NanoBitTM continues to increase to
meet these demands, the cross sectional area of the bit used for nanomachining becomes thinner and more susceptible to
bending under the forces applied during the nanomachining process. This is especially true when deeper features that
require HAR NanoBitsTM are being repaired. To overcome this trend RAVE LLC has developed a new repair process
that utilizes the strength of the bit shape. Repair of 45 nm node defects that require HAR NanoBitsTM will be
demonstrated using a new repair process and cantilever design.
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 concurrent with the normal
defect repair process. However,
known AFM scan artifacts can impact the accuracy and stability of the
photolithographic simulation results, especially for mask or pattern types which have not been previously studied by
the user. The relevant sources of these artifacts are identified and improvements in the AFM operation are
discussed which could minimize them. The quantitative relationships between the various artifact measures and
their corresponding effects on various simulation results (including relative transmission and CD) are examined for
both AIMSTM aerial imaging and wafer print. From this examination, error baselines are established and software,
as well as model setup, optimizations are proposed.
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.
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.
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.
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.
The effort to produce perfect dimension repairs of quartz bump defects on Alternating-Aperture Phase Shift Masks (AAPSM) has been brought to a new level with process developments to meet 90 nm technology node specifications. Decreasing photomask line and space dimensions pushes performance requirements for a mask repair system in terms of fine control in difficult to access structures on the mask surface. New repair strategies using a recently improved focused ion beam mask repair system for different defect types are discussed, along with their relative effectiveness. These strategies are then applied to the repair of full height extension and bridging defects in a line and space array. The role of quartz topography and its optical effects, Cr edge bias, and the combination of both strategies in a quartz bump repair are discussed. Additionally, effective process controls in repair are also discussed, along with analysis of metrology data received from a stylus nano-profilometer (SNP) system, and their relationship to potential imaging on the wafer by examination of AIMS data at a high numerical aperture. Several possible mask repair process flows are also reviewed in light of this work.
As advanced photolithography extends the ability to print feature sizes below the 100 nm technology node, various reticle enhancement techniques (RET) are being employed to improve resolution. An example of RET is the alternating phase shift mask (APSM), which currently challenges the ability of conventional repair techniques to repair even the most basic reticle defect. The phase shifting quartz bump is one defect type critical to the performance of APSM technology masks. These defects on the APSM reticle are caused by imperfections in the resist image during processing, resulting in a localized under or over etch of the quartz substrate. The integrated application of gas assisted etch (GAE), focused ion beam (FIB) reticle repair, and atomic force microscopy (AFM), provides a comprehensive solution for advanced reticle defect repair and characterization. Ion beam repair offers superior accuracy and precision for removal without significant damage to the underlying or adjacent quartz. The AFM technique provides quantitative measurement of 3D structures, including those associated with alternating phase shifters etched into quartz as well as embedded shifters. In the work presented in this paper, quartz bump defects were pre-scanned on an AFM tool and proprietary software algorithms were used to generate defect image and height map files for transfer to the FIB reticle repair tool via a network connection. The FIB tool then used these files to selectively control the ion dose during the corresponding quartz defect repair. A 193 nm APSM phase shift photomask with programmed defects in 400 nm line and space pattern was repaired using an FEI Stylus NanoProfilometer (SNP) and a FEI Accura 850 focus ion beam (FIB) tool. Using the APSM FIB repair method, the transmittance evaluated from 193 nm AIMS at the repair area was more than 90% without post-processing.
As advanced photolithography extends the ability to print feature sizes below the 100 nm technology node, various reticle enhancement techniques (RET) are being employed to improve resolution. An example of RET is the alternating phase shift mask (APSM), which currently challenges the ability of conventional repair techniques to repair even the most basic reticle defect. The phase shifting quartz bump is one defect type critical to the performance of APSM technology masks. These defects on the APSM reticle are caused by imperfections in the resist image during processing, resulting in a localized under or over etch of the quartz substrate. The integrated application of gas assisted etch (GAE), focused ion beam (FIB) reticle repair, and atomic force microscopy (AFM), provide a comprehensive solution for advanced reticle defect repair and characterization. Ion beam repair offers superior accuracy and precision for removal without significant damage to the underlying or adjacent quartz. The AFM technique provides quantitative measurement of 3D structures, including those associated with alternating phase shifters etched into quartz as well as embedded shifters. In the work presented in this paper, quartz bum defects were pre-scanned on an AFM tool and proprietary software algorithms were used to generate defect image and height map files for transfer to the FIB reticle repair tool via a network connection. The FIB tool then used these files to control selectively the ion dose during the corresponding quartz defect repair. A 193 nm APSM phase shift photomask with programmed defects in 400 nm line and space pattern was repaired using an FEI Stylus NanoProfilometer (SNP) and a FEI Accura 850 focus ion beam (FIB) tool. Using the APSM FIB repair method, the transmittance evaluated from 193 nm AIMS at the repair area was more than 90% without post-processing.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.