Since the introduction of 248 and 193 nm lithography sub-pellicle contamination has been a significant problem and a
major contributor to reticle costs and semiconductor yield losses. The most common contaminant identified has been
ammonium sulfate commonly called haze, however there have been many other contaminants identified and grouped in
the category as haze. In attempts to mitigate the cause of this problem various processes and manufacturing protocols
have been put in place to either prevent the problem or identify the source of the problem before there is a negative
impact in the wafer fab. In spite of efforts to manage the effects of sub-pellicle contamination in the wafer fab, the
problem continues to exist. Over the years we have identified many of the compounds and their sources that exist on the
sub-pellicle surface, however one has been elusive. This paper will provide both the identification of this compound and
The technology to selectively remove nanoparticles from a photomask surface by adhering it to an AFM tip
(BitClean) first introduced with the Merlin<sup>®</sup> 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
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
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
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 (BitClean<sup>TM</sup>) has been developed using the Merlin<sup>TM</sup> 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 NanoBit<sup>TM</sup> (PRE<sub>PP</sub>), and the resultant average removal throughput of particles unaffected by any other available
mask clean process.
Recently questions have been raised about whether high aspect ratio (HAR) NanoBits<sup>TM</sup> can be effectively utilized to
repair extension defects in 45 nm node and beyond. The primary concern has been how the effect of NanoBit<sup>TM</sup>
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 NanoBit<sup>TM</sup> 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 NanoBits<sup>TM</sup> 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 NanoBits<sup>TM</sup> will be
demonstrated using a new repair process and cantilever design.
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.