Industry roadmaps indicate that the introduction of Extreme Ultraviolet Lithography (EUVL) is on track for high volume
manufacturing. Although, there has been significant progress in each of the individual subsets of the EUVL
infrastructure, the absolute management of the process outside of the scanner and up to the point-of-exposure has been
highlighted as critical requirement for the adoption of EUVL. Significant changes in the EUV system environment and
mask architecture are driving a zero process tolerance level. Any unforeseen contamination introduced to the scanner
environment from the EUV mask could cause considerable downtime and yield loss. Absolute mask integrity at the
point-of-exposure must be guaranteed.
EUV mask cleaning processes-of-record have been developed and introduced to the industry . The issue is not longer
"how to clean the mask" but, "how to keep it clean". With the introduction of EUVL, mask cleanliness extends out
beyond the traditional mask cleaning tool. Complete control of contamination and/or particles during transportation,
handling and storage will require a holistic approach to mask management. A new environment specifically for EUV
mask integrity must be developed and fully tested for the sub 16nm half-pitch node introduction.
The SUSS MaskTrack® Pro (MTP) InSync was introduced as the solution for EUV mask integrity. SUSS demonstrated
the fully automated handling of EUV masks into and out of a Dual Pod System . Intrinsic cleanliness of each
individual handling and storage step of the inner pod (EIP) and EUV mask inside the MTP InSync Tool was investigated
and reported. A target specification of a PRP ≤ 0.08 as criterion for the cross contamination between EIP and the EUV
reticle during handling within MTP InSync has been achieved and therefore proofing the applicability for the Dual Pod
Moreover an appropriate automated handling, other aspects like backside particle contamination and EIP cleanliness
plays a significant role to ensure EUV mask integrity.
With this concept in mind a system for particle detection has been integrated into MTP InSync. This allows verifying the
POR performance for backside cleaning by measuring particles down to 150nm size. A dynamic capture rate of larger
97% at 200nm particle size based on PSLs was achieved; for EIP cleaning, a dry-cleaning technology is under
investigation. During feasibility studies high particle removal efficiency (PRE) results larger 99% has been achieved for
particles down to 100nm.
In this paper, the full scope and roadmap of the MTP InSync will be discussed. Preliminary results of backside particle
detection and challenges on EUV Inner Pod (EIP) cleaning will be presented.
This paper focuses on imec's activities to minimize particle contamination on reticles (front- and backside) for the latest
EUVL scanner, i.e. the NXE3100. Mask cleaning is performed on the HamaTech MaskTrack Pro® (MTP). Although
also front-side particles and other contamination are being tackled by cleaning, the prime purpose is the avoidance of
back-side particles which would lead to unacceptable overlay performance of the scanner and hence create yield loss, as
well as cause unscheduled scanner down situations for cleaning of the reticle clamp.
In the absence of a soft pellicle, the present approach to minimize particle adders during handling is to load EUV reticles
into the scanner via so-called dual pods. The inner pod as such acts as a removable hard pellicle. Through the installation
of the HamaTech MaskTrack Pro InSync® tool, interfaced to the MaskTrack Pro Cleaner, automated handling of EUV
reticles in such pods is enabled. This integrated solution for handling and storage is additionally being equipped with an
integrated reticle back-side inspection capability.
Extreme Ultraviolet Lithography (EUVL) is the most promising solution for technology nodes 16nm (hp) and below.
However, several unique EUV mask challenges must be resolved for a successful launch of the technology into the
market. Uncontrolled introduction of particles and/or contamination into the EUV scanner significantly increases the risk
for device yield loss and potentially scanner down-time. With the absence of a pellicle to protect the surface of the EUV
mask, a zero particle adder regime between final clean and the point-of-exposure is critical for the active areas of the
mask. A Dual Pod concept for handling EUV masks had been proposed by the industry as means to minimize the risk of
mask contamination during transport and storage.
SuSS-HamaTech introduces MaskTrackPro InSync as a fully automated solution for the handling of EUV masks in and
out of this Dual Pod System and therefore constitutes an interface between various tools inside the Fab. The intrinsic
cleanliness of each individual handling and storage step of the inner shell (EIP) of this Dual Pod and the EUV mask
inside the InSync Tool has been investigated to confirm the capability for minimizing the risk of cross-contamination.
An Entegris Dual Pod EUV-1000A-A110 has been used for the qualification. The particle detection for the qualification
procedure was executed with the TNO's RapidNano Particle Scanner, qualified for particle sizes down to 50nm (PSL
It has been shown that the target specification of < 2 particles @ 60nm per 25 cycles has been achieved. In case where
added particles were measured, the EIP has been identified as a potential root cause for Ni particle generation. Any direct
Ni-Al contact has to be avoided to mitigate the risk of material abrasion.
Before new equipment for handling of EUV reticles can be used, it should be shown that the apparatus is qualified for
operating at a sufficiently clean level. TNO developed a qualification procedure that is separated into two parts: reticle
handling and transport qualification and the qualification of the equipment. A statistical method was developed to include
the results of the handling and transport qualification into the qualification criterion for the equipment. As a result we are
able to calculate the minimum required experimental effort to prove that the particle contamination levels of the
equipment are within the requirements. The qualification procedure was applied to the TNO EUV reticle load port
module of the HamaTech MaskTrack Pro cleaning tool.
A Particle per Reticle Pass (PRP) between 0.005 and 0.076 for particles ≥ 80nm was measured for the reticle load port
module including handling and transport contribution. However, a high number of particles were found in the transport
test. As a result a much higher number of repeat cycles (more than a factor 6) were required to reduce the confidence
interval. Therefore, elimination of the transport step is absolutely required for a good qualification procedure. This can
be obtained by placing the inspection tool close to the equipment to be qualified. In this way, the required experimental
effort can be reduced significantly, saving both machine time and costs.