According to the ITRS Roadmap, the EUV mask requirement for 2X nm technology node is detection of defect size of
20 nm. The history of optical mask inspection tools involves continuous efforts to realize higher resolution and higher
throughput. In terms of productivity, considering resolution, throughput and cost, we studied the capability of EUV light
inspection and Electron Beam (EB) inspection, using Scanning Electron Microscope (SEM), including prolongation of
the conventional optical inspection. As a result of our study, the solution we propose is EB inspection using Projection
Electron Microscope (PEM) technique and an image acquisition technique to acquire inspection images with Time Delay
Integration (TDI) sensor while the stage is continually moving. We have developed an EUV mask inspection tool,
EBeyeM, whole design concept includes these techniques. EBeyeM for 2X nm technology node has the following targets,
for inspection sensitivity, defects whose size is 20 nm must be detected and, for throughput, inspection time for particle
and pattern inspection mode must be less than 2 hours and 13 hours in 100 mm square, respectively. Performance of the
proto-type EBeyeM was reported. EBeyeM for 2X nm technology node was remodeled in light of the correlation
between Signal to Noise Ratio (SNR) and defect sensitivity for the proto-type EBeyeM. The principal remodeling points
were increase of the number of incident electrons to TDI sensor by increasing beam current for illuminating optics and
realization of smaller pixel size for imaging optics.
This report presents the performance of the remodeled EBeyeM (=EBeyeM for 2X nm) and compares it with that of the
proto-type EBeyeM. Performances of image quality, inspection sensitivity and throughput reveal that the EBeyeM for
2X nm is improved. The current performance of the EBeyeM for 2X nm is inspection sensitivity of 20 nm order for both
pattern and particle inspection mode, and throughput is 2 hours in 100 mm square for particle inspection mode.

Performance of EBeyeM for EUV mask inspection

We are developing new electron beam inspection system, named EBeyeM, which features high speed and high
resolution inspection for EUV mask. Because EBeyeM has the projection electron microscope technique, the scan time
of EBeyeM is much faster than that of conventional SEM inspection system.
We developed prototype of EBeyeM. The aim of prototype system is to prove the concept of EBeyeM and to estimate
the specification of system for 2Xnm and 1Xnm EUV mask.
In this paper, we describe outline of EBeyeM and performance results of the prototype system. This system has two
inspection mode. One is particle inspection and the other is pattern defect inspection. As to the sensitivity of EBeyeM
prototype system, the development target is 30nm for the particle inspection mode and 50nm for pattern defect
inspection mode. The performance of this system was evaluated. We confirmed the particle inspection mode of the
prototype system could detect 30nm PSL(Polystyrene Latex) and the sensitivity was much higher than conventional
optical blank inspection system. And we confirmed that the pattern defect sensitivity of the prototype system was
around 45nm. It was recognized that both particle inspection mode and pattern defect inspection mode met the
development target. It was estimated by the performance results of the prototype system that the specification of
EBeyeM would be able to achieve for 2Xnm EUV mask. As to 1Xnm EUV mask, we are considering tool concept to
meet the specification.

Development of EB inspection system EBeyeM for EUV mask

The industry is transitioning EUV lithography from feasibility phase to technology development. EUV mask infrastructure needs to be prepared to support the technology development and ready to enable the implementation of EUV lithography for production. In this paper, we review the current status and assess the readiness of key infrastructure modules in EUV mask fabrication, inspection and control, and usage in a mask cycle: blank quality and inspection, pattern inspection, defect disposition and repair, pellicle integration, and handling of pelliclized masks.

EUV mask infrastructure readiness and gaps for TD and HVM

In order to realize EUV mask pattern defect inspection in 16nm node, we have developed new optics on a novel
projection electron microscopy (PEM) and a new inspection system with the new optics and a new mask handling and
imaging units, e.g., a high precision stage, an imaging detector, an imaging processing system, and so. on. This
inspection system enables us to make the inspection in high resolution and high speed as compared with conventional
DUV and EB inspection systems. The new optics on the novel PEM comprises an exposure and an imaging electron
beam optics (EOs). The optics is based on the new design concept to meet the required progress for 1Xnm EUV mask
inspection as compared to the current inspection system for 2Xnm node; The concept employs new techniques to
achieve the features: high energetic electron imaging optics to have low aberration, high transmittance efficiency, e.g.,
on the ratio of exposure current/emitted current, in the exposure and the imaging optics, respectively. The new handling
and imaging system are also based on the design concept of imaging in high resolution by combination operation among
the new optics on the novel PEM, the stage, and the detector. In this paper, we describe the basic performance evaluation
as concerning these features and the operation: 1) MTF inclination in hp44~100nm L/S pattern of the developed
imaging optics. 2) Secondary electron imaging by the integrated optics, i.e., both of the exposure and the imaging EOs,
on the novel PEM, 3) Secondary electron image acquisition operation in still mode on the new inspection system
assembled with the new optics on the novel PEM, the high precision stage, the detector, and so. on.. The results show the
new optics on the novel PEM is capable to meet the required progress for 1Xnm EUV mask inspection and the new
inspection system with the novel PEM operates in much feasibility in the electron image acquisition.

Development of inspection system for EUV mask with novel projection electron microscopy (PEM)

Photomask and Next-Generation Lithography Mask Technology XVII

Ever since the 180nm technology node the semiconductor industry has been battling the sub-wavelength regime in
optical lithography. During the same time development for a 13.5nm Extreme Ultraviolet [EUV] solution has been in
development, which would take us back from a λ/10 to a >λ regime again - at least for one node. Add to this the
potential to increase the wafer size as well, and we are at a major crossroads.
The introduction of EUV has been marred by many delays, but we are finally seeing the hardware development efforts
converge and multiple customers around the world embarking on this adventure. As it becomes clear that this preproduction
phase will occur at or below 20nmHP, it also becomes clear that this will happen at the limiting edge of
existing 19x-based patterned mask inspection technology, reaching the practical resolution limits at around 20nm HP
mask densities. Resolution is coupled with sensitivity and throughput such that the extended sensitivity may come at an
unreasonable throughput. Loss of resolution also badly impacts defect dispositioning, or classification, which becomes
impractical. As resolution is especially critical for die to database inspection, single die masks and masks with high flare
bias are at risk of not being inspectable with 19xnm based inspectors.
E-Beam based mask inspection has been proposed and demonstrated as a viable technology for patterned EUV mask
inspection. In this paper, we study the key questions of sensitivity and throughput, in both die-to-die and die-to-database
applications. We present new results, based on a new generation of E-Beam inspection technology, which has a higher
data rate at smaller spot sizes. We will demonstrate the feasibility of acceptable inspection time with EBMI. We also will
discuss die-to-data-base inspection and the advantage of using E-Beam imaging for meeting future requirements of
single- die EUV masks.

Applicability of e-beam mask inspection to EUV mask production

EUV lithography is regarded as the leading technology solution for the post-ArF era. Significant progress was made in
recent years in closing the gaps related to scanner technology. This progress rendered EUV mask defectivity and related
infrastructure as the primary risk for EUV lithography.
The smallness of mask features, the novel defectivity mechanisms associated with the multilayer reflecting coating, and
the stringent constraints on both multilayer and pattern imposed by the EUV wavelength - present a major challenge to
current inspection technology, which constitutes a predominant gap to EUVL production-worthiness.
Here we present results from an evaluation of a DUV mask inspection system and e-beam mask inspection technology
on EUV masks. On this 193nm DUV system, we studied sensitivity and contrast enhancements by resolution
enhancement techniques. We studied both pattern and blank inspection. Next, we studied image formation and
performance of e-beam mask inspection technology for patterned mask defects. We discuss the advantages and roadmap
of DUV and EBI mask inspection solutions for blank and patterned masks.

Evaluation of novel EUV mask inspection technologies

While EUV lithography is approaching the pre-production stage, improving mask defectivity is recognized as a top
challenge. The accepted strategy for EUV reticle qualification is to use a combination of a dedicated blank inspection
(BI) to visualize EUV-specific multi-layer (ML) defects and patterned-mask inspection (PMI) that must be capable to
meet the resolution requirements of the pattern. Actinic inspection is considered the strongest option for the blank
inspection because of the limitation of optical light to visualize the nm-high distortions within the ML. Earlier
publications showed that wafer inspection (WI) can potentially reveal such mask defects, This is, however, too late
within the process. In addition, existing PMI and wafer inspection approaches exhibit limitations in detection capability
and gaps are observed between detection of printed defects and defects detected on the mask (and the blank).
We compare existing inspection solutions for detection of EUV mask defects (193nm based mask inspection and
repeater analysis in a DUV wafer inspection) and present a feasibility study for use of a fast e-beam technology for mask
inspection. Finally, we discuss the prospects of existing DUV tools and future e-beam technology to support EUV reticle
inspection for current and future nodes.

EUV mask defectivity study by existing DUV tools and new E-beam technology

Extreme ultraviolet (EUV) e-beam patterned mask inspection (EBPMI) has been proposed by Applied Materials as a
cost-effective solution for high volume manufacturing (HVM) in mask shops and fabs. Electron beam inspection
technology is currently available for wafers. A recent publication described a successful sensitivity study of EUVs mask
using a technology demonstration platform. Here we present a new study using extreme e-beam conditions to show the
feasibility of using EBPMI in HVM. We examine potential changes in the reflectivity at the EUV wavelength after
exposure to high e-beam currents, demonstrating that reflectivity does not change due to e-beam scanning. We therefore
conclude that under the conditions tested, which include typical as well as extreme conditions, there is no evidence of
mask damage.

Ran Brikman

Papers

Applicability of e-beam mask inspection to EUV mask production

Evaluation of novel EUV mask inspection technologies

EUV mask defectivity study by existing DUV tools and new E-beam technology

Study of EUV mask e-beam inspection conditions for HVM