The lithography challenges posed by the 20 nm and 14 nm nodes continue to place strict minimum feature size
requirements on photomasks. The wide spread adoption of very aggressive Optical Proximity Correction (OPC) and
computational lithography techniques that are needed to maximize the lithographic process window at 20 nm and 14 nm
groundrules has increased the need for sub-resolution assist features (SRAFs) down to 50 nm on the mask. In addition,
the recent industry trend of migrating to use of negative tone develop and other tone inversion techniques on wafer in
order to use bright field masks with better lithography process window is requiring mask makers to reduce the minimum
feature size of opaque features on the reticle such as opaque SRAFs. Due to e-beam write time and pattern fidelity
requirements, the increased use of bright field masks means that mask makers must focus on improving the resolution of
their negative tone chemically amplified resist (NCAR) process.
In this paper we will describe the development and characterization of a high resolution bright field mask process that is
suitable for meeting 20 nm and early 14 nm optical lithography requirements. Work to develop and optimize use of an
improved chrome hard mask material on the thin OMOG binary mask blank1 in order to resolve smaller feature sizes on
the mask will be described. The improved dry etching characteristics of the new chrome hard mask material enabled the
use of a very thin (down to 65 nm) NCAR resist. A comparison of the minimum feature size, linearity, and through pitch
performance of different NCAR resist thicknesses will also be described. It was found that the combination of the
improved mask blank and thinner NCAR could allow achievement of 50 nm opaque SRAFs on the final mask.. In
addition, comparisons of the minimum feature size performance of different NCAR resist materials will be shown. A
description of the optimized cleaning processes and cleaning durability of the 50 nm opaque SRAFs will be provided.
Furthermore, the defect inspection results of the new high resolution mask process and substrate will be shared.
The lithography challenges posed by the 22 nm node continue to place stringent requirements on photomasks.
The dimensions of the mask features continue to shrink more deeply into the sub-wavelength scale. In this
regime residual mask electromagnetic field (EMF) effects due to mask topography can degrade the imaging
performance of critical mask patterns by degrading the common lithography process window and by magnifying
the impact of mask errors or MEEF. Based on this, an effort to reduce the mask topography effect by
decreasing the thickness of the mask absorber was conducted. In this paper, we will describe the results of our
effort to develop and characterize a binary mask substrate with an absorber that is approximately 20-25% thinner
than the absorber on the current Opaque MoSi on Glass (OMOG) binary mask substrate.
For expediency, the thin absorber development effort focused on using existing absorber materials and deposition
methods. It was found that significant changes in film composition and structure were needed to obtain a
substantially thinner blank while maintaining an optical density of 3.0 at 193 nm. Consequently, numerous
studies to assess the mask making performance of the thinner absorber material were required and will be
described. During these studies several significant mask making advantages of the thin absorber were
discovered. The lower film stress and thickness of the new absorber resulted in improved mask flatness and up
to a 60% reduction in process-induced mask pattern placement change. Improved cleaning durability was
another benefit. Furthermore, the improved EMF performance of the thinner absorber  was found to have the
potential to relieve mask manufacturing constraints on minimum opaque assist feature size and opaque corner to
Based on the results of evaluations performed to date, the thinner absorber has been found to be suitable for use
for fabricating masks for the 22 nm node and beyond.
Photomask flatness and image placement specifications for advanced technology masks are becoming more
stringent. Therefore, it is important to understand the various factors that affect final photomask flatness due
to the direct impact it has on image placement. Past studies have demonstrated that final photomask flatness
can be controlled by modifying the mounting process of photomask pellicle as well as changing the pellicle
material itself . In particular, our previous results demonstrate the ability to successfully eliminate
data deviations by remounting the same pellicle for each experiment. This paper focuses on the relationship
between mounting pressure and time on final photomask flatness. Our initial results indicate that mounting
time has minimal influence on final photomask flatness; however, final photomask flatness is greatly
impacted by varying mounting pressure. Finally we explore the relationship between the final photomask
flatness and the image placement for post pellicle mounting onto the photomask.
With the advancement of technology, the need to produce flatter photomasks is critical to
meet strict mask manufacturing requirements. Components such as pellicle mounting
techniques, pellicle frame height, frame material and adhesive all play an important role
in finished photomask flatness.1-5 In particular, recent studies have shown that adhesive
flexibility affect final photomask flatness significantly.6 This has motivated pellicle
suppliers to optimize adhesive properties in addition to evaluate new adhesives.
The paper describes the joint evaluations between IBM, Toppan and MLI, performed to
determine the effect of a new MLI adhesive on the distortion of photomasks. Due to the
nature of this adhesive, minimal mounting force is required. As a result of utilizing
extreme low mounting pressure, benefits such as decreased flatness distortion and ease of
adhesive removal are observed. The goal of this paper is to evaluate this new adhesive
offering and understand the various impacts it has on pelliclized photomasks for
Previous work has shown that photomask blank flatness as well as photomask patterning and pelliclization all play an
important role in finished photomask flatness. Additional studies have shown that pellicle mounting techniques,
pellicle adhesives, frame flatness and shape and pellicle mounting tools play a role as well. It has become clear that
frame flexibility, coupled with frame mounting surface flatness and shape are the principal factors influencing the
pellicle effect on the mask distortion. Pellicle suppliers have begun to evaluate various polymers as potential
replacements for the standard aluminum frame in current use. The elasticity of the frame adhesive has also been adjusted
to evaluate its effect on the pellicle influence on mask flatness.
This paper describes some joint evaluations between IBM, Toppan and ShinEtsu, performed to determine the effect of
pellicle frame composition,, mount surface flatness, adhesive elasticity and adhesive surface flatness on the distortion of
photolithography masks. It demonstrates that polymer pellicle frames with more flexible adhesive improve finished
mask flatness approximately the same amount as reducing the total frame standoff height of aluminum frames with
As technology advances, the demand for tighter photomask final flatness specifications becomes greater. Studies have
shown that the process of mounting a pellicle induces the largest change in flatness in photomask fabrication. Photomask
pellicles play an important role in flatness due to the many components in the mounting process. For example, pellicle
frame flatness, pellicle adhesive, mounting force, mounting time, mounting orientation and mask backing shape during
mount all can play a role in changing the mask shape during pellicle mount. Many of these factors have been
investigated over the last several years . Recent studies have demonstrated that the height of the pellicle
frame also has a significant impact on the final flatness with lower stand off frames resulting in reduced pellicle
influence on mask distortion . This paper will examine the flatness influence factor as a function of mounting
direction and mask backing variations. For these experiments, the same pellicle frame was remounted for each set of
experiments to eliminate external pellicle frame flatness factors and to minimize the amount of data deviations. Four
different types of mask backing types were selected that differed in the contact area with the mask in particular pressure
points. The mask backing types consist of a border frame, 4 point pressure points, a full backing plate (quartz substrate),
and a pellicle frame. In addition to using the four different types of mask backings, the pellicles were also mounted both
in the vertical and horizontal directions in determining final photomask flatness. This work demonstrates that frame
flatness and shape play the largest roles and mounting force, backing plate and mounting orientation have less of an
Advanced immersion lithography utilizes higher numerical aperture (NA) stepper lenses resulting in higher angles of
light illumination through photomasks. Transmission in conventional pellicles (830 nm thickness) is generally
maximized at 0 degree illumination and decreases significantly at the higher angles. Most pellicle suppliers have
developed thinner pellicle membranes (~280 nm) which allow considerably improved transmission of light at angles up
to 20 degrees. In addition, aluminum frames have been shortened, potentially allowing inspection closer to the inside of
the frame and reduced mask flatness distortion upon pellicle mount. Suppliers have also developed advanced adhesives
which reduce outgassing even beyond the low levels obtained with current 45 nm pellicles. In this paper, advanced
immersion pellicles from several suppliers are evaluated and compared with conventional 45 nm pellicles for the
following quality parameters: physical durability, foreign material, ease of demounting and glue removal, chemical
outgassing, mask flatness distortion and susceptibility to radiation damage. Improvements in mask inspection and
pellicle optical transmission at higher incident angles are also evaluated and are discussed.
As the required accuracy of the mask arises, Cr shading film thickness has been thinner gradually. CD linearity with
the thinner Cr film thickness has better performance. However, it is difficult to apply thinner Cr film thickness simply
under the condition of OD > 3, which is needed for wafer printing. So, we tried to develop new shading film. We adopted
MoSi film, because MoSi film has almost no micro loading effect compared with Cr film. MoSi shading film with
att.PSM satisfied OD > 3 at 193nm wavelength with good resist profile. But the issue was dry-etching selectivity, because
shading layer material was the same of att. PSM layer material. Therefore super thin Cr etching stopper was inserted
between MoSi shading layer and MoSi att.PSM layer.
The mask CD performance of new blank was evaluated for CD linearity, CD through pitch, and global loading effect.
This blank and mask process reduce loading effect, therefore the mask CD performance is improved remarkably. In
conclusion, the mask manufacturing process margin was able to be expanded by this new blank and method, and it is
expected that we can achieve the required specifications for att.PSM in 45nm node and beyond.
The attenuated phase-shift mask (att. PSM) is one of resolution enhancement technologies (RET) and has been
widely adopted for several device layers. And the high-transmission att. PSM, which has various structures and
transmittances, can be expected to have the advantages in process window. In this paper, the lithographic performances
(Contrast, MEEF and DOF) of high-T att. PSM were evaluated by using the 3D electro-magnetic field simulator. The
results showed that high-T att. PSM has better MEEF and partially better DOF than those of 6%-transmission MoSi
type. As the transmittance is getting higher, the smaller line CD is needed for OPC adjustment especially at narrow
pitch. In respect of film structure, it is found that there is no large difference among three high-T att. PSMs except for
MEEF at specific pitch. Remaining chrome on the high-T films causes the trade-off between contrast and MEEF. The
simulation results are compared with AIMS results measured by AIMSTM 45-193i of Carl Zeiss. The AIMS results of
actual masks agree with no-Hopkins mode simulation very well, while they do not agree with Hopkins mode simulation
especially at narrow pitch. Because the azimuthal polarization does not cause contrast loss, the differences between
AIMS mode (conventional) and Scanner mode (vector effect emulation) are small.
The immersion lithography for 45 nm generation has been developing aggressively for smaller critical dimension of semiconductor devices. The polarization lithography system is indispensable to have an advantage to use the immersion lithography with hyper NA (>1.0). As pattern size becomes smaller, mask induced polarization effects to polarization of exposure image seems not to be negligible. There are several issues about mask induced polarization. But dominant factor for mask induced polarization effect is not understood well.
In this paper, in case of monolayer mask of att.PSM, degree of polarization (DoP) strongly depends on film thickness and extinction coefficient from simulation and experimental results. DoP depends on material factor. And in case of double layer mask, DoP depends on total film thickness and extinction coefficient of both upper layer and bottom layer. So, DoP depends also on structure of mask.