Lean manufacturing is a systematic method of identifying and eliminating waste. Use of Lean manufacturing techniques
at the IBM photomask manufacturing facility has increased efficiency and productivity of the photomask process. Tools,
such as, value stream mapping, 5S and structured problem solving are widely used today. In this paper we describe a
step-by-step Lean technique used to systematically decrease defects resulting in reduced material costs, inspection costs
and cycle time. The method used consists of an 8-step approach commonly referred to as the 8D problem solving
process. This process allowed us to identify both prominent issues as well as more subtle problems requiring in depth
investigation. The methodology used is flexible and can be applied to numerous situations. Advantages to Lean
methodology are also discussed.
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 [1][2][3][4]. 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.
Nancy Zhou, Monica Barrett, Robert Nolan, Dennis Plouffe, Jason Ritter, Alfred Wagner, Michael Caterer, Takashi Mizoguchi, Satoshi Akutagawa, Kevin Duong, Corbin Imai, C. Wang
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
advanced technologies.
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 [1][2][3][4]. 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 [5]. 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
effect.
Nancy Zhou, Ken Racette, David Hasselbeck, Monica Barrett, Robert Nolan, Michael Caterer, Takashi Mizoguchi, Satoshi Akutagawa, Glenn Dickey, Toru Shirasaki
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
conventional adhesive.
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.
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