ible cleaning agent, but greases will
introduce contaminants that may
reduce the performance of the seals.
Although most FFKM seals will not
absorb grease, any substance applied
to the surface of a seal will be out-gassed or leached immediately upon
use in production, contaminating the
manufacturing process.
Process Considerations
Since the gases used to clean reaction chambers between process steps
are known to degrade seals, some fab
engineers may be tempted to use different gases for reaction chambers.
NF3 has been the semiconductor
industry’s standard cleaning gas for
many years, and its corrosiveness is
one of the reasons why durable FFKM
seals have become a common choice
for use in processing equipment. But
switching to another cleaning gas
would introduce new variables to
the semiconductor manufacturing
environment, which must be closely
guarded against yield-diminishing
factors. The wide variety of available
seals puts a premium on selecting the
right combination of gases and seals
for optimal processing conditions and
maximum seal life (Figure 3).
The most inhospitable areas for
seals within reaction chambers are
found in slit valves, sometimes called
gate valves. Due to the dynamics
of the valves and actuators that are
part of gate valve and door assem-blies, seals installed in this area are
subjected to highly abrasive forces.
For example, if the valves are not
pneumatically actuated, which is the
case in older models, or if their activation pressure is set high to assure
tight gate closures, the wear on the
seals will be greater. This can result
in premature seal failures, shortened
life cycles and particulate contamination. Because wafers come in direct
contact with these seals, this area is
very sensitive to physical and chemical contaminants. To maximize a
chamber’s useful life and extend the
amount of time between preventive
maintenance stops, the FFKM seals in
slit or gate valves must be compatible
with the process gases used in that
toolset.
In the rapidly changing semicon-
ductor industry, advancements from
one technology node to the next
smaller one come quickly. Issues such
as shrinking contamination toleranc-
es, new processing materials and the
advent of new fabrication schemes
and IC architectures can each affect
which sealing solution is the best for a
given application. Selecting the opti-
mal seal becomes even more difficult
when you consider that it requires an
understanding of not only FKM and
FFKM properties, but also the fillers,
their curatives and base polymers
that go into making a semiconductor-
grade seal.
NF3 Plasma Test Results—Weight Loss
30 minutes
60 minutes
Seal type
Filler
Weight loss (%)
Weight loss (%)
Material A
Material B
BaSO
1.14%
1.90%
1.54%
1.99%
Material C
Carbon Black
0.95%
1.19%
Material D
Nano-PTFE
3.19%
6.94%
Material E
Nano-PTFE
3.33%
6.88%
Material F SiO
2
+ TiO
2
4.73% 9.67%
Material G SiO
2
+ TiO
2
5.03% 9.03%
Material H SiO
2
4.67% 8.69%
Figure 3. Repeated exposure to NF3 cleaning gases can cause different degrees of weight loss in seals, depending on their composition.
A Call for Standards
Currently, the semiconductor industry has no international standards to
define the myriad of characteristics
that describe a sealing component.
Without standards, the engineers,
equipment operators and service technicians on the fab floor are left without
the necessary guidelines for the proper
care and handling of today’s sensitive
seals. Often the only reference sources
are data sheets that come with the
products. But these can be misleading
because seals that look alike in some
ways—such as having the same color
or durometer value (a measure of elastomeric hardness)—can yield different
performances (Figure 4).
These issues have led Applied Seals
North America to reach out to the
global semiconductor industry and
promote greater education on the
variety of sealing solutions available
today. At the core of this mission is
our pledge to work with the Semi-
