Key Elements Of Vacuum Chamber Design - Owens Design

Key Elements of Vacuum
Chamber Design:
Will they all fit on a napkin or envelope??
Neil Peacock
MKS Instruments, HPS Products
Boulder Colorado
neil_peacock@mksinst.com
23 Sept 2010

Intent
This talk is to be a guide, provide food for your
thought process, when arriving at specifications
for high to ultra-high vacuum chambers.
For more in-depth treatment of vacuum
technology or practices, I urge you to consult
some of the many text books on the subject or
consider short course offered by the AVS
(American Vacuum Society) or SVC (Society of
Vacuum Coaters).
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Important Aspects of Vacuum
Technology
Containment
Production (pumps)
Measurement (gauges and RGAs)
Control (valves, fittings)
It is the containment topic that we are going to talk about
today.
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Napkin vs. Back of Envelope…
Written documentation is needed to help
insure that the chamber will meet
expectations. This documentation will help
whoever is building the chamber, as well as
during system assembly, use, maintenance
and upgrades.
The first question is what size envelope or
napkin we’ll need to scribble the
documentation on. Let’s start examining
some of what needs to be covered in that
documentation.
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One of a kind vs. Cookie-Cutter
Is the chamber for or
part of an R&D system?
– Flexible so it can be used
for many experiments
– Expandable
! In this case, it is likely
that extra money
spent upfront for
flexibility will be paid
back.
Is the chamber going to
be a production item,
with many identical ones
made?
– Requirements such as
number of ports are
constant
– Presumably cost is an
issue.
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Unknown vs. the Known
Is the process something
new, groundbreaking?
Should function, come
ahead of form? Make
design trade-offs such as
for quick delivery?
Is there history? If so,
learn what has worked, or
hasn’t worked. Is this to
be an incremental
improvement—or next
generation. What
improvements were
thought of during the
previous generation’s
commissioning, use or
upgrades?
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Get Opinions, Input from Many
Sources!
Input from many directions through out the
design and fabrication of a chamber helps to
ensure that the chamber (and the process
performed in it) meet design criteria and
expectations.
Within your facility:
• Process Gurus
• Vacuum Expert
• Users
• Fabrication, Shop and
Assembly
• Maintenance
• Firmware/automation
Outside your facility:
• Other workers in the
same field
• Manufacturers
• Chamber and hardware
• Components
• Instrumentation
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Questions to Ask
Is the chamber going to be stand alone/free
standing? How will it be supported?
Is it part or section of a larger system? Such
as a ‘pod’ on a cluster tool, or unit/module on
a serial process like solar production….
What are access requirements
– for use
– for service—which ‘sides’ and components need
access—remember pumps, valves, instruments
! Footprint allowed for working system needs to
allow for disassembly, maintenance
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More Questions to ask…
How automated will the system need to be? Level of
operator training?
How is the chamber to be loaded in use? Will there
be a loadlock?
Where in the chamber will the process occur? Is it only
in some section of the chamber—under a target say.
This may mean the need for movement/robotics to
transport the substrate. How will the substrate be
located and held? Chuck, platen?
On heavy and large chambers, is a crane needed for
installation?
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Still more Questions!
What services need to be provided
– Electrical connections, with power ratings
– Gasses
– Heating, cooling requirements
– Viewports
Wavelength
Shutter
Weight of ‘attachments’
– Do they need support?
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Safety
“A vacuum chamber is a pressure vessel waiting
to happen.”
--Joel Bowers, LLNL & AVS Instructor
For many processes, gas is admitted to the
chamber. This makes the above statement a
possibility. Some steps to take:
– Use a burst disk or some other safety device
– Design to some pressure vessel standard
– Use a direct gauge for back filling
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Additional Safety Concerns
Handling of hazardous gases or materials
Electrical service—voltage and current levels
may be transferred into to the chamber
Personnel safety, especially on large
chambers where people enter
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Interior of Alcator CMOD with
person climbing in to work.
(Courtesy of Bob Childs)
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Minimize all Gas Sources
Point of vacuum technology is to get a low
pressure, low gas density environment
Remember our basic equation: P = Q/S
Keep in mind Q is really Q total . Sources of gas
are:
– outgassing
– diffusion
– permeation
– virtual leak
– real leak
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Virtual Leaks
Material issues
Welding
– NO double welds
Trapped volumes
– O-ring grooves
– Screw threads
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Materials
Process compatibility, requirements
Vacuum compatibility
Fabrication methods available
Strength
Availability
! Be open minded on use of different alloys or
materials
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Specific Material Concerns
Chamber
– Outgassing
– Surface finish
– Durabitlity, scratch resistance
– Weight
Seal
– Metal vs. Elastomers
Lubricants
Windows
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Outgassing Rates
Material Outgassing Rate
( Torr-liters/sec-cm 2 )
Aluminum (fresh) 6.3 x 10 -9 -9
OFHC Copper (mech. polished 3.5 x 10 -9 -9
Stainless Steel
(mechanically polished) 1.7 x 10 -9 -9
(vacuum baked at 250°C for 30 hrs) 3.0 x 10 -12
Aluminum
(vacuum baked at 250°C for 15 hrs) 4.0 x 10 -13
Pyrex (fresh) 7.4 x 10 -9 -9
Neoprene 3.0 x 10 -5 -5
Polystyrene 2.0 x 10 -5 -5
Plexiglas 3.1 x 10 -6 -6
Viton A 1.1 x 10 -6 -6
PVC (24 hr at 95% RH) 8.5 x 10 -7 -7
Teflon 6.5 x 10 -8 -8
Viton A (baked) 8.0 x 10 -9 -9
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Outgassing Rates, sst
Ref: M.H. Hablanian, ‘High-VacuumTechnology:
A Practical Guide’. 2 nd nd ed. 1997, CRC
Press
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Limitations of Elastomer Seals
Elastomers such as in seals can adversely affect
the ultimate pressure of a system.
Ways in which elastomers add to the gas load
are:
– Outgassing
– Permeation
– Water dissolved in the bulk:
Reported value for Viton-A, for air 4.3 atm-cm 3 /cm 3 of
Viton (de Csernatony, VACUUM 16,129, 1966)
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Chamber with Necessary O-ring
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Outgassing Rates of Common
Elastomers
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Gas Load due to Permeation
1.00E-06
1.00E-07
Leak Indication, mbar-l/sec
1.00E-08
1.00E-09
1.00E-10
1.00E-11
0:00:00 0:02:00 0:04:00 0:06:00 0:08:00 0:10:00
Time (h : m : sec)
22% comp,Viton,140 C, 3 Oct 08 22% comp, Viton, Room T, 4 Sept 08
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Temperature Effect on
Permeation
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Fabrication Methods
Machining from billet
– Expensive
– More likely for aluminum
Assembled
– By welding plates together
– Using tubing
Casting
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Chamber Made By Casting
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Chamber from Welded Plate
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Surface Treatments
Outgassing of internal surface is important
parameter from a functional sense.
Typical Surface treatments:
–Electropolishing
Maybe done offsite
–Beadblasting
Beadblasting of most seal surfaces is ok.
–Mechanical polishing
! Specify a surface treatment for function rather
than looks.
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Electropolished Chamber
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Cleaning Processes
What is the necessary requirement for ‘clean’?
How was it determined?
Customary types of cleaning are:
– Ultrasonic washing
– Pressure washing
– Wipe down
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Packaging and Shipping
Maintain the cleanliness
until assembly.
Protect seal surfaces,
etc.
How will it be shipped?
How much protection is
needed?
Different size chambers
have different
requirements
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A LONG Trip!
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Performance and Verification
Is some chamber performance verification needed?
If so, where is the verification to be done?
– At manufacturer’s or at customer site?
What parameter is to be used?
– Ultimate pressure?
– Pumpdown time?
– RGA scan ?
! Process or result base, such as quality of a film produced—
but this is not a chamber spec!
Should be before any process is run, or gas admitted
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Leak Testing
State a reasonable leak spec
HeMSLDT is most likely leak test method
– Rate of rise is another possible method
– Acoustic methods
How is the leak testing to be performed?
– Pump chamber with leak detector port attached to
chamber and spray outside of chamber.
– Pressurize the chamber and ‘sniff’
! Leak signal response time
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Putting Chamber into Service
Perform assembly under clean conditions to
maintain cleanliness.
Consider a ‘modular assembly’ procedure to
test component performance piece wise.
Leak testing a chamber/system during
assembly may utilize different techniques.
– Use system pumping to pump/rough for HeMSLT
– RGA
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Use and Maintenance
Involve maintenance dept. during set up
Log books for operators and maintenance—
from ‘Day 1’. Log
– Performance when new
– Performance at regular intervals
– Maintenance and upgrades
– Performance after maintenance
! Record/document improvements that should be
incorporated into future builds.
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Upgrades and Expansion Down
the Road
Process Gurus always want some better
performance later…
Additional instrumentation
– Include additional ports
Pump ports
– Go up a flange size?
Perhaps a modular design approach where
some parts can be reused, or easily modified
Use metal seals up front instead of (initially)
lower cost elastomers sealed
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Tolerances
Tight tolerances cost money!
Keep all tolerances reasonable
– Linear dimensions
– Port placement
– Port angular placement
– Alignment
! In a reasonably engineered product, only some
dimensions will be critical, and therefore have tight
tolerances.
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List Details Like Port size and Use
Chamber Ports Listing
1. Port for Turbo Pump (One 10-inch)
a. 10-inch Conflat
2. Port for Load Lock (One-10 or 12-inch)
a. 12-inch Conflat (Maybe only 10-inch).
3. Ports for sputtering sources (Four 8-inch)
a. Configured in “sputter up” orientation.
b. 2 at 180°, 3 at 120° (Dual and Triplet Co focal to allow future co sputtering)
c. Nominal 25° angle with substrate normal.
d. 16-inch distance from flange to substrate center.
e. All 8-inch Conflat
4. Substrate Mechanical Connection (“Touch-Off” Port) (One, 8-inch)
a. 8-inch Conflat.
b. On deposition side of substrate
5. View Ports (One 8-inch, One 4.5-inch, Three 2.75-inch)
a. 8-inch Conflat (View substrate from side).
b. 4.5-inch Conflat (View substrate from bottom).
c. 2.75-inch Conflat (Optical Pyrometer)
i. Located on deposition side of substrate
ii. Near but not normal (allow for particle sequestration).
d. 2.75-inch Conflat (Pair for Transmission Measurement)
i. Collinear pair aligned through center of substrate. Near normal
6. Gauge Ports (Four 2.75-inch)
a. 2.75-inch Conflat. For Ionization Gauge (assess base pressure at highvacuum)
b. 2.75-inch Conflat. For convection-enhance gauge (atmospheric pressure to
10 -4 torr, used for system control)
c. 2.75-inch Conflat. For high-precision capacitance manometer (0.1-100
mtorr, used for depositon process control).
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Lots of Ports!
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The Specification should now
include:
Material information
Bill of Materials
Dimensions with reasonable tolerances
Fabrication notes and methods
Cleaning requirements
Acceptance/performance verification
Packaging information
Plan for putting chamber into service
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Don’ts in Chamber Design
Don’t Forget all the design help available
– Manufacturers
– Classes such as AVS classes
– Software
Don’t design a chamber without looking at the whole
system ‘big picture’.
– Get all inputs
– Full documentation
Don’t use unreasonable tolerances
Don’t over specify material, surface finishes
Don’t disregard input, information from your chamber
vendor
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Do’s in Chamber Design
Do use good vacuum design principles
Do choose and involve chamber vendor at an
early stage
Do Share information, needs with vendor
Do be open to give and take with the chamber
vendor. Use their knowledge and experience.
Do keep vendor in the loop as the chamber is
put into service
! We like feedback from our customers. It helps
the next one.
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Napkin vs. Envelope…
A full ‘packet’ of documentation is needed. This will
cover issues from the thinking stage to use of the
system/chamber. Information will be helpful for both
your facility as well as vendors in the project, such as
MKS’ Chamber Facility.
A full chamber design will not fit on a napkin or an
envelope!
very – (unless you write very very small, or the envelope is big).
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Acknowledgments
Thank you for your interest in the presentation.
If you have questions, current or future
chamber needs, please contact us.
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