Key Elements of Vacuum Chamber Design: Will they all fit on a napkin or envelope??

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2 Key Elements of Vacuum Chamber Design: Will they all fit on a napkin or envelope?? Neil Peacock MKS Instruments, HPS Products Boulder Colorado [email protected] 23 Sept 2010

3 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). MKS Confidential 3

4 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. MKS Confidential 4

5 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. MKS Confidential 5

6 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. MKS Confidential 6

7 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? MKS Confidential 7

8 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 MKS Confidential 8

9 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 MKS Confidential 9

10 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? MKS Confidential 10

11 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? MKS Confidential 11

12 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 MKS Confidential 12

13 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 MKS Confidential 13

14 Interior of Alcator CMOD with person climbing in to work. (Courtesy of Bob Childs) MKS Confidential 14

15 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 MKS Confidential 15

16 Virtual Leaks Material issues Welding NO double welds Trapped volumes O-ring grooves Screw threads MKS Confidential 16

17 Materials Process compatibility, requirements Vacuum compatibility Fabrication methods available Strength Availability! Be open minded on use of different alloys or materials MKS Confidential 17

18 Specific Material Concerns Chamber Outgassing Surface finish Durabitlity, scratch resistance Weight Seal Metal vs. Elastomers Lubricants Windows MKS Confidential 18

19 Outgassing Rates Material Outgassing Rate ( Torr-liters/sec-cm 2 ) Aluminum (fresh) 6.3 x OFHC Copper (mech. polished 3.5 x Stainless Steel (mechanically polished) 1.7 x (vacuum baked at 250 C for 30 hrs) 3.0 x Aluminum (vacuum baked at 250 C for 15 hrs) 4.0 x Pyrex (fresh) 7.4 x Neoprene 3.0 x Polystyrene 2.0 x Plexiglas 3.1 x Viton A 1.1 x PVC (24 hr at 95% RH) 8.5 x Teflon 6.5 x Viton A (baked) 8.0 x MKS Confidential 19

20 Outgassing Rates, sst Ref: M.H. Hablanian, High-VacuumTechnology: A Practical Guide. 2 nd nd ed. 1997, CRC Press MKS Confidential 20

21 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) MKS Confidential 21

22 Chamber with Necessary O-ring MKS Confidential 22

23 Outgassing Rates of Common Elastomers MKS Confidential 23

24 Gas Load due to Permeation 1.00E E-07 Leak Indication, mbar-l/sec 1.00E E E E-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 MKS Confidential 24

25 Temperature Effect on Permeation MKS Confidential 25

26 Fabrication Methods Machining from billet Expensive More likely for aluminum Assembled By welding plates together Using tubing Casting MKS Confidential 26

27 Chamber Made By Casting MKS Confidential 27

28 Chamber from Welded Plate MKS Confidential 28

29 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. MKS Confidential 29

30 Electropolished Chamber MKS Confidential 30

31 Cleaning Processes What is the necessary requirement for clean? How was it determined? Customary types of cleaning are: Ultrasonic washing Pressure washing Wipe down MKS Confidential 31

32 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 MKS Confidential 32

33 A LONG Trip! MKS Confidential 33

34 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 MKS Confidential 34

35 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 MKS Confidential 35

36 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 MKS Confidential 36

37 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. MKS Confidential 37

38 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 MKS Confidential 38

39 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. MKS Confidential 39

40 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 inch Conflat (Optical Pyrometer) i. Located on deposition side of substrate ii. Near but not normal (allow for particle sequestration). d inch Conflat (Pair for Transmission Measurement) i. Collinear pair aligned through center of substrate. Near normal 6. Gauge Ports (Four 2.75-inch) a inch Conflat. For Ionization Gauge (assess base pressure at highvacuum) b inch Conflat. For convection-enhance gauge (atmospheric pressure to 10-4 torr, used for system control) c inch Conflat. For high-precision capacitance manometer ( mtorr, used for depositon process control). MKS Confidential 40

41 Lots of Ports! MKS Confidential 41

42 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 MKS Confidential 42

43 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 MKS Confidential 43

44 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. MKS Confidential 44

45 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). MKS Confidential 45

46 Acknowledgments Thank you for your interest in the presentation. If you have questions, current or future chamber needs, please contact us. MKS Confidential 46