High and Ultra High Vacuum Systems - …

1 high and Ultra high Vacuum SystemsPresented by: Chad Folkman & Scott RutherfordOverviewzHigh VacuumzConcernszPumps zQuick SolutionszUltra high VacuumzConcerns zGas BehaviorzCleaning and HandlingzPump AdjustmentszGaugeszExercisesHigh Vacuum SystemszPressure range z10-6to 10-8torrzApplicationszElectronic Devices zDepositions (sputtering, evaporation, pulsed laser)zPlasma EtchingzIon ImplantationszNon-surface material characterization (EDS, SEM, ) high Vacuum SystemszPumping Options zDiffusion zTurbomolecularzIonzCryogeninczMajor ConcernszOutgassing (major concern water contamination)zSmall leakszHow can we solve these problems???zCombine and optimize various portions of the classzChoose pump to meet desired needszHe leak detectionzMinimize outgassingCold Traps Prevents back streaming of oil from diffusion pump when cold traps run out of liquid nitrogen, with no loss in conductance.

2 Fill the 2" cold trap with 3 liters of liquid nitrogen in the morning and run all day without refilling. Introduce a cold trap into your system: high Vacuum Systems Wrap-UpzOutgassing is primary source of gas loadzDiffusion and permeation are a small part of the total gas gauges can be used in HV effectively from cold traps, filterszHigh grade oil where neededzNo single right answerzUse a system that meets your needsUHV - SystemszModern ApplicationszFundamental Particle StudieszFabrication of Magnetic Read/Write HeadszNumerous Semiconductor ProcesseszOpto-Electronic Device ProcessingzMaterial Surface CharacterizationUltra Highor Ultra CleanVacuum Systems ?

3 UHV - SystemsPressure (Torr)Mean Free Path (cm)Monolayer Formation time (sec) (160 feet) (31 miles) (37 min) Ultra (very long) ( days)Defining a Ultra high VacuumUHV - SystemsMajor Concerns:zOutgassing, Permeation and DiffusionzUltra clean surfaceszIncorrect data read out (gauges?)zPump type and usagezProcess feed throughs (electrical, translational, )Low high (N2, O2)80% H2O(g)20% N2, H2, CO2H2 Gas ConstituentsUHV Outgassing, Permeation and DiffusionTimePressure (Torr)1031010-310-610-9 VolumeOutgas/desorptionDiffusionPermeati onGas Load Limiting PumpdownOutgassing Load:Gases originate at surfacesPermeation Load:Gases originate outside of vesselDiffusion Load:Gases originate inside of vessel wallsUHV Outgassing MaterialOutgas Rate (Torr L/s cm^2)UHV OK ?

4 Brass10-6-10-7 NoStainless Steel10-8 10-13 YesCopper10-9 10-12 YesPolymers10-5-10-7 NoAluminum10-8-10-13 YesOutgassing Rate (q):Qoutgas= qoutgas*Area Factors Include: Material Surface treatments Temperature - DiffusionzGas load contributions by diffusion are similar to permeation however the gaseous species are present intrinsically to the Vacuum coefficient is a function of = Do*exp(-Ea/kBT) Case Study:While processing steel, H2impurities sit on the interstitial sites in the Fe lattice. Baking above 400 C will drive H2towards the walls of the chamber. -Iron BCC Latticewith H2 InterstitialUHV PermeationzDependent on type of gas and :zStainless Steels - higher permeation rates with higher carbon contentzCopper - low permeation rates for all gaseszPolymers - permeable to all gasesCase Study:H2has a high solubility in most metals and is thought to permeatethrough the walls of the chamber.

5 Decrease permeation by choosing different Ultra Clean SurfacesMotivation:Assure low outgassing of material under :Bead BlastingUltrasonicGlow Discharge (top right)ElectropolishingReactive Gas CleanChemical (Acid and Alkaline)Rough AbrasivesUHV Ultra Clean SurfaceszBaking OptionszTemporary Heat EnclosurezTemperatures up to or exceeding 400 oCzVacuum Oven (right)zTemperatures of up to 900 oCUHV Ultra Clean SurfacesCleaning method for 300 series stainless(Brookhaven National Laboratory)1. Degrease with ultrasonic agitation2. Hot alkaline pH 11 wash with air agitation3. Rinse cold tap water4. Rinse DI water with air agitation5. Dry in hot air oven6.

6 Vacuum bake at 950 C for 2h 7. Glow discharge clean8. Reactive gas cleanUHV Material HandlingCleaned Parts can be RecontaminatedzUnpowdered latex gloveszWrap in lint free-paper or wax-free aluminum foilzCertification for clean room useExample WCAM: Class 100<100 Particles/ft3 Particle: Dust, Air Borne Moisture, Killer Particles UHV - PumpsTurbo Pump Adjustments:zMust bake a minimum of 100 oC to get rid of water vaporzMust be magnetically levitatedzTwo in series will increase the compression ratio of H2zOil free scroll pump should be used for backingzLower limit of 10-9torr at best, will need a capture and/or cyropump to get lowerBackstreaming not acceptablefor pressure below 10-9 TorrUHV - PumpsCryopump Adjustments.

7 ZCannot bake over 100 C (indium gaskets)zMust change Viton sealed overpressure relief valves to knife generates some vibration zMight cause carbon adsorber to release dustzCool 2ndstage with a Er2Ni heat exchangerzThe stage can then reach a temperature of PumpsCapture Pumps (NEG, TSP, SIP):zUse multiple types of pumps zSIP can effectively pump noble gases zNEGs have relatively high pumping speeds for H2zH2pumping is improved in TSP if the surface was LN cooled instead of water cooled UHV - GaugeszBelow 10-6 TorrzRGA and Ionization gauges must be usedzBelow 10-10 TorrzGauges fight issues of ESD and electrode outgassingzLimited number of commercially available UHV gauges.

8 Residual Gas AnalyzerPrinciple of Ion GaugeUHV Example SystemUHV ChamberIon & TSP PumpTurboPumpScrollPumpUHV IonGaugeA Basic SimplifiedUHV System UHV Example SystemSystem Parameters: Scroll Pump connected to chamber through a KF-40, 3 feet (91 cm) long line. Diameter KF-40: cm Turbopump and Ion Pump connected to chamber through a 6-inch ( cm) diameter, 18-inch ( cm) long line. Rough Systems to 5X10-2torr with the scroll pump; pump with turbo till 1X10-6, then valve in ion pump. Shut off turbo at 1X10-9torr? Chamber: Stainless Steel; Length: 3 feet, diameter 2 feet volume: 267 liters: surface area (cm2) Roughing Pump: Speed: 10l/s (atm.)

9 To 1 torr); at 100 mtorr high Vacuum Pumps: Turbopump with 500 l/sec speed Ion Pump with 400 l/sec speed UHV Example Pumping time:From Atmosphere to 5X10-2torr: t = 278 sTurbo Pumping Time:1ST1 Spump1 CTSTS pumpFrom 5X10-2 torr to 1X10-6 torr: t = sST285 LsUHV Example SystemWhat is the maximum outgassing rate allowed to achieve 1X10-9 torr? Example Data Stainless Steel OutgassingMethodOutgassing Rate (torr*L/sec*cm2)1 hour5 hours10 hours20 hours40 hoursSand x x x 10-9 Mechanically x x x x10-11H2 Fired x10-11 Chem Cleaned x10-11 Glass Bead Honed x10-12 UHV Example Data Pumpdown PressureMethodPressure in TorrH2H2 OCOT otalPumped Under Vacuum for 75 x x x x baked out for 50 hours (150oC) x x x x baked out for 40 hours (300oC) x x x x baked out for 40 hours (400oC) x x x x 10-10 Questions1.

10 What types of pumps can you use to reach vacuums of 10-10torror less?Answer: SIP, TSP, NEG, Cryopump (Most be capture)2. Where can oil be used in an UHV system?Answer: No where3. What is the most effective method of removing hydrogen from the stainless steel walls?Answer: Bake at high temperatures (above 400 oC) Diffusion coefficient is exponentially proportional to temperature Questions4. If somone went through the trouble of fully cleaning a Vacuum chamber component and then had lunch (McDonalds). On return he brushed the component with his/hers fingers before putting gloves on. Would that system ever reach a UHV pressure?Answer: Yes, the gas load from outgassing will decrease with pumping time.