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64th IUVSTA Workshop, May 16-19, 2011 Problems of vacuum metrology for industrial applications that call for solutions by rarefied gas dynamics Karl Jousten, PTB, Berlin 1.Applications of vacuum and leak detection with conclusions for rarefied gas dynamics 2.Present state: Measurement standards for vacuum and low flow rates (leaks) 3.Four problems for rarefied gas dynamics 4.Conclusion

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 20112 Applications of vacuum in science Gravitational wave detectors Elementary particle physics: Accelerators, KATRIN Fusion: ITER Surface physics Conclusions In most cases just sufficiently low gas density In some cases complicated and extensive design calculations of vacuum system (ITER, KATRIN) Reliable pumping speed values needed! Applications of vacuum and leak detection Virgo-Detector, near Pisa with 3 km long vacuum tubes

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 20113 Pumping speed measurement Turbomolecular pump, Pfeiffer Vacuum Applications of vacuum and leak detection From science to industry, standardization: How and where to measure p? This ( and hence S) is defined by international standards, but is it a physical quantity for design and theoretical calculations? Conclusions: Physical relevance of standardized quantities needs to be adressed. p ?

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 20114 Microelectronic industry Applications of vacuum and leak detection MOCVD: Reactor for ferroelectric films Cluster tool AIS, Dresden Typical: fast processes

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 20115 Industrial applications: CD/DVD metallization TypeCathodePumpsCycle-time SINGULUS V Focus 1 Focus Cathode1 Turbo Molecular Pump 2,7 s SINGULUS V Focus 2 Focus Cathode2 Turbo Molecular Pumps 1,5 s SINGULUS V Smart 1 SMART CATHODE® 1 Turbo Molecular Pump 2,5 s SINGULUS V Smart 2 SMART CATHODE® 2 Turbo Molecular Pumps 1,9 s Applications of vacuum and leak detection

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 20116 Applications of vacuum and leak detection Other examples of fast processes: Leak tests of rims for cars (mainly aluminum for light wheels) Coating of bottles (food industry) 1.2 s … 2.5 s PET- bottle coating Fa. Sidel company Conclusions: Fast changes of pressure and gas flows need to be calculated for engineering design.

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 20117 Example of non-detructive leak test: pacemaker and air bag Required tightness: < 10 -7 Pa L/s ! Required tightness: < 10 -5 Pa L/s Applications of vacuum and leak detection Source: St. Jude Medical, Sweden

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 20118 Airconditioning in cars, refrigerators etc. : Environmental issues Required tightness: < 10 -3 Pa L/s (1 g/a) Applications of vacuum and leak detection Conclusions: Leak testing is normally performed with helium, but needed are leak rates for other gases and even liquids.

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 20119 For a long time until about 1990: Magnetic sectors are used for leak detection and quadrupole mass spectrometers (QMS) for both leak detection and analysis of background residual gas level causing the name Residual gas analyzers. Nowadays in addition QMS for: Gas purity, in-situ analysis for reagent gases and low-level components in semiconductor Industry. Sputter process control CVD monitoring, gas abatement analysis MBE source control End point detection (etching) Gas chromatography Applications of vacuum and leak detection Partial pressure measurement Etching: end point detection

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201110 Applications of QMS < 1E-2 Pa: Direct installation of QMS to process chamber. 1E-2 Pa: Differential pumping necessary with manifold, conductance, high vacuum pump, and total pressure gauge. Conductance for sputtering pressures PVD ( 0.1 Pa): Orifice, Dual inlet (RGA + process) for MOCVD (up to 100 kPa): Capillary Conclusions: Mass (gas species) discrimination within the measuring device? Ulvac Co Applications of vacuum and leak detection

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201111 1.Fast processes: dynamics 2.Physical relevance of standardized quantities: helium leak rate and S 3.QMS as process tool: Discrimination for partial pressure measurement 4.Design of complex vacuum systems Summary from applications

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201112 2. Present state: Measurement standards for vacuum and low flow rates (leaks)

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201113 Measurement standards for vacuum and low gas flow

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201114 Pressure balance as primary standard Measurement standards for vacuum and low gas flow

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201115 Static or series expansion system as primary standard V 1,p 1 V 2,p 2

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201116 V 4 100 L V 6 100 L V3V3 V 2 0,1 L 1L1L 1L1L 1L1L GAS INLET UUC V1V1 V7V7 V5V5 Example for static expansion PTB, SE2 Measurement standards for vacuum and low gas flow

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201117 Measurement standards for vacuum and low gas flow Static expansion system SE2, PTB, Berlin Accurate pressures from 10 -2 Pa to 10 3 Pa

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201118 Continuous expansion system as primary standard p2p2 p3p3 gas flow C 1 << C 2 p1p1 flowmeter Measurement standards for vacuum and low gas flow

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201119 p=const t p Gas Flow C V Gas Inlet V1 V2 V3 "Leak" CDG Measurement standards for vacuum and low gas flow Range: 10 -8 Pa L/s … 10 -1 Pa L/s Gas flow meter FM3, PTB, Berlin

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201120 FM3 FLOW DIVIDER p 0,V 0 UHV-VESSEL p 1, V 1 XHV-VESSEL p 2, V 2 GAS FLOW KP2 KP1 C 02 C 01 C2C2 C1C1 Accurate pressures from 10 -9 Pa to 10 -2 Pa Measurement standards for vacuum and low gas flow Primary standard CE3, PTB, Berlin

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201121 Measurement standards for vacuum and low gas flow

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201122 Valve 1 Testleak Valve 3 Waterbath T=const. Flowmeter Valve 2 QMS Traceability for leak measurements against vacuum Measurement standards for vacuum and low gas flow

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201123 Testleak Needle CDG 133 Pa FS CDG 133 kPa FS T1T1 T3T3 T2T2 T4T4 V1 V2 V3 V = 5.1 cm³ V = 6.1 cm³ Thermal insulation Leak measurements against atmosphere Measurement standards for vacuum and low gas flow

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201124 Measurement standards for vacuum and low gas flow Conclusions from present state measurement standards Accurate vacuum gauge calibration is possible from 10 -9 Pa to 10 5 Pa with uncertainties ranging from 0.001% up to 10% Accurate flow rate calibration is possible from 10 -8 Pa L/s up to 0.1 Pa L/s against vacuum, 10 -4 Pa L/s to 0.1 Pa L/s against atmosphere, with uncertainties ranging from 0.5% to 10% Only steady state conditions (constant pressure, equilibrium) In some ranges only some gas species (non-adsorbing) and pure gases Stable environmental conditions

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201125 Measurement standards for vacuum and low gas flow A comment on traceability Whenever experimental results are being compared with a physical model or theory (pressures, mass flow rate, conductance, accommodation coefficient etc.), true values of the experimental results are necessary. Characteristic for a true value is the number and the uncertainty of the value. Uncertainty is the interval in which the true value lies with a specified confidence limit (68%, 95%, …) around the given value. For true values and the respective uncertainty you need to have traceability to the SI. Traceability to the SI is given by complete calibration chain to a national primary standard for the given quantity (vacuum pressure, flow rate etc.) National primary standards are regularly checked internationally.

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201126 Measurement standards for vacuum and low gas flow Gap from present state measurement standards to applications To close this gap there will be a new project IND12 within the EMRP (European metrology research programme) funded by the EU. Among others the tasks are: Dynamic vacuum standard Leak rate conversion from calibrated rate (for gas species, environmental conditions) Joint research project (JRP) IND12: Duration 3 years, begins Sept 2011, 2.8 M

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201127 3. Four problems for rarefied gas dynamics 3.1 Dynamic vacuum standard 3.2 Predictable leak (flow) rate from secondary standards 3.3 QMS as process tool: Mass discrimination for partial pressure measurement 3.4 Physical relevance of standardized quantity S

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201128 3. Problems for rarefied gas dynamics 3.1 Dynamic vacuum standard

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201129 Dynamic vacuum pressures How fast are vacuum gauges? Which measurement principle is fast? Which electronic is needed? Resolution? Hystereses effects of gauges? Establish well defined dynamic pressures to test gauges Measurement standards for vacuum and low gas flow

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201130 Dynamic vacuum standard Goal: Pressure reduction from 100 kPa to 100 Pa within 1000 ms. Predictable on the time scale of ms and with an of u ( p )/ p ( t ) < 50% at all times. Extendible to fast pressure changes down to 0.1 Pa. Tests for optical method possible.

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201131 Dynamic vacuum standard Idea for realization: Expand the gas from a small volume into a large one by a duct or orifice of calculable conductance. Calculate p ( t ), T ( t ). Compare with pressure and temperature measurement. Conductance of fast valve >> conductance of orifice or duct Fast valve must open within about 10 ms … 50 ms.

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201132 Dynamic vacuum standard Rough estimate for necessary duct or orifice: In the case of orifice and molecular flow:

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201133 Dynamic vacuum standard Problems to be solved: Conductance must be known for any pressure between 100 kPa and 100 Pa, non-stationary flow. Which is best to calculate conductance for viscous flow: orifice or duct? Shall we generate conditions for choked flow? Temperature change, velocity of sound change, choked flow condition permanent? Can we calculate T(t) on the ms scale and test calculations? Can we calculate p(r) in V1? Is fast opening valve (DN40) available? If not, are their alternatives? Can we extend to lower pressures (< 100 Pa) and include desorption?

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201134 3. Problems for rarefied gas dynamics 3.2 Predictable leak elements

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201135 Used for: Calibrating leak detectors (linearity tests), partial pressure analyzers Gases and gas mixtures for leaks Most leak rate measurements are performed with helium, but the tightness for other gases, gas mixtures, even liquids is required. + Test conditions are different than the calibration conditions. Establish procedures to convert the quantities. Leak elements for industry

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201136 Secondary standard for leaks: Permeation leak (see figure), temperature dependent, gas specific Capillaries (less temperature dependent), crimped capillaries, Porous plugs (sintered material) Permeation leak type Crimped capillary leak type Gas flow Leak elements for industry

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201137 permeationporouscapillarycrimped Temperature dependence strongweak Stability under rough cond mediumbadmediumgood Operability under rough condition goodmedium bad Gas species flexibility noyes Rate easily changeable (T, p) noyes Predictable (gas, T, p) medium yes sizelargemediummedium-largesmall Leak elements for industry

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201138 Choice for industry: Permeation leak: stable, but not flexible, strong T-dependence, slow crimped capillaries: small, large flexibility, work (good result) or do not work, fast, geometry is poorly defined Leak elements for industry

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201139 Possible equations of gas flow rate or conductance for capillaries (Tison, 1993) 2 Knudsen equation 1 Slip-flow equation 3 Linearized Boltzmann equation Loyalka, 1990 4 Guthrie, 1949, Steckelmacher, 1951: Leak elements for industry Empirical, shows minimum Empirical Knudsen successive monotonic

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201140 Stuart Tison, Vacuum 44 (1993), 1171-1175 F.Sharipov, Handbuch Vakuumtechnik, Bild 5.25 Leak elements for industry

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201141 Stuart Tison, Vacuum 44 (1993), 1171-1175 p : 20 kPa … 2 MPa Crimped capillary Agreement slip-flow and exp fortuitous? Residuals from Slip Flow Model Leak elements for industry

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201142 Stuart Tison, Vacuum 44 (1993), 1171-1175 Regular capillary Leak elements for industry p : 20 kPa … 2 MPa In Future? Sharipov, 2010:

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201143 To extend calculations from regular capillary to crimped capillary: Geometry has to be well determined. Regular capillary: Uniformity of diameter? Advantage of crimped capillary may be that crimped part will dominate the result for mass flow. If geometry not well defined: Prediction from He calibration, p c, for other species, p? or … Courtesy M. Bergoglio, INRIM 600 µm Leak elements for industry

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201144 alternatively nano holes made by focused ion beams: Leak elements for industry

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201145 3. Problems for rarefied gas dynamics 3.3 Predict mass discrimination of high pressure quadrupole mass spectrometers

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201146 Mass discrimination in inlet stages for QMS

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201147 3. Problems for rarefied gas dynamics 3.4 Improve standards for pump speed measurements

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201148 Physical relevance of standardized S Infinite volume Equilibrium not disturbed by in- or outflow Vacuum pump Mechanical pumps All vacuum pumps, but p is not isotropic in molecular range The concept of pumping speed intrinsic pumping speed Infinite volume cannot be realized, reflected particles disturb equilibrium.

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201149 Physical relevance of standardized S Feng Yu-guo and Xu Ting-wei, The appropriate test domes for pumping speed measurement, Vacuum 30 (1980), 377…382. Concept of tubular test dome with diameter equal to pump inlet flange. Ideal gauge position: Simulates infinitely large dome Appropriate test dome: Ideal gauge position is independent of. Play with d/D and L/D to find appropriate test dome.

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201150 Physical relevance of standardized S Deficencies of calculation of Yu-guo: Only lower chamber simulated Transmission probability calculated with 0.1% with a few 10 000 particles only Optimum L/D could only be calculated with uncertainty of 10 % Conclusion however: L/D=1.5 is not optimal, lower values preferable.

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201151 Improving standard for pumping speed measurement Physical relevance of standardized S Repeat MC calculations to find better L/D and/or gauge position (d/D is less critical) Extend simulations to transitional flow Consider non-uniform across pump inlet area D. Consider disturbed angular distribution of reflected particles inside pump

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201152 Conclusion Primary standards for pressure and low flow rates are available world wide These standards give traceability to SI. This traceability is needed whenever theory/simulation of rarefied gas flow is compared with experimental result Industry quite often needs conditions other than ideal Rarefied gas dynamics can help in designing new standards and predict behaviour of standards under industrial conditions: standard for fast changing pressure, predict leak elements, predict mass discrimination, design standard for physical S.

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Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201153 Dome of the Reichstag in Berlin

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