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Problems of vacuum metrology for industrial applications that call for solutions by rarefied gas dynamics Karl Jousten,

Problems of vacuum metrology for industrial applications that call for solutions by rarefied gas dynamics Karl Jousten, PTB, Berlin. Applications of vacuum and leak detection with conclusions for rarefied gas dynamics Present state: Measurement standards for vacuum and low flow rates (leaks)

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Problems of vacuum metrology for industrial applications that call for solutions by rarefied gas dynamics Karl Jousten,

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  1. Problems of vacuum metrology for industrial applications that call for solutions by rarefied gas dynamicsKarl Jousten, PTB, Berlin Applications of vacuum and leak detection with conclusions for rarefied gas dynamics Present state: Measurement standards for vacuum and low flow rates (leaks) Four problems for rarefied gas dynamics Conclusion

  2. Applications of vacuum and leak detection • 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! Virgo-Detector, near Pisa with 3 km long vacuum tubes Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 20112

  3. Applications of vacuum and leak detection From science to industry, standardization: • Pumping speed measurement p ? • How and where to measurep? • This (and henceS)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. Turbomolecular pump, Pfeiffer Vacuum Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 20113

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

  5. Applications of vacuum and leak detection • Industrial applications: CD/DVD metallization Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 20115

  6. 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) PET- bottle coating Fa. Sidel company 1.2 s … 2.5 s Conclusions: Fast changes of pressure and gas flows need to be calculated for engineering design. Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 20116

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

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

  9. Applications of vacuum and leak detection • 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 Partial pressure measurement Etching: end point detection Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 20119

  10. Applications of vacuum and leak detection 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 Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201110

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

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

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

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

  15. V1,p1 • Static or series expansion system as primary standard V2,p2 Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201115

  16. GAS INLET V2 0,1 L 1 L UUC V3 V6 100 L V4 100 L V1 V7 V5 1 L 1 L Measurement standards for vacuum and low gas flow Example for static expansion PTB, SE2 Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201116

  17. Measurement standards for vacuum and low gas flow Accurate pressures from 10-2 Pa to 103 Pa Static expansion system SE2, PTB, Berlin Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201117

  18. flowmeter p3 p2 p1 C1<< C2 gas flow Measurement standards for vacuum and low gas flow • Continuous expansion system as primary standard Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201118

  19. V2 DV Gas Flow CDG V3 p=const C "Leak" V1 Dp t Gas Inlet 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 Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201119

  20. FM3 GAS FLOW C02 C01 FLOW DIVIDER p0,V0 XHV-VESSEL p2, V2 UHV-VESSEL p1, V1 KP2 C2 C1 KP1 Measurement standards for vacuum and low gas flow Primary standard CE3, PTB, Berlin Accurate pressures from 10-9 Pa to 10-2 Pa Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201120

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

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

  23. Testleak CDG 133 kPa FS T1 Needle V1 V2 T2 V = 5.1 cm³ T3 CDG 133 Pa FS V3 T4 V = 6.1 cm³ Thermal insulation Measurement standards for vacuum and low gas flow Leak measurements against atmosphere Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201123

  24. 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 105 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 Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201124

  25. 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. Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201125

  26. 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€ Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201126

  27. 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 Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201127

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

  29. Measurement standards for vacuum and low gas flow 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 Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201129

  30. 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. Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201130

  31. 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. Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201131

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

  33. 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? Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201133

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

  35. Leak elements for industry 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. Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201135

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

  37. Leak elements for industry Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201137

  38. Leak elements for industry 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 Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201138

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

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

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

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

  43. Leak elements for industry 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, pc, for other species, p? or … 600 µm Courtesy M. Bergoglio, INRIM Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201143

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

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

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

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

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

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

  50. 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. Problems of vacuum metrology for rarefied gas dynamics, IUVSTA WS 64, 201150

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