vacuum metrology for production environments m. bergoglio the european metrology research programme...

Vacuum metrology for production environments

M. BERGOGLIO

The European Metrology Research Programme (EMRP) is a metrology-focused European programme of coordinated R&D that facilitates closer integration of national research programmes. The EMRP is supported by the European Commission and the participating countries within the European Association of National Metrology Institutes.

The EMRP is jointly funded by the EMRP participating countries within EURAMET and the European Union

Giornata di studio Metrologia del vuoto negli ambienti industriali - TORINO - 27 giugno 2013

JRP start date and duration: September 1, 2011; 3 years JRP-Coordinator: Dr. Karl Jousten, PTB

JRP-Partners:PTB, Germany CEM, Spain CMI, Czech Republic IMT, Slovenia INRIM, Italy LNE, France TUBITAK UME, Turkey

Danfoss, Denmark INFICON AG, Liechtenstein INFICON GmbH, Germany Lazzero, Italy 5Pascal, Italy VACOM, Germany

REG1: UNIGE, ItalyREG2: UTH University of Thessaly, REG3: KIT Karlsruhe Institute of Technology


Total eligible costs: 2.8 M€EURAMET contribution: 1.3 M€ (45%)National contribution: 1.5 M€

290 labour months


Historically, vacuum has been an important tool in industry and has been used in many applications, ranging from protecting light filaments from chemical degradation to controlling the flow of current in electronics.The use of vacuum is still important today, in modern semiconductor industry and fusion power research. However, vacuum is poorly understood when used outside the laboratory, as traditional measurements are unsuitable and based on the pressures of pure gases in stable conditions.This project will improve vacuum measurements in conditions representative of those found in industry. The improved measurements will lead to a more efficient use of vacuum and better end products.


The existing vacuum measurement standards in the EU provide traceability from 10-9 Pa to 105 Pa for pure gases under static or stationary equilibrium conditions.


Some NMIs also operate standards for very low gas flows (10-15 mol/s to 10-8 mol/s) which are suitable to calibrate leak rates of standard leaks for helium and some other pure gases.

Currently, no facility in the EU exists for calibrating vacuum gauges for dynamic pressures or for calibrating quadrupole mass spectrometers (QMS). Therefore, traceable outgassing rate measurements with QMS are not possible. Furthermore, there is no generally accepted way of converting leak rates from helium to other gases or environmental conditions different from the calibration.


• providing industry with a calibration facility to measure the response times of vacuum gauges for fast dynamic pressure changes

• enabling users of calibrated leaks to predict leak rates under industrial environmental conditions which are needed to meet regulations

• providing industry with a calibration facility to characterise and calibrate QMS. This is needed to control processes more reliably

• providing traceability for outgassing rate measurements with QMS and also with the use of reference materials for outgassing

This JRP will go beyond the state of the art by:


WP1 Dynamic vacuum calibration facility

WP2 Leak measurement and testing

WP3 Partial pressure and outgassing rate measurement


Novel dynamic vacuum calibration facility :

Provision of a vacuum system with very fast pressure changes in rough vacuum

Enabling the detection of very fast pressure changes (the pressure will decrease from 100 kPa to 100 Pa within 1 s or less) by suitable vacuum gauges with simultaneous measurement of very fast temperature changes.

Data on the relaxation time of vacuum gauges for fast pressure changes.

Qualification of suitable gauges for dynamic vacuum pressure changes

WP1 Dynamic vacuum calibration facility


PTB provides a calibration facility for the dynamic response of vacuum gauges with the pressure changing from 100 kPa to 100 Pa within 1 s. A small and a large chamber separated by a well defined conductance and a fast moving valve were realized. The pressure decrease p(t) will be generated by opening the valve causing the gas to be expanded from the small into the large chamber. The mass flow through the orifice is calculated over the whole pressure range.


2121

1

21

11

VV

Vf

High-pressure volume:Low-pressure volume:Dead volume:

Expansion ratio

Dead volume offset

Final pressure

560401

21

101offs

p

VV

Vpp

153901

012

'11

'11

fp

pVVV

VVp

L 0,08745 V1 L 185,4 V2

L 0,03309 V '1


Fast opening valve•VAT DN40 gate valve

•Opened pneumatically via an

actuation pressure of 9 bar

•Molecular conductance is

approximately 81 L/s

•Characterisation with a high

speed camera (10000 fps)

•Opening time: 5,7 ms


Orifice

Orifice of conical geometry: diameter reduced from 8 mm to 3 mm, thickness of 2,6 mm.Designed to have a conductance of about 1 L / s in the molecular regime.Leads to an expansion into vacuum within 540 ms.


The orifice geometry is an important factor.

Orifice characterization in PTB.

Maximum deviation 1%,average deviation <0,2%.

Measurement 30.07.12 (Front side): Area = 7,099 mm2

Measured radius = 1,503 mm, Nominal radius = 1,5 mm

Orifice


INFICON Liechtenstein Tasks

Develop and donate a membrane sensor with associated signal processing equipment that can measure pressure changes in the range 100 Pa to 100 kPa with an up-date time of < 1 ms for use in a pressure standards laboratory

2 CDG 1000 Torr and 2 CDG 10 Torr delivered Time between measurement values approx. 700 μs < 1ms Output at 21 bit resolution Noise peak-peak < 0.5% F.S., typically 0.2 % F.S. Improvements to system still possible (i.e. static calibration, noise reduction)

Patent application filed


Pressure gauges

Inficon: Capacitance Diaphragm

Gauges (CDG)

VACOM: piezo-resistive

gauges


Dynamic expansion


Thermocouple

dfeedthrough =200 µm

dwire =25 µm

The gas expansion will be non-adiabatic so since gas pressure and temperature are related, a temperature sensor with very small heat capacity has designed to measure the gas temperature.


TC type KUsage of very thin wires dWire = 25 µm

Type K: Ni Cr(10%), Ni Al(5%)

LN2


Pressure distribution

t = 0.00012s t = 0.01s

t = 0.02s t = 0.2s

t = 0.0001s t = 0.00015s t = 0.001s t = 0.005s

t = 0.01s t = 0.05s t = 0.1s t = 0.2s

Velocity distribution

Temperature distribution

t = 0.00012s t = 0.0003s t = 0.001s t = 0.1s

t = 0.2s


Pressure measurement

Experimental conditions: p1 = 105 Pa, p2 = 0,05 Pa.Conical orifice between the two volumes.


First comparisons

Experimental conditions: p1 = 105 Pa, p2 = 103 Pa.Inficon CDGs, conical orifice between the two volumes.

• ANSYS CFX: Validation within the viscous regime, i.e the pressure was decreased streamwise from 105 Pa to 5000, 2500 and 1000 Pa.


INRIM optical method for Dynamic vacuum calibration facility

-the experiment is based on a homodyne Michelson interferometer

- The heart of the system is the double mirror multiplication set up ( angle between mirrors of ~ 0.4 °)

- Sensitivity: ~ 2.6 nm/Pa

27

The vertical and the horizontal components of the linearly polarized measurement beam are summed with the sine and cosine components of the circularly polarized reference beam generating two quadrature interference signals, which are amplified and sent to the acquisition system.

Marco Pisani , “A homodyne Michelson interferometer with sub-picometer resolution”, Meas. Sci. Technol. 20 (2009)

The laser source is a He–Ne frequency stabilized laser linearly polarized (λ ≈ 632.8 nm).

The Faraday isolator (FI) prevents feedback-induced instabilities and rotates the polarization by 45°.

The reference beam is sent to a fixed mirror M through a λ/8 retarder. It has the effect of giving a circular polarization to the beam returning to the BS.

The measurement beam is sent to the double mirror multiplication setup.

The beam reflected back is summed to that coming from mirror M on the BS and is sent to the detector assembly.A polarizing beam splitter (PBS) is used to separate the vertical and the horizontal components of the two beams and to address them towards photodetectors D1 and D2.


P /Pa n dn/n dL/L dL/mm @ L=1000 mm

98000 1.000259 0.000000 0.000000 0.0000

100 1.000000 0.000259 0.000259 0. 2585

From 98 kPa to 100 Pa

L = 335 mmdL = 86 µmS = 0.88 nm/Pa


Base for interferometer

Support for bonding of mirrors

Base: ULE, diameter 160 mm, thickness 20mmplanarity better than /10

Mirrors: ULE, 70x30x10 planarity better than /10 , orthogonal surface 10”


WP 2: Leak measurement and testing

Leak and small outflow measurements are very important in many branches of industry (cold storage facilities, air conditioning systems, etc). The most sensitive, versatile and accurate method for leak measurement is the permanent gas (helium) throughput measurement through the leak into vacuum. Nevertheless, the leaks usually occur under conditions different from those at measurement: different pressures, temperature, gas species and mixtures. Research is needed to provide industry with traceability under practical conditions.


The aim of the WP2, is the improvement of the knowledge of gas flow through nano/microchannels in terms of predictability for different gas species and environmental conditions with the focus on the industrial applications and conditions. Several leak elements were realized with a well known geometry in order to improve gas flow theory in the narrow ducts, to increase the accuracy of conversion function between different gases and to study metrological characteristics of the leaks (temperature coefficient, gas flow rate stability, influence of changing atmospheric pressure).


Study of leak elements performance: temperature coefficient, influence of atmospheric pressure changes, influence of the effects of gas mixture.

Development of a practical guide on metrological performance of leak detectors: either He leak detectors or infrared leak analyzers.

Technical training course for people working in leak testing field.


The aim of this workpackage is to provide dedicated calibration facilities for quadrupole mass spectrometers (QMS) and to investigate factors influencing metrological characteristics of QMS. Another aim is to develop model systems for outgassing rate measurements applying different methods, to compare them, and provide measurement traceability of these methods. There are no "certified reference materials" for outgassing rate available yet. Materials which exhibit reversible absorption of different gasses may be used for such purpose. We will investigate the suitability of different materials as e.g. high vacuum compatible polymers, nanostructures, porous silicon, zeolite and choose the most suitable one as reference outgassing material.

WP 3: Partial pressure and outgassing rate measurement


Three glass capillaries as leak elements operating in molecular regime

Outgassing sample chamber

2


QMS

Orifice having a conductance of 1L/s

Outgassing sample chamber - load lock - transportation system


Q M S

C alib ra tion gas

B A G

S R G

C D G Variab leLeakV alve

Vacuumpum p

(turbo + rotary)IMT


B ake-ou t oven to 400*CG as flow and “gas quan tity ” ca lib ra tion a ttachem en t

CFflange

He leakdetector TURB O

1

TURB O2

IONPUM P

S R G 3

B A G

C C G

C D G

calibration gases

ArHHeCOCONeKr

N

2

2

2

Q M S

C H 20.3 L

C H 1

S R G 2

S R G 1

IMT


Gas inlet

Auxiliary pump

primary flowmeter

To pumping system

RGA

Calibrated leak

IG

Outgassing chamber

SRG

INRIM


Study of stability over time of QMS sensitivity and other properties

Evaluate following characteristics: sensitivity SEM gain mass number stability resolution fragmentation factor of N2

minimum detectable partial pressure


- Determination of metrological characteristics of QMS for calibration purposes and definition of reference conditions to compare performance of instruments from different manufacturers

ISO TS on the calibration of QMS

ISO TS on the outgassing rate measurements


Gas inlet

Auxiliary pump

primary flowmeter

To pumping system

RGA

Calibrated leak

IG

Outgassing chamber

SRG

vacuum metrology for production environments m. bergoglio the european metrology research programme...

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