Review of investigation of influence of operational parameters on metrological characteristics of QMS within EMRP IND12 project

Transcription

1 Review of investigation of influence of operational parameters on metrological characteristics of QMS within EMRP IND12 project Janez Setina Institute of Metals and Technology, (IMT), Slovenia 1

2 Some operational parameters of QMS can be adjusted by the user. This can influence calibrated values of the instrument and may require recalibration of the instrument. We studied following operational parameters which can be changed or adjusted by the user: electron emission current electron energy in the ion source mass resolution Changes of these parameters influence: sensitivity linearity cracking (fragmentation) patterns of different gases. Another important fact: SEM gain is gas dependent 2

3 RGA instruments that were available in different NMIs: Pfeiffer Vacuum Prisma MKS Instruments Microvision+ INFICON TRANSPECTOR Hiden Analytical HALO 1 (3 instruments) (1 instrument) (1 instrument) (1 instrument) 3

4 Linearity versus electron emission current Participating laboratories measured linearity of their QMS instrument (sensitivity as a function of gas pressure) under following conditions: gasses: H 2, He, N 2, Ar detector: Faraday range of pressures: from 1-6 Pa to 1-3 Pa, three points per decade range of pressures: from 1-3 Pa to 1-2 Pa, five points per decade electron emission currents: o nominal value for given instrument I e,n o 2% of I e,n o 5% of I e,n 4

5 Bayard-Alpert gauge: I i p i I e l i p i S i ε i ionization efficiency <l> - mean electron path length S i gauge sensitivity HOT FILAMENT ION SOURCE ION COLLECTOR QMS: I I i, j i, j p p i i I S e i, j l i, j EXTR i, j TR i, j MULT i, j HOT FILAMENT ION SOURCE QUADRUPOL MASS FILTER ION COLLECTOR 5

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7 " G au g e co n st an t " ( S /Ie) / [ 1/P a] " G au g e co n st an t " ( S /Ie) / [ 1/P a] " Ga u g e c o n s ta n t" (S /Ie ) / [1 /P a ] "Gauge constant" (S/Ie) / [1/Pa] 1 Effect of electron emission current on sensitivity and linearity plotted is "gauge constant": S/I e for gas N UME 1E-6 1E IMT 1E-6 1E ma.4 ma.1 ma CMI ma.4 ma.1 ma CMI2 1E-6 1E E-6 1E ma.4 ma.1 ma 2 ma.4 ma.1 ma 7

8 " G au g e co n st an t " ( S /Ie) / [ 1/P a] " G a u g e c o n s ta n t" (S /Ie ) / [1 /P a ] " G au g e co n st an t " ( S /Ie) / [ 1/P a] N 2 UME He E-6 1E E-6 1E ma.4 ma.1 ma 2 ma.4 ma.1 ma Ar H 2 5 1E-6 1E ma.4 ma.1 ma

9 " G a u g e c o n s t a n t " ( S /Ie ) / [ 1 /P a ] " G a u g e c o n s t a n t " ( S /Ie ) / [ 1 /P a ] "Gauge constant" (S/Ie) / [1/Pa] "G a u g e c o n s t a n t " ( S /Ie ) / [ 1 /P a ] N 2 IMT He 1E-6 1E ma.4 ma.1 ma 1E-6 1E ma.4 ma.1 ma Ar H E-6 1E E-6 1E Ie = 2mA Ie =.4 ma Ie =.2 ma 2 ma.4 ma.1 ma 9

10 " G au g e co n st an t " ( S /Ie) / [ 1/P a] " G au g e co n st an t " ( S /Ie) / [ 1/P a] " G au g e co n st an t " ( S /Ie) / [ 1/P a] " G au g e co n st an t " ( S /Ie) / [ 1/P a] N 2 CMI2 He E-6 1E E-6 1E ma.4 ma.1 ma 2 ma.4 ma.1 ma Ar H E-6 1E E-6 1E ma.4 ma.1 ma 2 ma.4 ma.1 ma 1

11 " G au g e co n st an t " ( S /Ie) / [ 1/P a] " G au g e co n st an t " ( S /Ie) / [ 1/P a] " G au g e co n st an t " ( S /Ie) / [ 1/P a] " G au g e co n st an t " ( S /Ie) / [ 1/P a] CMI1 N 2 He E-6 1E E-6 1E ma.4 ma.1 ma 2 ma.4 ma.1 ma Ar H E-6 1E E-6 1E ma.4 ma.1 ma 2 ma.4 ma.1 ma 11

12 I_14 /I_28 I_2 /I_4 Example of cracking pattern dependence on pressure and emission current UME - nitrogen CMI1 - argon E-6 1E E-6 1E ma.4 ma.1 ma 2 ma.4 ma.1 ma 12

13 Effect of electron energy in the ionizer Electron energy in the ionizer is given by the cathode to anode voltage V c. Electron energy has significant influence on ionization probabilities and also on cracking patterns of gas molecules. Participating laboratories measured: 1. sensitivity of their QMS instrument for the main peak of gas as a function of cathode to anode voltage V c under following conditions: gasses: H 2, He, N 2, Ar and CO 2 manufacturer's recommended V c,.8xv c and 1.2xV c or wider range detector: Faraday gas pressure: 5x1-4 Pa (easily measurable by SRG) electron emission current: 2% of I e,n 2. cracking pattern of gases N 2, Ar and CO 2 under same conditions. 13

14 s en s it iv it y 1 e-6 A /P a s en s it iv it y 1 e-6 A /P a s ens itiv ity A/Pa (@.4m A) s en s it iv it y A / P a s en s it iv it y A / P a Effect of electron energy on sensitivity plotted is sensitivity S at I e =.4 ma (LNE: I e =.2 ma) 5E-7 4E-7 UME 6E-7 5E-7 LNE 3E-7 2E-7 1E electron energy He N2 Ar CO2 4E-7 3E-7 2E-7 1E electron energy He N2 Ar CO CMI1 CMI2 IMT electron energy H2 He N2 Ar CO electron energy H2 He N2 Ar CO2 2E-7 1.6E-7 1.2E-7 8E-8 4E electron energy H2 He N2 Ar CO2 CO 14

15 S e n s itiv ity / [A /P a ] 1E-6 1E-7 Sensitivity for N 2 as a function of electron energy 1E-8 1E1 1E2 1E3 1E4 Energy / ev CMI1 CMI2 LNE UME IMT CEM 15

16 C O 2 : I _ 1 2 / I _ 4 4 C O 2 : I _ 1 6 / I _ 4 4 C O 2 : I _ 2 8 / I _ 4 4 Cracking pattern of CO 2 as a function of electron energy (UME and CMI) Electron energy / (ev) Electron energy / (ev) Electron energy / (ev) UME CMI-QMS1 CMI_QMS2 UME CMI-QMS1 CMI_QMS2 UME CMI-QMS1 CMI_QMS2 16

17 Effect of mass resolution (peak width) on sensitivity Mass resolution setting can have significant influence on quadrupole filter transmission probability. Different transmission probabilities for different ions affect the sensitivity and also cracking patterns. Participating laboratories measured: 1. sensitivity of their QMS instrument (for the main peak of gas) at different mass resolution settings of QMS, and under following conditions: gases: H 2, He, N 2, Ar and CO 2 detector: Faraday gas pressure: 5x1-4 Pa (easily measurable by SRG) electron emission current: 2% of I e,n 2. cracking pattern of gases N 2, Ar, and CO 2 under same conditions: QMS instruments were adjusted at least to following three resolution settings: o Δm =.8, 1. and 1.2, or in a wider range 17

18 rela tiv e s e n s it iv it y rela tiv e s e n s it iv it y rela tiv e s e n s it iv it y rela tiv e s e n s it iv it y UME delta_m Effect of mass resolution on sensitivity plotted is relative sensitivity S/S ΔM=1 IMT delta_m CMI1 He N2 Ar CO delta_m CMI2 1 He N2 Ar CO delta_m H2 He N2 Ar CO2 H2 He N2 Ar CO2 18

19 SEM gain for different gasses There is little published data on the dependence of SEM gain on different ions. Different SEM gain for different ions will result in different relative sensitivities and also different cracking patterns for Faraday and SEM detector. Participants measured SEM gain for different ions (main peaks and fragments under following conditions: gasses: H 2, He, N 2, Ar and CO 2 gas pressure around 1x1-5 Pa electron emission current: I e,n 19

20 N o r m a liz e d g a in N o rm a l iz e d g a in N o rm a l iz e d g a in R e la tiv e g a i n Effect of gas species on SEM gain - plotted is normalized gain S/S N2(28) UME LNE He He+ N+ Ar++ N2+ Ar Mass CMI1 & CMI2 QMS1 QMS N+ O+ C+ Ar++ N2+ Ar+ CO Mass H2+ IMT H2+ He+ Ar++ N2+ CO2+ Ar He+ CH4+ C+ N+ N2+ Ar++ Ar+ CO Kr Mass Mass 2

21 Main conclusions from the analysis of the results are: Sensitivity is not a linear function of electron emission current as in ionization gauges. When emission current is changed, also potential distribution inside the ion source is changed, which influences ion energies, extraction efficiency and focusing of ions into quadrupole filter. Changing electron energy in the ionizer has different effect for different ion sources. When electron energy is changed the ion source shall be re-optimized for ion extraction and focusing. Large nonlinearities of sensitivity as a function of gas pressure were found even in the pressure range below 1-4 Pa which indicates that QMS instruments shall be calibrated over the whole operating range. 21

22 Changing the mass resolution had similar effect in all studied instruments. To the first approximation the relative change of sensitivity is proportional to the change of resolution in the range from.8 amu to 1.2 amu. Cracking patterns for N 2 (14/28) and Ar (2/4) were in some instruments significantly dependent on pressure also in the pressure range below 1-4 Pa. The calibration procedure of QMS shall therefore include determination of cracking pattern over the whole range of calibration. SEM gain depends on the type of ion which is detected, so the relative sensitivities for different gases for SEM and Faraday are different (typically up to a factor 1.5). Will a QMS user be hapy after receiving "nonlinear" calibration results? Will manufacturers be hapy after receiving compalints about linearity? 22

23 Acknowledgement Presented study was a joint work of several national metrology institutes. Contributions of Alper Elkatmis (TUBITAK UME, Turkey), Frédéric Boineau (LNE, France), Martin Vicar (CMI, Czech Republic) and Salustiano Ruiz (CEM, Spain) are greatly acknowledged. 23

24 Table I. Instrument details Participants QMS Electron emission Type of ion source Quadrupole rod diameter Mass range Filament Type UME Inficon TRANSPECTOR H2M /ma /mm /amu 2 open Thorium oxide iridium IMT PFEIFFER Prisma Plus 2 grid ion source Tungsten QMG22 M2 LNE MKS Microvision Plus 1 open Twin Tungsten CMI 2 QMS s: PFEIFFER Prisma QME 2 2 open, radial HS Yttria CEM HIDDEN HALO 1 1 open N/A 1-1 Oxide coated iridium 24