Kvadrupólová hmotnostní spektrometrie
reaktivního plazmatu
Jan Benedikt
Ruhr-University Bochum
Simon Schneider
Simon Große-Kreul
Dirk Ellerweg
Simon Hübner
Achim von Keudell
Thanks to:
1
Motivation: analysis of the plasma
Example of CCP or ICP plasmas
Stable species x highly reactive species x ions
Measurement of
stable products
2
A-C:H coated waferA-C:H coated waferd Analyzerd Analyzer
Motivation: analysis of the plasma
Measurement of
O density and
ion flux to the substrate
A. von Keudell,et al., Plasma Process. Polym. 7, 327 (2010)
Example of CCP or ICP plasmas
Stable species x highly reactive species x ions
a-C:H coated wafer
0 10 20 30 40 50 60 70 80 90 100
0
1
2
3
4
5
EtchRate(nm/s)
O2
concentration (%)
10 Pa
Ar/O2 ICP
3
Motivation: analysis of the
HiPIMS plasmas
Example of HiPIMS discharges
- highly transient plasma
- mainly reactive short-lived species
Even stable species (such as Ar or O2)
have a spatial density profile
Breilmann et al.,
J. Phys. D: Appl. Phys. 48 (2015) 295202
Ionization zones (“spokes”)
4
Particles
Ions
Sampling
Plasma
1 bar£
Energy
Analyser
m/z
Analyser Detector
Vacuum £ 10 mbar
-5
Ion transfer
Ion
Source
or Ion
Optics
Analyte
Transfer to analyzer
Preparation for
analysis
Motivation: Analysis of unknown analyte
Separation of
components
according to
their properties
Identification
Quantification
Mass spectrometry in general
5
Outline
Particles
Ions
Sampling
Plasma
1 bar£
Energy
Analyser
m/z
Analyser Detector
Vacuum £ 10 mbar
-5
Ion transfer
Ion
Source
or Ion
Optics
1 Basics of MS - components
2 Species identification and quantification
3 Sampling
4 Examples
6
Literature
7
MS components: electron impact ionizer
Filament: thermionic electron emission
Electron source: heated filament
heating circuit
Accelerating voltage (~ Eelectrons)
8
MS components: electron impact ionizer
9
MS components: Quadrupole Mass Filter
Ion trajectories
Combined RF and DC electric fields for mass analysis
10
Bild: Atomi
11
MS components: Detectors
Secondary electron
multipliers (SEM)
Channeltron
Faraday cup
With discrete dynodes
13
MS components: Detectors
Detector is a „consumable“ – has a limited lifetime depending on overall number of counts measured!!!
The curve shifts during the
„life“ of a detector
Measure and adjust
the operating voltage regularly!!!
Typical lifetime ~ 1-5 years
Never measure here
14
MS components: Detectors
Remark: The Use of Channeltron® Detectors
The Channeltron® Electron Multiplier has a history of dependability in mass spectrometer applications.
The following instructions and precautions are presented here in order that the user can achieve the
maximum useful lifetime of a Channeltron detector.
1. Mounting work should be done in clean vacuum fashion, i.e., the detector should be handled with talc
free finger cots or lint free gloves. Care should be taken to avoid dust, lint, or other particulate matter.
Nothing should touch the active areas of the detector.
2. Channeltrons are normally operated at pressures of 10-5 or lower. Higher pressure operation is
observed to increase the background current and can result in shortened life. Do not apply high
voltage at pressures greater than 10-4 torr as arcing can occur and permanent destruction of the
Channeltron surface is possible.
3. Channeltrons are customarily operated at 1500 to 3000 volts. The maximum rated voltage difference
between input and output leads is 3000 volts. Care should be taken to operate at a voltage which
gives sufficient gain to achieve acceptable results. Higher gains will shorten Channeltron lifetimes in
inverse proportion, i.e. 2x the gain results in 1/2 the potential lifetime.
4. During the first few days of operation of a new detector, it is recommended that high output currents
be avoided (i.e. inputs above 10-9 amps while operating at gains in excess of 107). Taking this initial
burn-in precaution can prevent premature failure.
5. Backstreaming from oil diffusion pumps or roughing pumps should not be permitted. It is
recommended that cold traps and molecular sieve traps be operated and maintained to
manufacturers specifications.
Warranty - All multipliers come with a one year prorated warranty starting at the date of shipment. Multipliers with insufficient gain or
excessive noise should be returned to S.I.S. for evaluation and testing. If the multiplier proves to be defective due to manufacturing defects it will be
replaced at no charge during the first three months of use and prorated thereafter based on a one year life and a gain of 1 x 105 at 3 KV. Multipliers
which test properly or which were damaged due to operator fault or carelessness will not be replaced, and user will be billed --- for testing.
Channeltron® is a registered trademark of Burle Electro Optics Corp.
15
MS components: single ion lens
Used to guide and focus the ions in the MS
All components together: for example HIDEN PSM
17
MS components: combination of ion lenses
Ion extraction Ionizer Bessel box
Quadrupole
Simulation: Simion 8.1 SW
MS components: energy filters
Ion extraction Ionizer Bessel box
Simulation: Simion 8.1 SW
Benedikt et al., J. Phys. D: Appl. Phys. 45 (2012) 403001
20
All components together: for example HIDEN EQP
Outline
Particles
Ions
Sampling
Plasma
1 bar£
Energy
Analyser
m/z
Analyser Detector
Vacuum £ 10 mbar
-5
Ion transfer
Ion
Source
or Ion
Optics
1 Basics of MS - components
2 Species identification and quantification
3 Sampling
4 Examples
21
electron impact
ionizer
quadrupole mass filter
detector
(electron multiplier)
+
Si
ni,ionizer
ionizerielieionizeriii nEILmmTS ,)()()(  
Quantification of neutral species
mass filter
and detector
ionizer detected species
ep
<10-5 mbar
  ,
,
( )
,
( )
cal ionizercal el
i ionizer i cal i
i el cal
nE
n F m m S
E S


   
Signal calibration: measurement of species with known density
Mass spectrometry
ionizercalelcaleionizercalcalcal nEILmmTS ,)()()(  
22
0 10 20 30 40 50 60 70 80 90
0
1
2
3
4
5
6
0 20 40 60 80
1.4
1.6
1.8
29 Pa
13 Pa
SQMS
/i
/ni
(x10
-16
)
amu
ratio
Mass dependent MS transmission function
The mass-to-charge (m/q) dependent MS response can be calibrated
by stable gases of known densities:
  ,
,
( )
,
( )
cal ionizercal el
i ionizer i cal i
i el cal
nE
n F m m S
E S


   
typically ~(m/q)-r, where r ~ 0.5 - 1
23
Electron Impact Ionization Cross Section
Known for most of the stable gases
Highest sensitivity at
electron energy
around 70 eV
Typical shape
Benedikt et al., J. Phys. D: Appl. Phys. 45 (2012) 403001
24
Electron Impact Ionization Cross Section
However: at high Eel also dissociation or multiple ionization possible
fragment ions
CH4
ions appear at
many masses
Benedikt et al., J. Phys. D: Appl. Phys. 45 (2012) 403001
25
Electron Impact Ionization Cross Section
However: at high Eel also dissociation or multiple ionization possible
Consoli et al., J. Phys. Chem. A, 2008, 112 (45), 11319 26
Threshold Ionisation Mass Spectrometry (TIMS)
Possible solution for identification of overlapping mass spectra
 formation of fragment ions limited or avoided
CH4
measure here, close to the ionization threshold
Benedikt et al., J. Phys. D: Appl. Phys. 45 (2012) 403001
27
C2H+: ion can originate from two sources:
Dissociative ionization of C2H2:
C2H2 + e-  C2H+ + H + 2e- 17.22 eV
Direct ionization of C2H:
C2H + e-  C2H+ + 2e- 11.62 eV
TIMS measurements: C2H radical
10 11 12 13 14 15 16 17 18 19
0
20
40
60
80
100
ETP off
ETP on
C2H+
appearance potential
counts/s
electron energy [eV] C2H2 flow
[sccs]
15.5 eV electron energy used
0 5 10 15 20
0
2
4
6
8
density[m-3](x1016)
C2H
Chemistry model
10 11 12 13 14 15 16 17 18 19
1
10
100
1000
10000 plasma off
plasma on
C2H+ (m/z = 25)
iontů/s
energie elektronů [eV]
11.6 eV
17.2 eV
28
TIMS measurements: other hydrocarbons radicals
Benedikt et al., JVST A 23 (2005) 1400
29
ETP - expanding
thermal plasma
Outline
Particles
Ions
Sampling
Plasma
1 bar£
Energy
Analyser
m/z
Analyser Detector
Vacuum £ 10 mbar
-5
Ion transfer
Ion
Source
or Ion
Optics
1 Basics of MS - components
2 Species identification and quantification
3 Sampling
4 Examples
How to connect measured ionizer
density with density in the plasma?
What is the use of differential pumping…?
How to sample ions?
30
Gas mixture (Plasma)
ni
pumping
P – pumping speed
Measurement of stable species
Pressure in MS must be < 10-5 mbar
– differential pumping necessary:
= ni·C(A,T,mi...)/P(pump)ni_ionizer = Fluxi/P
Residual Gas Analysis (RGA)
orifice with area A = r2
and gas conductivity C
ni_ionizer = f(geom.Tg,mi,...).ni
  ,
,
( )
,
( )
cal ionizercal el
i ionizer i cal i
i el cal
nE
n F m m S
E S


   
How to connect it with density at the sampling orifice?  differential pumping
31
Gas mixture (Plasma)
ni
pumping
P – pumping speed
Measurement of stable species
Pressure in MS must be < 10-5 mbar
– differential pumping necessary:
However:
When species reactive at the surface (1)  lost at the surface 
ni_ion.  small
RGA does not work for the reactive species!
= ni·C(A,T,mi...)/P(pump)ni_ionizer = Fluxi/P
Residual Gas Analysis (RGA)
orifice with area A = r2
and gas conductivity C
ni_ionizer = f(geom.Tg,mi,...).ni
  ,
,
( )
,
( )
cal ionizercal el
i ionizer i cal i
i el cal
nE
n F m m S
E S


   
How to connect it with density at the sampling orifice?  differential pumping
32
Formation of molecular beam depends on Knudsen number Kn=
l
d
Kn > 1
Free molecular flow without collisions
Measurement of reactive neutrals: Molecular Beam Sampling
x
Density in the beam easy to determine:
Orifice aspect ratio important
- sharp edge needed!
nBeam
  ,
,
( )
,
( )
cal ionizercal el
i ionizer i cal i
i el cal
nE
n F m m S
E S


   
How to connect it with density at the sampling orifice?  molecular beam sampling
x (position of the ionizer) should be as small as possible!
33
pumping P2
ni_ionizer_BG = ni·C1.C2/P1P2
 Reactive species measurement possible
Beam
chopper
Molecular beam
Background density:
ni_ionizer_Beam = f(geom., Tg, mi, mcg,...)·ni
A2=r2
2
P1
Gas mixture (Plasma)
ni
(2) measured with chopper blocking the beam
ni_ionizer = ni_ionizer_BG + ni_ionizer_Beam
Density in the beam:
A1=r1
2
Multiple differential pumping stages + formation of molecular beam
measured as difference (1) – (2)
(1) measured without chopper blocking the beam
Ionizer density:
Measurement of reactive neutrals: Molecular Beam Sampling
34
Example: CFx species measurement
Single stage differential pumping
ni_ionizer_Beam = 1/4·ni·(r/x)2
ni_ionizer_BG = ni·C(A,T)/P
Singh H, Coburn J W and Graves D B 1999 J. Vac. Sci. Technol. A 17 2447
35
Example: CFx species measurement
Tripple stage differential pumping
ni_ionizer_BG = ni·C1·C2·C3/(P1P2P3) ni_ionizer_Beam = 1/4·ni·(r/x)2
Singh H, Coburn J W and Graves D B 1999 J. Vac. Sci. Technol. A 17 2447
36
Comparison beam x background densities
37
Molecular beam sampling – ionizer issue
Measurement of the pulsed
molecular beam have shown
that the “closed” ionizer can
be filled with “beam particles”
 problem in the calibration!
S. Große-Kreul et al.,
accepted in J. Phys. D
38
Issue of a closed and open ionizer
closed ionizer open ionizer
39
Outline
Particles
Ions
Sampling
Plasma
1 bar£
Energy
Analyser
m/z
Analyser Detector
Vacuum £ 10 mbar
-5
Ion transfer
Ion
Source
or Ion
Optics
1 Basics of MS - components
2 Species identification and quantification
3 Sampling
4 Examples
How to connect measured ionizer
density with density in the plasma?
What is the use of differential pumping…?
How to sample ions?
40
Mass spectrometry of ions
Ions manipulated
and focused into MS
with ion optics
No ionization and
no background
correction are needed
More diff. pumping
stages needed only for
measurement of
atm. plasmas
But only relativ fluxes
are measured,
not densities!
The ion lenses have
to be properly tuned
and calibrated
41
Tuning of ion lenses – depends on ion energy
avoiding chromatic (energy) aberratition
Hamers E, van Sark W, Bezemer J, Goedheer W and van der Weg W 1998 Int. J. Mass Spectrom. 173 91
Calibration of the ion optics - energy scale
He/N2 atmospheric plasma
Negative  does not make really sense…
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0
0.0
0.5
1.0
1.5
2.0
2.5
3.0N+
2
signal(105
c/s)
PSM parameter 'energy'
S. Große-Kreul et al., Plasma Sources Sci. Technol. 24 (2015) 044008
Experimental setup
PSM mass spectrometer from HIDEN Analytical
Energy filter: „Bessel Box“ with parameters: cylinder, endcap, energy
What is the real ion energy?
Results
Variation of the Bessel-box parameters: cylinder, endcap, energy
0.0
0.5
0.0
0.5
0.0
0.5
0.0
0.5
0.0
0.5
0.0
0.5
0.0
0.5
-10 -9 -8 -7 -6 -5 -4 -3 -2 -1 0
0.0
0.5
1, -17
2, -16
3, -15
4, -14
normalizedN+
2
signal(a.u.)
PSM parameter 'energy'
5, -13
6, -12
7, -11
8, -10
S. Große-Kreul et al., Plasma Sources Sci. Technol. 24 (2015) 044008
Simulation of ion optics in the sampling system
SIMION simulations
Real ion energy to maximize the transmission efficiency with all
tuned MS parameters: Eions = +0.8 eV
S. Große-Kreul et al., Plasma Sources Sci. Technol. 24 (2015) 044008 46
Simulation of ion optics x measurement
SIMION simulations
Real ion energy to maximize the transmission efficiency with all
tuned MS parameters: Eions = +0.8 eV
S. Große-Kreul et al., Plasma Sources Sci. Technol. 24 (2015) 044008#
S. Große-Kreul et al., Eur. Phys. J. D (2016), DOI: 10.1140/epjd/e2016-60601-4
47
Ion measurement from atmopsheric plasmas
S. Große-Kreul et al., Plasma Sources Sci. Technol. 24 (2015) 044008#
S. Große-Kreul et al., Eur. Phys. J. D (2016), DOI: 10.1140/epjd/e2016-60601-4
Seeded He beam – all ions reach the same velocity in the expansion –
energy scales linearly with their mass!
He/0.3%N2 discharge
0 energy
48
Outline
Particles
Ions
Sampling
Plasma
1 bar£
Energy
Analyser
m/z
Analyser Detector
Vacuum £ 10 mbar
-5
Ion transfer
Ion
Source
or Ion
Optics
1 Basics of MS - components
2 Species identification and quantification
3 Sampling
4 Examples
49
Example: analysis of an
etch process of a-C:H
Gas on (Ar + O2)
Gas off
Plasma running (200 W ICP)
O2
+
CO+
50
Example: a-C:H etching mechanism in Ar/O2 ICP
A. von Keudell,et al., Plasma Process. Polym. 7, 327 (2010)
51
"Cascaded arc":
thermisches Plasma
in Ar
"Plug-down"
Plasmachemie
C2H2 Fluss
T1
MS
T2
Ionisator
Chopper
Ti  Pumpen
p ~ 30 Pa
Benedikt et al., J. Phys. Chem. A 2005, 109, 10153
Example: MS of radicals in C2H2 plasma
52
Example: reaction path in Ar/C2H2 plasma
C3H3
C2H2
C
C2H C2CHCH2
C4,C4H
C2nH0,1,2
C4H2
C3H C3
C6H2C5H C5
`
auf dem Saturn-Mond Titan
Januar 2005:
Huygens Sonde!
in Fusionsreaktoren
bei der Verbrennung
bei der Verbrennung
Neu:
bei der Abscheidung
von a-C:H Schichten
+ Ar+,e+
C2H2
+ C4H2
+ H
+ Ar+,e+
C2H2
+ C4H2
+ H
im interstellaren
Raum
Benedikt et al., J. Phys. Chem. A 2005, 109, 10153
53
Example: Ion energy
distribution functions
in rf-plasma
[92] Zeuner M, Neumann H and Meichsner J
1997 J. Appl. Phys. 81 2985
54
Example: Ion energy
distribution functions
in HiPIMS plasmas
Breilmann et al.,
J. Phys. D: Appl. Phys. 48 (2015) 295202
Ionization zones (“spokes”)
0 10 20 30 40 50 60
104
105
106
107 plasma bez "spouku" 15 A
plasma se "spouky" 70 A (spokes)
ionty/s
energie iontu [eV]
Cr+
55
Conclusions
MS is a powerful diagnostic for plasma analysis:
• Detects the relative fluxes of positive and negative
ions including the information about their energies
• Provides absolute densities of neutral stable and
reactive species
• Careful design of MS diagnostic setup important
(is not trivial)
• Can be successfully applied to analysis of
atmospheric pressure plasmas
56