Transcript Plasma and ion bombardment File

XXX Thin Film Technology
Doctoral course
Plasma and ion bombardment
(8 credits)
Jari Koskinen, Sami Franssila
[email protected]
1.9.2016
Contents
•
Plasma
–
basic physics, parameters, ionization
–
types of plasma
–
generation of plasma
–
emission of ions,
•
plasma systems
•
2nd hour ion beam surface interactions
–
collisions, cascades
–
range
–
sputtering
–
simulations
–
mixing
2
Plasma
•Plasma
• Gas of positive ions, electrons and (mostly)
neutral atoms
• Etymology: Greek: “moulded” - plasma fills the
chamber
• Charge neutrality ne = ni
• Colliding electrons ionise atoms
• Ions and electrons accelerate in electric field
• Collisions excite atoms
• De-excitation creates photons – visible light
3
Important plasma parameters
•
•
•
•
Oscillations
Debye length
mean free path
ionization crossection
4
Hannu Koskinen Univ of Helsinki
5
hot&dense
<< 1
cold&sparce
Hannu Koskinen Univ of Helsinki
6
7
Different types of plasmas
Thin film plasma processes
Wikipedia
8
Hannu Koskinen Univ of Helsinki
n = density of atoms (and ions)
Total collistion cross section:
σtotal = σexitation + σion + σattachment+ σother
Bunshah, Handbook of Deposition Technologies for
Films and Coatings Noyes
9
Electron temperature
Bunshah, Handbook of Deposition Technologies for
Films and Coatings Noyes
10
Electron and ion temperature
Bunshah, Handbook of Deposition Technologies for
Films and Coatings Noyes
11
Plasma sheath
e.g. for practical sputter plasma
ds ≈ some tens x λD
Bunshah, Handbook of Deposition Technologies for
Films and Coatings Noyes
12
Cold cathode discharge
Bunshah, Handbook of Deposition Technologies for
Films and Coatings Noyes
13
Types of disharge
Typical mode in sputter deposition
Mahan, Physical Vapor Deposition of Thin Films, Wiley
14
Luminous regions in DC plasma
ions
neutralize
secondary
electrons have
slowed for max
ionization
electrons have
accelerated
sufficiently for
ionization
Mahan, Physical Vapor Deposition of Thin Films, Wiley
15
Practical sputtering plasma -1
•
•
•
•
•
•
Argon pressure 1 torr
atom density (n) 3 x 1016 cm-3
ni=ne 1010 cm-3
ionization fraction 3 x 10-7 (weakly ionized plasma)
ion temperature Ti 300K
electron temperature Te 23,000K
16
Densities and temperatures in process
plasmas
ions and neutrals
back scattered
form cathode
seconday
electrons thru
cathode sheath ions accelerated to
cathode
electrons in main
plasma
dissociation
products:
ions&neutrals
ions in main
plasma
process gas atoms&neutrals
17
Practical sputtering plasma -2
• VDC 1000V
• Vp 8V
• Current density at cathode 2 mA/cm2
• Cathode sheath L 2 mm
• mean free path λ 50 µm
Mahan, Physical Vapor Deposition of Thin Films, Wiley
18
Circuit models of DC plasma discharge
Mahan, Physical Vapor Deposition of Thin Films, Wiley
19
Ion energy at cathode
Ar+(hot) + Ar(cold)  Ar(hot)+Ar+(cold)
σ = 2.5 x 10-15 cm-3
Mahan, Physical Vapor Deposition of Thin Films, Wiley
20
AC plasma methods
21
AC plasma
Bunshah, Handbook of Deposition Technologies for
Films and Coatings Noyes
22
Forming of self-bias in AC discharge
Mahan, Physical Vapor Deposition of Thin Films, Wiley
23
Self bias at electrodes
n
n= 4 (sometimes 2)
No simple model.
One argument: “
impedance of smaller
are electrode is higher
-> higher potential
difference”
Sivu 24
Circuit models of RF plasma discharge
Mahan, Physical Vapor Deposition of Thin Films, Wiley
25
RF Plasma glow discharge
26
http://www.spectruma.de
Arc plasma
27
Arc discharge deposition
Arc discharge video
Arc disharge – cathode spot
www.shm-cz.cz/files/schema01.jpg
Arc discharge process
• arc current concentrated into filaments – arcs
• intense electron emission
•intense ion emission due to electron current ( atoms/electrons – 1/100)
•ionization of atoms – formation of plasma
•flow of ions to cathode – intense sputtering of atoms
• 106 - 108 A/m2
• overlapping thermal spikes
• materials is melted and sublimated in cathode spots
• cathode spots move randomly or could be steered by using magnets
• electons ionize vapor and create more electrons – increase of current
• ions accelerate
Timko, Nordlund
simulations
• due to potential difference in plasma
http://prb.aps.org/suppleme
• due to multiple collisions with fast electrons
ntal/PRB/v81/i18/e184109
• macro particles (up to 10 µm diam.I are formed
Filtered arc
HIPIMS
32
HIPIMS
W. Sproul, AEPSE 2009 Tutorial
“Pulsed Plasma
Diffusion”
HIPIMS
W. Sproul, AEPSE 2009 Tutorial
HIPIMS
W. Sproul, AEPSE 2009 Tutorial
HIPIMS Cr
W. Sproul, AEPSE 2009 Tutorial
HIPIMS
W. Sproul, AEPSE 2009 Tutorial
Fluxes of ions in HIPIMS
J. Vac. Sci. Technol. A, Vol. 28, No. 4, Jul/Aug 2010
Sivu 38
HIPIMS denser films
W. Sproul, AEPSE 2009 Tutorial
Reactive sputtering
W. Sproul, AEPSE 2009 Tutorial
Reactive sputtering
W. Sproul, AEPSE 2009 Tutorial
Reactive sputtering
W. Sproul, AEPSE 2009 Tutorial
Reactive sputtering
W. Sproul, AEPSE 2009 Tutorial
Reactive sputtering
W. Sproul, AEPSE 2009 Tutorial
Reactive sputtering
W. Sproul, AEPSE 2009 Tutorial
Ion solid interarctions
46
Energetic ion surface interactions
Secondary electrons
Desorption, cleaning
Sputtering
Collision cascade, thermal spike
K. Nordlund
doping, compounds
Range of ions
Sivu 53
Range
Sivu 54
Collision cascades
Sivu 55
Range and stopping
range:
enegy loss:
stopping:
Sivu 56
Reduced stopping
Sivu 57
10 keV Si recoil atom in silicon
K. Nordlund
58
1 keV C+ in glass, Range
59
Range and damage 30 keV Ne+ in ZrO2
60
Kai Nordlund Univ of Helsinki
Simulations
• http://beam.acclab.helsinki.fi/~knordlun/anims.html
61
Sputtering
• Source of atoms and ions
• Cleaning: Removing lose atoms, impurities, oxides
Sivu 62
Sputter constant
low ion energies < 1 keV
Sivu 63
Sputtering yield
64
Sputter yield angle dependence
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Sputter yield angle dependence and energy distribution
66
Sputter yield angle dependence and energy distribution
67
Energy distribution of sputteres atoms
Usb/2
1/E2
Sivu 68
Preferential sputtering
Sivu 69
TRIM and SRIM simulations
• http://www.srim.org/
Sivu 70