lecture 16 pvd
TRANSCRIPT
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Copyright A.J. StecklJ.C. Heikenfeld
All rights reserved2007
Lecture 16
Physical Vapor Deposition I
Definition for Physical Vapor Deposition (PVD)
-molecules are removed from a source, transported in vacuum, anddeposited on substrate (physi-sorption)
- in contrast chemical vapor deposition (CVD) involves chemical reaction
- need vacuum: the pressure usually < 10-2 Torr. (760 Torr = 1 atm)
At 1 atm : P = 760Torr Lm=
5 103
760 6.6 10
6cm 66nm
At 1 mTorr : Lm=
5 103
103
= 5cm
At 10-5Torr : L
m=
5 103
105
= 500cm = 5 meters!
Lmcm( ) =
5 103
P,
P = Pressure in Torr
Need vacuum in order to:
- prevent incorporation of background molecules (oxygen, etc.)
- minimize intermolecular collision (mean free path, Lm) so that moleculescombine only when they reach the substrate
moleculeor atom
source
d < Lm substrate
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Copyright A.J. StecklJ.C. Heikenfeld
All rights reserved2007
Lecture 16
Physical Vapor Deposition I
How is low pressure achieved?
1 atm = 760 Torr.
Mechanical pump (~10-3 Torr)
TurboMolecular Pump (~10-6 Torr)
Cryogenic Pump (~10-9 Torr)
>50,000 rpm!
liquid He cooled
down to ~ 10K!
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Copyright A.J. StecklJ.C. Heikenfeld
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Lecture 16PVD Techniques
A.Evaporation
- evaporation (from solid) or sublimation (solid)
- material held in a boat or crucible
- heat: direct electric current through resistor
indirect high current e-beam
local heating by e-beam less contamination
B.Molecular Beam Epitaxy (MBE)
- specially designed effusion cell (thermal evap)
- can also use plasma and low-pressure gases
- deposit material with atomic control (layer-by-layer)
C.Plasma-Assisted Deposition
- DC or RF sputtering
reactive sputtering
magnetron sputtering
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Copyright A.J. StecklJ.C. Heikenfeld
All rights reserved2007
Lecture 16Vapor Pressure
Fig. 12-1 Vapor pressure curves for selected materials.
W
Ta
MoNi
Cr
Au
Melting Pt.
typical requiredvapor pressure
Al
use
evaporation
usesputtering
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Copyright A.J. StecklJ.C. Heikenfeld
All rights reserved2007
Lecture 16Thermal Evaporation
Crucible Basket Coated Boat
Conical BasketCoils
Note angulardependence ofevaporated material fromvarious sources
/s
90 1800
material material
0
90
180
substratebad designnon-uniform film better approach
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Copyright A.J. StecklJ.C. Heikenfeld
All rights reserved2007
Lecture 16e-Beam Evaporation
Bent Beam Approaches:Bent Beam Approaches:
-no back-deposition from crucible to e-gun minimize contamination
- also more compact
Indirectly Heated:Indirectly Heated:local heating by electron beam less contamination
- e-beam current (usually in hundred mA), electron energy ~1-3 keV
InlineInline ApproachApproach
Target material
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Copyright A.J. StecklJ.C. Heikenfeld
All rights reserved2007
Lecture 16Molecular Beam Epitaxy
Fig. 12-6
A basic MBE
deposition system.
Dinger [13].
Molecular beam epitaxy (MBE) uses evaporation but
- low pressure (
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Copyright A.J. StecklJ.C. Heikenfeld
All rights reserved2007
Lecture 16MBE Systems
Veeco MBE Systems
thermally isolatedeffusion cell
(allow high temperature)
Crucibles - conical evap. profile
production: 4x4 wafersR&D machine
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Copyright A.J. StecklJ.C. Heikenfeld
All rights reserved2007
Lecture 16Sputter Deposition
Physical bombardment of heavy and inert atoms (Ar) causes atoms or
molecules at target to be removed
example:RFsputtering Ar Ar+ e-
substrate
target
chamberwall
~
C
1) RF voltage creates a plasma ofAr+ and e-
2) target:plasma capacitance has less
area that wall:plasma capacitance
3) therefore plasma (voltage drop)
occurs near the target
~10 mTorr
substrate
target
chamberwall
~
C
4) e- smaller mass than Ar+ move quicklyenough in RF (MHz) field to reach the target
5) these electrons build up -DC voltage on
target (~100s V)
6) negative voltage causes Ar+ acceleration
toward target and sputtering of material
deposited material
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Copyright A.J. StecklJ.C. Heikenfeld
All rights reserved2007
Lecture 16Sputter Deposition Equipment
3 sputtertargets
RF matching network
Loadlock
power/controls
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Copyright A.J. StecklJ.C. Heikenfeld
All rights reserved2007
Lecture 16Sputtering Techniques
(A) Sputter Deposition Ar gas: easy to achieve plasma (i.e. breakdown) & high mass (~40
AMU)
DC or RF power can generate plasma
DC only for conductive target, RF for both conductive & insulatingtargets
Efficient: no major differences for conductive target material
(B) Reactive Sputtering
If compound or alloy not available, it can be formed by chemical reaction
Examples: Si target + reactive gas N* (N2) Si3N4
(C) Planar Magnetron Sputtering (electron cyclotron)
Permanent magnet increases the plasma density
100 to 500 gauss
High deposition rate (> sputtering or evaporation)
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Copyright A.J. StecklJ.C. Heikenfeld
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Lecture 16Sputtering Techniques
N
S
N
S
N
S
N
S
S
N
S
N
S
N
material
e-
e-
magnetic field increases path length for electron- increased ionization of ArAr++ e-
-increasedflux of Ar+and sputter rate
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Copyright A.J. StecklJ.C. Heikenfeld
All rights reserved2007
Lecture 16
Calendar
Dec. 7Dec. 6
Final Exam
8:00AM
Dec. 5
WEEK
Dec. 4
FINALS
Dec. 3
Nov. 29
Q & A
899 Rhodes Hall
Nov. 27
Physical VaporDeposition
Lecture 16
Nov. 22
No School
Thanksgiving
Nov. 20
Lithography/
Resist
Lecture 15
Nov. 15
Etching
Lecture 14
Nov. 13
QUIZ #2
Nov. 8
Ion Implantation:Dose/Damage
Lecture 13
Nov. 6
Ion Implantation:Mechanisms
Lecture 12
Nov. 1
Diffusion:
npn BJT
Lecture 11
Oct. 30
Diffusion in Si
Lecture 10
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