ICOPS Minicourse on Plasma Processing Technology

1
ICOPS Minicourseon Plasma Processing Technology

• Part 1 Vacuum Basics
• Jeff Hopwood
• Northeastern University

2
Goals

• To review basic vacuum technology
• Pressure, pumps, gauges
• To review gas flow and conductance
• To understand the flux of vapor phase material to
  a substrate
• To understand mean free path, l

3
Vacuum (units)
4
Rough Vacuum

• Mechanical Pumps typically create a base
  pressure of 1-10 mTorr or 0.13-1.3 Pa

Warning Certain process gases are incompatible
with pump fluids and pose severe safety risks!
Rotary Vane Pump (Campbell)
5
High Vacuum Pumping

• Cryopumps condense gases on cold surfaces to
  produce vacuum
• Typically there are three cold surfaces
• Inlet array condenses water and hydrocarbons
  (60-100 Kelvin)
• Condensing array pumps argon, nitrogen and most
  other gases (10-20 K)
• Adsorption is needed to trap helium, hydrogen and
  neon in activated carbon at 10-12 K. These gases
  are pumped very slowly!

(Campbell)
Warning all pumped gases are trapped inside the
pump, so explosive, toxic and corrosive gases are
not recommended. No mech. pump is needed until
regen.
adapted from www.helixtechnology.com
6
High Vacuum Pumping
Process chamber
Turbomolecular Pump High rotation speed turbine
imparts momentum to gas atoms Inlet pressures
lt10 mTorr Foreline pressure lt 1 Torr Requires a
rough pump Good choice for toxic and explosive
gases -gases are not trapped in pump All
gases are pumped at approx. the same rate Pumping
Speeds 20 2000 liters per sec
foreline
adapted from Lesker.com
7
High Vacuum Pumping
Diffusion Pump The process gas is entrained by
the downward flow of vaporized
pumping fluid. Benefits Low cost, reliable, and
rugged. High pumping speed 2000
l/s Caution The process chamber will
be contaminated by pumping fluid. A cold trap
must be used between the diffusion pump and the
process chamber. Not recommended for clean
processes.
Process chamber
Water- cooled walls
Foreline -to mech pump
Heater/Pumping Fluid
adapted from Lesker.com
8
Flow Rate

• Typically gas flows are cited in units of
  standard cubic centimeters per minute (sccm) or
  standard liters per minute (slm)
• Standard refers to T273K, P 1 atm.
• Example
• Process gas flow of 50 sccm at 5 mTorr (_at_300k)
  requires
• 50 cm-3min-1(760Torr/5x10-3Torr)(300/273)(1min/60s
  ec)(1/103)
• 140 liters/sec of pumping speed at the
  chamber pump port

9
Conductance Limitation
50 sccm
Conductance depends on geometry and pressure (use
tabulated data)
5 mTorr
140 l/s
Q/(P1 P2) Fixed Throughput, Q Q 0.005
Torr x 140 l/s 0.7 Torr-l/s
gt 140 l/s since P2ltP1
Corifice ¼ (pa2)ltvgt l/s Ctube pa3
(2ltvgt/3L) if mean free path gtgt a, L (see Mahan,
2000)
10
Pressure Measurement
RGA A simple mass spectrometer
Vacuum Gauge Selection adapted from Lesker.com
11
Residual Gas Analysis
Low pressure systems are dominated by water vapor
as seen in this RGA of a chamber backfilled with
4x10-5 torr of argon Why? H2O is a polar molecule
that is difficult to pump from the walls --gt
bake-out the chamber
Leak?
Source Pfeiffer vacuum products
12
Gas Density (n)

• Ideal Gas Law
• PV NkT
• Gas density at 1 Pascal at room temp.
• N/V n P/kT
• (1 N/m2)/(1.3807x10-23J/K)(300 K)
• 1 (kg-m/s2)/m2/4.1x10-21 kg-m2/s2
• 2.4x1020 atoms per m3
• 2.4x1014 cm-3 at 1 Pa
• Rule of Thumb
• n(T) 3.2x1013 cm-3 x (300/T) at a pressure
  of 1 mTorr

13
Gas Kinetics
Maxwellian Distribution
Average speed of an atom
Flux of atoms to the x-y plane surface
Very important!
(Campbell)
14
Example

• A vacuum chamber has a base pressure of 10-6
  Torr. Assuming that this is dominated by water
  vapor, what is the flux of H2O to a substrate
  placed in this chamber?
• n 3.2x1013 cm-3/mTorr 10-3 mTorr 3.2x1010
  cm-3
• ltvgt (8kT/pM)1/2 59200 cm/s
• Gz (¼)nltvgt 4.74x1014 molecules per cm2 per
  sec!
• This is approximately one monolayer of H2O every
  second
• at 10-6 Torr base pressure.

15
Collisions and Mean Free Path
Gas Density n P/ kT
Cross-section s pd2
l 1/sn
d
Ar
16
ICOPS Minicourseon Plasma Processing Technology
Part 2 Plasma Basics Jeff Hopwood Northeastern
University
17
Plasma an ionized gas consisting of atoms,
electrons, ions, molecules, molecular fragments,
and electronically excited species (informal
definition)
www.geo.mtu.edu/weather/aurora/
18
Plasma the fourth state of matter
solid (ice)
19
DC Plasma (or AC Fluorescent Lampwhy AC?)
Argon Mercury _at_ 0.05 atm.
-


lamp endcap
20
Paschen Curve
F. Paschen, Ann. Phys. Chem., Ser. 3 37, 69
(1889).
http//www.duniway.com/images/pdf/pg/Paschen-Curve
.pdf
21
What do we need to know about plasma?
Wall
Wall
PLASMA
substrate
22
Power Absorbed
Power
Wall
Wall
PLASMA
electrons ne, Te
substrate
23
Power Absorbed DC

• DC power
• General electrical mobility and conductivity
• Mobility me qlttgt/m q/nmme
• Where lttgt is the average time between collisions
• and nm is the collision frequency (collisions per
  second)
• Electron Conductivity sDC qneme q2ne/nmme
• DC power absorbed

24
Power Absorbed RF

• RF/microwave power
• Ohmic Heating
• Generic electron-neutral collision frequency
• nm 5x10-8 ngasTe1/2 (s-1)
• ngas (cm-3),
  Te(eV).
• Example Find the pressure at which rf ohmic
  heating becomes ineffective nm 0.1w, Te 2eV
• w 13.56 MHz 2p 85.2Mrad/s
• ngas 0.185.2x106/5x10-8(2)1/2
  1.2x1014 cm-3 3.7 mTorr

f13.56 MHz
An electron oscillates in a rf electric field
without gaining energy unless electron collisions
occur
Hopwood and Mantei, JVST A21, S139 (2003)
25
Stochastic Heatingan electron enters and exits a
region of high field for a fraction of an rf
cyclet0 ltlt 2p/w
Reflecting Boundary (plasma sheath)
Emax
ERF
z
x
-
E 0
vx(t0) gt vx(0)
The usual mechanism for heating electrons using
RF electric fields at low pressures
26
Wave/Resonant Heating
BDC
E0
v
y
F q(vxB)
x
Hopwood and Mantei, JVST A21, S139 (2003)
27
Electron Collisions
Power
Wall
Wall
PLASMA
electrons ne, Te
substrate
28
Electron Collisions

• Elastic Collisions
• Ar e ? Ar e
• Gas heating energy is coupled from e to the gas
• Excitation Collisions
• Ar ehot ? Ar ecold, Ar ? Ar hn
• Responsible for the characteristic plasma glow
• EelectrongtEexc (11.55 eV for argon)
• Ionization Collisions
• Ar ehot ? Ar 2ecold
• Couples electrical energy into producing more e_
• Eelectron gt Eiz (15.76 eV for argon)
• Dissociation
• O2 ehot ? 2O ecold or O2 ehot ? O O
  ecold
• Creates reactive chemical species within the
  plasma
• Eelectron gt Ediss (5.12 eV for oxygen)

29
Collision Cross Sections

• Unlike the hard sphere model, real collision
  cross sections are a function of electron kinetic
  energy s(E), or electron velocity s(v).
• We must find the expected collision frequency by
  averaging over all E or v.

becomes
(cm3s-1)
30
Graphically
f(E)
f(E) or s(E)
sAr(E)
Note the exponential tail of energetic electrons
is responsible for ionization
Electron energy, E
Te
Eiz
The RATE CONSTANT Kiz(Te) ? Kizoexp(-Eizo/Te)
curve fitting
31
Graphically
Hot electrons more ionization
f(E)
f(E) or s(E)
sAr(E)
Note the exponential tail of energetic electrons
is responsible for ionization
Electron energy, E
Te
Eiz
The RATE CONSTANT Kiz(Te) ? Kizoexp(-Eizo/Te)
curve fitting
32
Examples of Numerically Determined Rate Constants
(Lieberman, 2005)
33
Generation Rate of Plasma Species by Electron
Collisions

• y e ? x e
• dnx/dt Kxneny
• For example,
• Ar e ? Ar e e
• dne/dt Kiznengas
• is the number of electrons (and ions) generated
• per cm3 per second

34
Electron-Ion Recombination
Three-Body Problem e Ar M ? Ar M the
third body is needed to conserve energy and
momentum in the recombination process
volume recombination
wall recombination
-
M
-
M
M


wall recombination dominates at low pressure
because three body collisions are rare
35
Transport to Surfaces
Power
Wall
Wall
PLASMA
electrons ne, Te
substrate
36
Electron and Ion Loss to the Substrate and
Walls- the plasma sheath -
ne?ni r ? 0
chamber
electrons are much more mobile than ions me
qlttgt/me gtgt qlttigt/mi mi
37
Electron and Ion Loss to the Substrate and
Walls- the plasma sheath -

low energy electrons are trapped within the
plasma, but ions are accelerated by the sheath
potential to the chamber walls and substrate
38
Ion Flux

• The ion flux to a solid object is determined by
  the Bohm velocity (or sound speed) of the ion
• uB (kTe/mi)1/2 9.8x105 (Te/M)1/2 cm/s
• 9.8x105 (3 eV/40 amu)1/2 2.5x105 cm/s
• and the ion flux is given by Gi uBni
  (cm-2s-1)
• (this is the ion speed at the edge of the sheath)

39
Electron Flux

• Only the most energetic electrons can overcome
  the sheath potential, Vs.
• Ge ¼ neltvegt exp (qVs/kTe)

flux to surface
Boltzmann factor
f(E)
Electron energy, E
Te
qVs
40
Sheath Potential, Vs

• In the steady state, the electron and ion fluxes
  to the chamber/substrate must be equal, if there
  is no external current path
• Ge Gi
• ¼ neltvegt exp (qVs/kTe) uBni (kTe/mi)1/2 ne
• giving
• Vs -Teln(mi/2pme) -5Te
• This is often called the floating potential
• Isolated surfaces have a negative potential
  relative to the plasma.

41
Ion Energy
Ex Assuming argon with Te 3 eV, the ion
energy at the cathode is Ei q(1 kV
4.7Te) 1014 eV ignoring ion-neutral collision
within s, and the ion energy at the anode is
Ei 4.7 Te 14 eV Ion mean free path li
1/ngassi 3/p (cm) for Ar where p is the
pressure in mTorr Here li 3/100 cm or 0.3 mm _at_
0.1 torr NOTE sgtgtli ? Ei ltlt 1014 eV!
42
Particle Conservationand Electron Temperature

• A simple model for electron temperature can be
  found for a steady state plasma
• of ions created/sec of ions lost/sec
• KizngasneV uBniAeff
• Kiz/uB Kizoe-Eiz/kTe /(kTe/mi)1/2 Aeff/(V
  ngas)
• 1/deffngas
• (Vplasma volume, Aeff effective chamber area,
  deff V/Aeff)

43

• The electron temperature (Te) is a unique
  function of
• gas density, ngas (pressure)
• chamber size, deff V/Aeff
• gas type Kiz, Eiz

Example Two large parallel plates separated by 2
cm are used to sustain an argon plasma at 25
mTorr. Find Te. deff V/Aeff pR2d / (pR2
pR2) d/2 ngasdeff (253.2x1019m-3)(0.01m)
0.8e19 m-2 Te 3 eV (Note we have assume
that the plasma density is uniform)
44
Power Conservation and Electron Density, ne

• Power Absorbed by the Plasma Power Lost from
  the Plasma
• Pabs qniuBEionq(¼neltvegteVs/kTe )EelecAeff
  (PheatPlightPdiss)
• qneuBAeff(Eion Eelec Ec)
• where EC is the collisional energy lost in
  creating an electron-ion pair due to ionization,
  light, dissociative collisions, and heat
• EC nizEiz nexEex ndissEdiss
  nm(3me/mi)Te/niz

Pion
Pelectron
2Te
qVs
45
Collisional Energy Loss
46
Electron Density Example

• Continuing with the previous example
• A plasma is sustained in argon at 25 mTorr
  between to parallel plates separated by 2 cm.
  The radius of the plates is 20 cm and the power
  absorbed by the plasma is 100 watts. Find ne.
• 100 W qneuBAeff(Eion Eelec Ec)
• (1.6x10-19C)ne(2.5x105cm/s)(2px202 cm2) x
• (5Te 2Te 55 eV)
• ? ne 1.3x1010 cm-3
• Find ne if the gas is N2, assuming that Te 3 eV
• 100 W (1.6x10-19C)ne(2.5x105cm/s)(2px202
  cm2)(5Te 2Te 400 eV)
• ? ne 2.3 x 109 cm-3

47
Example (contd)

• Repeat the previous example using argon, BUT
  include an electrode voltage of 1000v that is
  applied to one plate to sustain the plasma.
• 100 W qneuBAeff(Eion Eelec Ec)
• (1.6x10-19C)ne(2.5x105cm/s)(px202 cm2) x
• (5Te 2Te 55 eV)(1000 eV5Te) 2Te 55
  eV
• ? ne 1.7x109 cm-3

anode
cathode
48
Secondary ElectronsGe gsec Gi , where
gsec0.1-10 and Ee qVs
Power
Wall
Wall
PLASMA
electrons ne, Te
secondary electrons
secondary electrons
substrate
49
Summary
Wall
Wall
PLASMA
substrate
50
Basic Plasma Technology
51
Basic Plasma TechnologySputtering Magnetron
DC Pulsed RF
S
S
N
Target
N
N
S
Substrate
to pump
52
Basic Plasma TechnologyCapacitively Coupled
Plasma
0.4 60 MHz
Hopwood and Mantei, JVST A21, S139 (2003)
53
Basic Plasma TechnologyElectron Cyclotron
Resonance Plasma
Hopwood and Mantei, JVST A21, S139 (2003)
54
Basic Plasma TechnologyInductively Coupled Plasma
0.4 13.56 MHz
Hopwood and Mantei, JVST A21, S139 (2003)
55
ICOPS Minicourseon Plasma Processing Technology
Part 3 Physical Vapor Deposition Jeff
Hopwood Northeastern University
56
OUTLINE

• Evaporation
• Sputtering
• Ionized Physical Vapor Deposition

57
Deposition by Evaporation

• Heating materials until the vapor pressure is
  non-zero followed by condensation of the vapor on
  a (relatively cold) substrate.
• electron beam evaporation
• thermal evaporation
• molecular beam epitaxy
• laser ablation
• arc deposition

58
Two Types of Evaporation
Quasi-equilibrium liquid-vapor equilibrium
within the cell
Non-equilibrium vapor is emitted into a low
pressure volume no liquid-vapor equilibrium
S.M. Rossnagel, J. Vac. Sci. Technol. A 21,
Sep-Oct 2003
59
Typical e-beam evaporator
60
Vapor Pressure vs. Temperature
Differing vapor pressures make evaporation of
alloys quite difficult Ex TiW Solutions Rod-f
ed evaporation Multiple evaporators
61
Evaporative Flux and Conformality
62
Sputtering Outline

• RF Diodes vs. Magnetrons
• electron and ion density
• Mechanism collision cascades
• sputter yield
• angular distribution
• Thomson distribution
• Reflected neutrals and ion-assisted dep.
• film morphology and film stress
• Sputtering Alloys
• Reactive sputtering

63
Sputtering System
64
Magnetron Sputtering
B-field traps secondary electrons near the target
surface
TARGET 300v
B
P 0.1 5 mTorr B 200 G VTARGET 300 v Ee
300 eV ? 300 eV / (15.76 eV/ion) 19 ions
per secondary rce ve/wce 3 mm

ne 1012 cm-3

ne 109 cm-3
65
(No Transcript)
66
Physical Outcomes of Ion Bombardment
Surface Binding Energy, Usb
Collision Cascade
67
Sputtering YieldY(E) number of ejected atoms
per incident ion
Empirical Yield Y(E) 6.4x10-3 mT g5/3
E1/4(1-Eth/E)3.5 where g 4mgmT / (mgmT) 2
Eth 4Usb/g
J. Bohdansky, J. Roth, and H.L. Bay, An
analytical formula and important parameters for
low-energy ion sputtering, J. Appl. Phys. 51(5)
2861- (1980). J.E. Mahan, Physical Vapor
Deposition of Thin Films, p. 207ff (Wiley, New
York, 2000).
68
Angular Distribution of Sputtered Atoms

• Gs (E,q) Y(E) Gi (cos q)/p

TARGET
Gi
69
Thompson Distribution of Energies for Sputtered
Neutral Atoms
Es
Most probable energy is half the surface binding
energy, Usb/2 There is a very broad high energy
tail, such that ltEsgt 10s eV
70
Energetic DepositionEnhances adatom surface
mobility ? promotes dense films, film stress
71
Sputtering of Alloys

• Alloys may be stoichiometrically sputtered, even
  if the component materials have different sputter
  yields, due to conservation of mass
• The target surface must be conditioned by
  pre-sputtering prior to actual deposition

YagtYb
conditioning makes the surface deficient in
element a
72
Reactive Sputtering
N2, O2, (Ar)
Metals
Metal-nitrides and metal-oxides
73
Reactive Sputtering
metal target, e.g. Ti
poisoned target, e.g. TiN
S.M. Rossnagel, J. Vac. Sci. Technol. A 21,
Sep-Oct 2003
74
Ionized Physical Vapor DepositionIPVD
75
IPVD Outline

• Introduction
• Definitions
• Motivations
• Example Application
• The physics of IPVD
• The evolution of IPVD technology
• Unbalanced magnetron
• geometric filtering of neutrals (collimated,
  long-throw)
• auxiliary high density plasma
• ICP and ECR
• high power density sputtering
• SIP, hollow cathode magnetron, pulsed sputtering
• Deposition and modeling
• Summary and discussion

76
Ionized-PVD Definition

• Physical vapor deposition in which more than half
  of the deposited atoms arrive at the substrate as
  ions.
• e.g., for sputtering of metals Gm gt Gm at the
  substrate.
• Includes sputtering, evaporation, arcs, laser
  ablation

77
Motivation

• The energy and direction of ionized depositing
  species are easily controlled with electrostatic
  fields and/or sheath voltage.
• In contrast, neutral depositing species are
  difficult to control.

78
Comparison of Sputtering Techniques
       
tt
w
d
tb
(tb/tt)
(d/w)
Ref S.M. Rossnagel, J. Vac. Sci. Technol. B,
16(5), 2585 (1998)
79
Example ApplicationDeposition into High Aspect
Ratio Trenches and Vias
J. Forster, Ionized Physical Vapor Deposition,
Academic, 2000.
J. Hopwood, Ionized Physical Vapor Deposition,
Academic, 2000.
80
Example ApplicationA dual damascene process
J. Hopwood, Ionized Physical Vapor Deposition,
Academic, 2000.
81
Outline

• Introduction
• Definitions
• Motivations
• Example Application
• The physics of IPVD
• The evolution of IPVD technology
• Unbalanced magnetron
• geometric filtering of neutrals (collimated,
  long-throw)
• auxiliary high density plasma
• ICP and ECR
• high power density sputtering
• SIP, hollow cathode magnetron, pulsed sputtering
• Deposition and modeling
• Summary and discussion

82
Ionized PVD Physics

• Ionization mechanism
• Sputter neutral energies
• Ionization mean free path
• thermalization vs. long path length
• Ionized flux vs Ionization fraction
• Spatial Distribution Diffusion

83
Ionization MechanismPenning ionization vs.
Electron collisions

• Penning ionization Ar M ? M Ar
• Eex gt 11.55 eV for argon
• Eiz 6 - 8 eV for most metals
• Kp sp(kTg/M)1/2
• Electron impact M e ? M 2e
• for moderate sputter rates, nAr gtgt nM
• Te is determined by argon ionization energy
• Eiz(argon) gtgt Eiz (metal)
• Kiz ko exp(-Eiz(M)/kTe(Ar))

84
IPVD Physics the metal
Ionization of thermal metal atoms, M

• Lifetime
• of an ion
• diffusion
• to walls (R,L)

Particle balance creation rate of metal ions
(Penning, electron impact, and 2-step) is equal
to the loss of metal ions due to diffusion to the
chamber walls and substrate
85
IPVD Physics the argon
generation and loss of Ar
generation and loss of Ar
86
IPVD Physics metal ionization
electron density, from Pabs
ion lifetime
argon density (pressure)
excited argon lifetime
rate constant for excited Ar
rate constant for Penning ionization of metal
rate constant for electron impact ionization of
metal
87
Ionization MechanismPenning ionization vs.
Electron collisions
Typical sputtering, ne1010 cm-3 Penning
Dominates ArM?MAr Ionization is lt5
IPVD, ne1012 cm-3 Electron Impact Dominates M
e ? M 2e Ionization is gt50
J. Hopwood, J. Appl. Phys, 1995
88
Sputtered Neutral Energyand Ionization MFP
MFP5 cm required to ionize 50 Al
?iz vs / Kizne
from W.M. Holber, Ionized Physical Vapor
Deposition, Academic, 2000.
ne 2x1012 cm-3 Te 3 eV
50 of Al has Egt6 eV
50 ionization requires at least ne1012 over a
distance of 10 cm
89
High Pressure IPVDThermalize, Ionize, Collimate
10-50 mTorr lth 24/p cm
presheath
90
Limitation due to the Presheathpresheath width ?
ion mean free path ? collisions ? decreased
collimation of ions
91
Titanium Transverse Temperature at the Sheath
Edge (s) and Ionized Flux Fraction ()     Target
Power 1 kW
  - This measurement corresponds to an ion
divergence of 5o to an unbiased wafer -
Consistent with Monte-Carlo simulations ?
increase V0 to narrow the angular distribution
92
Help from the Presheath

• Ions are accelerated by the presheath region into
  the wafer
• ion flux GM 0.61 nM(kTe/M)1/2
• Thermal neutrals simply diffuse to the wafer
• neutral flux GM 1/4nM(8kTM/pM)1/2
• Ionization of the depositing metal flux is
• GM/GM k(nM/nM)(Te/TM)1/2

Typically, Te gtgt TM
93
Neutral and Ion Diffusion
J. Hopwood, Ionized Physical Vapor Deposition,
Academic, 2000.
Li, Vyvoda, and Graves, Ionized Physical Vapor
Deposition, Academic, 2000.
Experiment
2D Model
T
W

94
Outline

• Introduction
• Definitions
• Motivations
• Example Application
• The physics of IPVD
• The evolution of IPVD technology
• Unbalanced magnetron
• geometric filtering of neutrals (collimated,
  long-throw)
• auxiliary high density plasma
• ICP and ECR
• high power density sputtering
• SIP, hollow cathode magnetron, pulsed sputtering
• Deposition and modeling
• Summary and discussion

95
The Evolution of IPVD

• Unbalanced Magnetron
• Geometric Filtering of Errant Neutrals
• Magnetron plus
• Inductively Coupled Plasma
• ECR Plasma
• Self-ionized Unbalanced Reprise
• High power density/Geometric/Pulsing

96
Unbalanced Magnetron

• Unbalanced magnetic field allows electrons and
  ions to escape away from target
• ne 1012, but not over a distance of 10 cm.

• Metal ionization lt50, but a much greater Ar
  flux than balanced magnetron
• Allows large argon ion-to-metal flux ratios

6 cm
Windows and Savvides, J. Vac. Sci. Technol. A 4,
453 (1986)
97
Geometric Filtering of High-Angle Neutrals

• Collimated Sputtering
• Rossnagel et al, J. Vac. Sci. Technol A9, 261
  (1991).

• Long-throw Sputtering
• Motegi et al, J. Vac. Sci. Technol. B 13, 1906
  (1995).

98

• ECR ionized evaporation
• Holber et al, J. Vac. Sci. Technol. A 11, 2903
  (1993).

99
Magnetron Plus

• Inductively Coupled Plasma (ICP)
• Electron Cyclotron Resonant Plasma (ECR)
• Helicon Wave Plasma
• all provide ne 1012 cm-3 over gt10 cm

100
Magnetron plus
plus ICP from M. Yamashita, J. Vac. Sci.
Technol. A 7, 151, (1989).
plus ECR from W.M. Holber, Ionized Physical
Vapor Deposition, Academic, 2000.
101
Self-ionized IPVD Unbalanced Magnetron Reprise

• Increase electron density
• Increase plasma length
• Use geometric filtering of neutrals
• Low pressure (no thermalization reqd.)
• Medium-Long throw distance
• Simplified operation no auxiliary plasma is
  required for ionization

102
Self-ionized Plasma, SIP
Hollow Cathode Magnetron
Helmer, Lai, and Anderson, US Patent 5,482,611,
Jan. 9, 1996
Fu et al, US Patent 6,251,242, June 6, 2002.
103
Self-ionized IPVD Unbalanced Magnetron
Reprise

• Increase electron density
• Higher power (10s kW) in smaller area of
  magnetic field
• Requires aggressive cooling/rotation/pulsed power
• Increase plasma length
• Intense plasma inside hollow cathode
• Use geometric filtering of neutrals
• Ions are extracted by magnetized electrons?
• Neutrals are transported across cathode ?

K.Lai, Ionized Physical Vapor Deposition,
Academic Press, 2000.
Target
-

104
Self-ionized IPVD Pulsed Target Power

• Pulsed Power
• 2000V x 1200 A
• 50 100 ms pulse
• 50 Hz rep rate
• Typically,
• 600 W/cm2
• Ppeak 100 kW
• ne 1-5x1012 cm-3
• Pave 500 W
• K.Macak, V.Kouznetsov, J.Schneider, U.Helmersson,
  I.Petrov, Ionized sputter deposition using an
  extremely high density plasma,J. Vac. Sci.
  Technol. A 18, 1533 (2000).

105
Outline

• Introduction
• Definitions
• Motivations
• Example Application
• The physics of IPVD
• The evolution of IPVD technology
• Unbalanced magnetron
• geometric filtering of neutrals (collimated,
  long-throw)
• auxiliary high density plasma
• ICP and ECR
• high power density sputtering
• SIP, hollow cathode magnetron, pulsed sputtering
• Deposition and modeling
• Summary and discussion

106
Deposition Modeling
A comparison of models and measured film
characteristics 1. metal deposition by IPVD 2.
metal-nitride reactive IPVD
107
Ionization of Metal no substrate bias (Y0)

• Higher ionization of the metal results in more
  deposition at the bottom of the trench
• Inward growth of the overburden forms a keyhole
  structure
• S. Hamaguchi and S. M. Rossnagel, J. Vac. Sci.
  Technol. B 13, 183 (1995).

33
50
67
108
Substrate Biasing

• Energetic ions bombard the film and cause
• faceting
• sputtering and redeposition
• A primary means of coating the sidewalls of
  trenches
• V.Arunachalam, S.Rauf, D.G.Coronell, and P.L.G.
  Ventzek, J. Appl. Phys. 90, 64 (2001)

Lu and Kushner, JVST A 19, 2652 (2001)
109
Surface Diffusion Thermal and Ion Induced
110
Reactive SputteringTiN deposition using IPVD
contour lines are the film resistivity
Tanaka, Kim, Forster, and Xu, J. Vac. Sci.
Technol. B 17, 416 (1999).
111
Reactive SputteringTiN deposition using IPVD
Tanaka, Kim, Forster, and Xu, J. Vac. Sci.
Technol. B 17, 416 (1999).
112
Reactive SputteringTiN deposition using IPVD
Tanaka, Kim, Forster, and Xu, J. Vac. Sci.
Technol. B 17, 416 (1999).
113
Plasma Composition in Ti/N2/Ar
15-30 dissociation of N2
K. Tao, et al., J. Appl. Phys. 91, 4040 (2002)
114
Plasma Composition in Ti/N2/Ar
15 mTorr, ne 5x1011 cm-3, Tg 400 K
K. Tao, et al., J. Appl. Phys. 91, 4040 (2002)
115
Film Composition in a TrenchLess nitrogen is
transported to bottom of the trench
(Eiz(N2)gtgtEiz(Ti))
4 N2 in Ar
10 N2 in Ar
N
N
metal mode
nitride mode
D. Mao, J. Appl. Phys., Vol. 96, No. 1, 820, 1
July 2004 0-d chemistry, 2-d fluid, Monte-Carlo
sheath, geom. flux
116
Experimental (RBS) and Simulated Composition
Ratios
metal mode
nitride mode
1 kW/1kW/50 sccm Ar
from D. Mao, PhD Thesis, Northeastern University,
2003
117
Summary

• IPVD allows for energetic deposition of dense
  films into high aspect ratio microstructures
• Recent advances have provided a relatively simple
  technology Self-Ionized Plasma
• Issues with multicomponent IPVD
• disparate ionization potentials and dissociation

118
Some Recommended Reference Materials

• Basic Low Pressure Plasma Physics and Processing
• M.A. Lieberman and A.J. Lichtenberg, Principles
  of Plasma Discharges and Materials Processing
  (Wiley, 2005)
• D. Manos and D. Flamm, eds., Plasma Etching
  (Academic Press, 1989)
• Vacuum Science and Physical Vapor Deposition
• J. E. Mahan, Physical Vapor Deposition of Thin
  Films (Wiley, 2000)
• S.A. Campbell, The Science and Engineering of
  Microelectronic Fabrication, (Oxford, 2001)
• J. Hopwood, ed., Ionized Physical Vapor
  Deposition (Academic Press, 2000)