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Combinatorial RF Magnetron Sputtering Combinatorial RF Magnetron Sputtering for Rapid Materials Discovery: for Rapid Materials Discovery: Methodology and ApplicationsMethodology and Applications
Philip D. RackPhilip D. Rack, Jason D. , Jason D. FowlkesFowlkes, and, and YuepengYuepeng DengDengDepartment of Materials Science and Engineering Department of Materials Science and Engineering
University of TennesseeUniversity of Tennesseeprackprack@@utkutk..eduedu
Definitions
Plasma - partially ionized gas containing an equal number of positive and negative charges, as well as some other number of none ionized gas particlesGlow discharge - globally neutral, but contains regions of net positive and negative chargeMost thin film processes utilize glow discharges, but “plasmas” and “glow discharges” are often used interchangeably
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Plasma Properties
Plasma Density (n) – number of species/cm3107 – 1020
Typical glow discharges and arcs have an electron and ion density ~ 108 – 1014
DC Glow Discharge
Before application of the potential, gas molecules are electrically neutral and the gas at room temperature will contain very few if any charged particles. Occasionally however, a free electron may be released from a molecule by the interaction of, for example, a cosmic ray or other natural radiation, a photon, or a random high energy collision with another particle.
0V
A → A+ + e-
hv
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DC Glow DischargeWhen a large voltage is applied between the electrodes, say 100 V/cm, any free electrons which may be present are rapidly accelerated toward the anode. They quickly attain high velocity (kinetic energy) because THEY HAVE SUCH LOW MASS. Since kinetic energy can be related to temperature, the electrons are “hot” - they achieve extremely high temperatures because of their low mass, in an environment of heavy, slow-moving “cold” gas molecules.
100V
A+
e-
- +
slow“cold”
“hot”fast
Cathode Anode
DC Glow DischargeElectrons begin to collide with gas molecules, and the collisions can be either elastic or inelastic.
Elastic collisions deplete very little of the electron’s energy and do not significantly influence the molecules because of the great mass difference between electrons and molecules: Mass of electron = 9.11 e-31 kg, Mass of Argon = 6.64e20 kg.Inelastic collisions excite the molecules of gas or ionize them by completely removing an electron. (The excitation - relaxation processes are responsible for the glow)
100V
e- (100eV) + A
- +
e- (100eV) + A
e- (100eV) + A
e- (<100eV) + A*
elastic
inelastic
Cathode Anode
e- (100eV) + A e- (<100eV) + A+ + e-inelastic
A* A + photon (glow)
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DC Glow Discharge
Other electron/particleinelastic events
e- (100eV) + AB e- (<100eV) + A + B + e-inelastic
e- (100eV) + AB e- (<100eV) + A+ + B + 2e-inelastic
e- (100eV) + AB e- (<100eV) + A+ + B- + e-inelastic
Dissociation/Fragmentation
DissociativeIonization
Dissociative Ionization with Attachment
DC Glow Discharge
Newly produced electrons are accelerated toward the anode and the process cascades (Breakdown).
100V- +
A+e-e-
e-A+e
-
e-
A+e-
e-
A+e-
e-
A+e-
e-
A+e-
e-
A+e-
e-
Cathode Anode
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DC Glow Discharge
With sufficient voltage, the gas rapidly becomes filled with positive and negative particles throughout its volume, i.e. it becomes ionized.
100V- +
Cathode Anode
DC Glow Discharge
Positive ions are accelerated toward the negative electrode (cathode). Collision with the cathode causes the emission of secondary electronswhich are emitted from the cathode into the plasma.
100V- +
A+e-
Cathode Anode
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Secondary Electron Coefficient
Secondary Electron Coefficient (δ) vs Incident Electron Energy
Secondary Electron Coefficient (γi)vs Incident Ion Energy
DC Glow Discharge
Free electrons from secondary emission and from ionization are accelerated in the field to continue the above processes, and a steady state self-sustaining discharge is obtained.
A+e- e-
e-A+e-
e-
Cathode
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Sputtering
( ) ( )cosI Iθ θ=
Target
0
45
90
Target
Dark space
Positive Glow
V010
V
Self
bias
Ar+ Ar+
SubstrateAngular Distribution
Rf Magnetron Sputtering System
Load-lockchamber
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Source 1
substrate
Source 2
Source 3
Simultaneous 3 Source Sputtering
Angular Distribution
( ) ( )cosnI Iθ θ=
Target
0
45
n~10
Modified Cosine Distribution
05
1015202530354045
0 1 2 3 4 5 6 7 8Position (cm)
Film
Thi
ckne
ss (n
m) Ni Uniform Film
Cu Uniform
0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0
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Process Modeling
{ } ( )360 32.7
0 01[ ] 360 90
3 30 0
21 1 1 1
cos sin1 cos cos
sin
2
nP
j k j ki i
total ij i j ij
i j
d d PtSC nVqd d
n n rr
θ θ φ θφ θ
θ φ θθ
π
= == =
= = = =
+
= = ∆ ∆
∫ ∫∫ ∫∑ ∑ ∑ ∑
Ф
θsubstrate
r
Input variables:Source power, voltage, current
Material sputter yieldSource tilt angle
Substrate positionSource time
Determines substrate composition as a function of position
MATLab Process ModelBinary Composition Profile
Al
ZrCu
Ternary Composition Profile
AlZr
Cu
Thickness Modeling
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Recent Applications
Ternary Phase Diagrams: Fe-Ni-CrWith Pharr et al.
Catalysts for Carbon Nanofiber Growth: Cu-Ni
With Simpson et al.Bulk Metallic Glass Alloy Development
With Liaw et al.Ultraviolet Emitting Materials: Y3Al5O12:Gd
Fe-Ni-Cr Ternary Phase Diagrams
Co-sputter Fe (160W), Cr (60W), Ni (60W) onto (1 –1 0 2) single crystal sapphire substratesAnneal 200, 400, 600, 800 oC for 2 hoursRapid synchrotron fluorescence and XRD measurementsFuture Work: Nano-indentation
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Non-Equilibrium Ternary Phase Diagrams (Fe-Ni-Cr)
Fe
NiCr
synchrotron beam12 keV
0.25 x 1 mm2
CCD (diffraction)
detector
Fluorescence detector
With Pharr et al.
Modeled versus Measured Composition
Cr
Fe Ni
Cr
Fe Ni
Measured Composition Space Modeled Composition Space
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Phase Diagram Temperature Evolution
As deposited 200oC 400oC
600oC 800oC Equilibrium
Phase Analysis versus Temperature
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Particle Size
0
1020
3040
50
0 200 400 600 800Annealing Temperature (oC)
XRD
Par
ticle
Siz
e (n
m)
a-Mn bcc sigma fcc
Carbon Nanofiber CatalystCu-Ni Alloy
0102030405060708090
-5 -4 -3 -2 -1 0 1 2 3 4 5Distance from Center (cm)
Ato
mic
Per
cent
(Cu
& N
i)
ModeledResults
MeasuredResults
Ni Cu
Alloy Strip Deposited on Si
With Klien et al.
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Carbon Nanofiber CatalystCu-Ni Alloy
10 at% 10 at% CuCu
20 at% 20 at% CuCu
37 at% 37 at% CuCu
80 at% 80 at% CuCu
90 at% 90 at% CuCu
The morphology and shape of vertically–aligned carbon nanofibers are a strong function of the composition of the Cu–Ni catalyst particle that acts as the nucleation site for individual fiber growth. An optimum fiber geometry is realized at 80% Cu.
250nm
With Klien et al.
Glass substrate
ITO (1500A)
Si (1500A)PVX
Lab 5: Al-Cu Phase Diagram
MSE 300
0 10 20 30 400
10
20
0
5
10
15
20Magnetron Sputtering Configuration
x [cm]y [cm]
z [c
m]
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Al-Cu Phase Diagram
Atomic % On Substrate
0 2 4 6 8 10cm
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Test Setup
Base pressure = 6x10-7 TorrOperating pressure = 5 mTorrQ (Ar) = 25 sccmPower Al = 200WPower Cu = 34WS (Al) = 1.2S (Cu) = 2.3Gun Tilt (Al,Cu) = 7,7 mmBias = 0 VDCSustrate Height = 7.5 cmTemp = 30 ºCTime = 1.5 hr