AVS 56th International Symposium & ExhibitionNovember 9, 2009 San Jose, California
a Department of Materials Science and Engineeringb Department of Nuclear, Plasma, and Radiological Engineering
Contact: [email protected]
Time-resolved plasma characterization in modulated pulse plasma (MPP)
magnetron sputtering
A.N. Clouda, R.E. Flautab, M.J. Neumannb, S.L. Rohdeb, and D.N. Ruzicb
AVS 56th International Symposium & ExhibitionNovember 9, 2009 San Jose, California
Overview
• Introduction and motivation
• Experimental apparatus and diagnostics
• Vacuum system and magnetron
• Triple Langmuir probe
• Gridded energy analyzer (GEA)
• Quartz crystal microbalance (QCM)
• Results
• Time-resolved electron temperature and density
• Growth rate dependence on plateau current and repetition rate
• Time-resolved ion current at the substrate level
• Conclusions
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AVS 56th International Symposium & ExhibitionNovember 9, 2009 San Jose, California
Introduction and motivation
3
AVS 56th International Symposium & ExhibitionNovember 9, 2009 San Jose, California
Modulated Pulse Plasma (MPP)
• Relatively new method of applying the basic principles of HPPMS / HIPIMS
• Allows the generation of an arbitrary voltage waveform
• Most studies of discharges produced by this technology have been inherently time-averaged.• Time-averaged plasma diagnostics• Film properties
• In order to intelligently apply this technology and create improvement, the underlying physics must be understood.
• We are conducting time-resolved diagnostics of this interesting type of discharge.
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AVS 56th International Symposium & ExhibitionNovember 9, 2009 San Jose, California
Multi-step power delivery of MPP
• Step 1 – Ignition• Step 2 – Low power (DC-like) discharge• Step 3 – Current ramp• Step 4 – High power discharge
5
Voltage
Current
Power
AVS 56th International Symposium & ExhibitionNovember 9, 2009 San Jose, California
Experimental apparatus and diagnostics
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AVS 56th International Symposium & ExhibitionNovember 9, 2009 San Jose, California
Magnetron sputtering tool 7
MRC Galaxy
• Planar circular rotating magnetron
• Designed for 20kW DC sputtering
14” (36 cm) diameter sputtering
targets
• 1000 cm2
• <150 W/cm2 power density
AVS 56th International Symposium & ExhibitionNovember 9, 2009 San Jose, California
Triple probe theory and setup8
From T.K. Gray
• Probe 2 is allowed to float in the plasma.
• Probes 1 and 3 are biased using a floating voltage source.
Probe 1 is held above floating potential while probe 3 is held
below Vf. While ΔV13 remains constant, the exact values for V1
and V3 are dependant on the need to satisfy Kirchhoff’s current
law.
• Determining electron temperature (t):
• To determine the electron density (t), the following
relation is solved for ne:
•Assumptions:
• Maxwellian electron energy distribution function
• Collisionless thin sheath
• No interaction between probe tips
From S. Chen and T. Sekiguchi.
Instantaneous direct-display system of
plasma parameters by means of triple probe.
J. Appl. Phys., 26(8):2363{2375, 1965.
Probe tips
AVS 56th International Symposium & ExhibitionNovember 9, 2009 San Jose, California
Gridded energy analyzer
• Gridded Energy Analyzer
• Custom built at CPMI
• Can be used as an ion collector and ion energy discriminator
• Schematic:
• Quartz crystal microbalance
• Used to determine deposition rate
• Also can be used in conjunction with the GEA to determine ionization fraction
• Previous work at CPMI has shown ~6% metal ionization at the substrate level in this sputtering tool.
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Range of voltage to measure energy
AVS 56th International Symposium & ExhibitionNovember 9, 2009 San Jose, California
Results
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AVS 56th International Symposium & ExhibitionNovember 9, 2009 San Jose, California
0.00E+00
5.00E+10
1.00E+11
1.50E+11
2.00E+11
2.50E+11
3.00E+11
-0.0014 -0.0012 -0.001 -0.0008 -0.0006 -0.0004 -0.0002 0 0.0002 0.0004 0.0006
t (s)
ne (
eV
)
0
5
10
15
20
25
30
35
-0.0014 -0.0012 -0.001 -0.0008 -0.0006 -0.0004 -0.0002 0 0.0002 0.0004 0.0006
t (s)
kTe
(eV
)
Triple probe results (1)11
• Pressure: 2 mTorr
• Distance from target:~12.5 cm (far)
• Plateau “temperature” is ~20 eV.
• Peak density is 0.9 x 1011 cm-3
.
• Density tracks Z-pulser current on target.
• High energy electrons are present, likely responsible for ionizing the metal atoms.
Voltage
Current
Power
Electron “Temp.”
Electron Density
AVS 56th International Symposium & ExhibitionNovember 9, 2009 San Jose, California
-5.00E+10
0.00E+00
5.00E+10
1.00E+11
1.50E+11
2.00E+11
2.50E+11
3.00E+11
3.50E+11
4.00E+11
4.50E+11
-0.0014 -0.0012 -0.001 -0.0008 -0.0006 -0.0004 -0.0002 0 0.0002 0.0004 0.0006
t (s)
n e (c
m-3
)
0
5
10
15
20
25
30
35
40
-0.0014 -0.0012 -0.001 -0.0008 -0.0006 -0.0004 -0.0002 0 0.0002 0.0004 0.0006
t (s)
kTe
(eV
)
Triple probe results (2)12
• Pressure: 2 mTorr
• Distance from target:~6.3 cm (near)
• Plateau “temperature” is ~20 eV.
• Peak density is 1.4 x 1011 cm-3
.
• Density is higher near the target as expected.
Voltage
Current
Power
Electron “Temp.”
Electron Density
AVS 56th International Symposium & ExhibitionNovember 9, 2009 San Jose, California
-5.00E+10
0.00E+00
5.00E+10
1.00E+11
1.50E+11
2.00E+11
2.50E+11
3.00E+11
3.50E+11
-0.0014 -0.0012 -0.001 -0.0008 -0.0006 -0.0004 -0.0002 0 0.0002 0.0004 0.0006
t (s)
n e (c
m-3
)
Triple probe results (3)13
• Pressure: 30 mTorr
• Distance from target:~12.5 cm (far)
• Plateau “temperature” is ~24 eV.
• Peak density is 1.3 x 1011 cm-3.
• Higher pressure of process gas leads to higher density as expected (compared to the density at same distance, lower pressure).
Voltage
Current
Power
Electron “Temp.”
Electron Density
0
5
10
15
20
25
30
-0.0014 -0.0012 -0.001 -0.0008 -0.0006 -0.0004 -0.0002 0 0.0002 0.0004 0.0006
t (s)
kTe
(eV
)
AVS 56th International Symposium & ExhibitionNovember 9, 2009 San Jose, California
0.00E+00
1.00E+11
2.00E+11
3.00E+11
4.00E+11
5.00E+11
6.00E+11
-0.0014 -0.0012 -0.001 -0.0008 -0.0006 -0.0004 -0.0002 0 0.0002 0.0004 0.0006
t (s)
n e (c
m-3
)
0
5
10
15
20
25
30
35
40
45
50
-0.0014 -0.0012 -0.001 -0.0008 -0.0006 -0.0004 -0.0002 0 0.0002 0.0004 0.0006
t (s)
kT
e (
eV
)
Triple probe results (4)14
• Pressure: 30 mTorr
• Distance from target:~6.3 cm (near)
• Plateau “temperature” ~22 eV.
• Peak density is 1.6 x 1011 cm-3.
• Again, density is slightly higher near the target.
Voltage
Current
Power
Electron “Temp.”
Electron Density
AVS 56th International Symposium & ExhibitionNovember 9, 2009 San Jose, California
Growth rate behavior• Lower pressure
gives higher deposition rate.
• Deposition rate not proportional to current plateau value
• Deposition rate not constant with power
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Deposition rate versus time as deposition conditions are altered.
Pressure (mTorr)
Peak Current (A)
Deposition Rate (Å/s)
30 230 1.86
2 160 3.92
2 125 4.52
2 40 5.13
Pressure (mTorr)
Peak Current (A)
Deposition Rate (Å/s)
2 172 2.55
2 135 2.20
2 122 2.02
2 54 1.60
Constant average power (2.0 kW)Constant repetition rate (39 ±1 Hz)
AVS 56th International Symposium & ExhibitionNovember 9, 2009 San Jose, California
Time-resolved ion current at the substrate
• When do the ions arrive at the substrate?
• At 2mTorr, 160A plateau current:
• Note that these are not necessarily metal ions; most likely Ar+.
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-0.2
-0.15
-0.1
-0.05
0
0.05
0.1
0.15
0.2
0.25
0.3
-0.0015 -0.001 -0.0005 0 0.0005 0.001 0.0015 0.002
t (s)
Ion
Curr
ent (
mA)
Ion current follows the shape of
plasma density curves found
with triple probe.
Voltage
Current
Power
ion current to grid
AVS 56th International Symposium & ExhibitionNovember 9, 2009 San Jose, California
Energy of time resolved ion current17
-0.4
-0.3
-0.2
-0.1
0
0.1
0.2
0.3
0.4
-6 -5 -4 -3 -2 -1 0 1 2 3
Stopping potential (V)
Cu
rren
t (m
A)
2 mTorr
30 mTorr
At 30 mTorr ions have less than 1 eV
of energy at substrate.
At 2 mTorr ions have less than 3 eV
of energy at substrate.
AVS 56th International Symposium & ExhibitionNovember 9, 2009 San Jose, California
Conclusions
• The plasma is very hot during the pulse.
• 20 eV and greater.
• Likely a non-Maxwellian electron energy distribution
• Density is on the order of 2 x 1011 cm-3 and follows input current.
• Density increases with pressure and falls off with distance from target.
• Deposition rates are not strictly a function of power or plateau current.
• Energy of ions reaching substrate is very low (< 3eV), though we are not measuring metal ions at this point.
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AVS 56th International Symposium & ExhibitionNovember 9, 2009 San Jose, California
Thank you for your attention.
Andrew N. CloudPhD candidate, Department of Materials Science and Engineering
University of Illinois at Urbana-Champaign
Acknowledgements:
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Graduate student support provided by the National Defense Science and Engineering Graduate research fellowship program (NDSEG).
This research was funded in part by a grant from the National Science Foundation, under Grant #CMMI09-53057.