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Technological Plasmas Research Group Gregory Clarke
Time resolved diagnostics for pulsed magnetron
plasmas
Technological Plasmas Research Group Gregory Clarke
Magnetrons
MagnetronVariable magnetic field
SubstratesGlass, polymers,
metals etc
TargetMetallic and semi-conducting
Pulsed DC Power supply
Frequencies 0 – 350 kHz
Chamber
GasesMixtures of Ar,
O2 , N2 etc
NS
SN
NS
Technological Plasmas Research Group Gregory Clarke
Analysis techniques• Probes:
– Electrical: Langmuir, double, triple, emissive– Energy: Thermal– Magnetic field: B-dot
• Optical emission spectroscopy
• Film characteristics: Structure, topography, composition
• Optical imaging
• Energy resolved mass spectroscopy
Technological Plasmas Research Group Gregory Clarke
Optical imaging
• ICCD camera fitted with a zoom lens
• Observe different species by the use of filters
• Short exposure times (50 ns)
• Sweep exposure window through pulse cycle
• Record temporal and spatial evolution
Purpose:
To observe the effect of the driving voltage waveform on the spatial
and temporal distribution of emission from plasma
Magnetron
SubstrateICCD
Camera
P C
Window
Target
Filters
Power suppl
y
Oscilloscope Delay generat
or
Chamber
Technological Plasmas Research Group Gregory Clarke
Filters
720 740 760 7800.0
0.5
1.0
Nor
mal
ised
inte
nsity
(ar
b un
its)
Wavelength (nm)
751.5750.4
• Several optical filters were employed.
• Optical emission spectroscopy performed to identify the spectral lines within the bandwidth of each filter.
• Filter with a central wavelength of 750 nm, chosen so as to observe two transitions in argon neutrals.
Technological Plasmas Research Group Gregory Clarke
Sample image
Cathode
Substrate
The red box represents the
temporal location when
the data recorded
Technological Plasmas Research Group Gregory Clarke
Movie: Raw data
Technological Plasmas Research Group Gregory Clarke
Optical imaging: Abel inversion
Technique: Data collected along ‘line of sight’ can be used to produce radial profiles
R
rdy)2r2y(
dy/)y(dI1)r(E
where,
E(r) = emissivity of the plasma
I (y) = line integrated intensity
R = radius of the plasma
y = displacement of the intensity profile
r = radial distance from the axis of symmetry
Central axis
•Standard two dimensional images can be processed to produce radial profiles that are perpendicular to the line of sight
Plasma
cathode
r
y
R
Technological Plasmas Research Group Gregory Clarke
Movie: Abel inverted data
Technological Plasmas Research Group Gregory Clarke
Detached region 1016 m-3
0 20 40 60 800
20
40
60
80
Axi
al d
ista
nce
z (m
m)
Radial distance r (mm)
0 2 0 4 0 6 0 8 00
2 0
4 0
6 0
8 0
Axi
al d
ista
nce
z (m
m)
R a d ia l d is ta n c e r (m m )
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 800
510
15
2025
30
3540
45
50
5560
65
7075
80
probe faces drift
cold electron density during "on" time (x 1016m-3)
Axial distance (mm)
Rad
ial
dis
tan
ce (
mm
)
0
0.1125
0.2250
0.3375
0.4500
0.5625
0.6750
0.7875
0.9000
1.013
1.125
1.238
1.350
1.463
1.575
1.688
1.800
0.0
0.4
0.8
1.2
1.6
0.25
0.20
0.15
0.10
0.05
0.00
Normalised emissivity (arb units) Axial distance z (mm)
Emissivity ‘Cold’ electron density
Electron density plots courtesy of Dr. Alena Vetushka
Technological Plasmas Research Group Gregory Clarke
Energy resolved mass spectroscopy
• Energy resolved mass analyser modified to enable time resolved measurements
• Argon ion energy distribution functions recorded throughout the duration of the pulse cycle
• Exposure time of 1 s
• Sweep exposure window through pulse cycle
Purpose:
To observe the effect of the driving voltage waveform on the ion energy distribution functions (IEDF’s) of argon ions arriving at the
substrate
mass spectrometersubstrat
emagnetron
target chamber
central axis of chamber
Technological Plasmas Research Group Gregory Clarke
Movie: IEDF 1
Data recorded using: 1 s steps between successive data sets
Technological Plasmas Research Group Gregory Clarke
Movie: IEDF 2
Data recorded using: 100 ns steps between successive data sets
Technological Plasmas Research Group Gregory Clarke
Method of production ?
Time dependent variation in plasma potential assessed via emissive probe
0 2 4 6 8 10-1000
-800
-600
-400
-200
0
200
Pulse off
Vpl 150 V
Vpl 25 V
Vo
ltag
e (
V)
Time(s)
Target Plasma
Vpl 5 V
Pulse on
Technological Plasmas Research Group Gregory Clarke
Conclusions• Imaging
– Yield information on the structure of the discharge– The presence of different electron energy groups
• Time and energy resolved mass spectroscopy
– Record the temporal variation in the energy of ions arriving at the substrate
– Results suggest methods of production
Results are in agreement with those suggested by other techniques
Technological Plasmas Research Group Gregory Clarke
Acknowledgements
o EPSRC
o Dr Alena Vetushka (probe measurements)
o Dr Paul Bryant (Abel inversion)
o Prof Nick Braithwaite
o Mr Alan Roby