Transcript Slide 1

Time resolved diagnostics for
pulsed magnetron plasmas
Technological Plasmas Research Group
Gregory Clarke
Magnetrons
Chamber
Gases
Mixtures of Ar, O2 ,
N2 etc
Substrates
Glass, polymers,
metals etc
Target
Metallic and
semi-conducting
N
S
S
N
N
S
Magnetron
Variable
magnetic field
Pulsed DC Power supply
Frequencies 0 – 350 kHz
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
Purpose:
To observe the effect of the driving voltage waveform on the spatial and
temporal distribution of emission from plasma
Chamber
•
•
ICCD camera fitted with a zoom
lens
Substrate
Observe different species by the
use of filters
Target
•
Short exposure times (50 ns)
•
Sweep exposure window through
pulse cycle
•
Record temporal and spatial
evolution
Window
Filters
ICCD
Camera
Magnetron
PC
Delay
generator
Oscilloscope
Power
supply
Technological Plasmas Research Group
Gregory Clarke
Filters
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.
1.0
Normalised intensity
(arb units)
•
750.4
751.5
0.5
0.0
720
740
760
780
Wavelength (nm)
Technological Plasmas Research Group
Gregory Clarke
Sample image
Substrate
Cathode
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
1 R dI( y) / dy
E( r )   
dy
r
( y2  r 2 )
cathode
y
where,
E(r) = emissivity of the plasma
r
I (y) = line integrated intensity
R = radius of the plasma
y = displacement of the intensity profile
r = radial distance from the axis of symmetry R
Central
axis
Plasma
•Standard two dimensional images can be processed to produce radial profiles
that are perpendicular to the line of sight
Technological Plasmas Research Group
Gregory Clarke
Movie: Abel inverted data
Technological Plasmas Research Group
Gregory Clarke
Detached region
‘Cold’ electron
density
cold electron density during "on" time (x 10 m )
16
0.15
0.10
0.05
0.00
60
Radial distance (mm)
0.20
80
40
20
0
0
20
40
60
80
75
70
65
60
55
50
45
40
35
30
25
20
15
10
5
0
 1016 m-3
-3
80
Axial distance z (mm)
0.25
Axial
(mm)
distance zz (mm)
Axial distance
Normalised emissivity (arb units)
Emissivity
0
Radial distance r (mm)
1.800
1.688
1.575
1.463
1.350
1.238
1.125
1.013
0.9000
0.7875
0.6750
0.5625
0.4500
0.3375
0.2250
0.1125
0
1.6
60
1.2
40
0.8
20
0
80 0
0.4
20
40
60
0.0
80 probe faces drift
5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80
Axial distance (mm)
Radial distance r (mm)
Electron density plots courtesy of Dr. Alena Vetushka
Technological Plasmas Research Group
Gregory Clarke
Energy resolved mass
spectroscopy
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
•
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
target
chamber
central
axis of
chamber
magnetron
substrate
Technological Plasmas Research Group
mass
spectrometer
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 ?
Vpl  150 V
200
Vpl  25 V
Vpl  5 V
Voltage (V)
0
-200
-400
Target
Plasma
-600
-800
Pulse off
Pulse on
-1000
0
2
4
6
8
10
Time(s)
Time dependent variation in plasma potential assessed via emissive probe
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
Technological Plasmas Research Group
Gregory Clarke