Gregory ClarkeTechnological Plasmas Research Group Time resolved diagnostics for pulsed magnetron...

Technological Plasmas Research Group Gregory Clarke

Time resolved diagnostics for pulsed magnetron

plasmas


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


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


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


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.


Sample image

Cathode

Substrate

The red box represents the

temporal location when

the data recorded


Movie: Raw data


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


Movie: Abel inverted data


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


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


Movie: IEDF 1

Data recorded using: 1 s steps between successive data sets


Movie: IEDF 2

Data recorded using: 100 ns steps between successive data sets


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


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


Acknowledgements

o EPSRC

o Dr Alena Vetushka (probe measurements)

o Dr Paul Bryant (Abel inversion)

o Prof Nick Braithwaite

o Mr Alan Roby

Gregory ClarkeTechnological Plasmas Research Group Time resolved diagnostics for pulsed magnetron...

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