plasma-based tools for activated eb-pvd of tbc systems
TRANSCRIPT
INTRODUCTION
F R A U N H O F E R I N S T I T U T E F O R E L E C T R O N B E A M A N D P L A S M A T E C H N O L O G Y F E P, D R E S D E N , G E R M A N Y
B. ZIMMERMANN, G. MATTAUSCH, B. SCHEFFEL, J.-P. HEINSS, F.-H. RÖGNER, C. METZNER
PLASMA-BASED TOOLS FOR ACTIVATED EB-PVD OF TBC SYSTEMS
HOLLOW CATHODE ARC PLASMA SOURCE LAVOPLAS DISCHARGE-BASED HIGH-POWER EB GUN EASYBEAM
REACTIVE PLASMA-ACTIVATED EB-PVD OF YSZ LAYERS
CONCLUSION
without plasma with plasma
June 2014 - Thermal Barrier Coatings IV
Poster online (PDF)
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REFERENCES AND ACKNOWLEDGEMENTS
Corresponding Contact
CORRESPONDING CONTACTF r a u n h o f e r - I n s t i t u t f ü r E l e k t r o n e n - s t r a h l - u n d P l a s m a t e c h n i k F E P
W i n t e r b e r g s t r a ß e 2 80 1 2 7 7 D r e s d e n , G e r m a n y
w w w. f e p . f r a u n h o f e r. d e
D r. B u r k h a r d Z i m m e r m a n nb u r k h a r d . z i m m e r m a n n @ f e p . f r a u n h o f e r. d e
P h o n e + 4 9 3 5 1 2 5 8 6 3 8 6
Physical Vapor Deposition (PVD) techniques are
increasingly applied in the field of surface enginee-
ring, functionalization, and protection in order to
meet high demands on corrosion resistance, ther-
mal stability, or mechanical, optical, and electrical
properties. However, depending on the required
layer properties, high rate electron beam (EB-)PVD
processes often call for additional plasma activation
in order to combine high rate film growth with
outstanding film quality by ionized vapor, enhanced
reactive gas reactivity and hence elevated or tailo-
red particle energy. In this poster, plasma-based
EB tools with reference to plasma-activated EB-PVD
e.g. of TBC systems are presented.
A new type of cost-efficient EB guns has been
developed at Fraunhofer FEP, where beam electron
emission from the cathode is stimulated by ion
bombardment from a high-voltage glow discharge.
Furthermore, a high-power large-volume plasma
source based on the hollow cathode arc discharge
has been established as a compact, universal and
flexible tool for efficient substrate pre-treatment
and etching as well as assisting high rate PVD pro-
cesses. The effect of the hollow cathode arc plasma
for sputter etching of metallic substrates and for
plasma-activation of EB-PVD of YSZ is shown to
document its high application potential for the field
of PVD technology.
Plasma pretreatment is an essential process step in
order to clean the substrate surface before coating
and to improve the layer adhesion. In the following,
hollow cathode enhanced sputter etching for the
example of Cu is shown.
Parameters:
• discharge current: 100-200 A
• substrate at ground potential
• positive hollow cathode bias voltage: 500 V
Result:
The etching rate increases with discharge power
and reaches high static values of up to 40 nm / s.
The discharge-based EB gun has been presented as a tool, which has the potential to allow for lower purchase cost in existing EB applications, or to cover coating application fields, where the EB technology has been
too expensive so far. The high-power plasma activation with the hollow cathode arc plasma source has been shown to be very effective for plasma etching as well as for layer densification or tailoring of film properties,
which is interesting e.g. for the fields of diffusion barrier coatings or morphology-adapted interlayers.
During plasma activation, vapor and reactive gas are excited and ionized before condensing on the subst-
rate. Furthermore, their energy is increased due to acceleration within the plasma sheath or by a variable
bias voltage resulting in densified and smoothed coatings. For high-rate processes such as EB-PVD, the
high-density plasma of the hollow cathode arc is necessary in order to reach sufficient ion current densities
on the substrate.
A ring anode and a magnetic field coil are arranged coaxially around the tantalum cathode tube flown
through by the working gas argon:
→ diffuse arc discharge within the cathode tube
→ large volume plasma in the process chamber
An axial magnetic field allows for reduced working gas flow rates resulting in strongly increased plasma
density and range due to a larger cathode drop potential and electron energies at discharge powers of up to 30 kW.
A block cathode made from LaB6 or a re-
fractory metal is mounted in a field-forming
cathode holder. In the cathode chamber, a
high-voltage glow discharge (HVGD) is
ignited (working gas: He, H2)
→ cathode is heated up by plasma ions
→ free electron generation via
secondary electron emission as well
as thermionic emission
The hollow cathode arc consists of two plasma regions:
• internal plasma: electrons are thermionically emitted from the hot
cathode heated by impinging ions within the tube
• external plasma: a low-voltage beam of electrons from the internal
plasma ionize the gas in the process chamber
Features in comparison to conventional EB guns:
• simplified electrical circuitry and high-voltage (HV) supply:
only one high voltage cable – no additional cathode heating supply
floating on HV level necessary
• simplified mechanical setup: cathode unit consists of a simple
cathode holder without sophisticated heating system components
• gun-specific vacuum stage can be omitted: cathode chamber
work pressure in the range of 1-5 Pa, consequently no differential
pumping necessary – evacuation of the gun via process chamber for
process pressures up to 0.5 Pa
HOLLOW CATHODE ENHANCED SPUTTER ETCHINGEXPERIMENTAL SETUP PLASMA-ACTIVATED PVD OF YSZ LAYERS
Electron gun
Plasma source
Radiation heater
Electron beam
Crucible
Rod feed
Coating window
Movable substrate holder
Plasma
Reactivegas input
Emissionmonitor
Parameters for EB-PVD of YSZ
(8 mol%) on steel substrates:
• pressure < 0.5 Pa
• substrate temperature: 900 °C
• deposition rate: 40 nm / s
• thickness 5 µm
glow discharge plasma
cathode holder
cathode
EB
max. 40 kVmax. 120 kW
Picture of the hollow cathode arc plasma source LAVOPLAS
Cathode and anode potentials as well as the electron density on three axial positions from the plasma source
The EB current is controlled by the cathode chamber pressure, which is set by the working gas flow rate
Static etching rate on copper at different hollow cathode discharge powers SEM pictures of the YSZ films deposited by EB-PVD without (left) and with (right) plasma activation
Fraunhofer FEP‘s high-power EB gun EasyBeam3D diagrams of the electron density and of the the electron temperature at a discharge current of 50 A and a chamber pressure of 0.1 and 3.4 Pa, respectively
Results:
The application of plasma led to an ion current den-
sity of 25 mA / cm2 onto the substrate. REM shows
denser and smoother microstructure. The XRD
phase composition analysis revealed a significant
change in texture from {111} to {100}. The micro-
hardness was increased from 5 to 20 GPa.
10 cm
10 cm