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)

G . M a t t a u s c h e t a l . : 5 5 t h S V C A n n u a l Te c h n i c a l C o n f e r e n c e P r o c e e d i n g s , 1 7 9 - 1 8 5 ( 2 0 1 2 )P. F e i n ä u g l e e t a l . : 5 4 t h S V C A n n u a l Te c h n i c a l C o n f e r e n c e P r o c e e d i n g s , 2 0 2 - 2 0 9 ( 2 0 1 1 )B . Z i m m e r m a n n e t a l . : S u r f a c e a n d C o a t i n g s Te c h n o l o g y 2 0 5 , S 3 9 3 - S 3 9 6 ( 2 0 1 1 )J . - P. H e i n ß e t a l . , E P 2 0 8 7 5 0 3 B 1 , “ D e v i c e f o r t h e p r e - t r e a t m e n t o f s u b s t r a t e s ” , 3 1 . 1 0 . 2 0 0 7

E s s e n t i a l r e s u l t s w e r e o b t a i n e d i n p u b l i c p r o j e c t f u n d e d b y F r e e S t a t e o f S a x o n y „ N e w t e c h -n o l o g i e s f o r s o l a r a p p l i c a t i o n s “ ( F Z 1 4 2 7 4 / 2 4 7 3 )

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