TCOs by sputtering – Milestones of 40 years
Bernd Szyszka
1
, Ruslan Muydinov
1
, Stefan Körner
1
, Manuel Hartig
1
, Darja Erfurt
2
, Reiner
Klenk
2
, Marc Daniel Heinemann
2
, Christian Kaufmann
2
, Bernd Stannowski
2
, Rutger
Schlatmann
2
, Alexander Steigert
3
, Michael Siemers
4
, Stephan Ulrich
4
, Volker Sittinger
4
,
Andreas Pflug
4
1
TU Berlin, Chair Technology of Thin Film Device TFD,
Einsteinufer 25, Office HFT 5-2, 10587 Berlin, Germany
2
HZB EE-IP
3
HZB EE-IH
4
Fraunhofer IST
E-mail:
Key words: IOH, AZO, IZO, ITO, ATO, graded layers, magnetron sputtering, hollow
cathode gas flow sputtering, serial co-sputtering, high power impulse sputtering
Glow discharge sputtering is one of the oldest deposition techniques that utilizes energetic
activation to promote surface diffusion at the substrate and thus, to achieve dense and well
adherent coatings at low substrate temperature. The technology of sputtering is also scalable
to industrial application and large areas. Therefore, numerous efforts have been developed in
the last 40 years to tailor the properties of TCO films by sputter deposition. TCOs by
sputtering are key components for a large variety of optoelectronic products such as flat panel
displays, thin film solar cells, LEDs and OLEDs and for spectral selective applications such
as durable heat mirrors. This paper gives an overview on the history and current
achievements in TCO sputter deposition. Starting from early work on diode sputtering, we
address the development of ceramic target magnetron sputtering towards soft growth
deposition by RF superimposed DC sputtering for optoelectronics and towards high power
impulse sputtering for durable, wear resistant applications such as the ice free windshield.
Novel concepts for high mobility materials such IOH (In
2
O
3
:H) will be reviewed, relying also
on ceramic target sputtering. Furthermore, concepts for the control of oxygen partial pressure
during reactive sputtering allow also for high quality TCO films, especially in the field of
photovoltaics. The development of such processes has been started in the early 1980s by
means of baffles to achieve pressure gradients and nowadays by means of fast closed loop
control concepts to stabilize the non-stable transition mode of the reactive magnetron
discharge. Sputtering of TCOs is also used by ion beam sputtering for special applications in
precision optics. Furthermore, high pressure sputter processes such as the hollow cathode
gasflow sputtering are subject to intense research due to favorable features of these processes
in particular in terms of soft growth deposition by means of adjustable, intense, but low
energetic ion bombardment. New opportunities for tailored doping and thus for the control of
phase deposition are given by the novel technique of rotatable target serial co-sputtering.
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