Plasma Technology  

Linear self limiting growth measured by in situ spectroscopic
ellipsometry at 25 300 °C deposition temperatures

80 nm thick Al2O3 film in 2.5 µm wide
trenches with an aspect ratio of 10 : 1

Courtesy of TU and Philips Eindhoven

Al2O3 ALD (radical assisted by remote plasma)

metal precursor: TMA (tri methyl aluminium)

non metal precursor: O radicals and O2

temperature controlled vapour draw

dose control by fast pulse ALD valve

deposition temperature: 25° - 400° C

cycle time < 4 sec (for 200 mm wafer)
(shorter for smaller substrates, ca 3 sec)

1.2 A/ cycle (saturated dose at 200° C)
18 A/ min, > 100 nm/ hr (for 200 mm wafer)
(faster for smaller substrates)

uniformity: < ± 0.5 - 2 %
(depending on substrate size)
repeatability < ± 1 %

C < 2% , H < 2.5% (at 200 °C)
Al2Ox, x = 3.05 by RBS and ERD

C, H, O impurities at 25°C are < 2%

refractive index 1.63

breakthrough voltage > 8 MV/ cm

dielectric constant > 8.5


growth rate vs TMA dose time at 200° C


growth rate vs plasma time:
A decreasing growth rate with decreasing
plasma time indicates incomplete surface
activation (removal of CH3 groups).


AFM RMS analysis shows very smooth films:
c-Si substrate: 0.0555 nm
20 nm Al2O3: 0.0589 nm



Why remote plasma ALD ?

A "remote plasma" makes sure, the substrates
are NOT in contact with the plasma !

The remote plasma just cracks molecules,
so that very reactive species can be used
for the growth process.

Such reactive species often enable a very
efficient plasma preclean/ conditioning of the
substrates, lead to cleaner films and lower
the deposition temperature.

In Oxford systems it is possible to run
ALD processes using
- the thermal only method
- ozone assisted processes
- remote plasma assisted processes
together without any hardware change.
Multiple step processes using all technologies
can be chosen from the software.

low temperature ALD down to 25° C
is enabled by the use of O radicals;
this is not practical using thermal
H2O processes.




ALD schematic
valve between remote ICP source
and chamber,
spectroscopic ellipsometry optional


At a given temperature radical assisted
ALD gives higher film desities than
purely thermal ALD.


radical assisted Al2O3 ALD at 20° C
very low water vapour tansmission rate






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