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
efficient plasma preclean/ conditioning of the
substrates, lead to cleaner films and lower
the deposition temperature.
In Oxford systems it is possible
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
valve between remote ICP source
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