Materials Edwards vFinal DR 18/12/08 12:19 Page 49
MATERIALS
49
Cleaning step
Because the gases used here are so radically
different to those used in the deposition step, some
people choose to use a different abatement
strategy for the cleaning step specifically
optimised for this duty, and select between
abatement technologies on the signal from the
process tool using a diverter valve.
The key challenges for chamber cleaning are
the treatment of the toxic, global warming and
corrosive gases utilised in the process, and the fact
that SiF
4
will form solids (SiO
2
) when oxidised or
reacted with water.
As with the deposition step, combustion is the
most effective technology, the differences being
how by-products are managed. The simplest and
cheapest way is again to use air-cooling. To TABLE 3: Cost comparison of chamber cleaning methods looking at
achieve efficient removal of fluorine typically potential penalties for using said methods in particular areas of the
requires the use of a wet scrubber to remove chamber cleaning process.
water-soluble hydrogen fluoride, HF, which
fluorine will ideally be converted into in the
combustor. However, water is expensive, and water
treatment/disposal is even more expensive, so
there is a potential cost penalty for doing so.
These factors are compared in table 3.
Selecting an abatement strategy
The choice of abatement strategy depends on a
number of factors, such as local regulatory
requirements (e.g. TA Luft compliance in
Germany), the availability of key utilities, safety
considerations, footprint, capital cost and running
cost.
At the simplest level, a large capacity
combustor like Edwards’ Spectra Z 3000 provides
an all dry combustion abatement solution that
meets many customers’ needs, especially in terms puts the waste products (primarily HF) into water. Fig2: Preferred
of minimising costs, typically discharging into a This configuration has passed German TA Luft configuration for TA
facility central scrubber. It is able to treat up to testing and is running at a number of customer Luft complient gas
3000 slm of exhaust gas flow and does not require sites globally. abatement
any water whatsoever, but on its own it does not
meet the strictest emission requirements such as Summary
TA Luft. However, this approach is commonly used Thin Film Silicon solar cell technology is a
in flat panel manufacturing. promising means of producing large area solar
To achieve the highest levels of performance, a cells at low cost. Incorporating a µc-Si layer into
set up shown like the one in Figure 2 is required: the structure significantly increases the solar
The above solution adds powder filtration efficiency, but adds to the process exhaust
downstream of the Spectra Z to remove and challenge too. By paying careful attention to the
collect silica during the deposition step. During the chemistry of both the deposition and chamber
cleaning step, the process exhaust is diverted to a cleaning steps, exhaust management solutions
dedicated Thermal Processor Unit (TPU) that is have been developed that can meet these
optimised to treat the chamber clean gases and challenges whilst minimising the costs.
REFERENCES:
[1]European Renewable Energy Centres Agency http://www.eurec.be/
[2]European Commission Vision Report http://ec.europa.eu/research/energy/pdf/vision-report-final.pdf
[3]Silane MSDS http://www.vngas.com/pdf/g97.pdf
[4]NASA Safety Standard for Hydrogen and Hydrogen Systems http://www.hq.nasa.gov/office/codeq/doctree/canceled/871916.pdf
[5]SF6 Destruction Reaction Efficiency of the TPU, J-B Chevrier et Al, IMDC Conference 2002
[6]Effects of Leak Size and Geometry on Release of 100% Silane (ESH B001), SEMATECH, 1996
http://www.sematech.org/docubase/document/3168aeng.pdf
December 2008 / January 2009 www.euroasiasemiconductor.com
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