SOLARMATERIALS
air flow, and collect the solids on a dry filter bed.
The different technologies for abating the
deposition gases are compared in table 2.
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 SiF4 will form solids
(SiO2) when oxidised or reacted with water. TABLE 3: Cost comparison of chamber cleaning methods looking at
potential penalties for using said methods in particular areas of the
As with the deposition step, combustion is the chamber cleaning process.
most effective technology, the differences being
how by-products are managed. The simplest and
cheapest way is again to use air-cooling. To process exhaust is diverted to a dedicated Thermal
achieve efficient removal of fluorine typically Processor Unit (TPU) that is optimised to treat the
requires the use of a wet scrubber to remove chamber clean gases and puts the waste products
water-soluble hydrogen fluoride, HF, which fluorine (primarily HF) into water.
will ideally be converted into in the combustor.
However, water is expensive, and water Thin Film Silicon solar cell technology is a
treatment/disposal is even more expensive, so promising means of producing large area solar
19
there is a potential cost penalty for doing so. These cells at low cost. Incorporating a mc-Si layer into
factors are compared in table 3. the structure significantly increases the solar
www
efficiency, but adds to the process exhaust
.solar
Selecting an abatement strategy challenge too. By paying careful attention to the
The choice of abatement strategy depends on a chemistry of both the deposition and chamber Fig2: Preferred
-pv-management.com
number of factors, such as local regulatory cleaning steps, exhaust management solutions configuration for TA
requirements (e.g. TA Luft compliance in have been developed that can meet these Luft complient gas
Germany), the availability of key utilities, safety challenges whilst minimising the costs. abatement
considerations, footprint, capital cost and running
cost. At the simplest level, a large capacity
combustor provides an all dry combustion
abatement solution that meets many customers’
Issue I 2009
needs. It is able to treat up to 3000 slm of exhaust
gas flow and does not require any water, but on its
own it does not meet the strictest emission
requirements. However, this approach is
commonly used in flat panel manufacturing.
To achieve the highest levels of performance, a set
up shown like the one in Figure 2 is required:
This solution adds powder filtration downstream of
the Spectra Z to remove and collect silica during
the deposition step. During the cleaning step, the
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
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