32
MATERIALS
risk for medium purity. Although it can be met The third device type, the flow through gauge
with pressure vacuum rinsing. However, this (FTG), does not have this problem. It is mounted
process requires, an increased time expenditure. directly into the piping, the pressure gauge has a
dead space free measuring material chamber and
Due to construction of pressure gauges with no for this reason offers an excellent rinsing
clearance a dead space can emerge between the behaviour. As in most pressure reducers and valves
bourdon tube and the process connection with VCR for high purity media the chamber is metallically
sealing contour. If humidity and oxygen sealed. For this reason no other sealing is required.
concentrate there, corrosion can occur. Besides The device works with diaphragm elements made of
particles can also get stuck there and then be Inconel and is designed for pressure from -1 to 9.
dispensed to the process medium together with
humidity and oxygen. The patented FTG design is developed in such a
way that all components in contact with medium
Possible consequences are shown vividly by the are being rinsed. Besides these components are
example from the semiconductor industry. The electro polished. This guarantees an outstanding
industry uses Silane (SiH
4
) very often. Exposure to surface quality (Ra
≤
0.25 µm). The surface quality
air leads to combustion which results in emerging almost completely excludes adhesion of the
silicon oxygen compounds. This product again particles and concentration of water and oxygen.
contaminates the supply cables and fittings, which Samples of the check measurements for the device
significantly compromises process stability and with nominal size 2” points this out: after a 10
medium purity. minute measurement three particles 0.01 µm≤
have been detected. The humidity level after
An alternative to the bourdon tube pressure gauge approx. eight minutes was at 0.1 ppb. During the
represents a pressure gauge with diaphragm oxygen test the value 0.2 ppb has been registered.
elements. This product is mostly used for ranges
with lower pressure and high requirements to All three peak values are many times over smaller
overload protection and corrosive media (great if compared to the data of conventional pressure
material variance). Furthermore, it is characterised gauges with bourdon tube. Compared to these
by an easy to clean geometry of the components in devices the rinsing time of the flow through gauge
contact with medium. Still the connection to the is reduced by more than a half.
piping corresponds to that of the bourdon tube Result: noticeably shorter commissioning and
pressure gauge. Lack of the flow also causes maintenance times of the system combined with
significant sedimentations which can return into higher medium purity due to use of the flow
the process. through gauge.
www.euroasiasemiconductor.com October 2008
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