INFICON Cool Drawer Single Sensor - Manual (Page 48)

4 - 8
PN
07
4-
60
9-
P1
A
Cool Drawer Single and Dual Sensors Operating Manual
4.3.2 Maintain the Temperature of the Crystal
Periodically measure the water flow rate through the crystal sensor to verify that it
meets or exceeds the value specified on
page 1-6 .
Depending upon the condition of the cooling water used, the addition of an in-line
water filtering cartridge may be necessary to prevent flow obstructions.
Many systems use parallel water supply taps that provide high total flows. In a
parallel water supply system, an obstruction or closed valve in the pipe that
supplies water to the sensor head may not result in a noticeable reduction of total
flow. Therefore, monitor the flow leaving the sensor, not the flow entering the
sensor.
The crystal requires sufficient water cooling to sustain proper operational and
temperature stability. Ideally, a constant heat load is balanced by a constant flow of
water at a constant temperature. INFICON quartz crystals are designed to provide
the best possible stability under normal operating conditions. However, no crystal
can completely eliminate the effects of varying heat loads, such as radiated energy
emanating from the evaporant source or from substrate heaters.
4.3.3 Use the Optimum Crystal Type
Silver crystals are recommended for sputtering applications. Certain materials,
especially dielectrics, may not adhere strongly to the crystal surface and may
cause erratic readings. For many dielectrics, adhesion is improved by using Alloy
crystals. Gold is preferred for other applications. Contact INFICON for an
appropriate crystal for the specific application, refer to
section 1.3 on page 1-3 .
4.3.4 Crystal Concerns when Opening the Chamber
Thick deposits of some materials, such as SiO, Si and Ni, will normally peel off the
crystal when it is exposed to air, due to changes in film stress caused by gas
absorption. When peeling material is observed, replace the crystal.