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FTM = Film Thickness Monitor.

Both the sputterer and the evaporator are equipped with film thickness monitors. These use quartz microbalances to monitor the amount of substance deposited on them. In the case of the sputterer the FTM can be used to automatically control the thickness of the films deposited on the sample. In the evaporator you must manually control the shutter to determine the thicnkess.

The FTM heads use quartz crystals as the sensor, eventually these fail and must be replaced (spares and instructions in the clean room drawers, seek advice).

While the FTMs are pretty accurate they rely on acoustic impeadance / material desnity data and a callibration factor (tooling factor). Since these are not necessarily well defined any film thicnkess that needs to be made with good accuracy requires the FTMs to be callibrated and for this callibration to be taken into account when coating.

The tooling factor in the sputterer can only be set crudely so it is impossible to get the commanded thickness to accurately reflect the actual thickness. Instead you have to rely on calibration factors.