6–7
Transpector CPM Operating Manual
6.3.2.1 Turbo Molecular Pump Status
Pump rotational speed is the RPM at which the Turbo Molecular Pump is operating.
Normal speed is 80% of full speed (72,000 RPM). Full speed is 90,000 RPM.
With the corrosive Turbo Molecular Pumping system, the
nitrogen purge valve with regulator is connected to the
purge port of the pump. The nitrogen purge valve is
always open when the corrosive Turbo Molecular Pump
is running. This protects the bearings from corrosive gas
attack and evaporation of bearing lubricant.
6.4 Nitrogen Purge Valve for the Turbo Molecular Pump on
Corrosive Pumping Systems
On corrosive pumping systems, the nitrogen purge valve provides a continuous
flow of dry nitrogen to the bearings of the Turbo Molecular Pump.
The nitrogen purge valve opens when the Turbo Molecular Pump is turned on, and
closes when the pump is shut down. Over-pressurization is avoided by pressure
relief of the Foreline Pump valves. Over-pressure exits the exhaust. There is no
software control of the nitrogen purge valve; it is coupled with Foreline Pump
operation.
6.5 Filament Control
6.5.1 Interlock
On pump down, emission will automatically turn on when the Turbo Molecular
Pump reaches full speed (90,000 RPM). The emission will automatically turn off if
the pump speed is below 72,000 RPM.
6.5.2 Total Pressure Calibration
To protect the filament, Transpector CPM has a factory-calibrated total pressure
lens that measures the total pressure in the closed ion source. The filament will turn
off (within 50 ms) after the pressure in the ion source rises above the total pressure
setpoint, typically 1E-3 Torr @ 40 eV 200 A for a CVD closed ion source.
The total pressure reading is calibrated with the ionizer set to the default low
emission settings (200 A emission; 40 eV electron energy). The default value for
the over-pressure setpoint is 1 to 3 mTorr.
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