Rev 2015-03-02 23
GV10x OPERATION AND SAFETY MANUAL
4.3.5. After plasma ignition, slowly rotate C2 to reduce Wr to 0. A value of Wr < 15%
of the Actual Power is acceptable.
4.4. Changing the GV10x Asher Operating Pressure
The GV10x Source can operate in a pressure range between 2.0 Torr and <5.0 mTorr and
produce plasma at pressure as low as E-4 Torr . The GV10x Source is fitted with a 15-
turn Variable Constriction Precision Needle Valve. To begin, ~5mTorr [0.7 Pa]
pressure is recommended. Opening or closing the Needle Valve varies the quantity of
plasma gas (air, O
2
, hydrogen, etc) delivered to the Source.
Although more radicals are produced in the plasma at higher pressures, the number of
radicals available in the vacuum chamber for the cleaning process is increased by
lowering the pressure. When the pressure in the chamber is decreased, the mean free
path of the radicals increases and the rate of recombinations in the gas (which would
reduce the number of available radicals) decreases.
To maximize the cleaning rate, the GV10x should be operated at the minimum pressure
needed to maintain plasma with Wr~0W. Since the GV10x Source can run at high
vacuum, the host vacuum system TMP does not need to be shut down during
hydrocarbon removal.
About Auto and Manual Ignition
If the plasma ignites soon after RF Power is turned on without adjustment
of C2, then it is auto-igniting. Once the GV10x Source is tuned, auto-
ignition will usually occur at pressures > 5 E-3 Torr upon startup. Auto-
ignition at pressure <E-3 Torr is difficult because there are fewer
molecules in the plasma region to create a cascade that will strike the
plasma. When the Source has been pumped to low pressure for a period
of time, it is necessary to open the Variable Constriction to raise the
pressure to > 5 E-3 Torr to ignite the plasma.
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