SPI Plasma-Prep™ II Plasma Etcher, Cleaner and Asher
Measuring the power of the plasma in the chamber
Measurement of the power:
There are a number of problems in the measurement of the power in the chamber of the Plasma Prep II.
The easy way is to measure the power to the electrodes and assume that the power level inside the
chamber is about the same, which we believe it is. The power to the electrodes is the product of
the voltage, the current and the phase relationship between the voltage and the current. We believe
that the two are approximately in phase. The plate current typically varies between 0 and 100
milliamperes, depending on the instrument settings. The plate voltage under load is nominally
1000 volts (it is somewhat higher when the power is not coupled to the chamber). The nominal power
output of the PlasmaPrep II is 100 watts. To a first approximation, the power to the chamber in
watts is equal to the plate current in milliamperes.
When the Plasma Prep II is going to be used exclusively as a plasma cleaner, and is ordered specifically
for that application, we supply the unit for operation at 10 watts. Everything about the unit is the
same except for some of the internal electronics.
We are often times asked if we could supply the Plasma Prep II "with a switch" so that one could switch
back and forth between these two power extremes, or better still, a system that would feature a continuously
variable power in the chamber. We have spent a lot of time trying to engineer a solution to this requirement
but when ever we do the economic calculations, such a hybrid unit comes out costing far more than the cost of
two separate units. We know that there are competitive units on the market that do have such a variable power
feature, but they also cost many times more than the price of two Plasma Prep II units, one configured for 100
watts and another configured for 10 watts.
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Friday July 25, 2008
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