Hercules^{®}:Plasma Metrology System 
Can Hercules collect data from 6 chambers of 3 Dry Etch tools for instance? 
Yes it can if there is a proper data collection system (as Maestria). But one needs six Hercules^{®} systems if one wants to do it simultaneously. 
Does AC 100 V power can drive Hercules^{®}? 
No problem at all. This is the most common case since often the power line of the tool is used. 
Is there a possibility to use it for DC magnetron sputtering? 
No, DC does not provide th effect which is utilized by SEERS. 
I want to know measurable pressure range under the conditions that gasses and RF power can be fixed. 
This depends on RF power and the gases used. The spec says up to 35 Pa (250 mTorr). This is very conservative, often (e.g., O_{2}) it works also at 50 Pa (350 mTorr). 
I want to know which application were done by SEERS and which application were done by NEED. 
NEED is brand new und the highpressure approach for more than 60 Pa (0.5 Torr) and basically specially made for PECVD. Almost all etch application will use SEERS also in future. 
Is it possible to do measurement through Quartz furnace wall that have the thickness about 5 to 15 mm? What is the maximum thickness of the furnace wall that the measurement can be carried out? 
If that is quartz liner which covers the whole chamber wall, it will work independent of the thickness of the quartz liner. Hercules^{®} measures at some SCCM chamber through a ceramics liner. 15 mm are still fine, much more would be tricky and must be discussed in connection with the chamber design. 
Could you explain
how the nonlinearity of the plasma is
related to frequency domain in the simplified model of RF plasma? 
The nonlinearity of the sheath (dark space) at the
wafer generaties the harmonics.
Example for the simple term [x(t)]^{2} in the RF sheath equation:
The Fourier transform provides X*X (convolution) and its frequency
shift rule show the occurance of a new harmonic frequency (multiple of
basic frequency).
A simple is
cos^{2} (2 π f t) = 0.5 [1 + cos (2 π
f t)]
where the square term provides a signal with double generator frequency 2 π
f .

What is the
difference between VI probe and the plasma
metrology system Hercules^{®}? 
A VI probe delivers voltage V, RF current I, and the
phase angle φ between V and I outside the chamber. From this data one can calculate
resistance using an simple eqivalent circuit with series circuit of capacitance C and resistance R.
A VI probe delivers NO plasma parameters, just parameters from
somewhere outside the chamber. That means FDC for the RF subsystem YES,
process control NO.
In contrast to the VI probe, Hercules^{® }measures
and uses the full RF spectrum (up to 1 GHz) is a modelbased sensor
system with a real plasma model including nonlinear effects. 