Developed in collaboration with
The University of Liverpool and GEC Marconi Materials Technology,
Caswell, PlasmaChromTM uses chromaticity
laws to quantify the changes in colour of a plasma in order to both
identify events such as endpoints and inconsistencies, such as flow
or pressure perturbations.
In this way diagnosis of non-uniformity
of plasma processes is made easy for the first time. PlasmaChromTM
has identified process endpoints far below the resolution
of monochromators and other analysis techniques and has seen perturbations
of both pressure and gas flow below the resolution of the available capacitance
manometer and mass flowmeters.
PlasmaChromTM uses highly sensitive proprietary
techniques to quantify colour and luminosity variations. These variations
can then be used for diagnostics, decision making or closed loop control.
Furthermore, because the technique is continuously sensitive throughout
the spectrum, changes are detected which are beyond the sensitivity and
speed of dispersive instruments such as grating monochromators.
As a diagnostic instrument
The CPC 100 is linked via a standard RS232 port to a PC where the data can
be displayed, stored and manipulated using PlasmaWare TM proprietary
software. This can be used for fault diagnosis, process transfer or process
qualification in plasma etch and deposition.
Figure 1 shows that
the optical data is sensitive to a 1 x 10-3 Torr pressure
fluctuation with a possible end point indicated at 5-600sec
Figure 2 is a chromaticity
plot of figure 1 and shows the pressure fluctuation, the process taking
place end then a clear, unequivocal end point.
The chromatic technique is sensitive
to gas flow changes below 0.1 % FS and one user reports diagnosis
of MFC overshoot.
As a decision making instrument
The CPC 100 detects the modulation in plasma output occurring at process
end point during plasma etching and deposition. Although extremely sensitive,
the instrument easily identifies and extracts interference caused by external
influences such as RF power instabilities and system pressure fluctuations.
As an optical thickness monitor
The CPC 101 monitors real-time optical data from the substrate; this is
processed by a neural network to produce a thickness fit during either etch
or deposition. Once a process is 'learned', the thickness is output in real-time
for process control.
As a process controller
The CPC 300 uses the demonstrated sensitivity of the CPC 100 to provide
closed loop control of critical parameters such as gas mixture, RF power
and pressure in plasma processes such as etching, plasma deposition and
reactive sputtering. Statistical control strategies may be embedded in the
instrument or upon the customer's control platform.
PlasmaChromTM and PlasmaWareTM
are a novel methodology for plasma diagnostics, process control
and indeed any application where chromaticity measurements have impact on
an industrial process. New applications are being reported continuously
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