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Infineon Technologies DresdenAdvanced Data
Processing
Combining full IEP spectrum with an
interferometric signal for depth etch endpoint
detection
Frank Hoffmann, Infineon Technologies Dresden
GmbH Co. OHG Knut Voigtländer, Advanced Data
Processing GmbH
Method Description

• Model quality depending on target signal period
  and phase- blue very good modeling possible
  with large signal period.- green
  sufficient modeling with fast oscillating
  target- red too fast oscillating target no
  good modeling possible

• This approach uses full spectra time signals to
  form the interferometric reference trace by
  combining the individual wavelengths.

Fig. 3 With PCA decomposition the independent
signals can be discovered. A Modeling procedure
is used to try to superimpose these signals to
fit a given fast oscillating target signal.
5s
10s

• A PCA (principle component analysis) based method
  is used to decompose the full spectra into its
  linear independent components. A nonlinear
  optimization is used for a suited superposition
  of these components providing the final combined
  interferometric time signal.

20s
Fig. 2 Set of reference measurements containing
the full spectra the time behavior even of the
shortest available wavelength has long signal
period and is not suited for exact endpoint
control.
very good modeling for 20s target period
modeling not possible for 5s target period
for 10s target modeling is just possible
Fig. 4
8th European Advanced Equipment Control /
Advanced Process Control (AEC/APC) Conference
Dresden - Germany, April 18 - 20, 2007