The European Physical Journal Applied Physics

Focus on Plasma Processes

In situ diagnostic of etch plasmas for process control using quantum cascade laser absorption spectroscopy

N. Langa1, J. Röpckea1, S. Wegea2 and A. Steinbacha2

Leibniz Institute for Plasma Science and Technology Greifswald, F.-Hausdorff-Str. 2, 17489 Greifswald, Germany

Qimonda Dresden, Königsbrücker Str. 180, 01099 Dresden, Germany


The combination of quantum cascade lasers and infra red absorption spectroscopy (QCLAS) opens up new possibilities for plasma process monitoring and control. First measurements are reported with an especially designed quantum cascade laser arrangement for application in semiconductor industrial environments to track the approach for in situ process control in silicon etch plasmas. In gas mixtures with N2 and in microwave (MW) plasmas at pressures below 30 Pa concentrations of C4F6 and of SiF4 were measured simultaneously online for the first time. It could be demonstrated, that using quantum cascade lasers (QCL) it is possible to control ex situ mass flow controllers (MFC) based on in situ measured species concentrations in the gas phase and in the MW plasma bulk.

(Received June 30 2009)

(Revised September 18 2009)

(Accepted November 6 2009)

(Online publication December 11 2009)


  • 07.57.Ty – Infrared spectrometers, auxiliary equipment, and techniques;
  • 52.70.Kz – Optical measurements;
  • 52.80.-s – Electric discharges