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