Quantum cascade laser based monitoring of CF₂ radical concentration as a diagnostic tool of dielectric etching plasma processes

Dielectric etching plasma processes for modern interlevel dielectrics become more and more complex by the introduction of new ultra low-k dielectrics. One challenge is the minimization of sidewall damage, while etching ultra low-k porous SiCOH by fluorocarbon plasmas. The optimization of this process requires a deeper understanding of the concentration of the CF₂ radical, which acts as precursor in the polymerization of the etch sample surfaces. In an industrial dielectric etching plasma reactor, the CF₂ radical was measured in situ using a continuous wave quantum cascade laser (cw-QCL) around 1106.2 cm⁻¹. We measured Doppler-resolved ro-vibrational absorption lines and determined absolute densities using transitions in the ν₃ fundamental band of CF₂ with the aid of an improved simulation of the line strengths. We found that the CF₂ radical concentration during the etching plasma process directly correlates to the layer structure of the etched wafer. Hence, this correlation can serve as a diagnostic tool of dielectric etching plasma processes. Applying QCL based absorption spectroscopy opens up the way for advanced process monitoring and etching controlling in semiconductor manufacturing