In–situ Time–Resolved Infrared Spectroscopic Study of Silicon–Oxide Surface during Selective Etching over Silicon in Fluorocarbon Plasma

We investigated how fluorocarbon (CF) film formation evolves from the beginning of the etching process and how it reaches a steady state at a specific thickness. Using in–situ time–resolved infrared spectroscopy with attenuated total reflection method, we measured the spectra every 2 s and observed CF film formation during plasma etching of silicon oxide. The observed spectra overlapped: a band at around 1200–1400 cm-1 caused by CF bonds overlapped with a trough at below 1300 cm-1 caused by silicon oxygen bonds. By deconvolving each component of the spectra in the series, we obtained the time–resolved intensity profiles. We found that the CF film was deposited and that its thickness reached a steady state during etching. The time evolution was fitted by a model based on the balance of rates between deposition and sputtering of the CF film.