Surface Analysis for Selective SiO2 Etching by Reflectance Photoelastic Modulated Fourier Transform Infrared Spectroscopy

Photoelastic modulated fourier transform infrared (PEM FTIR) spectroscopy has been used to study the bonding structure and compositions of fluorocarbon films generated during etching with CHF 3 /CO surface wave plasma (SWP). The C=C (stretching vibration mode at 1600 cm -1 ), C–C (940 cm -1 ), C–F (1032, 1164, 1260, 1291 cm -1 ), =C–H (780 cm -1 ) and C=O (1790 cm -1 ) peaks on the polymer films were identified using reflectance PEM FTIR. In addition to the peak assignment, the C–F spectra were fitted to three peaks–1280, 1250, 1200 cm -1 , with Gaussian splitting, respectively. Comparing the etching results with the variation of FTIR spectra, it was found that the selectivity of SiO 2 to poly-Si and photoresist with CO mixing ratio to CHF 3 is correlated to the area ratio of [C=C]/[C–F] and [C=C]/[C=O]. The XPS result was also compared to reflectance PEM FTIR data to reveal the availability of reflectance PEM FTIR application. It was confirmed that there existed a good agreement between PEM FTIR and XPS data. When we integrated all the results from PEM FTIR, XPS and optical emission spectroscopy (OES), we found that the element of the C=C bond on the polymer surface played an important role as an etch inhibitor. The reflectance PEM FTIR measurement on the etched surface is considered to lead to an understanding the properties of polymer films generated during oxide etching.