Quantitative Analysis of CF_4 Produced in the SiO_2 Etching Process Using c-C_4F_8, C_3F_8, and C_2F_6 Plasmas by In Situ Mass Spectrometry

摘要

The use of CF_3~(2+) as a specific product ion to selectively quantify CF_4 produced in the SiO_2 etching process using plasmas of perfluorocompounds (PFCs), such, as c-C_4F_8, C_3F_8, and C_2F_6, has been proposed and investigated in the present experiments by measuring mass spectra inside and outside the plasmas. It is known that the CF_3~(2+) ion does not appear in the mass spectra of any stable PFCs, except for CF_4. It is confirmed in the present experiments that the quantity of CF_3~(2+) originating from the CF_3 radical in the mass spectra measured in situ is negligible. Other unstable chemical species in the plasmas are too small in quantity to explain the intensity of CF_3~(2+) appearing in the mass spectra measured in situ, even if they could produce stable CF_3~(2+) by ionization. It is therefore concluded that CF_3~(2+) can be used as a fingerprint of CF_4 in mass Spectrometry. Application of this new method for the quantitative analysis of CF_4 produced in the SiO_2 etching process using PFC plasmas results in CF_4 production advancing significantly not only in the etching region of SiO_2 but also in the downstream region of the plasmas.