Quantitative Analysis of CF4 Produced in the SiO2 Etching Process Using c-C4F8, C3F8, and C2F6 Plasmas by In Situ Mass Spectrometry

Abstract

The use of CF32+ as a specific product ion to selectively quantify CF4 produced in the SiO2 etching process using plasmas of perfluorocompounds (PFCs), such as c-C4F8, C3F8, and C2F6, has been proposed and investigated in the present experiments by measuring mass spectra inside and outside the plasmas. It is known that the CF32+ ion does not appear in the mass spectra of any stable PFCs, except for CF4. It is confirmed in the present experiments that the quantity of CF32+ originating from the CF3 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 CF32+ appearing in the mass spectra measured in situ, even if they could produce stable CF32+ by ionization. It is therefore concluded that CF32+ can be used as a fingerprint of CF4 in mass spectrometry. Application of this new method for the quantitative analysis of CF4 produced in the SiO2 etching process using PFC plasmas results in CF4 production advancing significantly not only in the etching region of SiO2 but also in the downstream region of the plasmas.