Laser-induced fluorescence study of silicon etching process: detection of SiF2 and CF2 radicals

Using a laser-induced fluorescence (LIF) technique, SiF2 and CF2 radicals are detected during the downstream etching of silicon with a discharge of CF4 gas. It is confirmed that SiF2 radical is desorbed from the surface in the etching of silicon by fluorine atom. Addition of O2 gas to the CF4 discharge enhances the LIF intensity of SiF2 radical and extinguishes that of CF2. Mechanism of the increase of etching rate of silicon by addition of O2 is discussed on the basis of the results of LIF measurements. The etching rate of silicon is proportional to the LIF intensity of SiF2, when the microwave power of the discharge is changed. The relationship between the intensity of chemiluminescent continuum and the concentration of SiF2 is revealed, which suggests that the chemiluminescence is attributed to the emission of SiF*3 which is produced by the reaction between SiF2 and fluorine atoms in the gas phase. There is no signal of SiF2 during the etching of either SiO2 or SiNx.