Highly Selective SiO 2 Etching Using CF 4/C 2H 4

The relationship between the chemical structure of a polymer film and SiO2/Si selectivity was studied using X-ray photoelectron spectroscopy (XPS) and Fourier transfer infrared spectroscopy (FT-IR)-attenuated total reflection (ATR) measurements to achieve a highly selective SiO2 etching using mixed gases based on CF4. The analysis of the chemical structure of the deposited polymer film revealed that the formation of a polymer film with a low F/C ratio on the Si surface is necessary for a lower etch rate of Si, and the formation of a polymer film with a low concentration of C–H x species on the SiO2 surface is necessary to increase the etch rate of SiO2. Therefore, highly selective etching requires a deposited polymer film with a low concentration of fluorine and hydrogen atoms. The chemical structures of the deposited films depends on the exhaust rate. Based on these results, a highly selective SiO2 etching with a SiO2/Si selectivity of over 2000 was achieved at the low temperature of 20°C by controlling the exhaust rate using mixed gases of CF4 and C2H4.