Role of CF2in the etching of SiO2, Si3N4and Si in fluorocarbon plasma

The CF 2 density and etch rate of SiO 2 , Si 3 N 4 and Si are investigated as a function of gas pressure and O 2 flow rate in fluorocarbon plasma. As the pressure increases, the self-bias voltage decreases whereas the SiO 2 etch rate increases. Previous study has shown that SiO 2 etch rate is proportional to the self-bias voltage. This result indicates that other etching parameters contribute to the SiO 2 etching. Generally, the CF 2 radical is considered as a precursor for fluorocarbon layer formation. At a given power, defluorination of fluorocarbon under high-energy ion bombardment is a main source of fluorine for SiO 2 etching. When more CF 2 radical in plasma, SiO 2 etch rate is increased because more fluorine can be provided. In this case, CF 2 is considered as a reactant for SiO 2 etching. The etch rate of Si 3 N 4 and Si is mainly determined by the polymer thickness formed on its surface which is dominated by the CF 2 density in plasma. Etching results obtained by varying O 2 flow rate also support the proposition.