Influence of Reaction Products and Oxygen on Highly Selective Electron Cyclotron Resonance Ion Stream Etching of Si

The behavior of reaction products during Si etching by electron cyclotron resonance (ECR) ion stream etching with Cl2 is investigated using the emission of SiCl as a monitor of the reaction products. A strong correlation is found between the emission intensity of SiCl and the SiO2 etch rate, and it is confirmed that an increase in the reaction products promotes SiO2 etching. As the SiO2 etching mechanism, we propose the occurrrence of a reaction with a volatile compound, (SiCl3)2O, on the SiO2 surface. When O2 is added to Cl2, the concentration of reaction products in the plasma decreases. This is shown to occur because the redesorption of the reaction products from the chamber wall is hindered by O2. The suppression of SiO2 etching upon O2 addition is related not only to the oxidation of the SiO2 surface but also to the decrease in reaction product concentration in the plasma.