The transition of electron energy distribution function according to Ar/O2 gas ratio in capacitively coupled plasmas

In semiconductor manufacturing, oxygen plasmas are widely used in many processes such as photoresist ashing, polymer removal, oxidation, or deposition of thin-film oxides. These applications are adopted based on the advantages of oxygen plasmas in chemical diversity, such as several types of ions (e.g., O^-, O⁺, and O₂⁺) and chemically reactive species. Meanwhile, mixing Ar gas suitable for oxygen plasma can effectively generate ions and chemically reactive species under the same conditions. This work investigates the plasma characteristics by changing the mixture ratio of argon and oxygen using a two-dimensional particle-in-cell simulation parallelized with GPUs [1, 2]. The change in EEPF is observed according to the increase of the oxygen ratio. As the argon gas ratio decrease in an intermediate-pressure case (1 Torr), the electron energy probability function changes from the Druyvesteyn to the bi-Maxwellian distribution.