Rare gas metastable atom density in diluted O ₂ RF plasmas

Rare gas diluted O ₂ plasmas are gaining interests for application to high quality SiO ₂ film formation. The density of rare gas metastable atoms and O atom in rare gas diluted O ₂ radio frequency (RF) capacitively coupled plasma (CCP) was measured by optical absorption spectroscopy (OAS). Decreases of rare gas metastable densities due to addition of O ₂ indicate efficient O atom production by rare gas metastables via collisional quenching. Krypton metastable had highest density among four rare gas species for fixed RF power. The decrease of Ar metastable density due to O ₂ addition showed quantitative agreement with reported quenching rate coefficient. Detailed discussion on different gas pressures illustrates reduced O ₂ fraction is the key for selective production of O atoms through rare gas metastables.