Study of CO₂ ashing for porous SiOCH film using 100 MHz/13.56 MHz dual frequency superimposed capacitive coupled plasma

CO₂ plasma has advantages over O₂ and N₂/H₂ plasma in low damage resist ashing processes for porous SiOCH films. To understand why CO₂ plasma has advantages, the authors investigated the damage mechanisms in O₂, N₂/H₂, and CO₂ plasma using 100 MHz/13.56 MHz dual frequency superimposed capacitive coupled plasma. According to the results of pallet for plasma evaluation tests, O radical, vacuum ultraviolet light, and ions were the main cause of damage to the porous SiOCH films in the O₂ plasma, the N₂/H₂ plasma, and the CO₂ plasma, respectively. The authors believe that CO₂ plasma has fewer O radicals in it than O₂ plasma and is less intense than the light produced by a N₂/H₂ plasma. To suppress damage further, the authors propose controlling the O radicals by using pulse-modulated 100 MHz CO₂ plasma.