In this work, the ability of reducing reaction byproduct from chemical vapor deposition of SiON thin film is explored changing balance gas, time and power within the wafer discharging process. In order to control the surface remaining NH<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf><sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup>byproduct, which is reported to induce profile deviation in photolithography patterning, post N2O plasma treatment has been widely used. However, the N2O plasma treatment has inherent limitation of utilizing greenhouse gas and imperfect removal efficiency. Although N2 is generally considered to be inert due to the stable triple N-N bond, based on the material screening and DFT calculation, we newly postulated that N* radical from N2 plasma may reduce NH<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf><sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup>ions more efficiently compared with O* radical from N2O plasma, possibly by the more favored H<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup>dissociation reaction between NH<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf><sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup> and NH3 (-32.6 eV for N* radical driven pathway / −21.9 eV for O* radical driven pathway). Indeed, by using slight plasma power generated during the wafer discharging stage and changing balance gas from N2O to N2, the surface remaining NH<inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf><sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">+</sup>ion was removed by almost 100% confirmed by High Performance Ion Chromatography (HPIC). Additionally, critical dimension uniformity of EUV patterning was also improved by 0.03nm in ADI and 0.11nm in ACI states, respectively. We believe that our finding exploits new strategy for controlling surface condition of hard mask with more simplified and sustainable method.