Evolution of reactive plasma processes by radical control

Around the 1970s, reactive plasma was a black box, and research, development, and manufacturing, such as semiconductor production, were conducted on a trial-and-error basis. This was mainly due to the fact that behaviors of radicals in reactive plasmas were unknown. In order to innovate this scientifically, we developed an ultra-compact vacuum ultraviolet absorption spectroscopy and quantitatively clarified the gas-phase dynamics of H, N, O, C, and F atomic radicals in process plasmas and their sticking coefficients on material surfaces, which had not been known before. The densities of molecular radicals were also measured by various means, including infrared diode laser absorption spectroscopy, appearance mass spectrometry, cavity down absorption spectroscopy, and laser-induced fluorescence, to systematically clarify the gas-phase and surface interface reactions of radicals in reactive plasma processes. Based on these results, we proposed a radical-controlled plasma process and succeeded in fabricating ultrafine nanopatterns of organic thin films and synthesizing carbon nanowalls and elucidating their properties. Furthermore, we developed a radical-controlled ultrahigh-density, low-temperature atmospheric pressure plasma. In addition to elucidating the behavior of radicals in this atmospheric pressure plasma, we discovered that bioactive substances induced by this plasma selectively kill cancer cells and clarified the reaction mechanism. In this talk, I will introduce the results of the radical-controlled reactive plasma process and look forward to the future society that this process will open up.