Endpoint detection technology refers to evaluating the change of plasma emission from one or several specific wavelengths to gauge the progress of the plasma etching process.
Plasma consists of energetic electrons, ions, neutral process gases, radicals. Energetic electrons can excite the electrons inside atoms, molecules, and ions to higher energy levels. When the excited electrons fall back to a lower energy level, photons with characteristic energy will be emitted in the process. Those photons carry important information about the gas species that existed inside the plasma.
During the oxygen plasma photoresist ashing process, byproducts like COx, H2O will be generated inside the plasma chamber. Those by-products will change the plasma emission spectrum as shown in the photo above. If the plasma equipment can monitor the emission intensity at 486, 657nm, the plasma ashing equipment can accurately control the plasma etching and plasma stripping process.