RF CCP source operable in the sub-mTorr regime

This study presents a radio frequency (RF) capacitively coupled plasma (CCP) source that achieves plasma ignition in the sub-mTorr regime, enabled through a new design employing a cylindrical powered electrode and a central grounded rod electrode. Experimentally, breakdown voltage measurements from sub-mTorr to several tens of mTorr confirmed successful plasma ignition in the RF CCP source at pressures as low as 0.1 mTorr. Electromagnetic simulations were then conducted to analyze the electric field and magnetic field distributions as well as electron trajectories in both the developed source and a conventional parallel-plate CCP source. Based on the results, the ultra-low-pressure discharge mechanism is initially explained. Furthermore, electron density measurements were made to characterize the plasma properties in the ultra-low-pressure environment. The reported ultra-low-pressure plasma, achieved without external magnetic fields, could enable the precise control of ion energy and directionality required for high aspect ratio etching. The developed RF CCP source also provides fundamental insights for plasma source design to support next-generation semiconductor manufacturing processes.