ION ENERGY-DISTRIBUTIONS IN DUAL-MODE AND SINGLE-MODE MICROWAVE RADIOFREQUENCY PLASMA/

Ion energy distribution functions (IEDF) were measured at the surface of a grounded or a rf-powered electrode exposed to a microwave (MW, 2. 45 GHz) or a rf (13.56 MHz) discharge in argon. The IEDFs measured on the grounded electrode in both the rf and the MW modes show a higher c ontribution of low-energy ions when the pressure is raised. The maximu m ion energy E(m) decreased from 12.0 to 8.5 eV in the MW plasma, but remained at 26+/-0.5 eV in the rf plasma. The mean ion energy (E) over bar decreased from 6.1 to 3.8 eV (MW) and from 16.0 to 12.0 eV (rf) w hen the pressure was raised from 30 to 210 mTorr. The IEDFs in the rf mode exhibit a single peak, while a bimodal structure is observed in t he MW mode. When the electrode is rf powered to achieve a negative de bias voltage V-B, the E(m) values reach similar to 1.2eV(B) (rf) and s imilar to 1.1eV(B) (MW), respectively. The IEDFs in the rf mode displa y a multiple peaked structure which is associated with a rf-modulated sheath. In the dual-frequency MW/rf mode the IEDF is single peaked, na rrow, and centered around eV(B). A nearly tenfold increase in the ion flux is observed when increasing the MW input power, while the ion ene rgy remains unchanged for a constant V-B value. This allows an indepen dent control of ion energy and ion flux, suitable for the control of m aterial properties in plasma processing. (C) 1995 American Institute o f Physics.