MASS-RESOLVED ION ENERGY MEASUREMENTS AT BOTH ELECTRODES OF A 13.56MHZ PLASMA IN CF4

The ion energy distributions (IEDs) at the electrodes ina capacitively coupled 13.56 MHz plasma in CF4 have been measured mass resolved with a Balzers quadrupole in combination with a home-built energy analyzer . Mass-resolved determination offers the possibility to compare the LE D of different ions achieved in the same sheath. The IEDs have been de termined at both the largest and the smallest electrode. Apart from th e IEDs of the CF4 species, the IEDs of ionic species in plasmas in arg on and nitrogen also were determined. Apart from the CF4 ionic species CF3+ CF2+, CF+, and F+, CHF2+ ions also are present in the CF4 plasma due to residual water in the reactor. Because the CHF2+ ions are not produced in the sheath and because we do not detect elastically scatte red ions, the IEDs of these ions show the typical bimodal distribution for rf plasmas which corresponds to an IED of ions which have not col lided in the sheath. From these IEDs we can obtain the sheath characte ristics, such as the averaged sheath potential. From the IEDs of CFnions one can conclude that, in the sheath of the CF4 plasma, a large n umber of chemical reactions takes place between the CnF(n)(+)7 ions an d the neutrals. (C) 1995 American Institute of Physics.