The ion energy distributions ͑IEDs͒ at the electrodes in a capacitively coupled 13.56 MHz plasma in CF 4 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 IED of different ions achieved in the same sheath. The IEDs have been determined at both the largest and the smallest electrode. Apart from the IEDs of the CF 4 species, the IEDs of ionic species in plasmas in argon and

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... lasmas in argon and nitrogen also were determined. Apart from the CF 4 ionic species CF 3 ϩ , CF 2 ϩ , CF ϩ , and F ϩ , CHF 2 ϩ ions also are present in the CF 4 plasma due to residual water in the reactor. Because the CHF 2 ϩ ions are not produced in the sheath and because we do not detect elastically scattered ions, the IEDs of these ions show the typical bimodal distribution for rf plasmas which corresponds to an IED of ions which have not collided in the sheath. From these IEDs we can obtain the sheath characteristics, such as the averaged sheath potential. From the IEDs of CF n ϩ ions one can conclude that, in the sheath of the CF 4 plasma, a large number of chemical reactions takes place between the CF n ϩ ions and the neutrals.