Quantification of fluorine in SiFx etch residues on silicon with proton induced γ-emission

Reactive ion etching of Si wafers with a CF4 plasma results in the formation of a very thin layer of SiFx. Quantification of the fluorine areal density as a function of plasma parameters is important for models describing the etching process. The Eindhoven AVF cyclotron has been used to quantify the amount of deposited fluorine using the 19F(p,p'¿)19F reaction detecting the 110 and 197 keV ¿-lines with a hyperpure Ge detector. The energy of the proton beam was chosen to be 2.76 MeV thereby limiting the Compton background by suppressing excitation of the fourth excited state (5/2+) of 29Si. Quantification was obtained through the use of an implantation standard. A detection limit of 1 × 1014 F/cm2 was obtained and two series of pilot experiments were carried out in which gas discharge pressure and plasma power density have been varied.