An improved source of intense beams of fluorine atoms

The construction of an improved source of intense beams of fluorine atoms is described. The source is ideally suited for crossed beam studies of chemical reactions and also for high aspect-ratio etching of silicon. In the new source the MgF2 single crystal oven chamber used in our earlier source (Faubel et al 1996a J. Phys. D: Appl. Phys. 29 1885) has been replaced by a CaF2 single crystal. The more favourable high temperature mechanical properties and lower rate of evaporation of CaF2 permit higher temperatures of up to 1200 deg. C compared with 1000 deg. C previously and a corresponding higher degree of dissociation of 50-60% in a 20% mixture of F2 in Kr at source stagnation pressures of 17 bar. The advantages of the new source are demonstrated with time-of-flight spectra measured for scattering from an He secondary beam and in reactive scattering from H2