A hyperthermal (0.1–4 eV) F atom beam source suitable for surface etching investigations

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Abstract
Using laser vaporization of cryogenic films of XeF2, a beam of F atoms is produced with most probable kinetic energy variable from 0.3 to 1.1 eV. Fluorine atoms are observed with energies up to 4.3 eV. Also present in the beam are F2, Xe, XeF, XeF2, and impurity H and HF. The beams are produced by vaporizing thin films of XeF2 with 266 nm photons of a quadrupled Nd:YAG laser (∼0.5 J cm−2, 5 ns). The kinetic energy of the F atoms can be increased monotonically by decreasing the repetition rate of the vaporization laser from 1 to 0.1 Hz while the deposition rate of XeF2 is constant. The relative velocities of the heavier species are always less than that of the F atoms, but their most probable energies are greater than the energy of the F beam. This result suggests that a hydrodynamic flow of the lighter species propels the heavier F2, Xe, XeF, and XeF2 particles to higher velocities. Evidence is presented that complete desorption of the XeF2 film occurs within the vaporization area during each laser pulse, from which a desorption yield can be estimated. Such a source may be suitable for novel studies of anisotropic etching of semiconductor substrates with energetic reactive species.

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