Inelastic electron scattering and energy-selective negative ion reactions in molecular films on silicon surfaces

Careful control of plasma chemistry, particularly the negative ion production and reaction channels, could lead to nanoscale patterning, growth, and etching strategies. Since the energies of anion and electron surface collisions are relatively low (<10 eV) in plasmas, these interactions are essentially damage free with respect to the buried interface and subsurface region. Thus, renewed interest has arisen that takes advantage of negative ion surface chemistry in film deposition and nanopatterning. We review (i) the transient negative ion states such as shape and dissociative electron attachment resonances produced during electron molecule scattering, (ii) the many body interactions and substrate-effects on the resonance energies, widths and cross sections and (iii) examples of post-dissociation interactions of the reactive fragments and anions that may lead to controlled etching or growth. Specifically, we summarize past and recent studies on electron scattering with gas- and condensed-phase H₂O, CF₄, SiCl₄ and O₂ targets. We then discuss recent examples of energy selective oxidation and fluorination of hydrogen terminated silicon surfaces and comment on the general applicability of low-energy electrons and negative ion surface chemistry in film deposition, nanopatterning and growth strategies.