SI XEF2 ETCHING - REACTION LAYER DYNAMICS AND SURFACE ROUGHENING/

The etching of Si(100) is studied quantitatively in a molecular beam s etup. After exposing the silicon surface to XeF2 doses between 10(2) a nd 10(4) monolayers (MLs) of XeF2, thermal desorption spectroscopy is used to study the SiFx content of the reaction layer. Large values of the fluorine content (up to 30 ML) are observed. These are explained b y surface roughening due to the etching process, which increases the e ffective surface by up to a factor of 6 after 10(5) ML of XeF2, corres ponding to 10(4) ML of etched Si. This implies a porous or canyon-like structure. The dose dependence of the fluorine content is not single exponential; it increases rapidly for the first 10(2) ML and much more slowly thereafter, saturating after approximately 10(4) ML. This beha viour is described by the rapid formation of a monolayer of SiFx speci es in the initial regime, followed by the slow formation of a steady s tate multilayer of SiF-SiF2-SiF3 and SiF2-SiF3 chains. The etch rate s hows a similar dose dependence, increasing from 12% of the incident fl ux in the monolayer regime to 20% in the multilayer regime. Finally, i t is shown that fluorine diffusion into the silicon bulk is not an imp ortant process in the reaction layer formation. (C) 1996 American Vacu um Society.