The formation and desorption mechanisms of SiCl4 on Si(100), which are some
of the main reaction pathways in etching silicon with chlorine, have been
studied with first-principle calculations. Starting from the Si(100)-(2 x 1
) surface with 1 ML (monolayer) of chlorine to saturate the dangling bonds
of Si-Si dimers, further addition of chlorine atoms leads to the breaking o
f the dimer bonds or back-bonds and, therefore, formation of SiCl2(ad) whic
h has a high desorption energy barrier. When chlorine atoms penetrate below
the first silicon layer, they couple with SiCl2(ad) to form various precur
sors of SiCl4(ad). The calculations have identified three physisorbed SiCl4
(ad) species, and four chemisorbed SiCl4(ad) species. The formation and des
orption barriers of these species are lower than that of SiCl2(ad). Hence,
at low temperatures, SiCl2 desorption is barred by its high desorption ener
gy, which makes the formation and desorption of SiCl4 more favorable, At hi
gh temperatures, desorption of SiCl2 can proceed and thus reduces the proba
bility of SiCl4(ad) formation. The availability of hyperthermal chlorine sp
ecies or ion bombardment can promote both the formation of SiCl4(ad) and de
sorption of SiCl2(ad), and thereby increases the etching rate and changes t
he reaction dynamics, A mild energetic condition will favor the formation a
nd desorption of SiCl4. The etching mechanism model provides a good framewo
rk to explain the experimental data in the literature on etching silicon wi
th thermal and hyperthermal chlorine. (C) 1999 Elsevier Science B.V. All ri
ghts reserved.