Etching of Oxides - Electrochemistry of Silicon and Its Oxide - page 156

solutions, and may also have a significant effect on the etching process.
Verhaverbeke et al. 238 further suggested that in addition to HF dimer, which
is a dominant species in solutions with a concentration higher than 1M, is also an
important etching species. Thus, depending on relative dominance of the species, the
following parallel reactions may be involved:
HF, and may further participate in the reaction with the intermediates to
complete in the dissolution process.
may also be an important species involved in the dissolution process. Accord-
ing to Monk et al., 451 the etching of film is probably a two-step process. In the
first step, interacts with the surface which opens the network so that, in the
second step, more of the fluorinated species is able to attack the silicon in the films.
Thus, adding to HF solutions results in higher etch rates. The importance of as
postulated by Osseo-Asare, 123 is in the regulation of the surface potential. According to
Osseo-Asare, the formation of the Si-F bond is the rate-determining step. is partic-
ularly important as its adsorption on the surface determines the surface concentration
of Si-OH which is the site for fluoride adsorption. Adsorption of positive ions, such as
which changes the electronic configuration of the surface, is considered to also be
important in the etching reactions of quartz. 671 On the other hand, White 786 found that
DF exhibits a weak isotope effect of and found no isotope effect for
so that protons may not play a major role in the rate-determining step in the etching
reaction.
A number of pathways may be possible in the formation of surface species leading
to breaking of the Si-O bonds as has been suggested by Monk et al. 800 Figure 4.35I