Etching of Oxides - Electrochemistry of Silicon and Its Oxide - page 143

resulting from this investigation are listed in Table 4.1. Figure 4.14 shows that in
the etch rate of quartz is a linear function of concentration. 670 The
etching process of quartz in HF solutions is found to be limited by the surface reac-
tions and not affected by the resistance to diffusion. This is in agreement with the rela-
tively high activation energy, 0.44 eV, and with the much lower etch rates relative to
other oxides as illustrated in Fig. 4.2. 670,709 The dissolution can be catalyzed by salts
such as NaCl, and LiCl. 916 The catalytic effect, which is a strong function of
pH, is attributed to the competitive adsorption of cations at surface hydroxyls.
The etch rate of quartz depends on the crystallographic orientation of the surface.
Table 4.3 shows the etch rate on the surface with different orientations. 671 The differ-
ence among the four orientations can be as large as 1000-fold. The etched surface

morphology is a function of solution composition and temperature, particularly the con-
gives terraces but no pits, a centration of positive ions. An etching bath with added