Etching of Oxides - Electrochemistry of Silicon and Its Oxide - page 139

solution, which results in a decrease in pH, only slightly increases the etch rate of ther-
mally oxidized silicon. 657 Addition of increases the etch rate sensitivity to the
nonuniformities in oxides. It is found, for example, that 2.3% HF + 2.1% is
extremely sensitive to differences in density, stoichiometry, bond strain, and impurities
in the silicon dioxide films; it etches various types of glasses and mixed oxide layers
much more rapidly than pure silicon oxides. 115,232 As another example, in 0.1% HF +
70% solution, the etch rate strongly depends on impurity
concentration in the oxide, so that the etch rate profile can be used to determine the
diffusion of boron into silicon from a doped glass source. 426 In pure solution
containing no HF, the etch rate of silicon oxide is very low as shown in Fig. 4.7. 800
Surfactants may be added to etching solutions for surface roughness control.
According to Myamoto et ., 468

al possible surfactants are hydrocarbon anionic

hydrocarbon cationic