Etching of Silicon - Electrochemistry of Silicon and Its Oxide - page 293

7.3.4. Effect of Other Oxidants

-Si and p- Si in a
tion. 14 According to Bressers et al . solu-
tions, is mainly of chemical nature. At the OCP Si reacts directly with without
involving charge carriers in the bands. The reduction of at cathodic potentials is
facilitated by the electrons from the conduction band. The etch rate, which is indepen-
dent of doping type and surface orientation, is limited by the mass transport of the
in the solution. Thus, as shown in Fig. 7.11 for p -Si, the etch rate is almost constant at
cathodic potentials at which no electron is present on the surface. On the other hand,
the etch rate of n -Si decreases to zero at cathodic potentials because is efficiently
reduced with the conduction band electrons. The reactions involved in the etching of
silicon and reduction of are discussed in Chapter 6.
Figure 7.12 shows the effect of H 2 O 2 on the etching in NH 4 F of different con-
centrations. 884 The etch rate is 0.1-0.3 Å/s in the concentration range of

Figure 7.11 shows the etch rates of n -containing HF solu-

14

the etching process, unlike that in the HNO

3

to 1.3wt

%NH 3 F with 5wt % . It increases rapidly with further increasing fluoride

concentration. The reduction of on silicon in HF solutions is similar to Br 2 ,

being primarily a conduction band process with very little hole injection into the

valence band. 629