Silicon/Electrolyte Interface - Electrochemistry of Silicon and Its Oxide - page 61

decreases to one-third when the surface is rinsed with pure water for about 10 s. 563 For
the (111) surface after immersion in 1.5% HF, the fluoride coverage drops from 12%
to 5% after immersion in deionized water for 5 s and to less than 1% after 0.5 h. 635 The
fluorine sites are replaced by OH groups, producing a OH-terminated surface. 126,563
Thus, for the surface that is dominantly terminated by fluorine, dipping in concentrated
HF solutions followed by a water rinse results in a hydroxyl-rich surface.
The instability of fluorine termination can readily be explained by the theory for
hydrogen termination, that is, bonding with fluorine significantly weakens the back
silicon-silicon bond leading to the dissolution of the atoms bonded by fluorine.
2.3.3. Adsorption of Metal and Organic Impurities
In addition to adsorption of hydrogen, hydroxyl, and fluorine, the silicon surface
may also contain trace amounts of other species due to the impurities present in the
solution. A clean silicon surface is easily contaminated by metal impurities in water or
solutions. For example, the surface concentration of metals after immersion in dilute
containing 1-3 ppb of Ba, Cu, Ni, Sr, Zn, K, Al, Ca, Cr, and Fe can be in the