NaOH dissolution, silicon

In a study of the dissolution of silicon in NaOH (51), it was found that the ill surfaces have a slower etching rate than the 100 and 110 surfaces. Furthermore, from Fig, 7 it can be seen that within experimental error, the 100 and the llO surfaces etch at the same rate. It is known that the slowest etching planes form the limiting facets on a concave surface, while the fastest etching planes form die limiting facets on a convex surface. To prove that the ill planes had die slow. 

Fig. 7. Dependence of the dissolution rate of silicon in 10% NaOH on temperature.

In many respects the action of NaOH on aluminum and silicon is similar. Streicher (52) reported an activation energy of 13.7 kcal/mole for the dissolution of aluminum in 2% NaOH. Orem (53) studied the action of 15% NaOH on spheres of aluminum and on holes drilled into plates whose surfaces were oriented in the three main crystallographic planes. He found that the relationship between the etch rates was ill < 110 < 100. ... 

To make sols containing up to 50% -SiO by dissolving silicon. Bobb (114) claims the use of an aqueous solution of an inorganic base (NaOH, KOH) to catalyze the dissolution at 50-100 C and stabilize the resulting sol. It is remarkable that sols made at 90-95 C were said to be very viscous but when made at 98-lOO C were of normal low viscosity. Particle sizes were between 15 and 45 nm. Also the sols were unusual in that they did not form hard gels when acidified, but only soft coacervates. These differences are unexplained. An alcosol is obtained when silicon is used an an anode and dissolved by electrolysis in an alcohol-water mixture. Acid or a metal salt is added to provide conductivity according to Tripp (91) or Chilton (115). 

Substrate = silicon Micromachining = nEDM milling Electrodes diameter [ m] = 20, 50, 75, 300 Silicon dissolution = NaOH Og solution... 

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