Effect of magnesium in KOH solution on the anisotropic wet etching of silicon

Etching characteristics of single crystal silicon in KOH solution containing magnesium were investigated. Etch rate of silicon slightly decreases by the Mg of the order of 10 ppm in 32 wt.% KOH, while the etched surface roughness did not change. In order to evaluate the effects of ppm-level Mg in KOH solution for a number of crystallographic orientations, the etching experiment using a hemispherical single crystal silicon specimen was performed. The anisotropy of etch rate was almost the same as that without addition, and the etch rate decreased at almost all orientations with an addition of 26 ppm. The surface roughening caused by the ppb-level of Cu in KOH solution could be fully recovered by adding Mg of the order of 10 ppm in KOH solution.