Effects of metallic impurities on anisotropic etching of silicon in aqueous KOH-solutions

Various effects of metallic impurities dissolved in aqueous KOH solutions on the anisotropic etching of silicon are investigated. The changes of the anisotropy, surface roughness of {100} and {111} planes and the shape of convex corners are presented. Metals such as iron, sodium, chromium, aluminum and zinc cause an increase, and copper and nickel a decrease in the etch anisotropy. The observed surface roughness increases strongly with impurity content. At lower contents of metallic impurities the angle of the convex corners have a value near 150°. However, with rising metallic ion content the value goes down to 143°