NH4OH-based etchants for silicon micromachining. Influence of additives and stability of passivation layers

Solution based on ammonium hydroxide and water were investigated for anisotropic etching of monocrystalline silicon. In 2.65 M NH sub 3 solutions at 80 degree C, the addition of H sub 2 O sub 2 in a concentration between 0.65 x 10 high -2 M and 1.84 x 10 high -2 M increases the silicon etch rate in the (100) direction to 75 mym/h, which is a factor of about 2.5 higher compared to pure etchants. In addition, when the pH value was adjusted above 11.3, silicon etching proceeds in H sub 2 O sub 2 -doped solutions without formation of pyramidal-shaped hillocks. The influence of the pH value and H sub 2 O sub 2 concentration on the etching behaviour is discussed in detail. Passivation layers, like silicon oxides and silicon nitrides formed under various preparation conditions, and metals show excellent stability in AHW solutions. The temperature dependence of etch rates as well as the influence of post-treatments on the etching behaviour is discussed.