Study on etching anisotropy of Si(hkl) planes in solutions with different KOH and isopropyl alcohol concentrations

The paper deals with wet chemical anisotropic etching of Si(hkl) wafers in KOH solutions containing isopropyl alcohol. The impact of KOH and alcohol concentrations on the etch rates of (hkl) planes is shown. The effect of KOH concentration in pure KOH solutions resembles the one in KOH solutions non-saturated with alcohol and is different from the one in KOH solutions saturated with isopropanol. The increase in alcohol concentration in the etching solution generally reduces the etch rates of the selected (hkl) planes. However, when the alcohol concentration reaches the saturation level, the (100) and (311) etch rates increase. This is difficult to explain since the increased alcohol concentration should cause enhanced adsorption of the alcohol molecules on Si surface, as it is suggested by surface tension measurements. Thus, the denser adsorption layer should lead to the etch rate reduction. The influence of isopropanol concentration on the morphology of the (hkl) surfaces is also studied. The increase in the alcohol concentration leads to disappearance of hillocks on (100) and (h11) surfaces.